It appears the Environmental Protection Agency has found a place for long-term storage of mine waste near Silverton.

The EPA announced this week it is proposing a waste repository for the Bonita Peak Mining District Superfund site on top of the existing tailings impoundment near the Mayflower Mill, about 2 miles northeast of Silverton off County Road 2.

The site, EPA officials say, would serve as a long-term option to store waste that is generated from Superfund cleanup actions, as well as sludge from the water treatment plant that takes in discharges from the Gold King Mine.

“It’s going to be there for the long haul to accommodate any waste we’ll need to remove,” said Christina Progess, the EPA’s lead for the Superfund site.

The proposal comes with one caveat, however: The property is owned by Sunnyside Gold Corp. The EPA has asked for approval from Silverton’s last operating mining company and has yet to hear back.

Gina Myers, a spokeswoman for Sunnyside Gold, said in an email to The Durango Herald that “SGC ... had previously offered EPA the use of Mayflower ground for storage of sludge from the underutilized treatment plant.”

Myers did not clarify whether Sunnyside Gold will allow EPA access or not.

The need for a centrally located, permanent dump site for mine waste has been an ongoing issue for EPA ever since the Superfund was declared in fall 2016, about a year after the agency triggered a blowout at the Gold King Mine.

The water treatment plant constructed after the blowout generates up to 6,000 cubic yards of sludge a year – or about a football field buried in 3 feet of muck – and there’s little room on-site for storage. And in the future, the EPA will need a place to take waste removed from other projects.

In the past few years, the EPA had proposed hauling the waste 70 miles to a landfill south of Durango. The agency also had a temporary fix, mixing sludge with the Kittimac tailings pile about 6 miles north of Silverton.

In August 2019, Sunnyside Gold offered the EPA access to its property at the Mayflower tailings repository, a large series of four impoundments of historic mine waste rock that operated until the early 2000s.

“(The site) is an ideal and proven site for a repository for the water-treatment plant, and, in the interest of good faith and improving water quality, SGC has granted EPA access for this evaluative work,” the company said at the time.

Progess said the EPA sent Sunnyside Gold a consent for access request and hopes to hear of a final decision by mid-August.

“We’re hoping they give us access,” Progess said. “We’d have to evaluate our options if they don’t and figure out the best path forward.”

What complicates matters, however, is that Sunnyside Gold is considered a “potentially responsible party,” a term the EPA uses for companies that may be on the hook for cleanup costs in a Superfund.

Over the past couple of years, Sunnyside Gold has outright refused EPA work orders in the watershed, called for the EPA to recuse itself from leading the cleanup and questioned the scope and necessity of the Superfund site.

If access were granted, the EPA would start a phased approach at the Mayflower tailings, Progess said. A liner would be placed on top of the existing piles for the new waste, which would then be capped.

All told, the EPA’s plan would have the capacity to store up to 609,000 cubic yards of mine waste and sludge. Use of the site, however, would vary year to year, depending on current projects and need.

“It’s really big ... progress on-site to have a repository we can use for decades to come,” Progess said. “That’s really going to set us up well for success in the future.”

The EPA’s Bonita Peak Superfund consists of 48 mining-related sites around Silverton, seen as the worst loaders of heavy metals into the Animas River, impacting water quality and aquatic life throughout the watershed.

The Mayflower tailings are suspected of leaching heavy metals into the Animas River, which has prompted Sunnyside Gold to conduct its own multi-year investigation into the matter.

Progess said the investigation remains ongoing, and the EPA would use a different, more stable location at Impoundment 1 on the site to store its waste to begin with. She said leaching is suspected at Impoundment 4.

“We feel comfortable starting the work at Impoundment 1,” she said. “That will allow us years of use while the investigation on Impoundment 4 can continue.”

The public can comment on the proposed plan until Aug. 27. A virtual public hearing will be held at 6 p.m. Aug 11.

Progess said the EPA hopes to have the site constructed and ready for use by fall 2021, about the time storage at the water-treatment plant for the Gold King Mine is expected to reach capacity.

“The need to expedite access for construction is really essential,” she said.

To comment or view project details, visit www.epa.gov/superfund/bonita-peak.

jromeo@durangoherald.com