- The Idarado mine is located between the towns of Telluride (population 1,950) and Ouray (population 750) in San Miguel and Ouray counties.
- A mountain ridge separates the Telluride District from the Red Mountain District.
- The mine extends beneath this ridge, with the western portal located about 2 miles east of Telluride.
- In the Telluride District, there are seven infiltration lagoons and six tailings ponds.
- The eastern portal of the mine in the Red Mountain District is located about 11 miles south of Ouray.
- This district consists of historic buildings, inactive mines and five tailings ponds along Red Mountain Creek.
- Gold and silver mining began in the 1870s in the San Juan Mountains around the present-day towns of Telluride, Ouray and Silverton.
- There were many small shaft and placer mines throughout the mountains, and mining activity peaked from 1905 to 1911.
- Many of the mines were shut down by 1928. During World War II, demand for minerals again grew.
- The many small mining claims were consolidated into large company holdings such as the Idarado.
- The Idarado mines and mill operated until 1978.
- The majority of mined land reclamation has been completed by the Idarado Mining Co., a subsidiary of Newmont Gold Co.
The major human health concern is possible exposure to heavy metals in the tailings, specifically lead and cadmium. However, human contact with tailings is minimal. The main impact to the aquatic system is from zinc, cadmium, manganese and changes in pH.
- The tailings piles contain elevated lead levels (1,300 to 10,000 ppm) and lead concentrations in some soil samples in Telluride are elevated.
- A 1986 study, financed by Idarado Mining Co., found 7 percent of the children tested had blood lead levels above 10 ug/dL and the average was 6.1 ug/dL.
- The Centers for Disease Control and Prevention (CDC) had established 5 ug/dL as the blood lead level of concern for children.
- In a communitywide study, nine to 21 children were tested for blood lead each year from 1993 to 1997. The average blood lead concentration each year was 4.2 ug/dL.
- High zinc concentrations adversely affect aquatic life in local rivers and creeks.
- The rivers are not sources of municipal drinking water.
- Farmers and ranchers.
- In 1983 Colorado filed suit against the Idarado Mining Co. for natural resource damages under CERCLA. The state was involved in either court actions or negotiations with the company until July 1992 when a negotiated remedy was finalized in federal court.
- The cleanup involved stabilizing and revegetating the 11 large tailings piles, clearing sediments from the underground mine, diverting surface runoff around mine wastes, and rerouting internal mine waters away from highly mineralized regions in the underground workings.
- All work has been completed except for some tailings in Society Turn. The state is in negotiations with the landowner to obtain access to complete the work on this site.
- The mining company paid for natural resource restoration in the area and to enhance fish habitat.
- Idarado Mining Co. completed a majority of the construction phase of the Idarado remediation in December 1997.
- In September 2000, the state, Idarado and Telecam signed a three-party agreement wherein Telecam assumed responsibility to remediate Society Turn Tailings 2 and 3, located on its property. Society Turn 2 South, "the beach," will be remediated into a ball field while also providing parking spaces at that location. Negotiations continue with San Miguel Valley Corp., owner of Society Turn Tailings pile No. 1, regarding remediation of tailings at that location.
- The Idarado crew completed enlarging the infiltration lagoons at the upper end of the San Miguel Valley to increase their capacity to accommodate spring flows from the Mill Level Tunnel.
- Revegetation of a portion of Telluride tailings piles 5-6 (TT5-6) was conducted during spring 2001 to improve growth of a portion of the side slope.
- As part of Idarado's proposed "Legacy Project" to develop its property in the east end of the valley, the state approved an alternative source of soil in the event that direct revegetation of the tailings is not successful, which, as specified in the Remedial Action Plan (RAP), would require the tailings to be covered with soil and revegetated. In November 2001, the people of Telluride voted not to annex the Legacy Project into the town of Telluride, however.
- Thus far, the mine cleanup effort has been successful, with the major remedial elements constructed and functioning as designed.