HYDROGEOLOGY OF THE PALOUSE GROUND WATER BASIN

Situated in the rolling hills of the Palouse in northern Idaho and eastern Washington, the Palouse Ground Water Basin supplies drinking water to the cities of Moscow, Idaho and Pullman, Washington; University of Idaho; Washington State University; and Latah and Whitman Counties. The delineation of aquifers in the Basin appears to correlate well with the geologic stratigraphic units of the Columbia River Basalt Group. The upper aquifer occurs primarily in the eastern portion of the Basin and is associated with the Wanapum Formation. The lower aquifer occurs throughout the Basin and is associated with the Grande Ronde Formation. General hydrologic boundaries of the lower aquifer include crystalline rock to the north, east, and south. Hydrologic boundaries are not well defined to the west and there is gap to the north. Short-term water-level decline has been noted in the upper aquifer. Long-term water level decline has been noted in the deeper aquifer. Understanding the hydrogeology of the Palouse Ground Water Basin is critical in order to best manage this precious resource.