HomeMy WebLinkAboutGoal 11 Exception Discussion - So County
TO: Board of County Commissioners
FROM: Peter Russell, Senior Transportation Planner
DATE: December 22, 2014
MEETING: December 29, 2014
SUBJECT: Work session with staff on Goal 11 exception to allow sewers on rural
lands in southern Deschutes County
BACKGROUND
The Department of Environmental Quality (DEQ) convened an advisory committee in
2010 to study the problem in southern Deschutes County of nitrates, shallow
groundwater, on-site septic systems, and rural sewer systems. The advisory committee
recommended the problem be addressed with sewers rather than upgraded on-site
septic systems. Sewering rural lands require an exception to Statewide Planning Goal
11, Public Facilities Planning. Such an exception is specifically allowed to mitigate a
public health hazard. The DEQ advisory committee in 2013 recommended pursuing this
course.
PROPOSAL
Deschutes County has worked with the Department of Land Conservation and
Development (DLCD) and DEQ on preparing draft findings for a Goal 11 Exception.
The County set a Dec. 18 deadline to receive the materials from DEQ and DLCD to
read and prepare a summary for the Board of County Commissioners’ (Board) Dec. 29
work session. DLCD delivered the materials on Dec. 19.
Staff has not had time to review and prepare a summary for the Board, but will be
prepared to discuss the DEQ/DLCD materials at the Dec. 29 work session. Staff has
also completed a draft request for proposals (RFP) for a traffic analysis to comply with
the Transportation Planning Rule (TPR) as part of the Goal 11 process.
DEQ/DLCD plan to hold outreach meetings over the winter in southern Deschutes
County to hear feedback from the public. The Goal 11 exception findings could be
modified based on that feedback.
Once the draft burden of proof for the Goal 11 exception is finalized, the County will
follow its normal process for a land use application. This will include a work session
with the Planning Commission, then a public hearing before the Planning Commission,
a work session before the Board, and then a public hearing before the Board.
December 19, 2014
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DRAFT FINDINGS
GOAL 11 EXCEPTION TO ALLOW SEWER SERVICE TO RURAL
LANDS IN SOUTH DESCHUTES COUNTY
The amendments to Deschutes County’s Comprehensive Plan are described in
Ordinance 2015-XXX, Exhibits A, B, and C. New language is underscored and deleted
text is shown as strikethrough.
I. ACTION
This report supports an amendment to the Deschutes County comprehensive plan to
include an exception to Statewide Planning Goal 11 , “Public Facilities and Services,” to
allow sewer service to rural land in South Deschutes County. See Attachment A for a
map of the affected area.
The specific parcels that would receive sewer service have not been identified and the
financing mechanism to establish treatment and disposal facilities has not been
developed. Development of these specific elements of a South Deschutes County
sewage facilities plan would not be practical until the area is eligible for sewer service.
For reasons explained in these findings, an exception to Goal 11 is justified.
II. BACKGROUND
A. Groundwater Quality of in South Deschutes County
The La Pine sub-basin of the Upper Deschutes River is underlain by a shallow aquifer
that currently supplies the primary source of drinking water for approximately 18,000
people. The soils in the region are highly porous and permeable with no impervious
layer that protects the aquifer from pollution sources. In addition, the region’s soils are
young, pumice-based (volcanic), and relatively lo w in organic matter. Recharge from
natural (precipitation) or human (residential onsite system discharges or irrigation)
sources moves rapidly down through surface soils to the aquifer.
The water table ranges in depth from less than two feet to about thirty feet below land
surface. Recharge (precipitation that reaches groundwater) from infiltration of
precipitation averages 2.0 inches per year; the balance of water from precipitation
evaporates, transpires, or discharges via surface runoff to rivers. Groundwater
discharges in the basin include baseflow contributions to the Deschutes and Little
Deschutes Rivers, evapotranspiration by vegetation, and water pumped from wells.
Regional groundwater characteristics include temperatures that are among the lowest in
the state, generally 42.5°F (6° C) to 48.2° F (9° C) and high dissolved oxygen content
(3 mg/L to 6 mg/L). Groundwater velocities are low and, at the water table, groundwater
is generally oxic (oxygen rich conditions); however, at depths ranging from near zero to
more than fifty feet below the water table it becomes suboxic (depleted oxygen
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conditions) and natural nitrate reduction (denitrification) can occur.1 Denitrification thus
keeps deeper portions of the La Pine aquifer essentially nitrate-free, but the oxic
portions remain vulnerable to nitrate contamination from onsite systems, the primary
anthropogenic source. Nitrate contamination of the oxic groundwater is a concern in this
region because the shallow oxic aquifer is the desired drinking water supply for
individual domestic wells and because of the potential for nitrogen-enriched
groundwater to discharge to the nitrogen-limited rivers in the region.2
Development in rural areas threatens groundwater quality in southern Deschutes
County through onsite system discharges. About 15,000 lots of one-half to one-acre in
size were platted prior to enactment of Oregon’s land use planning laws in the 1960s
and 1970s. These lots are located within a corridor near the scenic Deschutes River
and the Little Deschutes River. Subdivision developers marketed these lots nationally
with no promise of infrastructure improvements and without an understanding of the
region’s high water table or the aquifer’s vulnerability. Currently, about 6,400 improved
lots in the La Pine region use conventional onsite systems and individually owned
drinking water wells. Most of these wells draw from the most vulnerable upper 100 feet
of the aquifer.
South Deschutes County has been the focus of extensive local, state and federal
attention beginning in the early 1980s with the identification of significant groundwater
impacts from onsite wastewater treatment systems in the La Pine Unincorporated
Community. Provided below is a timeline of events related to water quality in the region.
The Department of Land Conservation and Development (DLCD) in July 1996 began a
program to study the more than 12,000 residential lots platted in the 1960s and ‘70s in
an area of approximately 42 square miles, which are primarily served by on-site septic
systems. The Department of Environmental Quality (DEQ) assisted with the process as
did the United States Geological Survey (USGS), which produced a model of
groundwater movement and pollution. The result was this area of southern Deschutes
County was at risk of having nitrate levels exceed federal and state standards for
drinking water. A final report was issued to DLCD in 1999.
DEQ and Deschutes County have been working cooperatively for more than a decade
to find an appropriate solution to this growing concern. In 2008, the county adopted
ordinances effectively requiring advanced treatment technology systems that would
reduce nitrate concentrations in wastewater. One of the ordinances was repealed as the
result of a successful citizens’ referendum vote in 2009 to overturn the ordinances and
the other was repealed by the Board of County Commissioners in 2011. In October
2009, Deschutes County Commissioners requested that DEQ take over the effort t o find
appropriate solutions to the increasing groundwater contamination caused by wide use
of onsite wastewater treatment and disposal.
1 Oregon Health Authority Fact Sheet on Nitrates, available at
http://public.health.oregon.gov/HealthyEnvironments/DrinkingWater/Monitoring/HealthEffects/Pages/nitrat
e.aspx.
2 The U.S. Environmental Protection Agency’s Drinking Water Standards are available at
http://water.epa.gov/drink/contaminants/index.cfm .
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Since that time, DEQ has engaged a steering committee comprised of Deschutes and
Klamath County citizens to consider local circumstances and make recommendations
for a long-term solution. DEQ received the recommendations from the committee in
summer 2013.3 One of those recommendations was to pursue an area wide Goal 11
exception to allow a broader range of options for domestic wastewater treatment and
disposal.
B. Land Use and Zoning Considerations
Providing centralized sewer service to some or all of the area is among the options
under consideration to address the groundwater quality challenge explained above. For
the area outside the La Pine urban growth boundary, provision of sewer service is
limited by this provision in Statewide Planning Goal 11:
Local Governments shall not allow the establishment or extension of
sewer systems outside urban growth boundaries or unincorporated
community boundaries, or allow extensions of sewer lines from within
urban growth boundaries or unincorporated community boundaries to
serve land outside those boundaries, except where the new or extended
system is the only practicable alternative to mitigate a public health hazard
and will not adversely affect farm or forest land.
This provision of Goal 11 is implemented by OAR 660 -011-0060. This rule is quoted
and discussed in subsection IV.C of this report.
Statutes and the statewide planning goals provide an opportunity for relief from goal
requirements on a case-by-case basis through an “exceptions” process. This report
supplies facts and findings to support an exception to Goal 11 for South Deschutes
County to permit sewer service to rural land.
These findings do not support or propose changing the designation of any property on
the Deschutes County comprehensive plan or zoning map. The purpose of sewerage is
to serve existing and planned residential development to alleviate groundwater
contamination from onsite wastewater disposal systems, not to increase the
development potential of the area.
III. AFFECTED AREA
The area affected by the exception is generally comprised of unincorporated, nonfederal
property located between Sunriver and the Klamath County border. A map specifically
identifying the location of lands subject to this exception is included as Attachment.
3 ODEQ. 2013. South Deschutes/North Klamath Groundwater Protection: Report and Recommendations.
Nigg, E. and R. Baggett. 32pp. http://www.deq.state.or.us/wq/onsite/docs/SDNKreportrec.pdf
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IV. REVIEW CRITERIA
Ordinance 2014-XXX adopts these findings for a Goal 11 exception to allow sewer
service to rural lands in southern Deschutes County. Deschutes County lacks specific
approval criteria in Deschutes County Code (DCC) Titles 18, 22, or 23 for a legislative
plan and text amendment. The county is a co-applicant with DEQ, which has partnered
with DLCD; these findings demonstrate compliance with the applicable Oregon Revised
Statutes (ORS), Oregon Administrative Rules (OAR), statewide planning goals, and the
county’s comprehensive plan. DEQ and DLCD were the subject experts for the ORS,
OAR, and Statewide Planning Goals and prepared the findings for those areas; County
staff prepared the findings that pertained to the Comprehensive Plan.
The findings address requirements contained in the following state and local
regulations:
A. ORS 197, Comprehensive Land Use Planning
B. OAR Chapter 660, Division 4, Interpretation of Goal 2 Exceptions Process
C. OAR Chapter 660, Division 11, Public Facilities Planning
D. OAR Chapter 660, Division 12, Transportation Planning
E. Statewide Planning Goal 11, Public Facilities and Services
F. Other Statewide Planning Goals
G. Deschutes County Comprehensive Plan
H. Newberry Country: A Plan for Southern Deschutes County
A. ORS 197.732, Goal Exceptions
The pertinent sections of ORS 197.732 with findings are provided below.
(2) A local government may adopt an exception to a goal if:
(a) The land subject to the exception is physically developed to the extent
that it is no longer available for uses allowed by the applicable goal;
(b) The land subject to the exception is irrevocably committed as
described by Land Conservation and Development Commission rule to
uses not allowed by the applicable goal because existing adjacent uses
and other relevant factors make uses allowed by the applicable goal
impracticable; or
(c) The following standards are met:
(A) Reasons justify why the state policy embodied in the applicable
goals should not apply;
(B) Areas that do not require a new exception cannot reasonably
accommodate the use;
(C) The long term environmental, economic, social and energy
consequences resulting from the use at the proposed site with
measures designed to reduce adverse impacts are not significantly
more adverse than would typically result from the same proposal
being located in areas requiring a goal exception other than the
proposed site; and
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(D) The proposed uses are compatible with other adjacent uses or
will be so rendered through measures designed to reduce adverse
impacts.
FINDINGS: The provisions of ORS 197.732 are further refined and interpreted by
Statewide Planning Goal 2 and OAR chapter 660, divisions 4 and 11.The legal tests
established in state statute are satisfied by adequately responding to the applicable
provisions of the administrative rules. Please see the applicant’s response to
OAR chapter 660, divisions 4 and 11 in Subsections IV.B. and IV.C. of this report.
(4) A local government approving or denying a proposed exception shall set forth
findings of fact and a statement of reasons that demonstrate that the standards
of subsection (2) of this section have or have not been met.
FINDING: The findings in this document provide the factual basis for the Goal 11
exception based on the standards of the applicable administrative rules and county
comprehensive plan policies.
B. OAR chapter 660, division 4: Interpretation of Goal 2 Exceptions Process
Pertinent rules relating to exceptions generally, with findings, are provided below.
OAR 660-004-0000(2): An exception is a decision to exclude certain land from
the requirements of one or more applicable statewide goals in accordance with
the process specified in Goal 2, Part II, Exceptions. The documentation for an
exception must be set forth in a local government’s comprehensive plan. Such
documentation must support a conclusion that the standards for an exception
have been met. The conclusion shall be based on findings of fact supported by
substantial evidence in the record of the local proceeding and by a statement of
reasons that explains why the proposed use not allowed by the applicable goal,
or a use authorized by a statewide planning goal that cannot comply with the
approval standards for that type of use, should be provided for. The exceptions
process is not to be used to indicate that a jurisdiction disagrees with a goal.
FINDING: This Goal 11 exception is supported by facts and evidence and a statement
of reasons why the proposal should be approved contained in this report. These items
are offered in detail in the response to the provisions of OAR 660-004-0020 and -0022
and OAR 660-011-0060(9), below.
OAR 660-004-0010(1): The exceptions process is not applicable to Statewide
Goal 1 “Citizen Involvement” and Goal 2 “Land Use Planning.” The exceptions
process is generally applicable to all or part of those statewide goals that
prescribe or restrict certain uses of resource land, restrict urban uses on rural
land, or limit the provision of certain public facilities and services. These
statewide goals include but are not limited to:
* * *
(c) Goal 11 “Public Facilities and Services” as provided in OAR 660-011-
0060(9); * * *
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FINDING: The administrative rule expressly recognizes that Goal 11 could be subject to
an exception proposal. Subsection C of this section addresses the standards specified
in OAR 660-011-0060(9), which is the applicable exception language.
660-004-0018, Planning and Zoning for Exception Areas
(4) “Reasons” Exceptions:
(a) When a local government takes an exception under the “Reasons”
section of ORS 197.732(1)(c) and OAR 660-004-0020 through 660-004-
0022, plan and zone designations must limit the uses, density, public
facilities and services, and activities to only those that are justified in the
exception.
FINDINGS: The purpose of this Goal 11 exception is to allow sewer service on rural
lands in southern Deschutes County. This exception does not authorize any other uses
that would not be permissible under the existing comprehensive plan and implementing
ordinances. The exception does not amend existing limits in the plan on uses, densities,
or activities. The exception findings do justify a change in limitations on a public facility –
sewerage – but the uses served by the sewer are not proposed to become more
intensive as a result of the new service. The county plan must limit sewer service to
those areas justified in this exception.
OAR 660-004-0020(2): The four standards in Goal 2 Part II(c) required to be
addressed when taking an exception to a goal are described in subsections (a)
through (d) of this section, including general requirements applicable to each of
the factors:
(a) “Reasons justify why the state policy embodied in the applicable goals
should not apply.” The exception shall set forth the facts and assumptions
used as the basis for determining that a state policy embodied in a goal
should not apply to specific properties or situations, including the amount
of land for the use being planned and why the use requires a location on
resource land;
FINDINGS: In this case, the applicable state policy resides in Goal 11. The application
seeks relief from this provision of Goal 11:
Local Governments shall not allow the establishment or extension of
sewer systems outside urban growth boundaries or unincorporated
community boundaries, or allow extensions of sewer lines from within
urban growth boundaries or unincorporated community boundaries to
serve land outside those boundaries, except where the new or extended
system is the only practicable alternative to mitigate a public health hazard
and will not adversely affect farm or forest land.
OAR 660-004-0020(2)(a) essentially requires a three-part response: (1) a description of
the reason or reasons that justify why the state policy embodied in the applicable goal
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should not apply; (2) a description of the use being planned; and (3) why the use
requires a location on resource land.
Reasons Goal 11 Should Not Apply. The Goal 11 prohibition on providing sewer
service to rural land should not apply to South Deschutes County because onsite
sewage treatment and disposal systems are not protecting the groundwater quality in
the area. For the reasons explained below, sewerage is needed to prevent continued
contamination of groundwater.
Residents of south Deschutes and north Klamath counties face challenging wastewater
disposal conditions. The area has porous, sandy, pumice soil derived from volcanic
events and a shallow, vulnerable aquifer, both of which allow for the potential
contamination of drinking water. These local conditions are unusual, as other parts of
the state have finer silt and clay-like subsurface soil that can form a protective layer
above the groundwater.
Historical groundwater contamination in the downtown core of La Pine offers a good
illustration of the challenges facing much of the region. Studies of groundwater
contamination, hydrology and the effects of nitrates were conducted in southern
Deschutes County beginning in the late 1970s. Well monitoring and analysis in La Pine
was performed in response to very high nitrate concentrations in drinking water . Nitrate
concentrations in drinking water wells commonly exceeded the drinking water standard
of 10 mg/L nitrate-nitrogen and were elevated as high as 42 mg/L and were linked to
wastewater disposal from individual septic systems.4 Elevated (i.e., above natural
background) levels of nitrate-nitrogen entering groundwater are likely to also be
associated with other wastewater contaminants entering the groundwater.
Contamination in La Pine became so severe in the early 1980s that La Pine constructed
a sewer system providing better treatment and land disposal of wastewater in order to
reduce nitrogen concentrations in drinking water supplies. The operation of this sewer
system resulted in markedly improved groundwater quality in town. Monitoring wells for
the wastewater treatment plant have demonstrated steadily improving groundwater
conditions following improved treatment and disposal.
This historical contamination is both evidence of the vulnerability of the aquifer and a
cause for concern throughout the region, as the soil and groundwater conditions in
La Pine are similar to those throughout much of southern Deschutes and northern
Klamath counties.
Other surveys and studies over the years point to increasing groundwater contamination
throughout the region. A survey of groundwater data in 1993 and mo deling in 1995 by
DEQ indicated elevated nitrate concentrations and concern for future aquifer -wide
4 Oregon Health Authority Fact Sheet on Nitrates, available at
http://public.health.oregon.gov/HealthyEnvironments/DrinkingW ater/Monitoring/HealthEffects/Pages/nitrat
e.aspx.
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increases. Recent sampling of monitoring wells in the area demonstrated a small but
statistically significant increase in nitrate concentration between 1995 and 2011.5
The U.S. Geological Survey completed a La Pine National Demonstration Project and
mathematical modeling effort in 2007.6 The demonstration project was designed to test
innovative treatment technologies that would reduce nitrogen loading to groundwater
from onsite systems. The USGS also produced a three-dimensional model to estimate
the effects of nitrates in the shallow aquifer of a large area in southern Deschutes and
northern Klamath counties.7
These studies have reached the conclusion that the groundwater aquifer is vulnerable
to increasing concentrations of nitrates and other contaminants associated with
domestic sewage. The USGS study predicted nitrate concentrations increasing above
the federally adopted drinking water standard throughout the area over time.
Concentrations would increase for about 140 years after full build-out, at which time
more than 9,000 acres would have groundwater concentrations exceeding 10 mg/L.
Deschutes County attempted to address the area-wide groundwater problem through
various ordinances and requirements. For a period of time, certain residential
developments were required by county ordinance to install Advanced Treatment
Technology (ATT) onsite wastewater treatment and disposal systems. After those
ordinances were repealed and rescinded, the county asked DEQ to take the lead in
groundwater protection. DEQ then began conducting site -by-site groundwater risk
assessments to determine which sites were required to install ATT systems while the
county ordinances were in effect.
The nitrogen-reducing ATTs provide the best onsite treatment option, but they do not
truly address the long-term problem or offer the best level of groundwater protection for
the area as a whole. As steering committee members acknowledged in their
recommendations, the area would be best served by allowing more options to deal with
the larger concerns of area-wide contamination. The steering committee also
acknowledged the limitations of the ATT requirement and recommended a moratorium
on such systems until a more comprehensive solution could be made available to land
owners.
The steering committee realized that such options would require an area-wide exception
to Goal 11, and they recommended DEQ and Deschutes County pursue the exception.
DEQ agrees with this recommendation because an exception to Goal 11 provides
5 NEED CITATIONS TO THESE STUDIES
6 Williams, J.S., D.S. Morgan and S.R. Hinkle. 2007. Questions and answers about the effects of septic
systems on water quality in the La Pine area, Oregon. USGS Factsheet 2007-3103.
http://pubs.usgs.gov/fs/2007/3103/
7 Morgan, D.S., S.R. Hinkle, R.J. Weick. 2007. Evaluation of approaches for managing nitrate loading
from on-site wastewater systems near La Pine, Oregon USGS Scientific Investigations Report 2007-5237
http://pubs.usgs.gov/sir/2007/5237/
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residents with a tool to pursue meaningful and long-term groundwater protection in a
way that is not currently available to them.
An area-wide Goal 11 exception would allow for an acceptable level of wastewater
control and is necessary to protect public health in the area over the long term. The
area requires a regional solution to what is truly an area-wide problem – one with risk
increasing the longer a comprehensive solution is not in place. Up to this point, public
agencies including DEQ have looked at individual property risk on a site-by-site basis.
This strategy will fail because it prohibits greater regional planning and infrastructure to
address a significant and regional public health risk.
This risk is compounded by the relatively high density of development in the area, as
more than 75 percent of the approximately 14,000 properties in the area are two acres
or smaller. There is little precipitation in the area to dilute contaminants . Too many
septic systems were discharging into porous soil and over time there would be
increasing contamination of the shallow, vulnerable aquifer that many people were
using as their drinking water supply
The Use Being Planned. In this case, most of the area proposed for sewage service
has already been developed with permitted residential uses. In most exception
proposals, “the use being planned” would add to the built environment by enabling
development activity (i.e., residential, industrial, commercial, etc.) not allowed by the
existing zoning. Goal 11 exceptions require a different perspective.
The Land Use Board of Appeals (LUBA) has held, “In the context of a Goal 11
exception to extend public facilities to serve proposed development of lands outside the
urban growth boundary, the ‘proposed use’ can only be the proposed development to
be served by the facility extension and not the extended public facility.” Todd v. City of
Florence, 52 Or LUBA 445 (2006). In this case, the “use being planned” is __ existing
residential units and __ potential new units allowed by existing zoning.
This situation resembles Todd because it would authorize the establishment or
extension of sewer service in order to support development. This situation is
distinguishable because the proposed facility in this case is necessary to support the
“use being planned” in order to improve the area’s groundwater quality over time. The
subject lands are planned and zoned to receive residential development. Failing to
authorize sewer service will eventually create unacceptable levels of contamination in
the groundwater and place citizens at risk of health concerns.
Location on Resource Land. This Goal 11 exception does not generally request a
location on resource land. Instead, sewer service would be available to residential
development on lands planned and zoned for residential use. Small amounts of
resource lands are includes but no upzoning will occur. Most of this development exists.
Some potential for future development on existing platted lots is possible.
OAR 660-004-0020(2) (continued)
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(b) “Areas that do not require a new exception cannot reasonably
accommodate the use”. The exception must meet the following
requirements:
(A) The exception shall indicate on a map or otherwise describe the
location of possible alternative areas considered for the use that do
not require a new exception. The area for which the exception is
taken shall be identified;
(B) To show why the particular site is justified, it is necessary to
discuss why other areas that do not require a new exception cannot
reasonably accommodate the proposed use. Economic factors may
be considered along with other relevant factors in determining that
the use cannot reasonably be accommodated in other areas. Under
this test the following questions shall be addressed:
(i) Can the proposed use be reasonably accommodated on
nonresource land that would not require an exception,
including increasing the density of uses on nonresource
land? If not, why not?
(ii) Can the proposed use be reasonably accommodated on
resource land that is already irrevocably committed to
nonresource uses not allowed by the applicable Goal,
including resource land in existing unincorporated
communities, or by increasing the density of uses on
committed lands? If not, why not?
(iii) Can the proposed use be reasonably accommodated
inside an urban growth boundary? If not, why not?
(iv) Can the proposed use be reasonably accommodated
without the provision of a proposed public facility or service?
If not, why not?
(C) The “alternative areas” standard in paragraph B may be met by
a broad review of similar types of areas rather than a review of
specific alternative sites. Initially, a local government adopting an
exception need assess only whether those similar types of areas in
the vicinity could not reasonably accommodate the proposed use.
Site specific comparisons are not required of a local government
taking an exception unless another party to the local proceeding
describes specific sites that can more reasonably accommodate
the proposed use. A detailed evaluation of specific alternative sites
is thus not required unless such sites are specifically described,
with facts to support the assertion that the sites are more
reasonable, by another party during the local exceptions
proceeding.
FINDINGS: Regarding OAR 660-004-0020(2)(b)(A), a map of the area subject to this
exception is provided in Attachment A.
Regarding paragraph (b)(B), areas that do not require a new exception cannot
reasonably accommodate the use because, as described above, the use in this case is
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residential development on lands planned and zoned for that use, with some resource
lands included that are. Identified resource lands have an existing settlement pattern
and are either adjacent to rural residential exception areas or surrounded by federal
land. This Goal 11 exception will create the ability to support existing homes and some
future households with sewer service, which is necessary to preserve the integrity of the
area’s groundwater. The existing homes and lands planned and zoned for development
will continue to occupy their current locations and will continue to utilize local aquifers as
a domestic water source. Utilizing a different area is not possible. In other words, the
development pattern is where it is.
To best protect public health, the exception area includes unincorporated, nonfederal
portions of Deschutes County except those areas already authorized for sewers
generally located south of Sunriver and north of Klamath County (see Attachment A).
This is generally the area in Deschutes County studied by the USGS (see Attachment
G). Deschutes County determined that groundwater protection is necessary for this area
because groundwater was determined to be vulnerable to contamination from individual
onsite wastewater disposal systems.
The exception area includes all existing platted lots and other lands necessary for
community water supply and wastewater treatment infrastructure. No up-zoning or
increases in development densities other than allowed by current zoning shall occur
within the Goal 11 exception area.
Regarding accommodation of the use on nonresource land or existing exceptions land
(paragraphs (b)(B)(i) and (ii)), these provisions assume the proposal is for an exception
to Goal 3 or Goal 4 – the “resource goals.” The “applicable goal” in this case is Goal 11.
“Uses not allowed by the applicable goal” in this case are not “nonresource uses,” but
rather rural uses provided with sewer service. To address the these provisions in the
context of a Goal 11 exception, the purpose of the exception is to allow an additional
option – sewerage – for contending with a groundwater quality problem associate d with
existing residential development. LUBA has ruled that “the use” in a Goal 11 exception
is the development at the end of the sewer line, not the sewer line itself (Todd v. City of
Florence, 52 Or LUBA 445 (2006)). Existing homes cannot reasonably be expected to
relocate. The small amount of future development currently permitted in the area could
potentially be prohibited and those development rights transferred to a different location
that does not require an exception, but that would not contribute significantly to solving
the groundwater problem or alleviate the need for this exception.
For these same reasons, the proposed use cannot be reasonably accommodated inside
an urban growth boundary (paragraph (b)(B)(iii)). This Goal 11 exception will create the
ability to support existing homes and some future households with sewer service, which
is necessary to preserve the integrity of the area’s groundwat er. The existing homes
and lands planned and zoned for development will continue to occupy their current
locations and will continue to utilize local aquifers as a domestic water source.
In this Goal 11 exception, the “use being planned” is existing homes and some new
residences on lands planned and zoned for residential development. The proposed
facilities would be sewer service that is not otherwise available under Goal 11. Existing
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and possible residential development in these areas cannot be reasonably
accommodated without the opportunity to receive sewer service because, as described
in this document, sewer service is necessary to guard against unacceptable levels of
pollution in the area’s groundwater that would expose citizens to health risks.
OAR 660-004-0020(2) (continued)
(c) “The long-term environmental, economic, social and energy
consequences resulting from the use at the proposed site with measures
designed to reduce adverse impacts are not significantly more adverse
than would typically result from the same proposal being located in areas
requiring a goal exception other than the proposed site.” The exception
shall describe: the characteristics of each alternative area considered by
the jurisdiction in which an exception might be taken, the t ypical
advantages and disadvantages of using the area for a use not allowed by
the Goal, and the typical positive and negative consequences resulting
from the use at the proposed site with measures designed to reduce
adverse impacts. A detailed evaluation of specific alternative sites is not
required unless such sites are specifically described with facts to support
the assertion that the sites have significantly fewer adverse impacts during
the local exceptions proceeding. The exception shall include the reasons
why the consequences of the use at the chosen site are not significantly
more adverse than would typically result from the same proposal being
located in areas requiring a goal exception other than the proposed site.
Such reasons shall include but are not limited to a description of: the facts
used to determine which resource land is least productive, the ability to
sustain resource uses near the proposed use, and the long-term economic
impact on the general area caused by irreversible removal of the land from
the resource base. Other possible impacts to be addressed include the
effects of the proposed use on the water table, on the costs of improving
roads and on the costs to special service districts;
FINDING: The “use being planned” is composed of existing dwellings and some new
dwellings allowed outright on land planned and zoned for residential use and under
certain restrictions on lands zoned for resource use. The proposed public service
includes sewer service that is not otherwise allowed under Goal 11. OAR 660-004-
0020(2)(c) requires an analysis of impacts from the use being located in alternative
“areas.” In this exception, the area in question will be the same for any alternative. This
criterion arguably does not apply. Instead, the environmental, social, economic, and
energy (ESEE) consequences of providing sewer service compared to not providing
that service are presented herein.
Environmental Consequences. A long-term environmental consequence of no sewer
service has been studied by DEQ and USGS (see footnotes 5, 6 and 7) All of these
studies showed long-term degradation of groundwater quality caused by residential
onsite sewage disposal systems. Since a large majority of the residential uses already
exist, limiting additional development will not solve the problem. Nitrates will continue to
accumulate in the groundwater, which is also the areas’ drinking water, ultimately
PAGE 13 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
exceeding safe drinking water standards. See subsection II.A, “Groundwater Quality of
in South Deschutes County,” in these findings.
A long-term environmental consequence of providing sewer service to some or all of the
affected area will be a slowing and ultimately a reversal of the degradation of water
quality South Deschutes County.
Since the problem this exception is intended to solve relates to safe drinking water,
provision of drinking water to the affected area is another potential solution option that
should be considered. The long-term environmental consequences of providing drinking
water to the area instead of providing sewer service include continued contamination of
groundwater. Groundwater is not just drinking water. It also serves as a barometer of
overall ecosystem health. To put it another way, a healthy ecosystem does not have
contaminated ground water. Providing drinking water service rather than sewer service
may solve the safe drinking water problem, but it does not solve the larger issue of
groundwater quality in South Deschutes County.
On balance, the long-term environmental consequences of providing sewer service to
the affected area are positive because groundwater quality in the affected area will at
least get no worse, and is likely to improve.
Economic Consequences. Providing sewer service will have long-term economic
consequences, while not providing the service will have different economic
consequences. The affected area is rural and no service district currently exists to
establish the system, so there is no existing tax base to subsidize a sewer system
project. Costs will be entirely borne by residents and property owners within the affected
area (with any state or federal assistance that may materialize).
If sewer service is not provided, groundwater quality will continue to degrade and
Deschutes County will at some point in the future be forced to contend with a water
supply that does not meet safe drinking water standards. Waiting to address the
problem will result in a more widespread issue because additional dwellings will have
been built. A larger network of sewer lines and a higher-capacity treatment system will
likely be required if a solution to the groundwater quality problem is not addressed
sooner. While the potential number of ratepayers may be greater in the future, diluting
each individual user’s rate, this does not necessarily make the no-build alternative the
lower-cost option. Interest rates are at an historically low level and construction c osts
tend to increase over time.
Establishing a sewer system is expensive. No feasibility studies have been conducted
so the most appropriate system technology has not been determined. The sequencing
of installation has not been established (it is not anticipated that the entire affected area
will be sewered at once, if ever). Completion of these plans would not be prudent before
approval of this Goal 11 exception. Consequently, a financing plan has not been
completed and detailed costs of the system are not available, but general conclusions
can be made nonetheless. In any case, it is reasonable to assume that installation and
operation of an entirely new sewer system will lead to relatively high rates for ea ch
hookup in the affected area.
PAGE 14 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
The alternative long-term economic consequences are not “build” versus “no-build,” but
rather “now” or “later.” Addressing the problem before it gets worse has long-term
economic benefits to ratepayers in the affected area.
Social and Energy Consequences. No social or energy consequences have been
identified that would be different for the alternatives under consideration.
Summary. The long-term ESEE consequences of establishing a sewer system to
address groundwater quality problems in the affected area versus continuing with onsite
sewage disposal systems favors establishing a system. The long-term environmental
consequences clearly favor establishment of the system. The long-term economic
consequences are not as clearly in favor of the system but available information shows
that establishing a system earlier will be beneficial. The long-term social and energy
consequences of various alternatives are the same for each alternative.
OAR 660-004-0020(2) (continued)
(d) “The proposed uses are compatible with other adjacent uses or will be
so rendered through measures designed to reduce adverse impacts.” The
exception shall describe how the proposed use will be rendered
compatible with adjacent land uses. The exception shall demonstrate that
the proposed use is situated in such a manner as to be compatible with
surrounding natural resources and resource management or production
practices. “Compatible” is not intended as an absolute term meaning no
interference or adverse impacts of any type with adjacent uses.
FINDING: The “proposed uses” are existing homes and some new households on lands
planned and zoned for residential development. The prohibition in Goal 11 on sewer
service to rural lands works in concert with Goal 14, “Urbanization,” to direct urban
development inside urban growth boundaries. That is, comprehensive plans are to
provide for an orderly transition from rural to urban uses. A patchwork of urban-type
subdivisions scattered across the landscape is generally incompatible with adjacent
farm and forest uses and wildlife habitat conservation. Rural residents often find nearby
high-density development incompatible with their rural environment. Sewer service does
not cause, but it enables, a checkerboard pattern of high-density subdivisions.
The Deschutes County comprehensive plan and zoning limit development in the
affected area to a rural level of development. The rural residential zoning is limited to
one dwelling per lot and new lots must be 10 acres in size. Resource zoning under goal
3 & 4 require even larger minimum parcel sizes and have greater restrictions regarding
land divisions. Sewer service allowed under this exception will not increase the
residential density of the area beyond what would develop without the sewer because
the county comprehensive plan and zoning will not change .
OAR 660-004-0020(3): If the exception involves more than one area for which
the reasons and circumstances are the same, the areas may be considered as a
PAGE 15 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
group. Each of the areas shall be identified on a map, or their location otherwise
described, and keyed to the appropriate findings.
FINDING: To best protect public health, the exception area includes unincorporated,
nonfederal portions of Deschutes County except those areas already authorized for
sewers generally located south of Sunriver and north of Klamath County (see
Attachment A). This is the general area in Deschutes County studied by USGS.
Deschutes County determined that this area is necessary for groundwater protection
and where groundwater was determined to be vulnerable to contamination from
individual onsite wastewater disposal systems.
OAR 660-004-0020(4): For the expansion of an unincorporated community
described under OAR 660-022-0010, including an urban unincorporated
community pursuant to OAR 660-022-0040 (2), the reasons exception
requirements necessary to address standards 2 through 4 of Goal 2, Part II(c), as
described in of subsections (2)(b), (c) and (d) of this rule, are modified to also
include the following: * * *
FINDING: The exception does not involve an expansion of an unincorporated
community described under OAR 660-022-0010. Therefore, the provisions of OAR 660-
004-0020(4) are not applicable.
OAR 660-004-0022: An exception under Goal 2, Part II(c) may be taken for any
use not allowed by the applicable goal(s) or for a use authorized by a statewide
planning goal that cannot comply with the approval standards for that type of use.
* * * Reasons that may allow an exception to Goal 11 to provide sewer service to
rural lands are described in OAR 660-011-0060. * * *
FINDING: Sewer service to rural land is not permitted by Goal 11. The criteria in
OAR 660-011-0060 area addressed below.
C. OAR chapter 660, division 11: Public Facilities Planning
Pertinent rules relating to implementation of Goal 11, with findings, are provided below.
OAR 660-011-0060(2): Except as provided in sections (3), (4), (8), and (9) of this
rule, and consistent with Goal 11, a local government shall not allow:
(a) The establishment of new sewer systems outside urban growth
boundaries or unincorporated community boundaries;
(b) The extension of sewer lines from within urban growth boundaries or
unincorporated community boundaries in order to serve uses on land
outside those boundaries;
(c) The extension of sewer systems that currently serve land outside
urban growth boundaries and unincorporated community boundaries in
order to serve uses that are outside such boundaries and are not served
by the system on July 28, 1998.
PAGE 16 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
FINDINGS: This rule section provides a prohibition on most rural sewer service.
Subsection (2)(a) of this rule is pertinent to the circumstances in South Deschutes
County. The proposed system has not yet been designed, so the affected area may be
served by establishment of new sewer system (subsection (a)) or by extension of lines
from within an urban growth boundary (La Pine) or unincorporated community
(Sunriver) to these lands outside the community (subsection (b)). OAR 660-011-
0060(2)(c) does not apply.
Because of this prohibition, which implements the same prohibition in Goal 11, an
exception to Goal 11 is required to establish or extend a sewer system to the affected
area. The reasons Goal 11 should not apply, and findings showing the exception
complies with relevant administrative rules, are provided in the previous section of this
findings document. OAR 660-011-0060(3), (4), and (8), referenced in Section (2), do not
apply to the circumstances in the affected area and therefore are not relevant to this
exception. Specifically, no components of a sewer system to serve lands inside an
urban growth boundary are proposed, there is no specifically declared public health
hazard, and there is no existing sewer district or sanitary authority.
OAR 660-011-0060(9): A local government may allow the establishment of new
sewer systems or the extension of sewer lines not otherwise provided for in
section (4) of this rule, or allow a use to connect to an existing sewer line not
otherwise provided for in section (8) of this rule, provided the standards for an
exception to Goal 11 have been met, and provided the local government adopts
land use regulations that prohibit the sewer system from serving any uses or
areas other than those justified in the exception. Appropriate reasons and facts
for an exception to Goal 11 include but are not limited to the following:
(a) The new system, or extension of an existing system, is necessary to
avoid an imminent and significant public health hazard that would
otherwise result if the sewer service is not provided; and, there is no
practicable alternative to the sewer system in order to avoid the imminent
public health hazard, or
(b) The extension of an existing sewer system will serve land that, by
operation of federal law, is not subject to statewide planning Goal 11 and,
if necessary, Goal 14.
FINDINGS: Subsections (a) and (b) represent two alternative justifications for an
exception to Goal 11. However, Deschutes County finds that this language is not
exclusive. In other words, it is possible to justify an exception to Goal 11 under
circumstances that do not comport with OAR 660-011-0060(9)(a) or (b). See Foland v.
Jackson County, 61 Or LUBA 264 (2010).
In this case, the reason Goal 11 should not apply relates to long-term effects on water
quality. See findings for compliance with OAR chapter 660, division 4 in the previous
section of this findings document. After decades of studies and monitoring, DEQ has
determined that there is a growing health threat of groundwater contamination caused
by onsite septic systems in the area of south Deschutes and north Klamath counties.
Public health can best be protected through a range of treatment and disposal options
not allowed under Goal 11.
PAGE 17 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
There has not been “an imminent health hazard” as referenced in subsection (a). Many
studies over the years show groundwater contamination in the La Pine study area. Most
recently, the USGS studies and reports indicated a slow-moving but expanding plume of
human effluent-tainted groundwater. Over time, that plume will spread to deep areas of
the aquifer and will become so widespread that the drinking water becomes unusable.
There is a real threat from nitrates, pharmaceuticals, personal hygiene byproducts and
organic wastewater compounds entering groundwater. The current trend must be
reversed to protect human health in the long term. This contamination is occurring at a
rate that allows for some planning; the threat to public health is not imminent, but it is
inevitable.
This rule requires that the Goal 11 exception be accompanied by “land use regulations
that prohibit the sewer system from serving any uses or areas other than those justified
in the exception” adopted by Deschutes County. Along with this exceptions document,
the county adopts new Comprehensive Plan Policy __, which states: ______________.
D. OAR chapter 660, division 12: Transportation Planning
OAR 660-012-0060, “Plan and Land Use Regulation Amendments,” requires
consideration of the effects of development allowed through a plan amendment on
transportation facilities.8 Specifically, the rule requires a determination of whether the
8 OAR 660-012-0060 provides, in relevant part:
(1) If an amendment to a functional plan, an acknowledged comprehensive plan, or a land use
regulation (including a zoning map) would significantly affect an existing or planned transportation
facility, then the local government must put in place measures as provided in section (2) of this
rule, unless the amendment is allowed under section (3), (9) or (10) of this rule. A plan or land
use regulation amendment significantly affects a transportation facility if it would:
(a) Change the functional classification of an existing or planned transportation facility
(exclusive of correction of map errors in an adopted plan);
(b) Change standards implementing a functional classification system; or
(c) Result in any of the effects listed in paragraphs (A) through (C) of this subsection
based on projected conditions measured at the end of the planning period identified in the
adopted TSP. As part of evaluating projected conditions, the amount of traffic projected to be
generated within the area of the amendment may be reduced if the amendment includes an
enforceable, ongoing requirement that would demonstrably limit traffic generation, including, but
not limited to, transportation demand management. This reduction may diminish or completely
eliminate the significant effect of the amendment.
(A) Types or levels of travel or access that are inconsistent with the functional
classification of an existing or planned transportation facility;
(B) Degrade the performance of an existing or planned transportation facility such that it
would not meet the performance standards identified in the TSP or comprehensive plan; or
(C) Degrade the performance of an existing or planned transportation facility that is
otherwise projected to not meet the performance standards identified in the TSP or
comprehensive plan.
(2) If a local government determines that there would be a significant effect, then the local
government must ensure that allowed land uses are consistent with the identified function,
capacity, and performance standards of the facility measured at the end of the planning period
identified in the adopted TSP through one or a combination of the remedies listed in (a) through
(e) below, unless the amendment meets the balancing test in subsection (2)(e) of this section or
qualifies for partial mitigation in section (11) of this rule. A local government using subsection
(2)(e), section (3), section (10) or section (11) to approve an amendment recognizes that
PAGE 18 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
newly allowed uses will “significantly affect” on existing or planned facilities, and if there
is a significant effect, then the local government must “ensure that allowed land uses
are consistent with the identified function, capacity, and performance standards of the
facility.”
_____[more]_______
additional motor vehicle traffic congestion may result and that other facility providers would not be
expected to provide additional capacity for motor vehicles in response to this congestion.
(a) Adopting measures that demonstrate allowed land uses are consistent with the
planned function, capacity, and performance standards of the transportation facility.
(b) Amending the TSP or comprehensive plan to provide transportation facilities,
improvements or services adequate to support the proposed land uses consistent with the
requirements of this division; such amendments shall include a funding plan or mechanism
consistent with section (4) or include an amendment to the transportation finance plan so that the
facility, improvement, or service will be provided by the end of the planning period.
(c) Amending the TSP to modify the planned function, capacity or performance standards
of the transportation facility.
(d) Providing other measures as a condition of development or through a development
agreement or similar funding method, including, but not limited to, transportation system
management measures or minor transportation improvements. Local governments shall, as part
of the amendment, specify when measures or improvements provided pursuant to this subsection
will be provided.
(e) Providing improvements that would benefit modes other than the significantly affected
mode, improvements to facilities other than the significantly affected facility, or improvements at
other locations, if the provider of the significantly affected facility provides a written statement that
the system-wide benefits are sufficient to balance the significant effect, even though the
improvements would not result in consistency for all performance standards.
(3) Notwithstanding sections (1) and (2) of this rule, a local government may approve an
amendment that would significantly affect an existing transportation facility without assuring that
the allowed land uses are consistent with the function, capacity and performance standards of the
facility where:
(a) In the absence of the amendment, planned transportation facilities, improvements and
services as set forth in section (4) of this rule would not be adequate to achieve consistency with
the identified function, capacity or performance standard for that facility by the end of the planning
period identified in the adopted TSP;
(b) Development resulting from the amendment will, at a minimum, mitigate the impacts
of the amendment in a manner that avoids further degradation to the performance of the facility
by the time of the development through one or a combination of transportation improvements or
measures;
(c) The amendment does not involve property located in an interchange area as defined
in paragraph (4)(d)(C); and
(d) For affected state highways, ODOT provides a written statement that the proposed
funding and timing for the identified mitigation improvements or measures are, at a minimum,
sufficient to avoid further degradation to the performance of the affected state highway. However,
if a local government provides the appropriate ODOT regional office with written notice of a
proposed amendment in a manner that provides ODOT reasonable opportunity to submit a
written statement into the record of the local government proceeding, and ODOT does not
provide a written statement, then the local government may proceed with applying subsections
(a) through (c) of this section.
PAGE 19 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
E. Statewide Planning Goals
1. Goal 1: Citizen Involvement
FINDING: Deschutes County conducted multiple workshops and public hearings
regarding groundwater quality in the southern part of the county generally and on the
exception proposal specifically. Any interested was provided the opportunity to offer
evidence and testimony as part of the review process. This exception was reviewed in
accordance with Deschutes County public involvement requirements and Goal 1.
2. Goal 2: Land Use Planning
FINDING: The Goal 2 exceptions process is further interpreted and implemented by the
provisions of OAR chapter 660, divisions 4 and 11. See Subsections IV.B. and IV.C. of
this exceptions document for findings regarding compliance with these rules. The
applicable administrative rule provisions have been identified and addressed. Goal 2 is
satisfied.
3. Goal 3: Agricultural Lands
FINDING: This Goal 11 exception includes only a small amount of lands subject to Goal
3. Nothing in this exception would change the allowed uses in these minority portions of
the exception area. Therefore, Goal 3 is not implicated.
4. Goal 4: Forest Land
FINDING: This Goal 11 exception includes only a small amount of lands subject to Goal
4. Nothing in this exception would change the allowed uses in these minority portions
of the exception area. Therefore, Goal 4 is not implicated.
5. Goal 5: Natural Resources, Scenic and Historic Areas, and Open Spaces
FINDING: This exception does not authorize development beyond what is currently
allowed by the acknowledged comprehensive plan. Existing plan and code provisions
enacted by Deschutes County to protect resources under Goal 5 will remain effective.
This Goal 11 exception does not conflict with the requirements of Goal 5.
6. Goal 6: Air, Water and Land Resources Quality
Goal 6 provides:
All waste and process discharges from future development, when
combined with such discharges from existing developments shall not
threaten to violate, or violate applicable state or federal environmental
quality statutes, rules and standards. With respect to the air, water and
land resources of the applicable air sheds and river basins described or
included in state environmental quality statutes, rules, standards and
implementation plans, such discharges shall not (1) exceed the carrying
capacity of such resources, considering long range needs; (2) degrade
such resources; or (3) threaten the availability of such resources.
