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CITY GROUNDWATER STUDY

Helena has been exploring groundwater supply for years

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Water moves through a settling chamber of the water purification process at the Missouri River Water Treatment Center.

Over two decades ago, Helena drilled a well to see what aquifers lie beneath the valley floor. It conducted tests and got the well approved as a public water supply, but the project largely went dormant until now.

The city commission approved a contract on Sept. 20 to drill three test wells near the Missouri River Treatment Plant, though municipal groundwater exploration goes back at least to the 1980s. The project comes as the region deals with a warming climate and strain on surface water supplies like at the Ten Mile Water Treatment Plant, which brings in and treats water as it flows by.

“If there’s not enough water in the creek, we can’t treat enough water,” Interim City Engineer Jamie Clark said, adding this was the first time they’ve had issues in his eight years here. “This summer was just dry, extraordinarily so.”

The wells would make use of city rights to over 10 million gallons per day for June through August and 5 million gallons per day for September through May. That’s under a 1992 water reservation by the Montana Board of Natural Resources and Conservation, according to commission documents.

The reservation, the largest in the Upper Missouri Closed Basin, is generally use-it-or-lose-it with a deadline at the end of 2025. A city report prepared by the company HydroSolutions last year reviewed earlier work and put forward plans to develop the reservation before the clock ran out.

In 1998, the city drilled a new well and deepened an existing test hole from the 1980s near the Missouri plant to explore the groundwater supply, according to the report. Domestic and irrigation wells mostly use a shallow aquifer, generally less than 150 feet deep, but the test hole had reached a deeper aquifer starting 335 feet down.

The 1998 well hit the deep aquifer at 350 feet down and another aquifer below it starting at over 500 feet deep, which a subsequent report named D1 and D2. These deep aquifers were also found by later wells and the 2020 report said their occurrence “remains an encouraging groundwater target,” as they are less vulnerable to contamination than surface sources.

Further drilling didn’t happen because of “unsatisfactory PW1 [well] yield results,” according to the report, and Public Works Director Ryan Leland said the city budget sidelined the project.

The drought this summer demonstrated the importance of developing groundwater supplies, Leland said to the commission. While the city has seven irrigation wells, and the 55-foot Eureka Well near downtown, the report said it has left its groundwater reservation largely unused so far.

Limited treatment needs are a popular benefit of groundwater over surface sources, according to Ed Cosens with O’Keefe Drilling, which won the Helena drilling contract.

The company dealt with shallow domestic wells temporarily running dry this summer in Butte, where it’s based, the Montana Standard reported. Cosens said things have leveled out since then.

Aquifer water levels can change with the seasons, the Helena report said. Data indicated water levels at the Missouri plant test hole varied seasonally by as much 11 feet, though other wells had less fluctuation.

Well interference, or how much new city wells could lower water levels for nearby deep wells, was uncertain according to the report. Clark said the reservation is limited to deep aquifers and should not impact shallow wells.

The city plans to integrate groundwater as an assurance policy, Clark said, backing up surface sources for the city's water supply.

The test wells approved last month would look for good spots to access the aquifer and the city aims to complete the whole project by around 2024, Leland said to the commission.

Inspections on the Missouri plant well and test hole for the report last year found they were in good condition, though the well would need to be re-certified for use.

“The City’s water reservation provides a tremendous opportunity to secure water for future growth within a closed basin,” the report read, adding, “The need to proceed as quickly as possible cannot be over emphasized.”

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