Anaconda Copper Yerington Mine Anaconda Copper Yerington Mine
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SDMS DOCID# 1116447 Public Review Draft Public Review Draft Remedial Investigation Report Arimetco Facilities Operable Unit 8 Remedial Investigation Report Arimetco Facilities Operable Unit 8 Anaconda Copper Yerington Mine Anaconda Copper Yerington Mine Prepared for: Prepared for: Contract No. 68-W-98-225/WA No. 273-RICO-09GU Contract No. 68-W-98-225/WA No. 273-RICO-09GU U.S. Environmental Protection Agency Region 9 U.S. Environmental Protection Agency 75 Hawthorne Street Region 9 San Francisco, California 94105 75 Hawthorne Street San Francisco, California 94105 Prepared by: Prepared by: 50 West Liberty Street, Suite 205 Reno, Nevada 89501 50 West Liberty Street, Suite 205 Reno, Nevada 89501 July 2008 ES052008022RDD July 2008 Public Review Draft Remedial Investigation Report Arimetco Facilities Operable Unit 8 Anaconda Copper Yerington Mine Prepared for: Contract No. 68-W-98-225/WA No. 273-RICO-09GU U.S. Environmental Protection Agency Region 9 75 Hawthorne Street San Francisco, California 94105 Prepared by: CH2M HILL, Inc. 50 West Liberty Street, Suite 205 Reno, Nevada 89501 July 2008 ARIMETCO FACILITIES OPERABLE UNIT 8 ANACONDA COPPER YERINGTON MINE REMEDIAL INVESTIGATION REPORT EPA CONTRACT NO. 68-W-98-225 EPA WORK ASSIGNMENT NO. 273-RICO-09GU CH2M HILL PROJECT NO. 354946.RR.01 NONDISCLOSURE STATEMENT This document has been prepared for the U.S. Environmental Protection Agency under Contract No. 68-W-98-225. The material contained herein is not to be disclosed to, discussed with, or made available to any persons for any reason without the prior expressed approval of a responsible official of the U.S. Environmental Protection Agency Executive Summary The U.S. Environmental Protection Agency (EPA), under the authority of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) as amended, is conducting a remedial investigation (RI) and feasibility study (FS) to characterize potential contamination associated with the Arimetco Facilities Operable Unit 8 (OU-8) of the Anaconda Copper Yerington Mine (Anaconda or Site). This RI report, prepared as part of Work Assignment No. 273-RICO-09GU, summarizes the RI fieldwork and presents the results of Arimetco heap leach pad (HLP) tailings and drain-down solution sample analyses. Data from five Arimetco HLPs were obtained to characterize the OU-8 HLPs and provide preliminary data regarding HLP-specific drain-down solutions. These data assess residual chemicals in the HLPs, evaluate the quantity and drain-down rate of entrained drain-down solution within the HLPs, provide initial chemical data for the Arimetco ponds, and assess threats to human and ecological receptors. HLP materials were found to contain some areas with slightly elevated radiological counts, although none of the counts were greater than three standard deviations above the mean background count rate. Samples were collected for analysis of physical properties; total petroleum hydrocarbons (TPH) as diesel, kerosene, and motor oil; metals; synthetic precipitation leaching procedure (SPLP); geochemical; geotechnical; and agricultural properties. The analyses show that pH values ranged from 2.66 to 7.89; arsenic, copper, and iron concentrations exceeded the EPA Region 9 residential preliminary remediation goal (PRG); and, according to the SPLP results, aluminum, copper, iron, and manganese concentrations exceeded the primary or secondary maximum contaminant level (MCL). One sample contained TPH (as diesel) above Nevada’s cleanup goal of 100 milligrams per kilogram. Geochemical results indicated that all Arimetco HLPs are classified as having a low potential to generate acid. Trace element concentrations in Meteoric Water Mobility Procedure (MWMP) leachate were generally higher than in SPLP leachate because of the lower amount of extractant liquid used. Overall, MWMP results corroborate the main tendencies predicted by the SPLP results and indicate that the HLPs have some metal leachability capacity left, mainly in the form of soluble aluminum, copper, iron, and manganese, and, to a lesser extent, arsenic, beryllium, cadmium, chromium, cobalt, mercury, and nickel. Agricultural data show that low pH values and water-holding capacity would limit estab- lishment and growth of plant communities on the HLPs. Geotechnical results suggest that the HLPs are mostly composed of well-graded sand to well-graded gravel. Fines typically did not exceed 15 percent and the wet density ranged from 104 to 154 pounds per cubic foot (lb/ft3). Moisture content ranged from 3.1 to 13.4 percent, dry density ranged from 97 to 141 pounds per cubic foot, and specific gravity ranged from 2.64 to 2.81. Cohesion values ranged from 109 to 3,084 pounds per square foot and