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NPL Site Narrative for Silver Mountain Mine

Loomis, Washington

Federal Register Notice:  June 10, 1986

Conditions at proposal (October 15, 1984): Silver Mountain Mine covers 5 acres in Loomis, a remote area of Okanogan County, Washington. In 1980 and 1981, the mine used cyanide in its processing operations. Approximately 1,100 gallons of cyanide were poured over silver tailings, which had been placed on top of a plastic liner, in an effort to extract gold. The water running off the pile was collected in a basin, also lined with plastic. The site contains more than 2,500 tons of contaminated tailings and 20,000 gallons of contaminated liquid. At one time, the liquid contained 1,100 parts per million (ppm) cyanide, according to analyses conducted by the State. In November 1983, the State treated the liquid, reducing cyanide levels to 9 ppm. Contamination of ground water in the area is considered probable. Although the site is located in a remote area, the concentrations of cyanide present a potential health hazard.

Status (January 1986): The Washington Department of Ecology stabilized the site in June 1985. This activity included: (1) draining the leachate and removing it for off-site treatment, (2) covering the site with a 3/4-inch cotton liner and a plastic liner, (3) securing the liners with tires, (4) removing drums that previously contained hazardous materials, (5) removing a wooden structure that appeared insecure, and (6) fencing the site with barbed wire. The life of the liner is estimated at 20 years. The State concluded after this operation that the site "will not get worse, yet further study is warranted...to determine if contaminants have reached the ground water, and to determine appropriate and cost-effective means to decontaminate the ore heap." The State plans to visually inspect the site every couple of months to ensure security of the liner and fence.

Status (June 10, 1986): This mining site is being placed on the NPL because it is a noncoal site with mining operations that occurred after August 3, 1977, the enactment date of the Surface Mining Control and Reclamation Act (SMCRA). Thus, it is neither regulated by SMCRA nor eligible for funds from the SMCRA Abandoned Mine Land Reclamation Program.

For more information about the hazardous substances identified in this narrative summary, including general information regarding the effects of exposure to these substances on human health, please see the Agency for Toxic Substances and Disease Registry (ATSDR) ToxFAQs. ATSDR ToxFAQs can be found on the Internet at ATSDR - ToxFAQs (http://www.atsdr.cdc.gov/toxfaqs/index.asp) or by telephone at 1-888-42-ATSDR or 1-888-422-8737.

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