The Rathdrum Prairie Aquifer (RPA) is the Idaho portion of the Spokane Valley-Rathdrum Prairie Aquifer (SVRPA) that covers an area of about 250 square miles in Idaho. The RPA extends from Lake Pend Oreille southward to Coeur d’Alene and Post Falls and then westward to the Idaho-Washington state line. The aquifer is recharged by seepage from peripheral lakes, subwatersheds, and the Spokane River along with precipitation that falls on the Rathdrum Prairie.
The gravel, cobbles, and boulders forming the RPA were deposited 8 to 18 thousand years ago by enormous catastrophic floods created by the failure of a glacial ice dam near the Idaho-Montana border, which released billions of gallons of water. Flood waters traveled through the Rathdrum Prairie into Washington state to the Columbia River and on to the Pacific Ocean. The large volume and flow rate carried away all the smaller silt and sand and left very coarse material that is characteristic of the Rathdrum Prairie.
As the principal drinking water source, the RPA is an important resource for Kootenai County and its residents. Special protection was deemed necessary due to the coarse gravel, cobbles, and boulders that compose the aquifer, because contaminants could easily flow downward from the surface. The aquifer received a Sole Source Aquifer Designation by EPA in 1978 and the Sensitive Resource Aquifer designation by Idaho in 1997. The RPA is the only sensitive resource aquifer in Idaho. These aquifer designations provide for higher water quality standards and added protection.
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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 in the federal register in February 1978. Because of this classification, all activities that could impact the water quality of the RPA must be carried out so they maintain or improve the existing quality of the ground water.
Contact the DEQ Coeur d’Alene Regional Office to request a .kml, .kmz, or .shp file of the aquifer boundary.
Early inhabitants of the Rathdrum Prairie include the Kootenai Tribe of Idaho and the Coeur d’Alene Indians, followed by settlers, miners, and farmers.
In the early 1900s, a majority of drinking or irrigation water on the Rathdrum Prairie was derived from local streams, rivers, and lakes. Today, nearly all the water used for drinking and irrigation comes from groundwater, including the Rathdrum Prairie Aquifer.
In 2002, Newport Generation, Cogentrix Energy, and Avista Utilities applied for water rights to drill wells on the Rathdrum Prairie to obtain groundwater for proposed cogeneration plants. About 18 million gallons of groundwater per day would have been used in the plants. Significant concern was expressed about using so much water and whether the aquifer could sustain such use. The water rights were granted for one of the proposed projects that would use only a small portion of the 18 million gallons per day and the other projects were eventually denied.
Population growth, evolving water uses, and land conversion continues to present new challenges for the RPA, particularly the potential for groundwater contamination from septic discharge, urban runoff, and industrial chemicals.
The geology of the Spokane Valley-Rathdrum Prairie area is the result of multiple geologic events that have occurred over hundreds of millions of years creating both our landscape and the aquifer of today. Understanding the geologic events of the past helps us better understand our environment and current issues. There are five significant geologic units that compose most of the rock types found in the Rathdrum Prairie area—Belt Supergroup rocks, the Kaniksu Batholith, Columbia River flood basalts, Glacial Lake Missoula flood deposits, and unconsolidated deposits.
Hydrogeology is the study of water under the earth’s surface. If a geologic formation has significant quantities of water, it is called an aquifer. An aquifer is defined as a formation that contains sufficient saturated, permeable material to yield significant quantities of water to wells and springs. The Rathdrum Prairie Aquifer (RPA) is the primary source of drinking and irrigation water for everyone living on the Rathdrum Prairie.
DEQ’s Coeur d’Alene Regional Office (CRO) provides groundwater education and outreach as part of the RPA Protection Program and in collaboration with the Panhandle Health District, Kootenai County Aquifer Protection District, and The Confluence Project. CRO region provides groundwater outreach to all interested stakeholders including schools in Kootenai County that are over the RPA.
Elementary School Curriculum
An understanding of the basic concepts of groundwater is key to understanding how the RPA works. The study of groundwater is called hydrogeology. Hydrogeology investigates how water occurs and moves through the earth. The elementary school aquifer education curriculum contains a number of lesson plans and animations.
