ARCHIVED REPORTS_QUARTERLY REPORT - SECOND QUARTER 2008

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3. RESULTS Results of the May (pre-startup) and June (quarterly) sampling 18 June 2008 are presented in Tables 2, 3 and 5 and are also depicted in Figures 4, 6 and 8. Complete laboratory reports are presented in Appendix B. Table 7 summarizes the well construction characteristics including well screen intervals. For comparative purposes, cumulative potentiometric elevations are presented in Table 8 and cumulative groundwater results for selected VOCs from current and historic sampling events are included in Table 9. The groundwater recirculation pilot study was started on 19 May 2008 utilizing paired groundwater extraction and injection wells EW-11B and IW-BH2A and ran continuously through the end of the quarter. The extraction/injection flow rate was monitored weekly and maintained between the RWQCB required rate of 0.5 to 1.0 gallons per minute (GPM). 3.1 Groundwater Results During the June 2008 quarterly monitoring event, groundwater elevations in the intermediate wells varied from 10.50 and 11.56 ft below mean sea level. On average, water levels decreased by approximately 4.46 feet between the March 2008 and June 2008 quarterly sampling events. Based on the water level data collected on 18 June 2008, the ground flow direction appears to be moving away from a hydraulic mound interpolated to be in the vicinity of active injection well IW-BH2A and MW-9B. Historically, MW-9B has represented the highest water elevation on site and this pattern has continued. A hydraulic depression is interpolated to be in the vicinity of active extraction well EW-I 1B and monitoring well MW-4B. Historically, groundwater has been interpreted to flow to the northeast or northwest; however, the flow direction has been variable. The groundwater gradient in the intermediate aquifer ranged from 0.004 ft/ft and 0.01 ft/ft. Carbon tetrachloride was detected in all six monitoring wells sampled. Compared to the March 2008 event, carbon tetrachloride concentrations increased in four wells( MW- 4B, MW-5B, MW-9B, and MW-10B) and decreased in one well (MW-3B). The highest value of carbon tetrachloride detected was 860 gg/L in monitoring well MW-4B. Historically, the highest value of carbon tetrachloride recorded at the site was in May 2005 when a carbon tetrachloride concentration of 1,700 gg/L was detected at MW-9B. Chloroform was detected in all six monitoring wells sampled. Compared to the March 2008 event, chloroform concentrations increased in three wells (MW-5B, MW-9B, and MW-10B) and decreased in two wells (MW-3B and MW-4B). The highest value of chloroform detected was 140 gg/L in monitoring well MW-9B; historically the highest value of chloroform detected in the groundwater at the site was 220 µg/L on November 2005 and March 2006 at monitoring well MW-IOB. There were also low levels (less than 15 gg/1)of 1,2-dichloroethane, 1,2- 8