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3.3 Groundwater Sampling <br />3.3.1 Baseline Groundwater Sampling Event <br />Within three months of the start of mining activities, a baseline sampling event will be <br />conducted in select monitoring wells. The objective of this event is to determine current <br />groundwater quality conditions in and adjacent to the mining azea and to establish a <br />baseline prior to start of dewatering operations. Groundwater samples will be obtained <br />from the following wells and analyzed for dissolved BTEX per EPA Method 8020. <br />Wells containing product will not be sampled. <br />?? WP-3, MW-7EP, MW-SEP, MW-2, MW-4, MW-6, MW-3EP, MW-IEP, <br />MW-2E, MW-3E, MW-2W, MW-3 W, MW-9W, MW-9E, and RW-6 <br />3.3.2 Performance Monitoring <br />Wells MW-SEP, MW-6, and MW-7EP, have been established as sentinel wells at the site. <br />These wells do not contain product and were installed to monitor for the potential <br />movement of product present in wells to the north (MW-2, MW-4, and WP-3), towazd <br />the south during dewatering. This is highly unlikely because Trenches 1 and 2 will <br />provide a positive hydraulic gradient against the groundwater to the north. Frequent <br />gauging of fluid levels in the sentinel wells will be the best indicator of any possible <br />movement of any potential contamination as a result of the dewatering activities. In <br />addition, the sentinel wells will also be sampled for dissolved BTEX one week after the <br />start of dewatering, and then monthly for two more months. The results will be <br />compazed to the baseline sampling results and evaluated along with the fluid level <br />information. If BTEX concentrations increase in these wells, then adjustments will be <br />made to the head in the trenches and the wells will continue to be monitored. The trigger <br />criteria and response actions aze further detailed in Table 2. <br />The water in Trenches No. 1 and 2 will also be sampled during mining. Groundwater <br />samples will be obtained using a bailer from both trenches one week after start of <br />dewatering, monthly for 2 months, and then on a quarterly basis for one yeaz. The <br />samples will be obtained approximately one foot below the surface water level and <br />analyzed for BTEX. This sampling will indicate whether there is any potential <br />dissolution of contaminants from the trench sidewalk into the groundwater. If increasing <br />BTEX concentrations are seen in three consecutive samples, then the head in the trenches <br />will be reduced so that contact with any contaminated overburden soil is minimized. The <br />trigger criteria and response actions aze further detailed in Table 2. <br />3.3.3. Point of Compliance Well Sampling <br />Three wells immediately downgradient of the mining azea will be designated as Point of <br />Compliance (POC) wells. The primary purpose of these wells is to monitor for any <br />potential groundwater contamination that may leave the site as a result of the mining <br />activities. This is highly unlikely because dewatering will create a capture zone and will <br />l0 <br />