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Demonstration of Compliance Climax Molybdenum Company <br /> With Regulation 41 Permit M-1977-493 <br /> 2.3 Manganese Background Information <br /> Manganese has been observed at concentrations greater than the Regulation 41 CBSG table <br /> value standard in the nearly all of the POC and internal monitoring wells at the site. Background <br /> information for manganese in the area of the Climax Mine demonstrates that the dissolved form <br /> of this parameter is substantially variable in groundwater. <br /> Manganese is abundant in the earth's crust, distributed mainly as manganese oxides, and as <br /> such is a common constituent in groundwater. The principle controls of manganese concentration <br /> in groundwater are water chemistry, specifically pH and redox conditions, and to a lesser degree <br /> host rock geology and microbial activity(Homonck, et al., 2010). The chemistry of manganese is <br /> similar to iron, in that both metals participate in redox processes in weathering environments. <br /> Manganese, however, has three potential valence states (Mn2+, Mn3+ and Mn4+)rather than the <br /> two of iron. Dissolved manganese(Mn2+), the form of manganese monitored at Climax, occurs in <br /> a range of groundwater environments including acidic, low-oxygen environments, acidic and <br /> oxidized environments, and alkaline and reduced environments, although dissolved manganese <br /> concentrations tend to decrease as pH increases (Fey et al., 2002). The precipitation of <br /> manganese oxides under alkaline and oxidized environments is generally in co-precipitation with <br /> iron and, under some conditions, other metal ions including lead, zinc, copper, and nickel (Hem, <br /> 1989). <br /> Iron and manganese concentrations tend to display more temporal variability than other <br /> constituents at many of the Climax monitoring locations. Although limited redox data are available <br /> for most of the monitoring locations, it is likely that this temporal variability may be a function of <br /> the sensitivity to pH and redox conditions. For this reason, sulfate and TDS may be more <br /> conservative indicators of potential mining-related sources. <br /> Furthermore, the most restrictive CBSG table value for manganese (as well as sulfate and iron) <br /> are domestic water supply — drinking water standards, based on EPA guidance for secondary <br /> drinking water maximum contaminant levels (MCLs). These are drinking water standards set for <br /> aesthetic and technical reasons rather than human health reasons. <br /> Manganese concentrations in groundwater are substantially variable in Climax monitoring wells. <br /> Manganese has been detected in the range of 0.005 to 4.7 mg/L within the Arkansas River <br /> Watershed, 0.005 to 1.3 mg/L within the Eagle River Watershed, and 0.001 to 0.190 mg/L within <br /> the Tenmile Creek Watershed. The range of values reported at Climax are within the variable <br /> range of manganese values reported in other areas of Colorado unrelated to mine sites. In the <br /> Denver Basin, manganese concentrations in groundwater have been reported to range from <br /> <0.0001 to 2.5 mg/L (Musgrove et al., 2014), and in the Piceance Basin in Western Colorado <br /> reported manganese concentrations range from <0.0002 to 8.9 mg/L (Thomas and McMahon, <br /> 2012). Klusman and Edwards (1977) reported 95% of observed manganese concentrations in <br /> samples collected outside the Front Range Colorado Mineral Belt ranged from 0.006 to 1.2 mg/L, <br /> compared to a range of 0.003 to 12.3 mg/L within the Front Range Colorado Mineral Belt. <br /> Klusman and Edwards (1997) also showed the complexity of the data is not described by simple <br /> statistical descriptions. Large changes in manganese concentrations(up to 200x)were observed <br /> to occur over relatively short distances. <br /> December 2016 4 <br />