Photo by Jana Bounds


The groundwater search continues on the mountain

The Cascade area is putting incredible demands on the Big Sky County Water and Sewer District (BSCWSD) system. Finding groundwater on the mountain to sustain growth is a pressing issue and something the district has been proactively pursuing.

Mark Cunane, an engineer with Western Groundwater Services, LLC. was hired by the district to help identify new sites for water supply. Two test wells that were drilled this past summer produced less than ideal results. The Cascade pressure zone currently includes 185 parcels of which 171 were identified as single family residential homes and 10 were considered condominiums or townhouses, according to a recent report by Cunane.

Montana Bureau of Mines, Groundwater Investigation Program just completed a groundwater investigation of the Big Sky Resort Area. Montana Bureau of Mines Hydrologist James Rose offered to meet with BSCWSD representatives to share some of the findings help make the search for water more an educated guess based on scientific principles than simply drilling with crossed fingers.

Rose discussed those findings in a meeting with BSCWSD general manager Ron Edwards, BSCWSD superintendent Jim Muscat, Cunane and BSCWSD board member Peter Manka about a month ago.

The area is geologically unique and challenging for finding quality water, he explained. Anticline folds, a faultline, drill depths, bedrock, mud, shale, sandstone, iron, hydrogen sulphur, rock glaciers, intrusive rocks – technical lingo that speaks to an uncertain path. The real issues are the shale and the geologic layers being “tilted, folded and broken up at numerous faults due to the intrusion of the bedrock that makes up Lone Mountain and secondarily by a large regional fault.”

“Shale is very fine grained and compacted material, so there is little space within the rock to store water, and water essentially does not move through shale. Most wells at Big Sky now draw water from thin sandstone layers within the shales, but the available sandstones vary by location within the resort,” Rose said.

Additional tilting, faulting and folding occurred in many directions thanks to a “major regional fault” that extends northwest-southeast, along the north boundary of Big Sky properties.

Rose explained that the fault raised the mountains north of Big Sky up against the bedrock at Big Sky.

“Along the ridge at the north side of Big Sky, the bedrock layers are tilted vertically up to 90 degrees and more. The fault movement also impacted bedrock through all of Big Sky and to the south, causing many of the geologic layers to fold, and tilt to the north,” he said.

The result of all this movement is that the bedrock containing groundwater – or sandstones – are no longer continuous and connected layers that extend for much distance. The folding and faulting impedes groundwater movement through the formations, he said. This means that a pumping well can only draw water from a limited area of connected aquifer, “which itself is thin sandstone layers that can only contain a limited amount of water.”

Significant snowfall helps the water situation in Big Sky, since the snowmelt can seep in and replenish the groundwater supply each year.

Rose explained that there are a few geologic layers in a few limited locations that might possibly be worth pursuing to augment the water supply.

“Due to the multiple episodes of folding and faulting, and the fact that much of the ground is covered by glacial sediments that hide geologic details at the surface, it is difficult to definitely identify a good groundwater source without actually drilling a well and testing the productivity,” he said. Present well performance and information from past drilling do not present a convincing case that there is a single large capacity long- term groundwater supply, he explained. The potential solution: drill more smaller- capacity wells at specific locations that each supply lesser amounts of water.

“It’s a big crapshoot, it’s like oil and gas exploratory stuff,” Edwards said during the meeting held in the BSCWSD basement. The BSCWSD board was recently presented with two main options. They could drill significantly deeper at previously drilled wells that had been selected for their convenience for hooking-up to the system – as much as 3,300 feet of further drilling would be required to attempt to get to the Madison aquifer at one of the initial wells. That path would equal exponential cost and no guarantee of success, Cunane explained. Or, they could begin shallower exploratory drilling at sites owned by Boyne Resorts that were strategically selected by Cunane for the increased likelihood of water, thanks to the mapping by Rose.

The board decided on the second option for now. Cunane estimated $248,000 to complete all the test wells. BSCWSD has $100,000 in budget without dipping into reserves. The plan is to prioritize certain wells for this summer, working collaboratively with Big Sky Resort to gain easements.

“Find the water first,” Muscat said. “We’re to the point now to where the more we drill, the more we learn how precious this resource is.”

Board member Brian Wheeler said that all of Cunane’s selected sites should be put on the list for exploratory drilling. Cunane is going to be busy this summer, Edwards said.

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