USGS Washington Water Science Center
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More than 70 percent of the population of Washington and Oregon resides in the Puget Sound-Willamette Trough, which stretches north-south on the western side of the Cascade Range. The area is one of the principal regional ground-water systems in the Nation, but little is known about the quantity and quality of the ground water, the regional flow system, or the interaction of the system with surface water and local rock material. The USGS has included the Puget Sound-Willamette Trough in its Regional Aquifer System Analysis (RASA) program, which systematically assesses the principal regional aquifer systems in the Nation. The study provides to water resource managers and community planners comprehensive information on the regionís aquifer systems that is needed to make a wide range of management and planning decisions, both locally and regionally.
To obtain a better understanding of the regional ground-water system in the Puget Sound-Willamette Trough, the USGS is combining existing data and data collected during the RASA study to describe the geologic framework and hydrogeologic characteristics of the principal aquifers and to determine regional ground-water flow. Hydrologists are estimating water budgets for selected areas of the aquifer system and using this information to describe the regional water budget. The study includes determining the composition of native waters, the chemical interaction of the water with aquifer material, and quality of the water in selected areas. The USGS is using information from this study in numerical ground-water-flow models to simulate how the regional aquifer system operates.