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HomeMy WebLinkAbout07 Chapter 3 Project DescriptionLa Pine National Decentralized Wastewater Treatment Demonstration Project Project Area Description Page 3-1 Chapter 3: Project Area Description Description of Study Area The two major unincorporated communities within the La Pine Project study area (Figure 3-1) are Sunriver and La Pine. These communities lie approximately 13 and 25 miles south of the city of Bend, respectively. The study area encompassed approximately 125 square miles and extended from Benham Falls north of Sunriver to the Deschutes County line south of La Pine. The major water bodies in the study area include the Deschutes, Little Deschutes, Fall and Spring rivers. Most development in the study area occurred in a 20-mile long corridor of US Highway 97. The area is predominantly residential with an urban density in a rural region. Most residential lots were one-half to 1 acre in size. In the northern portion of the study area, most development occurs west of the Deschutes River and between the Deschutes and Little Deschutes rivers west of US Highway 97. In the southern portion, development was predominantly west of the Little Deschutes River, with exceptions around Wickiup Junction (approximately 3 mile north of La Pine) and within La Pine city limits. A septic tank effluent, gravity discharge (STEG) sewer system was installed in the business district of La Pine in the early 1990’s. Sunriver has its own sewer system. In addition, the Oregon Water Wonderland subdivision between the Deschutes and Little Deschutes rivers just south of Sunriver and the River Meadows subdivision west of the Deschutes River and south of Oregon Water Wonderland have small community sewers and wastewater treatment facilities. Information about the nitrogen reduction capabilities of these systems was not readily available at the time of this writing. Wastewater in all remaining areas is disposed by individual onsite wastewater treatment systems. Land Use / Demographic Setting The La Pine region of central Oregon spans southern Deschutes County and northern Klamath County and includes a significant portion of the upper Deschutes River watershed. The region has inherited significant issues in the form of platted subdivisions that pre-date land use law and which include high densities that are required to be served by onsite wastewater systems and individual water supply wells. The level of services in these areas (e.g. fire, police, roads, water, and sewage) are significantly different than what a similar neighborhood in an urban are would receive. The groundwater quality in southern Deschutes County, Oregon is threatened by nitrate contamination from onsite system discharge. (Hinkle, 2007; Morgan, 2007) There are 15,000 lots of one-half to one-acre in size that were platted in the 1960s and 1970s, prior to the enactment of Oregon’s land use planning laws, located within a 125 square mile corridor near the scenic Deschutes River and the smaller Little Deschutes River. Without an understanding of the high water table or the aquifer’s water quality, and with no promise of infrastructure, these lots were marketed nationally to prospective buyers. There are currently between 5,800-6,000 improved lots in the La Pine region study area served with conventional onsite systems and individually owned drinking water wells. Most of these wells draw from the most vulnerable upper 100 feet of the aquifer. The major environmental, wildland/residential interface, and infrastructure issues facing the region were identified in a public process undertaken by Deschutes County in 1996. The Regional Problem Solving (RPS) Project laid the groundwork for the La Pine National Decentralized Wastewater Treatment Demonstration Project (La Pine Project) by investigating solutions to the issues and gaining public consensus on the appropriate course of action. Because the La Pine sub-basin of the Upper Deschutes River is underlain by a shallow unconfined aquifer that serves as the only drinking water source, a primary issue identified by the RPS project was that of protecting the region’s drinking water from the impacts of onsite wastewater systems. The county contracted with an engineering firm to study the expansion or creation of centralized sewers in the area in the late 1990’s. Public feedback to the results of the study indicated that the county should pursue an onsite wastewater treatment option because the public found sewers to be economically and socially infeasible. In addition, existing state laws limit centralized wastewater treatment systems in unincorporated areas. As a result, the Oregon Department of Environmental Quality (DEQ), in cooperation and coordination with Deschutes County and