Bill Hensley has capped a few landfills — 225 by his estimate — in his day.
Standing atop Teton County’s pile of trash, looking down at the sun-kissed Snake River valley, Hensley deemed it among the prettiest.
“It’s sort of a toss-up between this and Half Moon Bay in California,” the Peak GeoSolutions engineer said.
“It’s a similar sort of canyon feel, but you’re looking out at the Pacific,” he said.
Below, crews worked on an ambitious project to permanently cap a landfill containing up to 750,000 cubic yards of waste dating back more than half a century.
This fall, drivers-by south of town have probably noticed crews rolling out layers of black synthetic material over the Horsethief Canyon hill.
The landfill, which used to reach all the way to the highway, opened around 1960 and officially closed in 1989.
It sat unused as Teton County began transferring trash to landfills elsewhere, as it does today.
“Now, we’re doing a closure for environmental reasons,” Hensley said.
When officials detected groundwater contamination threatening water sources like the Snake River and Flat Creek, the Wyoming Department of Environmental Quality mandated the landfill be officially capped and closed by the end of 2019.
So began a complicated, phased process to excavate the highway-facing side of the landfill, move all the trash to the forest and close it all up for good.
Sealing the landfill prevents runoff from the heap from contaminating nearby bodies of water.
The effort started in 2016 with clearing waste from county land and heaping it onto the portion of the landfill sitting on the neighboring Bridger-Teton National Forest, which also wanted to protect local waterways from contamination.
(When asked if workers found any cool trash in the process, Hensley said an employee salvaged a 1980s newspaper, but his supervisor required he toss it because it was stinking up the office.)
That created stable land for Integrated Solid Waste and Recycling to build new infrastructure where the waste used to be. Over the past five years a new scale house and two transfer stations were added to support the operation of transporting Teton County’s garbage to an Idaho landfill.
One of the stations is set to convert to a hub for a new food waste composting program in 2020. The waste excavation project also created space to divert trash from the landfill, such as sorting and storage areas for scrap metal and organic waste.
The landfill now contains all the trash on U.S. Forest Service property. It isn’t lined on the bottom, so it’s in direct contact with the ground, said Integrated Solid Waste and Recycling Superintendent Brenda Ashworth.
“That was the general practice for landfills in the ’50s, ’60s,” Ashworth said. “We know better now, so we line our landfills.”
Capping the landfill means first loading about 6 inches of sand atop the trash pile, Hensley said.
That’s followed by two black synthetic liners. Those layers filter sediment out of the hill’s stormwater.
Meanwhile, chimneylike pipes scattered around the hill allow methane gas — generated by the decomposing waste — to escape. Without venting the methane could dislodge the cap.
The 913,000 square feet of liners are about 60% laid, Hensley said. Contractors use fusion welders to impenetrably seam the liners together.
Then, 2 feet of plants will cover the sand and another 6 inches of topsoil and vegetation will be laid over the whole thing using a seed mix from the Forest Service, Ashworth said.
“You want it to blend in” for the casual observer, she said, but passersby will probably still be able to tell the landfill is not natural.
For Ashworth the project is important because it’s meant to protect the groundwater.
“The broader picture is addressing the environmental concerns, the groundwater, and managing that waste mass in a prudent fashion,” Ashworth said.
After the capping wraps up this year the landfill will continue to be monitored for at least another 30 years.