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Environmental Health | Rathdrum Prairie Aquifer

         Rathdrum Prairie Aquifer





The Rathdrum Prairie Aquifer is a drinking water gem that deserves special treatment to preserve its pristine quality.


Here's what you can do to help protect it:

  • Before fertilizing, test your soil to learn what kind of fertilizer you need.
  • Follow directions on your fertilizer and pesticides.
  • Don't overwater.
  • Don't dispose of chemicals down the drain.
  • Don't dump wastes, including carwash water, into grated storm drains.
  • Recycle household chemical waste.


The Spokane Valley-Rathdrum Prairie Aquifer formed during the last ice age, 12,000 to 20,000 years ago, when massive floods spread across northern Idaho and eastern Washington. The Spokane floods occurred when an ice dam holding back 500 cubic miles of water in Glacial Lake Missoula broke. Waters raced across the land, dropping sands, gravels and boulders. Scientists believe these floods may have occurred dozens of times.


Where is it?

The aquifer lies below 325 square miles of land surface in northern Idaho and eastern Washington, and is the sole source of drinking water for the region's 450,000 people.


What composes it?

The aquifer is composed of glacial outwash--sands, gravels and cobbles. It is extremely permeable, high in groundwater velocity and susceptible to contamination. Coeur d'Alene Lake and the Spokane River contribute about one-third of the water flow in the aquifer. Precipitation contributes another third. The lake watersheds of Hayden, Spirit, Twin, Hauser and Pend Oreille provide most of the additional flow crossing the state line.


How big is it?

At the Idaho/Washington border, total flow is estimated by the Idaho Department of Environmental Quality (DEQ) to be 750 cubic feet per second or 485 million gallons per day. The movement of water particles ranges from less than a foot to almost 50 feet per day as it flows west from Idaho to Washington. The depth to the water table varies from 450 feet in Idaho to only 50 feet at some points in Washington. Water discharges from the aquifer into the Spokane River via spring just west of Spokane.


Is the water quality safe?

The vulnerability of the resource was originally proven in the mid-1970s with detections of elevated nitrates down-gradient of densely populated areas relying on septic systems for disposal of wastewater. Recently, industrial solvents and pesticides have been found in public water supply wells. Despite many protection efforts, a few water supply wells were abandoned due to contamination. In 1993, high levels of the solvent trichloroethylene (TCE) were discovered in the Sunrise Terrace Water System, forcing the system to hook to the City of Coeur d'Alene's water system.


History of Protection Programs

In the 1970s, both northern Idaho and Spokane County obtained grants under Section 208 of the federal Clean Water Act to pursue studies aimed at developing management plans for the aquifer. These studies began with well sampling networks. In all, hundreds of wells were sampled in the two states. The results of a year of monitoring showed the water quality was still good, but definite trends of deterioration could be attributed to human activities on the ground surface above.


Sole Source Drinking Water

In 1980, the Spokane Valley-Rathdrum Prairie Aquifer was declared a "sole source" drinking water supply pursuant to Section 142e of the federal Safe Drinking Water Act (P.L. 93-523). This designation requires all federally assisted projects to use aquifer protection measures. In addition, it proclaimed the significance of this groundwater resource to the region as well as provided support for local protection efforts.


Special Resource Water

In 1980, the Rathdrum Prairie Aquifer was designated as a Special Resource Water in the Idaho Water Quality Standards and Wastewater Treatment Requirements. This resulted in increased protection for this resource. Since the completion of the 208-funded aquifer protection plans, Spokane and northern Idaho officials and citizens have worked to implement an integrated protection program.

Aiding significantly in this effort was an annual congressional appropriation of about $1 million to Spokane County, the DEQ and Panhandle Health District (PHD) from 1988-94. The appropriation, which is no longer available, was divided evenly between Idaho and Washington. Since the late 1980s, the Idaho and Washington programs have cooperatively shared studies, strategies and solutions to protect the aquifer.


Working Together

In Idaho, DEQ and PHD have taken the lead in protecting this resource using the authority granted to them under federal and/or state law. DEQ's primary role in aquifer protection is to provide technical expertise and support to local government and business. Examples of DEQ programs include sewering, land application and directing clean-up activities. PHD implements aquifer protection activities via regulations adopted by its Board of Health to manage storage and handling of critical materials and subsurface sewage disposal. This cooperative arrangement is the key to a comprehensive protection program and is further designed to avoid duplication of effort.


Aquifer Protection District

Aquifer protection has revolved around the simple premise that we must prevent contamination before it occurs. Remediation of contaminated ground water is extremely costly, if not impossible. More than 17 million gallons of critical materials--fuel, paint, chemicals, etc.--sit above the aquifer

In 2006, Kootenai County voters overwhelmingly approved the formation of the state's first Aquifer Protection District to ensure the area can continue to pay for the programs and services necessary to protect the aquifer. Private property owners in the district pay no more than $12 a year for aquifer protection programs and services. Commercial property owners pay no more than $24 a year.

The Aquifer Protection District has funded PHD's management of critical materials at fixed locations, water quality sampling and sewage management. An advisory board appointed by the Kootenai County Board of Commissioners recommends to commissioners how the money raised should be spent each year.


Download the Spokane Valley-Rathdrum Prairie Aquifer Atlas (Very large file)

Aquifer Survival Guide (pdf brochure)


Questions? Call us at (208) 415-5220.


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