the US Geological Survey (USGS), obtained funding from the US Environmental Protection Agency (EPA) to define onsite wastewater treatment tools and mechanisms to protect the region’s groundwater. A short history of the work undertaken in the region related to groundwater protection is provided in Table 3-1. La Pine National Decentralized Wastewater Treatment Demonstration Project Page 3-2 Project Area Description Projected buildout will occur in 10 to 15 years if the 1990 to 2005 building rate continues. Based on these projections, there will be 26,000 people occupying approximately 9,700 homes served by onsite systems by 2025. Continual reliance on conventional onsite systems would cause nitrate concentrations to exceed federal and state drinking water standards (10 mg/L) over large areas within the community. Table 3-1. A timeline of groundwater protection work in the region leading to and through the La Pine Project. Year Action 1982 La Pine Aquifer Study finds high nitrate levels in the groundwater underlying what is now the city of La Pine. 1986 La Pine core area sewered (STEG system). 1994 Oregon DEQ finds increasing nitrate levels outside of the La Pine area. 1996 Deschutes County receives Regional Problem Solving grant to identify problems and evaluate solutions. 1997 Sewer feasibility study for the region 1998 Public feedback to pursue onsite systems as a solution 1999 Oregon DEQ receives $5.5 million La Pine National Demonstration Project grant 1999-2004 Field sampling to measure groundwater quality and nitrogen reducing system performance Three-dimensional groundwater and nutrient fate and transport model developed, calibrated and future scenarios run. 2005 Oregon DEQ amends state rule to allow counties to issue permits for the use of nitrogen reducing systems for individual residences. Hydrogeologic Setting The La Pine subbasin encompasses approximately 640 square miles. The Cascade Range bounds the study area on the west and the Newberry volcano on the east. Volcanic rocks form the northern and southern boundaries of the subbasin. A volcanic north-south trending ridge of small shield volcanoes and lava flows is present through the central portion of the La Pine subbasin. The soils in the region are highly porous and permeable with no intervening layer protecting the aquifer. These young pumice soils are relatively low in organic matter and show rapid downward movement of water from precipitation and septic effluent. The 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). The water table ranges in depth from less than two feet to about thirty feet below land surface. Recharge occurs from infiltration of precipitation and averages 2.0 inches per year. Groundwater discharges by way of the Deschutes and Little Deschutes Rivers, evapotranspiration, and wells. Groundwater velocities are low and, at the water table, groundwater is generally oxic. However, at depths ranging from near zero to more than fifty feet below the water table groundwater becomes suboxic, a boundary where nitrate denitrifies. Denitrification thus keeps 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 of nitrogen. (Hinkle, 2007; Morgan 2007) The La Pine subbasin consists of volcaniclastic deposits. These valley fill deposits are underlain by Miocene- Pliocene volcanic ash a substantial thickness of Quaternary valley fill sediment of alluvial (fluvial) and lacustrine (lake) origin, flow tuffs, volcaniclastic sediments, and lava flows (Sherrod and Smith, 1989). Miocene-Pliocene and Quaternary age lavas interfinger with the valley fill deposits along the subbasin margins. The valley fill sediments are covered by 3 to 5 feet of pumice from the Holocene eruption of Mount Mazama. Groundwater occurs in most of the rocks in the La Pine subbasin. The underlying bedrock of fractured lava, interflow zones, and coarse-grained volcaniclastic sediments, are generally highly productive (Caldwell, 1997). The shallow Quaternary fine to coarse sand, fine to coarse gravel and cinder fluvial deposits are particularly productive. Most wells in the study area are screened in these fluvial deposits. Less permeable silts and clays comprise much of the lacustrine deposits. In some areas of the subbasin, the lacustrine deposits overlie and are intercalated with the fluvial deposits. Lacustrine deposits are exposed in bluffs along portions of the Deschutes River (Cameron and La Pine National Decentralized Wastewater Treatment Demonstration Project Project Area Description Page 3-3 Major, 1987). Because of the intercalated and discontinuous nature of the fluvial and lacustrine deposits, the La Pine aquifer is considered unconfined. Groundwater table elevation measurements indicate groundwater flow is generally northeastward west of the Deschutes River and