The study area for this evaluation in the northern portion of Douglas County, WA, has very little local groundwater usage.
The study included monitoring and analyzing a 72-hour pumping test at 250 gpm.
Groundwater produced from the test well was conveyed to a distant location for discharge.
Explorations encountered a multi-layered aquifer system separated by impermeable sedimentary deposits.
Douglas County Aquifer Storage and Recovery Feasibility Evaluation
Subsurface exploration and testing for the Washington Department of Ecology to evaluate site suitability for temporary storage of Columbia River water in basalt aquifers.
The Washington Department of Ecology contracted with GeoEngineers to explore and evaluate aquifer conditions in a 5-square-mile study area located in the northern portion of Douglas County, WA. The contract resulted from the Washington State Legislature’s 2006 directive to the Department of Ecology to aggressively pursue water-supply development in the Columbia River basin through storage and conservation programs.
Developing reservoirs for surface water storage in the Columbia River basin has proven to be extremely difficult. Environmental impacts, including limited availability of land, cultural considerations and cost, have severely limited feasible options. As a possible alternative, or supplement, to water storage in surface reservoirs, the Department of Ecology with GeoEngineers’ help is evaluating potential locations for subsurface water storage and retrieval in aquifers of the Columbia River Basalt Group.
The upland plateau study area for this evaluation has very little local groundwater usage and is not served by the US Bureau of Reclamation’s Columbia Basin Project. Through the study, the Department of Ecology and GeoEngineers identified a multi-layered aquifer system with characteristics that appear favorable for an aquifer storage and recovery (ASR) project. Supplemental exploration and testing are planned to examine project feasibility on a larger scale.
Approach
The Washington Department of Ecology and GeoEngineers developed a detailed scope of services for field explorations and testing to evaluate geologic and aquifer conditions in the study area. GeoEngineers implemented the field program over a six-month period between October 2012 and April 2013. The field studies included contracting and monitoring the completion of one test well to a final depth of 400 feet, and five observation wells at varying distances from the test well. Aquifer testing included a step-rate pumping test, a 72-hour constant-rate pumping test, water quality sampling and water level recovery monitoring. GeoEngineers followed the field investigations with detailed analysis of the aquifer testing data and evaluation of project feasibility.
Results
The field program identified the presence of two basalt aquifers separated by a thick unit of sediment that effectively isolated the two water-bearing zones. Based on GeoEngineers’ analyses, the lower basalt aquifer appears to be suitable for temporary storage of water from the Columbia River with minimal impacts to existing groundwater users and the surrounding environment. The Washington Department of Ecology is pleased with the study results and plans to evaluate project feasibility further with expanded subsurface exploration and testing.
Innovation
This was the first detailed hydrologic study in the northwest corner of the Columbia Plateau and demonstrated that favorable conditions for aquifer storage and recovery may exist in the region.
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