Sludge pond capped at Bunker Hill Superfund site
This aerial photo shows where work is being done to cap the former Bunker Hill sludge pond on top of the Central Impoundment Area. The old pond, pictured in the top left of the photo, was filled in 2023. The new three-bay sludge impoundment area, pictured top right, is where the waste materials from the nearby Central Treatment Plant are being stored.
Courtesy photo
KELLOGG — Work throughout the Bunker Hill Superfund Site has ramped up for the season, including the finalization of a project on top of the site’s central impoundment area.
The Bunker Hill CIA was built in 1928 as a repository for tailings, mine waste, gypsum and acid mine drainage, but was covered and capped more than two decades ago as part of the cleanup efforts within the Superfund site.
For the past 30 years, sludge from the nearby Central Treatment Plant has been disposed of in an 8-acre lined pond atop the CIA, but in 2023, the pond was at max capacity and will now be sealed.
The CTP was built in 1974, with the specific goal of treating wastewater from the nearby Bunker Hill Mine, but the plant was upgraded in 2021, and a new groundwater collection system was installed.
According to Jocelyn Carver, EPA remedial project manager, sludge is a semisolid material and the byproduct of the wastewater treatment being done at the CTP. During the treatment, lime is used to neutralize the highly acidic water to create the sludge, which contains toxic heavy metals, including lead.
Because of the high toxicity of the waste materials, the disposal requires a thorough containment and capping process.
“There are several layers used to create a robust sludge pond cover system,” Carver said.
This covering will match the existing covering that was placed over the CIA.
Now that the sludge pond is being capped, the EPA is utilizing three lined cells for sludge impoundment and disposal. These cells sit on top of the CIA and have been in use since the original pond was filled in 2023.
Because of the nature of the materials and the specificity of the project, getting to the construction phase has been slow going, but work on the cap began last month, and Carver anticipates it will be completed by August.
“Each design iteration for the old sludge pond cover system was reviewed and commented on by a robust product delivery team and has undergone internal review by the U.S Army Corps of Engineers,” Carver said.