2012-10-01_REVISION - M1977284 (9)

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Mineral Joe Mine Environmental Protection Plan 14 jarosite in the Navajo and Entrada Sandstone is associated with anomalous amounts of copper, lead, zinc, and arsenic. 5.4.1.2 Selenium The SPLP results for the Mineral Joe waste rock exceeded the drinking water standard for selenium by a factor of 2.2. Similarly, the SPLP results from the nearby JD -8 Mine ore pile representative composite samples exceeded the drinking water standard by a factor of 2.4 to 2.8. Selenium occurs naturally in wells in the Paradox Basin at concentrations above the agricultural standard of 0.02 mg/L, based on several samples from exploration holes, off-site wells, monitoring wells, and production well PW -3 at the nearby Pinon Ridge site (Golder, 2009). Background selenium concentrations from five wells at the Pinon Ridge site (EX -15, EX -23, MW -6, MW -8B, and the BLM well) exceeded the domestic water supply standard of 0.05 mg/L (Golder, 2009). Selenium is common in shale in sedimentary rocks of the western U.S. and in uranium deposits of the Colorado Plateau where selenium substitutes for sulfur in the pyrite structure (Coleman and Delevaux 1957). Golder (2009) reported that the highest selenium concentration from a monitoring or production well was 0.24 mg/L from a sample collected at MW -6 in November 2008. This value is nearly twice the concentration of selenium in SPLP leachates from the Mineral Joe waste rock pile and the JD -8 Mine temporary ore stockpile. 5.4.1.3 Fluoride SPLP results from the Mineral Joe waste rock met the drinking water standard for fluoride, as did half of the representative ore pile composite sample SPLP results from the adjacent JD -8 Mine. However, SPLP results for one of the representative ore pile composite from the JD -8 Mine exceeded the drinking water standard for fluoride by a factor of 1.7. 5.4.1.4 Molybdenum No federal drinking water standard exists for molybdenum. However, Colorado has established a groundwater standard of 0.035 mg/L. SPLP results from the Mineral Joe waste rock (0.3 mg/L) exceeded the Colorado groundwater standard by a factor of 9, while SPLP leachates from representative composite samples of the temporary ore pile (0.5 -0.6 mg/L) exceeded the Colorado groundwater standard by 14 to 17 times. Golder (2009) reported that background molybdenum concentrations in some background or baseline wells at the Pinon Ridge site exceeded the CDPHE standards. The report on 2010 monitoring of production wells at the Pinon Ridge site did not show any exceedences of Colorado molybdenum samples in the limited number of production wells (PWs) sampled (Energy Fuels, 2011). 5.4.1.5 Sulfate Sulfate concentrations in SPLP leachates from composite samples of waste rock from the Mineral Joe Mine and ore from the nearby JD -8 Mine exceeded secondary drinking water standards by a factor of three to six. Sulfate is ubiquitous in groundwater in the Paradox Valley. Golder (2009) found that groundwater at the Hermosa/Chinle contact in the Paradox Valley had sulfate concentrations ranging from 1,070 to 1,810 mg/L. These values for naturally occurring sulfate in groundwater are higher than the SPLP leachate concentrations in waste rock from the Mineral Joe Mine and ore from the JD -8 Mine. SMCLs are non - mandatory, non - enforceable water quality standards that are established only as guidelines to assist public water systems in managing their drinking water for aesthetic considerations, such as taste, color and odor. These contaminants are not considered to present a risk to human health at the SMCL (EPA, 2012). 5.4.1.6 Total Dissolved Solids Total dissolved solids (TDS) concentrations in SPLP leachates from composite samples of waste rock from the Mineral Joe Mine and ore from the nearby JD -8 Mine exceeded secondary drinking water standards by 4148B.120927 Whetstone Associates •