In an effort to remove heavy metals and provide cleaner water to Idaho’s Coeur D’Alene River, U.S. Army Corps of Engineers’ officials are supervising the dismantling and corresponding upgrade of an existing central treatment plant in Kellogg, Idaho.
The plant, which currently treats two million gallons of wastewater issuing daily from the Bunker Hill Mine, is being upgraded as part of a $48.6 million contract between the U.S. Army Corps of Engineers and prime contractor Wood Environmental and Infrastructure Services.
The work will improve overall water quality by collecting and treating zinc-contaminated groundwater that flows through mine waste and contaminated sediments under the mine’s central impoundment area before discharging into the Coeur d’Alene River’s south fork. The plant removes zinc and other metals by precipitating them as hydroxides in a sludge that is subsequently disposed in an impoundment area. The upgraded plant will produce high density sludge, and the project includes construction of a new 110,000 cubic yard membrane lined sludge impoundment area designed to last 30 years.
“This project will provide reliable long-term treatment of contaminated mine waters and groundwater which will result in much cleaner waters flowing into the Coeur d’Alene River, Lake Coeur d’Alene and into the Spokane River,” said Rodney Zion, Corps’ project engineer.
Prior to upgrades, the plant's water treatment capacity was approximately 2,500 gallons per minute, or gpm. While that amount may seem adequate, Zion explained that heavy precipitation and spring snowmelt events infiltrate the mine and the corresponding increase in mine water discharge can approach the plant’s previous maximum treatment capacity. Capacity is also being expanded to accommodate the treatment of contaminated groundwaters. The upgraded facility will be able to treat 5,000 gpm and is designed to accommodate future expansion to 10,000 gpm.
The project also includes constructing an 8,000 foot-long soil-bentonite cutoff wall installed 25 feet deep to intercept and capture contaminated groundwater flowing beneath the mine’s 270-acre central impoundment area.
“Bentonite is a specific type of clay that is highly impermeable,” Zion said. “The bentonite is blended with soil and that blended backfill is placed into a trench, creating an underground barrier to block contaminated groundwater from flowing under the impoundment area and into the Coeur d’Alene River drainage system.”
Contaminated flows intercepted by the soil-bentonite cutoff wall will be diverted to a new groundwater collection system and then routed back to the plant for treatment. Project officials estimate the groundwater collection and treatment will reduce the zinc load flowing below the central impoundment area by up to 90 percent.
While upgrades occur at the main plant, a temporary treatment system was constructed to ensure uninterrupted treatment of contaminated waters.
The original plant was constructed in 1974 by Bunker Hill Corporation, the owner and operator of the smelter complex and Bunker Hill Mine at the time. In 1983, the Bunker Hill Mine and Smelting Complex was added to the National Priorities List as a Superfund site.
Construction of the upgraded facility is expected to be complete in 2020 and is part of required remedial action under the U.S. Environmental Protection Agency’s Superfund program.
“The work we’re doing in the field right now represents the culmination of a lot of collaborative effort between the Corps, EPA and the state of Idaho,” Zion said. “The project is a large investment of work into the cleanup of the Coeur d’Alene River Basin and it’s been an honor to help improve the environment and the lives of people living here.”
| Date Taken: | 11.15.2018 |
| Date Posted: | 12.20.2018 13:34 |
| Story ID: | 304596 |
| Location: | KELLOGG, ID, US |
| Web Views: | 407 |
| Downloads: | 0 |
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