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Report calls for diversion projects on Palouse waterways

Aug. 19, 2022 Updated Fri., Aug. 19, 2022 at 5:47 p.m.

By William L. Spence Lewiston Tribune

Efforts to augment water supplies on the Palouse Basin and reduce demand on the regional aquifer took another step forward Thursday, with the completion of an alternative water supply report.

The document builds on a 2017 study commissioned by the Palouse Basin Aquifer Committee.

As an initial step, it recommends that water diversion projects be located on Paradise Creek near Moscow and the South Fork of the Palouse River near Pullman. Surface water would be treated and pumped into the existing community water distribution systems.

Stronger conservation measures would also help decrease future demand.

During a meeting Thursday, however, committee members stressed that this is just a starting point for further conversations, both with regulatory agencies, stakeholders and the public.

“This is the start of a process, not the end,” said Moscow Public Works director and Deputy City Supervisor Tyler Palmer.

“We’re not swinging for the fences,” added Paul Kimmell, the regional business manager for Avista. “We just want to get on base, and this gets us moving.”

Water supply on the Palouse Basin has been an issue of concern for decades.

The basin’s upper and lower aquifers are the sole source of drinking water for Moscow and Pullman. Nearly 2.5 billion gallons are pumped each year, not including farm irrigation or residential water wells.

Water levels in the lower aquifer have dropped nearly 30 feet since 1990. Conservation efforts have slowed the rate of decline from about one foot to three-quarters of a foot per year, but future population growth will add to the demand.

Previous studies estimated about 2.3 billion gallons of additional water per year will be needed by 2065, both to meet future demand and to help stabilize the deep aquifer.

The 2017 report highlighted four primary options for supplying that additional water. They included:

Diverting water from the Snake River and pumping it to Moscow and Pullman.

Diverting and treating surface water from the North Fork or South Fork Palouse River and/or Paradise Creek and injecting it into the aquifers.

Building a wastewater reuse system that would use reclaimed wastewater for irrigation purposes.

Constructing a dam and reservoir on Flannigan Creek near Moscow.

A combination approach would be needed, as none of the options could satisfy the entire future demand by themselves.

Alta Science & Engineering of Moscow was hired in 2020 to further refine the 2017 study. It added the Paradise Creek/South Fork diversion projects as a fifth, modified option.

The Palouse Basin Aquifer Committee — which includes representatives from Moscow, Pullman, University of Idaho, Washington State University, Latah County and Whitman County — is recommending that as the preferred alternative.

During Thursday’s meeting, committee members noted that the other four options are still viable. However, the Paradise Creek/South Fork proposal is a simpler option; at $74 million — including $48 million for the two diversion systems and $26 million for conservation measures — it’s also the least expensive approach.

“All of these (alternatives) will stay on the board as we move forward, but this is a good option to maintain some positive momentum,” Palmer said. “We’re getting out of the chute on a problem that’s been stagnant for a long time.”

Kimmell noted that a lot of questions still need to be addressed before any final decision is made to move forward. Landowners need to be consulted, as well as political leaders and regulatory agencies, and public acceptance will be critical.

Committee members will meet with city, county and university officials in September to update them on the various water supply alternatives.

The report and its recommendations will also be a topic during the annual Palouse Basin Water Summit, which takes place from 4:30 to 8:30 p.m. Oct. 18 at the SEL Event Center in Pullman.

A copy of Alta Engineering’s final report will also be posted on the Palouse Basin Aquifer Committee’s website, at

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