More than 15 years after cleanup began, work to close a toxic former copper and zinc mine in the Hancock County town of Brooksville is set to start in October and continue through next summer.
The former Callahan Mine site on Cape Rosier was mined starting at least as far back as the 1880s before scaling up in 1968 for a four-year stint as the world’s only known intertidal heavy metal mine, washing out to Penobscot Bay.
It was designated a Superfund site in 2002, a federal listing that allows the U.S. Environmental Protection Agency to clean up contaminated sites. Remediation work started on the ground in 2010.
The closure will mark the conclusion of years of work and tens of millions in federal dollars to contain harmful toxins in and around the site, one of 14 current Superfund locations in Maine.
Closure work will be led by Orono-based contractor Sargent Corp., which announced a timeline Tuesday for projects including capping a pile of waste rock with stone and an impermeable liner, plus other “general site improvements.”
The last major cleanup step involved capping waste rocks from metal mining, a process that officials estimated earlier this year would take 1,500 truckloads of additional rocky material and topsoil.
EPA and Sargent officials did not respond Tuesday afternoon to inquiries about the closure.
The town of Brooksville posted on Facebook Tuesday that Sargent trucks would begin arriving that day “for the final steps in securing the site,” running until January and starting again next spring.
The Callahan Mine was an open-pit operation extracting mostly copper and zinc — and, later, briefly an experimental salmon and oyster farm.
By 1972, the corporation behind it had extracted all it could, the Maine Monitor previously reported, and breached dams that had held water back to allow digging, flooding the site. An experiment raising fish there was briefly the largest pen salmon operation on the eastern seaboard before facing financial problems and going out of business, according to the Monitor.
Contamination later traced back to the mine site included waste rock with high levels of arsenic and lead on neighboring residential properties and groundwater contaminated with heavy metals. The site itself had levels of polychlorinated biphenyl, or PCBs, which are toxins that can cause cancer, among other environmental issues.
After years of studies, remediation work started on the ground in 2010. Last fall, the second-to-last phase of the project dredged thousands of cubic yards of contaminated sediment from Goose Cove and piped it into a former mine pit for containment.
Goose Pond, the now-flooded former open pit mine, drains into Goose Cove, which is located on Penobscot Bay.
The last active remediation step involves capping a large pile of waste rock left over from mining operations, which was condensed into one pile from several piles over the last three years, cleanup officials said earlier this year. That will prevent rainfall from draining through the rocks and causing metals to leach into the nearby estuary.
Sargent was awarded a $5.4 million contract from the U.S. Army Corps of Engineers in May to cover about 13 acres of mining waste with a foot of crushed stone and layers of engineered materials, according to government bid documents. It also includes site work such as drainage feature installation and wetland improvement.
When closure begins, up to six trucks per day will deliver materials to the mine site, according to Sargent. They will approach from Route 176 near Black Corner and through the village of Brooksville to the Cape Rosier site. That’s required because there wasn’t enough clean material onsite to use for the cap, project officials previously said.
The mine will still be monitored after active work winds down.
“It’s going to require an eternity of long-term monitoring,” state project manager Iver McLeod said of the site in January.
The former mine has been owned for decades by the Ohio-based nonprofit Smith Cove Preservation Trust. Trust officer James Beneson told the Weekly Packet newspaper in March that his family’s goal is to reforest and “attempt to restore the property to some sort of wild state.”
