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1 <br /> FIRST QUARTER,2001 <br />' GROUNDWATER MONITORING REPORT <br /> USA STATION#110- STOCKTON <br /> APRIL 2001 <br />' 3.1 Groundwater Flow and Gradient <br />' Groundwater data collected at the site indicates that depths to groundwater ranged from 52.34- <br /> feet below ground surface (bgs) in MW-2 to 57.43-feet bgs in MW-6P. The groundwater <br />' elevations ranged from-30.73-feet below mean sea level(MSL) in MW-49 to -31.82-feet MSL in <br /> MW-0. Groundwater elevation measurements indicate groundwater was flowing to the <br /> southeast at a hydraulic gradient of approximately 0.006-feet/feet. A review of the historical field <br /> data suggests that the groundwater generally flows to the east with minor fluctuations to the north <br /> and south, as shown on Figure 5. <br /> 3.2 Results of Laboratory Analyses <br /> All petroleum compounds were non-detect (ND) at the method detection limit in MW-4-P. TPH <br /> G and BTEX were ND at the method detection limit in MW-2, MW-1P, MW-4P, MW-SP, and <br /> MW-6P. TPH G was reported in monitoring wells MW-1, MW-2P and MW-3P at 160 <br /> micrograms per liter (µg11), 740 µg/1 and 280 µg/l, respectively. Benzene was detected in MW- <br /> 2P at 1.5 gg/l. Toluene was reported in MW 1, MW-2P and MW-3P at 7.9 µg/l, 4.0µg/1 and 13 <br /> µg/1, respectively. Ethylbenzene was reported in MW-2P at 0.51 µg/l. Xylenes were also <br /> reported in MW-2P and MW-3P at 1.6,ug/l and 0.97µg/1, respectively. Using EPA Method <br />' 8020, MTBE was reported in MW-1, MW-2P and MW-3P at 65 µg11, 34µg/1 and 23 µg/1, <br /> respectively. <br />' Using EPA Method 8260B MTBE was reported in MW-1, MW-2P and MW-3P at 69 4g/1, 25 <br /> µg/l, and 30 µg/l, respectively. DIPE was reported in MW-3P, MW-5P and MW-6P at 6.2 µg/1, <br />' I30µg/1 and 45 ,ug/l, respectively. TBA was reported in MW-2-P at 11 µg/l. All other <br /> oxygenates were ND at the method detection limit for this sampling event. 1,2-DCA was <br /> reported in five of the eight wells sampled (MW-1P, MW-2P, MW-3P, MW-5P, and MW-6P) at <br /> tconcentrations of 31 µg/1, 85 µg/1, 1.2µg/1, 16µg/1, and 15 µg/1, respectively. <br /> The groundwater analytical results for this sampling event are summarized in Tables 2 and 3, and <br />' shown on Figures 6 and 7. Copies of laboratory reports with COC documentation are included <br /> in Appendix B. <br />' 3.3 Discussion <br /> The appearance of DIPE in the perimeter wells (MW-3-P, MW-5-P and MW-6-P) and not in the <br />' interior wells seem to support our earlier suspicions that the groundwater at this site is being <br /> impacted by an off-site source, probably the former Chevron site across from Farmington Road. <br />' 4.0 SCHEDULE <br /> The second quarter sampling event for 2001 willbe conducted in April 2001 and the monitoring <br />' report will be submitted by May 15, 2001. <br />' 3 <br />