PAGE 20 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
FINDING: This Goal 11 exception does not authorize development beyond what is
authorized by the acknowledged comprehensive plan. This exception is intended to
further the policy articulated in Goal 6 by preventing future violation of applicable
environmental quality standards and exceedance of the carrying capacity of water and
land resources of South Deschutes County. All future sewerage permitted as a result of
this exception will be subject to permitting though DEQ to ensure all waste discharges
comply with applicable standards and regulations.
7. Goal 7: Natural Hazards
FINDING: Existing plan and code provisions enacted by Deschutes County to protect
life and property from natural hazards under Goal 7 will remain effective. This Goal 11
exception does not conflict with the requirements of Goal 7.
8. Goal 8: Recreational Needs
FINDING: No provision of Goal 8 applies to this exception. While there are recreation
facilities in the affected area, the sewer service permitted by this Goal 11 exception will
not detrimentally affect the capacity of these facilities to fulfill the recre ation needs of the
area. The exception does not conflict with the requirements of Goal 8.
9. Goal 9: Economic Development
FINDING: Goal 9 provides, in part, “Comprehensive plans and policies shall contribute
to a stable and healthy economy in all regions of the state.” The sewer service permitted
as a consequence of this exception will serve residential use and therefore should have
no effect on the stability of the economy in Deschutes County or Central Oregon. The
exception does not conflict with the requirements of Goal 9.
10. Goal 10: Housing
FINDING: Goal 10 and its implementing rules direct that needed housing to be
accommodated inside urban growth boundaries. This Goal 11 exception does not affect
lands within an urban growth boundary and is not designed to create housing
opportunities beyond what are currently designated in the acknowledged
comprehensive plan. Goal 10 does not apply.
11. Goal 11: Public Facilities
FINDING: Goal 11 is addressed in Subsection IV.D. of this exception document.
12. Goal 12: Transportation
FINDING: Goal 12 is addressed in Subsection IV.E. of this exception document.
13. Goal 13: Energy Conservation
Goal 13 provides:
PAGE 21 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
Land and uses developed on the land shall be managed and controlled so
as to maximize the conservation of all forms of energy, based upon sound
economic principles.
FINDING: This Goal 11 exception does not authorize development beyond what is
currently allowed by the acknowledged comprehensive plan. This exception does not
conflict with the requirements of Goal 13.
14. Goal 14: Urbanization
FINDING: Goal 14 requires that comprehensive plans provide for “an orderly and
efficient transition from rural to urban land use.” Sewer service by its nature tends to be
associated with urban uses. Because sewer systems are expensive to install, maintain,
and operate, system operators tend to maximize the number of hookups to share costs
and minimize the length of lines to minimize expenses. More, denser development
leads to urbanization.
However, the land proposed to be served by the sewer system permitted by this
exception is currently planned and zoned to allow a rural level of use. Deschutes
County concurrently adopts Comprehensive Plan Policy __, which states:
“______________.” Rural use will be maintained by the plan and zoning provisions. The
plan for South Deschutes County will continue to provide for an orderly and efficient
transition from rural to urban land use, so the exception does not conflict with Goal 14.
15. Goals 15 through 19
FINDING: Goal 15 relates to the Willamette River and Goals 16 through 19 relate to the
coastal zone and ocean. None of these are applicable to this Goal 11 exception.
F. Deschutes County Comprehensive Plan
Chapter 2 of the county plan, “Resource Management,” includes the following policies
under Goal 5, “Protect and improve water quality in the Deschutes River Basin.”
Policy 2.5.19 Coordinate with stakeholders to address water-related public health
issues.
a. Support amendments to State regulations to permit centralized sewer systems
in areas with high levels of existing or potential development or identified water
quality concerns.
b. If a public health hazard is declared in rural Deschutes County, expedite
actions such as legislative amendments allowing sewers or similar infrastructure.
Finding: A goundwater-related public health issue has been identified, as described in
Subsection II.A of this exceptions document. Deschutes County has coordinated with
residents and property owners in South Deschutes County for at least 20 years in an
effort to resolve the identified issue. DEQ formed a steering committee of local residents
to address the issue, and the committee recommended this Goal 11 exception.
Deschutes County has coordinated with DEQ and DLCD throughout the local review
PAGE 22 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
process. The county has complied with this policy in the development of a solution to
groundwater quality issues in the affected area.
Policy 2.5.20 Work with the community to expand the range of tools available to
protect groundwater quality by reviewing new technologies, including tools to
improve the quality and reduce the quantity of rural and agricult ural stormwater
runoff.
FINDING: This Goal 11 exception is part of a larger effort to add tools for addressing the
groundwater quality issues in South Deschutes County. The county formerly required
Advanced Treatment Technology systems for onsite sewage disposal; this effort proved
unsuccessful but it demonstrates that Deschutes County has continued to search for a
reasonable solution to rising nitrate levels in the groundwater. The specific technology
that will be used to provide sewage disposal and treatment in the area has not been
determined. Approval of new technology will ultimately be DEQ’s responsibility, but
Deschutes County, through this Goal 11 exception, shall remove barriers to reasonable
alternative technologies.
G. Newberry Country: A Plan for Southern Deschutes County, 2012-2032
Deschutes County adopted a land use plan specifically for the southern part of the
county in 2013 (Ordinance 2013-007). Pertinent goals and policies from this plan are
addressed below.
Goal 5: Address high groundwater lots and zoning and surveying issues.
Policy 5.1 Develop a work plan with affected stakeholders to determine the
future development and conservation potential of approximately 1,500 high
groundwater lots. The work plan will need to incorporate the potential for an
unknown number of lots to be served by centralized sewer or other methods of
collection in the future, which would make them developable, where that
possibility may not currently exist. The work plan shall, at a minimum, analyze:
a. The impact of the newly permitted development on roads, riparian
areas, wildlife habitat, and wetlands; and
b. Acquisition options such as purchasing the lots, land transfe rs or other
ideas.
FINDING: This Goal 11 exception will allow the potential establishment of sewers on
rural lands in South Deschutes County. The provided maps and written description of
the affected area encompasses the approximately 1,500 lots with high groundwater.
The section of this exceptions document dealing with Statewide Planning Goals 5, 6, 7,
and 12 addresses Policy 5.1.a. See Subsection IV. E. of this section. As no property is
being purchased at this time, Policy 5.1.b does not apply. The Goal 11 exception is
consistent with Goal 5 and its policies from the Newberry Country Plan.
Goal 9: Partner with the Oregon Department of Environmental Quality (DEQ) to
protect groundwater and public health.
PAGE 23 OF 23 – DRAFT EXHIBIT “X” TO ORDINANCE 2015-XXX
Policy 9.1 Explore opportunities for Goal 11 exceptions and the full range of
advance wastewater treatment opportunities, including but not limited to, the use
of onsite alternative treatment technology, centralized sewer systems and cluster
systems.
Policy 9.2 Conduct a joint Board of County Commissioner/Planning Commission
hearing in Newberry Country to:
a. Discuss the South County/Northern Klamath County steering committee
recommendations; and
b. Allow for public comments
FINDING: This Goal 11 exception is expressly specified in Policy 9.1. The Board of
County Commissioners and Planning Commission held a joint meeting in La Pine on
July 25, 2013, to hear the recommendations from the South County/Northern Klamath
County steering committee and received public comments.
V. ATTACHMENTS
A. Map of Areas Subject to the Goal 11 Exception.
B. Amendment to Deschutes County Comprehensive Plan.
C. Amendment to Deschutes County Comprehensive Plan.
D. Oregon Health Authority Fact Sheet on Nitrates.
E. U.S. Environmental Protection Agency Drinking Water Standards.
F. South Deschutes/North Klamath Groundwater Protection: Report and
Recommendations. ODEQ, 2013
G. Evaluation of Approaches for Managing Nitrate Loading from On-Site
Wastewater Systems near La Pine, Oregon. USGS, 2007
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R
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2
2
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BR
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SPRING RIVER RD
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DAWN RD
TWIN DR
LAVA DR
PARK DR
PIERCE RD
F S 4 4 2 0
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L
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FOR
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L
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ST
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L
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FS4410
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3
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D
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A
W
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0
4
0
JA
C
K
P
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N
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L
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P
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ROSL
A
N
D
R
D
COVINA RD
ME
A
D
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W
L
N
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H
S
T
3RD S
T
BO
U
N
D
A
R
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D
W A G O N T R A I L
R D
JACINTO RD
PI
N
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D
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BI
G
T
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M
B
E
R
D
R
LA
Z
Y
R
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V
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R
D
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DYKE RD
ELSINORE RD
LAPINE STATE RECREATION RD
HO
L
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D
A
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D
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DAVIS AVE
HO
W
A
R
D
L
N
DO
R
R
A
N
C
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M
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A
D
O
W
R
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DOWNEY RD
DO
E
L
N
LEONA LN
MI
T
T
S
W
A
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DEEDON RD
AZUSA RD
RIM DR
PI
N
E
W
O
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D
A
V
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W
B
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R
R
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R
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M
A
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I
T
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D
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BIG RIVER DR
BES
S
O
N
R
D
4T
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S
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DEER AVE
DU
S
T
A
N
R
D
JACK
P
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N
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R
D
OLD MILL RD
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D
S
T
SNOW GOOSE RD
ST
E
A
R
N
S
R
D
RA
N
C
H
D
R
WO
L
F
S
T
PARKWAY DR
FINLEY BUTTE RD
SW
A
N
R
D
FONTANA RD
STAGESTOP DR
P
O
W
E
R
L
I
N
E
R
D
HERMOSA RD
CAGLE RD
BL
U
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A
G
L
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R
D
GLENDALE RD
VANDEVERT
R
D
AN
T
L
E
R
L
N
FIR R
D
DE
E
R
F
O
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S
T
D
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S I L V E R FOXDR
WE
S
T
D
R
ZA
G
T
L
N
EL
D
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R
B
E
R
R
Y
L
N
ALPINE DR
SK
I
D
G
E
L
R
D
N E S T P I NE DR
RU
S
S
E
L
L
R
D
L U N A R D R
R I V E R R D
1ST ST
CE
N
T
E
R
D
R
WO
O
D
S
T
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C
K
D
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PI
N
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F
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T
D
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RI
V
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R
L
A
N
D
A
V
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DE
E
R
S
T
WRIGHT AVE
UPLAND
R
D
HALE RD
RIVER DR
CA
R
I
B
O
U
D
R
DR
A
F
T
E
R
R
D
HO
M
E
S
T
E
A
D
W
A
Y
GROSS DR
KINGSBURG RD
ASH
R
D
8T
H
S
T
AN
D
R
E
W
S
R
D
A
M
M
O
N
R
D
AQUA RD
RO
C
K
S
A
N
D
R
D
RAIL DR
MILKY
W
A
Y
RA
I
N
B
O
W
D
R
WILLIAM FOSS RD
BR
O
W
N
I
N
G
D
R
S
U
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ARPINE
BUTTERD
WHITE
P
I
N
E
W
A
Y
LIVELY LN
CAMINO DE ORO AVE
PINE DROP LN
RA
I
L
R
O
A
D
S
T
OT
T
E
R
D
R
DEER RUN LN
SA
N
D
P
IP
E
R
R
D
DI
A
N
N
E
R
D
C
O
L
L
A
R
D
R
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Y
D
W
A
Y
PONDEROS A LOOP
LE
C
H
N
E
R
L
N
HAWKS LAIR RD
BATES ST
SA
V
A
G
E
D
R
DI
A
M
O
N
D
B
A
R
R
A
N
C
H
R
D
BL
A
C
K
D
U
C
K
R
D
BAKERSFIELD RD
MO
R
S
O
N
S
T
AMBER LN
SHARP DR
LIBERTY RD
PE
N
G
R
A
S
T
GREEN FOREST RD
T W I N R I V E RSDR
ELK AVE HI
N
K
L
E
W
A
Y
SHAWNEECIR
BIG MEADOW DR
YO
H
O
D
R
CO
A
C
H
R
D
DEL PINO DR
PR
E
B
L
E
W
A
Y
FEDERAL RD
EV
A
N
S
W
A
Y
WAYNE DR
CORNELL DR
MA
R
S
H
H
A
W
K
R
D
FIR LN
OLD WOOD RD
FAUN LN
PASADENA RD
PAULINA AVE
CE
L
E
S
T
I
A
L
D
R
DE
E
P
W
O
O
D
S
R
D
LAGUNA RD
MEADOW RD
RI
C
H
A
R
D
W
A
Y
WE
N
D
Y
R
D
JUNIPER RD
E C L I P S E D R
FALL RIVER DR
SLY DR
PITCH CT
OXNARD RD
MERCED RD
CASCADE LN
S U B A L P I N E
HASHK N I F E R D
AR
C
T
I
C
D
R
INDIGO LN
B
E
A
R
L
N
OA
K
D
R
READ LOOP
CO
M
E
T
D
R
EL
M
D
R
BUENA VISTA DR
HEIERMAN DR
DE
E
R
F
I
E
L
D
D
R
RE
M
I
N
G
T
O
N
D
R
PIN
E
C
R
E
S
T
L
N
C A N O E C AMP DR
ABBOT DR
PINE LN
CE
D
A
R
R
D
ME
T
E
O
R
D
R
EMERALD DR
RI
V
E
R
P
I
N
E
R
D
BRANT DR
BLUEHERONDR
IRONBAR K
LODGEPOLE LN
SHADY LN
LESLIE DR
PI
N
E
L
O
O
P
D
R
PI
N
E
G
R
O
V
E
R
D
PR
I
M
R
O
S
E
L
N
FS4320556
BO
N
A
N
Z
A
L
N
COUGAR LN
AS
H
D
R
KI
W
A
L
N
N SUGARPINE W A Y
CRAN
E
D
R
PRAI
R
I
E
D
R
B E N C H L E G R D
NORWALK RD
DICK RD
GOLDEN
A
S
T
O
R
R
D
WOODLAND DR
COOPER DR
MAYFIELD DR
K
O
K
A
N
E
E
W
A
Y
SP
R
A
G
U
E
L
O
O
P
GRAY WOLF LN
EAGLES NEST RD
S SUGARPINE WAY
WINCHESTER DR
SNOWBERRY LN
SCAUP DR
D A N C I N G R O C K L O O
P
T R A I L M E R E CIR
GO
T
H
A
R
D
W
A
Y
WH
E
E
L
E
R
R
D
JO
R
Y
R
D
SEED RD
M
A
P
L
E
D
R
CH
I
E
F
P
A
U
L
I
N
A
D
R
PAULINA VIEW RD
SOUTH DR
P O N Y E X P R E S S
W A Y
SHELLIE LN
HA
N
N
R
D
SUTTER ST
HELBROCK DR
RILEY DR
W
I
L
D
RIV
E
R
W
AY
B R O O K I E W A Y
C A S C A D E DR
LOOP D R
WOODCHIP LN
NORTH DR
W
O
O
D
D
U
CKDR
BOX WAY
B R O O K S L N
TORRANCE RD
UN
I
O
N
R
D
WA
L
K
E
R
S
T
GIN
A
L
N
WELLS RD
P
H
I
L
L
I
P
S
W
A
Y
CEDAR LN
TA
R
R
Y
L
N
FOXTAILRD
F O R E S T
R D
KASSERMAN DR
HEATH DR
WE
L
C
H
R
D
S LAPINE DR
RIVERLOOPDR W
KILLDEER DR
CUB D
R
EI
D
E
R
R
D
GRIMM RD
G R A Y S Q U I R R E L D R
WHITE BUCK AVE
SHERRIE W A Y
MU
R
R
Y
D
R
WHI T E O A K P L
HE
I
D
I
C
T
PO
L
E
P
I
N
E
R
D
BLACKTAIL LN
F O R D H AM D R
O S P R E Y R D
JA
C
K
P
I
N
E
W
A
Y
BE
A
R
S
T
YORKIE LN
SUN COUNTRY DR
ELKHORN LN
MULE DEER LN
MAL
L
A
R
D
D
R
S C H O O L H O U S E R D
B
I
R
C
H
R
D
KINGFISHER DR
ISLA
N
D
L
O
O
P
W
A
Y
FE
S
T
I
S
A
V
E
LO
S
T
P
O
N
D
E
R
O
S
A
R
D
PI
N
E
S
T
WHITE TAIL LN
PA
R
K
E
R
R
D
EL
K
D
R
BEAVER DR
DERRINGER DR
CA
S
C
A
D
E
S
T
MERGANSER DR
SH
A
Y
L
N
WA
L
L
I
N
G
L
N
DO
E
L
O
O
P
SIL
V
E
R
L
A
K
E
L
N
CASPERDR
LITTLE
RIV
ERDR
P
I
N
E
P
L
BLUE BIRD LN
WI
C
K
I
U
P
A
V
E
E M E A D O WRD
STRAWN RD
RIVERLOOP D R E
DILLON WAY
HO
L
T
Z
C
L
A
W
R
D
SE
E
V
E
R
S
R
D
L
O
W
E
L
L
W
A
Y
FRIENDLY ST
YODER LN
FRANCES LN
MOUNTAIN SHEEP LN
WA
Y
S
I
D
E
L
O
O
P
B
R
E
N
D
A
D
R
P RAI RIE VIEW DR
LACAR LN
MI
T
C
H
E
L
L
R
D
W
I
L
L
O
W
S
T
BEVERLY LN
GULL DR
BASSETT DR
O
L
D
S
T
A
G
E
R
D
NA
T
I
O
N
A
L
R
D
LOST LN
P
O
N
D
E
R
O
S
A
R
D
ELENA LN
CANVASBACK DR
JACOBSEN RD
CURLEW DR
AL
L
E
N
D
R
GUSS WAY
AVO C E T D R
AN
C
H
O
R
W
A
Y
FA
W
N
L
O
O
P
HE
M
L
O
C
K
R
D
CO
N
E
P
L
DIPPER LN
S
F A W N
D R
PLEASANT ST
WILLOW LN
TIM
B
E
R
L
A
N
E
L
O
O
P
BIG BUCK LN
AL
P
S
C
T
MA
R
T
E
N
L
N
G REENWOOD DR
GLE
N
W
O
O
D
D
R
BA
N
D
L
E
Y
R
D
RU GUELFI RD
AL
J
E
A
N
R
D
SPRINGWOOD RD
KO
K
A
N
E
E
L
N
T R E E
D U C K
R D
TEIL CT
BO
N
N
I
E
W
A
Y
WALK ER WAY
HARLEQUIN DR
EGRET DR
GREBE RD
SERP E N T I N E D R
TRUMPETER LN
L I CH EN WAY
SHEILA WAY
MOUNT
AIN
G
O
A
T
L
N
CU
L
T
U
S
L
N
MU
N
S
O
N
S
T
CO
Y
O
T
E
R
D
ASSEMBLY WAY
BLACKFEATHER LN
AUKLET DR
C E N T R A L W A Y
QUARTZ HILL
PIN
E
T
R
E
E
D
R
TA
N
O
A
K
P
L
WADDELL RD
V E L V E T C T
PENNY CT
B
E
A
R
D
R
DI
A
N
A
L
N
BU
F
F
L
E
H
E
A
D
R
D
PO
L
A
R
R
D
FINDLEY
D
R
V
A
L
E
C
T
GOLDEN EYE DR
BU
R
L
MOCKINGBIRD LN
F
S
4
3
5
0
MO
W
I
C
H
L
N
RO
B
I
N
L
N
MEMORIAL LN
SACRAMENTO RD
CON T O R T A P L
MO
O
S
E
R
D
S
U
N
D
O
W
N
D
R
WAGO N T R L
L
O
G
B
R
I
D
G
E
D
R
FISHER LN
HU
S
K
Y
L
N
PA
M
L
N
YA
E
G
E
R
W
A
Y
PINTAIL DR
S
PRUCECT
RAINBOW
C
T
CALDWELL DR
E
D
E
N
S
T
HAKKILA AVE
BU
T
T
E
D
R
HOLG A T E C T
SH
I
E
L
D
S
D
R
RANCH PL
AUTUMNCT
MOUNTAIN VIEW LN
ASPEN
P
L
A
L
I
C
E
D
R
SABLE
RO C K L O O P
G A T E H O USELN
LU
C
K
Y
L
N
GROSS LN
EVERGREEN LN
BETTY DR
SA
N
T
A
B
A
R
B
A
R
A
D
R
WYATT DR
S W I S S P I N E
CW REEVE
S
L
N
BI
V
O
U
A
C
R
D
JUDD LN
PI
N
E
C
T
F I R E G L A S S L O O P
S
N
O
W
F
L
A
K
E
L
N
CA
R
I
B
O
U
R
D
F E R N DELLLN
PO
W
E
L
L
L
N
C R E S C E N T C R E E K D R
NUTHATCH WAY
FAIRWAY LN
CARRINGTON
AVE
RI
L
E
Y
L
N
E N T E R P RISE DR
SITKA
WO
O
D
C
H
U
C
K
D
R
GADWALL DR
WIDGEON DR
N O B L E F I R
NORTHWO O D D R
TURQUOISE DR
VISTA LN
TEL
E
G
R
A
P
H
R
D
C A MBIUM
S P R I N G R I V E R DR
FRONTAGE RD
DEE
R
R
U
N
R
D
B E AR B ER
R
Y
SUZA CT
P I N N A C L E L N
HA
F
D
A
H
L
L
N
SUTTER CT
TRACY RD
B U L L W H I P D R
VE N T U R E L N
MEADOW WAY
JIL
L
I
A
N
L
N
B A R B E R R Y
C I R
C A L D E R A S P R I N G S D R
W A G O N MASTER WAY
F
O
R
E
S
T
W
A
Y
GUSS
L
N
FALCON LN
MANNING CT
CASSIDY DR
BO
B
W
H
I
T
E
C
T
EASTWIND CT
HA
R
P
E
R
R
D
LISA LN
LA
D
Y
B
U
G
L
N
THOLSTRUP DR
EARL CT E
ROSEMEAD
MO
S
S
R
D
BRADLEY RD
H O L L I N S H E A D P L
KODIAK LN
WOODGRE E N C T
C
A
R
E
F
R
E
E
L
N
NATOMA CT
L O N E E A G L E L N D G
P
L
A
I
N
V
I
E
W
D
R
D I S C O V E R Y L N
EARL CT W
HE
N
L
N
RANDY CT
BULL BAT LN
PR
O
N
G
H
O
R
N
D
R
LAKE LN
H O L G A T E R D
L O S T
R I D E R LOOP
YELLOWPINELO
O
P
M E S Q U I T E
BUSHBERRY CT
P E P P E R M I L L C I R
TRADER LN
KE
L
V
E
L
C
T
TALLWOOD CT
D E E R L N
K N O B C O N E
SN
I
P
E
R
D
C A R T E R C T
BITTER BRUSH RD
R I V E R B I R C H
LONGLEAF P I N E
SUNSET LN
W O O D D U C K C T
RE
D
F
O
X
L
N
JA C K P I N E R D
HO
M
E
S
T
E
A
D
R
D
TREE L A N D C T
CLUSTERCABIN L N
YELLOWOOD CT
CURL L E AF
CEDAR CT
BURLWOOD LN
TR
O
U
T
L
N
VICTORY WAY
BL
U
E
W
O
O
D
A
V
E
W
HITEWATE R L O O P
WILLOW CT
BETTY CT
HOLIDAY LN
MINK CT
RE
D
P
I
N
E
WH
I
S
P
E
R
I
N
G
P
I
N
E
S
R
D
CHIPMUNK LN
S
U
N
R
I
S
E
C
T
FO
X
G
L
E
N
L
O
O
P
E
L
K
L
N
S
T
A
T
I
O
N
M
A
S
T
E
R
W
A
Y
HOLIDAY C
T
BEAR PAW LN
ST
I
L
L
W
E
L
L
S
T
SPRING BUTTE LN
G L O W S T O N E L O O P
WESTWIND CT
DR
A
K
E
D
R
DARIN LN
HEA
R
T
W
O
O
D
W
RIG
H
T
P
OI NT WA Y
J
A
M
I
E
W
A
Y
LAUR ELRD
RED BEAR LN
BEAVERPL
LIVEWOOD CT
EAG
L
E
C
T
RANI WAY
E A G L E
L N
RE
E
V
E
C
T
HEMLOCK CT
SA
L
Z
E
R
S
T
BRISTLECONE LN
CASSIDY CT
BR
O
O
K
T
R
O
U
T
C
T
ST
A
G
S
T
SNOW CAP R
D
AG
U
I
L
A
R
C
T
SU G ARBERRY
FO
U
N
T
A
I
N
E
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Legend
La Pine City Limit
Urban Unincorporated Community
County Zoning
Exclusive Farm Use - La Pine Subzone
Forest Use 1
Forest Use 2
Flood Plain
Multiple Use Agricultural
Open Space & Conservation
Rural Industrial
Rural Commercial
Rural Residential
Surface Mining
Rural Service Center Zoning
RSC M/C - Mixed Use / Commercial
La Pine Zoning
Mixed Use Commercial
Commercial / Residential Mixed Use
Commercial District
Neighborhood Commercial
Neighborhood Community Facility Limited
Traditional Commercial
Public Facility
Riparian Area - Little Deschutes River
Open Space & Park
Master Plan Residential
Residential District
Residential Multi-Family
Industrial
00 . 510.25
Miles
Zoning
Z
June 4, 2014
N:\Custom\County\CDD\Planning\PeterRussell\SouthCountyZoning\ProjectFiles\SoCoZoning.mxd
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Direct
Public Health > Healthy Environments > Drinking Water > Monitoring & Reporting > Health Effects of Contaminants > Nitrate
Nitrate
More Resources
• Drinking Water Data
Online
• Site Map
• For Consumers
Contact Us
• Center for Health
Protection
• Drinking Water Services
Nitrate in Drinking Water - Frequently Asked Questions
On this page:
• General information about nitrate and its health effects
• Safely using nitrate-contaminated water
• Learning about nitrate levels in your drinking water
• Removing nitrate from drinking water
• For more information
General information about nitrate and its health effects
What is nitrate and where does it come from?
Nitrate is a naturally occurring oxide of nitrogen. Nitrogen is present in the air and reacts with oxygen
and ozone to produce nitrate. Nitrate is an essential component of living things and is a major part of
animal manure, human sewage waste and commercial fertilizers. Nitrates and nitrites can be
associated with septic systems and have been used for centuries as fertilizers, in explosives and as
food preservatives.
When does nitrate in drinking water become a health concern?
Nitrate is measured in milligrams per liter (mg/L) (1 mg/L = 1 part per million (ppm)). Nitrate occurs
naturally in surface and groundwater at concentrations up to 1-2 mg/L. At these naturally occurring
levels, nitrate is not harmful to health.
The U.S. Environmental Protection Agency (EPA) has established the safe drinking water standard
(also called maximum contaminant level) for nitrate as 10 mg/L as measured nitrogen (NO 3 -N). If your
water has nitrate levels above 10 mg/L, it is advisable to switch to bottled water.
How can nitrate affect my health?
Nitrate is a potential health hazard. Drinking water that has high levels of nitrate can cause health
effects such as:
• Methemoglobinemia or "blue baby syndrome," which results from nitrate decreasing the blood's
capacity to carry oxygen, especially in infants who receive baby formula mixed with water
containing nitrate above 10 mg/L.
• Potential increased risk of:
o Recurrent respiratory infections,
o Thyroid dysfunction,
o Negative reproductive outcomes such as spontaneous abortion and
o Certain cancers including cancer of the stomach or bladder.
Safely using nitrate-contaminated water
Can I wash my food with nitrate-contaminated water?
If nitrate levels in your water are above 10 mg/L, you should use bottled water or water from a safe
source to wash, prepare and cook your food.
Can I irrigate or water my garden with nitrate-contaminated water?
Yes.
What about bathing and showering?
Nitrate does not easily enter the body through the skin. Bathing, swimming and showering with water
that has levels of nitrate over 10 mg/L is safe as long as you avoid swallowing the water. Supervise
small children when they are bathing and brushing teeth to ensure they do not swallow the water.
What about washing dishes, utensils and food preparation areas?
Only a very small amount of water clings to smooth surfaces, like dishes. Water having more than 10
mg/L of nitrate can be safely used to wash and sanitize dishes, tables and eating utensils.
What about general cleaning and laundry?
Very little water remains on washed surfaces and in laundered fabrics. Because these articles are not
placed in the mouth, water having more than 10 mg/L of nitrate can be safely used for general cleaning
and washing of clothing, bedding and linens.
What about my pets?
Animals should not drink water that is above 10 mg/L.
Learning about nitrate levels in your drinking water
For people on municipal or public water systems:
Public drinking water providers are required to monitor for nitrate and ensure levels remain below the
drinking water standard of 10 mg/L. They are also required to make those results public. If your water
comes from a public water system, you can find results on the Oregon Drinking Water Services Data
Online website. Your drinking water provider is also required to provide a Consumer Confidence
Report to its customers every year. This report contains the most recent nitrate test results.
For private well owners:
If your drinking water comes from your own well, you will have to find a laboratory that does water
testing for private property owners. These labs can provide information and instructions for getting your
well water tested. For a list of accredited laboratories in Oregon, contact the Oregon Environmental
Laboratory Accreditation Program (ORELAP) or view the list online: ORELAP Accredited Laboratories
(pdf).
Water containing 5-10 mg/L nitrate as nitrogen should be tested every quarter for at least one year to
determine if levels are increasing or vary seasonally. Since nitrate levels can vary over time, annual
testing is recommended at a minimum for all drinking water sources.
Removing nitrate from drinking water
For public drinking water system operators:
Nitrate can be reduced or removed entirely from drinking water, but treatment processes are
expensive and require careful maintenance and monitoring. Current treatments include ion exchange
resins, reverse osmosis, electrodialysis and either biological or chemical denitrification. If treatment is
not possible for your system, you should consider developing a different water source, blending with a
different source or connecting to another safe water source in the area. Water that is to be used for
drinking, beverage-making or food preparation can be obtained from a known safe source and used on
a temporary basis. Non-ingestion uses of water pose much less hazard, but are not entirely safe if
nitrate levels are significantly above the drinking water limit. Before deciding on treatment equipment,
contact Oregon Drinking Water Services for information and advice.
For private surface water intake owners:
Don't boil the water!
Boiling contaminated water does not remove nitrate; it can increase nitrate levels.
Private well treatment options:
First, make sure that you are not contributing to the problem. Take action to prevent nitrate sources on
your property from contaminating your own groundwater (e.g., properly maintain your septic system,
reduce fertilizer use within 100 feet of the well and move livestock or manure piles away from the well
area). Non-treatment options include developing a different water source, blending in water from
another source or connecting to another safe water source in the area.
Several treatment methods can remove nitrate from drinking water, including ion exchange and
reverse osmosis; ion exchange is the most common. Treatment equipment must be carefully
maintained in order to work properly and might not be effective if nitrate levels are very high. Treated
water should be tested at least once a year. Untreated water should be tested at least every three
years.
Check to be sure that any treatment system is certified by a recognized, third-party testing organization
that meets strict testing procedures established by the American National Standards Institute (ANSI)
and National Sanitation Foundation (NSF) International.
For more information
• Private surface water intake owners that have questions and concerns about nitrate in their water
can contact the Center for Health Protection by phone at 971-673-0400 or by email at
general.toxicology@state.or.us.
• U.S. Environmental Protection Agency – Nitrate in Drinking Water
Updated: March 2013
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Water: Drinking Water Contaminants
You are here: Water Drinking Water Drinking Water Contaminants
Drinking Water Contaminants
• Drinking Water Contaminants Home
• Basic Information about Drinking Water Contaminants
On this Page
• National Primary Drinking Water Regulations
• List of Drinking Water Contaminants and (MCLs)
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• List of Secondary Drinking Water Regulations
• Unregulated Contaminants
National Primary Drinking Water Regulations
National Primary Drinking Water Regulations (NPDWRs or primary standards) are legally enforceable
standards that apply to public water systems. Primary standards protect public health by limiting the
levels of contaminants in drinking water. Visit the list of regulated contaminants with links for more
details.
• List of Contaminants and their Maximum Contaminant Levels (MCLs)
• Regulation Development
• EPA's Regulated Contaminant Timeline (PDF) (1 pp, 86 K ) (About PDF)
• National Primary Drinking Water Regulations- The complete regulations regarding these
contaminants is available from the Code of Federal Regulations Website
Information on this section
• Alphabetical List (PDF) (6 pp, 924 K) (About PDF) EPA 816-F-09-0004, May 2009
List of Contaminants and their (MCLs)
An alphabetical listing with links to fact sheets on the primary drinking water regulations.
• Microorganisms
• Disinfectants
• Disinfection Byproducts
• Inorganic Chemicals
• Organic Chemicals
• Radionuclides
Microorganisms
Contaminant MCLG1
(mg/L)2
MCL or
TT1
(mg/L)2
Potential Health Effects from
Long-Term Exposure Above the
MCL (unless specified as short-
term)
Sources of
Contaminant in
Drinking Water
Cryptosporidium zero TT3 Gastrointestinal illness (such as
diarrhea, vomiting, and cramps)
Human and animal
fecal waste
Microorganisms
Contaminant MCLG1
(mg/L)2
MCL or
TT1
(mg/L)2
Potential Health Effects from
Long-Term Exposure Above the
MCL (unless specified as short-
term)
Sources of
Contaminant in
Drinking Water
Giardia lamblia zero TT3 Gastrointestinal illness (such as
diarrhea, vomiting, and cramps)
Human and animal
fecal waste
Heterotrophic
plate count (HPC)
n/a TT3
HPC has no health effects; it is an
analytic method used to measure
the variety of bacteria that are
common in water. The lower the
concentration of bacteria in
drinking water, the better
maintained the water system is.
HPC measures a
range of bacteria
that are naturally
present in the
environment
Legionella zero TT3 Legionnaire's Disease, a type of
pneumonia
Found naturally in
water; multiplies in
heating systems
Total Coliforms
(including fecal
coliform and E.
Coli)
zero 5.0%4
Not a health threat in itself; it is
used to indicate whether other
potentially harmful bacteria may
be present5
Coliforms are
naturally present in
the environment; as
well as feces; fecal
coliforms and E. coli
only come from
human and animal
fecal waste.
Turbidity n/a TT3
Turbidity is a measure of the
cloudiness of water. It is used to
indicate water quality and filtration
effectiveness (such as whether
disease-causing organisms are
present). Higher turbidity levels
are often associated with higher
levels of disease-causing
microorganisms such as viruses,
parasites and some bacteria.
These organisms can cause
symptoms such as nausea,
cramps, diarrhea, and associated
Soil runoff
Microorganisms
Contaminant MCLG1
(mg/L)2
MCL or
TT1
(mg/L)2
Potential Health Effects from
Long-Term Exposure Above the
MCL (unless specified as short-
term)
Sources of
Contaminant in
Drinking Water
headaches.
Viruses (enteric) zero TT3 Gastrointestinal illness (such as
diarrhea, vomiting, and cramps)
Human and animal
fecal waste
Top of page
Disinfection Byproducts
Contaminant MCLG1
(mg/L)2
MCL or
TT1
(mg/L)2
Potential Health Effects from
Long-Term Exposure Above
the MCL (unless specified as
short-term)
Sources of
Contaminant in
Drinking Water
Bromate zero 0.010 Increased risk of cancer
Byproduct of
drinking water
disinfection
Chlorite 0.8 1.0
Anemia; infants and young
children: nervous system
effects
Byproduct of
drinking water
disinfection
Haloacetic acids
(HAA5)
n/a6 0.0607 Increased risk of cancer
Byproduct of
drinking water
disinfection
Total
Trihalomethanes
(TTHMs)
--> n/a6 -->
0.0807
Liver, kidney or central
nervous system problems;
increased risk of cancer
Byproduct of
drinking water
disinfection
Top of page
Disinfectants
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health Effects from Long-
Term Exposure Above the MCL
(unless specified as short-term)
Sources of
Contaminant in
Drinking Water
Chloramines
(as Cl 2 )
MRDLG=41 MRDL=4.01 Eye/nose irritation; stomach
discomfort, anemia
Water additive
used to control
microbes
Chlorine (as
Cl 2 )
MRDLG=41 MRDL=4.01 Eye/nose irritation; stomach
discomfort
Water additive
used to control
microbes
Chlorine
dioxide (as
ClO 2 )
MRDLG=0.81 MRDL=0.81 Anemia; infants and young children:
nervous system effects
Water additive
used to control
microbes
Top of page
Inorganic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health Effects from Long-
Term Exposure Above the MCL
(unless specified as short-term)
Sources of
Contaminant in
Drinking Water
Antimony 0.006 0.006 Increase in blood cholesterol;
decrease in blood sugar
Discharge from
petroleum refineries;
fire retardants;
ceramics; electronics;
solder
Arsenic 0 0.010 as of
01/23/06
Skin damage or problems with
circulatory systems, and may have
increased risk of getting cancer
Erosion of natural
deposits; runoff from
orchards, runoff from
glass and
electronicsproduction
wastes
Asbestos
(fiber > 10
micrometers)
7
million
fibers
per
liter
(MFL)
7 MFL Increased risk of developing benign
intestinal polyps
Decay of asbestos
cement in water
mains; erosion of
natural deposits
Inorganic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health Effects from Long-
Term Exposure Above the MCL
(unless specified as short-term)
Sources of
Contaminant in
Drinking Water
Barium 2 2 Increase in blood pressure
Discharge of drilling
wastes; discharge
from metal refineries;
erosion of natural
deposits
Beryllium 0.004 0.004 Intestinal lesions
Discharge from metal
refineries and coal-
burning factories;
discharge from
electrical, aerospace,
and defense
industries
Cadmium 0.005 0.005 Kidney damage
Corrosion of
galvanized pipes;
erosion of natural
deposits; discharge
from metal refineries;
runoff from waste
batteries and paints
Chromium
(total)
0.1 0.1 Allergic dermatitis
Discharge from steel
and pulp mills;
erosion of natural
deposits
Copper 1.3 TT7; Action
Level=1.3
Short term exposure:
Gastrointestinal distress
Long term exposure: Liver or
kidney damage
People with Wilson's Disease should
consult their personal doctor if the
amount of copper in their water
exceeds the action level
Corrosion of
household plumbing
systems; erosion of
natural deposits
Inorganic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health Effects from Long-
Term Exposure Above the MCL
(unless specified as short-term)
Sources of
Contaminant in
Drinking Water
Cyanide (as
free cyanide)
0.2 0.2 Nerve damage or thyroid problems
Discharge from
steel/metal factories;
discharge from
plastic and fertilizer
factories
Fluoride 4.0 4.0
Bone disease (pain and tenderness
of the bones); Children may get
mottled teeth
Water additive which
promotes strong
teeth; erosion of
natural deposits;
discharge from
fertilizer and
aluminum factories
Lead zero TT7; Action
Level=0.015
Infants and children: Delays in
physical or mental development;
children could show slight deficits
in attention span and learning
abilities
Adults: Kidney problems; high
blood pressure
Corrosion of
household plumbing
systems; erosion of
natural deposits
Mercury
(inorganic)
0.002 0.002 Kidney damage
Erosion of natural
deposits; discharge
from refineries and
factories; runoff from
landfills and
croplands
Nitrate
(measured
as Nitrogen)
10 10
Infants below the age of six months
who drink water containing nitrate
in excess of the MCL could become
seriously ill and, if untreated, may
die. Symptoms include shortness of
breath and blue-baby syndrome.
Runoff from fertilizer
use; leaking from
septic tanks, sewage;
erosion of natural
deposits
Nitrite 1 1 Infants below the age of six months Runoff from fertilizer
Inorganic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health Effects from Long-
Term Exposure Above the MCL
(unless specified as short-term)
Sources of
Contaminant in
Drinking Water
(measured
as Nitrogen)
who drink water containing nitrite
in excess of the MCL could become
seriously ill and, if untreated, may
die. Symptoms include shortness of
breath and blue-baby syndrome.
use; leaking from
septic tanks, sewage;
erosion of natural
deposits
Selenium 0.05 0.05
Hair or fingernail loss; numbness in
fingers or toes; circulatory
problems
Discharge from
petroleum refineries;
erosion of natural
deposits; discharge
from mines
Thallium 0.0005 0.002 Hair loss; changes in blood; kidney,
intestine, or liver problems
Leaching from ore-
processing sites;
discharge from
electronics, glass,
and drug factories
Top of page
Organic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health
Effects from Long-
Term Exposure
Above the MCL
(unless specified as
short-term)
Sources of
Contaminant in
Drinking Water
Acrylamide zero TT8
Nervous system or
blood problems;
increased risk of
cancer
Added to water during
sewage/wastewater
treatment
Alachlor zero 0.002 Eye, liver, kidney or
spleen problems;
anemia; increased
risk of cancer
Runoff from herbicide
used on row crops
Organic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health
Effects from Long-
Term Exposure
Above the MCL
(unless specified as
short-term)
Sources of
Contaminant in
Drinking Water
Atrazine 0.003 0.003
Cardiovascular
system or
reproductive
problems
Runoff from herbicide
used on row crops
Benzene zero 0.005
Anemia; decrease
in blood platelets;
increased risk of
cancer
Discharge from
factories; leaching
from gas storage
tanks and landfills
Benzo(a)pyrene (PAHs) zero 0.0002
Reproductive
difficulties;
increased risk of
cancer
Leaching from linings
of water storage tanks
and distribution lines
Carbofuran 0.04 0.04
Problems with
blood, nervous
system, or
reproductive
system
Leaching of soil
fumigant used on rice
and alfalfa
Carbon tetrachloride zero 0.005
Liver problems;
increased risk of
cancer
Discharge from
chemical plants and
other industrial
activities
Chlordane zero 0.002
Liver or nervous
system problems;
increased risk of
cancer
Residue of banned
termiticide
Chlorobenzene 0.1 0.1 Liver or kidney
problems
Discharge from
chemical and
agricultural chemical
factories
Organic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health
Effects from Long-
Term Exposure
Above the MCL
(unless specified as
short-term)
Sources of
Contaminant in
Drinking Water
2,4-D 0.07 0.07
Kidney, liver, or
adrenal gland
problems
Runoff from herbicide
used on row crops
Dalapon 0.2 0.2 Minor kidney
changes
Runoff from herbicide
used on rights of way
1,2-Dibromo-3-
chloropropane (DBCP)
zero 0.0002
Reproductive
difficulties;
increased risk of
cancer
Runoff/leaching from
soil fumigant used on
soybeans, cotton,
pineapples, and
orchards
o-Dichlorobenzene 0.6 0.6
Liver, kidney, or
circulatory system
problems
Discharge from
industrial chemical
factories
p-Dichlorobenzene 0.075 0.075
Anemia; liver,
kidney or spleen
damage; changes
in blood
Discharge from
industrial chemical
factories
1,2-Dichloroethane zero 0.005 Increased risk of
cancer
Discharge from
industrial chemical
factories
1,1-Dichloroethylene 0.007 0.007 Liver problems
Discharge from
industrial chemical
factories
cis-1,2-Dichloroethylene 0.07 0.07 Liver problems
Discharge from
industrial chemical
factories
trans-1,2-Dichloroethylene 0.1 0.1 Liver problems Discharge from
industrial chemical
Organic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health
Effects from Long-
Term Exposure
Above the MCL
(unless specified as
short-term)
Sources of
Contaminant in
Drinking Water
factories
Dichloromethane zero 0.005
Liver problems;
increased risk of
cancer
Discharge from drug
and chemical factories
1,2-Dichloropropane zero 0.005 Increased risk of
cancer
Discharge from
industrial chemical
factories
Di(2-ethylhexyl) adipate 0.4 0.4
Weight loss, liver
problems, or
possible
reproductive
difficulties.
Discharge from
chemical factories
Di(2-ethylhexyl) phthalate zero 0.006
Reproductive
difficulties; liver
problems;
increased risk of
cancer
Discharge from rubber
and chemical factories
Dinoseb 0.007 0.007 Reproductive
difficulties
Runoff from herbicide
used on soybeans and
vegetables
Dioxin (2,3,7,8-TCDD) zero 0.00000003
Reproductive
difficulties;
increased risk of
cancer
Emissions from waste
incineration and other
combustion; discharge
from chemical
factories
Diquat 0.02 0.02 Cataracts Runoff from herbicide
use
Endothall 0.1 0.1 Stomach and Runoff from herbicide
Organic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health
Effects from Long-
Term Exposure
Above the MCL
(unless specified as
short-term)
Sources of
Contaminant in
Drinking Water
intestinal problems use
Endrin 0.002 0.002 Liver problems Residue of banned
insecticide
Epichlorohydrin zero TT8
Increased cancer
risk, and over a
long period of
time, stomach
problems
Discharge from
industrial chemical
factories; an impurity
of some water
treatment chemicals
Ethylbenzene 0.7 0.7 Liver or kidneys
problems
Discharge from
petroleum refineries
Ethylene dibromide zero 0.00005
Problems with liver,
stomach,
reproductive
system, or kidneys;
increased risk of
cancer
Discharge from
petroleum refineries
Glyphosate 0.7 0.7
Kidney problems;
reproductive
difficulties
Runoff from herbicide
use
Heptachlor zero 0.0004
Liver damage;
increased risk of
cancer
Residue of banned
termiticide
Heptachlor epoxide zero 0.0002
Liver damage;
increased risk of
cancer
Breakdown of
heptachlor
Hexachlorobenzene zero 0.001
Liver or kidney
problems;
reproductive
Discharge from metal
refineries and
agricultural chemical
Organic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health
Effects from Long-
Term Exposure
Above the MCL
(unless specified as
short-term)
Sources of
Contaminant in
Drinking Water
difficulties;
increased risk of
cancer
factories
Hexachlorocyclopentadiene 0.05 0.05 Kidney or stomach
problems
Discharge from
chemical factories
Lindane 0.0002 0.0002 Liver or kidney
problems
Runoff/leaching from
insecticide used on
cattle, lumber,
gardens
Methoxychlor 0.04 0.04 Reproductive
difficulties
Runoff/leaching from
insecticide used on
fruits, vegetables,
alfalfa, livestock
Oxamyl (Vydate) 0.2 0.2 Slight nervous
system effects
Runoff/leaching from
insecticide used on
apples, potatoes, and
tomatoes
Polychlorinated biphenyls
(PCBs)
zero 0.0005
Skin changes;
thymus gland
problems; immune
deficiencies;
reproductive or
nervous system
difficulties;
increased risk of
cancer
Runoff from landfills;
discharge of waste
chemicals
Pentachlorophenol zero 0.001
Liver or kidney
problems;
increased cancer
Discharge from wood
preserving factories
Organic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health
Effects from Long-
Term Exposure
Above the MCL
(unless specified as
short-term)
Sources of
Contaminant in
Drinking Water
risk
Picloram 0.5 0.5 Liver problems Herbicide runoff
Simazine 0.004 0.004 Problems with
blood Herbicide runoff
Styrene 0.1 0.1
Liver, kidney, or
circulatory system
problems
Discharge from rubber
and plastic factories;
leaching from landfills
Tetrachloroethylene zero 0.005
Liver problems;
increased risk of
cancer
Discharge from
factories and dry
cleaners
Toluene 1 1
Nervous system,
kidney, or liver
problems
Discharge from
petroleum factories
Toxaphene zero 0.003
Kidney, liver, or
thyroid problems;
increased risk of
cancer
Runoff/leaching from
insecticide used on
cotton and cattle
2,4,5-TP (Silvex) 0.05 0.05 Liver problems Residue of banned
herbicide
1,2,4-Trichlorobenzene 0.07 0.07 Changes in adrenal
glands
Discharge from textile
finishing factories
1,1,1-Trichloroethane 0.20 0.2
Liver, nervous
system, or
circulatory
problems
Discharge from metal
degreasing sites and
other factories
1,1,2-Trichloroethane 0.003 0.005 Liver, kidney, or Discharge from
Organic Chemicals
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health
Effects from Long-
Term Exposure
Above the MCL
(unless specified as
short-term)
Sources of
Contaminant in
Drinking Water
immune system
problems
industrial chemical
factories
Trichloroethylene zero 0.005
Liver problems;
increased risk of
cancer
Discharge from metal
degreasing sites and
other factories
Vinyl chloride zero 0.002 Increased risk of
cancer
Leaching from PVC
pipes; discharge from
plastic factories
Xylenes (total) 10 10 Nervous system
damage
Discharge from
petroleum factories;
discharge from
chemical factories
Top of page
Radionuclides
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health Effects
from Long-Term
Exposure Above the
MCL (unless specified as
short-term)
Sources of Contaminant in
Drinking Water
Alpha particles
none7 ---
-------
zero
15 picocuries
per Liter
(pCi/L)
Increased risk of cancer
Erosion of natural deposits of
certain minerals that are
radioactive and may emit a
form of radiation known as
alpha radiation
Beta particles
and photon
emitters
none7 ---
-------
zero
4 millirems
per year Increased risk of cancer
Decay of natural and man-
made deposits of
certain minerals that are
radioactive and may emit forms
Radionuclides
Contaminant MCLG1
(mg/L)2
MCL or TT1
(mg/L)2
Potential Health Effects
from Long-Term
Exposure Above the
MCL (unless specified as
short-term)
Sources of Contaminant in
Drinking Water
of radiation known as photons
and beta radiation
Radium 226 and
Radium 228
(combined)
none7 ---
-------
zero
5 pCi/L Increased risk of cancer Erosion of natural deposits
Uranium zero 30 ug/L as
of 12/08/03
Increased risk of cancer,
kidney toxicity Erosion of natural deposits
Top of page
Notes
1 Definitions:
• Maximum Contaminant Level Goal (MCLG) - The level of a contaminant in drinking water
below which there is no known or expected risk to health. MCLGs allow for a margin of
safety and are non-enforceable public health goals.
