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Groundwater study: State hydrogeologists continue research on Bitterroot Valley aquifer

Montana Bureau of Mines and Geology hydrogeologist Dean Snyder helps guide an acoustic Doppler river provider across the Bitterroot River just south of Hamilton Wednesday afternoon. A team of hyrdrogeologists have been working in the Hamilton area for the past year to gather information on the area's groundwater. Their findings are expected to be available in a public report released sometime in 2016.

Wednesday was a good day to be part of an investigative team working to uncover the secrets of the Bitterroot Valley aquifer around Hamilton.

In the morning, Montana Bureau of Mines and Geology research hydrogeologists Ginette Abdo and Todd Myse received tentative approval to place as many as three new monitoring wells on strategically selected county-owned lands between Skalkaho and Woodside.

In the afternoon, the researchers took advantage of the unusually warm weather to skirt a sophisticated acoustic Doppler current profiler across the Bitterroot River at Anglers Roost, in their ongoing effort to gather information important to understanding the relationship between the ground and surface water in the valley.

“It’s huge for us to be able to come out here in February and not have to deal with any ice,” said Abdo. “It’s huge for us to be able to gather this information during the non-irrigation season. That’s a key.”

Abdo serves as the senior research hydrogeologist for the state’s Ground Water Investigation Program.

That program was established by the Montana Legislature as a means to accomplish research necessary to better understand groundwater resources across the state.

Every day in Montana, an average of about 272 million gallons of water is extracted from the state’s aquifers for domestic and agricultural uses. In some places in the state, including most of the Bitterroot Valley, groundwater is the only reliable year-round source of water for household use and for livestock.

The groundwater investigation program has documented the importance of the irrigation projects, including canals similar to those that course through the Bitterroot, as an important source of water for groundwater recharge.

In Helena’s North Hills, the model created by the program showed that groundwater could drop up to 20 feet over the next 20 years if residential development continued. In Bozeman, the investigative team found that land-use changes, including reduction in flood-irrigated acres near town, reduced groundwater flow but only caused small changes in groundwater levels.

The Bitterroot Valley was one of the first projects a steering committee identified for a groundwater study after the program began in 2009. At that time, there was a good deal more development occurring in the valley and there were questions on what that meant for the groundwater resource.

“When the list was first developed, the Bitterroot was high on the flagpole because of all the residential development that was occurring and the potential impacts to groundwater from wells and septic systems,” Abdo said.

The hydrogeologists started gathering information from about 90 wells and 30 surface water sites between Skalkaho Creek and Woodside Junction last year. They will continue to gather that information through the fall of this year before writing a report and developing a groundwater model that should be available to the public sometime in 2016.

So far, the researchers said they haven’t seen anything that would indicate nitrate levels were too high in the well and surface water they’ve sampled.

On Wednesday, Abdo and Myse asked the Ravalli County commissioners for permission to dig three test wells and several smaller monitoring wells on park property in the Skalkaho Creek area, on the Ravalli County Golf Course, and at Blodgett Park.

Once the wells are in place, the researchers will conduct a drawdown of the aquifer by pumping water continuously over the course of three to five days. The drawdown will be monitored in the nearby smaller monitoring wells.

The researchers will carefully monitor the time the aquifer takes to recharge.

The drawdown will happen one time. The researchers didn’t expect that any of the neighboring properties would be impacted by the test.

The commission agreed unanimously to grant the bureau authority to pursue access agreements for the monitoring project at all three locations.

After finishing with the commission, the research team moved its operation to the field to take advantage of an ice-free Bitterroot River.

They met fellow hydrogeologist Dean Snyder at Anglers Roost to measure the current flows in the river using a system that maps river velocity and depth using a system similar to sonar. The equipment is mounted onto the top of a float that would probably work well as a boogie board. It’s pulled from one bank to the other several times while the sophisticated tracking equipment sends readings back to a nearby laptop computer via a Bluetooth connection.

The information they gathered will be compiled with even more flow information collected from seven tributaries of the Bitterroot between Skalkaho and Woodside.

From there, they will let their computers go to work to create a water budget that could provide some insight into what role groundwater plays in the Bitterroot River.

“It’s a typical tool of the trade,” Abdo said.

Currently, Myse said there is a lot of interest in the connectivity between surface and ground waters.

Beyond creating a water budget for the Bitterroot to help determine that interaction, the researchers also collect small bottles of water that hold their own interesting clues.

“We collect isotopes all through the project,” Myse said. “Each source of water has its own different isotope. It’s like each source has its own fingerprint. That can tell us a lot about what’s going on between surface and groundwater.”

Reporter Perry Backus can be reached at pbackus@ravallirepublic.com.

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Associate Editor

Reporter for The Ravalli Republic.