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Stiles Mining Resource <br /> Groundwater Monitoring and Mitigation Plan <br /> December 2022 <br /> Page 6 <br /> 3.7.2 Evaluation of Existing Data Set <br /> If confirmation sampling results confirm parameter exceedance(s) in POC well(s), ASCI will <br /> evaluate the existing data set (i.e., most recent and historic sample results, potentiometric flow <br /> maps, etc.)within thirty(30) days to try and determine if adverse impacts are potentially sourced <br /> from the mine or from an off-site source.Data will specifically be reviewed for the concentration(s) <br /> of the exceeding parameter(s)reported in up-gradient monitoring wells to identify current or past <br /> exceedance(s), elevated concentration(s), and/or any identifiable trends. <br /> ■ If exceedance(s) are not potentially attributable to the mining operation, ASCI will <br /> provide DBMS a summary of the evaluation conducted and coordinate the appropriate <br /> path forward(e.g., continue with the current groundwater quality monitoring program <br /> schedule). <br /> ■ If exceedance(s) are potentially attributable to the mining operation,ASCI will notify <br /> DRMS and any down-gradient adjacent well owners within 600-feet of the potential off- <br /> site impacts to groundwater and implement POC Well Exceedance Groundwater Quality <br /> Monitoring as detailed in Section 3.7.3. <br /> 3.7.3 POC Well Exceedance Groundwater Quality Monitoring <br /> As no chemical treatment or other processes which could potentially introduce contaminants to <br /> groundwater are used as part of the mining process,it is likely any exceedance(s)due to the mining <br /> operation would be from a naturally occurring source (e.g., underlying bedrock) and only be <br /> temporary. The POC Well Exceedance groundwater monitoring schedule will consist of quarterly <br /> sampling events for all site monitoring wells(MW-I through MW-7)with the first event beginning <br /> in the following quarter from when the initial exceedance(s) were detected. Quarterly monitoring <br /> will continue until two (2) consecutive quarters of monitoring data indicates that results for the <br /> previously exceeding parameter(s) are at or below site-specific groundwater quality benchmark <br /> value(s) in POC wells. ASCI will offer to sample down-gradient adjacent well owner wells within <br /> 600-feet wells at no cost to them during each sampling event for this period. Once two (2) <br /> consecutive quarters of groundwater monitoring indicate results are at or below site-specific <br /> groundwater quality benchmark value(s) for the previously exceeding parameter(s), ASCI will <br /> submit results to DRMS and return to the current groundwater monitoring schedule.If exceedances <br /> are reported in POC well(s) for the previously exceeding parameter(s) in two (2) consecutive <br /> quarters of POC Well Exceedance monitoring, ASCI will work with DRMS and down-gradient <br /> adjacent well owners within 600-feet to determine if corrective action measures are appropriate. <br /> 3.7.4 Potential Corrective Action Measures <br /> ASCI will work with DRMS and down-gradient adjacent well owners within 600-feet to address <br /> the on-going impacts to groundwater quality, as appropriate. The following activities may <br /> potentially be implemented: <br />