Spokane Aquifer System

The source of drinking water for over 500,000 people, the Spokane Valley-Rathdrum Prairie (SVRP) Aquifer is a natural treasure of North Idaho and Eastern Washington.

The Spokane Valley – Rathdrum Prarie Aquifer

The Spokane Valley – Rathdrum Prairie Aquifer was created by Ice Age floods that deposited a thick layer of boulders and gravel. This rock and gravel layer is now filled with water and extends 135 square miles from Pend Oreille Lake in Idaho to just past the western edge of the City of Spokane. It ranges in surface depth from a few feet in some areas to as much as 500 feet in others. We are working and living over our drinking water source.

Since our water is beneath us, it is important that we follow good stewardship practices and understand that anything poured on the ground, into our rivers or streams or in storm drains end up in the aquifer. (City of Spokane)

What is an Aquifer?

An aquifer is an underground body of permeable rock that contains or transmits groundwater. In this case permeable means that they have openings where liquids and gases can pass through. Sedimentary rock such as sandstone, as well as sand and gravel, are examples of rock with water-bearing potential. Aquifers typically fill with water from rain or melted snow that drains into the ground. The water moves downward until it meets less permeable rock. (Spokane County)

Aquifers act as reservoirs for groundwater and wells drilled into aquifers provide water for drinking, agriculture, and industrial uses. Aquifers can dry up when people drain them faster than nature can refill them. Because aquifers fill with water that drains from the surface of the Earth, they can be contaminated by any chemical or toxic substance found on the surface. (Spokane County)

Types of Aquifers

There are two types of aquifers.

An unconfined aquifer is covered by permeable rock and can receive water from the surface. The water table of an unconfined aquifer rises or falls depending on the amount of water entering and leaving the aquifer. It is only partly filled with water.

In contrast, a confined aquifer lies between two layers of less permeable rocks and is filled with water. Water trickles down through cracks in the upper layer of less permeable rock, a nearby water source, such as an underground river or lake, or a nearby unconfined aquifer.

An artesian well is a type of confined aquifer that flows upward to the Earth’s surface without the need for pumping. The artesian well sits below the water table at the bottom of U-shaped aquifers. Pressure from water in the long sides of the aquifer pushes the water up the well shaft. (Spokane County) .

Is Spokane’s Water Safe to Drink?

Spokane’s aquifer system is an unconfined aquifer which is directly affected by our community activities. Everything that ends up on the ground or poured into rivers and streams could end up in your drinking water. An example of some forms of contaminants include:

  • Leaching from defective (poorly engineered) landfills and cemeteries
  • Septic tank leaching
  • Medication disposal
  • Overflow of untreated sewage from storm events and system failures
  • Washing, bathing and swimming
  • Industrial manufacturing waste
  • Use of pesticides in rural areas
  • Deicer on public roadways
  • Other human activities

To learn more about where your water comes from, what is in it, and what you can do to protect your family and home please call 509-381-7818 or schedule your FREE in-home water test here.

Works Cited

City of Spokane Water Department. “Your Water Supply Source.” The City of Spokane’s 2018 Water Quality Report. 2018. https://www.spokanecounty.org/1203/Aquifers-Groundwater Accessed 12/27/2019.

Spokane County. “Aquifers / Groundwater.” Spokane County Water Resources. https://static.spokanecity.org/documents/publicworks/water/2018-water-quality-report.pdf Accessed 12/27/2019

Spokane Aquifer Joint Board. “Household Contaminants.” Local Water Utilities United for Safe Drinking Water.https://www.spokaneaquifer.org/education-awareness/community-resources/household-contaminants/ Accessed 12/27/2019.

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