Beyond the beauty: Yellowstone’s emergency wastewater system chugs along

BILLINGS – Tucked out of sight, amid the beauty of Yellowstone National Park’s geysers and wildlife, is an essential service for the roughly 4 million people who visit each year – sewage treatment plants.

“This is a very important part of park operations,” said Duane Bubac, chief of design and facility management.

Wastewater is not something that comes to mind when driving the park’s Grand Loop to view the spouting plume of steam from Old Faithful geyser or the subtle colors of the Grand Canyon of the Yellowstone, but without systems to treat effluent the rotten egg smell could be coming from something less intriguing than a fumarole.

The importance of this infrastructure was highlighted in June 2022 when a 500-year flood washed out the sewer line running alongside the Gardner River from Mammoth Hot Springs, the park’s headquarters, to the nearby Montana community of Gardiner and its wastewater treatment plant. The line was quickly turned off once the break was realized, but park staff then had to scramble to find a backup plan. The rupture led to the closure of Mammoth Hot Springs Hotel, one of Yellowstone’s historic attractions, and also a large producer of wastewater.

In the wake of the break, the park facilities staff resurrected an old sewage treatment system that relied on percolation ponds last used in the 1960s.

“We were under a huge time crunch on this,” Bubac said.

Temporary fix

At the same time, the crew was scrambling to find a more long-term solution. By winter, work was underway to assemble a $30 million temporary treatment system that would be shipped in prefabricated components, but water and air lines still had to be constructed to connect the components.

“It was a pretty ambitious schedule we originally planned,” said Molly Ohlen, a civil engineer for the park. “Then getting it constructed took longer than we hoped, but it was still much faster than a normal construction would be.”

Pushing back the completion date were subzero temperatures and 2 feet of snow that made work such as excavation of frozen ground even more difficult. Ground-warming blankets were deployed. Outside dirt had to be brought in for backfill that was not frozen.

“So definitely the weather caused a lot of complexities with the earth work,” Ohlen said.

Meeting standards for construction and soil compaction in such cold weather was more complicated, and the team also needed information on geotechnical data, soil analysis and groundwater in the area where the plant was assembled.

“We wanted to make sure we weren’t making problems further down the road,” said Jason Murphy, facilities manager for utility system operations in Yellowstone.

New technology

Since going online earlier this year, the new membrane bioreactor plant has been working well, with it meeting or exceeding effluent design parameters as it handled a peak of 170,000 to 180,000 gallons of waste in high-use days this summer. (Mammoth Hot Springs Hotel has since reopened.) The plant’s maximum capacity is 300,000 gallons a day. Treated water is discharged to percolation ponds where the water evaporates or seeps into the ground.

“That’s a technology that is good for providing really excellent treatment in a small footprint,” Ohlen said. “So it was good for this site so we could minimize disturbance but get the best possible treatment.”

The park is proposing to install similar systems as it upgrades its wastewater treatment facilities at Old Faithful, Grant and Canyon villages. The work will be paid for by funding from the Great American Outdoors Act.

“We were fortunate to get the level of funding that we did to replace some of these old systems,” Bubac said.

Until those plants are built, the new system at Mammoth serves as a training ground for park operators to learn the updated technology, Murphy said.

“It’s cool to have this technology to play with and learn from,” he said. “I think it’s going to be adaptable or resilient because our flows change here in Mammoth or anywhere in the park. So I can see the plant adapting to those seasonal variations.”

Upgrades

Grant Village will be the first targeted for wastewater treatment plant replacement. The existing system was last updated in the 1980s. Designing the new system has taken two years. It’s estimated the work will take about three years, given that access to the more remote section of the park in winter is only by snowcoach or snowmobile. That limits excavation and dirt work to a window between late May to November or December, Murphy explained.

The Old Faithful wastewater system was more recently upgraded around 2000, but the Park Service wants to enhance and rehabilitate the infrastructure for pretreatment to make it easier for the system to handle vault toilet waste.

“That’s the specific challenge we have with wastewater,” Ohlen said. “We’ve had a large increase in day visitors.”

Most visitors aren’t staying at park hotels that are directly plumbed into the system where the wastewater is diluted by shower water and dishwater. Consequently, the vault toilets collect highly concentrated waste, in addition to trash, which can mess up the biological component of a sewage plant’s treatment process.

“You can’t show up at a wastewater treatment plant with 10,000 gallons of vault waste and just dump it into the process,” Murphy said. “You’ve got to be able to trickle it into the process without upsetting it.”

Murphy roughly estimated each wastewater system may see 15,000 to 20,000 gallons of vault toilet waste a week during the peak of the summer season.

Reconnecting

As noted, the Mammoth treatment plant is meant to be temporary until a new sewer line can be run to Gardiner’s plant. The holdup is a final plan for the new road connecting Mammoth to Gardiner. The sewer line will use the road as a right of way to avoid additional ground disturbance.

A temporary road was quickly built in 2022 on an old stagecoach route away from the Gardner River. But the new route has its own problems, such as several winding turns and a steeper climb and descent into Mammoth. When there’s ice on the road, travel can be especially tricky, and this is one of the few sections of road in Yellowstone that remains open year-round to auto traffic. From Mammoth, travelers can drive on to Silver Gate and Cooke City, just outside the park’s Northeast Entrance.

Even before the sewage line from Mammoth to Gardiner was severed, problems had plagued the system. The community of Gardiner filed a lawsuit against the park due to high arsenic levels in the Mammoth effluent. Just before the line was severed in 2022, the Park Service had completed much of its work to keep naturally occurring arsenic-tainted groundwater from infiltrating the system through old pipes and flowing in via manhole covers, Ohlen noted.

“In an upcoming project, that we have funds coming for already, we are going to work on further reducing (infiltration and inflow), targeting problem areas based on all the condition assessment data we have now,” Ohlen said. “So we are going to continue to work on that.”

The facilities staff will treat the new temporary system like it’s there to stay, Murphy said. Who knows, in another disaster situation it could be needed somewhere else in Yellowstone or another national park, he added.