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TH MD QUARTER,2000 GROUNDWATER MONITORING REPORT USA STATION#110- STOCKTON SEPTEMBER,2000 ' 3.1 Groundwater Flow and Gradient Groundwater data collected at the site indicates that depths to groundwater ranged from 55 30- feet below ground surface (bgs) in MW-1 to 56 41-feet bgs in MW-2P The groundwater elevations ranged from-29 69-feet below mean sea level(MSL) in MW-1 to ' -30 90-feet MSL in MW-5P Gauging data from MW-4P and MW-6P appear anomalous with over 12-feet of depth difference from the previous quarter This data was not used to calculate ' groundwater flow and gradient determination Repeatable results will determine the validity of this data Groundwater elevation measurements indicate groundwater was flowing to the northeast at a ' hydraulic gradient of approxunately 003-feet/feet at the time of this gauging event A review of the historical field data suggests that the groundwater generally flows to the east with minor ' fluctuations to the north and south, as shown on Figure 5 3.2 Results of Laboratory Analyses All petroleum compounds were non-detect (ND) at the method detection limit in MW-2, MW-4P, MW-5P, and MW-6P for this sampling event TPH G was reported in monitoring wells MW-1, MW-2P and MW-3P at 160 micrograms per titer (µg/1), 1,300µg/1 and 68 µg/l, respectively Benzene was detected only in well MW-2P at 70 µg11 Toluene was reported m MW-1, MW-2P and MW-3P at 4 6 µg/1, 5 8 µg/1 and 2 7µg/i, respectively Ethylbenzene was reported in MW- 1P and MW-2P at 1 1 1.4g11 and 4 2 Ag/l, respectively Xylenes were also reported in MW-1 and MW-2P at 0 70µg/1 and 7 9µg/l, respectively MTBE was ND by EPA Method 8020 in all ' wells sampled this quarter, except MW-1, MW-2P and MW-3P where it was reported at 28 µg/l, 31 µg/1 and 65 µg11, respectively ' 1,2-DCA was reported m four of the eight wells sampled(MW-1P, MW-2P, MW-3P, and MW- 6P) at concentrations of 26µg11, 15 µg/l, 1 1 µg/1, and 5 1 µg/l, respectively Confirmation analyses for MTBE using EPA Method 8260B reported concentrations in MW-2P, MW-3P and ' MW-1 at 28 µg/l, 71 µg11 and 33 µg/l, respectively DIPE was reported in MW-3P, MW-5P and MW-6P at 6 3 µg/l, 140µg/l and 21 µg/l TBA was reported in MW-2P, MW-3P and MW-5P at 62 µg/l, 13 µg/1 and 12 µg11, respectively All other samples were ND at the method detection ' limit for this sampling event The groundwater analytical results for this sampling event are summarized in Tables 2 and 3,and ' shown on Figures 6 and 7 Copies of laboratory reports with COC documentation are included in Appendix B 4.0 SCHEDULE The fourth quarter sampling event for 2000 will be conducted the week of October 2, 2000 and the monitoring report will be submitted by December 15, 2000 ' 3