Drinking Water Needs Protections The Aquifer

The Spokane-Rathdrum Prairie Aquifer is an underground river that flows west from Idaho.

The largest in the country, the aquifer feeds wells that can provide up to 220 million gallons per day of good drinking water.

It was given federal protection in 1979 as the sole source of Spokane’s drinking water. Several major studies have tracked its path and identified activities that threaten it.

Nitrate contamination from septic tanks has decreased in the aquifer, a result of major sewer construction in Washington and Idaho over the past two decades.

But a 1998 study concluded the aquifer is vulnerable to a variety of contamination threats.

Five of Spokane’s eight large drinking water wells are located in highly developed urban areas with a variety of industrial hazards.

The aquifer is also affected by stormwater runoff and by chlorides from winter de-icing programs, recent Spokane County studies say. But drinking water quality is rarely violated in wells tapping the aquifer.

City and county officials are working on several programs to reduce the threats. Last year, they got an additional $5 million from the state to continue efforts to protect the water supply.