varied more than any other geotech- nical parameter measured. The friction angle ranged from 34 to 43 degrees and was within the anticipated range. RDD/081480009 (NLH3789.DOC) ES-1 EXECUTIVE SUMMARY Samples from drain-down solutions exhibited pH and specific conductance values ranging from 1.9 to 2.8 and 31,000 to 45,000 micromhos per centimeter, respectively. Metals, specifically aluminum, antimony, arsenic, beryllium, boron, cadmium, chromium, copper, iron, lead, manganese, mercury, thallium and zinc exceeded primary or secondary drinking water MCLs. Radiological measurements generally exceeding the MCL for thorium isotopes 228, 230, and 232; uranium isotopes 234, 235, 238; and gross alpha particles. TPH (as diesel and kerosene) ranged from 750 to 2,100 micrograms per liter (μg/L), and all but one drain- down solution sample exceeded Nevada’s cleanup guideline of 1,000 μg/L for TPH. An assessment of data quality for HLP material and drain-down solution samples concludes that these data satisfy the assumptions under which the data quality objectives (CH2M HILL, 2007a) and the data collection design were developed. The data are within tolerable decision error rates and support the stated objectives; the data are adequate and complete pursuant to EPA guidelines (EPA, 1994). Remedial investigation activities have characterized the nature and distribution of radiological isotopes, physical properties and base metals in the HLPs and their associated ponds and ditches. Potential remaining sources of contamination include the following: • Metals, specifically arsenic, copper, and iron on the surface and within the HLPs • Radiological constituents • Drain-down solution entrained within the HLPs • Drain-down solution stored at the base of the HLPs or contained within their associated ponds and ditches Geochemical and physical techniques were used to evaluate the fate and transport of mining-related constituents in connection with Arimetco HLPs to assist with evaluating potential risks. The evaluation shows that the leaching capacity of the HLPs is significant mainly because of large amounts of sulfate and trace metals that remain. Although stable, the HLPs each contain between 1,076,000 and 7,599,000 cubic yards of material, and substantial quantities of drain-down solutions are expected to remain entrained in the HLPs. Screening-level risk assessments were performed to assess whether HLP materials and the drain-down solutions pose a threat to human health or the environment. The evaluation of human health risks used conservative screening criteria (residential/industrial PRGs, drinking water MCLs, and tap water PRGs). The evaluation concluded that potential exposure to Group A HLP materials are at the upper end of the EPA cancer risk manage- ment range. The residential cancer risk for potential exposure to Group B HLP materials exceeds the EPA cancer risk management range. Industrial cancer risk is at the upper end of the EPA cancer risk management range. The noncancer health hazards for exposure to Group A HLP materials exceed a hazard index of 1 for residential exposures; noncancer health hazards for exposure to Group B HLP materials exceed a hazard index of 1 for residential and industrial exposures. Drain-down solutions exceeded the drinking water MCLs for eight metals. Risks to terrestrial receptors were Indicated by the screening-level ecological risk assessment of HLP materials; six metals exceeded the screening values for virtually all receptor groups. Lead exceeded screening values for all receptors except soil ES-2 RDD/081480009 (NLH3789.DOC) EXECUTIVE SUMMARY invertebrates; antimony, cadmium, and zinc exceeded screening levels in upper trophic level receptors (i.e., birds and mammals). Evidence suggests that drain-down solution in the leachate ponds adversely affects birds. A comparison of metal concentrations and pH in the ponds having the acute toxicity values found in literature suggest that aluminum, copper, and pH are at levels acutely lethal to birds and mammals. Radiological constituents in drain-down solutions exceeded the chronic effects threshold but might not adversely affect ecological receptors because of the limited habitat and the scarcity of available food resources. In summary, drain-down solutions are adversely affecting ecological receptors, specifically birds, and potentially the environment. CH2M HILL concludes that sufficient data and information are available to support the OU-8 FS process. The RI provides the following summary: • The composition and characteristics of the HLPs are sufficiently determined. • HLP geotechnical and geochemical parameters are characterized. • HLP slopes appear to be relatively stable, are close to the angle of repose; surface unraveling is evident. • Long-term steady-state outflow (for precipitation