Northwestward east of the Little Deschutes River (Figure 3-2). In the northern portion of the study area, regional groundwater flow becomes northeastward. Stream gauging measurements for the Deschutes and Little Deschutes rivers indicated the rivers gain in flow (Friday and Miller, 1984;Moffatt, et. all, 1990; Gorman, 1996 unpublished data). The source of the gain is groundwater discharge. Spring River and Fall River originate from springs in the volcanic rocks indicating the productivity of the fractured volcanic rocks. Soils Soils have been formed on the airfall pumice deposits from the eruption of Mt. Mazama about 6,700 years ago. This pumice covers an older soil (paleosol) that developed on alluvium in the basin. The general soil profile is consistent throughout the basin and appears not to have been influenced by erosional activities except in areas adjacent to the existing river channels and within recent flood plains. The texture of the pumice material varies from that of gravelly coarse sand to a loamy (soils with rapid or very rapid permeability). The buried soil horizon which underlies the pumice deposits range from 10 inches to 3 feet thick and consist of loamy material, texture varying from fine sandy loam to silt loams. The materials, which underlie the buried soil horizons, are typically coarse-grained gravels and sands with discontinuous lenses of silt and clay, associated with the top of the alluvial deposit. A recent soil survey (NRCS, unpublished report) indicates broad areas that have a distinctive pattern of soils, relief, and drainage. Tutni-Sunriver-Cryaquolls Association occurs on pumice-mantled stream terraces and flood plains. Shanahan-Steiger and Lapine Associations occur on pumice-mantled and lava plains and hills (Figure 3-3). Tutni soils are on stream terraces. These soils are more than 60 inches deep to bedrock and are somewhat poorly drained. They have a very dark grayish brown loamy coarse sand surface layer; a mottled, dark grayish brown very gravelly coarse sand substratum; and a very dark grayish brown sandy loam buried layer. Depth to a seasonal high water table is 18 to 48 inches. Sunriver soils are on stream terraces. These soils are more than 60 inches deep to bedrock and are somewhat poorly drained. They have a very dark gray sandy loam surface layer; a mottled, light brownish gray coarse sand subsoil; and a mottled, very dark gray sandy loam buried layer. Depth to a seasonal high water table is 24 to 48 inches. Cryaquolls are on flood plains. These soils are more than 60 inches deep to bedrock and are poorly drained and very poorly drained. They have a dark brown silt, silt loam, or gravelly loamy sand surface layer; a very dark gray, mottled sandy loam, loam, silt loam, or loamy sand subsoil; and a very dark gray sand substratum. A seasonal high water table is at the surface to a depth of 24 inches below the surface. These soils are subject to rare flooding. Of minor extent in this unit are Wickiup soils on stream terraces, Steiger soils are more than 60 inches deep to bedrock and are somewhat excessively drained. These soils have a dark grayish brown loamy coarse sand surface layer, a pale yellow gravelly coarse sand substratum, and a dark yellowish brown loam buried layer. Depth to buried layer is 40 to 60 inches or more. Lapine are more than 60 inches deep to bedrock and are excessively drained soils formed in pumice and ash. These soils have a very dark grayish brown and dark brown gravelly loamy coarse sand surface layer and a very pale brown and light gray gravelly to extremely gravelly coarse sand substratum. Shanahan soils are more than 60 inches deep to bedrock and are somewhat excessively drained. These soils have a dark brown loamy coarse sand surface layer, a yellowish brown and brown loamy coarse sand and coarse sand substratum, and a dark brown loam and gravelly sandy loam buried layer. Depth to the buried layer is 20 to 40 inches. Climate According to the Oregon Climate Service, the La Pine region, which is in the rain shadow of the Cascade range, has a high desert climate. The average elevation of the La Pine region is about 4,200 feet above mean sea level. The Wickiup Dam NOAA weather station is at an elevation of 4,360 feet above mean sea level and most closely represents the La Pine region temperature and rainfall conditions. Summer (June-August) mean monthly maximum La Pine National Decentralized Wastewater Treatment Demonstration Project Page 3-4 Project Area Description and minimum temperatures for the period of 1961 to 1990 at the Wickiup Dam weather station range from 80 to 42 oF, respectively (27 to 6 °C). Winter (December – March) monthly maximum and minimum temperatures range from 46 to 17 oF (8 to –8 °C). Extreme temperatures are not unusual for