2022-12-16_PERMIT FILE - M2021067

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Stiles Mining Resource Groundwater Monitoring and Mitigation Plan December 2022 Page 8 4.3 GROUNDWATER LEVEL DATA EVALUATION AND REPORTING ASCI will compare monthly post-operational groundwater levels against the baseline groundwater level data for each well within two (2) weeks of collection to aid in determining if any potential adverse impacts to off-site wells has occurred. The primary triggers for determining potential adverse off-site impacts to groundwater levels in nearby wells will be if post-operational groundwater level(s)drop to half of the baseline groundwater level(s)in one(1)or more of the up- gradient wells(MW-1 through MW-3), in MW-7,or if ASCI is contacted with a complaint. ASCI will report groundwater level data in a groundwater monitoring report that will be submitted to DBMS as supplemental information with the annual report for the mine each year. 4.4 MITIGATION MEASURES FOR GROUNDWATER LEVEL IMPACTS 4.4.1 Collect Groundwater Levels in Nearby Well(s) Should groundwater elevation drop below half of the baseline level in one or more of the up- gradient monitoring wells (MW-1 through MW-3), in MW-7, or if ASCI is contacted with a complaint,ASCI will contact owner(s)of potentially impacted nearby well(s)to inquire about any issues and/or to assess the groundwater level conditions in the well(s), as applicable. ASCI will collect groundwater level measurement(s) in the nearby well(s)if allowed by the well owner(s). ■ If groundwater level(s)in nearby well(s) do not indicate a potential adverse impact due to the mining operation,ASCI will continue with the current groundwater level monitoring schedule. ■ If groundwater level(s) in nearby well(s)do indicate a potential adverse impact due to the mining operation,ASCI will begin review of the existing data set as detailed in Section 4.4.2. 4.4.2 Evaluation of Existing Data Set If groundwater level measurement(s) on nearby well(s) indicate a potential adverse impact or if ASCI is denied permission to collect a groundwater measurement after being contacted with a complaint, ASCI will evaluate the existing data set (i.e., most recent and historic measurements, potentiometric flow maps, etc.) within fourteen(14)days to try and determine if adverse impacts are potentially sourced from pumping at the mine.Data will specifically be compared with the pre- operational and post-operational groundwater elevation data set for the Site and nearby well(s), as available, to determine any groundwater elevation trends. If appropriate, ASCI will collect groundwater levels from on-site and off-site wells to evaluate current groundwater level conditions in a single measurement event. ■ If off-site groundwater level impacts are not potentially attributable to the mining operation, ASCI will continue with the current groundwater level monitoring schedule. ■ If off-site groundwater level impacts are potentially attributable to the mining operation, ASCI will discuss corrective action measures available with the impacted well owner.