Groundwater quality in the La Pine area of southern Deschutes County is at risk of nitrate contamination from onsite sewage treatment system discharge to groundwater. Nitrate concentrations detected in groundwater indicate that degradation of groundwater quality is in process in the densely developed areas. Most onsite systems in the region are conventional systems located in highly porous and permeable (rapidly draining) soils with no intervening layer protecting the underlying shallow aquifer.
The US Environmental Protection Agency has funded Deschutes County Environmental Health Division, Oregon Department of Environmental Quality and the US Geological Survey to work cooperatively to address the issue of groundwater contamination from onsite systems in south Deschutes County.
The primary objective of the La Pine Demonstration Project was identify ways to protect the La Pine sub-basin's water quality, including the primary source of drinking water, while allowing planned development to occur through a holistic approach using new pollution reducing onsite wastewater treatment systems. This approach also building on our understanding of how groundwater flows and what happens to nitrates and other pollutants in the groundwater. This information will be used to determine the appropriate development density or pollution loading that can be accommodated by the natural systems in the sub-basin.
The Project worked included eight major tasks over a five-year period:
- Install new and retrofit existing systems with 200 or more innovative onsite systems by a grant and/or low-interest loan program. A subset of these systems will be monitored intensively for three years as a field test program for denitrifying treatment systems.
- Establish a regional monitoring well network of up to 130 wells. This network will support both the innovative system field test program and the 3-dimensional modeling work.
- Set up an onsite system maintenance structure.
- Develop a funding program to assist in low-interest loans for onsite system repair and/or replacement using the appropriate technology.
- Collect and analyze field data on new and retrofitted onsite systems and from the groundwater monitoring network. This work directly supports the innovative system field test program and the 3-D modeling work.
- Conduct laboratory analytical testing of onsite system effluent and groundwater samples. This data is used to evaluate the innovative treatment systems and to develop the 3-D model scenarios.
- Conduct three-dimensional groundwater flow and nitrate fate and transport modeling, lot size optimization modeling for nitrate loading reduction, and identify areas and/or neighborhoods of concern for development of a comprehensive groundwater protection strategy.
- Prepare quarterly progress reports and a final project report