UM Western to conduct aquifer tests on West Bench

The Ground Water Investigation Program needs volunteers

ENNIS—The testing of some wells has already begun on the West Bench, but the Ground Water Investigation Program (GWIP) is still looking to expand the number of test sites for its data collection, set to continue until December of 2019.

Montana Bureau of Mines and Geology (MBMG) hydrogeologist Andy Bobst is the team lead on the project, which will examine the potential effects of residential development on the local aquifer. The goal for the project is to test around 80 wells.

“In order to do any sort of investigation like this, one of the most critical parts is being able to access wells and surface water sites so we can monitor the area,” says Bobst. “That usually entails coming out about once a month to see how the wells respond to things like snowmelt and irrigation.”

The GWIP project emerged when the Madison County Planning Board approached MBMG and asked for more information before moving forward with further development. 

GWIP is a non-regulatory body that conducts research on the most urgent water issues in the state. When a local question arises, it is ranked in terms of urgency and passed to GWIP, which is a branch of Montana Tech in Butte.

“We don’t try and tell people how to do things,” says Bobst. “We just help provide information, to allow them be aware of the potential effects of certain actions.”


Ennis Aquifer

The reason for this project is the variance of the types of aquifer seen in the Madison Valley. Down in the river valley, Bobst says, the aquifer is much more porous and has different recharge sources, which means that area of the aquifer is fairly productive. When a well is installed there, it’s “cone of depression” is fairly small.

The cone of depression is the area in the aquifer that a well has to pull from in order to draw sufficient water. When the well is placed in a more productive area of the aquifer, it doesn’t have to draw from as large of a geographic area or draw as deeply into the ground as it would in an area with a less productive aquifer.

That’s where the West Bench comes in.

The aquifer on the West Bench isn’t porous, unconsolidated sediment, Bobst says. It’s largely made of bedrock, which is significantly less permeable. 

Cracks or fissures in a bedrock aquifer also allow for groundwater to settle much deeper into the aquifer, which means some wells have to be dug much deeper than they otherwise would in order to reach the water table.

That means that the cone of depression for each well is larger, so each new installation will interact differently with the wells around it. That is exactly what GWIP will test.

“It’s unique in the Ennis area, because there’s a lot of development up on the bedrock area,” says Bobst. “It’s a much less productive aquifer, which means two things: you’re not going to be able to pump as much water from a well, and you’re much more likely to affect your neighbors.”



The tests that GWIP conducts are very low-key, says Bobst. He compares the monthly observation tests to a visit from the meter reader: GWIP shows up, uses a tape to measure the level of the water in the well, records it, and leaves again.

There are other kinds of tests that will allow GWIP to examine how wells interact with one another and how they affect the local aquifer. They’ll conduct these tests on about 20 wells, a quarter of their total test field. 

Aquifer tests involve pumping a well for about eight hours, then monitoring it to see how quickly it recharges and what impact it has—if any—on nearby wells. 

On very few of the total test field—as many as eight wells total—GWIP will conduct the most significant tests: a 72-hour pump that will help identify the cone of depression, the efficiency of the aquifer’s recharge and the rate at which a well can pull water in different locations.

In some cases, GWIP will install new wells, purely to see how pumping an existing well will affect it. 

Bobst says in certain cases, people have been concerned about wear and tear on their pumps that comes with running them for so long a period. In those cases, he says, GWIP simply installs a pump on their own well, and watches how it works in conjunction with the existing well.

In addition to the practical, hands-on tests GWIP will conduct, the investigation will also allow researchers to develop groundwater flow models. 

While slightly less glamorous than the field work elements, Bobst says the models will allow them to understand how different intensities of development will impact the aquifer locally over time.

“It’s a very locally-based, issue-based program” he says. “And that’s pretty unique for this part of the west. We want to give people an understanding of the effects of certain kinds of development. How much would it affect your neighbors and the aquifer?”


Getting involved

The project has already begun, but Bobst says an emphasis right now is growing the local well network up to the project goal of 80 from the current 45. GWIP is in search of local landowners and well users who would be willing to allow them to test their wells as part of the investigation.

To learn more about GWIP and the Ennis groundwater investigation project, or to get involved with the program, visit the project website at Or, call Bobst at 406-496-4409 or Mary Sutherland, the project’s modeler, at 406-496-4410.

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The Madisonian

65 N. MT Hwy 287
Ennis, MT 59729

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