USGS Washington Water Science Center
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WA260 - Columbia Plateau Regional Aquifer Systems Analysis (RASA) Project - Completed FY1999
Problem - The Regional Aquifer Systems Analysis (RASA) program of the U.S. Geological Survey (USGS) was initiated in FY78 to provide information on a regional scale of the major ground-water systems in the country. This information is to include the aquifer boundaries, description of the flow system, geohydrologic and hydraulic characteristics, and water quality. Flow models are being constructed to understand the ground-water flow systems and to analyze the impacts due to stresses that have led to changes. The flow models also provide a means of evaluation of the effects of future development of the systems. The Columbia River Basalt Group was selected as one of the RASA studies and was started in FY83.
Objectives - To obtain a better understanding of the regional ground-water system of the Columbia River Basalt aquifer by: (1) Describing the geologic framework; (2) Describing the geohydrologic characteristics of the system; (3) Determining the water budget within the Plateau; (4) Determining water quality, flow paths, residence time, and water-rock interactions; (5) Developing a data-base management and application system for water use, quantity, and quality data; and (6) Developing a regional flow model to understand the aquifer system including the sensitivity of the hydraulic parameters, components of the water budget, geologic framework, and the hydrologic impacts of proposed future development.
Approach -Data from drillers' logs, geophysical logs, and mass water-level measurements will be stored in Ground Water Site Inventory (GWSI) data base. These data plus pumpage data on crops, irrigated land, and pump efficiencies will be used in a recharge estimation model which calculates daily water budgets. A steady-state ground-water model for predevelopment and time-averaged 1983-85 conditions and a transient model for predevelopment to 1985 will be conceptualized, calibrated, and operated so that we may evaluate the impact of hypothetical ground-water development. In addition we will describe water-quality characteristics of the major formations in the Columbia River Basalt Group including development and testing of a geochemical model.