• Maximum Contaminant Level (MCL) - The highest level of a contaminant that is allowed in
drinking water. MCLs are set as close to MCLGs as feasible using the best available
treatment technology and taking cost into consideration. MCLs are enforceable standards.
• Maximum Residual Disinfectant Level Goal (MRDLG) - The level of a drinking water
disinfectant below which there is no known or expected risk to health. MRDLGs do not
reflect the benefits of the use of disinfectants to control microbial contaminants.)
• Treatment Technique (TT) - A required process intended to reduce the level of a contaminant
in drinking water.
• Maximum Residual Disinfectant Level (MRDL) - The highest level of a disinfectant allowed in
drinking water. There is convincing evidence that addition of a disinfectant is necessary for
control of microbial contaminants.
• 2 Units are in milligrams per liter (mg/L) unless otherwise noted. Milligrams per liter are
equivalent to parts per million (PPM).
3 EPA's surface water treatment rules require systems using surface water or ground water
under the direct influence of surface water to
o (1) disinfect their water, and
o (2) filter their water or
o meet criteria for avoiding filtration so that the following contaminants are controlled
at the following levels:
o
Cryptosporidium: Unfiltered systems are required to include Cryptosporidium
in their existing watershed control provisions
Giardia lamblia: 99.9% removal/inactivation.
Viruses: 99.99% removal/inactivation.
Legionella: No limit, but EPA believes that if Giardia and viruses are
removed/inactivated, according to the treatment techniques in the Surface
Water Treatment Rule, Legionella will also be controlled.
Turbidity: For systems that use conventional or direct filtration, at no time
can turbidity (cloudiness of water) go higher than 1 Nephelometric Turbidity
Unit (NTU), and samples for turbidity must be less than or equal to 0.3
NTUs in at least 95 percent of the samples in any month. Systems that use
filtration other than the conventional or direct filtration must follow state
limits, which must include turbidity at no time exceeding 5 NTUs.
Heterotrophic Plate Count (HPC): No more than 500 bacterial colonies per
milliliter.
Long Term 1 Enhanced Surface Water Treatment: Surface water systems or
groundwater under the direct influence (GWUDI) systems serving fewer than
10,000 people must comply with the applicable Long Term 1 Enhanced
Surface Water Treatment Rule provisions (such as turbidity standards,
individual filter monitoring, Cryptosporidium removal requirements,
updated watershed control requirements for unfiltered systems).
Long Term 2 Enhanced Surface Water Treatment Rule: This rule applies to all
surface water systems or ground water systems under the direct influence
of surface water. The rule targets additional Cryptosporidium treatment
requirements for higher risk systems and includes provisions to reduce
risks from uncovered finished water storage facilities and to ensure that the
systems maintain microbial protection as they take steps to reduce the
formation of disinfection byproducts.
Filter Backwash Recycling: The Filter Backwash Recycling Rule requires
systems that recycle to return specific recycle flows through all processes of
the system's existing conventional or direct filtration system or at an
alternate location approved by the state.
4 No more than 5.0% samples total coliform-positive (TC-positive) in a month. (For water
systems that collect fewer than 40 routine samples per month, no more than one sample
can be total coliform-positive per month.) Every sample that has total coliform must be
analyzed for either fecal coliforms or E. coli if two consecutive TC-positive samples, and
one is also positive for E.coli fecal coliforms, system has an acute MCL violation.
5 Fecal coliform and E. coli are bacteria whose presence indicates that the water may be
contaminated with human or animal wastes. Disease-causing microbes (pathogens) in
these wastes can cause diarrhea, cramps, nausea, headaches, or other symptoms. These
pathogens may pose a special health risk for infants, young children, and people with
severely compromised immune systems.
6 Although there is no collective MCLG for this contaminant group, there are
individual MCLGs for some of the individual contaminants:
o Trihalomethanes: bromodichloromethane (zero); bromoform (zero);
dibromochloromethane (0.06 mg/L): chloroform (0.07 mg/L.
o Haloacetic acids: dichloroacetic acid (zero); trichloroacetic acid (0.02 mg/L);
monochloroacetic acid (0.07 mg/L). Bromoacetic acid and dibromoacetic acid are
regulated with this group but have no MCLGs.
7 Lead and copper are regulated by a treatment technique that requires systems to control
the corrosiveness of their water. If more than 10% of tap water samples exceed the action
level, water systems must take additional steps. For copper, the action level is 1.3 mg/L,
and for lead is 0.015 mg/L.
8 Each water system must certify, in writing, to the state (using third-party or
manufacturer's certification) that when acrylamide and epichlorohydrin are used to treat
water, the combination (or product) of dose and monomer level does not exceed the levels
specified, as follows:
o Acrylamide = 0.05% dosed at 1 mg/L (or equivalent)
o Epichlorohydrin = 0.01% dosed at 20 mg/L (or equivalent)
Top of page
National Secondary Drinking Water Regulations
National Secondary Drinking Water Regulations (NSDWRs or secondary standards) are non-
enforceable guidelines regulating contaminants that may cause cosmetic effects (such as
skin or tooth discoloration) or aesthetic effects (such as taste, odor, or color) in drinking
water. EPA recommends secondary standards to water systems but does not require
systems to comply. However, states may choose to adopt them as enforceable standards.
o National Secondary Drinking Water Regulations - The complete regulations regarding
these contaminants is available from the Code of Federal Regulations Web Site.
o For more information, read Secondary Drinking Water Regulations: Guidance for
Nuisance Chemicals.
List of National Secondary Drinking Water Regulations
Contaminant Secondary Standard
Aluminum 0.05 to 0.2 mg/L
Chloride 250 mg/L
Color 15 (color units)
Copper 1.0 mg/L
Corrosivity noncorrosive
Fluoride 2.0 mg/L
Foaming Agents 0.5 mg/L
Iron 0.3 mg/L
Manganese 0.05 mg/L
Odor 3 threshold odor number
pH 6.5-8.5
Silver 0.10 mg/L
Sulfate 250 mg/L
Total Dissolved Solids 500 mg/L
Zinc 5 mg/L
Top of page
Unregulated Contaminants
This list of contaminants which, at the time of publication, are not subject to any proposed
or promulgated national primary drinking water regulation (NSDWRs), are known or
anticipated to occur in public water systems, and may require regulations under the Safe
Drinking Water Act (SDWA). For more information check out the list, or visit the Drinking
Water Contaminant Candidate List (CCL) website.
o Drinking Water Contaminant Candidate List (CCL) website
o Unregulated Contaminant Monitoring Program (UCM)
o Information on specific unregulated contaminants
MTBE (methyl-t-butyl ether) in drinking water
Oregon Department of Environmental Quality
South Deschutes/North Klamath
Groundwater Protection:
Report and Recommendations
By: Eric Nigg and Robert Baggett
July 2013
Groundwater Program
Water Quality
Division
811 SW 6th Avenue
Portland, OR 97204
Phone: (541) 633-2036
(800) 452-4011
Fax: (541) 388-8283
Contact: Robert Baggett
www.oregon.gov/DEQ
DEQ is a leader in
restoring, maintaining and
enhancing the quality of
Oregon’s air, land and
water.
State of Oregon Department of Environmental Quality
This report prepared by:
Oregon Department of Environmental Quality
811 SW 6th Avenue
Portland, OR 97204
1-800-452-4011
www.oregon.gov/deq
Contact:
Robert Baggett
541-633-2036
Alternative formats (Braille, large type) of this document can be made available.
Contact DEQ’s Office of Communications & Outreach, Portland, at
503-229-5696, or toll-free in Oregon at 1-800-452-4011, ext. 5696.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality i
Contents
Executive Summary 1
Committee Background and History 2
Recommendations 5
Goal 11 Exception (Unanimously Approved 1/9/13) ..........................................................................5
Groundwater Monitoring (Unanimously Approved 3/5/13) ...............................................................5
Governance (Unanimously Approved 4/2/13) ....................................................................................6
Livestock (Unanimously Approved 1/9/13) ........................................................................................6
Point Sources (Unanimously Approved 1/9/13)..................................................................................6
ATT Moratorium (Approved 7-1 on 6/4/13) .......................................................................................6
Disadvantaged Community Financing Solutions (Approved 7 - 1 on 6/4/13) ....................................7
Outreach and Community Education (Unanimously Approved 6/4/13) .............................................7
Alternative “Green” Solutions (Unanimously Approved 6/4/13) .......................................................7
Arguments 8
Goal 11 Exception: Argument in Favor .................................................................................................................................. 8
Groundwater Monitoring: Argument in Favor ........................................................................................................................ 9
Governance Entity: Argument in Favor .................................................................................................................................. 9
ATT Moratorium: Argument in Favor ..............................................................................................10
ATT Moratorium: Argument in Favor .................................................................................................................................. 11
ATT Moratorium: Argument Against (David Crider)........................................................................................................... 11
Groundwater Monitoring Funding: Argument in Favor ........................................................................................................ 11
Livestock Ordinance: Argument in Favor ............................................................................................................................. 12
Point Source Regulation and Monitoring: Argument in Favor ............................................................................................. 12
Disadvantaged Community Financing Solutions: Argument in Favor ................................................................................. 12
Outreach and Community Education: Argument in Favor .................................................................................................... 12
Green Solutions: Argument in Favor .................................................................................................................................... 13
Appendix A 14
Appendix B 15
Meeting Dates/Times ............................................................................................................................................................ 15
Appendix C 19
List of Presenters ................................................................................................................................................................... 19
Appendix D 20
Southern Deschutes County and Northern Klamath County Groundwater Protection Project Steering
Committee Charter ................................................................................................................................................................ 20
I. Purpose ..........................................................................................................................................20
II. Background ..................................................................................................................................20
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality ii
III. Committee Charge .................................................................................................................22
IV. Decision Making Process .......................................................................................................23
V. Public Involvement ................................................................................................................23
VI. Committee Meeting Schedule, Work Plan and Guidelines ....................................................23
VII. Communications and Media Coverage: .................................................................................25
VIII. Process Support ..................................................................................................................25
IX. Committee Membership .........................................................................................................25
Appendix E 27
Appendix F 28
Acknowledgements ............................................................................................................................................................... 28
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 1
Executive Summary
There is a long history of groundwater contamination from septic systems in Southern Deschutes
County. Severe groundwater contamination in the area of La Pine motivated partners to build a
wastewater treatment and disposal plant to serve the city in the late 1980s. Conditions within the
City of La Pine have improved, but regional shallow groundwater outside of the city has shown
continued elevated levels of nitrates, which can be a “tracer” indicating the presence of partially
treated sewage. Testing and research indicate the vast majority of contamination comes from
onsite (septic) wastewater treatment systems, meaning discharge from residential septic systems
is seeping into the groundwater that is used as a primary drinking water source.
The problem is caused by existing developed and undeveloped platted lots, local geology and
geography. The area has porous, sandy pumice soil derived from volcanic events and many
shallow groundwater aquifers, both of which allow the potential for contamination. These local
conditions are unusual, as other parts of the state have finer silt and clay-like surface and sub-
surface soils that can form protective layers above groundwater.
In an effort to protect groundwater throughout the area, Deschutes County passed an ordinance in
2008 requiring homeowners to upgrade their septic systems. Voters overturned that ordinance in
a special election the next year, spurring Deschutes County to seek DEQ’s assistance in
addressing the problem. Soon after, DEQ sought volunteers for a local citizen Steering
Committee to recommend affordable solutions to protect area groundwater. DEQ solicited
volunteers through a direct mailing that went to more than 10,500 residences in the area.
DEQ interviewed two dozen candidates and selected 11 regular members and three alternates.
Members met regularly for almost three years, spending considerable time learning and
discussing many issues related to septic systems and groundwater contamination. The group
studied topics including geology, soils, hydrogeology, toxicology, and septic system technology.
They also learned about the political, financial and regulatory entities involved in wastewater
management.
The committee ultimately considered and approved a list of ten recommendations to address
groundwater contamination in the area. They also conducted extensive public outreach to talk
directly with the community about the problem and the potential solutions.
The recommendations include a range of ideas, strategies and best practices. Among these
recommendations is an exception to state planning rules that would allow multi-residence
wastewater treatment systems outside of existing urban growth boundaries and sanitary districts,
and allow establishment of a sanitary authority. They include establishing a groundwater
monitoring program and a moratorium of the current Alternative Treatment Technology (ATT)
requirement while some of the recommendations are being pursued. There is also a
recommendation to continue offering education and outreach to the community.
In June 2013, the committee fulfilled its goal of providing these recommendations to DEQ.
Having fulfilled its mission, the committee then voted to disband.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 2
Committee Background and
History
The committee began with a question: Does the area have a groundwater contamination problem?
In a word, the answer was yes. The area’s shallow, unprotected groundwater and pumice-based
sandy soils mean that water soluble substances put on or in the ground will likely end up in the
groundwater. While fertilizers, pesticides and livestock manure can contribute contaminants to
the groundwater, most groundwater contamination comes from individual onsite septic systems.
All types of onsite systems in the region – standard septic, sand filter and ATT systems --
discharge contaminants into the ground. Over time, many of these contaminants drain through the
sandy, porous soil and reach the groundwater, which can be as low as two feet below the ground
surface in some areas.
Compounding the risk is the fact that there are about 14,000 properties in the area with over 75%
of the properties in neighborhoods having parcels of 2 acre or less in size. Add in the fact that
there is minimal precipitation in the area to dilute contaminants and the problem becomes clear:
too many septic systems are discharging to porous soil and over time there will be increasing
contamination of the shallow vulnerable aquifers that many people are using as their drinking
water supply.
Members learned to distinguish between the slower rate of aquifer-wide contamination and the
more immediate threat to contaminated wells located in some neighborhoods. The committee also
learned a lot about how the pumice soils naturally filters some pathogens, while more water-
soluble substances like nitrates, detergents, pharmaceuticals and personal care products were
more likely to reach groundwater. The committee also reviewed well test data, confirming that
the risk of contamination varied by neighborhood based on a range of factors.
Another important realization by the committee was learning that there was very little risk of the
contamination reaching the deep wells that serve places like Bend and Sunriver. Although many
people – including elected officials and the media – claimed otherwise, analysis showed very
little risk of contamination extending beyond the Upper Deschutes River-La Pine Sub Basin.
Water quality tests and studies conducted on the regional aquifers indicate that the risk to people
outside of this area is actually quite low.
In order to obtain more current data, the committee urged DEQ to conduct re-testing on about 51
sites throughout the region. Those results showed slight – though statistically significant –
increases in groundwater contamination when compared to testing on the same sites conducted
years earlier. However, that increase was not as great as previously predicted.
Although the committee was established by DEQ, members recognized that the breadth of the
problem would require assistance from a number of other agencies. Whenever possible, the
committee relied on personnel and resources from those agencies, including inviting guest
speakers to some meetings. Those speakers were useful in helping committee members see the
problem from other perspectives.
Once the committee members had a comprehensive grasp of the problem and its causes, they
considered the options. They could:
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 3
1. Do nothing and maintain the status quo
2. Protect public health by treating the drinking water supply
3. Promote more monitoring and site-specific testing
4. Take a phased approach to reduce contamination
5. Promote a “one size fits all” solution and apply it to the entire area
A lot of thought and discussion went into the five options listed above. In general, the thought
process behind each of the above considerations is as follows:
1. The committee very much wanted to be good stewards of the environment, so doing
nothing was not determined to be a viable option. Also, with the requirement to install
ATT systems, “doing nothing” meant continuing to require homeowners to spend
considerable money on a “solution” that actually resulted in significant contamination for
a majority of residents.
2. Members also believed that if the community did not take steps to address the problem
now, it would only grow worse in the coming years. Once groundwater contamination
becomes widespread, it can be difficult – if not impossible – to get rid of. Addressing the
problem relatively early, rather than waiting decades longer, seemed the most prudent
action. For all of these reasons, doing nothing to address groundwater contamination was
not considered an option for the committee.
3. The committee talked about whether the problem was really related to drinking water,
groundwater, or both. While some people believe the problem can best be addressed by
ensuring safe drinking water, that approach ignores the environmental damage being
caused to the groundwater and to local rivers and streams. Members discussed numerous
ways to ensure safe drinking water, including filtrations, requiring public water systems
and drilling deeper individual wells. But each of these solutions was insufficient in
treating the larger issues, and they presented a whole new set of technical challenges not
dissimilar from dealing with wastewater itself. Ultimately, the committee felt that treating
drinking water might solve some of the human health impacts, though it would do
nothing to address the larger environmental problems of groundwater contamination.
4. Throughout the nearly three years that the committee met, the importance of monitoring
became more and more evident. Members talked about how any potential solution should
include widespread monitoring of groundwater and well testing. Monitoring was seen to
be the only reliable way to gauge the seriousness of the problem, and the more data that
is available the easier it is to start working toward site/neighborhood-specific solutions to
the problem. Additionally, a good monitoring program would be useful in determining
effectiveness of the protective solutions.
5. When the committee looked at neighborhoods throughout the region, it became clear that
some areas would need different approaches and solutions. Members spent a lot of time
considering different risk criteria, including housing density, depth of the first
groundwater, depth of drinking water wells, local subsurface geology and the relative age
of septic systems. Also, in some areas, different solutions might need to be phased in
over a longer period of time. With all of these variables taken together, members realized
they may need to take a phased, long-term approach to the problem.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 4
6. The one-size-fits-all solution was rejected by both the voters and committee members. As
the committee learned more about the situation it became clear that the ATT one-size-
fits-all solution would not have adequately protected the groundwater in some areas
while requiring expensive alternative solution that were unnecessary in other areas.
Because of the unique characteristics of affected neighborhoods, the inflexibility of a one
size fits all solution would be extremely costly while not adequately protecting the
groundwater.
After significant discussion, the committee decided to focus their time and attention on options
three and four. So, with those aims in mind, the committee met with many experts in a variety of
related fields. They spoke with science and research-based experts, including a hydrologist, soil
engineer, chemist, and toxicologist. They learned directly from industry experts about the various
types of septic treatment systems available.
The committee also learned quite a bit about sanitation authorities, special districts and state laws
pertaining to the extension of sewer lines outside of urban growth boundaries and existing
districts. Members also discussed low interest loans, grants and other financing options.
The committee met nearly 50 times, including 33 regular meetings, eight work sessions and five
community outreach meetings. The committee also visited the Sunriver Resort and Eagle Crest
Resort Wastewater Treatment Plants and staffed an information booth at the 2012 La Pine
Frontier Days 4th of July Celebration. A list of people who presented information to the
committee is included in the appendix. People can also access audio files of every meeting and
find other reference materials at
http://www.southdeschutesnorthklamathgroundwater.com/documents. More project information
is also available at http://www.deq.state.or.us/wq/onsite/sdesch-nklam.htm.
After nearly three years of discussing nearly every facet of the problem and debating potential
solutions, the group turned their focus to the recommendations. The committee finalized those
recommendations in June 2013.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 5
Recommendations
Goal 11 Exception (Unanimously Approved 1/9/13)
• Provide a Goal 11 exception for the at-risk areas in South Deschutes and North Klamath
counties for the following reasons:
o Lots were platted prior to statewide goals requiring 10 acre rural lots (in
Deschutes County.
South Deschutes County currently of 10271 non-sewer lots:
6174 (60%) are 1 acre or less
8737 (85%) are 2 acres or less
o North Klamath County currently of 4181 lots
2177 (52%) are 1 acre or less
3140 (75%) are 2 acre or less
o Provide better treatment opportunities than individual on site systems for the
protection of groundwater, both in reducing nitrates and better treatment of other
contaminants
• This exception will allow the extension of sewers into the area
• This exception will allow groups of citizens to implement public sewage treatment
systems, such as cluster systems. These decentralized cluster systems would not require
huge infrastructure expense
• These centralized systems will allow better treatment of contaminants beyond nitrates
and better treatment than ATT onsite systems.
• This Goal 11 exception would not mandate a system be installed.
Groundwater Monitoring (Unanimously Approved 3/5/13)
• Request that DEQ design a testing program to determine whether there is a groundwater
contamination problem, and if so, where it might be located.
o Tests first water
o Start with highest risk sections (neighborhoods) identified by (existing well test
data, density, well depth). See MonitorCriteria.xlsx for simple ranking.
o Uses representative samples of the neighborhoods
o Do 10% – 20% of neighborhoods each year
• If sample results from the first water test warrant it, increase the number of wells tested to
possibly include additional first water wells and drinking water wells in the
neighborhood. Alternatively, provide an on-demand targeted testing approach that tests
source, receptor, and transport.
• What should be tested for?
o Nitrates cheap test – 10 minute sample for nitrate testing only. Flush take sample.
o Retest wells with highest nitrate detection levels for other contaminants (such as
pharmaceuticals…)
• Monitoring managed by a sanitation authority with DEQ doing the monitoring until a
sanitation authority is established.
• Use this monitoring program in addition to the real estate transaction data
• The DEQ should pursue all sustainable funding opportunities to support groundwater
monitoring in the area.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 6
Governance (Unanimously Approved 4/2/13)
Form a Sanitation Authority to protect the groundwater in the affected area spanning South
Deschutes and North Klamath counties.
• The Authority will manage groundwater monitoring.
• The Authority will help with neighborhood implementation of community waste water
systems (allowed under the Goal 11 exception).
• The Authority can assist in establishing Local Improvement District (LID), a special
district or similar entity to finance community waste water systems for areas within the
Authority where they are necessary.
• Authority will explore financing options that may include: grants, loans and taxes
• Provide required maintenance and management for community waste water systems
within the Authority
• Ensure individual systems are maintained (pumped and serviced as necessary)
• Manage the overall basin nitrate load and risk to groundwater
• Monitor performance based standards for alternative solutions (see green solutions)
Livestock (Unanimously Approved 1/9/13)
• In Deschutes County (Klamath has an ordinance) institute an ordinance that limits the
number of livestock per acre to reduce risk to groundwater contamination. For instance
Klamath ordinance is: R2 zone allows two large animals (horse, etc.) and 24 small
animals (chickens, etc. not dogs or cats) PER ACRE.
• Provide education about how best to manage livestock to reduce risk to groundwater
o How to treat waste
o How to dispose of deceased livestock
Point Sources (Unanimously Approved 1/9/13)
• Point Sources (nurseries, golf courses)
o Investigate establishing a permitting/groundwater monitoring program for all
golf courses, nurseries and other point sources
• Commercial RV and Manufactured/mobile Home Parks.
o Require equivalent treatment as residential (ensure equal regulations and
treatment for residence and commercial).
o Require a Water Pollution Control Facilities Permit for new and existing
properties.
ATT Moratorium (Approved 7-1 on 6/4/13)
• The moratorium will have an end date with specific community actions to include a Goal
11 exception, a monitoring program and a governance entity or substantial progress
toward its creation must have been made. Five years seems reasonable. An extension
might be necessary, based on progress made toward the above goals.
• When the Governance Entity is created, it will work with DEQ and the counties to
determine what happens at the moratorium end date.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 7
• During the moratorium, property owners that have to do a major repair have the option of
installing an ATT or repairing or replacing existing systems without an upgrade. This is
done with the understanding that if progress is not made toward program goals (listed
above in paragraph 1), they will have to upgrade. The moratorium would extend to
undeveloped lots that already have existing systems in place.
• The moratorium would apply to new development.
Disadvantaged Community Financing Solutions (Approved 7 - 1 on 6/4/13)
• DEQ shall research how other states have established financial aid for sewage treatment
solutions and propose an approach to use in Oregon.
Outreach and Community Education (Unanimously Approved 6/4/13)
• With the delivery of these recommendations the Citizen Advisory Committee has
completed our charter and will disband
• Prior to disbanding initial outreach materials will be developed
• To ensure ongoing community involvement with groundwater protection an outreach
committee should be formed that will
o Identify and outreach opportunities
o Coordinate outreach delivery. Members from the current committee may be
called on to participate in or lead the outreach events
o Maintain and improve outreach materials
• This committee should be made up of people with marketing/outreach interest and
experience, and should be a small team of no more than 5 people with support from DEQ
and the counties.
• This committee should have access to enough funding to make outreach successful
Alternative “Green” Solutions (Unanimously Approved 6/4/13)
Disposing of human waste is a worldwide problem. There are many innovating approaches being
developed. People in the affected areas must be able to use new approaches to treat human
effluent.
In order to use current and future new technologies the DEQ must develop performance standards
for treatment and any system that provides the necessary performance level should be acceptable
if effective safeguards are in place to ensure the new systems are properly used and maintained.
With the advent of Oregon grey water permitting a composting toilet solution should be
acceptable. To ensure the toilets are used effectively:
• Inspection of composting systems could be added to or included in current grey water
permit language; an additional fee for that inspection of the composting component might
need to be considered.
• Language and parameters for disposal of the composted material is already established.
• The cost of permits for composting toilets should remain affordable.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 8
Arguments
Goal 11 Exception: Argument in Favor
All onsite systems discharge contaminants including nitrates. Chart 6.2 below shows the nitrate
discharge from various systems tested during the La Pine National Demonstration Project.
The discharge and water
soluble substances are pulled
down by gravity until they
meet the groundwater. Area
precipitation also joins the
groundwater. Because we
have a low amount of
precipitation in the area the
effluent discharge doesn’t get
diluted like it does in wetter
areas. As neighborhood lot
sizes decrease the
concentrations of discharge in
the groundwater increases
geometrically.
Effect of Parcel Size on
Effluent
Concentrations in
Groundwater –
the chart on the right shows
that ½ acre lot
neighborhoods (point A)
will reach an equilibrium
point where over 50% of
the groundwater comes
from onsite septic systems.
The type of system
installed doesn’t affect this
ratio, though it may reduce
certain pollutants in the
groundwater.
Because many lots in the
South Deschutes/North Klamath area were platted before Oregon’s land use rules were in place
the number of small lots in the area resemble a more urban configuration. The breakdown of lot
sizes for each county in the area are:
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 9
South Deschutes County currently of 10271 non-sewer lots:
• 6174 (60%) are 1 acre or less
• 8737 (85%) are 2 acres or less
North Klamath County currently of 4181 lots
• 2177 (52%) are 1 acre or less
• 3140 (75%) are 2 acre or less
Based on these lot sizes 85% of Deschutes and 75% of Klamath county properties in the area are
at risk of having groundwater that is comprised of at least 25% of partially treated sewage.
In addition there are a number of sewer systems in the area and some required a Goal 11
exception. These exceptions clearly indicate the onsite systems are not adequate in densely
populated neighborhoods.
Clearly onsite systems are not an adequate approach to protect the groundwater and therefore we
need a broadly defined Goal 11 exception for the area so protection of groundwater and drinking
water is adequate.
Committee Member Comment on the Goal 11 Exception (John Blakinger): I think one of the key
successes the committee had was bringing Department of Land Conservation and Development
(DLCD), DEQ and Deschutes and Klamath counties together about the Goal 11 exception. We've
come a long way toward a Goal 11 exception.
Groundwater Monitoring: Argument in Favor
Having reliable data about groundwater contamination in the area is essential to deciding when
and where additional treatment approaches must be installed.
The committee urged DEQ to conduct re-testing on about 51 sites throughout the region. Those
results showed slight – though statistically significant – increases in groundwater contamination
when compared to testing on the same sites conducted years earlier. However, that increase was
not as great as previously predicted.
The real-estate transaction well test data may be a useful indicator of where a problem may be.
One limitation of real estate transaction test data is that it is not designed to provide
contamination levels of first water, which the committee wanted to protect. Instead of sampling
first water, it sampled wells of various depths.
To get a more accurate picture of groundwater contamination in the area, a monitoring program
must be implemented. Such a program would also support a phased approach chosen by the
committee, and could help dictate where more or less treatment is needed.
Governance Entity: Argument in Favor
A governance entity will manage and analyze the groundwater monitoring data. It would also
help implement community wastewater treatment solutions. The entity could oversee
maintenance of all systems and provide cost savings through economies of scale.
When it is determined an area must implement a special treatment solution the Governance entity
could help with bridge financing.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 10
The entity will have access to funding through long-term loans, grants and taxes. By pooling our
money together we’ll be able to assist those who have financial limitations, and spread the cost of
treatment solutions over time.
Financing examples:
• Loan: For example, if a solution that costs $15,000 per property where financed through
a 2% 30 year loan, the payment for each property (not including operational costs) would
be $55.44 per month.
• Taxes: if a $0.50 per $1000 of assessed value ($50/year for a$100,000 property) were
instituted it would bring in about $600,000 per year for the area.
The governance entity will be managed by an elected board of residents so it will be under
community control.
Committee Member Comment on Governance (David Crider): The public will have to decide if
they want another governance entity governing our septic issues. The public may want to address
septic issues by neighborhood and or subdivisions without the governance entity and the taxes
that go with it. The solution is to start now working on a phase solution to groundwater protection
and carry it forward.
ATT Moratorium: Argument in Favor
What value does de-nitrification offer?
1. In some USGS reports nitrates are referred to as a tracer or indicator of septic effluent.
Why would we want to reduce the indicator? Won't that give people a false sense of
security when nitrate levels in drinking water is 2 mg/l instead of 5 mg/l - even though
the percentage of well water coming from septic is unchanged (at 10 %)?
2. The health impact of nitrates is controversial. The blue baby syndrome concern that
triggered the EPA nitrate standard set in 1951 has been widely discredited. There are
some medical journal articles that suggest a health risk link, but the evidence is mixed.
See appendix for links to nitrate health impact studies.
3. The impact to rivers in the area from high nitrates is questionable. Quoting from report,
Scientific Investigations Report 2007–5239.
“Contributions of toxic ground water, and therefore, potential contributions of NO3 - to
rivers in the study area probably are limited primarily to areas where rivers bend toward
the outside of the riparian environment. Thus, contributions of NO3 - to rivers likely are
restricted to relatively small areas of river reaches. However, the potential effects of such
N loads to rivers might not be negligible because rivers can be highly sensitive to
changes in nutrient fluxes (nutrient over-enrichment represents the single greatest source
of impairment to rivers in the United States; U.S. Environmental Protection Agency,
1998).”
In dense neighborhoods ATT systems will not protect the groundwater even from nitrates (see
Goal 11 argument above), therefore the ATT systems should not be installed in dense
neighborhoods (less than 2 acre lots).
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 11
There are limited funds in the area so we should use them to solve the long-term problem. The
moratorium would be for 5 years so the long-term solution: Goal 11 Exception, Groundwater
Monitoring and Governance Entity can be put in place.
A moratorium would have wide support and demonstrate to the community that the government
agencies are interested in long-term concerns and solutions. The moratorium will help generate
community support for those long-term solutions.
Nitrate contamination is not an imminent threat to human health. While there is an increasing
trend of contamination, it is progressing slower than predicted, which allows more time to
address the problem over the long term.
ATT Moratorium: Argument in Favor
The original ATT ordinance was an area-wide requirement largely put in place based on
predictions of future contamination in the area.
In 2011 the committee initiated a retest of some of the wells measured in previous studies.
A statistician reviewed the results of the 39 wells that were retested, and based on a t-test
determined there is an increasing trend in the measured contaminant - Nitrate-Nitrogen (or
Nitrate-N). This trend is below the rate that led to the ordinance. The retest was done about 16
years after the original samples, with an average increase in the contaminant of .17 (median) to
.49 (mean) over that period.
In addition he reviewed the Real-estate transaction database to determine area-wide trends in
contamination levels (based on Nitrate-Nitrogen (or Nitrate-N). Again he determined there was
an increasing trend though not at the rate that led to the ordinance. The 10 year increase of the
contaminant: Regression analysis .005 - .444 mg/liter, Sen Slope analysis .25 - .405 mg/liter.
This analysis demonstrates that the contamination is not increasing at the rate that was predicted
before, and therefore we have time to implement an effective, long-term solution.
ATT Moratorium: Argument Against (David Crider)
Public water systems have a set-back from septic systems. However, in Northern Klamath County
along the river and wetlands, four public water systems well fields are being protected by the
current ATT system requirement. An ATT moratorium would put those four system’s shallow
wells 70 feet deep at risk for unknown contamination! Those public water systems and an
unknown number of private wells in the same area provide drinking water to 300 plus
households. An ATT Moratorium is not protecting groundwater while someone else is going to
try for a long-term solution.
Groundwater Monitoring Funding: Argument in
Favor
Monitoring is important, and it takes money. We believe money dedicated to increasing
monitoring is well spent, and DEQ should pursue all options to secure funds for this purpose.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 12
Livestock Ordinance: Argument in Favor
Klamath County limits the number of livestock allowed per acre in an effort to reduce the risk of
groundwater contamination. Deschutes County could benefit from a similar ordinance. The
county could also provide education to people about how to treat livestock waste and dispose of
animal carcasses.
Point Source Regulation and Monitoring:
Argument in Favor
DEQ should consider establishing a monitoring system for such sources as nurseries and golf
courses. Both have the potential to contaminate groundwater, mainly through the application of
fertilizers. In addition manufactured home and RV parks should also be monitored to ensure safe
treatment of human sewage. The agency currently does not monitor such potential sources. A
monitoring program could provide more information and lead to regulation in order to protect the
groundwater from those sources.
Disadvantaged Community Financing Solutions:
Argument in Favor
Other states have recently approved language that directs state environmental agencies to more
closely consider cost before requiring community solutions to environmental problems. As some
parts of south Deschutes and north Klamath counties are economically challenged, DEQ should
analyze the financial cost to homeowners before taking further action to address groundwater
contamination. Some homeowners in the area are living on fixed monthly incomes and may not
be able to afford the septic upgrades DEQ will require. This recommendation doesn’t ask DEQ to
do anything except look at how other states have approached these types of situations, and then to
consider the financial means of the community before requiring solutions, while still protecting
the groundwater.
Outreach and Community Education: Argument in
Favor
Community education is about more than these recommendations. It is about spreading better
information about stewardship, including how we can make more informed decisions to protect
our groundwater. It is also important for people to better understand the shallow groundwater that
exists in most of the region. In particular, it is important to understand how susceptible the
groundwater it is to contamination, including from things like herbicides.
It is crucial that citizens have as much information as possible about groundwater contamination
in South Deschutes and North Klamath counties. They need to be made aware of the problem and
the various solutions being proposed. The committee made a big effort to educate the community
about the issue, and that effort should continue even after the committee itself has disbanded. The
issue of groundwater contamination is not going away any time soon, and the more people know
about it the more likely it is that they will be committed to finding solutions.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 13
Green Solutions: Argument in Favor
Simple doesn’t mean less effective. The use of composting toilets and greywater treatment can be
an effective solution, and consideration for their use should not be so readily dismissed.
With the area of concern so broad this decentralized use should be embraced as it has been in
Scandinavian countries since the 70’s. A huge reduction in water in composting toilets as
compared to conventional flush toilets would be a benefit.
Pharmaceuticals, including amoxicillin for example, are reduced in the composting process (see
http://www2.gtz.de/Dokumente/oe44/ecosan/en-degradation-of-amoxicillin-in-composting-toilet-
2006.pdf). Nitrate loading of streams and rivers that result in low oxygen issues would be
negligible with the use of composting toilets.
Nitrate reduction is accomplished to a greater degree than the currently mandated ATT’s. Where
an ATT has issues on property used only as a vacation home, composting toilets do not have this
problem; they continue to work when not in use.
A greywater septic system with a smaller requirement for its leach field is a viable solution for
smaller lots in some of the area of concern.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 14
Appendix A
Nitrates impact are controversial, may even be healthful
http://www.ncbi.nlm.nih.gov/pubmed/18268290
Individual studies that suggest potential health risks:
Nitrate can help create carcinogenic N-nitroso compounds in obese men:
http://www.ncbi.nlm.nih.gov/pubmed/22833653
Nitrates plus vitamin pills = higher breast cancer rate:
http://www.ncbi.nlm.nih.gov/pubmed/22642949
Nitrates plus Viagra = hypotension and syncope:
http://www.ncbi.nlm.nih.gov/pubmed/23140258
Nitrates can cause subclinical hypothyroidism in women:
http://www.ncbi.nlm.nih.gov/pubmed/22339761
Nitrates can cause papillary and follicular thyroid cancer in older men:
http://www.ncbi.nlm.nih.gov/pubmed/20824705
Nitrate is a dietary risk in stomach cancer: http://www.ncbi.nlm.nih.gov/pubmed/22844547
Gastric cancer: http://www.ncbi.nlm.nih.gov/pubmed/22757672
Esophageal cancer: http://www.ncbi.nlm.nih.gov/pubmed/22146401
Colon cancer: http://www.ncbi.nlm.nih.gov/pubmed/21976196
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 15
Appendix B
Meeting Dates/Times
Steering Committee Work Session
6 p.m., June 19, 2013
Steering Committee Meeting
6 p.m., June 4, 2013
Steering Committee Meeting
6 p.m., May 7, 2013
Steering Committee Community Outreach
6:30 p.m., April 22, 2013
Steering Committee Meeting
6 p.m., April 2, 2013
Steering Committee Community Outreach
6:30 p.m., March 20, 2013
Steering Committee Meeting
6 p.m., March 5, 2013
Steering Committee Work Session
6 p.m., February 28, 2013
Steering Committee Meeting
6 p.m., February 5, 2013
Steering Committee Community Outreach
6 p.m., January 24, 2013
Steering Committee Meeting
6 p.m., January 9, 2013
Steering Committee Work Session
6 p.m., December 13, 2012
Steering Committee Meeting
6 p.m., December 4, 2012
Steering Committee Work Session
6 p.m., November 14, 2012
Steering Committee Meeting
6 p.m., November 6, 2012
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 16
Steering Committee Community Outreach
6:30 p.m., October 25, 2012
Steering Committee Meeting
6 p.m., October 2, 2012
Steering Committee Community Outreach
6 p.m., September 13, 2012
Steering Committee Meeting
6 p.m., September Sept. 4, 2012
Steering Committee Work Session
2 p.m., August 30, 2012
Steering Committee Work Session
6 p.m., August 21, 2012
Steering Committee Work Session
2 p.m., August 15, 2012
Steering Committee Meeting
6 p.m., August 7, 2012
Steering Committee Meeting
6 p.m., July 11, 2012
Steering Committee Meeting
6 p.m., June 5, 2012
Steering Committee Meeting
6 p.m., May 1, 2012
Steering Committee Meeting
6 p.m., April 3, 2012
Steering Committee Meeting
6 p.m., March 6, 2012
Steering Committee Meeting
6 p.m., February 7, 2012
Steering Committee Meeting
6 p.m., January 9, 2012
Steering Committee Meeting
6 p.m., December 6, 2011
Steering Committee Meeting
6 p.m., November 1, 2011
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 17
Steering Committee Meeting
6 p.m., October 4, 2011
Steering Committee Meeting
6 p.m., September 13, 2011
Steering Committee Meeting
6 p.m., August 2, 2011
Steering Committee Meeting
6 p.m., July 14, 2011
Steering Committee Meeting
6 p.m., June 15, 2011
Steering Committee Meeting
6 p.m., May 3, 2011
Steering Committee Meeting
6 p.m., April 5, 2011
Steering Committee Meeting
6 p.m., March 1, 2011
Steering Committee Meeting
6 p.m., February 1, 2011
Steering Committee Meeting
6 p.m., January 4, 2011
Steering Committee Meeting
6 p.m., December 7, 2010
Steering Committee Meeting
6 p.m., November 9, 2010
Steering Committee Meeting
6 p.m., September 9, 2010
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 18
Steering committee Co-Chair John Blakinger engages the public at a community outreach session at
Thousand Trails Community Club near Sun River on March 20, 2013
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 19
Appendix C
List of Presenters
02-01-11 - Eric Moeggenberg, Oregon Dept. of Ag, Impacts of Livestock to Groundwater
03-01-11 - Rich Hill, DEQ Groundwater Hydrogeologist, La Pine Area Municipal Land
Application
05-03-11 - Steve Hinkle, USGS - review of USGS Studies of the La Pine Area
06-15-11 - Jason Churchill, Orenco Systems, Nitrate & Statistics
09-13-11 - Brenda Hoppe, Oregon Health Authority, Nitrate & Private Well Water Safety
12-06-11 - Dan Harschbarger, N. Klamath Co. resident, Herbicide-picloram spray event
01-09-12 - Brent Nicholas, Oregon Dept. of Ag, Herbicide-picloram spray event
02-07-12 - Dale Mitchell, Oregon Dept. of Ag, PARC, Herbicide-picloram spray event
03-06-12 - Steve Wert, Individual & Cluster Onsite Wastewater System Technologies
03-06-12 - John Huddle, Statistics
05-15-12 – Laurie Craighead, Deschutes County District Attorneys Office, Sanitary Authorities
and Districts
06-21-12 - Ken Jones, Attorney, Specializing In Special Districts in Oregon
07-11-12 - Jon Jinings, Dept. of Land Conservation & Development, Goal 11 Exception Criteria
08-07-12 - Ron Doughten, DEQ Graywater Reuse Coordinator, Graywater Reuse Requirements
11-06-12 - Morgan Brown, Whole Water Systems, Green Solutions to Wastewater Reuse
02-28-13 - Bill Cagle, Orenco Systems, Cluster Onsite Systems Technology, Design, Costs
02-28-13 - Melora Golden, Mathew Lippincott, Molly Danielsson, Oregon ReCode, Green
Methods of Wastewater Disposal
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 20
Appendix D
Southern Deschutes County and Northern
Klamath County Groundwater Protection Project
Steering Committee Charter
The Oregon Department of Environmental Quality DEQ has the responsibility and authority for
protecting all waters in the state, including groundwater. Through public awareness, outreach and
establishment of committees DEQ seeks input and recommendations in these efforts.
For any collaborative process to operate smoothly, it is necessary for those involved to agree at
the outset on the purpose for the process and on the procedures by which the group will govern its
discussions, deliberations, and decision-making.
The members of the S. Deschutes/N. Klamath Groundwater Protection Project Steering
Committee agree to operate under this Charter.
I. Purpose
The purpose of the committee is to provide recommendations to the DEQ on how to best protect
the groundwater and prevent groundwater contamination of surface waters in the area of South
Deschutes and North Klamath Counties. These recommendations may impact areas beyond the
boundaries of the USGS study described below.
The committee will be an advisory level forum for collaborative efforts related to development of
a groundwater contamination reduction and protection plan. The participants are voluntarily
working together to achieve a mutually acceptable outcome that satisfies, to the greatest degree
possible, the interests of all citizens in the groundwater protection area. The committee will be
responsible for all decisions and actions that are publicly identified as the committee’s.
II. Background
In some areas of Oregon, groundwater contamination comes from a combination of agricultural
chemicals, animal waste and individual septic systems. Based on studies, the aquifers beneath the
developed residential areas in both south Deschutes and north Klamath Counties are showing an
increasing trend of nitrate contamination. The major source of contamination is from onsite septic
systems.
In 1999 a groundwater work group, jointly formed by DEQ and Deschutes County, recommended
taking action and creating an area-wide rule to address groundwater contamination concerns in
the southern portion of the county. As a result of those recommendations as well as assistance
from local, state and federal agencies and support from political leaders at all levels, DEQ and
Deschutes County received federal funding from the United States Environmental Protection
Agency EPA for the La Pine National Decentralized Wastewater Treatment Demonstration
Project and a USGS groundwater study and modeling project.
Extensive field research and study shows that within the defined study area, the underlying
groundwater of south Deschutes and north Klamath Counties is threatened by continued use and
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 21
placement of traditional onsite wastewater treatment systems (traditional meaning - standard,
pressure distribution and sand filter systems).
The United States Geological Service USGS conducted a hydrological study that included
portions of Deschutes and Klamath Counties within Townships, 19, 20, 21, 22, and 23, and
Ranges 9, 10, and 11, see figure 1 on page 3. The primary objective of the study was to develop a
thorough understanding of the hydrologic and chemical processes that affect the movement and
fate of nitrogen within the shallow aquifers of the study area. A secondary objective was to
provide a method for analyzing the effects of existing and future development on water quality.
