Spokane Valley

The Spokane Valley Rathdrum Prairie Aquifer consists of very coarse sand and gravels that were deposited approximately 12,000 to 15,000 years ago at the end of the last ice age. Huge lakes were formed in Montana by ice dams. As these ice dams were breached and re-formed as many as 40 times, a series of catastrophic floods poured through the Spokane Valley depositing boulders and gravel. These materials are so permeable that most water infiltrates directly into the ground. For that reason, there are no tributaries to the Spokane River in the Spokane Valley. Runoff through adjacent highlands form a series of lakes at the periphery of the valley (e.g.,Newman and Liberty Lakes) and the streams from these lakes totally infiltrate into the ground before they reach the Spokane River.

The high permeability of the aquifer makes it highly susceptible to contamination from the surface. Because the Spokane aquifer is the primary source of water to residents of the area, and concerns of residents regarding the quality of their water, the Environmental Protection Agency designated it as a sole source aquifer by in 1978. This was the second aquifer in the nation to receive this designation. This step increased public awareness and supported development of special management practices by local agencies. Presently, aquifer protection efforts are managed by Spokane County's Water Resources Program and the Department of Ecology in Washington, and by the Department of Environmental Quality and the Panhandle Health District in Idaho.