USGS Washington Water Science Center
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WA309 - Computer Simulation of Ground-Water Flow in the Pullman-Moscow Basin, Washington and Idaho - Completed FY1989
Problem - Virtually all of the water used within the Pullman-Moscow basin is derived from ground water contained within the basalts underlying the area. Four major users, the towns of Pullman, Washington, and Moscow, Idaho, Washington State University, and the University of Idaho are responsible for approximately 99 percent of the total water withdrawn from the basalts. Ground-water levels began to decline following initiation of pumpage. This decline not only has continued but in recent years has accelerated. Surface water is not presently a viable alternative; as a result, the Pullman-Moscow area has been the subject of numerous ground-water investigations by the U.S. Geological Survey (USGS) in cooperation with the four major users.
Objectives - To quantify the ground-water system of the Pullman-Moscow basin in sufficient detail that the effect of existing and future stresses on it can be predicted.
Approach - The overall approach will be to refine the existing model of the basin by: (1) Using results of the Sodium and Regional Aquifer Systems Analysis (RASA) projects (Project Numbers 281 and 260, respectively) to better quantify the geology and hydraulic properties of modelled units; (2) Collecting additional field data including ground-water levels and information on the interconnection between streams in the area and the ground-water system to permit additional calibration and verification of the model, and (3) Redefining the model boundaries based on field data, including observed water-level declines and seepage runs. The investigation will be conducted as a dual effort between the University of Idaho and the Survey.
WA167 - Evaluation Of Ground Water Availability In The Pullman Area, Whitman County, Washington - Completed FY1977
Problem - The Pullman-Moscow Ground-Water Basin is occupied in part by the cities of Pullman, Washington and Moscow, Idaho. Municipal and industrial supplies for both cities are drawn from basalt aquifers, the only significant source of good-quality water in this area. Water levels in and near the cities are declining at a rate that indicates progressive depletion of the groundwater reservoir. Alternative sources are the Palouse or the Snake Rivers, but very large costs would be involved in developing a firm supply from either source. It is therefore necessary to obtain quantitative information on the ground-water system.
Objectives - A better knowledge of the hydrologic system, how it functions, how much water is recoverable, and how long it will last is essential for effective management of the resource--and for adequate planning for future alternate water supply (costly importation of surface water). previous studies have provided valuable but inadequate data; additional data will be obtained as necessary and analyzed to project rates of depletion and "life" of the ground-water reservoir under various pumping regimes so management alternatives can be studied.
Approach - Water-level and well-log data will be updated and reanalyzed, using modern maps with accurate altitudes and water levels measured periodically to determine ground-water gradients and define flow paths. Aquifer tests will be conducted where needed to better define T and S. The continuity between the shallow and deeper basalts will be analyzed. From these data a general picture of the seriousness of the situation--imminence of depletion--can be determined. If needed, additional drilling, gravity, and other geophysical surveys will be made, and the general digital model constructed for testing management alternatives.