The animations are also available on CD from DEQ’s RPA coordinator. Also included is a suggested materials list.
At the end of each lesson plan is a certificate of achievement that the teacher may sign and award to the student after he/she has successfully completed the lesson. After all lessons have been completed, a diploma designating the student as an “Apprentice Hydrogeologist” may be awarded. Download the diploma below; contact DEQ’s RPA hydrogeologist to have the diploma signed by DEQ staff.
Middle School Curriculum
| Lesson Name | Lesson Plan | Animation Format |
|---|---|---|
| #1 Hydrologic Cycle | Where does water come from, and where does it go? | Video Link |
| #2 Groundwater | How does water under the earth’s surface move? | Video Link |
| #3 Drinking Water | Where does my drinking water come from? | Video Link |
| #4 Groundwater Contamination | What is groundwater contamination? | Video Link |
| #5 Aquifer Simulation Model | What will the groundwater do? |
High School Curriculum
| Lesson Name | Lesson Plan |
|---|---|
| #1 Darcy’s Law | Darcy’s Law – How does water move through an aquifer? A permeameter is needed for this exercise and is available for loan to teachers at the DEQ Coeur d’Alene Regional Office. |
| #2 Groundwater Contours | Groundwater Contours – How do we determine groundwater flow direction and gradient? |
| #3 Contaminants | What is groundwater contamination? Group A) (Group B) – Contaminant Fate and Transport Spreadsheet |
| #4 Groundwater | What does my water have in it? – If your school is within the Kootenai County Aquifer Protection District boundaries (over the RPA or contributing watersheds), the materials and analytical costs may be provided at no cost. Contact DEQ’s RPA hydrogeologist for additional information. |
Take a Quiz
Test your knowledge about the Rathdrum Prairie Aquifer.
Note to Teachers
The lesson plans and animations are provided to help teachers with aquifer education. Training for teachers in using the lesson plans and aquifer simulation model is available. If your school is located within the Kootenai County Aquifer Protection District fee boundaries, you may be eligible to receive the materials and aquifer simulation model at no charge. Contact DEQ’s RPA hydrogeologist for additional information.
DEQ has gathered a repository of Spokane Valley-Rathdrum Prairie Aquifer reports and publications that can be viewed at the link below. Please contact Seth Oliver if any materials are missing and need to be added.
Additional resources:
- Bureau of Reclamation
- City of Coeur d’Alene
- City of Hayden
- City of Post Falls
- Idaho Geological Survey
- Idaho Water Resource Board
- Idaho Washington Aquifer Collaboration
- Kootenai County Aquifer Protection District Board
- Kootenai Environmental Alliance
- Panhandle Health District
- Sensitive Aquifer Recharge Area (SARA) Mapper
- Spokane County Water Resources
- Spokane Riverkeeper
- Spokane River Forum
- The Aquifer and You – SVRPA
- US Geological Survey SVRPA Website
- Water Purveyor Map
The population in the area over the RPA is projected to potentially grow to 400,000 by the year 2060, which could impact water quality. DEQ completed a yearlong water quality investigation, which included sampling numerous water wells in the RPA and along with the peripheral lakes. General results indicate that the drinking water quality is very good.
- Nitrate-Nitrogen: All the water samples obtained and analyzed had concentrations well below the drinking water standards of 10 milligrams per liter.
- Arsenic and Uranium: Arsenic analytical results indicated concentrations were below the allowed maximum contaminant level of 10 and 30 micrograms per liter respectively in all wells.
- CFC’s and SF6: Age dating of the RPA ground water showed mixed results. The chlorofluorocarbons indicated either very high concentrations or very low concentrations, most likely reflecting chemical changes that take place when water is recharged through the thick unsaturated zone or from the peripheral lakes.
- Deuterium and Oxygen-18: The 2H and 18O analytical results from many of the ground water wells reflect ratios of the two isotopes that are very similar to the upgradient surface water bodies indicating significant recharge from the lake.
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. To learn more about the Rathdrum Prairie AgriMet station and current or historical weather conditions, visit the BOR AgriMet website.
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Senior Hydrogeologist