1998-07-28_GENERAL DOCUMENTS - M1977493

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_ _4 „ URS Operating Services,Inc. ARR for ESL'Climax START,EPA Region Vlll Revision: 0 ` Contract No.68-W5-0031 Date: 04/1998 Pate 3 of 37 From 1859 to 1917, placer mining for gold, silver, lead, and zinc was conducted by miners with small individual claims(Climax Molybdenum Company(CMC) 1980). From 1924 to 1980..mining operations at the CM site expanded. CM created a series of tailings ponds to control waste products associated with the mining process(CMC 1980). The Robinson Tailings Pond, Tenmile Tailings Pond, and Mayflower Treatment Pond were constructed in 1935, 1958, and 1977, respectively. From 1982 until 1995,CM reduced production and operated at approximately 15 percent capacity. Interim reclamation began in 1994 on active areas of the property,and final reclamation began on areas no longer needed for operations(CMC 1994). In April 1995,CM began operating at less than 33 percent capacity with approximately 150 employees. The Robinson Tailings Pond is considered closed and only the Tenmile Tailings Pond is used for tailings deposition(CMC 1995). Currently, the CM site is not actively operating(CMC 1997). When the CM site was operating, ore was removed from the southeastern portion of the CM property,was passed through the crushing and milling facility,and was then passed through a series of processes using cyanide, pine oil, and lime. These processes separated, removed, and concentrated the molybdenum from the ore. Tailings and process waters were then delivered to the Robinson Tailings Pond and the water was recycled for CM use(CMC 1993). The CM site is permitted by the Colorado Department of Public Health and the Environment,Water Quality.Control Division (CDPHE-WQCD) for the release of treated process waters to Tenmile Creek under the terms and conditions of the Colorado Discharge Permit System, Permit #CO- 0000248. Historically, cyanide,copper, and zinc have been the primary contaminants discharged from the CM site that have exceeded NPDES discharge limitations(Colorado Department of Public Health and the Environment, Water Quality Control Division(CDPHE-WQCD) 1992). In 1994, URS completed an SSI during which elevated concentrations(as defined in Section 4.1, Data.Validation and Interpretation) of arsenic, copper, silver, and zinc were identified in stream sediments with varying frequency from the CM NPDES outfall to approximately 3.1 miles downstream of the CM NPDES outfall. Elevated concentrations (as defined in Section 4.1,Data Validation and Interpretation)of aluminum and zinc were identified in surface water from the CM NPDES outfall to approximately 3.1 miles downstream of the CM NPDES outfall. These samples were collected at high flow during spring snowmelt(URS 1994). 75-51119.00 F:\START\CLIMAX\Final.ARR\CLIMAX.TXT.wpd:bas