the region, ranging from >100 to –30 oF (>38 to –34 °C). Monthly maximum and minimum precipitation for summer and winter ranges from <0.7 inches to >3.68 inches. The mean annual precipitation ranges between 14 and 21 inches. Snowfall during winter months is common with monthly means of 19 to 22 inches. The frost free period can vary from 10 to 50 days. Figure 3-1: Study area La Pine National Decentralized Wastewater Treatment Demonstration Project Project Area Description Page 3-5 1720000 1740000 1760000 gp y 1720000 1740000 1760000 Oregon Stateplane Coordinate System (Easting) -40000 -20000 0 20000 40000 60000 80000 100000 Oregon stateplane Coordinate System (Northing)-40000 -20000 0 20000 40000 60000 80000 100000 4265 42494250 4245 4225 4227 4219 42184203 4219 4230 4229 4225 4196 4212 4219 4211 4212 4196 4184 4179 42644265 4177 4177 4174 4183 4170 4166 4167 4169 4169 4185 416441654161 4158 4165 4156 4136 4261 4242 4217 4223 4220 4224 4232 4221 4226 4214 4195 4161 4168 4201 4198 4152 4183 4175 4186 4207 4206 4210 4217 4200 4241 4213 4195 Masten Rd. Burgess Rd. Pringle Butte SouthSouth Century Rd.S. Century Rd. State Park Rd. Anns Butte Pistol Butte Sitkum Butte La Pine Wickiup Jct. Sunriver R11ER10ER9E M2 M2' Flowpath modelling cross-section Oregon Department of Environmental Quality Symbols T23S T22S T21S T20S T19S Benham Falls Model Boundary 43o55'00"43o55'00" 121o22'30"121o37'00" 43o32'30"43o32'30" 121o22'30" Sunriver-La Pine Groundwater Modelling Study N 121o37'30" 1994 SHALLOW GROUNDWATER STATIC LEVEL ELEVATIONS Model study area boundary Shallow wells (50 feet deep) with static water level elevation (feet above msl) 4 2 4 0 Shallow static water level elevation contour (feet above msl); contour interval is 5 feet; measured 9/94 4240ModelBoundary Scale: Oregon Stateplane Coordinate System - North (in Feet) La Pine State Park M1 M1' M2 M2' File: Gw-contr(5-15-98) May 1998 Figure 3-2. Groundwater table based on 1994 synoptic water level measurements. La Pine National Decentralized Wastewater Treatment Demonstration Project Page 3-6 Project Area Description 1680000 1700000 1720000 1740000 1760000 1680000 1700000 1720000 1740000 1760000 Oregon Stateplane (North) Coordinate System -40000 -20000 0 20000 40000 60000 80000 100000-40000 -20000 0 20000 40000 60000 80000 100000Oregon Stateplane Coordinate System -North (Northing in Feet)Sunriver 1 1 2 2 2 2 1 3 Key Tutni-Sunriver-Cryaquolls Association1 2 Shanahan-Steiger Association 3 Lapine Association Study Area Boundary La Pine Basin General Soil Map Grid: Oregon Stateplane- North Coordinate System (in Feet) Base Map: MacLeod and Sherrod, 1992, Reconnaissance geologic map of the west half of the Cresent 1o by 2o Quadrangle, central Oregon, USGS Map I-2215. Deschutes County Environmental Health Division Oregon Department of Environmental Quality DataSource: Natural Resource and Conservation Service, unpublished data La Pine Approximate contact of general soil unit Figure 3-3. General soil associations in the La Pine sub-basin. La Pine National Decentralized Wastewater Treatment Demonstration Project Project Area Description Page 3-7 References Caldwell R. R., 1997, “Chemical study of the regional ground-water flow and ground-water/surface-water interaction in the Upper Deschutes Basin, Oregon.” U.S. Geological Survey Water-Resources Investigation Report 97-4233. Cameron, K. A. and Major, J. J., 1987, “Reconnaissance investigation of sediment distribution, erosion, and transport in the upper Deschutes River, Deschutes County, Oregon, November 1986.” U.S. Geological Survey Water-Resources Investigation Report 87-4114. Friday, J., and Miller, S., 1984, “Statistical summaries of streamflow data in Oregon: Volume 1 – eastern Oregon.” U.S. Geological Survey Open-File Report 84-454. Hinkle, S.R., J.K. Bohlke, J.H. Duff, D.S. Morgan, R.J. Weick, 2007. Aquifer-scale controls on the distribution of nitrate and ammonium in groundwater near La Pine, Oregon, USA. Journal of Hydrology, 333, 486-503. Moffatt, R. L., Wellman, R. E., and Gordon, J. M., 1990, “Statistical summaries of streamflow data in Oregon: Volume 1 – Monthly and annual streamflow, and flow-duration values.” U.S. Geological Survey Open-File Report 90-118. Morgan, D.S., S.R. Hinkle, R.W. Weick, 2007. Evaluation of Approaches for Managing Nitrate Loading from On- Site Wastewater Systems near La Pine, Oregon. Scientific Investigations Report 2007-5237, 66 p. Norgren, G.H. and others, 1969, “General soil map report of the Deschutes drainage basin, Oregon.” U.S. Department of Agriculture, Soil Conservation Service. Oregon Climate Service, 1999, www.ocs.orst.edu. Zone 5, NOAA Wickiup Dam station. U.S. Department of Agriculture, Natural Resource and Conservation Service, 1999, unpublished data of the La Pine Basin soils.