Department of Ecology News Release - September 23, 2015

Walla Walla approved to store drinking water underground

WALLA WALLA – The city of Walla Walla is ensuring its community has a secure public water supply and fish are protected by storing drinking water in nearby basalt aquifers for later use.

The city is reducing its need to take surface water from Mill Creek during critical summer months when fish need cool, clean water for survival. In seasons with high flow, water will be withdrawn from the creek, treated and stored underground.

A new report from the Washington Department of Ecology concludes the city can divert water from Mill Creek and safely store it underground. The city injects treated drinking water into the basalt aquifers and an allotment is available for public supply needs.

“This is a smart, forward-thinking approach to long-term water supply by the city,” said Keith Stoffel Water Resources manager for Ecology’s eastern region. “Rather than relying solely on surface water, storing water underground provides them the ability to adapt to potential climate change impacts and wildfire.”

Mill Creek is the city’s main source of drinking water. The creek originates in the upland forest of the Blue Mountains.

Before approving the project, Ecology reviewed the overall impacts to groundwater quality while balancing the public need for a secure water supply and the associated environmental benefits. Walla Walla has already been diverting water as part of a long-term pilot project and the approval allows the project to continue with some new requirements.

Drinking water standards differ from Washington’s groundwater quality standards. Treated drinking water contains chemicals such as chlorine, which is safe for human health, but violates groundwater quality standards.

Ecology found the environmental and public benefit of the aquifer storage project will outweigh the potential groundwater quality impacts once upgrades are made to the current drinking water treatment technology.

The city must upgrade treatment technology for drinking water to reduce the chemicals that cause degradation before injecting the water into the aquifer. A monitoring plan must also be in place to ensure water in the reservoir is maintained at safe drinking water standards.

The report is subject to a 30-day appeal period before a final permit is issued. Appeals can be made to the state Pollution Control Hearings Board.


Brook Beeler, communications, 509-329-3478, and @ecyspokane