AMEC Earth & Environmental has signed a contract with the Colorado Department of Public Health and Environment (CDPHE) to assist with the Clear Creek federal Superfund cleanup project west of Denver.
Under the $300,000 contract, AMEC will develop systems to collect contaminated surface water and groundwater in Virginia Canyon/Idaho Springs and convey the water to an existing treatment facility.
Currently the water, contaminated by metals-laden acidic drainage from more than 70 inactive mines and a few active mines, flows into Clear Creek, a favored place for fishing and other recreation and a drinking water source for more that a quarter million people living in the Denver area. The drainage contains heavy metals such as iron, manganese, zinc and copper.
"The CDPHE evaluated proposals for the Virginia Canyon project from 20 very qualified engineering companies," said Jim Lewis, a CDPHE Superfund project manager. "AMEC was selected because of its ability to design a system addressing the metals contamination and because of the familiarity of its engineering personnel with Virginia Canyon hydrology."
The project will be managed by a member of AMEC's Lakewood, CO, staff, Bruce Curtis, PE, Ph.D.
In Virginia Canyon, AMEC envisions the construction of a sedimentation basin downstream of all mine sites. A six-inch-thick concrete cutoff wall extending underground to bedrock would be built at the downstream side of the sedimentation basin to prevent groundwater from migrating further down the canyon. The wall will be encased in high-density polyethylene sheets to protect the concrete from erosion. Three special drain pipes will be buried in aggregate and sand below the basin. The pipes, each 50 feet long and four inches wide, would be perforated on top to collect groundwater and water draining down from the basin, but solid on the bottom to allow the water to flow to a solid conveyance pipe.
The conveyance pipe, which would be buried below the frost line, then would transport the water approximately one mile to the Argo Tunnel treatment facility, and once treated, the water would be discharged to Clear Creek. The Argo facility, built in 1998, can treat 750 gallons per minute.
Additionally, from the Big Five Tunnel near Idaho Springs, AMEC plans to design a system that will capture drainage immediately after it leaves that mine's entrance and divert it to a tank, where solids will settle out. The acidic water periodically will be pumped 1.5 miles through a pipeline that will be built in coordination with a Colorado Department of Transportation drainage improvement project. The pipeline also will carry the water to the Argo Tunnel treatment facility.
"Significant metals loading to Clear Creek from the Big Five Tunnel discharge and from abandoned mine workings in Virginia Canyon have degraded the water quality of Clear Creek for numerous years," said CDPHE's Lewis. "Addressing the metals loading from Virginia Canyon is part of the overall remedy for the Clear Creek/Central City Superfund site."
