Remediation resumes at long-closed copper mine

Plans to finish remediation efforts at the former Rio Tinto Copper Mine near the Owyhee River in Elko County are under way.

Tetra Tech of Pasadena last week was awarded a $22 million contract to remediate and restore the 280-acre copper mine, which operated between 1932 and 1976 and was run by several companies, including Atlantic Richfield Company and Rio Tinto. The site includes the copper mine and mill, heap leach pads and several hillside tailing piles, and the ghost town of Rio Tinto. It’s located a few miles south of Mountain City in northern Elko County.

Tetra Tech’s client on the three-year project, Mountain City Remediation, will remove mine tailings from their proximity to Mill Creek to an on-site repository, which is expected to reduce runoff and discharges from the tailings piles from flowing into Mill Creek, a tributary of the east for of the Owyhee River. The project is funded by the Rio Tinto working group, which includes ARCO, Cleveland Cliffs Iron Company, DuPont and Cominco American.

Copper was mined at the site from 1932 through 1947, when copper prices fell and work ceased. Interest perked up again in 1965 with a number of operators re-working the tailings piles and leaching stockpiles of ore, as well as exploring the existing copper ore deposit. However, work ceased again in the late ’70s, and the site sat vacant until 1996, when remediation work first began.

The heap leach pad and two tailings piles were regraded, covered with clean soil and reseeded, and water barriers were installed around the structures to control seepage and runoff, which contain elevated amounts of copper, zinc, iron and manganese, from reaching Mill Creek.

Although copper levels in the Owyhee River don’t exceed safe levels for humans, the Nevada Department of Environmental Protection says, they do sometimes exceed quality standards to maintain aquatic life, especially in times of heavy rain and runoff. The Owyhee River, a tributary of the Snake River, flows 346 miles from its source north of Elko through Nevada, Idaho and Oregon.

Mountain City Remediation will remove mining materials from the remaining two tailings ponds in Mill Creek, which cover about 25 acres, to an unlined repository on a ridge near the former company townsite. Mountain City Remediation will remove more than 653,000 cubic yards of earth and create a clean pathway for Mill Creek, which was diverted into a channel flowing along the south side of Mill Creek Valley in the 1930s.

The Rio Tinto mine has long been listed as a Superfund alternate site.