Rathdrum Prairie Aquifer
The Rathdrum Prairie Aquifer (RPA) is a deposit largely made up of sand, gravel, cobbles, and boulders. The RPA covers an area of approximately 211 square miles in Idaho and extends from Lake Pend Oreille south to Coeur d’Alene and Post Falls and then west to the Idaho-Washington border. The aquifer extends into Washington and becomes part of the larger Rathdrum-Spokane Aquifer.
Water recharges the RPA through precipitation, runoff from the surrounding upland areas, and leakage from surrounding lakes. The water table is at an elevation above mean sea level of about 2,060 feet near Lake Pend Oreille and about 1,980 feet at the Idaho-Washington state line. The larger Rathdrum-Spokane Aquifer supplies drinking water to approximately 100,000 people in Kootenai County, Idaho, and another 400,000 people in Spokane County, Washington.
Evolving Use of the Aquifer
The earliest source of irrigation and drinking water in the area came from the numerous lakes in the area along the Spokane River. Eventually, as more wells were drilled, the Rathdrum Prairie Aquifer became the area's primary source of water and will continue to play a key role in sustaining the region. Learn more.
The boundary of the Rathdrum Prairie Aquifer is defined differently among various government agencies. DEQ has classified the RPA as a sensitive resource aquifer, following the boundary defined by EPA. Because of this classification, all activities that could impact the water quality of the RPA must be carried out so they maintain or improve existing quality of the ground water. Learn more.
When was the Rathdrum Prairie Aquifer formed? Only about 10–18,000 years ago. Learn more.
Hydrogeology is the study of water under the earth’s surface. The Rathdrum Prairie Aquifer is mainly made up of coarse sand, gravel, cobbles, and boulders, although areas of fine-grained silt and clay sediments can also be found. Learn more.
DEQ completed a yearlong water quality investigation of the Rathdrum Prairie Aquifer to determine if any contaminants were present, the source of contaminants, along with defining residence times, and recharge sources of the aquifer. Learn more.
Weather conditions—temperature, rain, humidity, and wind speed—can have a big influence on how much water is needed for irrigation and available to recharge the water in the aquifer. The Bureau of Reclamation's AgriMet station on the Rathdrum Prairie collects weather data for use in water quantity studies, but also reports the amount of water needed each day to irrigate lawns or crops to help conserve water. Learn more.
Lesson plans and animations about the Rathdrum Prairie Aquifer are available to teach elementary school children about this important natural resource. Link to curriculum.
Reports and Publications
A multitude of scientific reports and publications on the hydrogeology and geology of the Rathdrum Prairie Aquifer is available here.
Want to learn more? Visit the websites listed here.