The City of Moscow is investigating surface water alternatives due to a decline in the groundwater supplies of the Palouse Basin.
Since 1950, Moscow has obtained its water from two aquifers — a deep aquifer called the Grande Ronde and a shallower aquifer known as the Wanapum. While both have seen decline, the Grand Ronde, which also serves Pullman, has seen the most groundwater decline in past decades.
Steve Robischon, executive manager of the Palouse Basin Aquifer Committee, said water levels in the Grande Ronde have steadily decreased since they began measuring them in the 1930s.
“They used to be going down a little bit over a foot a year and now they’re going down a little bit under a foot a year,” Robischon said. “So the rate of decline has reduced, but water levels are still continuing to decline, year over year.”
The city seeks to offset the declines through an alternative source — surface water. The search for an alternative began with a phase one investigation, which studied the feasibility of putting a reservoir on Moscow Mountain.
Director of Public Works Les MacDonald said phase one was completed two years ago and produced four viable basins. However, he said only one of the four viable basins was truly cost-effective for Moscow.
“If we were looking purely at, you know, what the city can afford on its own and what might be the most viable to construct, then there really are two. But the cheapest one, if you will — the lowest price — is one that would build a low-level dam in the South Fork Palouse River drainage basin up in Moscow Mountain,” MacDonald said. “And, that would impound, annually, enough water to essentially offset what we currently use for irrigation in Moscow.”
MacDonald said the cost of this reservoir would be more than $6 million.
Recently, phase two of the investigation was completed and presented to the Moscow City Council. MacDonald described what this phase encompassed.
“Phase two says, essentially, ‘All right: first off, what are the water demands going to be in Moscow and the region? Get a picture of what the needs are going to be. And then, if we look at those options other than Moscow Mountain, what are they? What would they cost? And, you know, really, how do they compare to the Moscow Mountain options?'” MacDonald said. “So, that’s what the study does.”
The study included a number of recommendations for regional and local drinking and local non-drinking water options. Overall, the most cost-effective and attainable solutions included a direct pipeline to the Snake River for regional drinkable water with an approximate cost of $56.2 million, a direct diversion or active injection of Paradise Creek or South Fork Palouse River for local drinkable water with an approximate cost of $13 million and South Fork Palouse River for non-drinkable irrigation water with an approximate cost of more than $4.8 million.
Conservation has also been recommended as an inexpensive way to reduce the water decline. Robischon said conservation tends to be the least expensive option.
“I think when folks run the numbers, it seems as though conservation is the least expensive way to reduce the decline,” Robischon said. “After that, various surface water options are more or less expensive, depending upon the details of where the surface water is, where you need to put it, what type of treatment it needs to undergo.”
Robischon added that it is not up to the city or the University of Idaho to decide what options work best for Moscow, but it is up to the residents to make the decision.
MacDonald said that decision will have to be made soon.
“We can’t go on long-term doing what we’re doing,” MacDonald said. “We’re obviously going to have to make some changes … it’s not that there’s going to be one simple answer for any of it. It’s going to be a number of different things we take on as a community and as a region.”
MacDonald said the community is one step along the way, and there remains many steps ahead for whatever path Moscow decides to pursue.
Andrew Jenson can be reached at firstname.lastname@example.org