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MURTAUGH — A 30-year-old irrigation district is spending millions on aquifer recharge to raise groundwater levels in the Golden Valley area in western Cassia County.

The site of the new recharge project is one of four critical groundwater areas in the 110,000-acre irrigation district stretching from Declo to Rock Creek.

Thirteen members of the 200-member district are investing in two 30-inch pipelines that will deliver irrigation water to the Oakley fan during the growing season and recharge water during the winter.

The winterized trunk line, called the Buckhorn Pipeline, will deliver 120 acre-feet per day to be injected into active groundwater wells in the desert.

The project also includes replacing the district’s West Cassia Pipeline pumping station at the Snake River with a winterized station about five miles west of Burley. The pumping station pumps and lifts water some 300 feet above the river’s edge.

The irrigation district was the first in Idaho to address the declining groundwater level, said Randy Brown, district manager and chairman of the board.

The district’s High Plains Recharge Project in the 1990s was one of two pilot projects in the U.S. to study the effects of directly injecting surface water into groundwater wells.

The project took place long before the Idaho Water Resource Board recognized aquifer recharge as a “beneficial use” of a water right, Brown said.

The study concluded that direct recharge not only raised the level of the aquifer, it improved the quality of the groundwater because it increased water movement within the aquifer, aiding filtration.

The district began monitoring the groundwater levels in its wells and in 2010 discovered the water levels in some had dropped about 25 feet in six years, said Brian Higgs, water consultant for the district and water master for Basin 140.

To reverse the decline, the district started a recharge process called “soft conversion” by shutting down groundwater wells and leasing irrigation water from surface water districts. Southwest then installed the West Cassia Pipeline — three 24-inch pipelines — and its pumping station, to deliver 15,000 acre-feet of surface water per year to its members along the way to Golden Valley.

The district today is laying the Buckhorn Pipeline along the West Cassia Pipeline. The new pipeline will deliver an additional 20,000 acre-feet for soft conversion during the growing season and direct recharge during the off-season.

Southwest’s use of soft conversion recharge is the largest in the state, Brown said. The district has 52 pumping stations — valued at about $50 million — paid for by its members. The Buckhorn Pipeline has a $13 million price tag.

“It’s an unbelievable undertaking,” Higgs said.

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What’s in it for district members?

In 2015, surface water users and groundwater users negotiated a pivotal agreement to replenish the depleted Eastern Snake Plain Aquifer, which had reached its lowest level since 1912. The agreement, bartered by Idaho House Speaker Scott Bedke, R-Oakley, averted curtailment of junior groundwater rights by the Surface Water Coalition, which holds senior water rights.

Southwest Irrigation District, which has recharged for years, negotiated its own plan with the SWC to establish “safe harbor” from curtailment through its water management plan. The Buckhorn Pipeline soft conversion and recharge is part of that plan, Brown said.

In the settlement, the state of Idaho agreed to fund efforts to return 250,000 acre-feet per year into the ESPA. That includes the cost of winterizing Southwest’s Buckhorn Pipeline and its pumping station. The state also pays the district to transport the recharge water through its system.

The state is also funding recharge efforts at Murtaugh Lake on the Twin Falls Canal system, Wilson Lake on the North Side Canal system, and the recharge “workhorse” Mile Post 31 on the Gooding Milner Canal.

The Idaho Water Resource Board’s “current recharge water right is 1,200 cubic feet per second,” said Wesley Hipke, recharge project manager with the Idaho Department of Water Resources, “but currently we aren’t there yet. The board’s whole intent is to develop that capacity to use the full amount.”

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