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Point of Compliance Well Investigation <br /> <br /> <br /> <br />AECOM <br />13 <br /> <br />AECOM used results of the temporary well evaluation to identify permanent compliance well <br />locations where the alluvial groundwater chemistry would generally be expected to meet <br />compliance standards. Recommended permanent well locations are shown on Figure 13. The <br />first permanent well should be installed in the Wilson Creek drainage near the location of <br />POC-2. A permanent well in this area could serve as the groundwater point of compliance for <br />both the Wilson Creek and Taylor Creek alluvial groundwater systems. The recommendation to <br />install a permanent well in this area is based on the relatively low average concentrations of <br />dissolved manganese (0.39 mg/L), sulfate (597 mg/L), and TDS (1,427 mg/L) compared to the <br />other temporary monitoring well locations, including some that are farther downgradient. This <br />location is consistent with the recommended location for a permanent compliance well in the <br />Division’s adequacy review of Permit Revision 02 (Division of Reclamation, Mining and Safety <br />2006, 2007). <br />Similar to the Division’s recommendation for Good Spring Creek, AECOM also recommends <br />installing a second permanent compliance well in the Good Spring Creek drainage near the <br />present location of POC-10. This recommendation is based on the relatively low average <br />concentrations of dissolved manganese (0.29 mg/L), sulfate (610 mg/L), and TDS (1,331 mg/L) <br />compared to the other temporary monitoring wells. If the Division accepts these proposed point <br />of compliance well locations, we recommend installing the permanent wells within 10 to 20 feet <br />of the temporary wells at similar total depths. <br />Given language contained in Regulation 41, which allows consideration of existing ambient <br />water quality when establishing groundwater comparison values, AECOM believes that a hybrid <br />approach for defining compliance standards is appropriate for the Mine. The applicable <br />standard for each regulated groundwater constituent in the Mine Permit should be the higher of <br />the pre-1994 background UTL and the most stringent groundwater quality criteria from Tables 1 <br />through 4 of Regulation 41. Following this approach, proposed groundwater compliance <br />standards for the Mine are shown in Table 16. Except for manganese, sulfate, and TDS, the <br />proposed standards are identical to the most stringent Regulation 41 criteria. <br />