When Big Sky Water and Sewer District filled an empty Yellowstone Club wastewater pond this winter the ice-covered floor rose, pulling up an outflow pipe and ripping the pond liner, spilling 30 million gallons of wastewater and sediment into the Gallatin drainage.
In 2005, the Yellowstone Club constructed an 80-million-gallon wastewater pond on a ridge between two headwaters creeks of the Gallatin River. Citing rocky ground, engineers chose a pipe outfall rather than the more conventional approach of excavation, compaction, and backfilling. The outfall pipe begins near the floor of the pond, passes down through the pond liner and a water-tight boot, then down the mountain to a golf course irrigation system. A stainless steel screen sits atop the inlet to this outfall pipe via a slip connection, allowing it to easily pull off the pipe. A second pipe collects groundwater beneath the pond liner and carries it away from the pond.
According to a DEQ engineer report, the Yellowstone Club notified Montana DEQ the pond was leaking 15 gallons per minute (gpm) on August 10, 2012. DEQ advised the Yellowstone Club to drain the pond down “within a couple of years” and evaluate and fix the problem. Two years later the Yellowstone Club drained the pond and found and repaired several small punctures and a tear in the liner near the boot at the base of the pipe.
The leak continued at roughly 4 gpm into the following summer, resulting in a second draining and inspection. The liner was torn at the same location. A Yellowstone Club pond contractor reinforced the boot and reported the previous fix may not have been done properly. The contractor also clamped the inlet screen to the outflow pipe, rendering the slip-connection a fixed connection.
In late December of 2015, the pond was mostly empty, though 14-18 inches of ice covered the bottom when Big Sky Water and Sewer District began filling it with treated wastewater from the Big Sky Wastewater Treatment Facility. A leading causation theory goes as follows: as the pond level rose, the thick layer of ice rose, taking with it the screen, now firmly clamped to outflow pipe, pulling the pipe vertically away from the liner. On March 3rd, the pipe tore from the liner significantly.
Over the next three days, approximately 30 million gallons of treated wastewater rushed past the torn liner and through the groundwater outflow pipe. The wastewater scoured the hillside and carried unknown amounts of loose sediment into Second Mule Creek, over Ousel Falls, and eventually into the Gallatin River.
Wastewater ponds like those at the Yellowstone Club exist as a result of Big Sky’s incredible growth and emphasis on luxury. These wastewater ponds serve a dual purpose: (1) they store water for use on golf courses during dry summer months, and (2) by virtue of golf course application, the larger community theoretically reduces the amount of nutrient pollution discharged directly to local waterways, which already receive unnatural nutrient pollution.
Looking to the future and bigger picture, a few items are self-evident, while other questions remain. For instance, if golf course irrigation is a leading cause of nutrient pollution in Big sky waterways, perhaps now is the time to re-think wastewater disposal in the region. Likewise, (1) why is an 80-million-gallon wastewater storage pond allowed high above the headwaters of the Gallatin River, (2) why did DEQ allow the pond to leak for three years, and (3) was the chain of events creating the spill (such as clamping the screen on the outflow pipe) standard operating procedure or negligence on the part of the Yellowstone Club.
DEQ has approved a plan for to repair the broken pond and placed five conditions on its continued operation. We reviewed the engineering plan with an independent expert and the proposed fix appears to be satisfactory provided a minimum water depth is maintained above the outlet structure. We’re glad to see DEQ using sound engineering to ensure this won’t happen again. It’s critical now that we don’t lose sight of larger pollution control issues in the Big Sky area like regional wastewater treatment, capacity, and disposal, and the need to take a hard look at landscape transformation and stormwater pollution. We will be examining theses issues and identifying opportunities to collaborate with local stakeholders as Big Sky continues to develop.