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2016 study: Big Sky’s groundwater holding steady

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Hydrogeologist James Rose presents findings from the groundwater study to the Big Sky community on May 17. PHOTO BY GABRIELLE GASSER

By Gabrielle Gasser ASSOCIATE EDITOR

BIG SKY – A three-year assessment of Big Sky’s groundwater resources found that the water table remained relatively stable between 2013 and 2016 thanks to spring snowmelt recharging the system after peak-season pumping draws down the water.  

The Montana Bureau of Mines and Geology report providing data on Big Sky’s hydrogeologic system and a groundwater model was just completed last month. The study, which will be used by local organizations to inform future decisions, identified five objectives which included summarizing the aquifers in Big Sky, developing a groundwater model and evaluating the potential for development of other groundwater sources. 

The bureau gathered data during that three-year period for a study that was part of its Groundwater Investigation Program after the Gallatin River Task Force nominated the area for a study in 2012. The goal was to gain a picture of where Big Sky currently stands with water resources and to equip the community to plan for the future as more development increases demand.

“There’s not a great big aquifer here that you can draw hundreds of gallons of water a minute from,” said bureau Hydrogeologist James Rose. “It’s much smaller aquifer sources, water sources, and they’re also broken up into small segments.” 

Because of the complex geologic history of the Big Sky area, locating new water supply wells can be challenging amongst the various formations ranging from shale, which holds very little water, to sandstone which comprises the best aquifers. 

In a May 17 presentation to the Big Sky community, Rose highlighted the extremely varied nature of the hydrogeology of Big Sky, describing the groundwater as being scattered rather than concentrated in one main aquifer. He said too much drilling of one area would deplete that aquifer. 

Rose referred to the situation as a “balancing act,” saying that Big Sky needs to spread its water use across the multiple aquifers and take into account the fact that the area relies solely on groundwater, which is recharged solely by snowmelt each year in April, May and June. 

As Big Sky continues to grow and use more water, it will be more difficult for the system to rebound, Rose says.

“As you draw water for a longer period of time, you definitely impact more and … snow melt in the spring is really the only time you get recharged,” Rose said.

The task force, in cooperation with the Big Sky County Water and Sewer District, originally proposed this study out of concern for the growth of Big Sky and the additional water needs that come with it.

Now, equipped with a deeper understanding of Big Sky’s groundwater system, the task force will use the model provided by the study to understand how the changing climate will affect Big Sky’s aquifers and work to address some of the high nutrient concentrations contributing to harmful algae blooms in the Gallatin River.

“We’re working with the Gallatin Local Water Quality District to do some additional groundwater monitoring, and some tracers to better understand [nutrient concentrations and sources,]” said Kristin Gardner, chief executive and science officer of the task force.

Moving forward, the intention, according to Rose, is to have the Big Sky community take the information provided by the study and use it to make informed water management decisions. His organization laid the groundwork to characterize the groundwater system in Big Sky and gather three years of data, he said, now it’s in the hands of the community. 

“I just hope there’s a commitment with our community to move forward with the monitoring,” Gardner said. “It is such an important part to better understand how growth is impacting the groundwater.”

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