Discharge from onsite wastewater (septic) systems is considered a primary and significant source
of anthropogenic nitrogen pollution to shallow groundwater in the study area.
The demonstration project showed that some new types of individual onsite wastewater systems
that were specifically designed to enhance nitrate removal through de-nitrification can better
protect groundwater. In addition, the possible extension of existing community sewer systems
and the use of cluster onsite wastewater systems with the same proven de-nitrification capabilities
are options to consider in protecting the shallow groundwater aquifers throughout the area.
Some area aquifers have no natural protective barriers to the ground surface, are very vulnerable
to contamination from surface activities, are interconnected, and have surface water (river)
influences.
Generally water tables in the area are shallow, typically is less than 20 ft below land surface, and
in some low-lying areas rises seasonally to within 2 ft of land surface. Sandy soils derived from
pumice contain little organic matter and allow rapid infiltration of onsite wastewater effluent.1
Groundwater in the shallow aquifer is becoming contaminated with nitrates and if left unchecked,
will eventually reach unsafe levels. The EPA has set a maximum contaminant level for nitrate in
drinking water to be 10 mg/l. An increasing trend of nitrate contamination can often indicate that
other forms of domestic wastewater contaminants may be entering the groundwater.
To protect the quality of drinking water in the local aquifers, Deschutes County Commissioners
passed an ordinance in 2008 to require eventual upgrades on all septic systems. County voters
overturned the ordinance in a special election in March 2009. As result, in July 2009 Deschutes
County Commissioners asked DEQ to take the lead in the efforts to resolve the issue. DEQ hosted
town hall meetings in February and May 2010 with citizens and agreed to assemble a steering
committee of citizens representing the South Deschutes and North Klamath affected areas to meet
with and provide recommendations to DEQ.
1 U.S. GEOLOGICAL SURVEY Scientific Investigations Report 2007–5237, http://pubs.usgs.gov/sir/2007/5237/section2.html
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 22
Figure 1. Location of study area and extent of the nitrate fate and transport model.
III. Committee Charge
DEQ and the committee will assess information needs and agree on a process to move forward.
1. DEQ and the committee will focus on the following:
a. How to keep all citizens in the affected area informed of the process
b. What must we resolve before moving forward
c. What new information do we need to move forward
d. What options/solutions need to be considered
e. Other areas as defined
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 23
DEQ and the committee can form subgroups and designate subgroup members as needed. At the
direction of DEQ and the committee, subgroup members may develop draft products such as
research briefs, planning documents and other items and make recommendations to DEQ and the
committee. Subgroups will not make decisions on behalf of DEQ and the committee.
Scientific and technical input will be provided on an “as-needed” basis by DEQ staff, committee
members, staff from other identified local, state, and federal agencies, consultants or other
designated entities or experts as agreed upon by DEQ and the committee. To the extent DEQ or a
committee member is relying on the expertise of scientific or technical staff, those scientific or
technical staff must be made available for discussion with other members of the committee if
requested or needed. These technical advisers will not make decisions on behalf of DEQ and the
committee.
Alternate committee members (see Section X – Committee Membership) are invited to
participate in discussions and all related matters. Alternates offer input but may not vote or
concur on procedural or substantive decisions unless they are taking the place of an absent
member. Alternate members must abide by the operating principles within this document. When a
member is absent an attending alternate will be a fully voting member of the committee. The
chair will select the alternate in a rotation.
2. The committee will produce a draft report that summarizes research, key discussions and
recommendations. DEQ staff will draft the report in collaboration with the committee chair
and the committee members will review it for completeness. Once finalized all members will
be asked to sign the report.
IV. Decision Making Process
The committee will operate collaboratively. The committee will strive to reach the consent of all
members, and may require voting to determine the positions of members. If the committee cannot
agree within a reasonable amount of time, the final report will note the different perspectives on
the issue or issues. DEQ is the final decision-maker in the process.
V. Public Involvement
All meetings will be open to the public. For the committee to function without interruption,
public comments will be taken during specified times as noted on each meeting agenda.
Additionally, citizens who wish to discuss proposals are encouraged to communicate directly
with committee members or DEQ project staff.
VI. Committee Meeting Schedule, Work Plan and Guidelines
1. Committee Meeting
At least seven members must be present to make decisions.
Committee meetings will likely be evening meetings (6:00 pm to 9:00 pm) to assist with
public outreach and involvement. Half-day meetings (9:00 am - noon or 1:30pm - 4:30pm)
or an occasional all-day meeting (9:00 am-4:00 pm with a 1-hour lunch) may be necessary.
All meetings will be held in the La Pine area unless an alternate location is identified by the
committee. The duration of the committee is one year, but may be extended as necessary.
Routine monthly meetings are currently scheduled for the first Tuesday of every month from
Dec. 2010 to June 2011 at the Midstate Community Meeting Room located at 16755 Finley
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 24
Butte Road in La Pine. The meeting dates are December 7, January 4, February 1, March 1,
April 5, and June 7. The meetings will be held in the evening with members arriving at 5:45
PM, the meeting starting at 6 PM and ending at 9 PM. Changes to the meeting schedule or
location may occur as necessary.
2. Process Overview
a. Meeting Materials: DEQ staff will prepare and make materials available to committee
members through a web posting or mailing at least one week prior to each meeting. The
committee chairperson will collaborate with DEQ staff on agenda development.
b. Meeting Summaries: DEQ staff will prepare and post committee meeting notes and the
audio recording on the DEQ website. Minutes will summarize significant issues raised
during the discussion and committee recommendations.
c. Public Records and Confidentiality: Committee records, such as formal documents,
discussion drafts, meeting summaries, and exhibits are public records and will be posted
with the committee record on DEQ’s website. All committee communications are public
record and will be disclosed if requested.
d. Process Conclusion: The committee will submit a report and recommendations to DEQ.
The report will include sections for individual views if agreement was not reached on a
topic.
3. Ground Rules
All committee members commit to each of the following:
a. Comply with Oregon ethics laws.
b. Attend each meeting to ensure continuity throughout the process. If a committee member
is absent for two consecutive meetings, he or she may be replaced by an alternate
member.
c. Review proposed or draft documents and reports in a timely manner (by a date agreed
upon by the committee).
d. Treat everyone and their opinions with respect.
e. Engage in good faith discussions.
f. Act in good faith in all aspects of the collaborative effort.
g. Refrain from personal attacks or prejudiced statements against other committee members.
h. Express consistent views and opinions in the committee and in other forums.
i. Allow one person to speak at a time.
j. Comment constructively and specifically on issues.
k. Consult regularly with constituencies and provide their input.
l. Stay focused on the specific charge as outlined in this charter.
m. Will not represent one’s personal or organization’s views as views of the committee.
n. Will not represent or misrepresent the views of any other member, group, or the
committee as a whole.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 25
4. Information Exchange
Committee members will provide information as much in advance as possible of the meeting.
The members will also share all relevant information with each other to the maximum extent
possible. If a member believes the relevant information is proprietary in nature, the member
will provide a general description of the information and the reason for not providing it.
VII. Communications and Media Coverage:
Eric Nigg, DEQ’s Eastern Region water quality manager, or Robert Baggett, the steering
committee’s assigned DEQ staff, will respond to media inquiries associated with the
organization, structure, process, and charge of the committee. The chair or appointee of the
committee will represent and speak for the committee to the media.
While free to communicate with the media and others, committee members recognize that the
collaborative process is enhanced when they raise ideas and concerns at a formal committee
meeting. Additionally, members recognize that the way in which positions are publicly
represented may affect the ability of the committee to work together.
VIII. Process Support
DEQ is responsible for providing staff support to the committee by providing background and
technical information about the technologies available to protect groundwater, public health and
the environment. DEQ will consult with other agencies and stakeholders, as needed, to support
the committee. Some agencies and stakeholders may be asked to provide or present information
to the committee.
IX. Committee Membership
The committee will be comprised of 11 primary members and some alternate members. Alternate
members attend meetings and are ready to step in if a primary member is absent or leaves the
committee. Alternates will take turns filling in for absent committee members. If a primary
member leaves the committee, the remaining primary members will select a replacement from the
alternative members. If a tie vote occurs DEQ will make the final selection.
Any member may withdraw from the committee at any time after discussing the withdrawal with
the DEQ project staff and committee chair. Any member that withdraws from the committee shall
remain bound by the good faith and other provisions of these operating principles.
Present and future committee members will be appointed by DEQ Deputy Director Joni
Hammond.
The initial appointment of committee members is for one year. Towards the end of the year, with
consultation of the committee, DEQ will consider extending member appointments, rotating
alternate members into the committee, and/or seeking some new applicants for the committee.
The committee will be chaired by John Blakinger, and co-chaired by Robert Ray as approved by
the DEQ Deputy Director Joni Hammond.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 26
The chair will be responsible for:
• Facilitating meetings;
• Working with DEQ staff to set the agenda
• Keeping members focused on the issues and objectives;
• Ensuring that all members adhere to the process and ground rules;
• Representing the committee to the media.
Primary committee members: John Blakinger; David Crider; Judy Forsythe; Bill Gaetano; Aileen
Harmon; Gary Mose; Marietta Qual; Robert Ray; Conrad Ruel; Leon Shields; Lee Wilkins
Alternate committee members: Allen Hammermann; Ray McKinley; Sunni Rounds
Agency-technical advisors: TBA
DEQ project staff:
Linda Hayes-Gorman, Eastern Region Administrator, (541) 633-2018
Eric Nigg, Eastern Region Water Quality Program Manager, (541) 633-2035
Robert Baggett, Natural Resource Specialist 4 and SD/NK GWPP Coordinator (541) 633-2036
Greg Svelund, Eastern Region Communication and Outreach Rep. (541) 633-2008
By my signature I agree to the conditions stated within this charter and any future amendments
agreed to by the committee and DEQ.
John Blakinger, David Crider, Judy Forsythe, Bill Gaetano, Aileen Harmon, Gary Mose, Marietta
Qual, Robert Ray, Conrad Ruel, Leon Shields, Lee Wilkins, Allen Hammermann, Ray McKinley,
Sunni Rounds.
A member of the public addresses the audience at a community outreach session at Thousand
Trails Community Club near Sun River on March 20, 2013
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 27
Appendix E
DEPARTMENT OF ENVIRONMENTAL QUALITY
SOUTH DESCHUTES COUNTY AND NORTH KLAMATH COUNTY
GROUNDWATER PROTECTION PROJECT STEERING COMMITTEE
STATEMENT OF ETHICS
To serve the public interest with compassion for the welfare of all people in the affected
areas, it is our obligation to act with integrity. To that end, we will perform our work without
bias.
• We shall avoid a conflict of interest or even the appearance of a conflict of
interest in our deliberations.
• We recognize that poor behavior on the part of any committee member can cloud
public opinion of this committee’s work.
• We will actively listen to the community concerns and endeavor to deal even-
handedly to ensure that recommendations are relevant to solutions of community
problems.
• We shall have special concern for the long range consequences of this
committee’s recommendations and we shall pay special attention to the inter-
relatedness of the issues.
• We shall not deliberately or with reckless indifference fail to provide adequate,
timely, clear and accurate information.
South Deschutes/North Klamath Groundwater Protection Project Steering Committee
State of Oregon Department of Environmental Quality 28
Appendix F
Acknowledgements
Thank you to the entities that assisted the steering committee process by allowing use and public
access to their facilities:
Midstate Electric, Community Meeting Room, 16755 Finley Butte Road, La Pine, OR
- 32 Committee Regular Meetings & 5 Committee Work Sessions
La Pine Senior Activity Center, 16450 Victory Way, La Pine, OR 97739
- Two Public Hearings & 3 Public Information Meetings
Crescent Community Club Building, Crescent Cut-Off Road, Crescent, OR
- A Community Outreach Meeting
Deschutes River Recreation Homesites (DRRH) Clubhouse, 17200 Milky Way
- A Community Outreach Meeting
Living Water of La Pine Church, 52410 Primrose Lane, La Pine, OR
- A Community Outreach Meeting
Thousand Trails Clubhouse, 17480 S. Century Drive, Bend, OR 97707
- A Community Outreach Meeting
High Lakes Christian Church, 52620 Day Rd., La Pine, OR 97739
- A Community Outreach Meeting
Special Thanks To:
All Final Steering Committee Members: John Blakinger, Co-Chair, Robert Ray, Co-Chair, David
Crider, Bill Gaetano, Allen Hammerman, Lola Nelson, Marrietta Qual, Conrad Ruel, Lee
Wilkins,
Other Steering Committee Members: Judy Forsythe, Aileen Harmon, Ray McKinely, Gary Mose,
Leon Shields
Shelley Miesen, Executive Assistant, Midstate Electric Cooperative
Tim Berg, GIS Specialist, Deschutes County Community Development
Bill Scally and Ed Criss, KITC FM 106.5
The Newberry Eagle, Central Oregon Nickel Ads and The FrontierAdvertiser
Evaluation of Approaches for Managing Nitrate
Loading from On-Site Wastewater Systems near
La Pine, Oregon
Scientific Investigations Report 2007–5237
Prepared in cooperation with the Oregon Department of Environmental Quality and
Deschutes County
U.S. Department of the Interior
U.S. Geological Survey
Cover: Photograph of Little Deschutes River near La Pine, Oregon. (Photograph taken
by David Morgan, U.S. Geological Survey, 2000.)
Evaluation of Approaches for Managing
Nitrate Loading from On-Site Wastewater
Systems near La Pine, Oregon
By David S. Morgan, Stephen R. Hinkle, U.S. Geological Survey, and
Rodney J. Weick, Oregon Department of Environmental Quality
Prepared in cooperation with the Oregon Department of Environmental Quality and
Deschutes County
Scientific Investigations Report 2007–5237
U.S. Department of the Interior
U.S. Geological Survey
U.S. Department of the Interior
DIRK KEMPTHORNE, Secretary
U.S. Geological Survey
Mark D. Myers, Director
U.S. Geological Survey, Reston, Virginia: 2007
For product and ordering information:World Wide Web: http://www.usgs.gov/pubprod
Telephone: 1-888-ASK-USGS
For more information on the USGS—the Federal source for science about the Earth, its natural and living resources,
natural hazards, and the environment:
World Wide Web: http://www.usgs.govTelephone: 1-888-ASK-USGS
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement
by the U.S. Government.
Although this report is in the public domain, permission must be secured from the individual copyright owners to
reproduce any copyrighted materials contained within this report.
Suggested citation:
Morgan, D.S., Hinkle, S.R., and Weick, R.J., 2007, Evaluation of approaches for managing nitrate loading from on-site
wastewater systems near La Pine, Oregon: U.S. Geological Survey Scientific Investigations Report 2007-5237, 66 p.
iii
Contents
Abstract ...........................................................................................................................................................1
Introduction.....................................................................................................................................................2
Purpose and Scope ..............................................................................................................................4
Description of Study Area ...................................................................................................................4
Conceptual Model of Ground-Water System ............................................................................................5
Geologic Setting ....................................................................................................................................5
Three-Dimensional Hydrogeologic Model .......................................................................................7
Subsurface Geologic Data .........................................................................................................7
Lithologic Unit Sections and Fluvial Sediment Mapping .......................................................7
Transition Probability Geostatistical Modeling .......................................................................8
Hydraulic Conductivity ................................................................................................................9
Ground-Water Recharge ...................................................................................................................12
Ground-Water Flow ............................................................................................................................14
Ground-Water Discharge ..................................................................................................................15
Streams and Springs .................................................................................................................15
Evapotranspiration ....................................................................................................................19
Wells .........................................................................................................................................19
Nitrogen Fate and Transport .............................................................................................................20
Nitrogen Loading from On-Site Wastewater Systems .................................................................22
Nitrate Fate and Transport Simulation Models .......................................................................................24
Modeling Approach ............................................................................................................................24
Model Parameters ..............................................................................................................................26
Hydraulic Conductivity ..............................................................................................................26
Porosity ........................................................................................................................................26
Dispersion ...................................................................................................................................26
Model Stresses ...................................................................................................................................26
Recharge .....................................................................................................................................27
Rivers .........................................................................................................................................27
Springs .........................................................................................................................................27
Evapotranspiration ....................................................................................................................27
Transect Model ...................................................................................................................................28
Boundaries and Discretization ................................................................................................28
Calibration and Sensitivity ........................................................................................................28
Simulated Travel Time and Comparison with Ground-Water Age .....................................31
Study-Area Model...............................................................................................................................31
Boundaries and Discretization ................................................................................................32
Calibration and Sensitivity ........................................................................................................32
Calibration of Ground-Water Flow .................................................................................32
Comparison of Simulated and Measured Nitrate Concentrations ...........................35
Management Scenario Simulations ................................................................................................36
iv
Nitrate Loading Management Model .......................................................................................................43
Formulation of Nitrate Loading Management Model ...................................................................43
Constraints on Ground-Water Nitrate Concentration ..........................................................43
Constraints on Discharge of Nitrate from Ground Water to Streams ...............................45
Constraints on Reduction of Nitrate Loading ........................................................................45
Response-Matrix Technique for Solution of Nitrate Loading Management Model ................46
Application of Model ..........................................................................................................................48
Sensitivity of Optimal Solution to Water-Quality Constraints .............................................49
Ground-Water Nitrate Concentration ............................................................................49
Ground-Water Nitrate Discharge Loading to Streams ...............................................50
Sensitivity of Optimal Solution to Nitrate Loading Constraints ..........................................50
Sensitivity of Optimal Solution to Cost Factors .....................................................................51
Spatial Distribution of Loading for Optimal Solution ............................................................52
Comparison of Scenario Simulations and Optimal Solution ...............................................53
Limitations and Appropriate Use of Models ............................................................................................56
Simulation Models ..............................................................................................................................56
Management Model ...........................................................................................................................57
Summary and Conclusions .........................................................................................................................57
Acknowledgments .......................................................................................................................................59
References Cited..........................................................................................................................................59
Appendix A. Vertical Hydraulic Head Gradient Data from Measurements Made
on the Deschutes and Little Deschutes Rivers, in the La Pine, Oregon,
Study Area, October 23– November 4, 2000 ..............................................................................63
Contents—Continued
Plate
Plate 1. Selected cross sections showing lithologic units of the La Pine region,
Oregon ……………………………………………………………………[In pocket]
v
Figures
Figure 1. Map showing location of La Pine study area, Oregon, and extent of the nitrate
fate and transport model …………………………………………………………3
Figure 2. Map showing generalized geology and hydrogeologic units of the La Pine
region, Oregon ……………………………………………………………………6
Figure 3. Cross sections showing three dimensional hydrogeologic model of the La
Pine, Oregon, study area …………………………………………………………10
Figure 4. Graphs showing distributions of estimated hydraulic conductivity values from
slug tests and well-yield data ……………………………………………………12
Figure 5. Map showing distribution of mean annual recharge, water-table elevation
contours (June 2000), and locations of monitoring wells in the La Pine,
Oregon, study area ………………………………………………………………13
Figure 6. Hydrographs showing water levels in selected wells in the La Pine, Oregon,
study area …………………………………………………………………………14
Figure 7. Map showing gaining and losing reaches of the Deschutes and Little
Deschutes Rivers and locations of measurement sites for gain-loss surveys
between October 1995 and October 2000 in the La Pine, Oregon, study area ……17
Figure 8. Map showing estimated thickness of oxic ground-water layer in the shallow
aquifer in the La Pine, Oregon, study area …………………………………………21
Figure 9. Graph showing annual and cumulative estimated nitrate loading from on-site
wastewater systems in the La Pine, Oregon study area, 1960–2005 ………………23
Figure 10. Map showing spatial relations between the upper Deschutes Basin regional
ground-water model, the La Pine study area model, and the transect model ……25
Figure 11. Plan and section views of the transect model showing simulated
water-levels, ground-water travel time, and particle paths in the La Pine,
Oregon, study area ………………………………………………………………29
Figure 12. Map showing contours of simulated and observed heads (June 2000) for the
La Pine, Oregon, study area ………………………………………………………34
Figure 13. Graph showing simulated head residuals and observed heads (June 2000)
from the La Pine, Oregon, study area ……………………………………………35
Figure 14. Boxplots showing measured and simulated nitrate concentrations in the La
Pine, Oregon, study area, 1999 ……………………………………………………36
Figure 15. Map showing simulated nitrate concentrations near the water table in the La
Pine, Oregon, study area, 1999 ……………………………………………………37
Figure 16. Graph showing historical nitrate loading from on-site wastewater systems
and eight nitrate loading scenarios tested with the study-area model ……………39
Figure 17. Map showing simulated equilibrium ground-water nitrate concentrations
near the water table for the base scenario in the La Pine, Oregon, study
area ………………………………………………………………………………41
Figure 18. Map showing simulated equilibrium ground-water nitrate concentrations
near the water table for 20 milligrams N per liter advanced treatment on-site
wastewater systems in the La Pine, Oregon, study area …………………………42
Figure 19. Map showing locations of management areas and ground-water nitrate
concentration constraint locations in the Nitrate Loading Management
Model for the La Pine, Oregon, study area ………………………………………44
vi
Figure 20. Map showing locations of management areas near Burgess Road and
management area 31 in the La Pine, Oregon, study area …………………………47
Figure 21. Graph showing sensitivity of optimal loading solutions to ground-water
nitrate concentration constraints in the La Pine, Oregon, study area ……………49
Figure 22. Graph showing sensitivity of optimal loading solutions to constraints on the
minimum reduction in ground-water discharge loading to streams in the La
Pine, Oregon, study area …………………………………………………………50
Figure 23. Graph showing sensitivity of optimal solution to minimum decentralized
wastewater treatment performance standards for future homes in the La
Pine, Oregon, study area …………………………………………………………51
Figure 24. Diagram showing sensitivity of optimal solutions to relative cost difference of
nitrate loading reduction for existing and future homes in the La Pine,
Oregon, study area ………………………………………………………………52
Figure 25. Map showing optimal reduction in nitrate loading from existing homes in the
La Pine, Oregon, study area ………………………………………………………54
Figure 26. Map showing optimal reduction in nitrate loading from future homes in the La
Pine, Oregon, study area …………………………………………………………55
Figure 27. Graphs showing comparison of loading and water quality between optimal
and nonoptimal management scenarios for the La Pine, Oregon, study area ……56
Figures—Continued
Tables
Table 1. Markov chain model parameters and transition probabilities in the final
hydrofacies model …………………………………………………………………9
Table 2. Hydraulic conductivity estimates from slug test data from wells near LaPine,
Oregon ……………………………………………………………………………11
Table 3. Basin information for water-level monitoring wells in the La Pine, Oregon,
study area …………………………………………………………………………15
Table 4. Summary of data from stream gain-loss surveys on the Deschutes and Little
Deschutes Rivers in the La Pine, Oregon, study area, 1995–2000 …………………18
Table 5. Values of horizontal and vertical hydraulic conductivity for hydrofacies based
on field data and model calibration in the La Pine, Oregon, study area ……………30
Table 6. Summary of eight on-site wastewater management scenarios tested with the
study-area model in the La Pine, Oregon, study area ……………………………39
Table 7. Summary of model simulation results for eight on-site wastewater
management scenarios tested with the study-area model in the La Pine,
Oregon, study area ………………………………………………………………40
Table 8. Response coefficients relating the effects of loading in nearby areas to the
nitrate concentration at a constraint location in management area 31 in the
La Pine, Oregon, study area ………………………………………………………48
vii
Conversion Factors, Datums, and Abbreviations and
Acronyms
Conversion Factors
Multiply By To obtain
acre 0.4047 hectare (ha)
cubic foot per second per mile (ft3/s/mi)0.04560 cubic meter per second per kilometer
(m3/s/km)
cubic foot per second (ft3/s)0.02832 cubic meter per second (m3/s)
cubic foot per second per square mile
[(ft3/s)/mi2]
0.01093 cubic meter per second per square kilometer
[(m3/s)/km2]
foot (ft)0.3048 meter (m)
foot per day (ft/d)0.3048 meter per day (m/d)
foot squared per day (ft2/d)*0.09290 meter squared per day (m2/d)
gallon (gal)3.785 liter (L)
gallon per day (gal/d)0.003785 cubic meter per day (m3/d)
inch (in.)2.54 centimeter (cm)
inch per year (in/yr)25.4 millimeter per year (mm/yr)
kilograms per day (kg/d)2.205 pound per day (lb/d)
kilogram per year (kg/yr)2.205 pound per year (lb/yr)
mile (mi)1.609 kilometer (km)
million gallons per day (Mgal/d)0.04381 cubic meter per second (m3/s)
pound, avoirdupois (lb)0.4536 kilogram (kg)
pound per year (lb/yr)0.4536 kilogram year (kg/yr)
square mile (mi2)2.590 square kilometer (km2)
*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times
foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot
squared per day (ft2/d), is used for convenience.
Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L)
or micrograms per liter (µg/L).
Datums
Vertical coordinate information is referenced to the North American Vertical Datum of 1929
(NAVD 29).
Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
Elevation, as used in this report, refers to distance above the vertical datum.
viii
Abbreviations and Acronyms
Abbreviations and Acronyms Meaning
kg N/yr kilograms of nitrogen per year
lb N/yr pounds of nitrogen per year
mg N/L milligrams of nitrogen per liter
my million years
NDP La Pine National On-Site Wastewater Demonstration Project
NLMM Nitrate Loading Management Model
ODEQ Oregon Department of Environmental Quality
PLSS Public Land Survey System
RMSE root mean square error
TDC Transferable Development Credit
USEPA U.S. Environmental Protection Agency
USGS U.S. Geological Survey
Conversion Factors, Datums, and Abbreviations and
Acronyms—Continued
Abstract
This report presents the results of a study by the U.S.
Geological Survey, done in cooperation with the Oregon
Department of Environmental Quality and Deschutes County,
to develop a better understanding of the effects of nitrogen
from on-site wastewater disposal systems on the quality of
ground water near La Pine in southern Deschutes County
and northern Klamath County, Oregon. Simulation models
were used to test the conceptual understanding of the system
and were coupled with optimization methods to develop the
Nitrate Loading Management Model, a decision-support tool
that can be used to efficiently evaluate alternative approaches
for managing nitrate loading from on-site wastewater systems.
The conceptual model of the system is based on geologic,
hydrologic, and geochemical data collected for this study, as
well as previous hydrogeologic and water quality studies and
field testing of on-site wastewater systems in the area by other
agencies.
On-site wastewater systems are the only significant
source of anthropogenic nitrogen to shallow ground water
in the study area. Between 1960 and 2005 estimated nitrate
loading from on-site wastewater systems increased from 3,900
to 91,000 pounds of nitrogen per year. When all remaining
lots are developed (in 2019 at current building rates), nitrate
loading is projected to reach nearly 150,000 pounds of
nitrogen per year. Low recharge rates (2–3 inches per year)
and ground-water flow velocities generally have limited the
extent of nitrate occurrence to discrete plumes within 20–30
feet of the water table; however, hydraulic-gradient and age
data indicate that, given sufficient time and additional loading,
nitrate will migrate to depths where many domestic wells
currently obtain water. In 2000, nitrate concentrations greater
than 4 milligrams nitrogen per liter (mg N/L) were detected in
10 percent of domestic wells sampled by Oregon Department
of Environmental Quality.
Numerical simulation models were constructed at transect
(2.4 square miles) and study-area (247 square miles) scales to
test the conceptual model and evaluate processes controlling
nitrate concentrations in ground water and potential
ground-water discharge of nitrate to streams. Simulation
of water-quality conditions for a projected future build-out
(base) scenario in which all existing lots are developed using
conventional on-site wastewater systems indicates that, at
equilibrium, average nitrate concentrations near the water
table will exceed 10 mg N/L over areas totaling 9,400 acres.
Other scenarios were simulated where future nitrate loading
was reduced using advanced treatment on-site systems and
a development transfer program. Seven other scenarios were
simulated with total nitrate loading reductions ranging from 15
to 94 percent; simulated reductions in the area where average
nitrate concentrations near the water table exceed 10 mg N/L
range from 22 to 99 percent at equilibrium. Simulations also
show that the ground-water system responds slowly to changes
in nitrate loading due to low recharge rates and ground-water
flow velocity. Consequently, reductions in nitrate loading
will not immediately reduce average nitrate concentrations
and the average concentration in the aquifer will continue to
increase for 25–50 years depending on the level and timing of
loading reduction. The capacity of the ground-water system
to receive on-site wastewater system effluent, which is related
to the density of homes, presence of upgradient residential
development, ground-water recharge rate, ground-water flow
velocity, and thickness of the oxic part of the aquifer, varies
within the study area.
Optimization capability was added to the study-area
simulation model and the combined simulation-optimization
model was used to evaluate alternative approaches to
management of nitrate loading from on-site wastewater
systems to the shallow alluvial aquifer. The Nitrate Loading
Management Model (NLMM) was formulated to find the
minimum reductions from projected future loading required
to maintain or restore ground-water nitrate concentrations
or ground-water discharge of nitrate to streams below user-
specified levels. Sensitivity analysis of the NLMM showed
that loading primarily is constrained by nitrate concentration
in the shallow part of the oxic ground-water system, within
5–10 feet of the water table.
Evaluation of Approaches for Managing Nitrate
Loading from On-Site Wastewater Systems near
La Pine, Oregon
By David S. Morgan1, Stephen R. Hinkle1, and Rodney J. Weick2
1 U.S. Geological Survey
2 Oregon Department of Environmental Quality
2 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Introduction
Rural residential areas near La Pine in southern
Deschutes County and northern Klamath County, Oregon
(fig. 1) have experienced rapid growth in recent years.
More than 9,000 residential lots, ranging in size from 0.5
to 10 acres, are in the area where existing and future homes
will rely on individual on-site wastewater systems and wells
for wastewater disposal and water supply. Most existing
wells have screened intervals within 50 ft of land surface and
extract water from alluvial sands and gravels that constitute
the primary aquifer in the area. The water table is shallow,
typically is less than 20 ft below land surface, and in some
low-lying areas rises seasonally to within 2 ft of land surface.
Sandy soils derived from pumice contain little organic matter
and allow rapid infiltration of on-site wastewater effluent.
The vulnerability of the shallow aquifer has led to
concern by County and State land-use and environmental-
health regulators that ground-water quality may be impaired if
development continues at planned densities using conventional
on-site wastewater systems. (In this report, conventional
on-site systems include standard, pressure-distribution, and
packed-bed [sand] filter systems). Another potential concern
is the quality of local streams. The Deschutes and Little
Deschutes Rivers, which flow through developed areas near
La Pine, have been listed as “water-quality impaired” for
temperature and turbidity; nutrient loading from ground water
has been identified as a potential contributor to excessive algal
growth in some reaches (Anderson, 2000; Jones, 2003) that
may exacerbate water-quality concerns.
On-site wastewater systems are the principal source of
nitrogen to the shallow ground-water system in the La Pine
area (Century West Engineering, 1982; Oregon Department
of Environmental Quality, 1994; Hinkle and others, 2007a).
On-site wastewater systems do not remove nitrogen from
wastewater; however, most nitrogen is converted from organic
nitrogen and ammonium to nitrate before it reaches the
saturated part of the ground-water system (water table). Once
in the saturated zone, nitrate generally is stable in the presence
of oxic ground water (ground water that contains dissolved
oxygen). Adsorption or chemical reactions within the flow
system do not readily remove nitrate. Nitrate is a human health
concern because it can cause methemoglobinemia (Blue-
Baby Syndrome) in infants (http://www.atsdr.cdc.gov/HEC/
CSEM/nitrate/). Nitrogen also is an environmental concern
as a potential source of nutrient enrichment to streams.
Nutrient enrichment contributes to algal blooms detected
in the Deschutes and Little Deschutes Rivers. The U.S.
Environmental Protection Agency (USEPA) has established
10 mg N/L as the maximum allowable nitrate concentration
in drinking water for public water supply systems. Oregon, by
statute, has established a nitrate concentration of 7 mg N/L as
the value at which action may be taken to control water-quality
degradation by regulatory means.
The present location of the city of La Pine (fig. 1) was the
first concentrated development within the study area. The first
building permits recorded in what was then called the “core
area” date from 1910. In 2006, the core area was incorporated
as the city of La Pine. Degradation of ground-water quality
by on-site wastewater systems was first documented in the
core area in 1979 by Oregon Department of Environmental
Quality (ODEQ) after samples from 46 wells revealed that
water from 8 wells contained nitrate concentrations greater
than 10 mg N/L (Cole, 2006) and a maximum of 26 mg N/L.
Nitrate concentrations in ground water as much as 41 mg N/L
were detected in a follow-up study in 1982 (Century
West Engineering, 1982). These results led to an ODEQ
administrative rule requiring community sewage collection,
treatment, and disposal for the core area. In 1993, ODEQ
sampled 36 wells in residential areas near La Pine as part
of its statewide Ambient Groundwater Monitoring Program
and detected nitrate concentrations greater than 2 mg N/L in
19 wells. They concluded that elevated concentrations were
caused by anthropogenic influences (on-site wastewater
systems) (Cole, 2006). Concentrations were greater than
10 mg N/L in 4 (11 percent) of the 36 wells sampled. In 1994,
Deschutes County requested that ODEQ further evaluate
ground-water quality in the area. Water from more than 120
domestic and public water-supply wells was sampled in 1994
and 1995 and ODEQ delineated several areas of elevated
nitrate concentrations underlying the most densely developed
parts of the region (R.J. Weick, ODEQ, written commun.,
1998; Cole, 2006). As part of the 1995 assessment, ODEQ
constructed simplified nitrate transport models which included
basic assumptions on nitrogen chemistry. The ODEQ transport
models predicted that nitrate concentrations would exceed
drinking water standards within 20 years of full build-out (R.J.
Weick, ODEQ, written commun., 1998; Cole, 2006).
In 1999, a nitrate concentration threshold of 5 mg N/L
was selected for the La Pine area by the Deschutes County
Working Group on Groundwater Issues for the South
Deschutes Basin to serve as a “proactive target to protect
the Basin’s groundwater quality.” The working group also
recommended that ODEQ “…address these problems and
concerns by considering the adoption of a geographic rule…
to protect the Basin’s groundwater resource.” (http://www.
co.deschutes.or.us/download.cfm?DownloadFile=507DDA68-
BDBD-57C1-902813CCF281DDF0).
Introduction 3
Figure 1. Location of La Pine study area, Oregon, and extent of the nitrate fate and transport model.
OR19-0049_fig 01
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83
T 19 S
T 20 S
T 24 S
T 23 S
T 22 S
T 21 S
R 11 ER 10 ER 9 E
DESCHUTES CO.
L
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KLAMATH CO.
EXPLANATION
Sewered area
Alluvium
Basalt, andesite
Existing home within model area and not served by sewer
Transect well locations
Geologic unit
Pauli
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Masten Road
River
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South
R
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Butt
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Finley
Drive
Burgess Road
5 KILOMETERS
5 MILES0
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43°35'
40'
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Ex
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DeschutesBasin
CascadeRange
NewberryVolcanoUpperDeschutesBasin
La Pineregion
OREGON
Bend
Sunriver Sunriver
La
Pine
La
Pine
Lo
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P
r
a
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i
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La Pine core area
Wickiup JunctionBurgesstransect
Century transect
4 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
In 1999, Deschutes County and ODEQ identified the
need for an improved understanding of the processes that
affect the transport and fate of nitrogen in the La Pine area
before making decisions among alternatives for managing
ground-water quality. To help achieve that understanding,
Deschutes County and ODEQ applied for and received
funding from the USEPA to evaluate methods to protect
ground-water quality in the area (Oregon Department
of Environmental Quality, 2004a) as part of the La Pine
National On-Site Wastewater Demonstration Project (NDP).
The objectives of the NDP also included (1) assessing the
effectiveness of advanced treatment (denitrifying) systems for
on-site wastewater and (2) developing a more complete and
useful understanding of processes that affect nitrogen in the
ground-water system. The second objective was the subject
of a cooperative study by the ODEQ, Deschutes County
Community Development Department (CDD) and the Oregon
Water Science Center of the U.S. Geological Survey (USGS).
The primary objective of this study was to develop
a thorough understanding of the hydrologic and chemical
processes that affect the movement and fate of nitrogen within
the shallow aquifers of the La Pine region. A secondary
objective was to provide a method for analyzing the effects
of existing and future development on water quality.
This understanding will provide local and State resource
management agencies with information and tools needed
to determine the probable effects of present and future land
use on nitrogen concentrations in the shallow aquifer and on
nitrogen loading from ground water to the Deschutes and
Little Deschutes Rivers.
Purpose and Scope
This report describes conceptual, simulation, and
management models of the ground-water system near the
community of La Pine in central Oregon. The description
of the conceptual model provides a background for the
development of the simulation and management models and
includes the geologic framework, hydrologic processes, and
processes affecting nitrate transport and fate. The description
of the simulation model includes a discussion of how the
processes and boundaries of the system were represented in
a computer simulation model, how the model was calibrated,
and the results of predictive simulations. The simulation model
was enhanced as a decision-support tool (management model)
by incorporating optimization techniques that allow users to
identify management solutions that will meet water quality
goals. The discussion of the management model includes
a description of the method of incorporating optimization
techniques with the simulation model, the formulation of
the management problem, and analysis of the sensitivity
of optimal management solutions to the values of various
constraints.
Description of Study Area
The La Pine study area encompasses about 250 mi2
within the Deschutes River drainage basin in central Oregon
(fig. 1). The area is drained by the Deschutes River and
tributaries including the Little Deschutes, Spring, and Fall
Rivers. Land-surface elevation ranges from about 4,000 ft near
the Deschutes River at the northern boundary of the study
area, to nearly 5,700 ft at the peaks of volcanic buttes in the
northwestern corner of the study area. Most of the study area
lies in the relatively low-relief alluvial plain of the Deschutes
and Little Deschutes Rivers at elevations between 4,150 and
4,300 ft. The populated areas in the study area include low and
medium density rural-residential subdivisions adjacent to and
between the Deschutes and Little Deschutes Rivers extending
northward from La Pine to the community of Sunriver (fig. 1).
The subdivisions are surrounded by Federal lands managed by
the U.S. Forest Service and Bureau of Land Management.
The study area boundaries were selected to include the
most densely populated parts of southern Deschutes County
and northern Klamath County, where on-site wastewater
systems are the predominant method of wastewater disposal
for existing and future residential development. The
boundaries also were selected to include the principal area of
the shallow alluvial aquifer that provides drinking water for
most of the population in the La Pine area. The data collection
and analysis for this study was focused in the 247 mi2 area of
the study-area flow and transport simulation model (fig. 1).
Residential development in the area began to accelerate in
the 1960s (Century West Engineering, 1982) and almost 3,000
new residential lots were created in the 1970s in response
to demand for vacation homes and full-time residences.
Although lots range in size from 0.5 to more than 10 acres,
58 percent of lots in the study area in 2000 were less than
1 acre and 82 percent were less than 2 acres. The population
of the area was less than 1,000 in 1960, and increased to about
5,600 in 1981 (Century West Engineering, 1982), and was
approximately 14,000 in 2000 (U.S. Bureau of the Census,
2000).
Land use is primarily low- to medium-density residential.
Commercial and medium density residential areas are in the
incorporated City of La Pine (including the La Pine “core
area” and Wickiup Junction area) and industrial development
is immediately east of the core area. Agricultural lands cover
less than 4 percent of the study area and most of that area is
nonirrigated pasture (Tim Berg, Deschutes County Community
Development Department, written commun., 2004).
The climate of the area primarily is controlled by
eastward moving air masses from the Pacific Ocean.
Orographic precipitation in the Cascade Range results in more
than 200 in/yr in some locations, although precipitation rates
in the lower part of the Deschutes River basin average as little
as 10 in/yr. Mean annual (1971–2000) precipitation in the La
Pine area ranges from 16 to 24 in. (Daly and Gibson, 2002).
Conceptual Model of Ground-Water System 5
Conceptual Model of
Ground-Water System
Geologic Setting
The La Pine study area of the upper Deschutes River
basin is a sediment-filled graben feature that lies within the
geologically complex transition area between three geologic
provinces: the Cascade Range, the Basin and Range Province,
and the High Lava Plains. The La Pine study area shares
attributes characteristic of each of these geologic provinces.
The Cascade Range forms the western margin of the La Pine
study area. Newberry volcano forms the eastern study area
margin and transition between the extensional Basin and
Range Province and the High Lava Plains. North to north-
northwest trending and northeast trending en echelon faults
define the eastern boundary of the graben forming the La Pine
study area.
The Cascade Range is a constructional feature of north-
south trending eruptive centers that extends from northern
California to southern British Columbia and has been
volcanically active for the past 35 million years (Sherrod and
Pickthorn, 1989). In central Oregon, these volcanic eruptive
centers are stratovolcanoes, such as the North, Middle, and
South Sister, and Mount Jefferson, all with elevations greater
than 10,000 ft (Lite and Gannett, 2002).
The Basin and Range Province is a region of crustal
extension that covers most of the western United States and
is characterized by north to northwest trending sub parallel
fault-bounded down-dropped grabens forming fault-block
ranges with basins typically 10–20 mi wide. In central
Oregon, the La Pine graben is defined by north-northwest
trending and northeast trending down-dropped faults (Allen,
1966; MacLeod and Sherrod, 1992) forming the sediment-
filled 10–15-mi wide subbasin with characteristics similar
to those of Basin and Range extensional features along the
northwestern transitional boundary in northeastern California
and northwestern Nevada.
The north–south trending graben that underlies the La
Pine study area is estimated to have down-dropped 1,800 to
2,400 ft based on gravity and aeromagnetic anomalies (Couch
and Foote, 1985; MacLeod and Sherrod, 1992) Formation
of the basin began during the mid-Pleistocene between
0.6 and 1 my (million years) ago (Couch and Foote, 1985;
Gettings and Griscom, 1988; Sherrod and Pickthorn, 1989;
MacLeod and Sherrod, 1992; MacLeod and others, 1995)
and subsequently has been filled with several hundred feet of
sediment. Nearly 1,400 ft of sediment have been penetrated by
deep water-supply wells drilled in the study area. Descriptions
of sediment lithology in drillers’ reports for water wells
indicate that graben formation was concurrent with volcanism
and late Pleistocene glacial outwash deposition. Periods of
active volcanism and quiescence and fluvial and lacustrine
deposition during graben development created a complex
sequence of intercalated lava flows, ignimbrites, and alluvial
deposits. The depositional history is further complicated by
fluvial-lacustrine deposition during the Pleistocene.
Many basin-fill sediments in the La Pine study area are
fine-grained lacustrine silt and clay. Within these fine-grained
deposits are fine to coarse fluvial sand and gravel channel-
fill deposits and discontinuous cinder, pumice- and ash-fall
beds. Methane, ammonium, and reduced iron detected in
water well samples (Hinkle and others, 2007a) from these
fine-grained deposits indicate a predominant quiescent marsh
and lake depositional environment with episodic volcanic
deposition. This low-energy depositional environment may
be related to the onset and development of Newberry volcano
about 0.7 my ago. MacLeod and others (1995) indicated that
Newberry lavas backed up against Cascade Range lava flows,
blocking the channel of the Deschutes River which created a
lake and marsh environment over much of the study area. A
pumice bed exposed near the top of the lacustrine deposits
and about 35 ft (10.8 m) below the fluvial/lacustrine contact
at Pringle Falls on the Deschutes River is 0.22 to 0.17 my old
(Herrero-Bervera and others, 1994).
About 0.2 my ago the depositional environment probably
underwent an abrupt change from lacustrine to predominantly
fluvial with deposition of heterogeneous silt, fine to coarse
sand, gravel, and pumaceous sand and gravel. These
deposits are likely associated with Pleistocene glaciation
of the Cascade Range and Newberry Volcano. These high-
energy deposits are capped by a study area wide 3–5 ft-thick
pumice- and ash-fall deposit from the Mt. Mazama eruption
of 7,627 ± 150 years ago (Zdanowicz and others, 1999). The
Deschutes, Little Deschutes, and Fall Rivers have reworked
and down-cut through the Mt. Mazama pumice and ash-fall
deposit. The high degree of heterogeneity noted in lithologic
descriptions in drillers’ reports indicate an active fluvial
depositional environment in the central and southern parts of
the La Pine study area and deposition more characteristic of a
lacustrine environment in the northern part of the study area.
Based on interpretation of more than 460 water-well logs,
fluvial silt, sand, and gravel deposits were determined to range
in thickness from less than 10 ft in the northern study area,
to as much as 100 ft in the central and southern parts of the
study area (fig. 2). A thin veneer of gravel overlying a paleosol
was observed in several monitoring wells in the study area.
The presence of the paleosol may represent post-Pleistocene
glacial soil development. The thin sand and gravel veneer
overlying the paleosol may represent the brief early Holocene
glacial event that predates the mid-Holocene Mt. Mazama
eruption.
6 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Figure 2. Generalized geology and hydrogeologic units of the La Pine region, Oregon.
OR19-0049_fig 02
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES CO.
L
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KLAMATH CO.
Spri
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Cresc
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Little
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5 KILOMETERS
5 MILES0
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Wickiup
Reservoir
97
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Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
A’
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EXPLANATION
Geologic unit
Alluvium
Basalt, andesite
Thickness of fluvial deposits, in feet within model boundary
0-20
20-40
40-60
60-80
80-100
Trace of section shown in plate 1
Other sections
Well used to construct sections
A A’
DeschutesBasin
CascadeRange
NewberryVolcanoUpperDeschutesBasin
La Pineregion
OREGON
Bend
Conceptual Model of Ground-Water System 7
Three-Dimensional Hydrogeologic Model
A detailed characterization of subsurface heterogeneity
can substantially improve the reliability of models of
ground-water contaminant transport (Fogg, 1986; Anderson
1987; Johnson and Dreiss, 1989). In this study, standard
hydrogeologic interpretation and analysis techniques,
including construction of two-dimensional geologic sections
and surface maps, were used in conjunction with transition
probability geostatistics to develop a three-dimensional
hydrogeologic model that represents the heterogeneity of the
complex glaciofluvial system.
Subsurface Geologic Data
The primary source of subsurface geologic data was
the nearly 5,400 drillers’ reports available (as of 1999) for
domestic and public water supply wells in the study area.
