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. Stiles Mining Resource <br /> Groundwater Monitoring and Mitigation Plan <br /> November 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. If appropriate (i.e., <br /> exceedance only slightly exceeds benchmark value),ASCI may conduct a statistical trend analysis <br /> to determine: 1) if exceedances are statistically significant increases over background; and/or 2) if <br /> a new site-specific comparison benchmark is appropriate. <br /> ■ If exceedance(s) are not potentially attributable to the mining operation and/or are not <br /> determined to be a statistically significant increase, ASCI will provide DRMS a summary <br /> of the evaluation conducted and coordinate the appropriate path forward(e.g., continue <br /> with the current groundwater quality monitoring program schedule, submit Technical <br /> Revision to change site-specific groundwater quality benchmark, etc.). <br /> ■ If exceedance(s) are potentially attributable to the mining operation and/or are <br /> determined to be a statistically significant increase, ASCI will notify DRMS and any <br /> down-gradient adjacent well owners within 600-feet of the potential off-site impacts to <br /> groundwater and implement POC Well Exceedance Groundwater Quality Monitoring as <br /> 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-1 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 POC Well Exceedance monitoring data <br /> indicates that results for the previously exceeding parameter(s) are at or below site-specific <br /> groundwater quality benchmark value(s) in POC wells. ASCI will offer to sample down-gradient <br /> adjacent well owner wells within 600-feet wells at no cost to them during each sampling event for <br /> this period. Once two(2) consecutive quarters of groundwater monitoring indicate results are at or <br /> below site-specific groundwater quality benchmark value(s), ASCI will submit results to DRMS <br /> and return to the current groundwater monitoring schedule. If exceedances are reported in POC <br /> well(s) for parameter(s) in two (2) consecutive quarters of POC Well Exceedance monitoring, <br /> ASCI will work with DRMS and down-gradient adjacent well owners within 600-feet to determine <br /> if additional assessment and/or potential corrective action measures, as detailed in Section 3.7.4, <br /> are necessary. <br />