Scientific Investigations Report 2007–5041
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2007–5041
The following data needs were identified during this investigation. The identified data could improve definitions of the hydrogeologic framework and ground-water budget of the SVRP aquifer.
Deep drilling at several locations along the axis of the SVRP aquifer from the south end of Lake Pend Oreille through the Rathdrum Prairie, Spokane Valley, Hillyard Trough, and Little Spokane River Valley would provide two important pieces of information. First, the presence or absence of fine-grained layers, and their thickness, in the deepest parts of the aquifer could be determined. Second, the depth to the bottom of the aquifer, represented by either the Basalt and fine-grained interbeds unit or the Bedrock unit, would allow for meaningful refinements to the approximate base of aquifer and aquifer thickness.
A more detailed analysis of the geologic and hydrologic setting near the southern ends of Spirit and Hoodoo Valleys would allow for a more complete understanding of aquifer characteristics and extent in those areas. The analysis likely would involve a field inventory of recently drilled wells and the drilling of new monitoring wells where coverage is poor. Analysis of the lithology encountered in those wells and the measurement of ground-water levels would allow for characterization of the aquifer as well as help determine the location of the ground-water divide between the two valleys and the Rathdrum Prairie.
Measurements or better estimates of seepage into the aquifer from Coeur d’Alene Lake and Lake Pend Oreille and subsurface outflow from the aquifer to Long Lake would strengthen the recharge and discharge estimates currently available for the aquifer. Among the data that would be useful in refining these estimates would be better definition of the cross-sectional area connecting the lakes to the aquifer and better characterization of the hydraulic properties of the sediments across this interface. A well-designed hydrochemical study incorporating analyses of environmental tracers, isotopic ratios, and ground-water age dating could potentially provide an independent means of quantifying recharge and discharge, and defining ground-water flow paths. An approach similar to that applied in the Middle Rio Grande Basin of New Mexico (Plummer and others, 2004) could improve understanding of the SVRP aquifer system.
U.S.
Department of the Interior | U.S. Geological
Survey
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