Although these reports are plentiful, the quality of lithologic
descriptions in the reports is inconsistent. The spatial
distribution of domestic wells also is not ideal for developing
a detailed, three-dimensional geologic model of the ground-
water system; as would be expected, domestic wells are
concentrated in areas of residential development and tend to be
completed at the shallowest depth that a satisfactory yield can
be obtained. A subset of 346 wells was visited as part of this
and previous studies (Gannett and others, 2001) to determine
accurate locations and collect water-level and other data. The
subset of wells visited was selected to provide the best spatial
distribution within the study area and good descriptions of
geologic materials penetrated by the well. Drillers’ reports for
an additional 118 wells were selected to provide information
in areas where field-located wells were not available. Although
these wells were not visited, the drillers’ reports included
superior descriptions of geologic materials and well locations
could be accurately estimated using tax lot information.
Descriptions of geologic materials were transcribed to
a database from the drillers’ reports using a standardized set
of lithologic descriptors developed for this study. A two-
letter descriptor was assigned to the primary lithology, and,
if needed, secondary lithology reported by the driller for
each depth interval. For example, if the driller reported a
layer of “gravel with sand” between 40 and 80 ft, the interval
was assigned a primary descriptor of GR for gravel and a
secondary descriptor of SA for sand. This system retained
most of the detail of the original description by the driller and
allowed for comparison and analysis of lithology between
wells. Thirty-six descriptors were used to describe primary
and secondary lithology. Combinations of the primary and
secondary descriptors resulted in 157 unique lithologic
descriptors for the 464 wells used in the analysis.
Lithologic Unit Sections and Fluvial Sediment
Mapping
The 157 unique lithologic descriptors were grouped
into six lithologic units. Five lithologic units comprised
unconsolidated sediments: clay-silt, pumice-sand, sand,
sand-gravel, and gravel. The sixth lithologic unit represented
consolidated and semi-consolidated volcanic rocks such
as basalt, basaltic andesite, and tuff. The lithologic unit
data for each well were stored in a Geographic Information
System (GIS) database that facilitated data interpretation and
construction of 34 two-dimensional cross sections through the
study area showing the thickness and extent of the primary
lithologic units. Locations of the sections are shown in figure 2
and selected sections are shown on plate 1.
Although deep wells are somewhat sparse in the study
area, the sections show that as much as 100 ft of fluvial silt,
sand, and gravel overlie predominately fine-grained lacustrine
sediments throughout the study area (plate 1). A relatively
sharp transition exists between the overlying fluvial sediments
and the basal lacustrine silt and clay, basalt, and volcaniclastic
deposits. The elevation of the top of the lacustrine sediments
was mapped using data from the 464 wells (fig. 2). Infrequent
sand and gravel lenses as well as pumice and ash beds are
present within the basal lacustrine sediments, but because of
their discontinuous nature, they are not regionally significant
sources of water to wells. The thickness of the fluvial
sediments that constitute the primary aquifers in the study area
was computed by subtracting the elevation of the top of the
basal lacustrine sediments from land surface elevation (fig. 2).
The greatest thicknesses of fluvial sediments are in the central,
east-central, and south-central parts of the study area where
higher elevations occur within the study area. Deposition
of Pleistocene alluvial sediments from fans emanating from
Newberry volcano contributes to the thickness of coarse
sediments on the eastern margin of the study area. The total
thickness (unsaturated and saturated) of fluvial sediments
exceeds 60 ft over much of this area. The fluvial sediments
are thinner in three areas: (1) within the floodplain of the
Little Deschutes River where they have been eroded, (2) at the
margins of the study area where they overlie shallow tuffs and
basaltic and andesitic volcanic rocks, and (3) in the northern
part of the study area where lacustrine sediments are closer to
the surface (fig. 2).
Interpretation of the geologic data during construction
of the two-dimensional sections revealed that there is a
greater degree of heterogeneity within the fluvial part of the
system than could be delineated using traditional methods
of interpretation using drillers’ reports as the primary data
source. The drillers’ reports were useful for defining the
vertical heterogeneity at each well location; however, because
8 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
of the distance between wells and the uncertainty in the
lithologic descriptions, it was not possible to accurately
represent the lateral heterogeneity of the fluvial hydrofacies.
Another consideration was the difficulty in constructing a
fully three-dimensional hydrogeologic model from the two-
dimensional representations in the lithofacies sections.
Important information on the nature and proportion
of lithologic units and dimensions and interconnectedness
of depositional features was gained through the process of
constructing the lithologic unit sections. This information
and the location of the lower boundary of the fluvial aquifer
system were used as supplemental information in the
development of the three-dimensional hydrogeologic model
described in the next section.
Transition Probability Geostatistical Modeling
A transition probability geostatistical approach was
used to model the heterogeneity of the fluvial sediments that
constitute the shallow aquifer near La Pine. The method was
applied using the suite of programs, Transition Probability
Geostatistical Software (T-PROGS), documented by Carle
(1999). T-PROGS implements a transition probability/Markov
approach to geostatistical analysis and simulation of spatial
distributions of categorical variables (such as hydrofacies).
The approach uses the probabilities of lateral and vertical
transitions between hydrofacies to define spatial variability.
The transition probabilities, volumetric proportion of facies,
and mean lengths of depositional features are the parameters
used to fit a three-dimensional Markov chain model to
geologic data from drillers’ logs and subjective knowledge
based on an understanding of the depositional environment.
Once a satisfactory Markov chain model is obtained, it is used
in sequential indicator simulation with simulated annealing
to produce realizations of the subsurface facies distributions
that are conditioned using the observed geologic data. One
advantage of the transition probability method is the ability to
easily incorporate subjective or “soft” geologic information
into the Markov chain model. Details on the theoretical
development of the transition probability method, as wells as
examples and comparisons with other methods, are given in
Carle and Fogg (1996, 1997), Carle and others (1998), and
Weissmann and others (1999).
The transition probability method was used to model the
distribution of facies within the fluvial sediments only. The
lacustrine sediments were not included because the transition
probability method is predicated on the assumption that all
the sediments within the modeled area were emplaced under
similar depositional conditions.
A hydrofacies is defined as one or more lithologic units
that have similar hydraulic characteristics. Three hydrofacies
were used in the hydrogeologic model: (1) clay-silt, (2) sand,
and (3) gravel. The five lithologic units used to subdivide the
fluvial sediments in the sections on plate 1 were reduced to
three hydrofacies by combining units with similar hydraulic
characteristics. The clay-silt hydrofacies represent flood
plain deposits with low hydraulic conductivity. The sand
hydrofacies include varying amounts of silt and represent
levee and proximal overbank deposits with moderate hydraulic
conductivity. The gravel hydrofacies includes varying amounts
of sand and represents channel deposits with high hydraulic
conductivity.
In the rare case where there are abundant, high
quality core data, geophysical logs, and detailed lithologic
descriptions, the parameters for the Markov model can be
estimated directly from bivariate statistics (variograms) for
the hydrofacies. More commonly, as in the La Pine study
area, most available geologic data are obtained from drillers’
reports. Another limitation of the well data stems from the lack
of correspondence between the scale of depositional features
(for example, channel deposits) that have mean lengths of
10s or 100s of feet, and the spacing of data points (wells)
that may be 100s or 1,000s of feet. The disparity in the scales
of the system and the data available to characterize it makes
quantifying lateral transition probabilities based solely on well
data difficult. However, the transition probability approach
provided a means of including the geologic knowledge gained
through the process of developing the two-dimensional
lithologic unit sections.
The mean lengths of the high-hydraulic conductivity
gravel hydrofacies and the low hydraulic conductivity clay-
silt hydrofacies were estimated by manually measuring the
length of lithologic units interpreted in the 34 lithologic unit
sections (examples shown on plate 1) and computing average
lengths for each hydrofacies in the lateral (strike and dip) and
vertical dimensions. The depositional strike was aligned with
the northeast-southwest strike of the study area (fig. 2). The
estimates of lateral mean lengths for the gravel hydrofacies
based on the lithologic unit sections were larger than expected
for channel deposits typically found in fluvial systems
analogous to the Little Deschutes and Deschutes River
systems in the La Pine study area. The lateral mean lengths for
the gravel hydrofacies were reduced based on measurements
of present channel geometry, and meander and oxbow features
identified from aerial photography. The estimated mean
lengths for the gravel hydrofacies were modified through
a trial and error process until the Markov chain model
produced a hydrofacies realization that was consistent with
geomorphologic observations.
Conceptual Model of Ground-Water System 9
The volumetric proportions of the hydrofacies were 10,
50, and 40-percent for gravel, sand, and clay-silt, respectively.
The sand hydrofacies was selected as the “background”
category because it represented the highest proportion of
materials in the system. The transition probabilities (table 1)
need only be specified for the nonbackground hydrofacies.
The probabilities are expressed as decimal percentages; for
example, there is a 30-percent probability of transitioning
from the gravel facies to the clay-silt facies in the strike or dip
direction, but only a 15-percent probability of transitioning
from clay-silt to gravel.
The grid used to create the fluvial hydrofacies model had
cell dimensions of 500 ft horizontally along the depositional
strike and dip and 5 ft vertically. These cell dimensions
were sufficiently small to allow good representation of the
gravel and clay-silt facies (within the sand matrix) with mean
horizontal and vertical lengths of 1,500–8,100 ft and 8–10 ft,
respectively (table 1). The overall dimensions of the modeled
region are 138,000 by 50,000 ft along the depositional
strike and dip, and 120 ft along the vertical dimension.
The T-PROGS program was used with the Markov chain
parameters to generate the three-dimensional distribution of
the fluvial hydrofacies. The elevation of the base of the fluvial
sediments was contoured using drillers’ log data; and cells
within the hydrogeologic model below the base of the fluvial
sediments were assigned to the lacustrine hydrofacies. The
surficial geologic map (fig. 2) was used to assign cells to the
basalt hydrofacies and land surface elevation from a DEM
was used to “remove” cells from the hydrogeologic model that
were above land surface. Sections through the complete three-
dimensional hydrogeologic model are shown in figure 3.
Once the appropriate parameters for the Markov Chain
model are determined, many equally probable realizations
of the hydrostratigraphy of the fluvial hydrofacies can be
simulated using the T-PROGS program. Each realization
would be consistent with the data from drillers’ logs
and interpretations made during construction of the two-
dimensional sections used to estimate the mean lengths.
The capability to generate many realizations of the
hydrostratigraphy represents a potentially powerful tool
for evaluating the effects of hydrogeologic uncertainty on
simulation models. Using multiple realizations, uncertainty
in simulated nitrate concentrations resulting from
uncertainty in the hydrogeologic model could be evaluated.
While time consuming, this capability could provide
important information on the sensitivity of model results to
hydrogeologic uncertainty.
This capability would be especially useful for
contaminant transport models in highly heterogeneous
systems with large contrasts in hydraulic conductivity between
hydrofacies where the objective was to simulate individual
contaminant plumes. This approach was not used in the
current study because (1) although the fluvial sediments in the
La Pine study area are somewhat heterogeneous, the hydraulic
conductivities of the hydrofacies that compose them fall within
a relatively small range; and (2) the purpose of the model in
this study was to estimate mean concentrations over relatively
large areas as a tool for evaluating watershed-scale wastewater
management approaches. Variability at the scale of individual
model cells caused by uncertainty in the hydrogeologic model
would not impose significant limitations on the use of the
model.
Hydraulic Conductivity
Hydraulic conductivity is the characteristic of a porous
medium that describes its ability to transmit water, and is
expressed in units of length per unit time (for example, feet per
day). The hydraulic conductivity of most geologic materials
is vertically anisotropic; that is, hydraulic conductivity is
greater in the horizontal direction than in the vertical direction.
Simulation of three dimensional ground-water flow, as was
done for this study, requires estimates of both the horizontal
and vertical components of hydraulic conductivity. Horizontal
hydraulic conductivity estimates were made for alluvial
sediments and volcanic rocks using data from well-yield tests
reported in 221 drillers’ reports and slug tests done in 24
monitoring wells constructed for this study.
Transmissivity is another measure of the ability of
porous materials to transmit water, and is equal to the product
of hydraulic conductivity and the saturated thickness of the
material. Transmissivity has units of length squared per time
(for example, feet squared per day) and can be estimated using
the Theis nonequilibrium equation and solving as reported in
Vorhis (1979). Minimum data required from the well-yield
test include pumping rate, drawdown, and time pumped. Only
field-located wells with complete construction information
that included well depth, casing diameter, and open or
screened intervals were used in the analysis. The method of
Vorhis (1979) yields a solution to the Theis equation in which
transmissivity is expressed as a function of storage coefficient.
Table 1. Markov chain model parameters and transition
probabilities in the final hydrofacies model.
Hydrofacies Mean length (feet)
Strike Dip Vertical
Gravel 3,000 1,500 10
Clay-silt 8,100 5,600 8
Hydrofacies
(From To)
Transition probability
(decimal percentage)
Gravel Clay-silt 0.3 0.3 0.4
Clay-silt Gravel .15 .15 .25
10 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
OR19-0049_fig 03
Above ground
Lacustrine clay-silt
Volcanics: basalt, andesite
Fluvial gravel
Fluvial sand
Fluvial clay-silt
EXPLANATION
Hydrofacies
4,350
4,300
4,250
4,200
4,150
4,100
EL
E
V
A
T
I
O
N
,
I
N
F
E
E
T
4,350
4,300
4,250
4,200
4,150
4,100
EL
E
V
A
T
I
O
N
,
I
N
F
E
E
T
4,350
4,300
4,250
4,200
4,150
4,100
EL
E
V
A
T
I
O
N
,
I
N
F
E
E
T
4,350
4,300
4,250
4,200
4,150
4,100
EL
E
V
A
T
I
O
N
,
I
N
F
E
E
T
4,350
4,300
4,250
4,200
4,150
4,100
EL
E
V
A
T
I
O
N
,
I
N
F
E
E
T
0
20
40
60
80
100
120
140
160
180
200
220
240
260
275
MO
D
E
L
R
O
W
N
U
M
B
E
R
4,350
4,300
4,250
4,200
4,150
4,100
EL
E
V
A
T
I
O
N
,
I
N
F
E
E
T
MODEL COLUMN NUMBER
0 10 20 30 40 50 60 70 80 90 100 Notes: Each row and column is
500 feet wide. Model is truncated
at elevation of 4,350 feet.
Figure 3. Three dimensional hydrogeologic model of the La Pine, Oregon, study area.
Conceptual Model of Ground-Water System 11
Appropriate transmissivity values were selected by assuming a
storage coefficient in the range normally assumed for confined
aquifers (0.001) for deep wells and a storage coefficient
(specific yield) in the range normally assumed for unconfined
aquifers (0.10) for shallow wells. Wells were assigned
unconfined storage coefficients if their open intervals did not
extend more than 30 ft below land surface in the northern part
of the study area or 50 ft in the southern part (south of the
confluence of Paulina Creek and the Little Deschutes River)
(fig. 1). Horizontal hydraulic conductivity was estimated at
each well by dividing the estimated transmissivity by the
length of the perforated and (or) uncased intervals of the well.
Horizontal hydraulic conductivities computed using
the well-yield test data range from 0.15 to 2,500 ft/d, with a
geometric mean of 60 ft/d and median of 21 ft/d. Gannet and
others (2001) reported similar results from an analysis of 175
well-yield tests in the La Pine basin, in which the median
transmissivity was 901 ft2/d. If a typical effective aquifer
thickness of 50 ft is assumed, the transmissivity reported
by Gannett and others (2001) is equivalent to a hydraulic
conductivity of 18 ft/d. If well-yield data are reported
accurately, the principal sources of error using this approach
are head losses due to poor well construction and uncertainty
in storage coefficient estimates. Sensitivity analysis showed
that transmissivity, and therefore hydraulic conductivity,
computed for a range of storage coefficients spanning three
orders of magnitude (10-1 to 10-4) differed by an average of
50 percent. Uncertainty related to storage coefficient is not
considered an important source of error. Overestimation of
hydraulic conductivity can occur using this method if a well
only partially penetrates a thick, homogeneous aquifer in
which substantial vertical flow toward the well can occur. The
effects of partial penetration are not likely to be important
in data from wells in the La Pine study area because the
heterogeneity of the alluvial sediments would limit vertical
flow near the well.
Slug tests were done at 24 monitoring wells installed
along two transects for this study. One transect was located in
the northern part of the study area near South Century Drive
and the other was located in the south-central part of the
area near Burgess Road (fig. 1). The Burgess Road transect
included tests of 17 wells at 6 sites and the South Century
Drive transect included tests of 8 wells at 6 sites (table 2).
Table 2. Hydraulic conductivity estimates from slug test data from wells near LaPine, Oregon.
[Slug tests were conducted in April and September 2000. Latitude and Longitude: in degrees, minutes, seconds; North American Datum of 1927. Altitude:
referenced to National Geodetic Vertical Datum of 1929. Abbreviations: USGS: U.S. Geological Survey. Symbols: –, no data]
USGS site
identification
No.
Project well
name Local No.
State
identification
No.
Latitude Longitude Altitude
(feet)
Depth
(feet)
Hydraulic
conductivity
(feet per day)
434202121301501 Burgess 5.1 22.00S/10.00E-02BBC01 DESC 52678 43°42'01.89"121°30'15.21"4,210.9 23.9 15
434202121301502 Burgess 5.2 22.00S/10.00E-02BBC02 DESC 52677 43°42'01.89"121°30'15.21"4,211.1 36.9 24
434202121301503 Burgess 5.3 22.00S/10.00E-02BBC03 DESC 52676 43°42'01.89"121°30'15.21"4,210.9 49.0 .6
434203121305401 Burgess 4.1 22.00S/10.00E-03ABC01 DESC 52681 43°42'02.68"121°30'53.68"4,223.6 26.5 18
434203121305402 Burgess 4.2 22.00S/10.00E-03ABC02 DESC 52679 43°42'02.68"121°30'53.68"4,223.3 33.2 58
434203121305403 Burgess 4.3 22.00S/10.00E-03ABC03 DESC 52680 43°42'02.68"121°30'53.68"4,223.3 49.3 6.4
434206121311701 Burgess 3.1 22.00S/10.00E-03BBD01 DESC 52684 43°42'05.78"121°31'17.04"4,233.4 22.5 11
434206121311702 Burgess 3.2 22.00S/10.00E-03BBD02 DESC 52682 43°42'05.78"121°31'17.04"4,233.3 30.5 45
434206121311703 Burgess 3.3 22.00S/10.00E-03BBD03 DESC 52683 43°42'05.78"121°31'17.04"4,233.4 38.6 55
434206121312901 Burgess 2.1 22.00S/10.00E-03BBB01 DESC 52688 43°42'05.67"121°31'28.92"4,239.2 23.1 17
434206121312902 Burgess 2.2 22.00S/10.00E-03BBB02 DESC 52686 43°42'05.67"121°31'28.92"4,239.0 30.0 23
434206121312903 Burgess 2.3 22.00S/10.00E-03BBB03 DESC 52687 43°42'05.67"121°31'28.92"4,239.0 36.3 –
434206121312904 Burgess 2.4 22.00S/10.00E-03BBB04 DESC 52685 43°42'05.67"121°31'28.92"4,239.0 52.3 7.7
434213121295901 Burgess 6.1 21.00S/10.00E-35CDC1 DESC 53163 43°42'12.64"121°29'59.34"4,198.6 14.7 9.0
434213121295902 Burgess 6.2 21.00S/10.00E-35CDC2 DESC 53159 43°42'12.64"121°29'59.34"4,198.7 45.0 1.3
434213121324101 Burgess 1.1 22.00S/10.00E-05AAA01 DESC 52690 43°42'13.02"121°32'41.42"4,257.7 34.7 64
434213121324102 Burgess 1.2 22.00S/10.00E-05AAA02 DESC 52689 43°42'13.02"121°32'41.42"4,257.6 50.5 33
434910121275501 Century 1.1 20.00S/11.00E-19CCC1 DESC 53166 43°49'10.08"121°27'55.27"4,178.2 12.1 12
434910121275502 Century 1.2 20.00S/11.00E-19CCC2 DESC 53178 43°49'10.08"121°27'55.27"4,178.0 68.3 .3
434945121273501 Century 2 20.00S/11.00E-19BDB DESC 53184 43°49'44.61"121°27'35.32"4,175.4 11.1 8.8
435007121272701 Century 3 20.00S/11.00E-18CDC1 DESC 53175 43°50'07.04"121°27'27.31"4,173.9 8.9 97
435026121272101 Century 4 20.00S/11.00E-18CAA DESC 53185 43°50'25.67"121°27'20.64"4,174.1 10.7 57
435030121271401 Century 5 20.00S/11.00E-18ACC1 DESC 53160 43°50'29.75"121°27'14.15"4,172.9 11.7 5.2
435035121270801 Century 6.1 20.00S/11.00E-18ACA1 DESC 53164 43°50'34.68"121°27'08.15"4,171.9 10.7 31
435035121270802 Century 6.2 20.00S/11.00E-18ACA2 DESC 53158 43°50'34.68"121°27'08.15"4,171.8 64.0 .8
12 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
The wells ranged from 8.9 to 68 ft deep and were completed
with 2-ft long screens. Falling- and rising-head tests were
run with initial-head displacements of 1–2 ft. Test data were
analyzed using the method of Bower and Rice (1976), with
the assumptions that the effects of storage can be ignored and
the change in saturated thickness of the aquifer is negligible.
Horizontal hydraulic conductivities computed using the slug
test data range from 0.3 to 98 ft/d, with a geometric mean of
25 ft/d and median of 15 ft/d (fig. 4, table 2). The 10th and
90th percentile values of hydraulic conductivity (0.6 and
60 ft/d) span only two orders of magnitude which, even when
considering that the tests selectively target coarser materials,
suggest that hydraulic conductivity is relatively uniform in the
area compared to some alluvial environments. The 10th–90th
percentile range in hydraulic conductivity for the well-yield
test data was 4 to 94 ft/d. The 10th percentile hydraulic
conductivity is greater for this data set because the slug tests
are conducted on water-supply wells selectively screened
to the most permeable sediments and more thoroughly
developed.
Median values from well-yield and slug test data were
similar (21 and 15 ft/d, respectively). Geometric mean
hydraulic conductivity values were greater for the well-yield
test data (60 ft/d) because several basalt wells included large
(> 100 ft/d) hydraulic conductivity values that skewed the
mean (fig. 4). The agreement between the median values from
both data sets indicates that both estimation methods provide
good information on the hydraulic characteristics of the basin-
fill sediments.
Ground-Water Recharge
The shallow alluvial ground-water system in the study
area is recharged primarily by infiltration of precipitation
(rainfall and snowmelt), with lesser amounts resulting
from lateral ground-water inflow and effluent from on-site
wastewater systems. Gannett and others (2001) estimated
ground-water recharge to the upper Deschutes River basin
from infiltration of precipitation using a water balance model
(Deep Percolation Model) developed by Bauer and Vaccaro
(1987). The water balance model is based on empirical
relations that quantify processes such as interception and
evaporation, snow accumulation and melt, plant transpiration,
and runoff. The model computes a complete daily water
balance for the soil zone using measured precipitation and
temperature and data describing land cover, vegetation, and
soil properties. The water balance was computed within
rectangular areas (cells), each with an area of 1.3 mi2. A
detailed description of application of the water balance model
to the upper Deschutes River basin, including model input, is
available in Boyd (1996) and a summary of the results for the
entire upper basin is given in Gannett and others (2001).
Computed recharge from the water balance model was
used to specify the initial spatial distribution of recharge
within the boundaries of the simulation model. Based on
calibration of simulation models in the La Pine area (see
“Nitrate Fate and Transport Simulation Models”), the
recharge distribution was reduced slightly; the final calibrated
distribution is shown in figure 5. The mean annual recharge
distribution ranges from about 2 to 20 in/yr with the greatest
recharge occurring in the upland areas; however, most of the
model area lies at lower elevations adjacent to the Deschutes
and Little Deschutes Rivers where mean annual recharge is
about 2 in/yr (fig. 5). The mean annual recharge rate for the
simulation model is 3.2 in/yr (58 ft3/s).
OR19-0049_Fig04
100
PERCENTAGE OF OBSERVATIONS WITH
HYDRAULIC CONDUCTIVITY LESS THAN INDICATED VALUE
0 10 20 30 40 50 60 70 80 90
HY
D
R
A
U
L
I
C
C
O
N
D
U
C
T
I
V
I
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Y
.
I
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F
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T
P
E
R
D
A
Y
0.1
1
10
100
1
10
100
1,000
10,000
Slug test data
(n=24)
Well yield test data
(n=221)
Figure 4. Distributions of estimated hydraulic
conductivity values from slug tests and well-yield data.
Conceptual Model of Ground-Water System 13
Figure 5. Distribution of mean annual recharge, water-table elevation contours (June 2000), and locations of monitoring wells in
the La Pine, Oregon, study area.
OR19-0049_fig 05
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES CO.
L
A
K
E
KLAMATH CO.
Spr
i
n
g
Riv
e
r
Fall
River
Cresc
e
n
t
Creek
Creek
Little
De
s
c
h
u
t
e
s
DE
S
C
H
U
T
E
S
RIV
E
R
Ri
v
e
r
Pauli
n
a
Lo
n
g
C
r
e
e
k
5 KILOMETERS
5 MILES0
0
Wickiup
Reservoir
97
97
31
31
Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
Extent of
s
t
u
d
y
-
a
r
e
a
m
o
d
e
l
EXPLANATION
Mean annual ground-water recharge, in inches per year
1-2
2-4
4-6
6-8
8-12
12-20
Line of equal water table elevation, in feet above North American Vertical Datum of 1929
Well location and measurement frequency
2-hour
Bimonthly
4220
4210
4220
4170
4230
41904180
4240
41
6
0
4260
4210
4220
4170
4
2
3
0
419
0418
0
4
2
4
0
416
0
4
2
6
0
4200
4250
4200
4
2
5
0
DeschutesBasin
CascadeRange
NewberryVolcanoUpperDeschutesBasin
La Pineregion
OREGON
Bend
14 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Effluent from on-site wastewater systems also contributes
to recharge of the shallow ground-water system. The annual
rate was estimated for 1999 when there were about 5,200
on-site wastewater systems in the study area. The average
daily volume of effluent produced per system depends on the
number of occupants and their water-use habits. Deschutes
County monitored several on-site systems as part of the La
Pine National On-Site Demonstration Project and determined
that the average daily effluent volume was 45 gallons per day
per person (B. Rich, written commun., Deschutes County,
2003). La Pine households averaged 2.55 persons in 2000
(U.S. Bureau of the Census, 2000), so each household would
produce an average of 115 gal/d. In 1999, about 5,200 on-site
systems would have contributed 0.6 Mgal/d, (0.9 ft3/s), of
recharge to the ground-water system.
Ground-Water Flow
Hydraulic head, or simply head, is a measure of the force
that drives ground-water movement. Ground water flows from
areas of high head to areas of low head. In an unconfined
aquifer, such as the shallow alluvial deposits in the La Pine
study area, the elevation of the water table represents the
head at the upper surface of the aquifer. The rate of change in
head with distance is called the hydraulic gradient, which is
the slope of the water table. Ground water in deeper aquifers
may be confined by lower permeability layers (for example,
silt or clay). Ground water in confined aquifers may be under
pressure, such that when a well penetrates the aquifer, ground
water will rise in the well casing to levels above the top of
the aquifer. The hydraulic gradient in the vertical direction is
positive if head increases with depth, which indicates ground
water is flowing upward; conversely, it is negative if head
decreases with depth, and ground water is flowing downward.
Water-level measurements were made in 192 wells in
June 2000. Water levels from 170 wells with screened intervals
in the upper 100 ft were used to construct a contour map of
the water-table surface (fig. 5) used to calibrate the simulation
model. Ground water in the shallow part of the system in the
La Pine study area generally flows toward the rivers, which
generally are gaining in the study area. Water-table contours
also indicate that shallow ground water moves toward low-
lying Long Prairie south of the La Pine core area (fig. 1).
The water table is typically within 20 ft of land surface
in the study area. The shallowest depths to water in the study
area are along the lower reach of the Deschutes River and the
entire Little Deschutes River. In many areas, the water table is
within 5 ft of land surface and seasonally inundates low lying
areas adjacent to the streams during high flows in the spring.
Ground-water levels vary with time in response to
changes in rates of recharge to and discharge from the ground-
water system. To characterize seasonal and shorter variations,
bi-monthly water-level measurements were made in 48 wells
and digital recorders measured water levels every 2 hours
in 9 additional wells. Most wells were monitored between
March 2000 and December 2001; however, several wells in
the bi-monthly network also were monitored between 1994
and 1998 as part of a previous study of the upper Deschutes
basin (Gannett and others, 2001). Two long-term observation
wells also are in the study area and are measured by the
Oregon Water Resources Department (OWRD). These wells,
one of which has been measured quarterly since 1945, provide
insights on the effects of withdrawals (pumping), decadal-
scale climate variation, and other influences.
Three well hydrographs are shown in figure 6 to illustrate
general observations regarding the response of ground-water
levels to seasonal and long-term variation in recharge. Basic
information for all wells included in the monitoring network
is listed in table 3. Additional information for these wells,
including the complete history of water-level data, is available
from the USGS National Water Information System (NWIS) at
http://waterdata.usgs.gov/or/nwis.
OR19-0049_fig06
USGS Site ID 43440012127580121S/11E-19ccc OWRD Well ID DESC 7620
CALENDAR YEAR
CALENDAR YEAR
19
4
5
19
5
0
19
5
5
19
6
0
19
6
5
19
7
0
19
7
5
19
8
0
19
8
5
19
9
0
19
9
5
20
0
0
20
0
5
10
15
20
25
30
35
40
USGS Site ID 43323112136030123S/09E-36bbc OWRD Well ID KLAM 136
30
35
40
USGS Site ID 43432812130460121S/10E-27dbb1OWRD Well ID DESC 53655
1994 1995 1996 1997 1998 1999 2000 2001
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Depth: 100 feet (deepened from 37 feet in 1964)Open interval: 70-100 feet
Depth: 21 feetOpen interval: 18-21 feet
Depth: 470 feetOpen interval: 145-470 feet
Figure 6. Water levels in selected wells in the La Pine,
Oregon, study area.
Conceptual Model of Ground-Water System 15
Recharge to the ground-water system from infiltration
of precipitation and snowmelt occurs primarily in winter and
early spring when evaporation and transpiration losses are at
a minimum and available moisture is at a maximum. When
recharge to the ground-water system exceeds discharge,
ground water is added to storage and water levels rise. The
response of hydraulic head to the annual recharge pulse in
the winter and early spring is attenuated in deeper wells, such
as KLAM 136 (fig. 6); however, the annual recharge pulse
causes seasonal water-level increases of as much as 5 ft in
shallow wells like DESC 53655 (fig. 6). The effects of longer-
term variation in climate are evident in shallow and deep
wells. Shallow (DESC 53655) and deep (KLAM 136) wells
responded to the wet years from 1996 to 1998, although the
response in the deep well was delayed and more gradual. The
long-term monitoring well DESC 7620 is relatively shallow
(100 ft) and shows that several wet and dry periods have
occurred in the basin since the mid-1940s (fig. 6). The dry
periods have an average length of 11 years. Based on the long-
term hydrograph at well DESC 7620, water levels measured at
wells in June 2000 and used to construct the water-table map
in figure 5 are representative of long-term (1945–2005) mean
water levels in the shallow part of the ground-water system.
Ground-Water Discharge
Ground water discharges to streams, springs, and wells,
and by evapotranspiration. Discharge to streams and springs
is the primary pathway for ground water to leave the shallow
aquifers in the study area. Discharge to streams occurs as
diffuse seepage through the streambed (below the water line),
as discrete springs or spring complexes that form tributaries
(for example, Fall River), and as seepage along the stream
bank (above the water line). Evapotranspiration, which
includes bare soil evaporation as well as transpiration by
plants, is another mechanism for discharge where the water
table is shallow. Pumping by wells also accounts for part of
the overall discharge from the shallow aquifers in the study
area.
Streams and Springs
The direction and rate of flow between ground water and
streams is directly related to the direction and magnitude of
the hydraulic gradient between the stream and the ground-
water system. For ground water to discharge to a stream,
the ground-water level must be greater than the stage of the
stream. The rate of discharge to the stream is proportional to
the difference between the ground-water level and the stream
stage.
Table 3. Basin information for water-level monitoring wells in the
La Pine, Oregon, study area.
[Abbreviations: USGS, U.S. Geological Survey. Frequency: B, bi-monthly; R,
recorder (every 2 hours)]
State
identification
No.
USGS site
identification No.Local No.Frequency
DESC 52676 434202121301503 22.00S/10.00E-02BBC03 R
DESC 52677 434202121301502 22.00S/10.00E-02BBC02 R
DESC 52678 434202121301501 22.00S/10.00E-02BBC01 R
DESC 52684 434206121311701 22.00S/10.00E-03BBD01 R
DESC 52690 434213121324101 22.00S/10.00E-05AAA01 R
DESC 53158 435035121270802 20.00S/11.00E-18ACA2 R
DESC 53164 435035121270801 20.00S/11.00E-18ACA1 R
DESC 53656 434328121304603 21.00S/10.00E-27DBB3 R
DESC 53660 434657121274101 21.00S/11.00E-06CBA R
DESC 937 433756121335501 22S/10E-30DDD B
DESC 968 434810121305201 20S/10E-34ABC B
DESC 1450 433850121302301 22S/10E-22DDD B
DESC 1529 434700121285701 21S/10E-01BCD B
DESC 1727 434731121341001 20S/10E-31DDC B
DESC 6593 434516121295101 21.00S/10.00E-14CDD B
DESC 6959 434400121291401 21S/10E-23DDD B
DESC 7618 434501121272401 21S/11E-18CDA3 B
DESC 7620 434400121275801 21S/11E-19CCC B
DESC 7740 434217121263801 21.00S/11.00E-32CCC B
DESC 9173 433948121300101 22S/10E-14CCA B
DESC 9303 434752121343101 20.00S/10.00E-31DBB B
DESC 9314 434534121323801 21.00S/10.00E-16BBB B
DESC 9655 433959121300801 22S/10E-14CBB02 B
DESC 9889 434041121330701 22.00S/10.00E-08DCC B
DESC 50418 435104121282301 20.00S/10.00E-12DCB B
DESC 52533 433847121302301 22.00S/10.00E-22DAA2 B
DESC 52679 434203121305402 22.00S/10.00E-03ABC02 B
DESC 52680 434203121305403 22.00S/10.00E-03ABC03 B
DESC 52681 434203121305401 22.00S/10.00E-03ABC01 B
DESC 52682 434206121311702 22.00S/10.00E-03BBD02 B
DESC 52683 434206121311703 22.00S/10.00E-03BBD03 B
DESC 52685 434206121312904 22.00S/10.00E-03BBB04 B
DESC 52686 434206121312902 22.00S/10.00E-03BBB02 B
DESC 52687 434206121312903 22.00S/10.00E-03BBB03 B
DESC 52688 434206121312901 22.00S/10.00E-03BBB01 B
DESC 52689 434213121324102 22.00S/10.00E-05AAA02 B
DESC 53159 434213121295902 21.00S/10.00E-35CDC2 B
DESC 53160 435030121271401 20.00S/11.00E-18ACC1 B
DESC 53163 434213121295901 21.00S/10.00E-35CDC1 B
DESC 53166 434910121275501 20.00S/11.00E-19CCC1 B
DESC 53174 435007121272702 20.00S/11.00E-18CDC2 B
DESC 53175 435007121272701 20.00S/11.00E-18CDC1 B
DESC 53177 435030121271402 20.00S/11.00E-18ACC2 B
DESC 53178 434910121275502 20.00S/11.00E-19CCC2 B
DESC 53184 434945121273501 20.00S/11.00E-19BDB B
DESC 53185 435026121272101 20.00S/11.00E-18CAA B
DESC 53651 434029121292401 22.00S/10.00E-11DCC B
DESC 53652 434026121314301 22.00S/10.00E-16AAB1 B
DESC 53653 434026121314302 22.00S/10.00E-16AAB2 B
DESC 53655 434328121304601 21.00S/10.00E-27DBB1 B
DESC 53657 434328121304602 21.00S/10.00E-27DBB2 B
DESC 53658 434212121335301 22.00S/10.00E-06AAB B
DESC 53659 433703121305101 22.00S/10.00E-34DCC B
DESC 53661 434226121282302 21.00S/10.00E-36ACD2 B
KLAM 136 433231121360301 23S/09E-36BBC B
KLAM 138 433152121281301 23S/10E-36DDC B
KLAM 51668 433625121354401 23.00S/09.00E-01DAC B
16 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Ground water discharge to streams and springs was
estimated from gain-loss surveys of the Deschutes and Little
Deschutes Rivers between October 1995 and October 2000.
Gain-loss surveys, sometimes termed “seepage studies”, are
used to measure increases or decreases in streamflow between
upstream and downstream measurement sites that can be
attributed to exchange of water between the stream channel
and the underlying ground-water system. The gain-loss
surveys were conducted by measuring streamflow at intervals
of 1 to 10 mi on the Deschutes River between Wickiup Dam
(river mile [RM] 226.7) and Benham Falls (RM 181.4) and
on the Little Deschutes River between Wagon Trail Ranch
(RM 43.0) and immediately upstream of the mouth (RM
0.5). Gaging stations are located below Wickiup Dam and
at Benham Falls on the Deschutes River and at RM 26.7 on
the Little Deschutes River (fig. 7). Tributary inflow to the
Deschutes River was measured from Fall, Spring, and Little
Deschutes Rivers, and tributary inflow to the Little Deschutes
River was measured from Paulina Creek and Long Creek. The
gain or loss to or from each reach was computed by summing
the upstream and tributary inflow to the reach and deducting
the downstream outflow and diversions. Any positive residual
was assumed to be discharge from ground water; negative
residuals were assumed to represent stream leakage (recharge)
to ground water. Streamflow measurements and estimated
gains and losses for surveys in October 1995, February 1996,
March 2000, and October 2000, are listed in table 4.
The gain-loss surveys of the Deschutes River show
net gains of 143 and 166 ft3/s in 1996 and 2000. Most gains
occur downstream of Harper’s Bridge, RM 191.7, where large
springs discharge near river level from basalt aquifers. Spring
discharge to this reach was about 170–180 ft3/s (15–20 percent
of flow) in the two gain-loss surveys. Between Wickiup Dam
(RM 226.7) and Harper’s Bridge the 1996 and 2000 surveys
show a possible net loss of 10–40 ft3/s. Between Harper’s
Bridge and General Patch Bridge, surveys showed net losses
of 54 and 24 ft3/s in 1996 and 2000, respectively. Although
the seepage results show apparent losses in this reach they are
similar in magnitude to the estimated error of measurement
(32–38 ft3/s). Other data (contours showing horizontal
hydraulic head gradients toward the river and upward vertical
gradients measured below the river bed) indicate that ground
water discharges to the river in this reach and seepage data
lack the accuracy to measure the gain in flow. Upstream of
General Patch Bridge, the Deschutes River receives ground-
water discharge of as much as 25 ft3/s, with most entering
the river downstream of the La Pine State Recreation Area.
The 10-mi reach upstream of Pringle Falls showed little or no
ground-water interaction in 1996 and 2000.
Overall, little net gain or loss was measured in flow of
the Deschutes River upstream of Harper’s Bridge, relative
to the total discharge of the river. This is probably due to
the low permeability of the ash and tephra deposits that
constitute much of the streambed and lack of major springs
discharging directly to the channel in this reach. However,
exchange between the river and the ground-water system may
be occurring at a smaller scale that cannot be resolved by
gain-loss surveys in which measurements are several miles
apart. The multitude of meander loops likely are hydraulically
connected by old channel deposits that may provide ground-
water flow pathways where stream water can leave the channel
and re-enter downstream.
The Little Deschutes River downstream of RM 43
showed net gains ranging from 6.7 to 19.8 ft3/s in the gain-loss
surveys conducted in October 1995, March 2000, and October
2000. All three surveys showed that the reach between Bridge
Drive (RM 15.9) and South Century Drive (RM 5.5) received
ground-water discharge; the gains in the reach ranged from
5.9 to 25.2 ft3/s (0.6 to 2.4 ft3/s/mi), although the measurement
error was nearly equal to the apparent 25.2 ft3/s gain in March
2000. Gains ranging from 2.9 to 28.5 ft3/s (0.2 to 1.8 ft3/s/ mi)
also were measured in the 16.3 mi reach upstream of the
gaging station (at RM 26.7). The reach from South Century
Drive (RM 5.5) to just upstream of the mouth (RM 0.5) had
little or no gain or loss in the October surveys (1995 and
2000); however, the March 2000 survey indicated a 35 ft3/s
loss in this reach.
Long Creek is an intermittent tributary to the Little
Deschutes that drains the area between Highways 97 and 31 to
the south of La Pine. This topographically low area probably
is an abandoned channel of the Little Deschutes River. Aerial
photography showing lush vegetation throughout summer
indicates that this area has a shallow water table and likely is
a ground-water discharge area. In a typical year, Long Creek
flows until the water-table declines below the streambed in
June–July and then remains dry until the water table rises in
response to winter-spring recharge.
The October surveys probably were representative of
average conditions (neutral or slight gains) on the lowermost
reach of the Little Deschutes River, whereas the March
2000 survey probably was affected by high flows (about
300 ft3/s) that occurred during the seepage measurements.
The area between the Deschutes River and Little Deschutes
immediately upstream of their confluence is underlain by
10–15 ft of pumice, sand, and fine gravel that overlie a dense,
low-permeability clay. The top of the clay is exposed in the
banks of the Deschutes and Little Deschutes Rivers a few feet
above the water surface at low flow. In late spring, ground-
water seepage is visible on the bank at the contact between the
sand and gravel and the clay. At high stream stage, as during
the March 2000 survey, surface water would move from the
channel into the exposed sand and gravel while the hydraulic
gradient between the stream and ground water is temporarily
reversed (stream stage is greater than the ground-water level).
Conceptual Model of Ground-Water System 17
Figure 7. Gaining and losing reaches of the Deschutes and Little Deschutes Rivers and locations of measurement sites for
gain-loss surveys between October 1995 and October 2000 in the La Pine, Oregon, study area. OR19-0049_fig 07
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES
L
A
K
E
KLAMATH
Sp
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Fall
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Cresc
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Lo
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e
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5 KILOMETERS
5 MILES0
0
Wickiup
Reservoir
97
97
31
31
Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
Ex
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0-35
24-54
1-2
11-24
1-6
170-180
0-12
3-29
6-25
RM 13.7
14063000
14056500
14057500
14064500
RM43.0
RM26.7
RM226.7
RM217.6
RM208.6
RM199.7
RM192.7
RM191.7
RM 181.4
RM5.5
RM0.5
EXPLANATION
Gain or loss for stream reach—Number is gain or loss in cubic feet per second
Gain—more certain
Gain—less certain
Loss—less certain
Loss—more certain
Gaging station with USGS site number—See table 4 for details
Discharge measurement site with river mile—See table 4 for details
6-25
RM43.0
14063000
Lo
n
g
P
r
a
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i
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18 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
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Conceptual Model of Ground-Water System 19
The surveys on the Little Deschutes River in October
1995 and October 2000 are surprisingly dissimilar considering
that the discharge and measurement error were relatively
low for each survey. The apparent net gain in October 2000
was nearly three times that measured in October 1995. The
difference between the results of the two surveys likely is
explained by the water-table elevation at the time of each
survey. In 1995, the basin had undergone several years of
less than-normal precipitation and ground-water levels had
fallen by nearly 20 ft over the previous decade in long-term
observation well DESC 7620 (fig. 6). The lowering of the
water table reduced the hydraulic gradient between the shallow
ground water and the stream and, therefore, the ground-water
discharge to the stream also was reduced. Between 1995 and
2000, ground-water levels recovered almost 15 ft, and based
on the gain-loss surveys, ground-water discharge to the Little
Deschutes River increased from 7 to nearly 20 ft3/s.
In October–November 2000, a survey was made of the
vertical hydraulic head gradient between the shallow ground-
water system and the Deschutes and Little Deschutes Rivers.
The purpose of the survey was to identify the locations
of gaining and losing reaches of the Little Deschutes and
Deschutes Rivers at a more detailed scale than possible using
the gain-loss surveys in which discharge measurements were
made at locations separated by as much as 10 mi. Hydraulic
gradient alone cannot be used to determine the volumetric
rate of flow between a stream and the aquifer. Stream-channel
profiles and bed lithology data (appendix A) also were
collected during the survey and later used to estimate the
stream bed conductance parameters required by the simulation
model. The simulation model was used to estimate the rate
of ground-water flow into or out of the stream; the simulated
rates were compared with estimates from the seepage surveys
during model calibration. Head gradient measurements were
made at 12 sites on the Deschutes River between RM 192.5
and RM 218.4 and 20 sites on the Little Deschutes River
between RM 2.0 and RM 42.6 (appendix A). The average
distance between head gradient measurements was 2 river
miles. Measurements were made using a portable hydraulic
potentiometer that was driven 1–3 ft into the streambed. The
relative head difference between the stream and ground water
was measured to the nearest 0.01 ft using a manometer. The
design of the potentiometer and details on the procedure
for measuring head gradients is given in Winter and others
(1988). The dimensionless vertical hydraulic head gradient
was computed at each location by dividing the head difference
(ground-water level minus stream stage) by the depth of the
center of the potentiometer screen below the stream bed.
Ground-water discharge was indicated at 18 of 20
measurement sites on the Little Deschutes River and at all 12
sites on the Deschutes River (appendix A). Vertical hydraulic
gradients ranged from -0.003 to 0.075 on the Little Deschutes
River (negative gradients indicate downward flow from the
river) and 0.010 to 0.060 on the Deschutes River. All gradients
were upward (indicating ground-water discharge to the river)
except for two sites on the Little Deschutes River (RM 28.1
and 29.5; fig. A1, table A1) where neutral or slight downward
gradients were measured.
Evapotranspiration
Ground-water discharge to the atmosphere can occur
by evaporation from bare soil and transpiration from the
leaves of phreatophytes (plants whose roots draw water from
the saturated zone). The rate of evaporation from bare soil
diminishes rapidly with increasing depth to the water table
and is negligible if the water table is more than 10 ft below
land surface (Brutsaert, 1982, p. 236). Transpiration rates are
dependent on the type and density of phreatophytes, climatic
conditions, quality of water, and depth to water (Robinson,
1958, p. 16). These processes usually are considered together
and referred to as evapotranspiration, or ET.
In June 2000, the water table was within 10 ft of land
surface over an area of about 22 mi2. The potential ET (PET)
rate is the maximum possible rate for the local climate
conditions if water is nonlimiting. As part of a regional
ground-water budget, Gannett and others (2001) estimated that
the PET for the saturated zone in the La Pine study area was
22 in/yr, which is equivalent to about 1.6 ft3/s/mi2. This rate
would occur only if the water table was at or near land surface
with full coverage of phreatophytes. Under these conditions,
the maximum rate of ground-water discharge from the study
area by ET would be 35 ft3/s. Because the water table is not at
land surface and the coverage of phreatophytes is considerably
less than 100 percent, a more reasonable estimate of total ET
from the study area is in the range of 10 to 20 ft3/s.
