2024-12-19_PERMIT FILE - M2024059 (6)

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4.5. Analytical Procedures The results from the analytical water quality testing will be evaluated through comparison with the State groundwater quality standards. The North Hangs Mine is not within any WQCC specified areas that would require conformance with anything other than statewide water quality standards. Baseline groundwater data can be found in Appendix 2. 4.6. Site-Specific Numeric Protection Levels Baseline water quality data gathering may show ambient levels of a regulated parameter at a level higher than that specified in Regulation 41. In such a case, WSM will propose a Site- Specific Numeric Protection Level. Site-Specific Numeric Protection Levels at the North Hangs Mine will be proposed after the five quarters of baseline sampling. They will be determined by the results of baseline water quality data. The Site-Specific Numeric Protection Levels will be based on the two-sigma (95-percentile) statistical value for the parameter sampled. 4.7. State Water Quality Standards The analytical results of water quality testing during mining will be compared to the regulatory limits established by Water Quality Control Commission (WQCC) and those otherwise defined by the DRMS. The groundwater of the North Hangs Mine is subject to the statewide groundwater quality standards as defined in Tables 1-4 of the WQCC Regulation 41. The site is not within any specified areas identified by the WQCC to have specific groundwater quality standards. If any exceedance of applicable water quality standards is detected during mining at the North Hangs Mine, the DRMS will be notified in accordance with Rule 3.1.7(9) and WSM will initiate a water quality mitigation plan as proposed by the DRMS. If any exceedances of the WQCC Regulation 41 basic groundwater standards are encountered, WSM will implement the following reporting and mitigation procedures: • Notify the DRMS of the exceedance within five (5) working days of receiving the analytical report from the laboratory. • Implement DRMS proposed corrective actions, as defined in a subsequent TR, such as the following: • Identify the potential cause or source of the exceedance. • Implement supplemental water quality sampling. Sampling and testing of the groundwater well will be increased until the parameter(s) drop below the allowable limit. Only parameter(s) that were in exceedance will be measured as part of this supplemental sampling. • Consult with the Garfield County Department of Environmental Health on appropriate mitigation methods of the exceedance. North Hangs Mine GW Monitoring Plan 12 U Lewicki&Associates December 2024