A BoiseDev Deep Dive

Mtn. Home Air Force Base building waterline to Snake River, Elmore Co. looks at options as aquifer declines

Mountain Home Air Force Base’s time pumping drinking water out of the ground will soon be coming to an end.

In the next three and a half years, the military installation is working with the Idaho Water Resources Board to bring online a new project to pipe water up from the Snake River into a new water treatment facility for the base. This will end the Air Force and its 4,800 people who work on the base’s dependence on the deteriorating Elmore County aquifer.

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Monitoring wells both at Mountain Home Air Force Base and throughout the county show the aquifer dropping at a pace of roughly one to two feet annually for years. This makes the future of the deep groundwater wells the City of Mountain Home and the Mountain Home Air Force Base uses to get water for irrigation and drinking water uncertain, leaving Elmore County residents to search for other solutions.

Lt Col Josh R. Aldred, the 366th Civil Engineering Squadron Commander and supervisor of public works on the base, said the combination of bringing Snake River water onto the military installation and other conservation measures will help secure the Air Force’s presence in Idaho for the foreseeable future.

“We do see the long-term trends with climate change,” Aldred told BoiseDev. “It’s going to be hotter and drier and this area is already a high desert, so water is a precious commodity. I think after the treatment plant is in it’s going to be a huge win for the sustainability of this mission for decades to come.”

Hotter summers = more burden on the aquifer

Mountain Home Air Force Base’s water rights to pump from the aquifer date back to the early days of World War 2 when the base was established.

Since then, the base has pulled water deep out of the ground like most of the other water users Elmore County to sustain its operations. This worked well until the early 2000s when the Idaho Department of Water Resources and other users started discussing the dropping aquifer. IDWR’s Water Project Section Manager Cynthia Bridge Clark said this decline is due to more water being pumped out of the ground than is seeping back in.

There are some users relying on surface water from reservoirs and other sources in Elmore County for irrigation, but most water comes from pumps deep in the ground. This means in unusually hot years, like the record-breaking summer of 2021, the irrigation districts run dry earlier, forcing water users to turn toward even more pumping. It all continues in a vicious cycle to deplete the declining water source.

A graph courtesy of Mountain Home Air Force Base showing declining aquifer levels since 2003.

Bridge Clark said even though Mountain Home Air Force Base only accounts for a small percentage of the water used in Elmore County, finding a source of water other than the ground helps slow the coming decline. Like in the rest of the Treasure Valley, agricultural irrigators make up the largest portion of water users.

“The reason this has become a project of interest is we recognize the base provides a significant economic benefit to the state and it is dependent on groundwater usage,” Bridge Clark said. “Providing an alternative supply to a large water user and offsetting pumping is a benefit to the aquifer as a whole.”

A state and federal partnership

The project will be split in two pieces.

The Air Force will pay for the water treatment plant on the base, which will be able to treat up to 3.5 million gallons per day. The design is not finalized yet, but Aldred said there is a possibility of the base slimming down the treatment plant’s capacity down to 2.5 million gallons per day to save costs and water.

The project is projected for competition in the summer of 2025 with an estimated price tag ranging from $33 to $39 million.

A map of the proposed pipeline from the C J Strike Reservoir to Mountain Home Air Force Base. Sections of this map featured detailed satellite images of the base, which were blurred by Mountain Home Air Force Base’s Public Affairs Department due to national security.

“We have been aggressively trying to save water in recent years,” he said. “We’re looking at some additional projects for xeriscaping and we’re trying to add more of that. That’s very good for saving water and it’s very low maintenance as well. It’s kind of a win-win for us to do more of that here on the installation.”

The other half of the project, the roughly 14-mile pipeline, will be covered by the Idaho Water Resources Board and also cost in the roughly $30 million range. The pipeline will travel from the C J Strike Reservoir along Highway 51 and enter the base near the main gate. The goal is for water to be flowing through the pipeline by the end of 2025.

Anderson Dam is key to Mountain Home’s future

Elmore County isn’t sitting idly by as the aquifer depletes, either.

County Commissioner Bud Corbus said the county is hoping an infusion of federal infrastructure dollars and help from the Idaho Department of Water Resources will help get two projects off the ground to help create a long-term, sustainable water supply in the area. This includes a pumping station and a pipeline to bring water from Anderson Dam down to Mountain Home, as well water rights to access more water that could come online after the dam is raised.

“Sooner or later, there’s going to come a time when there’s not going to be water there,” Corbus said. “You have to bring something in to sustain that water system underground because everything is being pumped from deep underground unlike the rest of the Treasure Valley. They have a river that recharges the whole system, where in Mountain Home we have nothing. It’s just underground.”

An aerial photo of Anderson Dam, courtesy of the Bureau of Reclamation.

Corbus said Elmore County has landed a permit to pump 200 cubic feet per second of water out of Anderson Dam for two months of the year during flooding. This can both help use excess water and keep Mountain Home sustainable long-term. But, the issue is getting the water from behind the dam into town.

This would require a pipeline and a pumping station costing upwards of $30 to $40 million. He said the county is working with an outside consultant to put together a few scenarios for possible bonds, local improvement districts or some other mechanism to pay for the project. Commissioners are also exploring using American Rescue Plan funds or applying for newly available federal grants.

Corbus’ other water-related hope is that the county can get some extra water after IDWR and the Bureau of Reclamation complete a recently approved project to raise Anderson Dam six feet. This increases the capacity of the dam by nearly 30,000-acre feet. If the pipeline and pump station are built, Corbus hopes 10,000-acre feet of that new water capacity can come down to Mountain Home.

The extra water means the pump station and pipeline project could be smaller and more attainable for the rural locality to afford.

“Now that $35 million dollar project has come all the way down to $10 or $15 million.”

Margaret Carmel - BoiseDev Sr. Reporter
Margaret Carmel is a BoiseDev reporter focused on the City of Boise, housing, homelessness and growth. Contact her at margaret@boisedev.com or by phone at (757)705-8066.

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