Wells
Eleven public-water supply systems (Oregon Department
of Human Services, 2005) served about 1,650 people in the
study area in 2000. The largest water purveyor, the La Pine
Water District, serves 800 residents in the central core area of
La Pine. A private water system serves about 350 residents
of neighborhoods north of South Century Drive, between the
Deschutes and Little Deschutes Rivers. Several other small
water systems serve about 500 residents of mobile home and
recreational vehicle parks scattered throughout the study area.
About 12,350 residents, about 90 percent of the population,
obtained their water from individual, privately-owned wells in
2000. Local water use data for self-supplied rural residents in
the study area was not available. Mean per capita withdrawals
for self-supplied rural domestic use in Oregon is estimated
to be 110 gal/d (Hutton and others, 2004); however, given
the limited amount of irrigated landscaping in the La Pine
20 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
area, this value probably is not applicable. Deschutes County
monitored wastewater effluent discharge at homes in the area
as part of the La Pine Demonstration Project and determined
the average per capita rate was 45 gal/d (Oregon Department
of Environmental Quality, 2004b). To estimate domestic
well withdrawals, it was assumed that outside water use was
equal to 25 percent of total use, making the total per capita
withdrawal rate equal to 60 gal/d. Assuming this rate for
each of the 14,000 residents, about 0.84 Mgal/d (1.3 ft3/s)
were withdrawn in 2000. Infiltration of effluent from on-site
wastewater systems returns is about 45 gal/d per capita
(0.63 Mgal/d total) to the ground-water system as recharge at
the water table, resulting in net withdrawals of 0.21 Mgal/d
(0.32 ft3/s).
Nitrogen Fate and Transport
As part of this study, Hinkle and others (2007a) applied
geochemical and isotopic tools at various scales to provide
a framework for understanding aquifer-scale nitrate source,
transport, and fate. (Other wastewater contaminants, such as
viruses and pharmaceuticals, were evaluated by Hinkle and
others [2005].) The conceptual model resulting from this work
was used to develop the transport simulation model.
Nitrogen concentration data, tracer-based apparent
ground-water ages, ratios of N/Cl-, N isotope data, and
ground-water flow directions indicate that on-site wastewater
effluent is the only significant anthropogenic nitrogen source
to shallow ground water in the area. High concentrations of
ammonium were measured in samples from deep ground
water. Nitrogen isotopes, N/Cl- and N/C ratios, tritium-
age data, and hydraulic-head gradients support a natural,
sedimentary organic matter source for the high concentrations
of ammonium in the deep aquifer, as opposed to an origin
from on-site wastewater derived nitrogen.
Most residential development in the La Pine area
has occurred since 1960, with accelerated growth during
1990–2005. As a result, loading of nitrate from on-site
wastewater systems is a relatively recent phenomenon that,
in combination with low ground-water recharge rates, has
resulted in high concentrations of nitrate near the water
table. Low recharge rates and flow velocities have, for now,
generally restricted nitrate occurrence to discrete plumes
within 20–30 ft of the water table. Concentrations of nitrate
typically are low in deeper, older ground water due to the
nature and timing of nitrate loading and transport, and to loss
by denitrification. Denitrification is the process of reducing
nitrate into gaseous nitrogen. The process is performed by
bacteria when dissolved oxygen (which is a more favorable
electron acceptor) is depleted, and bacteria turn to nitrate in
order to oxidize organic carbon or other electron donors.
Denitrification was identified as an important
geochemical process in the study area by Hinkle and others
(2007a), who reported various supporting evidence, including
nitrate/chloride relations, presence of excess N2 enriched in
15N, presence of N2O, and nitrate losses within a framework
of progressively reduced ground water, reflecting classical
geochemical evolution. Ground water in the study area evolves
from oxic to increasingly reduced conditions with increasing
depth below the water table. Suboxic conditions are achieved
in 15–30 years, and the boundary between oxic and suboxic
ground water is sharp. Nitrate is denitrified near the oxic-
suboxic boundary.
The denitrification process was simulated by specifying
the location of the oxic-suboxic boundary within the ground-
water system and applying the assumption that nitrate is
rapidly converted to nitrogen gas as it is transported across
the boundary. The location of the boundary was mapped
within the study-area using data from 256 wells where
dissolved oxygen concentrations were available (Hinkle and
others, 2007a). Oxic ground water was defined as water with
dissolved oxygen concentrations greater than to 0.5 mg/L. The
boundary between oxic and suboxic water was constrained at
each sampling site using information on the depth to the water
table and well construction. The elevation of the oxic/ suboxic
boundary cannot be exactly determined at wells; however,
the elevation can be constrained if depth to the water table
and the top of the screened interval of the well are known.
The presence of suboxic water indicates that the boundary
lies above the top of the screened interval and the presence of
oxic water indicates that the boundary lies below the top of
the screened interval. In the latter case, the well may yield a
mixture of oxic and suboxic water if the boundary lies within
the screened interval, or the water may be entirely oxic if the
boundary lies below the screened interval. In areas where
data were sparse, an understanding of general patterns of
occurrence of oxic and suboxic water was used to infer the
location of the boundary. The general absence of oxic water
below a depth of 50 ft below the water table helped constrain
the depth over large parts of the study area. Similarly, the
general absence of suboxic water in ground water within 10 ft
of the water table constrained the minimum thickness of the
oxic part of the aquifer. However, one limitation of the data
was the absence of wells in near-stream areas to constrain
the boundary location. The thickness of the oxic part of the
aquifer was contoured (fig. 8) and used to specify the location
of the oxic-suboxic boundary in the transport model. The
thickness of the oxic part of the aquifer decreases as ground
water moves toward discharge areas along the Deschutes
River, Little Deschutes River, and Long and Paulina Creeks.
This is consistent with the aging of ground water as it moves
along flow paths terminating at surface-water features in
the area. Details of the implementation of the boundary are
presented in the description of the simulation model.
Conceptual Model of Ground-Water System 21
Figure 8. Estimated thickness of oxic ground-water layer in the shallow aquifer in the La Pine, Oregon, study area.
OR19-0049_fig08
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES CO.
L
A
K
E
KLAMATH CO.
EXPLANATION
Estimated thickness of the oxic layer—In feet, where oxic ground water is defined as water with a dissolved oxygen concentration greater than 0.5 milligrams per liter.
10-12
20
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22 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Nitrogen Loading from On-Site Wastewater
Systems
The annual rate of nitrogen loading to the shallow
aquifer system from on-site wastewater systems was
estimated for 1960–2005. The simulation model was run
for 1960–99 using the estimated annual loading rates as
input and simulated nitrate concentrations were compared
with measured concentrations. Previous investigations
(Century West Engineering, 1982; Oregon Department of
Environmental Quality, 1994) have concluded that the only
significant anthropogenic source of nitrogen to the ground-
water system in the La Pine study area is effluent from on-site
wastewater systems. As previously described, Hinkle and
others (2007a) also cite several lines of geochemical evidence
supporting the conclusion that on-site wastewater systems are
the dominant anthropogenic nitrogen source. This conclusion
also is consistent with the low level of agricultural activity,
limited number of livestock, and infrequent use of turf (and
therefore fertilizer) in residential landscaping in the study
area (Century West Engineering, 1982; Oregon Department of
Environmental Quality, 1994; Hinkle and others, 2007a).
Annual nitrogen loading to ground water from on-site
wastewater-system effluent was estimated for each tax lot in
the study area annually from 1960 to 1999. The population
of the study area prior to 1960 was sufficiently small that
nitrogen loading was considered negligible. Nitrogen loading
estimates were compiled by tax lot, but later aggregated
across larger areas for input to the simulation model.
Sources considered for nitrogen loading estimates included
residential, schools, motels, restaurants, and recreational
vehicle and trailer parks. Tax lot data (location, property
class, improvement class, year built) were provided by
Deschutes County (Tim Berg, Deschutes County Department
of Community Development, written commun., 2001)
and Klamath County (Jim McClellan, Klamath County
Department of Management Information Services, written
commun., 2001). Nitrogen loading was assumed to begin
when lots were developed and end when lots were connected
to a centralized sewer system (see areas served by centralized
sewers in figure 1). Dates of sewer installation were provided
by ODEQ (Dick Nichols, ODEQ, written commun., 2001)
and La Pine Special Sewer District (Andy Newton, La Pine
Special Sewer District, oral commun., 2001). Nitrogen loads
were calculated for each of the approximately 5,200 lots that
were developed and used on-site wastewater systems in 1999.
Nitrogen loading for homes was assumed to equal the
product of the average number of persons per household
(2.55 persons/household in the study area [U.S. Bureau
of the Census, 1960, 1970, 1980, 1990, 2000]); average
volume of effluent discharged to the on-site system by
each person (45 gal/person/d or 170 L/person/d [U.S.
Environmental Protection Agency, 1980; Oregon Department
of Environmental Quality, 2004b]), and average nitrogen
concentration in on-site wastewater system effluent (61 mg
N/L in the study area [B. Rich, ODEQ, written commun.,
2001]). Nitrogen discharged from on-site wastewater systems
also was assumed to be completely oxidized to nitrate in
the unsaturated zone beneath the drain field. Using these
assumptions, the estimated potential average nitrogen loading
per home is 21 lb N/yr (9.7 kg N/yr).
The potential for nitrogen loss in the unsaturated zone
was evaluated by sampling packed-bed (sand) filter on-site
systems in the upper Deschutes Basin. Inflow to and outflow
from the sand filters was sampled at 15 sites in two networks.
The first network consisted of 10 sand filters, installed 0.9 to
9.1 years prior to sampling. The second network consisted of 5
new sand filters. The first network was sampled once (October
2001) and the second network was sampled approximately
bi-monthly for 3 years after installation (October 2000 –
November 2003). Samples were analyzed by ODEQ as part
of the La Pine NDP for nitrate, ammonium, total Kjeldahl
nitrogen, and chloride. Nitrogen concentrations were adjusted
for dilution and evaporation using chloride concentrations.
The adjusted nitrogen concentrations from the first sand-filter
network indicated median and mean nitrogen losses of 31
percent and 29 percent, respectively (ODEQ, unpub. data,
2004). Data from the second network showed that the sand
filters underwent a period of maturation after installation.
Using data from samples collected more than one year after
installation, adjusted nitrogen concentrations from the second
sand-filter network indicated median and mean nitrogen
losses of 11 percent (Oregon Department of Environmental
Quality, 2004b). The artificial unsaturated zone created by a
sand-filter on-site system would be expected to function much
like the natural unsaturated zone beneath standard on-site
systems in the study area and similar rates of nitrogen loss
would be expected beneath standard and sand-filter on-site
wastewater systems. Based on the range of nitrogen loss
indicated in the sand-filter sampling study (approximately
10 to 30 percent), nitrogen losses in the unsaturated zone
were assumed to average 25 percent for conventional on-site
systems (including standard, pressure-distribution, and sand-
filter systems) for computing loading rates. Nitrogen loss of
25 percent in the unsaturated zone would reduce the assumed
nitrogen concentration of effluent as it enters the saturated part
of the ground-water system (water table) from 61 mg N/L to
46 mg N/L. For the same effluent volume, the resulting annual
nitrogen loading to the ground-water system would be reduced
from 21 lb N/yr (9.7 kg N/yr) to 16 lb N/yr (7.3 kg N/yr).
Nitrogen loading estimates were further adjusted to
account for seasonal residency. For many years a significant
number of homes in the study area were second homes or
vacation rentals occupied only part of the year. In 1980, about
46 percent of the population in the study area was seasonal
(Century West Engineering, 1982). Seasonal residents made
up an estimated 20 percent of study area population in 2000
(Keven Bryan, La Pine Postmaster, oral commun., 2000;
Carla Crume, La Pine Chamber of Commerce, oral commun.,
2000). To account for seasonal residents in the estimates of
nitrate loading it was assumed that (1) a seasonal resident did
not occupy their home for 6 months of the year, (2) seasonal
Conceptual Model of Ground-Water System 23
residents were 46 percent of the population from 1960 to
1980, and (3) the percentage of seasonal residents decreased
from 46 to 20 percent between 1980 and 1999. Adjusted for
seasonal residency, residential nitrate loading estimates ranged
from 12 to 14 lb/yr (5.6 to 6.5 kg/yr) per home between 1960
and 1999.
About 9,300 residential lots in the study area depend
(or will depend) on on-site systems for wastewater disposal.
Nearly 8,200 lots are in Deschutes County and the remaining
1,100 lots are in Klamath County. About 1,800 additional
undeveloped lots in Deschutes County may not be suitable for
on-site wastewater systems due to extremely shallow water-
table conditions (Tim Berg, Deschutes County Community
Development Department, written commun., November 2005).
Another 485 lots in Deschutes County will be served by a
central sewer system scheduled to be completed in 2008 and
are not included in these totals (B. Rich, Deschutes County
Community Development Department, written commun.,
November 2005). As of 1999, homes with on-site systems
had been built on 4,800 and 390 lots in Deschutes County and
Klamath County, respectively. Assuming an average nitrogen
loading rate of 14 lb/yr (6.5 kg/yr) per home, total residential
loading in 1999 was 74,000 lb/yr (33,750 kg/yr). According
to Deschutes County records, about 1,000 new homes were
built between 2000 and 2005; this represents about 26 percent
of the 2000 inventory of 3,900 lots in the Deschutes County
part of the study area. Building data were not available for
the Klamath County part of the study area for 2000–2005,
however if the same growth rate is assumed, an additional
180 new homes would have been built during this period. The
estimated number of homes in the study area in 2005 was
6,370 with nitrogen loading of 91,000 lb/yr (41,400 kg/yr).
The remaining inventory of lots suitable for on-site systems
in 2005 was 2,930, which could potentially add 42,000 lb/yr
(19,000 kg/ yr) of nitrogen loading from on-site systems. These
residential loading estimates are based on the assumption that
20 percent of residents were seasonal in 1999 and 2005. If
all residents were full-time, the average nitrogen loading per
home would be 16 lb/yr (7.3 kg/yr) and the total loading from
on-site systems after all lots (9,300) were developed would be
about 150,000 lb/yr (67,900 kg/yr), or about 164 percent of the
2005 estimate.
As with homes, nitrogen loading for schools, motels,
restaurants, and recreational vehicle and trailer parks was
assumed to equal the product of the number of people using
the facilities, average volume of effluent generated per person,
and the average nitrogen concentration in on-site system
effluent (also assumed to be 46 mg N/L for these facilities).
In most instances, estimates of the number of people served
by on-site systems in study area schools, motels, restaurants
(data in terms of restaurant seats), and recreational vehicle
and trailer parks were obtained from employees at the
facilities and from the Deschutes County Department of
Environmental Health. Data could not be obtained directly
from some motels and recreational vehicle and trailer park
sites; in these instances, data obtained from similar sites were
applied. Average volumes of effluent generated in schools
were reported to be 3.2 gal/d (12 L/d) per elementary school
student and 5.3 gal/d (20 L/d) per middle school student (John
Rexford, Operations Manager, Bend-La Pine Public School
District, written commun., 2001); volumes for high school
students were assumed to be the same as for middle school
students. A volume of 14 gal/d (53 L/d) per restaurant seat
(obtained by adjusting the value reported by Frimpter and
others [1990], to estimated study area restaurant use) was used
in estimates for restaurants. A volume of 34 gal/d (130 L/d)
per person was used for motels (Tchobanoglous and Burton,
1991), and 45 gal/d (170 L/d) per person (same as for homes)
for recreational vehicle and trailer parks. In 1999, nitrogen
loading from nonresidential sources totaled about 6,600 lb/yr
(3,000 kg/yr).
Annual and cumulative nitrogen loading to the ground-
water system from 1960 through 2005 are shown in figure 9.
Annual rates for 1960–99 were estimated using the method
described above. The 2005 loading rate was based on updated
information on the number of homes built as of 2005; the
2000–2004 loading rates were estimated by assuming that
the number of homes (and loading) increased linearly during
the period and nonresidential loading remained constant at
the 1999 rate of 6,600 lb/yr (3,000 kg/yr). Loading increased
at a moderate rate as the population grew from 1960 to the
mid-1970s. In the late 1970s, a surge in building (and nitrogen
loading) occurred prior to enactment of more restrictive rules
for on-site systems. Construction of a sewer system for the
central business district of La Pine in 1989 caused only a
minor reduction in overall nitrogen loading that was followed
by rapid population growth and concurrent loading into the
2000s. In 2005, the cumulative mass of nitrogen added to
the ground-water system since 1960 was more than 2 million
pounds (900,000 kg). As the number of homes contributing
nitrogen to ground water increases, the cumulative mass of
nitrogen added to ground water rapidly increases. One-half
of the total mass of nitrogen added during the 45-year period
(1960–2005) was added during the last 12 years (1993–2005)
(fig. 9).
OR19-0049_fig09
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
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,
I
N
P
O
U
N
D
S
P
E
R
Y
E
A
R
T
I
M
E
S
1
,
0
0
0
0
40
20
60
80
120
100 Cumulative mass loaded
Loading rate
Figure 9. Annual and cumulative estimated nitrate
loading from on-site wastewater systems in the La Pine,
Oregon study area, 1960–2005.
24 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Nitrate Fate and Transport Simulation
Models
Computer models were used to simulate the physical and
chemical processes affecting the fate of nitrate in the shallow
aquifer system near La Pine. The purpose of developing the
models was to (1) test concepts of how hydrogeologic and
geochemical processes affect the movement of nitrate through
the ground-water system, and (2) provide tools that could be
used to evaluate future water-quality conditions and alternative
management options. This section describes the process of
constructing and calibrating simulation models at two scales:
(1) a transect model used to estimate model parameters and
boundary conditions along a ground-water flow path where
there is a detailed understanding of the flow system and
geochemical evolution of ground-water, and (2) a study-
area model covering the area where there are water-quality
management concerns.
This section includes: (1) discussion of the overall
modeling approach used to construct and calibrate the transect
and study-area models, (2) discussion of model parameters
that must be specified for both models and how the values
were estimated and modified during calibration, (3) discussion
of hydrologic stresses specified for both models, (4) a detailed
description of boundaries, discretization, and calibration of the
transect model, and (5) a detailed description of boundaries,
discretization, and calibration of the study-area model.
Alternative management options were evaluated first by using
the study-area model to simulate prescribed scenarios and then
by coupling the study-area model with optimization methods.
The coupled simulation and optimization model is referred to
as the Nitrate Loading Management Model (NLMM).
Modeling Approach
The study-area model includes 247 mi2 of southern
Deschutes and northern Klamath Counties (fig. 10) where
either existing or planned future development uses on-site
wastewater systems. The study-area model was used to
simulate the long-term effects of historical and future nitrate
loading from on-site wastewater systems on ground-water
quality in the study area.
The transect model is more detailed and includes 2.4 mi2
of the shallow aquifer system near Burgess Road (fig. 10).
The transect model was used during the calibration process to
(1) test basic concepts of ground-water flow and nitrate fate
and transport, and (2) refine estimates of model parameters
through calibration in part of the study area where abundant
geologic, hydrologic, and chemical data were available to
constrain the model.
A regional ground-water flow model of the 4,500 mi2
upper Deschutes River basin was developed by Gannet and
Lite, (2004) to address issues of water supply and ground-
water/surface-water interaction. The model does not have the
capability to simulate transport of nitrogen and the resolution
(grid cell size) of the model grid is not adequate near La Pine
to make this model an effective tool for addressing issues
related to on-site wastewater systems. The regional model
was used, however, to specify initial values of parameters and
boundary conditions for the study area and transect models.
The first step in developing the transect and study-area
models was to construct a ground-water flow model and
simulate the velocity and direction of ground-water movement.
This velocity distribution then was used in a solute-transport
model to simulate the advection and dispersion of nitrate
in the ground-water system. Steady-state flow conditions
were assumed for the ground-water velocity distribution;
that is, it was assumed that there were no changes in storage
and the direction of ground-water flow and velocity did not
significantly change during the simulation period. The steady-
state flow models (transect and study area) were calibrated
using observations (measurements) of hydraulic head, ground-
water discharge rates to rivers, and chlorofluorocarbon (CFC)
based time-of-travel estimates (Hinkle and others, 2007a). The
accuracy of the transport model was evaluated by simulating
nitrate loading during the 40-year period 1960–99 and
comparing statistical distributions of observed and simulated
ground-water nitrate concentrations.
Ground-water flow and nitrate transport were simulated
using the programs MODFLOW-96 and MT3DMS. The
U.S. Geological Survey’s MODFLOW model (Harbaugh and
McDonald, 1996) is a numerical simulation program capable
of simulating hydraulic heads and ground-water flow within a
three-dimensional system. The MT3DMS simulation program
(Zheng and Wang, 1999) uses the velocity field computed by
MODFLOW to simulate the movement of dissolved chemical
species in ground water due to advection and dispersion.
MT3DMS also is capable of simulating the effects of chemical
reactions on the concentration of dissolved species.
The study-area and transect models developed for this
study consist of a set of data input files that specify the
boundary and initial conditions, the hydraulic and transport
parameters, and the hydraulic and chemical sources and
sinks specific to the study area. These input files provide
the data required by the model programs (MODFLOW-96
and MT3DMS) to solve a complex set of partial differential
equations that compute ground-water head and flux as well as
solute concentration and flux in the subsurface.
Nitrate Fate and Transport Simulation Models 25
OR19-0049_fig10
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83
R. 9 E.R. 10 E.R. 11 E.
T.20 S.
T.21 S.
T.22 S.
T.19 S.
T.23 S.
T.24 S.
DESCHUTES CO.
L
A
K
E
C
O
.
KLAMATH CO.
EXPLANATION
Boundary conditions
River cell
Spring cell
Evapotranspiration cell
Sp
r
i
n
g
Ri
v
e
r
Fall
River
Cresc
e
n
t
Creek
Creek
Little
De
s
c
h
u
t
e
s
DE
S
C
H
U
T
E
S
RIV
E
R
Ri
v
e
r
Pauli
n
a
Lo
n
g
C
r
e
e
k
5 KILOMETERS
5 MILES0
0
Wickiup
Reservoir
97
97
31
31
Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
Ex
t
e
n
t
o
f
s
t
u
d
y
a
r
e
a
m
o
d
e
l
10 20 30 40 50 60 70 80 90 100
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
210
220
230
240
250
260
270
Columns
Ro
w
s
Extent of
transect model
Upper
Deschutes
Basin
Regional
Model
La Pine
study area
model
Lo
n
g
P
r
a
i
r
i
e
Figure 10. Spatial relations between the upper Deschutes Basin regional ground-water model, the La Pine study area model, and
the transect model.
26 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Model Parameters
Several parameters must be specified for each cell in a
model. These parameters, hydraulic conductivity, porosity, and
dispersion coefficient, define the characteristics of the porous
medium (geologic materials) that control the movement of
ground water and the fate and transport of nitrate.
Hydraulic Conductivity
Initial values of hydraulic conductivity for the five major
lithofacies in the hydrogeologic model were estimated using
(1) results from 24 slug tests done for this study, (2) analysis
of 221 well-yield tests reported by drillers, and (3) literature
values. The three fluvial hydrofacies, clay-silt, sand, and
gravel, were assigned values of 3, 25, and 57 ft/d, respectively,
based on mean values from the slug tests. The lacustrine
clay-silt hydrofacies was assigned a value of 1 ft/d. The initial
value for the basalt hydrofacies was 800 ft/d based on values
used by Gannett and Lite (2004) in the La Pine study area. The
initial values of vertical hydraulic conductivity were derived
by adopting the horizontal to vertical anisotropy ratio of 1,000
used in the regional model for the La Pine study area (Gannett
and Lite, 2004). The resulting initial values of vertical
hydraulic conductivity were 0.001, 0.003, 0.025, 0.057, and
0.8 ft/d for the lacustrine clay-silt, fluvial clay-silt, fluvial
sand, fluvial gravel, and basalt hydrofacies, respectively.
Initial values of horizontal and vertical hydraulic conductivity
were assigned to each cell in the model on the basis of the
hydrofacies represented in the cell.
Porosity
Effective porosity is defined as the amount of
interconnected pore space and fracture openings available for
the transmission of fluids, expressed as the ratio of the volume
of interconnected pores and openings to the volume of rock
(Lohman, 1972). Effective porosity generally is smaller than
the total porosity of the porous medium, reflecting that some
pore spaces may contain immobile water with zero ground-
water seepage velocity (Zheng and Wang, 1999). However, as
discussed in some detail by Zheng and Bennett (1995), this
so-called effective porosity cannot be readily measured in
the field due to the complexity of the pore structure. Rather,
it generally must be interpreted as a lumped parameter and
estimated during calibration by comparison of simulated and
observed solute movement or ground-water travel time. An
initial value of 0.30 was used for the effective porosity of all
five hydrofacies.
Dispersion
The solute transport model includes the process of
dispersion to account for factors such as diffusion, flow path
tortuosity, and heterogeneities in the porous media that cause
velocities to deviate from the average seepage velocity. The
geostatistical method used to simulate the distribution of
hydrofacies allowed the model to represent a great deal of the
large scale heterogeneity in hydraulic properties. The scale of
heterogeneities incorporated in the hydrogeologic model was,
however, limited to the scale of the model grid (200 and 500 ft
laterally for the transect and study-area models, respectively,
and 5 ft vertically for both models). Because much of the
heterogeneity occurs at scales that cannot be represented by
a grid cell, the dispersion coefficient was used to represent
the smaller (sub-grid cell) scale heterogeneity of the system.
Additional factors, such as temporal variations in recharge
rates and flow directions that affect solute transport often
are incorporated into simulations as dispersion (Goode and
Konikow, 1990).
Dispersion is represented by three dispersivity
coefficients—one for longitudinal dispersivity, which
represents dispersion along the primary flow axis, and two
for transverse dispersivity values, which represent dispersion
in the horizontal and vertical directions normal to the axis of
flow. MT3DMS allows the user to specify the longitudinal
dispersivity for each model layer and to set the transverse
horizontal and transverse vertical dispersivity values as a
fraction of the longitudinal dispersivity. The initial value for
the longitudinal dispersivity was set to 50 ft to represent sub-
grid cell heterogeneity. Typically, the horizontal transverse
dispersivity is much smaller than the longitudinal dispersivity
and the vertical transverse dispersivity is smaller still
(Zheng and Bennett, 1995). Initial values for the transverse
dispersivity were set to 5 and 0.5 ft for horizontal and vertical,
respectively. The final, calibrated longitudinal, transverse,
and vertical dispersivity values were 60, 6, and 0.06 ft,
respectively.
Model Stresses
Model stresses are the flows in and out of the ground-
water system that are specified or simulated by the model.
The stresses include recharge, discharge to springs and by
evapotranspiration (ET), and exchange between streams
and the ground-water system. Discharge by pumping wells
is another stress, however it was not included in the model
because seventy-five percent of domestic well pumping
is returned as recharge from on-site wastewater systems.
Nitrate Fate and Transport Simulation Models 27
Recharge is the only specified stress in the models; other
stresses are simulated by the model based on relations between
head in the ground-water system and stream or springs
elevation or the rooting depth of plants that discharge ground
water by ET.
Specified flux and head-dependent flux boundary
conditions were used to simulate movement of water
between the ground-water system and streams, springs, and
the atmosphere. Recharge by infiltration of precipitation
was represented by specifying flux to the water table using
the recharge (RCH) package (Harbaugh and McDonald,
1996). Streams and rivers, springs, and evapotranspiration
were represented using head-dependent flow boundary
options in MODFLOW-96 (RIV, DRN, and EVT packages).
The locations of cells designated as head-dependent flux
boundaries are shown in figure 10.
Recharge
The distribution of recharge by infiltration of
precipitation and snowmelt was estimated for the upper
Deschutes basin by Gannett and others (2001) using the Deep
Percolation Model (DPM) of Bauer and Vaccaro (1987).
The basin was modeled using a grid with cell dimensions
of 6,000 ft per side. Gannett and Lite (2004) used estimated
1993–95 mean annual recharge to simulate steady-state
conditions. The 1993–95 recharge distribution was used as
the initial estimate of recharge to the study-area model; values
for each cell were derived by overlaying the study-area model
grid with the DPM model grid using a GIS (fig. 5). Neither
recharge from on-site systems nor withdrawals by domestic
wells were included in the model because, in the context of
the overall water budget, these components are essentially
equal and offsetting. Reductions in water level near pumping
wells are not represented in the study-area model using this
approach. Individual domestic wells may influence ground-
water flow within localized areas (a few cells), but they
would not have a significant effect on the direction and rate
of ground-water flow at the scale the model is intended to be
used.
Rivers
Ground-water discharge to and recharge from streams
was simulated with the river (RIV) package of MODFLOW-96
(Harbaugh and McDonald, 1996). Data required by the RIV
package include: mean stream stage, stream-channel elevation,
and streambed conductance for each cell that contains a
stream. All major streams in the study area were simulated
using this method (fig. 10).
All stream-channel elevations were estimated using a
10-m digital elevation model (DEM). The mean stage was
estimated to be 4 ft above the streambed in the Deschutes
River, 2 ft above the streambed in Paulina Creek and Little
Deschutes River, and 1 ft above the streambed in Long Creek.
Streambed conductance (SC) is calculated using the equation:
SC KA
b
K
v
v
=,
where
is the vertical hydraulic conductivity of th he
streambed (LT ),
is the area of the streambed within t
1
A hhe cell (L ), and
is the thickness of the streambed (L).
2
b
Conductance values were variable depending on the
hydrofacies of the cell and the area of the stream within
the cell. The initial conductance values were calculated by
assuming that the vertical hydraulic conductivity of streambed
sediments was 1/100th of the horizontal hydraulic conductivity
of the cell. Streambed thickness was set to 1 ft throughout the
model.
Springs
Ground-water discharge to springs was simulated with
the drain (DRN) package of MODFLOW-96 (Harbaugh
and McDonald, 1996). Data required by the DRN package
include the spring elevation and conductance for each cell
that contains a spring. This package was used to represent
discharge from springs at the contact between the basin-
fill sediments and volcanic rocks on the west side of the
Deschutes River between the confluence with Spring River
and the northern boundary of the model (fig. 10). All spring
elevations were estimated using a 10-m digital elevation
model (DEM) data. The conductance parameter has the same
dimensions (L2T-1) as the streambed conductance; however,
the parameter cannot be easily related to measurable physical
characteristics of the springs. Initial values of conductance
ranged from 5,000 to 10,000 ft2/d and were adjusted during
calibration.
Evapotranspiration
Discharge from the water table by evapotranspiration
(ET) was simulated using the EVT package of MODFLOW-96
(Harbaugh and McDonald, 1996). ET can occur where plants
with roots extending to the water table (phreatophytes) use
ground water for transpiration or where the water table is
close enough to land surface to allow direct evaporation from
bare soil. The EVT package uses the assumption of a linear
relation between ET discharge and depth to the water table.
Data required to define this relation are the potential ET rate
(LT-1), depth below land surface at which ET ceases (extinction
28 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
depth), and land surface elevation (L). The potential ET rate
was specified as 1.0 ft/d, the extinction depth was 5 ft, and the
land surface elevation was specified from DEM data. Only
cells where the water table was estimated to be within 10 ft of
land surface were activated in the EVT package (fig. 10). The
nitrate concentration in ground water used by plants in the ET
process was specified as zero because the (1) part of model-
simulated ET that is due to plant transpiration (as opposed to
evaporation from bare soil) could not be determined, and (2)
nutrient uptake by phreatophytes is species dependent and not
well constrained.
Transect Model
The transect model was developed for a part of the
ground-water system near Burgess Road (fig. 10). This area
was selected for detailed scale modeling because it was
the site of intensive data collection and study of changes
in ground-water age and chemistry along a ground-water
flow path transect (Hinkle and others, 2007a). The 3.5-mi
long transect model comprises 17 wells at 6 sites (2–4 wells
per site) aligned with the predominant direction of ground-
water flow (fig. 11). In addition to ground-water age and
chemistry data, hydraulic head, lithologic data, and hydraulic
conductivity data were available from the transect wells to
construct and calibrate the transect model.
Boundaries and Discretization
The boundaries of the transect model (fig. 11) were
selected to coincide with hydrogeologic boundaries of the
local flow system. The western boundary of the model is a
no-flow boundary defined by the ground-water divide that
coincides with the surface-water drainage divide between the
Deschutes and Little Deschutes Rivers. The north and south
boundaries of the model are streamline boundaries that parallel
the principal direction of ground-water flow from the drainage
divide to the Little Deschutes River. The Little Deschutes
River, a discharge area, was simulated as a head-dependent
flux boundary. The initial conceptual model of the system
included a deep regional component of upward ground-water
flow across the lower model boundary. The concept for the
lower boundary was evaluated by applying a specified flux
across the lower model boundary based on data from the
regional ground-water flow model by Gannett and Lite (2004).
The upward flux estimates from the regional model did not
allow a good simulated match to observed conditions (head
and flux) when hydraulic conductivity and recharge values
were within reasonable ranges based on independent data.
Little or no upward flow from a deep regional source is needed
to simulate the observed distribution of head and estimated
ground-water flux to the Little Deschutes River. Upward
vertical gradients were measured in well pairs in the area and
geochemical evidence indicates that ground-water discharge
to areas near the rivers may have a deep regional component
(Hinkle and others, 2007a). Seepage estimates and simulations
using the transect model, however, indicate that the magnitude
of regional discharge must be small compared to local
recharge to the shallow alluvial aquifer. The lower boundary of
the transect model was specified as a no-flow boundary.
The numerical methods used by MODFLOW and
MT3DMS to solve the equations for ground-water flow and
solute transport require that the ground-water system be
divided into discrete rectangular volumes, called cells. The
rows, columns, and layers of cells that make up the three-
dimensional array are collectively referred to as the model
grid. The center of each cell defines a point at which the
hydraulic head and solute concentration is simulated. The
simulated head and concentration values are taken to represent
the average values within the cell.
The longest dimension of the model grid was aligned
to the principal direction of ground-water flow from west to
east. The grid consists of 18 rows, 92 columns and 15 layers
of cells, with each cell having dimensions of 200 ft in the row
and column directions and 5 ft in the vertical direction. The
three-dimensional transect model was 3.5 mi in the east-west
(column) direction, 0.7 mi wide in the north-south (row)
direction (normal to the principal direction of flow), and 75 ft
thick in the vertical (layer) direction (fig. 11).
A three-dimensional hydrofacies model of the fluvial
and lacustrine sediments within the transect flow model
was constructed using the methods previously described for
constructing the hydrofacies model for the study-area model.
A sectional view through the model along row 8 is shown
in figure 11C and illustrates the heterogeneity of the fluvial
sediments. Transition probability geostatistical methods were
used with the same model parameters (mean lengths, transition
probabilities, and proportions) as were used for the study-area
hydrofacies model, however the transect hydrofacies model
was discretized into cells with the same dimensions as the
transect simulation model.
Calibration and Sensitivity
The MODFLOW model was first calibrated to steady-
state flow conditions using head data from the June 2000
synoptic well measurement. Data were available from 26
wells within the transect model area (fig. 11); 17 wells were
piezometers installed as part of the Burgess Road transect
study and 9 were existing domestic water-supply wells.
Observations (either measurements or estimates)
of ground-water discharge to streams were available to
constrain model calibration; however, flux between the Little
Deschutes River and the shallow ground-water system was
difficult to characterize because of uncertainty in the seepage
measurements. The apparent gains and losses for the 13-mi
Nitrate Fate and Transport Simulation Models 29
Figure 11. Plan and section views of the transect model showing simulated water-levels, ground-water travel time, and particle
paths in the La Pine, Oregon, study area. (Location of the transect model is shown in figure 10.)
OR19-0049_fig 11
1
2 3
4 5
6
1
2 3 4
5
6
1
2 3 4
5
6
A. PLAN VIEW OF TRANSECT MODEL GRID
B. SIMULATED TRAVEL TIME
C. SIMULATED PARTICLE PATHS
4
2
3
0
4
2
2
5
4
2
2
0
4
2
1
5
4
2
1
0
4
2
0
5
4
2
0
0
4
1
9
5
4232
4228
4232
4224 4226
4226
4226
4223
4224 4212
4196 4192
41984198
4210
4226
1.1 – 11 yrs
1.2 – 27
2.1 – 16 yrs
2.2 – 31
2.3 – 52
2.4 – 53
3.1 – 20 yrs
3.2 – 25
3.3 – 43
4.1 – 24 yrs
4.2 – 25
4.3 – 38 5.1 – 33 yrs
5.2 – 48
5.3 – >60 6.1 – <34 yrs
6.2 – >47
Li
t
t
l
e
De
s
c
h
u
t
e
s
Ri
v
e
r
Row 8
75
F
E
E
T
60
0
F
E
E
T
75
F
E
E
T
18,400 FEET
Unsaturated
Lacustrine clay-silt
Volcanics: basalt, andesite
Fluvial gravel
Fluvial sand
Fluvial clay-silt
2
4230
Cell
Cell simulated as stream
Contour of simulated water-table elevation
Well location
Simulated travel time, in years
Transect well location
Measured water-table elevation, in feet, June 2000
Transect well No.
EXPLANATION
A. PLAN VIEW OF TRANSECT MODEL GRID B. SIMULATED TRAVEL TIME
C. SIMULATED PARTICLE PATHS
100-110
110-120
120-140
140-160
160-180
180-200
200-230
230-260
260-310
310-380
700-1,000
380-470
470-600
600-700
0-2
2-5
5-10
10-15
15-20
20-25
25-30
30-35
35-40
40-45
45-50
50-55
55-60
60-65
65-70
70-80
80-90
90-100
Transect well screen location
Simulated particle path
2 Transect well No.
Hydrofacies
Cell simulated as stream
Transect well screen location
2 Transect well
Transect well and screen number with Chloroflourocarbon-derived ground-water age1.1 – 11 yrs
4228
30 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
reach downstream of the gaging station (14063000) ranged
from a 2.6 ft3/s gain in October 1995 to a 1.6 ft3/s loss in
October 2000 (table 4). These 1995 and 2000 estimates were
less than the estimated error of measurement (± 3.9 ft3/s and
±6 ft3/s, respectively). A third seepage measurement in March
2000 indicated a 12 ft3/s loss in this reach, but this loss was
based on measurements at relatively high flow conditions
(about 300 ft3/s) with a larger associated error. For calibration
purposes, October low-flow data were interpreted to indicate
that net seepage to or from this reach (1) is small relative to
flow, and (2) probably varies in direction as well as magnitude
depending on annual or seasonal head relations between
shallow ground water and the stream. A key component of
the conceptual model of the shallow flow system is that, on
annual or longer time scales, there is net discharge to the
Little Deschutes River. On this basis, a range of discharge
to the stream for the transect model area was computed
using the October 1995 seepage (2.6 ft3/s) as the minimum
and the sum of seepage and estimated error of measurement
(6.5 ft3/s) as the probable maximum for the range. Dividing
seepage and estimated error of measurement by the length of
the reach (13 mi) yielded a range of 0.20 to 0.50 ft3/s/mi and
the resulting range of expected mean annual ground-water
discharge to the 1.3 mi reach of the Little Deschutes in the
model area was 0.3 to 0.7 ft3/s (rounded).
During the calibration process, parameters such as
horizontal and vertical hydraulic conductivity, recharge, and
streambed conductance were adjusted, using a trial-and-
error procedure, to obtain the best fit between observed and
simulated head and stream flux values. The transect model
also was used to evaluate estimates of upward vertical flux
across the lower boundary from the regional flow model.
Horizontal hydraulic conductivity (Kh) and vertical
hydraulic conductivity (Kv) values were assigned to each
cell according to the hydrofacies represented in the cell. The
probable range of Kh based on well-yield data and slug tests
and the calibrated Kh value that yielded the best model fit
are listed in table 5. The probable range of vertical hydraulic
conductivity for each hydrofacies was computed assuming that
the probable range of the horizontal to vertical anisotropy ratio
was 10 to 10,000 for the hydrofacies in the model area. The
vertical anisotrophy ratio in the final model was equal to 100
for all hydrofacies.
Streambed conductance was estimated on the basis
of the assumption that the vertical hydraulic conductivity
in streambed sediments was 1/100th of the horizontal
conductivity of the hydrofacies in the model cell. A series of
simulations were made to test model sensitivity to streambed
conductance values. Conductance values were modified
by adjusting the ratio of streambed Kv to aquifer Kh, over a
range of 0.001 to 0.1, but the transect model was relatively
insensitive to this parameter.
Recharge estimates for the transect model area range
from 1.5 to 2.1 in/yr. The lower end of the range was estimated
by using a water balance model for the upper Deschutes Basin
(Gannett and others, 2001); the upper end of the range was
computed by using CFC-derived age data from the Burgess
Road transect study (Hinkle and others, 2007a). The best
model fit was obtained with a slightly higher recharge rate
of 2.3 in/yr.
Hydraulic heads and discharge to the stream simulated
by the transect model were most sensitive to recharge and
horizontal hydraulic conductivity of the fluvial clay-silt
and lacustrine clay-silt hydrofacies. The fluvial sediments
are relatively thinner than the lower permeability lacustrine
sediments near the river and this tends to reduce the composite
transmissivity of the aquifer system. The location, thickness,
and extent of clay-silt hydrofacies within the fluvial sediments
are relatively unimportant factors controlling ground-water
flow because the contrast in hydraulic conductivity between
the gravel, sand, and clay-silt hydrofacies is small compared
to the contrast between the fluvial and lacustrine hydrofacies.
Fitting simulated to observed heads was accomplished
by adjusting values of hydraulic conductivity for each
hydrofacies, until a best model fit was obtained by trial and
error.
Table 5. Values of horizontal and vertical hydraulic conductivity for
hydrofacies based on field data and model calibration in the La Pine, Oregon,
study area.
[Abbreviations: Kh, horizontal hydraulic conductivity Kv, vertical hydraulic conductivity]
Hydrofacies
Horizontal hydraulic
conductivity, Kh
(feet per day)
Vertical hydraulic
conductivity, Kv
(feet per day)
Probable
range
Calibrated
value
Probable
range
Calibrated
value
Fluvial clay-silt 1–20 5 0.001–2 0.05
Fluvial sand 10–100 40 0.01–10 .40
Fluvial gravel 75–150 75 0.075–15 .75
Lacustrine clay-silt 0.1–10 10 0.0001–1 .10
Basalt 100–2,500 150 0.01–250 1.5
Nitrate Fate and Transport Simulation Models 31
The calibrated parameter values (table 5) and boundary
conditions produced a good model fit to head and flux
observations. Contours of simulated water-table elevation
compare well with observed water-table elevations at 15 wells
(fig. 11A) where measured heads represent the water table.
The root mean square error (RMSE) of the head residuals
at the 26 well locations was 2.7 ft. Model fit was slightly
better (RMSE = 2.3 ft) at the 17 transect wells, where head
measurements were more accurate because (1) measuring
point elevations at the wells were surveyed, whereas elevations
at other wells were estimated from topographic maps, and
(2) short (2-ft) screens in the transect wells provided better
observations of head within the 5-ft thick model cells, whereas
screens in other wells were longer and spanned multiple
model layers. The simulated heads have a slight bias that
results in a steeper slope of the water table toward the Little
Deschutes River. The bias probably could be reduced with
further calibration if the configuration of the lacustrine-fluvial
sediment boundary were modified; however, there was no
basis (using existing geologic data) to modify the hydrofacies
model and the bias was small and did not significantly affect
average simulated flow velocities.
Simulated Travel Time and Comparison with
Ground-Water Age
Estimates of ground-water age were used to further
constrain the calibration of the transect model. Ground-water
age estimates at 17 wells in 6 locations along the Burgess
Road transect (fig. 11B, C) were derived from analysis of
CFCs (Hinkle and others, 2007a). A particle tracking program,
MODPATH, (Pollock, 1994) was used to determine the
simulated travel time of ground-water from recharge locations
at the water table to the well screens where CFC samples were
collected from the 17 transect wells. The simulated travel
times were compared with the CFC-derived age estimates to
evaluate the accuracy of the simulated ground-water velocity
distribution.
MODPATH uses the cell-to-cell fluxes simulated by
MODFLOW to compute velocity field and path lines of
individual “particles” of water that may be started at any
location and tracked either forward to their discharge location
or backward to their recharge location. The only additional
parameter required by MODPATH (that is not required by
MODFLOW) is effective porosity. Effective porosity was
assumed to be 0.3 for each hydrofacies within the model. For
this analysis, 1,000 particles were placed in each of the 17
model cells that contained the screen of a transect well. The
particles were tracked backward to their recharge locations
at the water table (fig. 11C). Because of limitations of the
tracking program, particles could not be placed at the exact
location of the well screens within each cell, but were placed
at the center of the cell and distributed along a vertical line 5-ft
long (the thickness of the cell).
Simulated ground-water travel time distribution is shown
in figure 11B for row 8 of the transect model. The simulated
distribution shows a pattern similar to the distribution of
CFC-derived ages from the 17 transect wells. Generally,
ground-water travel times are less than 10 years within the
upper 5–15 ft of the saturated zone and travel times within
30–50 ft of the water table are less than 50 years. Simulated
ground-water travel times are notably greater than CFC ages
at well 4.3, the deepest at site 4. Travel times are difficult
to predict at this site because the screen for well 4.3 is near
the upper surface of the fine-grained, lacustrine clay-silt
hydrofacies. The model predicts that “older” water will occur
at this location because slow-moving water from the lacustrine
sediments re-enters the fluvial sediments as it follows flow
paths toward the discharge areas along the river. At the
discharge end of the flow path, near the Little Deschutes River,
older water occurs at shallower depths as it moves upward to
discharge to the river. The relation between ground-water age
and depth depicted in the section (fig. 11B) is analogous to the
relation between dissolved oxygen concentration and depth
described by Hinkle and others (2007a).
Study-Area Model
Initial estimates for many parameters in the study-
area model were derived from calibration and testing of the
transect model. The study-area model was first calibrated
for simulation of ground-water flow using observations of
head and discharge to streams. As with the transect model
calibration, simulated heads were compared with water-
level data from the synoptic measurement of 228 wells in
June 2000 (fig. 5). Simulated ground-water discharge to
streams was compared with estimates of discharge from
gain-loss measurements (fig. 7, table 4). The measured head
and discharge data were assumed to represent the long-term
average (steady-state) conditions in the ground-water system.
