The science behind Eastern Washington’s big aquifer

If you grew up in the Inland Northwest, chances are you learned about the massive underground Spokane Valley/Rathdrum Prairie Aquifer in your school days.

It’s gained a sort of mythical status in the local discourse, creating an impression that it has an almost magical ability to provide a seemingly endless supply of the tastiest fresh water this side of the Mississippi.

Although it is vast and justifiably mysterious, many locals are beginning to understand that our aquifer is more susceptible than its reputation led us to believe. But to truly grasp the shaky ground on which the aquifer’s longevity and quality rests, you have to take a deeper dive into the science of this incredible groundwater.

An aquifer isn’t just an underground pool. It is a complex geologic and hydrologic structure composed of various layers of gravel, sand, rock and silt that are saturated with flowing groundwater.

“What’s remarkable about aquifers, especially ours, is that they flow directly beneath us, much like subterranean rivers. The Spokane Valley/Rathdrum Prairie Aquifer stands out globally as one of the fastest-moving and highest water quality aquifers,” said Jeremy Jenkins, environmental manager with the Spokane Aquifer Joint Board.

Despite that it primarily flows beneath us, our aquifer has a living exchange with our surface water.

“Aquifers are not always totally underground and they have an incredible relationship with our surface waters,” said Katelyn Scott, a water protector with the Spokane Riverkeeper organization.

“Here in our aquifer you can even see the top of it in parts of the river. When you go down to the river west of Sullivan Road during the late summer time, you’ll see large cobble, and sometimes you can even see the water bubbling in from underground. That’s the aquifer!”

Our aquifer is what’s called an unconfined aquifer, which is a common type of aquifer found at the bottoms of valleys where the water settles into low areas and seeps into the permeable ground. That means precipitation is critical to our aquifer’s regeneration, or what is called groundwater recharge. Our local geography, our climate, the surface water and our water usage can all be seen as one connected system.

“Snowpack from the Idaho Panhandle is the main recharge source, and as winter snowpack decreases and population increases, we will see changes in the future,” Jenkins said. “Increased water usage over the aquifer during summer months leads to a decline in the underground water level. This decline directly affects the flow and water level of the Spokane River because the river and aquifer exchange water at multiple points between the outlet of Coeur d’Alene Lake and the aquifer’s western boundary near Riverside State Park.”

Although it is precipitation that regenerates our aquifer, it was a warming climate and a huge lake that first created it.

Lake Missoula existed during our planet’s last ice age and was created by an immense ice dam. This dam ruptured here and there, and each time it did it unleashed immense floods that swept across Eastern Washington and created the rippling landscape we have today. Not only did these floods carry incredible amounts of water, but also they carried sediment .

“As floodwaters surged down the Clark Fork river valley, veered south into the Rathdrum Prairie, and then flowed west through the Spokane Valley, they transported vast quantities of glacial debris, including boulders, gravel and sand,” Jenkins said.

“The valleys we inhabit today were subsequently filled as this glacial material settled out when the water velocity decreased. Our aquifer is now contained within these same gravel deposits left behind by the floods. Who knew that this natural formation would end up serving as the lifeblood of nearly 1 million people in the Coeur d’Alene-Spokane corridor?”

The Spokane Valley-Rathdrum Prairie Aquifer was designated as a “sole source” aquifer by the EPA in 1978, which officially recognized it as the principal source of drinking water for our region. This designation boosted public understanding of its value and ushered in new and improved management practices to protect its quality, such as pretreating stormwater and eliminating septic tanks.

It is because of our aquifer’s close relationship with surface water that waste management practices like these, as well as overall water usage, has such strong influence on the aquifer’s ability to regenerate and provide clean drinking water.

“Our river and aquifer are connected, which means when we pump water out of the aquifer we are also taking water away from the river. Every summer we see a large decline in river flows that aligns with our outdoor water use, and Spokane uses more water outdoors than most of the nation,” Scott said.

In a way, the detriment of local residents having such a direct effect on the aquifer can also be looked at as an opportunity for individual action. Jenkins recommends two primary ways local residents can aid in the good health of the aquifer.

“First is to properly dispose of waste materials in the right place. A helpful resource for this is spokanewastedirectory.org. Second is to use your water efficiently. This includes not watering the landscape during the day, fixing leaky fixtures and sprinklers when you find them, and learning much more at outdoorwateringnerds.org.”

Although it is deep below our feet, we interact with our aquifer every day, and it with us as we refill our water bottles, take the paddle boards to the lake or enjoy the serenity of our beautiful rivers. Its hydrogeology may be complex, but a little bit of science goes a long way in helping us understand how we can continue to enjoy this amazing natural feature for generations to come.