Once the study-area flow model was calibrated, the simulated
ground-water flow directions and velocity were used to
simulate the transport and fate of nitrate. Transport of nitrate
from on-site wastewater systems was simulated for 1960–99
using the estimated annual nitrate loading rates. The transport
model was evaluated by comparing the statistical distribution
of simulated nitrate concentration with statistical distributions
of measured nitrate concentrations from analyses available
mostly from domestic wells.
The transport model calibration period was divided into
40 1-year stress periods. During each 1-year period, the nitrate
loading rate in each model cell was specified. The specified
rate was dependent on the number and type (domestic,
commercial, etc.) of on-site wastewater systems present.
32 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Boundaries and Discretization
The model grid for the La Pine study-area model includes
an area of 247 mi2 (fig. 10). The grid is elongated along a
northeast-southwest trend that coincides with the orientation
of the structural basin, major drainages, and the depositional
strike and dip of the basin-fill sediments. The axes of the grid
also are orthogonal to the principal directions of ground-water
flow. There are 276 rows, 100 columns, and 24 layers in the
model grid. The lateral dimensions of each cell are 500 ft in
both the x and y directions. The upper 23 layers of the model
were each 5 ft thick and the bottom layer was 100 ft thick. The
coordinates of the lower left corner of the grid are 4,609,651
ft east and 696,295 ft north (Oregon State Plane north) and the
grid is rotated 15 degrees clockwise.
The fluvial sand and gravel aquifers that supply most
drinking water to wells in the area lie within the upper 100 ft
of sediments. Between depths of 10 to 100 ft, depending on
location in the study area, there is a transition from the coarser
fluvial sediments to predominately fine-grained lacustrine
sediments (fig. 2, pl. 1). As previously described, the fluvial
deposits are heterogeneous and include fine-grained facies of
clay, silt, and silty-sand. Similarly, coarse facies occur within
the lacustrine deposits, although they tend to be isolated
lenses. The simulation model was constructed to include the
upper 120 ft of sediments so that the model would include the
entire thickness of fluvial sediments. Each of the 24 model
layers had a thickness of 5 ft throughout the grid. The grid
for the study-area flow and transport model was defined to
exactly match the dimensions of the grid used to prepare the
three-dimensional hydrogeologic model described earlier in
this report.
Long-term well hydrographs (fig. 6) indicate that ground-
water flow in the shallow part of the system is in a state of
dynamic equilibrium. Seasonal and interannual variations
in water level and ground-water storage are due to climatic
variation, but no long term trend is evident in mean water
levels. The June 2000 synoptic water level measurements
(fig. 5) were assumed to represent the mean annual head
distribution for the system and were used as the head
observations used as calibration targets for the steady-state
study-area and transect flow models.
The lateral and bottom boundaries of the model were
selected to include the most densely developed part of the
study area and the shallow alluvial deposits that form the
primary aquifers. The lateral and bottom boundaries of the
model do not coincide with specific hydrologic or geologic
boundaries such as geologic contacts or ground-water flow
divides. The potential magnitude of flow across the lateral
and lower model boundaries was evaluated by model testing
and sensitivity analysis with both the transect and study area
models. The upper boundary of the model is the water table,
which is the top of the saturated part of the ground-water flow
system.
The study area transport model used steady-state flow
velocities to simulate nitrate fate and transport. Nitrate loading
from on-site wastewater systems was simulated for 1960–99
in forty 1-year periods. The loading for each period was
computed using building records and other information as
previously described (fig. 9). Nitrate loading was specified
in the transport model using the mass-loading option in the
source/sink mixing package of MT3DMS (Zheng and Wang,
1999). The mass loading rate to each cell, in kilograms per
day, was specified at the water table for each year of the
simulation. Initial nitrate concentrations were assumed to be
zero at the beginning of the simulation in 1960.
Based on the conceptual model for denitrification (Hinkle
and others, 2007a), the transition zone from oxic to suboxic
conditions was represented as a sharp boundary that does not
vary significantly with time. Although the redox boundary
would be expected to migrate as solid-phase electron donors
are consumed by dissolved oxygen and nitrate reduction, the
effectiveness of this approach for characterizing current zones
of nitrate stability and instability is supported by analysis of
data collected by ODEQ (Hinkle and others, 2007a). Hinkle
presents field data from the area showing that 95 percent of
samples with nitrate concentrations greater than 1.0 mg N/L
taken from wells with known construction were screened at
least partly within the mapped (fig. 8) oxic zone.
The position of the boundary within the models was
specified by subtracting the thickness of the oxic part of the
aquifer (fig. 8) from the water-table elevation (fig. 5) to obtain
the elevation of the oxic-suboxic boundary. The boundary
was assumed to be in each vertical stack of cells at the top of
the first fully suboxic cell. The boundary was implemented in
MT3DMS by using the ICBUND array to specify a constant
concentration of zero in suboxic cells (Zheng and Wang,
1999).
Calibration and Sensitivity
Calibration of Ground-Water Flow
Ground-water fluxes across the lateral and lower
boundaries of the study-area model initially were specified
on the basis of the regional ground-water flow model
developed by Gannett and Lite (2004). The uppermost layer
of the regional model was 100 ft thick and represented both
alluvial deposits and basalts. The regional model simulates
large subsurface flow through the permeable basalts that
underlie the northern part of the study area (fig. 2). Most
of the flow remains within the basalts of the regional flow
system and discharges to the Deschutes River and tributaries
north of the study area (Gannett and others, 2001). Some of
the flow through the basalts, however, discharges to springs
that contribute to the Deschutes, Fall, and Spring Rivers in
the northwestern part of the study-area model. These springs
Nitrate Fate and Transport Simulation Models 33
generally are located where high permeability basalts abut
lower permeability sediments, forcing ground water to
discharge at land surface (Gannett and others, 2001).
Where alluvial deposits occur at the lower and lateral
boundaries of the study area model, the flux simulated
between the regional and study-area models was generally
small. This is consistent with results of testing the transect
model that indicated upward leakage across the lower
boundary was not required to match the observed head
distribution and ground-water discharge to streams when using
reasonable values for recharge and hydraulic conductivity.
This result indicates that upward leakage is small compared to
local recharge from infiltration of precipitation.
When the simulated flux across the lower and lateral
model boundary was included in the simulation, the study-area
model had numerical stability problems in the northern part
of the model area, which is underlain by basalt. The stability
problems were characterized by large fluctuations in simulated
heads that were probably caused by (1) a large flux through a
relatively thin section (120 ft) of the basalts, and (2) adjacent
model cells with large contrasts in hydraulic conductivity
(high hydraulic conductivity basalts in immediate contact with
low conductivity alluvial deposits).
To test the sensitivity of model results to specified flux at
the lateral and lower model boundaries, a simulation was made
specifying zero flux at these boundaries. Simulated heads
and flux to streams were determined to be insensitive to the
regional model boundary flux where basalts were not present.
Few data points were available to constrain the heads in the
basalt uplands and, therefore, even though simulated heads
were affected in the basalts, it is difficult to assess how well
or poorly they match actual heads. The simulated discharge
to springs along the Fall, Spring, and Deschutes Rivers in
the northern part of the model area also were affected, but
the model showed much better stability. Nearly all potential
concerns related to nitrate from on-site wastewater systems
are focused on parts of the study area underlain by alluvial
deposits. Simulation of flux through the basalts and of
discharge from large springs at the basalt-alluvium contact
was of less importance and did not inhibit the ability of
the model to simulate conditions in the alluvial deposits;
therefore, to attain better model stability in the part of the
model representing basalts, the zero-flux boundary condition
was used for the lower and lateral boundaries of the study-area
model.
The contours defining the simulated steady-state
potentiometric head surface retain the general features of the
surface defined by contours of measured heads from the 2000
synoptic measurement (fig. 12). Both simulated and observed
flow directions (inferred from contours) support other data
(vertical head gradient and gain-loss measurements) that
indicate, on an annual basis, ground water discharges to nearly
all stream reaches in the study area.
The model simulated the general direction of ground-
water flow (northeast) accurately in the area between the
Deschutes and Little Deschutes Rivers in southeast T20S/
R10E and northeast T21S/R10E; however, the model did not
simulate as steep a horizontal hydraulic gradient as indicated
by the contours of observed heads shown in figure 12. The
location of this area between the two rivers and at the focal
point of ground-water flow for a large part of the study
area, make it difficult to characterize the mean annual head
distribution. Seasonal differences in the stage of the Deschutes
and Little Deschutes Rivers can cause relatively large seasonal
variations (5–10 ft) in ground-water levels. The period of
high river stage in spring coincides with the peak recharge
period for the shallow aquifer. These conditions lead to larger
horizontal head gradients, particularly in this area, when the
water levels used to construct the contours in figure 12 were
measured (June 2000). The simulated recharge and river
stage conditions represent mean annual conditions, as do the
simulated heads, whereas the contours shown in figure 12 may
represent a seasonal extreme. The transient influence of the
rivers makes it difficult to accurately simulate ground-water
flow velocity and direction in this area; however, the model
simulates the mean annual direction of flow and velocity
reasonably well. On-site wastewater systems are not used in
this area so it is not likely that the model would be used to
predict concentration in this area. Long Creek was represented
in the model using head-dependent flux boundaries for ET and
streams to account for discharge in the topographically low
area; the effects of ground-water discharge are reflected in the
V-shaped simulated and observed contours (fig. 12).
The mean absolute error for the 170 head observations
was 7.0 ft, or about 5 percent of the range of observed heads.
The difference between simulated and observed head ranged
from -20 to 45 ft (fig. 13). The largest differences generally
were at wells with long open intervals, in which the measured
head represents a composite head for a large thickness of the
system. The simulated heads used for comparison in such
cases were for the model layer closest to the center of the open
interval of the well. The differences between simulated and
observed head generally were less than 10 ft in the central part
of the study area, between the Deschutes and Little Deschutes
Rivers. Errors in the simulated heads will result in errors in the
ground-water velocity field that in turn will affect simulation
of nitrate transport. These errors would affect simulated
concentrations at small scales, but would not affect the average
simulated nitrate concentration over large areas.
Recharge to the water table, which was 98 percent of total
recharge, was the only specified component of the simulated
water budget. The mean annual recharge rate of 58 ft3/s was
equivalent to an average of 3.2 in/yr within the study area
model. The other components of recharge and discharge were
simulated using head-dependent boundary conditions, as
previously described. The simulated recharge from streams
34 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
OR19-0049_fig12
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES
L
A
K
E
KLAMATH
Sp
r
i
n
g
Ri
v
e
r
Fall
River
Cresc
e
n
t
Creek
Creek
Little
De
s
c
h
u
t
e
s
DE
S
C
H
U
T
E
S
RIV
E
R
Ri
v
e
r
Pauli
n
a
Lo
n
g
C
r
e
e
k
5 KILOMETERS
5 MILES0
0
Wickiup
Reservoir
97
97
31
31
Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
Ex
t
e
n
t
o
f
s
t
u
d
y
a
r
e
a
m
o
d
e
l
EXPLANATION
Water-level contours—In feet above National Geodetic Vertical Datum of 1929. Contour interval is 20 feet.
Simulated
Measured (June 2000)
4200
4200
Lo
n
g
P
r
a
i
r
i
e
42
1
0
4
2
2
0
4170
4190
418
0
4
2
4
0
4160
421
0
4
2
2
0
41
7
0
4
2
3
0
419
0
418
0
41
6
0
426
0
4200
425
0
42
0
0
4200
41
9
042
0
0
41
8
0
4
2
6
0
4270
4280
4
2
5
0
424
0
42204230
4210
42
9
0
41
6
0
4300
4310
4320
4330
4340
41
5
0
4170
4240
41
7
0
42
2
0
4230 4170
4
2
9
0
4280
4270
4260
4250
4240
4230
4220
4210
4200
4190
418
0
41
7
0
416
0
Figure 12. Contours of simulated and observed heads (June 2000) for the La Pine, Oregon, study area.
Nitrate Fate and Transport Simulation Models 35
was small (1.3 ft3/s) and was from a few isolated stream
reaches where simulated heads were less than the specified
stage of the stream. Because the simulated system is assumed
to be at steady state (no long-term change in storage), total
discharge is equal to recharge. Ground-water discharge to
streams accounts for 67 percent (39.5 ft3/s) of total discharge.
Simulated discharge to the Little Deschutes River is 15 ft3/s
which is within the range of 7 to 20 ft3/s expected on the
basis of measured discharge (table 4). Simulated ground-
water discharge to the Deschutes River was 12 ft3/s and was
consistent with measurement data for reaches upstream of
river mile 199.7. Downstream of river mile 199.7 on the
Deschutes River and on the Fall River, most ground-water
discharge emanates from the large springs where basaltic rocks
are in contact with the lower permeability alluvial sediments.
Recharge by subsurface inflow to the basaltic rocks that feed
these springs was not simulated in the study-area model. The
simulated discharge to ET of 16 ft3/s fell within the estimated
range of 10–20 ft3/s and was distributed within the floodplain,
where shallow water-table conditions persist through the dry
months (fig. 10).
Comparison of Simulated and Measured Nitrate
Concentrations
The study-area transport model simulates nitrate
concentrations in ground water and in ground-water discharge
to the near-stream environment. Simulated concentrations
are averages for the 500-ft wide by 500-ft long by 5-ft thick
model cells. With cells covering nearly 6 acres and minimum
lot sizes of 0.5 acre, each cell can contain as many as about
10 homes. Nitrate data collected for this study from closely
spaced sampling locations near the Burgess Road transect
model (Hinkle and others, 2007a) indicate that even in
mature, high-density residential areas, nitrate plumes have
not coalesced to a great degree, and concentrations are highly
variable at the scale of an individual model cell. Because
of the high variability of nitrate concentrations in a cell,
concentrations at individual wells cannot be simulated with the
study-area model. The inability to delineate the edges of, and
concentrations within, individual solute plumes is a limitation
of transport models at the watershed scale. This limitation
does not affect this study because the information from
the model is intended to help understand and predict water
quality conditions at scales larger than individual plumes
or wells; however, it does limit the degree that measured
nitrate concentration data from wells can be used for direct
comparison with simulated concentrations.
To assess of the ability of the study-area model to
represent the primary processes that affect nitrate movement
in the ground-water system, the statistical distribution
of simulated nitrate concentrations was compared with
distributions for two sets of measured nitrate concentrations
from wells. The first measured dataset was from a synoptic
sampling of 192 wells in June 2000 by ODEQ (Hinkle
and others, 2007a). Only data from the 109 wells where
ground water was oxic (dissolved oxygen concentration was
greater than 0.5 mg/L) were used in the comparison because
denitrification has been shown to be an important process
where ground water is suboxic (Hinkle and others, 2007a).
The second observed dataset was collected under a program
administered by Oregon Department of Human Services
Health Division (DHS), which requires that water from
domestic wells is tested whenever a property is sold. Nitrate
analyses from 1,572 such tests were available for homes in the
La Pine area (Rob Keller, ODEQ, written commun., August
2006). The DHS data were collected from 1989 to 2004.
Dissolved oxygen concentrations are not analyzed as part of
the DHS program so it was not possible to discriminate wells
that pump from the suboxic part of the system.
The simulated nitrate concentrations used for comparison
were from the end of the simulation period (1999) and were
taken from 1,398 cells randomly selected from locations
where active on-site wastewater systems existed. Only cells
that contained oxic ground water were selected (because
suboxic cells would have simulated concentrations of zero
by default) and more than one cell could be selected from
more than one layer in the same row/column. The statistical
distributions of measured nitrate concentrations and the
simulated concentrations are similar (fig. 14). The maximum
simulated nitrate concentration was 29 mg N/L, with a mean
of 2.0 mg N/L, and a median of 0.8 mg N/L, and 10 percent
Figure 13. Simulated head residuals and observed heads
(June 2000) from the La Pine, Oregon, study area.
OR19-0049_fig13
OBSERVED HEAD, IN FEET ABOVE NORTH AMERICAN DATUM 1983
4120 4140 4160 4180 4200 4220 4240 4260 4280 4300
RE
S
I
D
U
A
L
O
F
S
I
M
U
L
A
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E
D
H
E
A
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,
I
N
F
E
E
T
-30
-20
-10
0
10
20
30
40
50
36 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
of concentrations greater than 6 mg N/L. The maximum of
the ODEQ June 2000 synoptic nitrate concentration data
was 26 mg N/L, with a mean of 1.6 mg N/L, and a median
of 0.3 mg N/L, and 10 percent of concentrations greater
than 4 mg N/L. The maximum of the DHS real estate
nitrate concentration data was 22 mg N/L, with a mean of
1.6 mg N/L, and a median of 0.5 mg N/L, and 10 percent
of concentrations greater than 4.5 mg N/L. The primary
difference in the three nitrate concentration distributions was
the slightly greater proportion of high values in the simulated
concentration distribution. This difference is likely due to
simulated values being sampled from the entire thickness
of the oxic part of the system, including cells near the water
table where nitrate loading occurs and concentrations are
greatest. Samples from the measured datasets were collected
from wells where the screened intervals typically were below
the water table and would be less likely to include water
with high nitrate concentrations. Good agreement between
the summary statistics of the measured and simulated nitrate
concentrations (mean, median, 90th percentile, and maximum)
indicates that the simulated mass of nitrate in the ground-water
system at the end of the 1960–99 period, is similar to the mass
indicated by available sample data. This agreement increases
confidence that the primary processes affecting the fate and
transport of nitrate in the ground-water system are represented
in the simulation model. Even though the model does not
simulate concentrations at individual wells, it is a useful tool
for assessing the effects of on-site systems on average ground-
water nitrate concentrations at the scale required for evaluation
of management alternatives for protecting ground-water
quality.
The spatial distribution of simulated nitrate concentration
at the water table in 1999 is shown in figure 15 and closely
mirrors the locations of on-site wastewater systems (fig. 1).
The effect of ground-water movement on nitrate concentration
is evident where areas of high concentration are elongated
parallel to the primary directions of ground-water flow,
such as immediately south of Burgess Road. The effect of
denitrification on the simulated distribution is evident where
concentrations sharply decrease along easterly ground-water
flow paths that terminate at the Little Deschutes River, such
as in central T21S R10E (fig. 15). The sharp concentration
gradient is coincident with an area where the oxic part of the
system decreases in thickness (compare fig. 8). This decrease,
along with the downward component of advective transport,
forces a large fraction of the nitrate in the system to be
transported into the suboxic zone and lost to denitrification.
At the end of the simulation period (1999), the rate
of nitrate (as N) loading to the ground-water system
was 82,000 lb/yr (37,000 kg/yr). The simulated rate of
denitrification in the suboxic part of the system was 31,000 lb/
yr (13,900 kg/yr) and the simulated discharge of nitrate to the
near-stream environment was 8,000 lb/yr (3,650 kg/yr). The
remaining 43,000 lb/yr (19,400 kg/yr) was added to storage
in the shallow ground-water system. Nitrate added to storage
increased the mean concentration in the ground-water system
from essentially zero in 1960 to a mean of 2 mg N/L in 1999.
Management Scenario Simulations
Simulation models often are developed with the goal
of using them for predicting future effects of management
strategies. The study-area model was initially used in what is
referred to as a trial-and-error prediction mode. In this mode,
future scenarios are designed in which the nitrate loading
input to the model is varied according to a hypothetical
set of management strategies that could be imposed. The
locations and rates of loading over time are specified as input
to the simulation model and the model predicts the resulting
distribution of nitrate concentrations in the aquifer and the
discharge of nitrate to the streams. The scenario results
then are compared to assess whether management strategies
succeeded in meeting water-quality goals. This is referred to
as a trial-and-error procedure because often many simulations
must be made to find management strategies that meet
water quality goals. The results of the scenario simulations
are presented here for later comparison to results of the
simulation-optimization approach.
OR19-0049_fig14
OregonDepartmentofEnvironmentalQuality data
n=109
Simulated
0
5
10
15
20
25
30
n=1,398 Departmentof HumanServices data
n=1,572
NI
T
R
A
T
E
,
I
N
M
I
L
L
I
G
R
A
M
S
N
P
E
R
L
I
T
E
R
n=109 Number of observations
90th percentile
75th percentileMean
Median
25th percentile
10th percentile
Sample not included in the 10-90 percentile range
EXPLANATION
Figure 14. Measured and simulated nitrate concentrations
in the La Pine, Oregon, study area, 1999.
Nitrate Fate and Transport Simulation Models 37
Figure 15. Simulated nitrate concentrations near the water table in the La Pine, Oregon, study area, 1999.
OR19-0049_fig15
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES CO.
L
A
K
E
C
O
.
KLAMATH CO.
Spri
n
g
Riv
e
r
Fall
River
Cresc
e
n
t
Creek
Creek
Little
De
s
c
h
u
t
e
s
DE
S
C
H
U
T
E
S
RIV
E
R
Ri
v
e
r
Pauli
n
a
Lo
n
g
C
r
e
e
k
5 KILOMETERS
5 MILES0
0
Wickiup
Reservoir
97
97
31
31
Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
Extent of
s
t
u
d
y
a
r
e
a
m
o
d
e
l
EXPLANATION
Nitrate concentration, in milligrams N per liter
0
5
10
20
50
100
38 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
The calibrated simulation model was used to predict
the effects of eight decentralized wastewater management
scenarios on ground-water and surface-water quality. Scenario
number 1 was defined as the “base” scenario which would
be used to evaluate the effects of a “no action” management
strategy and serve as a benchmark for evaluating the benefits
of other management alternatives. Under the base scenario,
homes built on approximately 4,100 undeveloped lots
remaining in 2000 used conventional on-site wastewater
systems. Conventional systems were assumed to produce the
same effluent concentration (46 mg N/L) and loading as used
during the 1960-1999 model calibration simulations. The
remaining seven scenarios were defined by Deschutes County
using two primary management options to reduce nitrate
loading: (1) a transferable development credit (TDC) program
to reduce the number of on-site wastewater systems in the
area, and (2) advanced treatment on-site wastewater systems.
Deschutes County has modified the TDC program since the
scenarios were defined; however the goal of the original TDC
program was to reduce the number of on-site septic systems in
the area by shifting, or transferring, development to a receiving
area served by a community sewer and water system.
Advanced treatment on-site wastewater systems capable
of removing nitrogen were extensively field-tested as part of
the La Pine NDP (Barbara Rich, ODEQ, written commun.,
2003). Based on data from the field testing program, three
levels of nitrogen reduction performance were evaluated using
the simulation model. Three reduction levels, expressed as a
percentage of the nitrate concentration in effluent reaching
the water table from conventional systems (46 mg N/L),
were used: 57, 78, and 96 percent. These reductions would
be equivalent to effluent nitrate concentrations at the water
table of 20, 10, and 2 mg N/L, respectively. Four additional
scenarios were defined where advanced treatment systems
were combined with a TDC program in which development of
1,500 lots was moved to a receiving area served by centralized
sewer.
Additional assumptions for the scenarios included:
Development would continue at the 1990–99 rates of •
250 homes per year until full build-out (in 2019);
All new homes would use advanced treatment on-site •
wastewater systems; lots where new homes were built
each year were randomly determined;
Locations of existing homes where conventional •
on-site wastewater systems were upgraded to advanced
treatment systems were randomly selected in each
year;
Upgrades were done at a rate of 94 per year (based on •
historic rate of system repair permits issued by county)
until all on-site wastewater systems had been upgraded
(2056); and
For scenarios involving TDCs, 1,500 lots were •
randomly selected from a pool of 2,600 candidates
provided by Deschutes County.
Descriptions of the scenarios and the resulting nitrate
loading rates are summarized in table 6.
Each scenario was simulated for 140 years beginning
in 2000. The historical nitrate loading rates (1960-99) are
compared with estimated future loading rates (2000-2139) for
each scenario in figure 16.
Under the base scenario (number 1, table 6), all available
lots (as of 2000) were projected to be developed by 2019, and
figure 16 shows that estimated nitrogen loading continued to
increase until that time, after which loading remained constant
at a rate of 147,000 lb/yr. Simulation of the base scenario
showed that nitrate concentrations continued to increase
long after the maximum loading rate was reached in 2019.
This is because the amount of nitrate entering the ground-
water system will exceed the amount leaving the system until
equilibrium is reached. Equilibrium occurs when loading
is balanced by the sum of the rates of denitrification and
discharge of nitrate to streams. The simulation model suggests
that it could take more than 140 years to reach equilibrium for
scenario 1. At equilibrium, 78 percent of nitrogen entering the
system (114,000 lb/yr) will be transported to the suboxic part
of the aquifer and removed by denitrification. The remaining
22 percent (33,000 lb/yr) will be transported into the near-
stream areas adjacent to the Little Deschutes and Deschutes
Rivers. This should be considered an upper bound on the
amount of nitrate reaching the rivers because the current study
area model cannot account for processes (denitrification,
plant uptake, microbial uptake) that may remove nitrate from
ground water before it discharges to the rivers.
The simulated nitrate concentrations for scenario 1
exceeded 10 mg N/L over large areas prior to equilibrium,
however at equilibrium, the nitrate concentration near the
water table averaged more than 10 mg N/L over areas totaling
about 9,400 acres (table 7, fig. 17).
The results of the other seven scenarios showed
improved water-quality conditions for each level of increased
nitrate loading reduction. Simulations indicate significant
improvements in overall ground-water quality for all
performance levels tested if all new homes use advanced
treatment on-site wastewater systems and all existing homes
replace conventional on-site wastewater systems with
advanced treatment on-site wastewater systems. For the
20 mg N/L nitrate performance level without a TDC program
(scenario 3) the area where nitrate concentrations exceed the
10 mg N/L drinking-water standard is reduced by 80 percent
to about 1,900 acres (table 7, fig. 18) at equilibrium. A
further reduction in effluent nitrate concentration, to 10 mg
N/L, (scenarios 5 and 6) reduced the area where simulated
equilibrium nitrate concentrations exceed 10 mg N/L to
less than 700 acres. The maximum reduction, to 2 mg N/L,
(scenarios 7 and 8) resulted in only a few small areas with
concentrations greater than 10 mg N/L, and those areas were
related to nonresidential loading (RV parks) not reduced under
the scenarios.
Nitrate Fate and Transport Simulation Models 39
Table 6. Summary of eight on-site wastewater management scenarios tested with the study-area model in
the La Pine, Oregon, study area.
[TDC lots: assumes 1,500 lots eremoved from pool of candidate lots. Locations were randomly selected from 2,600 possible
lots. Retrofitting: assumes all on-site systems serving homes built prior to 2000 are retrofitted with advanced systems with
performance equal to systems installed in new homes. Retrofits are made at a rate of 94 per year until completed in 2057.
Abbreviations: TDC, transferable development credit; lb/yr, pound per year; mg N/L, milligram nitrogen per liter]
Scenario
Effluent
recharge
concentration
(mg N/L)
Percent
reduction
from standard
systems
TDC lots Retrofitting
Peak
loading
(lb/yr)
Peak
loading
year
Final
loading
(lb/yr)
1 46 0 No No 147,000 2019 147,000
2 46 0 Yes No 125,000 2013 125,000
3 20 57 No Yes 93,000 2019 65,300
4 20 57 Yes Yes 88,100 2013 55,900
5 10 78 No Yes 81,200 2000 34,200
6 10 78 Yes Yes 81,200 2000 29,500
7 2 96 No Yes 80,400 2000 9,200
8 2 96 Yes Yes 80,400 2000 8,300
OR19-0049_fig16
YEAR
NI
T
R
A
T
E
L
O
A
D
I
N
G
,
I
N
P
O
U
N
D
S
P
E
R
Y
E
A
R
X
1
,
0
0
0
1960 1980 2000 2020 2040 2060 2080 2100 2120 2140
1-Base scenario
2-TDCs only
3-20 mg/L
4-20 mg/L + TDCs
5-10 mg/L
6-10 mg/L + TDCs
7-2 mg/L 8-2 mg/L + TDCs
Historical
0
40
80
60
20
120
100
160
140
Figure 16. Historical nitrate loading from on-site
wastewater systems and eight nitrate loading scenarios
tested with the study-area model.
See table 6 for scenario descriptions. (mg/L, milligram per
liter; TDC, transferable development credit.)
40 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Each scenario in which conventional systems were
replaced with advanced treatment systems indicated that
ground-water nitrate concentrations would peak between
2027 and 2053 (about 25–50 years after loading reduction
begins) and then decrease to their equilibrium levels. Less
time is required to reach the peak and subsequent equilibrium
concentrations for scenarios with greater reductions in loading
(table 7).
The TDC program, as defined for these scenarios,
reduced the number of homes that would use on-site
wastewater systems by shifting or transferring development
of new homes to a receiving area with centralized wastewater
treatment. Using conventional on-site systems, the 1,500
homes selected for the TDC program in the scenarios would
contribute about 21,000 lb of nitrogen annually, with each
home adding 14 lb/yr to the aquifer. This equals nearly
14 percent of the total base scenario loading of 147,000 lb/ yr.
For other scenarios, in which advanced treatment on-site
wastewater systems are used, the effect of a program like this
is diminished. For example, if advanced treatment systems
reduce effluent concentration from 46 to 10 mg N/L, the
annual loading per home is reduced from 14 to 3 lb/yr. Under
this scenario, removing 1,500 homes only reduces total
loading by 4,500 lb/yr (3 percent). The relative effectiveness
of the TDC program in reducing loading at various levels
of assumed advanced on-site system performance is shown
in figure 16. Development transfer programs (like the TDC
program) might be most effectively applied in high-sensitivity
areas, where advanced treatment on-site wastewater systems
cannot meet loading reduction goals.
Results of trial-and-error simulations show that the
capacity to receive on-site wastewater system effluent and
maintain satisfactory water-quality conditions is variable
within the study area. The capacity of any area to receive
on-site wastewater system effluent is related to many factors,
including the density of homes, presence of upgradient
residential development, ground-water recharge rate, ground-
water flow velocity, and thickness of the oxic part of the
aquifer.
Each scenario tested with the simulation model was
limited to management strategies that were applied uniformly
in the study area. Typically, this is how simulation models
must be used because as the size and complexity of the water-
quality management problem increases, the decision makers’
ability to design scenarios with management strategies that
reflect variability in the loading capacity of individual areas
is diminished. Uniform management strategies, such as
requiring all on-site wastewater systems to meet the same
nitrate reduction standards, may be more costly than variable
management strategies that account for the variability in the
nitrate loading capacity of the ground-water system. Uniform
strategies that are stringent enough to protect water quality
in some areas may be more than is needed to protect water
quality in other areas. The simulation model represents
the hydrogeologic and chemical processes that cause this
variability, and by adding optimization capability to the model,
the nitrate loading capacity of the ground-water system can be
determined for individual management areas.
Table 7. Summary of model simulation results for eight on-site wastewater management scenarios tested with the study-area model in
the La Pine, Oregon, study area.
[Acres are based on simulated nitrate concentrations in the uppermost active (saturated) model cells. Equilibrium acreages are based on simulated nitrate
concentrations at end of simulation (2139). Peak acreages are based on simulated nitrate concentrations in the year when the highest concentrations occur for
each scenario. Abbreviations: TDC, transferable development credit; mg N/L, milligram nitrogen per liter; lb/yr, pound per year; mg/L, milligram per liter;
Symbol: –, no data]
Scenario
Effluent
recharge
concentration
(mg N/L)
TDC
Equilibrium Peak
Equilibrium
nitrate
loading
(lb/yr)
Reduction in
loading from
scenario 1
(percent)
Acres greater
than 10 mg/L
at equilibrium
Reduction
from
scenario 1
(percent)
Acres greater
than 10 mg/L
at peak
Reduction from
scenario 1
(percent)
Peak
concentration
year
1 46 No 147,000 –9,398 –9,398 –2139
2 46 Yes 125,000 15 7,317 22 7,317 22 2139
3 20 No 65,300 56 1,909 80 1,944 79 2053
4 20 Yes 55,900 62 1,433 85 1,456 85 2049
5 10 No 34,200 77 700 93 1,233 87 2038
6 10 Yes 29,500 80 619 93 1,153 88 2035
7 2 No 9,200 94 115 99 975 90 2027
8 2 Yes 8,300 94 109 99 975 90 2027
Nitrate Fate and Transport Simulation Models 41
OR19-0049_fig17
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES
L
A
K
E
KLAMATH
Spring
River
Fall
River
Cresc
e
n
t
Creek
Creek
Little
De
s
c
h
u
t
e
s
DE
S
C
H
U
T
E
S
RIV
E
R
Ri
v
e
r
Pauli
n
a
Lo
n
g
C
r
e
e
k
5 KILOMETERS
5 MILES0
0
Wickiup
Reservoir
97
97
31
31
Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
Extent of
s
t
u
d
y
a
r
e
a
m
o
d
e
l
EXPLANATION
Nitrate concentration, in milligrams N per liter
0
5
10
20
50
100
Figure 17. Simulated equilibrium ground-water nitrate concentrations near the water table for the base scenario (scenario 1,
table 6) in the La Pine, Oregon, study area. (Colors indicate maximum nitrate concentration in vertical dimension.)
42 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
OR19-0049_fig18
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES
L
A
K
E
KLAMATH
Spr
i
n
g
Riv
e
r
Fall
River
Cresc
e
n
t
Creek
Creek
Little
De
s
c
h
u
t
e
s
DE
S
C
H
U
T
E
S
RIV
E
R
Ri
v
e
r
Pauli
n
a
Lo
n
g
C
r
e
e
k
5 KILOMETERS
5 MILES0
0
Wickiup
Reservoir
97
97
31
31
Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
Extent of
s
t
u
d
y
a
r
e
a
m
o
d
e
l
EXPLANATION
Nitrate concentration, in milligrams N per liter
0
5
10
20
50
100
Figure 18. Simulated equilibrium ground-water nitrate concentrations near the water table for 20 milligrams N per liter advanced
treatment on-site wastewater systems (scenario 3, table 6) in the La Pine, Oregon, study area. (Colors indicate maximum nitrate
concentration in vertical dimension.)
Nitrate Loading Management Model 43
Nitrate Loading Management Model
The study-area simulation model was linked to
optimization methods to produce the Nitrate Loading
Management Model (NLMM). This section includes a
description of how the management model was formulated,
how it is solved, and how it can be used to evaluate alternative
strategies for managing nitrate loading to the shallow ground-
water system.
Formulation of Nitrate Loading Management
Model
To use optimization methods, management goals must
be formulated into a mathematical structure. The structure
of an optimization problem has three components that must
be defined: decision variables, an objective function, and
constraints.
One inherent value of the optimization approach is that
its use requires decision makers and stakeholders to quantify
planning goals and objectives as well as environmental
and other constraints. The La Pine NLMM was formulated
through a close collaboration with Deschutes County planners
and resource managers. The management objective of the
NLMM, to minimize the reduction from base scenario
nitrate loading from on-site wastewater systems, reflects the
goals of: (1) allowing as many platted lots as possible to be
developed under current development goals and policies,
and (2) minimizing the required reduction in nitrate loading
from existing on-site systems. Because costs are associated
with reducing loading either by not allowing development
or using advanced treatment on-site wastewater systems, the
management objective can be simply stated as “minimize
the cost” of meeting water-quality goals. The water-quality
goals are constraints on the management model and have
direct and quantifiable effects on the solution (or cost) and
their values often reflect regulatory requirements or economic
and community values. If regulatory standards apply, the
process of setting water-quality constraints is straightforward.
However, if less well defined economic or community values
are to be the basis for water quality constraints, then a trade-
off analysis is a common process for finding the balance
(or evaluating the relations) between costs and economic,
aesthetic, health, environmental, and other benefits. The
management model can assist in this process by quantifying
the relationships between constraints and management
objectives.
The NLMM was formulated mathematically to minimize
the reduction in nitrate loading (or cost of reduction) from
base scenario loading, subject to constraints on minimum
reductions in ground-water nitrate concentrations (relative to
base scenario), minimum reductions in ground-water discharge
nitrate loading to streams (relative to base scenario), and
minimum and maximum loading reductions for existing and
future homes in each management area.
The decision variables in the La Pine NLMM were the
reduction in nitrate loading (relative to base scenario nitrate
loading rates) that would be needed to maintain or achieve
desired water-quality conditions. See table 6 for a description
of the base scenario. (Nitrate loading rates were specified
using metric units [kilograms per day] in the NLMM and
these units are used in the following description of the model
for consistency.) To define decision variables, the study area
was divided into 97 management areas. The basic unit for
the management areas was a 160-acre area (quarter-section)
based on the Public Land Survey System. With the goal of
making the base scenario loading in each management area
approximately equal, as many as four quarter-sections (640
acres) were combined to form management areas in areas
with lower lot density. The average number of lots in each
management area was approximately 100 (fig. 19). The
model had 194 decision variables, NRi,j, because two decision
variables were defined for each management area: loading
reduction (kilograms per day, kg/d) for existing homes and
loading reduction for future homes. About 350 homes and lots
were not included in the NLMM because they were in low
density areas. These homes and lots represented only 7 kg/d of
the total base scenario loading.
The objective function of the NLMM was to minimize
the reduction in loading (from the base scenario), and is given
as
minimize uNR
NM
jij
j
NT
i
NM
,,
= =
∑ ∑
1 1
where
is the number of managemment areas,
is the number of management area types, whicNTh h
can be either 1 for existing homes or 2 for
future homes, and
is a dimensionless unit cost factor for nitrate
load
u j
iing reduction from existing or future homes.
(1)
Constraints on Ground-Water Nitrate
Concentration
The value of the objective function was limited by a set of
constraints on minimum reductions (relative to base scenario)
in ground-water nitrate concentrations, minimum reductions
(relative to base scenario) in ground-water discharge nitrate
loading to streams, and minimum and maximum loading
reductions to the aquifer for existing and future homes in each
management area.
44 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
OR19-0049_fig19
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES
L
A
K
E
KLAMATH
Sp
r
i
n
g
Ri
v
e
r
Fall
River
Cresc
e
n
t
Creek
Creek
Little
De
s
c
h
u
t
e
s
DE
S
C
H
U
T
E
S
RIV
E
R
Ri
v
e
r
Pauli
n
a
Lo
n
g
C
r
e
e
k
5 KILOMETERS
5 MILES0
0
Wickiup
Reservoir
97
97
31
31
Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
Ex
t
e
n
t
o
f
s
t
u
d
y
a
r
e
a
m
o
d
e
l
EXPLANATION
Management area
Location of homes
Existing (1999)
Future
Ground-water quality constraint location
See figure 20for details
Figure 19. Locations of management areas and ground-water nitrate concentration constraint locations in the Nitrate Loading
Management Model for the La Pine, Oregon, study area.
Nitrate Loading Management Model 45
Minimum reductions in ground-water nitrate
concentration constraints were set at 339 locations in the
simulation model. The minimum reduction values were
determined by simulating the base scenario equilibrium
concentration at each location and computing the reduction
necessary to meet a specified concentration value. For
example, if the base scenario nitrate concentration were
calculated by the simulation model to be 23 mg N/L and the
maximum allowable concentration was 7 mg N/L, then the
minimum reduction constraint at that location would be 16 mg
N/L.
Constraints were set at one or two locations in the
simulation model for each management area. One point was
selected to be sensitive to loading from existing homes and
another point was selected to be sensitive to loading from
future homes in the management area. The most sensitive
locations for existing and future loading were determined by
simulating loading only from existing or future homes in a
management area and determining the location (cell) in the
model where the highest simulated concentrations occurred.
If the same location were most sensitive to both existing and
future loading from a management area, then only one location
was set for that management area.
The model simulates three-dimensional flow and
transport; therefore, nitrate concentrations can vary with
depth. To account for the variation in concentration with
depth, shallow and deep constraints were specified at most
locations. The shallow constraint was specified 5–10 ft below
the water table (an average of 20 ft below land surface) and the
deep constraint was specified immediately above the suboxic
boundary (an average of 50 ft below land surface). Four
unique constraints (one shallow and one deep for both existing
and future homes) specified in each management area for each
of the 194 locations where concentration was constrained
would have required specified constraints in 388 model cells.
However, forty-nine locations were eliminated because the
same location was sensitive to loading from both existing and
future homes, and some cells were eliminated because the oxic
ground-water layer was only two cells thick and only one cell
was used. In all, there were 339 concentration constraint cells
at 174 locations in the NLMM (fig. 19).
Mathematically, the minimum ground-water
concentration reduction constraints were specified as
CRmink ≤ CRm,k,. (2)
The minimum concentration reduction was computed as
CRminm,k = Csqm,k – Cmaxk, (2a)
The effect of loading from the 350 homes and lots not
included in the NLMM was accounted for by simulating
equilibrium concentrations throughout the model that resulted
from base scenario loading at these 350 locations. The
resulting concentrations at each constraint site were used to
adjust the CRminm,k values at each site.
Constraints on Discharge of Nitrate from Ground
Water to Streams
The simulation model results indicated that nitrate from
on-site wastewater systems can reach streams through ground-
water discharge. Because the addition of nitrate to streams
could have a deleterious effect on stream quality, the NLMM
was configured to allow constraints on the amount of nitrate
discharged to streams. Constraints on minimum reduction
in discharge of nitrate from ground water to streams were
specified for 14 reaches on the Deschutes and Little Deschutes
Rivers. The minimum reduction values were determined
by simulating the base scenario equilibrium ground-water
discharge nitrate loading to each reach and computing the
reduction necessary to meet a specified discharge constraint.
For example, if the base scenario ground-water discharge of
nitrate to a reach was determined to be 3 kg/d and the specified
discharge constraint (maximum allowable discharge of nitrate)
was 1 kg/d, then the minimum reduction for that reach would
be 2 kg/d. Mathematically, the minimum reduction in ground-
water discharge nitrate loading to stream constraints were
specified as
DRminr ≤ DRr (3)
The minimum discharge loading reduction was computed as
DRminr = Dsqr – Dmaxr (3a)
Constraints on Reduction of Nitrate Loading
Minimum and maximum nitrate loading reduction
constraints were specified in the NLMM. Mathematically the
constraints were expressed as
NRminj ≤ NRj ≤ NRmaxj, (4)
where NRminj and NRmaxj are minimum and maximum
loading reduction constraints for existing (j=1) and future
(j=2) homes (units of kg/d). The loading reduction constraints
establish minimum or maximum loading reduction constraints
on either existing or future homes.
46 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Response-Matrix Technique for Solution of
Nitrate Loading Management Model
The optimization method used to solve the NLMM is
based on a widely applied technique for solving ground-water
management problems called the response-matrix technique.
The assumption that must be satisfied to use this technique
is that the nitrate concentrations at each constraint site are a
linear function of the loading rates in each management area.
By assuming linearity, determining the nitrate concentration
or ground-water discharge loading rate to streams is possible
at any location where a constraint is specified by summing
the contribution of loading in each management area to the
concentration or discharge at that location. The response-
matrix technique is described in detail by Gorelick and others
(1993) and Ahlfeld and Mulligan (2000). The response-
matrix approach has been used to solve ground-water waste-
management problems similar to the problem evaluated in this
work by Moosburner and Wood (1980), Gorelick (1982), and
Gorelick and Remson (1982).
The assumption that simulated nitrate concentration
and discharge nitrate loading to streams is a linear function
of loading to the aquifer was tested through a series of
simulations. The loading rate to a single management area
was varied in each simulation and the computed nitrate
concentrations at several constraint locations (model cells)
were recorded. When loading rate was plotted against
concentration for each location, the relation was shown to be
linear.
One requirement of this technique is that the effect of the
sources of nitrate loading on the ground-water velocity field
is known because the mass loading of nitrate is the product
of the nitrate concentration and hydraulic loading rate of the
on-site wastewater systems. Previous workers have assumed
that for concentrated pollutant sources, the source-water flow
rate (hydraulic loading rate) has a negligible influence on
the ground-water velocity field (Gorelick, 1982; Gorelick
and Remson, 1982). This also is the assumption used for this
study, where recharge from on-site wastewater systems to, and
domestic water-supply well withdrawals from, the shallow
aquifer are nearly equal, and both are small relative to natural
recharge rates. Therefore, the ground-water velocity field
without the influence of on-site wastewater systems as sources
of recharge was used to simulate transport.
Use of the response-matrix technique requires that
response functions for ground-water nitrate concentrations and
ground-water discharge of nitrate to streams are calculated at
each of the 339 model cells where concentration constraints
were specified and the 14 stream reaches where ground-water
discharge of nitrate was constrained. The response functions
were calculated by making 194 simulations, one for each
decision variable (97 management areas, each with decision
variables for loading reduction for existing and future homes).
The response to base scenario loading from either existing or
future homes in a single management area was simulated. The
spatial distribution of loading within each management area
was at the resolution of a model cell—500 ft in the x- and y-
dimensions. The purpose of these simulations was to compute
the change in concentration at each constraint location caused
by a unit change in loading at the location represented by
the decisions variable. Calculation of the unit change in
concentration was made using initial nitrate concentrations
of zero and simulating equilibrium concentrations. The base
scenario loading rates (kg/d) for existing and future homes
in management area i and type j were defined as Nsqi,j.
Concentration response coefficients, rc i,j,m,k, were computed as
rc C
Nijmk
mk
ij
sq
sq,,,
,
,
,= (5)
Ground-water discharge nitrate loading response coefficients,
rd i,j,r, for each stream reach were computed as
rd D
Nijr
r
ij
sq
sq,,
,
,= (6)
Units of milligrams per liter per kilogram per day were
used for concentration response coefficients and ground-
water discharge nitrate to stream response coefficients are
dimensionless. The magnitude of the response coefficient
is directly proportional to the sensitivity of the nitrate
concentration or discharge nitrate loading at a constraint site to
loading in a management area. This relation is illustrated for
the concentration constraint site 31-E-S (fig. 20), which is the
shallow concentration constraint site selected for its sensitivity
to loading from existing homes in management area 31.
Management area 31 is adjacent to the west bank of
the Little Deschutes River, approximately 1 to 1.5 mi north
of Burgess Road (fig. 20). The linear response coefficients,
rc i,j,k,m, for several nearby management areas and types of
homes (existing or future), show that loading in management
areas 31, 32, 50, 51, 52, and 53 significantly affect the
nitrate concentration at constraint location 31-E-S (table 7).
Management areas 48, 49, 63, and 64 have lesser effects.
Response coefficient values (table 8) indicate that the nitrate
concentration at site 31-E-S is not a simple function of the
number of homes in management area 31 or the distance
from the site to adjacent management areas. Table 8 shows
that the largest influence on concentration at point 31-E-S is
from future homes in area 31, followed by existing homes
in areas 31 and 50, future homes in areas 50 and 51, and
existing homes in area 51. Response coefficients indicate that
management area 32, the closest area to site 31-E-S, has less
influence on concentration than more distant areas because of
the direction of ground-water flow through the area (toward
the Little Deschutes River) and the location of site 31-E-S in
relation to homes in area 32.
Nitrate Loading Management Model 47
Assuming the system is linear, the reduction in nitrate
concentration, CRm,k , at constraint location m and depth k can
be calculated with the concentration response coefficients by
summation of the individual concentration reductions caused
by reductions in loading to existing and future homes in each
management area. The summation is written as
CR rc NRmkijmkij
j
NT
i
NM
,,,,,.=
= =
∑ ∑
1 1
(7)
OR19-0049_fig20
Base modified from U.S. Geological Survey
1:500,000 state base map, 1982 with digital data from U.S. Bureau
of the Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line Graphs published at 1:100,000
Publication projection is Lambert Conformal Conic
Standard parallels 42º20' and 44º40', central meridian -120º30'
Datum is North American Datum of 1983
R
1
0
E
R
9
E
R
1
0
E
T 21 S
T 22 S
Litt
l
e
De
s
c
h
u
t
e
s
Ri
v
e
r
0 1 MILE
0 1 KILOMETER
43°45'
121°35'32'30”121°30'
43°42'30”
EXPLANATION
Management area
Line of equal simulated water table elevation— In feet above NAD83. Contour interval is 10 feet
Location of homes
Existing (1999)
Future
Nitrate concentration constraint location 31-E-S
4220
97
Burgess Road
4
2
0
0
4
2
6
0
4
2
5
0
42
4
0
4220
42
3
0
4210
422
0
42
1
0
420
0
41
9
0
67
66 56
58
57 61
62
65 54
74
64
63
53
52
51 50
32
31
26
35
55 36
25
4948
44
46 45
47
43
41
42
30
29
27
Similarly, the reduction in ground-water discharge nitrate
loading to streams, DRr, can be calculated with the discharge
loading response coefficients by summation of the individual
discharge loading reductions caused by reductions in loading
to existing and future homes in each management area. The
summation is written as
DR rd NRrijrij
j
NT
i
NM=
= =
∑ ∑,,,.
1 1
(8)
Figure 20. Locations of management areas near Burgess Road and management area 31 in the La Pine, Oregon, study area.
48 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
These summations include 194 terms because there
are 97 management areas (NM) and 2 loading types (NT),
existing and future homes, in each management area. In each
summation, however, many terms are equal to zero because the
response coefficients are zero; this occurs when concentration
or discharge loading at a constraint location does not affect
loading in a management area.
The response matrix was prepared by running one
simulation for each decision variable in which loading
was applied only at the locations defined for that decision
variable (for example, existing homes in management area
31). The loading rate and resulting concentrations at each of
the constraint locations were used to compute the response
coefficient at each constraint location using equations 5 and 6.
A set of utility programs and scripts were developed to run the
194 simulations, extract the simulated concentration values at
constraint sites, compute the response coefficients, and format
the coefficients into a matrix for input to the optimization
program.
Table 8. Response coefficients relating the effects of loading in
nearby areas to the nitrate concentration at a constraint location
in management area 31 in the La Pine, Oregon, study area.
[Management area: 31—site 31-E-S in figure 20. Response coefficients are
in milligrams per liter per kilogram per day loading]
Management
area Type Response
coefficient
31 Future 14.85
50 Existing 11.10
31 Existing 9.92
50 Future 8.85
51 Future 3.49
51 Existing 3.07
32 Future 1.71
52 Future 1.56
52 Existing 1.31
53 Existing 0.75
32 Existing 0.74
53 Future 0.50
63 Existing 0.15
63 Future 0.15
64 Existing 0.03
64 Future 0.02
49 Existing 0.01
49 Future 0.01
48 Future 0.01
48 Existing 0.01
Response coefficients are the link between the simulation
model and the NLMM. The response coefficients are utilized
by the NLMM by replacing CRm,k (equation 2) with the right-
hand side of equation 7 and replacing DRr (equation 3) with
the right hand side of equation 8. The constraints for reduction
in nitrate concentration and discharge loading to streams are
then written as
CR rc NRmkijmkij
j
NT
i
NM
min ,,,,,,≤
= =
∑ ∑
1 1
(9)
and
DR rd NRrijrij
j
NT
i
NM
min ≤
= =
∑ ∑,,,.
1 1
(10)
Equations 9 and 10 replace equations 2 and 3 in the
NLMM.
The modified NLMM, defined by equations 1
(objective function), 4 (loading constraints), 9 (concentration
constraints), and 10 (discharge loading constraints), constitutes
a linear program. This program was solved using the “What’s
Best!” optimization program (LINDO Systems, 2003). This
set of solvers is implemented as an add-in to Microsoft Excel.
The response matrix and constraint definitions are defined
in the spreadsheet using special functions provided in the
“What’s Best!” add-in. The NLMM can mathematically
search for the minimum nitrate loading reductions for existing
and future homes in each management area that satisfy the
constraints on nitrate concentrations in ground water and
ground-water discharge loading of nitrate to streams. The
program also identifies management problems that are not
feasible. This occurs when at least one constraint cannot be
met with any combination of decision variable values.
Application of Model
In the application of the La Pine NLMM described
here, the values of constraints were varied in a sensitivity
analysis to explore relations between constraint values and
optimal loading rates to the aquifer. The three constraint
options used in the NLMM were varied and optimal solutions
were computed to demonstrate how decision makers might
use the model in a trade-off analysis to determine the effect
of constraint values on the objective of minimizing nitrate
loading reductions. The NLMM also was used to evaluate the
influence of a cost variable that accounts for differential costs
in reducing nitrate loading from existing and future homes.
Nitrate Loading Management Model 49
Sensitivity of Optimal Solution to Water-Quality
Constraints
Ground-Water Nitrate Concentration
Ground-water concentration constraints were specified
at as many as two locations for each management area: one
location was the most sensitive to loading from existing homes
in that management area, and one location was most sensitive
to loading from future homes. In 20 management areas, the
same location was most sensitive for both existing and future
homes. A shallow constraint was specified near the water
table at each these 174 locations (fig. 19). In addition, where
the oxic part of the aquifer was greater than 10-ft thick (163
locations), a deep constraint was specified. As described in
the discussion of the model formulation, the concentration
constraint values, CRminm,k, were computed (equation 2a) as
the minimum reduction from base scenario concentration that
would be required to meet a specified concentration limit,
Cmaxk.
Concentration constraints were varied to show the
relative sensitivity of optimal loading solutions to constraints
in different parts of the aquifer system. The total nitrate
loading for existing and future homes in all 97 management
areas was summed for each optimal solution to provide a
basis for comparing the sensitivity of the solutions to values
of the concentration constraints. The NLMM was solved
using a range of 1 to 25 mg N/L for the maximum allowable
concentration values for both the shallow (Cmaxs) and deep
(Cmaxd) constraint locations. This range was selected because
it includes most of the range of values that would constrain,
or bind, the optimal solution. Binding constraints limit the
amount of loading to the aquifer. Nonbinding constraints do
not limit the loading to the aquifer system, because of their
value or location.
The NLMM was used to compute optimal nitrate
loading rates for various combinations of shallow and deep
concentration constraints (fig. 21). Optimal solutions were
most sensitive to concentration constraints in the shallow part
of the ground-water system. This result was expected because
concentrations are greatest at the water table where loading
occurs, and decrease with depth and distance downgradient
from the source. The base scenario loading used in the
NLMM was 190 kg/d (153,000 lb/yr) and, as expected, this
is the optimal loading solution for the case where there are
no constraints specified. Curve A (fig. 21) shows the effect
on optimal loading when concentrations are constrained only
in the deep part of the system. Deep constraints do not limit
optimal loading until constraint values are less than 10 mg N/L
(point C, fig. 21). Specifying a nitrate concentration constraint
of 1 mg N/L in the deep part of the aquifer limited optimal
loading to 110 kg/d (point D). Curve B shows the effect on
optimal loading when concentrations are constrained only
in the shallow part of the system. Shallow constraints limit
optimal loading throughout the range, with loading limited
to 17 kg/d at a constraint value of 1 mg N/L (point E) and
168 kg/d at a constraint value of 25 mg N/L (point F). If a
regulatory limit, such as the ODEQ “action level” of 7 mg N/L
is applied to the shallow constraints (and no deep constraints
are specified), optimal loading is reduced to 84 kg/d (point
G)—a 56 percent reduction from base scenario loading. For
comparison, if no shallow constraints are specified and 7 mg
N/L is applied to the deep constraints, optimal loading is
reduced very little, to 183 kg/d (point H). Loading sensitivity
curves also are shown in figure 21 for shallow concentration
constraint (Cmaxs) values of 5, 10, 15, 20, and 25 mg N/L;
these curves were constructed by keeping the shallow
constraint constant at the indicated value and varying the
value of the deep constraint. For example, with shallow and
deep constraints of 5 and 15 mg N/L respectively (point I),
the optimal loading is 65 kg/d. For reference, the optimal
loading for shallow and deep concentration constraints of 7
and 3 mg N/L, respectively, is 84 kg/d and plots at point J in
figure 21. The effects of more- or less-stringent concentration
constraints on nitrate loading in the shallow and deep parts of
the ground-water system can be analyzed using figure 21.
OR19-0049_fig 21
NITRATE CONCENTRATION CONSTRAINT, MILLIGRAMS NITROGEN PER LITER
0 5 10 15 20 25
OP
T
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A
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P
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D
A
Y
0
50
100
150
200
250
Unconstrained loading = 190 kg/d
Cmaxs = 25
Cmaxs = 20
Cmaxs = 15
Cmaxs = 10
Cmaxs = 5
A Deep constraints only
B Shallow constraints only
C
D
E
F
G
I
J
H
EXPLANATION
Curve A—Relation between optimal loading and values of concentration
constraints at deep locations
Curve B—Relation between optimal loading and values of concentration
constraints at shallow locations
Points C-J—Optimal loading for combinations of shallow and deep
concentration constraints
C—Deep constraints set to 10 mg N/L, no shallow constraints
D—Deep constraints set to 1 mg N/L, no shallow constraints
E—Shallow constraints set to 1 mg N/L, no deep constraints
F—Shallow constraints set to 25 mg N/L, no deep constraints
G—Shallow constraints set to 7 mg N/L, no deep constraints
H—Deep constraints set to 7 mg N/L, no shallow constraints
I—Shallow constraints set to 5 mg N/L, deep constraints set to 15 mg N/L
J—Shallow constraints set to 7 mg N/L, deep constraints set to 3 mg N/L
Figure 21. Sensitivity of optimal loading solutions to
ground-water nitrate concentration constraints in the La
Pine, Oregon, study area.
50 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
These results can be used to assess trade-offs in
protection of water quality in the shallow and deep parts of the
aquifer. Few wells in the La Pine area are open to the upper
10 ft of the aquifer where the shallow constraints are specified.
Using these results, decision makers could evaluate the cost, in
terms of reduced loading, of protecting the shallowest part of
the system (within 10 ft of the water table) to the same degree
as the deeper part of the system (30–50 below the water table),
where most domestic wells obtain water.
Ground-Water Nitrate Discharge Loading to Streams
Fourteen stream reaches were defined where constraints
could be applied to ground-water nitrate discharge loading.
As described in the discussion of the model formulation, the
discharge loading constraint values, DRminr, were computed
(equation 3a) as the minimum reduction from base scenario
discharge loading that would be required to meet a specified
limit, Dmaxr. The beginning and end of each reach were
selected to coincide with confluences or road crossings.
The purpose of this analysis was to demonstrate how the
NLMM can be used to conjunctively manage water quality of
ground-water and surface-water resources using optimization
techniques. Discharge loading constraints were specified
by setting a minimum percent reduction from base scenario
ground-water discharge loading to streams. To determine
the sensitivity to discharge loading constraints, the percent
reduction was varied from 0 to 99 percent. Two sets of
solutions were computed with NLMM: 1) with no constraints
on ground-water concentrations, and 2) with shallow and
deep ground-water concentration constraints of 7 and 3 mg
N/L. Without concentration constraints, the discharge loading
constraint directly limited the loading to streams as would
be expected based on the formulation of the model (fig. 22).
However, with the limitations imposed on loading by
concentration constraints (7 and 3 mg N/L), discharge loading
constraints had no effect on loading to streams until the
constraint values were greater than about 50 percent reduction
(fig. 22). At values greater than 50 percent, most loading
reductions required to meet this constraint are needed in the
management areas adjacent to streams, where, according to
simulation results, shallow ground-water flow paths through
the thin oxic part of the ground-water system are connected to
the streams. With no concentration constraints and discharge
loading to streams constrained to a minimum reduction of
97 percent, the total loading to the system is about 100 kg/d.
By comparison, constraining concentration to 7 and 3 mg N/L
(shallow and deep, respectively) and constraining discharge
loading reduction to at least 97 percent requires that total
loading be reduced to about 40 kg/d (fig. 22). The additional
reduction in total loading required to meet the ground-water
concentration constraints, 60 kg/d, reflects the additional
costs of management strategies designed to protect both
ground-water quality and stream quality.
These results can be used to assess trade-offs in the
protection of surface-water quality. To make decisions on
the values of discharge constraints, the processes affecting
nitrate as it is transported through the near stream and riparian
environments need to be better understood (Hinkle and others,
2007b). The simulation model uses simple assumptions
regarding the fate and transport of nitrate in this part of the
ground-water system and the estimates of ground-water
discharge of nitrate to streams should be considered the upper
limits of possible discharge.
Sensitivity of Optimal Solution to Nitrate Loading
Constraints
Minimum and maximum loading reduction constraints,
NRmin and NRmax in equation 4, can be specified for existing
or future homes in the NLMM. The constraints are computed
as a percentage of the base scenario loading for the existing
or future homes in each management area. For example, if
base scenario loading for future homes in a management area
is 2 kg/d, and the desired loading reduction is a minimum of
25 percent of status-quo build-out loading, then NRmin would
be equal to 0.5 kg/d.
OR19-0049_fig 22
MINIMUM REDUCTION IN DISCHARGE LOADING TO STREAMS, PERCENT
0 20 40 60 80 100
NI
T
R
A
T
E
L
O
A
D
I
N
G
,
K
I
L
O
G
R
A
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S
N
P
E
R
D
A
Y
0
50
100
150
200
Total loading, without concentration constraints
Total loading, with concentration constraints
Discharge to streams, without concentration constraints
Discharge to streams, with concentration constraints
EXPLANATION
Figure 22. Sensitivity of optimal loading solutions to
constraints on the minimum reduction in ground-water
discharge loading to streams in the La Pine, Oregon, study
area.
Nitrate Loading Management Model 51
In this example, the loading constraints were used to
evaluate how specifying minimum nitrate reduction standards
for future homes would affect the overall loading and the
proportion of loading from existing homes. As formulated,
the NLMM also offers the ability to specify other constraints
on loading reduction, such as maximum loading reduction
for either future of existing homes. This type of constraint
could be used to reflect the limitations of alternative
treatment systems to reduce loading by more than a specified
percentage.
Optimal solutions were computed in which the minimum
reduction constraint for future homes varied and all other
constraints were constant. Ground-water concentration
constraints of 7 and 3 mg N/L were specified for the shallow
and deep sites, respectively, and ground-water discharge
nitrate loading to streams was unconstrained. All existing
on-site wastewater systems in the study area are assumed to
discharge effluent with 46 mg N/L nitrate, and this was the
performance level used to compute the base scenario loading
of 190 kg/d. Maximum loading reduction constraints were
96 percent of base scenario loading for both existing and
future homes; this constraint reflects the assumption that
the best attainable on-site wastewater system performance
is 2 mg N/L. The minimum loading reduction constraint
for future homes was specified on the basis of assumed
performance standards for on-site wastewater systems that
ranged from 2 to 46 mg N/L concentration in effluent that
recharged the ground-water system. Thus, in this series of
solutions, the 46 mg N/L performance level was the equivalent
of zero reduction from base scenario loading. The other
performance levels used were 2, 10, 20, and 30 mg N/L,
corresponding to minimum loading reductions of 96, 78, 57,
and 35 percent, respectively (fig. 23).
Under base scenario conditions, existing and future
homes will contribute 104 and 86 kg/d, respectively, to the
total loading of 190 kg/d. The results of this analysis show that
as the minimum loading reduction constraint for future homes
is increased from 0 to 96 percent, optimal loading from future
homes decreases from 38 to 3 kg/d and the associated total
loading decreases from 84 to 58 kg/d.
The reduction in loading to the aquifer from future homes
implemented using a minimum reduction constraint allows
higher loading rates to be maintained from existing homes
while still meeting concentration constraints. If no loading
reduction is required for future homes, loading from existing
homes will have to be reduced by 56 percent (from 104 to
46 kg/d). By requiring improved performance of on-site
wastewater systems in future homes, there is less need for
loading reduction from existing homes. For example, if a
96 percent reduction requirement is imposed for future homes,
loading from existing homes would have to be reduced by only
47 percent to meet ground-water concentration constraints
of 7 and 3 mg N/L for shallow and deep parts of the aquifer.
If it were less costly to reduce loading from future homes
by installing advanced treatment on-site wastewater systems
than requiring existing homes to be retrofitted with advanced
treatment on-site wastewater systems, then using this type of
constraint in the NLMM would allow planners to incorporate
specific on-site wastewater system performance standards for
future homes into the optimal solution.
Sensitivity of Optimal Solution to Cost Factors
The simulation model accounts for the physical and
geochemical complexities of the ground-water system and
this information is available to the NLMM through the
response coefficients that were computed using the study
area simulation model. Other variables (external to the
simulation model) also can be important in determining the
optimal nitrate loading solution. The cost of implementing
management strategies is the most common external variable
that affects management decisions. In many optimization
problems, the objective is to minimize the cost of satisfying
the constraints on the problem.
OR19-0049_fig 23
MINIMUM REQUIRED REDUCTION IN NITRATE LOADING
FROM NEW HOMES, IN PERCENT
0 35 57 78 96
OP
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A
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0
20
40
60
80
100
Existing homes
Future homes
Figure 23. Sensitivity of optimal solution to minimum
decentralized wastewater treatment performance
standards for future homes in the La Pine, Oregon, study
area.
52 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Reducing loading from on-site wastewater systems can
incur significant costs whether by limiting housing density
or installing and maintaining advanced treatment on-site
wastewater systems. The cost factor of reducing nitrate
loading, uj in equation 1 of the NLMM, can be used to account
for differences in cost for existing and future homes. If the
cost of nitrate reduction varies among decision variables in
other ways, such as geographically, cost variables can be
specified for individual management areas.
The sensitivity of the La Pine NLMM to differences in
the cost of reducing nitrate loading from existing and future
homes was evaluated by computing the optimal loading
solutions for a range of unit cost ratios. Arbitrary cost factors
were specified that resulted in ratios of existing to future unit
costs ranging from 0.11 (1:9) to 9.0 (9:1). For example, for
a cost ratio of 0.11, the cost factors for existing and future
loading reduction were 1 and 9, meaning that it was 9 times
more costly to reduce nitrate loading from future homes. To
define the extremes, two additional solutions were computed
in which the unit cost was set to zero, first for existing, and
then for future homes. The only constraints were ground-water
concentration constraints of 7 and 3 mg N/L for the shallow
and deep sites. The loading from existing and future homes for
each cost ratio are shown in figure 24.
The highest optimal total loading (84 kg/d) occurs when
the cost ratio (existing:future) is 1.0 (costs are equal). As the
ratio increases or decreases to favor reductions in future or
existing homes, respectively, the optimal balance in loading is
affected because the objective function (to minimize cost) is
most efficiently reduced by eliminating loading from homes
that have the lowest cost per unit reduction. As the cost ratio
increases or decreases from 1.0, the total loading that can
be maintained decreases because cost variables now act as
weighting factors that partially determine which management
areas and home types will have reduced loading. It is not likely
that the ratio of unit costs would fall outside the range of 0.43
to 2.33, within which the effect on total loading is relatively
small. The relative contributions to loading from existing and
future homes, however, do vary significantly within this range.
This indicates that wherever possible, true cost factors should
be incorporated into the NLMM to account for this important
external variable.
Spatial Distribution of Loading for Optimal
Solution
The NLMM computes the minimum loading reduction
needed from existing and future homes in each management
area to achieve the water-quality goals prescribed by a
constraint set. To illustrate the variation in optimal loading
between management areas, optimal reductions in loading
rates to each management area from both existing and future
homes were mapped for a specific set of constraints. The
constraints for this solution included (1) ground-water nitrate
concentrations could not exceed 7 mg N/L at shallow locations
and 3 mg N/L at deep locations, and (2) the maximum loading
reduction possible for either existing or future homes was 96
percent. The ground-water concentration limits were selected
to reflect the goals of minimizing loading reductions and
insuring protection of the part of the aquifer (30 to 50 ft below
the water table) where most domestic wells obtain water. The
96 percent limit on loading reduction is consistent with data
from the La Pine NDP that show that the best-performing
advanced treatment on-site wastewater systems tested are
capable of reducing nitrogen to about 2 mg N/L as nitrate in
effluent leaving the drain field. No constraints were placed on
discharge of nitrate to streams or minimum loading reduction
and no differential cost factors were included.
The optimal minimum reductions vary over a broad
range in the 97 management areas. The breadth of the range
is a reflection of the complex relations between development
location and density, hydrogeology, and geochemical
processes. For the specified constraints, the optimal reduction
in total loading is 107 kg/d, or 56 percent of the 190 kg/d of
loading projected for the base scenario. Contributions to build-
out loading were reduced from 104 to 46 kg/d for existing
OR19-0049_fig 24
NITRATE LOADING REDUCTION COST RATIO,
COST OF REDUCING EXISTING HOMES LOADING/
COST OF REDUCING FUTURE HOMES LOADING
Exi
s
t
i
n
g
=
0
0.1
1
0.2
5
0.4
3
0.6
6
1.0
0
1.5
0
2.3
3
4.0
0
9.0
0
Fut
u
r
e
=
0
OP
T
I
M
A
L
N
I
T
R
A
T
E
L
O
A
D
I
N
G
,
I
N
K
I
L
O
G
R
A
M
S
N
P
E
R
D
A
Y
0
20
40
60
80
100
Higher costs for existing homesHigher costs for future homes
Loading from future homes
Loading from existing homes
EQ
U
A
L
C
O
S
T
Optimal total loading
Figure 24. Sensitivity of optimal solutions to relative cost
difference of nitrate loading reduction for existing and
future homes in the La Pine, Oregon, study area.
Nitrate Loading Management Model 53
homes and from 86 to 38 kg/d for future homes. The optimal
reductions in each management area for existing and future
homes are shown in figures 25 and 26, respectively.
Overall, the loading from existing homes was reduced
by the same proportion, 56 percent, as the loading from
future homes because there was roughly the same number of
existing and future homes (undeveloped lots) in 2000. Locally,
the reductions in loading from existing and future homes
for individual management areas often were quite different.
For example, in management area 33, where most lots had
been developed by 2000, loading from existing homes and
future homes would need to be reduced by 81 and 67 percent,
respectively (figs. 25, 26). Even fewer undeveloped lots
were in the adjacent management area 34 and the entire
loading reduction needed to meet concentration constraints
(93 percent) would need to come from existing homes.
To further validate the assumption that the simulated
nitrate concentrations and ground-water discharge nitrate
loading to streams were linear functions of nitrate loading to
the aquifer, the base scenario loading (scenario 1) was reduced
in each management area by the percentages computed using
the NLMM (figs. 25, 26). This loading was used as input to
the study-area simulation model and the equilibrium nitrate
concentrations and discharge loading to streams simulated by
the study-area model were compared to the values computed
by the NLMM at the 339 concentration and 14 discharge
loading constraint locations and reaches. The simulated
concentrations and discharge loading were equal to the values
computed by the NLMM using the response coefficients
at all constraint locations and reaches. The detailed spatial
distribution of loading reduction illustrated in this example
could be used by decision makers to delineate ground-water
protection zones and set performance standards for on-site
wastewater systems to achieve the needed loading reductions.
Comparison of Scenario Simulations and Optimal
Solution
Simulated ground-water nitrate concentrations were used
to compare the results of the scenario simulations with the
results of an optimal solution computed using the NLMM.
For the comparison, concentration values were compiled at
the 339 NLMM constraint locations (fig. 19) for four of the
scenarios simulated using the simulation model in a “trial-
and-error” mode. The four scenarios (1, 3, 5, and 7 in table 6)
specified on-site wastewater concentrations at the water table
of 46, 20, 10, and 2 mg N/L, respectively. For this analysis, a
fifth scenario using a wastewater concentration of 30 mg N/L
also was simulated. Scenario 1 was the base scenario where
conventional on-site wastewater systems yield 46 mg N/L
nitrate at the water table. The other four scenarios are based
on the assumption that all existing and future homes would
install advanced treatment on-site wastewater systems that
reduce loading to the same standard. The optimal solution
used in the comparison is that in which ground-water nitrate
concentrations could not exceed 7 mg N/L at shallow sites and
3 mg N/L at deep sites, and the maximum loading reduction
possible for either existing or future homes was 96 percent.
The relative effectiveness of the management alternatives
used in each scenario was evaluated by comparing water-
quality improvements (as measured by the percentage of
constraint locations with nitrate concentrations greater than
7 mg N/L) with reduced loading for the scenarios and the
optimal solution (fig. 27). The base scenario (no loading
reduction) resulted in equilibrium concentrations greater
than 7 mg N/L for 46 percent of the constraint locations.
Using advanced treatment systems that can produce nitrate
concentrations of 30, 20, 10, and 2 mg N/L, reduced loading
by 35, 57, 78, and 96 percent and reduced the fraction of
constraint locations where ground-water concentrations
exceeded 7 mg N/L to 36, 26, 8, and 1 percent, respectively.
The optimal solution would reduce total loading
by 56 percent, and yet had only 3 constraint locations
(<1 percent) with concentrations greater than 7 mg N/L. These
three locations were affected by a small amount of unmanaged
loading from dispersed homes not included in the NLMM.
Loading reduction for the optimal solution was 106 kg/d,
which was nearly equivalent to the loading reduction in the
20 mg N/L scenario (3), in which 26 percent of the sites had
concentrations greater than 7 mg N/L. The 10 mg N/L and
2 mg N/L scenarios (5 and 7, respectively) are approximately
equivalent to the optimal solution in reducing nitrate
concentrations in ground water. Because they apply uniform
management strategies, however, loading must be reduced by
40–69 percent more than would be required under the optimal
solution to achieve similar results.
The scenarios are based on uniform management
strategies (for example, all new homes have advanced
treatment on-site wastewater systems and all existing systems
are replaced), whereas the optimal solution implements
loading reductions only where reductions are needed to
meet quality constraints. Decision makers would unlikely
be able to implement the optimal solution exactly because it
would be difficult to have variable on-site wastewater system
performance requirements across management areas as small
as those defined in the NLMM. More likely, decentralized
wastewater treatment would be managed over larger areas that
have similar nitrate loading capacity in the NLMM solution.
This approach could increase the overall loading reduction
required to meet water-quality standards, but still be less costly
than uniform management strategies.
54 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
OR19-0049_fig25
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES
L
A
K
E
KLAMATH
EXPLANATION
Management area with numberOptimal reduction from base scenario loading— In percent
0-10
11-35
36-57
58-78
79-100
16
Spr
i
n
g
Riv
e
r
Fall
River
Cresc
e
n
t
Creek
Creek
Little
De
s
c
h
u
t
e
s
DE
S
C
H
U
T
E
S
RIV
E
R
Ri
v
e
r
Pauli
n
a
Lo
n
g
C
r
e
e
k
5 KILOMETERS
5 MILES0
0
Wickiup
Reservoir
97
97
31
31
Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
Ex
t
e
n
t
o
f
s
t
u
d
y
a
r
e
a
m
o
d
e
l
77
76
88 89
91
87
86
85
84
2483
24
81
8079
78 75
73 7172
68 69 70
67
66
93
56 58
57
61 62
65 54
74
90
64
63
53 52
51 50 32 31
26
35
55 36 34
33
25
4948
44 46 45
47 43
41
40 39 38 37
42
30
29 27
28
1494
13 12
19
22 21
95
1718
16 15
44
11
23
10
9 8
7
1 6
2 3 5
59
60
92
20
Figure 25. Optimal reduction in nitrate loading from existing homes in the La Pine, Oregon, study area.
Nitrate Loading Management Model 55
OR19-0049_fig26
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES
L
A
K
E
KLAMATH
EXPLANATION
Management area with numberOptimal reduction from base scenario loading— In percent
0-10
11-35
36-57
58-78
79-100
16
Spr
i
n
g
Riv
e
r
Fall
River
Cresc
e
n
t
Creek
Creek
Little
De
s
c
h
u
t
e
s
DE
S
C
H
U
T
E
S
RIV
E
R
Ri
v
e
r
Pauli
n
a
Lo
n
g
C
r
e
e
k
5 KILOMETERS
5 MILES0
0
Wickiup
Reservoir
97
97
31
31
Burgess Road
Drive
Finley
Butt
e
Road
R
o
a
d
South
Century
Spring
River
Masten Road
Sunriver Sunriver
La
Pine
La
Pine
43°55'
50'
45'
121°40'35'30'25'121°20'
40'
43°35'
Ex
t
e
n
t
o
f
s
t
u
d
y
a
r
e
a
m
o
d
e
l
77
76
88 89
91
87
86
85
84
2483
24
81
8079
78 75
73 7172
68 69 70
67
66
93
56 58
57
61 62
65 54
74
90
64
63
53 52
51 50 32 31
26
35
55 36 34
33
25
4948
44 46 45
47 43
41
40 39 38 37
42
30
29 27
28
1494
13 12
19
22 21
95
1718
16 15
44
11
23
10
9 8
7
1 6
2 3 5
59
60
92
20
Figure 26. Optimal reduction in nitrate loading from future homes in the La Pine, Oregon, study area.
56 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
Limitations and Appropriate Use of
Models
The transect and study-area simulation models were
developed to generate a better understanding of the fate
and transport of nitrate from on-site wastewater systems at
multiple scales. The study-area model also may be used to
help evaluate alternative options for management of nitrate
loading from on-site wastewater systems. Limitations of
the modeling software, assumptions made during model
development, and results of model calibration and sensitivity
analysis all are factors that constrain the appropriate use of
these models and highlight potential future improvements.
A simulation model is a means for testing a conceptual
understanding of a system. Because ground-water flow
systems are inherently complex, simplifying assumptions must
be made in developing and applying model codes (Anderson
and Woessner, 1992). Models solve for average conditions
(for example, head or nitrate concentrations) within each cell
using parameters which are interpolated or extrapolated from
measurements, and (or) estimated during calibration. Practical
limitations on model size, and hence minimum cell size, are
imposed by the size and speed of available computers. More
commonly, however, it is the availability of data to define the
system that limits the scale and accuracy of the model. In light
OR19-0049_fig27
46 mg/Lsystems(Scenario 1)
30 mg/Lsystems Optimalsolution 20 mg/Lsystems(Scenario 3)
10 mg/Lsystems(Scenario 5)
2 mg/Lsystems(Scenario 7)
NI
T
R
A
T
E
L
O
A
D
I
N
G
R
E
D
U
C
T
I
O
N
,
IN
K
I
L
O
G
R
A
M
S
P
E
R
L
I
T
E
R
0
50
100
150
200
PE
R
C
E
N
T
A
G
E
O
F
S
I
T
E
S
G
R
E
A
T
E
R
T
H
A
N
7
M
I
L
L
I
G
R
A
M
S
P
E
R
L
I
T
E
R
0
10
20
30
40
50
Figure 27. Comparison of loading and water quality
between optimal and nonoptimal management scenarios
for the La Pine, Oregon, study area.
of this, the intent in developing the simulation models was not
to reproduce every detail of the natural system, but to portray
its important characteristics in sufficient detail to provide a
useful tool for testing the conceptual model and evaluating
alternative management options.
Simulation Models
The study-area simulation model is a decision-support
tool for evaluating the effects of wastewater management
alternatives on ground-water and surface-water quality at the
neighborhood to watershed scale. The study area and transect
models are not capable of simulating nitrate concentrations
at individual wells; however, the transect model (which has
more than twice the lateral resolution of the study-area model)
has sufficient detail to approximately simulate the location of
nitrate plumes.
The ground-water flow system was assumed to be
at steady-state, meaning that the velocity and direction of
ground-water flow did not change with time. Water-level
variation occurs seasonally and over the long term in response
to stresses like climatic variation. The variation can change
the velocity, and possibly direction, of ground-water flow over
periods ranging from hours to years depending on the cause; a
change in river stage might affect the system for hours to days
whereas an extended drought might have effects that last for
months to years. These changes in the flow system could have
effects on the fate and transport of nitrate not represented by
the simulation models. The simulation models are designed
to evaluate the long-term effects of options for management
of nitrate loading. The models should not be used to evaluate
short-term changes without considering the possible effects
of changes in the ground-water velocity distribution from the
steady-state conditions represented in the models.
The location of the boundary between the oxic and
suboxic parts of the ground-water system was mapped based
on dissolved oxygen concentrations in 256 wells sampled as
part of a synoptic sampling of private wells by ODEQ and
Deschutes County in June 2000. Because denitrification is
assumed to occur at the oxic-suboxic boundary and nitrate
concentration below the boundary (in the suboxic zone) is
specified as zero, simulated nitrate concentrations near and
below the boundary are sensitive to location. Uncertainty in
the boundary location will result in uncertainty in simulated
nitrate concentrations. The distribution of wells used to map
the boundary was generally good for a study area this size,
however, the boundary location is less certain in some areas.
For example, there were fewer wells available to constrain the
location of the boundary near the margin of the model area and
near streams. In these areas, model results should be evaluated
with respect to the effects of uncertainty on simulated nitrate
concentrations.
Summary and Conclusions 57
The ground-water discharge to evapotranspiration process
is simulated by the study-area model and accounts for the
mass of water lost from the system where deep-rooted plants
extract ground water for transpiration and where ground
water is shallow enough to be evaporated from bare soil.
Plants also may take up nutrients dissolved in ground water;
however, the rate of uptake is highly variable and poorly
understood in non-agricultural settings. Nutrients and other
solutes are not removed by evaporation and this process
results in concentration of solutes in ground water. For this
study, there was no basis for partitioning the mass of ground
water discharged by ET into its transpiration and evaporation
components and it was assumed that no nitrate was taken up
with the mass of water discharged by ET. This assumption
may bias simulated nitrate concentrations toward high values
in areas where ET is a significant part of ground-water
discharge.
Management Model
Because the NLMM was developed using optimization
methods with the study-area simulation model, the NLMM is
subject to the same limitations listed for the study-area model.
However, additional factors should be considered when using
the management model that relate to how the management
problem is formulated.
The sensitivity analysis of the NLMM presented in this
report illustrates how closely optimal solutions are tied to the
definition of the management problem. The NLMM solutions
were shown to be highly dependent on the value of the
maximum nitrate concentration constraint and on the number,
location, and depth of specified constraints. Assignment of the
constraints is an important part of developing a strategy for
protecting ground-water resources.
The management problem for this study was formulated
with the objective of minimizing the amount of reduction
in nitrate loading that would be required to meet specified
water-quality goals within management areas. Management
area boundaries were defined using the township and section
lines of the Public Land Survey System (PLSS) and included
areas ranging from 160 to 640 acres. The management-area
boundaries do not coincide with the hydrologic, geologic,
and geochemical boundaries that control the nitrate loading
capacity of the system. The loading capacity for some
management areas may be strongly controlled by loading in
part of the area close to where constraints were specified.
Large differences in computed optimal reduction requirements
can occur across management-area boundaries even though
there may be little difference in lot densities, recharge, depth
of the suboxic zone, or other factors that affect loading
capacity. Users of the NLMM need to be cognizant of the
effects of problem formulation on results and interject
knowledge of on-the-ground conditions when using model
results to support management decisions.
Summary and Conclusions
Ground-water is an important resource in the rural
communities of southern Deschutes and northern Klamath
County, near La Pine, Oregon. The primary aquifer, and
only source of drinking water to about 14,000 residents,
comprises alluvial sand and gravel deposits within 100 ft of
land surface. Nearly 60 percent of residential lots are less
than 1 acre and almost all homes use on-site wastewater
disposal systems. Nitrate concentrations greater than the
U.S. Environmental Protection Agency drinking water MCL
of 10 mg/L were discovered in the oldest developed part of
the area in the late 1970s and elevated concentrations have
subsequently been detected in more recently developed
areas. In 2000, nitrate concentrations greater than 4 mg N/L
were detected in 10 percent of domestic wells sampled by
Oregon Department of Environmental Quality. Because of
concern for the vulnerability of the ground-water resource,
the Oregon Department of Environmental Quality and
Deschutes County, in cooperation with the U.S. Geological
Survey, conducted a study to develop a better understanding
of the hydrologic and chemical processes that affect the
movement and fate of nitrogen within the shallow aquifers of
the La Pine region. Simulation models were used to test the
conceptual understanding of the system and were coupled with
optimization methods to provide a management model that
can be used to efficiently evaluate alternative approaches for
managing nitrate loading from on-site wastewater systems.
The geologic, hydrologic, and geochemical frameworks
for the conceptual and numerical models were developed
using several data sources including previous hydrogeologic
and water-quality studies in the area, an associated, large-
scale field experiment evaluating advanced treatment on-site
wastewater systems, literature for similar studies in other
areas, and extensive field data collection for this study.
The primary aquifer in the study area is composed of
complexly interbedded fluvial silt, sand, and gravel deposits.
A three-dimensional hydrofacies model of the fluvial system
was created with transition probability geostatistical methods
using parameters derived from analysis of two-dimensional
lithologic sections and lithologic data from more than 400
drillers’ logs. Five hydrofacies were included in the final
model: clay-silt, sand, gravel, lacustrine clay-silt, and basalt.
Mean annual ground-water recharge to the alluvial aquifer
is 3.2 in/yr, primarily from infiltration of precipitation and
snowmelt. Ground-water discharges to streams, springs, and
wells, and by evapotranspiration. The water-table generally
is within 5–20 ft of land surface and varies seasonally over
a range of a few feet in response to recharge and changing
stream stage.
58 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
On-site wastewater systems are the only significant
source of anthropogenic nitrogen to shallow ground water
in the study area. Low recharge rates and ground-water
flow velocities have, for now, generally restricted nitrate
occurrence to discrete plumes within 20–30 ft of the water
table. Concentrations of nitrate typically are low in deeper,
older ground water due to the nature and timing of nitrate
loading and transport, and to loss by denitrification. Ground
water in the study area evolves from oxic to increasingly
reduced conditions with increasing depth below the water
table. Suboxic conditions are achieved in 15–30 years, and the
transition zone from oxic to suboxic ground water is narrow.
Nitrate is denitrified near the oxic-suboxic boundary. Nitrate
loading from residential, commercial, and other sources
using on-site wastewater systems was estimated for 1960–99
using county building records, census data, monitoring data
from field studies of on-site systems, and literature values.
Adjusted for seasonal residency, residential loading estimates
ranged from 12 to 14 lbs/yr per home between 1960 and
1999. During this period total nitrogen loading increased from
3,900 to 81,000 lb/yr. Nitrogen loading increased by 17,000
to 98,000 lb/yr between 1999 and 2005. When all approved
lots are developed (projected to occur in 2019 at current
building rates), nitrogen loading is estimated to reach nearly
150,000 lb/yr.
Three-dimensional numerical simulation models were
constructed at transect (2.4 mi2) and study-area (247 mi2)
scales to simulate the fate and transport of nitrate within the
shallow ground-water system. The transect model was used
to test conceptual models at the site of a detailed geochemical
investigation along a 3.5-mi long flow path within the
study area. The study-area model was constructed at a scale
appropriate as a planning tool for prediction of average nitrate
concentrations in neighborhoods and subdivisions.
Calibration of the models was constrained by data
that included measured heads, measured and estimated
ground-water discharge to streams, time-of-travel estimated
from chlorofluorocarbon age dates, and measured ground-
water nitrate concentrations. Eight scenarios representing
nitrate-loading management strategies were simulated
for the 140-year period, 2000–2139. A base scenario was
simulated which assumed existing and future homes would
continue to use conventional on-site systems and nitrogen
loading would reach the projected maximum of nearly
150,000 lb/yr in 2019. Under this scenario, simulated nitrate
concentrations continue to increase until the rate of nitrate
loading to the aquifer system is balanced by nitrate losses to
denitrification and ground-water discharge to the nearstream
environment of the Deschutes and Little Deschutes Rivers.
At equilibrium, average nitrate concentrations near the water
table exceed 10 mg N/L over areas totaling 9,400 acres.
Other scenarios were simulated that evaluated the effects of
reduced loading on water quality. Scenarios in which nitrate
loading was reduced by 15–94 percent overall resulted in
reductions of 22–99 percent in the area where average nitrate
concentrations near the water table exceed 10 mg N/L at
equilibrium. Simulated ground-water ages agree with ground-
water age data and show that the system is slow to respond
to changes in nitrate loading due to low recharge rates and
ground-water flow velocity. Consequently, reductions in
nitrate loading will not immediately reduce average nitrate
concentrations and the average concentration in the aquifer
will continue to increase for 25–50 years depending on the
amount and timing of loading reduction. The time required for
average concentrations to decrease is, in part, also due to the
assumption that replacement of existing on-site wastewater
systems would take place over approximately 50 years.
Results of the scenario simulations showed that there is
variable capacity to receive on-site wastewater system effluent.
The capacity of an area to receive on-site wastewater system
effluent is related to many factors, including the density
of homes, presence of upgradient residential development,
ground-water recharge rate, ground-water flow velocity, and
thickness of the oxic part of the aquifer.
The study-area simulation model was used to develop a
decision-support tool by incorporating optimization methods.
The resulting model, the Nitrate Loading Management Model
(NLMM), was formulated to minimize the reduction from
estimated base scenario loading that would be needed to
maintain ground-water nitrate concentrations or ground-water
discharge of nitrate to streams below specified levels. The
NLMM uses the response matrix approach to find the optimal
(minimum) loading reductions in each of 97 management
areas that will meet the specified water-quality constraints.
The sensitivity of the optimal solutions (loading reductions)
to water-quality and other constraints was evaluated by
altering constraint values. The sensitivity of optimal solutions
to constraints allows decision makers to assess tradeoffs
between higher levels of water quality protection and the cost
of reducing nitrate loading. The sensitivity analysis of the
NLMM showed that optimal (minimum) loading reductions
were most sensitive to the constraints on ground-water nitrate
concentration in the shallow part of the oxic ground-water
system, within 5–10 ft of the water table.
References Cited 59
Acknowledgments
We gratefully acknowledge the cooperation and
assistance of the hundreds of residents of southern Deschutes
and northern Klamath Counties who gave us permission to
collect geologic and water-level data from their wells, allowed
us access to their property, and provided other information
that proved invaluable to this study. This study also benefited
greatly from the dedicated efforts of many Deschutes County
Community Development Department employees; special
thanks go to Barbara Rich, Dan Haldeman, Catherine Morrow,
Todd Cleveland, Peter Gutowsky, and Tim Berg. Oregon
Department of Environmental Quality employees Bill Mason,
Diane Naglee, Robert Bagget, and Dick Nichols, also provided
valuable assistance during the study. Joe Miller, Nicholas Zerr,
and Justin Rohrbaugh, all formerly of the U.S. Geological
Survey, also are acknowledged for their valuable assistance in
collecting and compiling data for this investigation.
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of flow in groundwater systems: San Diego, Calif.,
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Allen, J.E., 1966, The Cascade Range volcanic-tectonic
depression of Oregon, in Transactions of the Lunar
Geological Field Conference, Bend, Oregon, August 1965:
Oregon Department of Mineral Industries, p. 21-23.
Anderson, C.W., 2000, Framework for regional, coordinated
monitoring in the middle and upper Deschutes River basins,
Oregon: U.S. Geological Survey Open-File Report 00-386,
81 p.
Anderson, M.P., 1987, Field studies in groundwater
hydrology—A new era: Reviews in Geophysics, v. 25, no.
2, p. 141-147.
Anderson, M.P., and Woessner, W.W., 1992, Applied ground-
water modeling: San Diego, Calif., Academic Press, Inc.,
381 p.
Bauer, H.H., and Vaccaro, J.J., 1987, Documentation of a deep
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62 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
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Appendix A 63
Appendix A. Vertical Hydraulic Head Gradient Data from Measurements Made
on the Deschutes and Little Deschutes Rivers, in the La Pine, Oregon, Study
Area, October 23– November 4, 2000.
Figure A1. Locations of vertical head gradient measurement sites in the La Pine, Oregon, study area.
OR19-0049_figA1
Base modified from U.S. Geological
Survey
1:500,000 state base map, 1982 with
digital data from U.S. Bureau of the
Census, TIGER/Line (R), 1990 and
U.S. Geological Survey Digital Line
Graphs published at 1:100,000
Publication projection is
Lambert Conformal Conic
Standard parallels 42º20' and 44º40',
central meridian -120º30'
Datum is NAD83R 9 E R 10 E R 11 E
T 21 S
T 22 S
T 23 S
T 24 S
T 20 S
T 19 S
DESCHUTES
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64 Evaluation of Approaches for Managing Nitate Loading from On-Site Wastewater Systems near La Pine, Oregon
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(1
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,
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d
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2
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.
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7
-
6
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4
3
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2
2
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1
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1
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3
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6
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3
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4
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2
4
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1
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3
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4
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5
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1
f
t
,
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l
d
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2
f
t
.
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0
-
8
N
4
3
.
6
2
8
.
7
1
-
1
2
1
.
5
8
5
.
8
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1
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4
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2
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0
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0
4
.
0
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5
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F
S
A
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M
L
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1
0
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i
l
t
>
1
f
t
,
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o
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e
l
d
a
t
2
f
t
.
L4
2
-
6
N
4
3
.
6
1
7
.
5
6
-
1
2
1
.
6
0
0
.
1
7
1
0
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2
4
-
0
0
1
.
5
4
0
3
.
0
5
0
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C
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R
ML
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1
0
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i
l
t
>
1
f
t
,
n
o
y
i
e
l
d
a
t
2
f
t
.
Manuscript approved for publication, September 29, 2007
Prepared by the USGS Publishing Network,
Publishing Service Center, Tacoma, Washington
Bob Crist
Bill Gibbs
Debra Grillo
Jackie Olson
Bobbie Jo Richey
Sharon Wahlstrom
For more information concerning the research in this report, contact
Director, Oregon Water Science Center
U.S. Geological Survey, 2130 SW 5th Avenue
Portland, Oregon 97201
http://or.water.usgs.gov
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