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i utilizing EPA Method 8260B Groundwater well purge and sample logs are contained in Attachment 1 I ANALYTICAL RESULTS None of the analytes of interest were detected in the groundwater sample collected from MW-2 TPHg was detected in samples collected from wells MW-2P, MW-3P, and MW-1 at concentrations of 320 micrograms per liter (µg/l), 70 µg/1, and 510 µg11, respectively Benzene was detected in the sample collected from MW-2P at a concentration of I1 µg11 MTBE was detected in the samples collected from MW-2P, MW-3P, and MW-1 at concentrations of 260 µg/1, 32 pg/l, and 490 µg11, respectively DIPE was detected in the samples collected from MW- IP, MW-2P, MW-3P, MW-4P, MW-5P, and MW-6P at concentrations of 120 µg11, 26 pg/l, 130 µg11, 1 0 µg/l, 75 µg11, and 79 pg/l, respectively TBA was detected in the sample collected from MW-2P at a concentration of 96 µg11 1,2-DCA was detected in samples collected from MW-1P, MW-2P, MW-3P, MW-5P, and MW-6P at concentrations of 10 pg/l, 9 3 µg11, 19 pg/l, 17 pg/l, and 8 7 µg/1, respectively A summary of analytical results is presented in Table 2 Laboratory data sheets and chain-of- custody documentation are contained in Attachment 2 CONCLUSIONS AND RECOMMENDATIONS The groundwater flow direction on August 11, 2004, was generally toward the south, which represents a reversal with respect to the previous quarter, and is a return to the predominate historical direction Based on the results of the third. quarter 2004 monitoring episode, we recommend continued quarterly monitoring Please contact our office at (209) 579-2221 if you have any questions or comments Respectfully submitted, ATC Associates Inc p ,r Tadd Hafne 1x *' Project Geologist eanne Homsey, P E , CA Registered Civil Engineer No 47410 cc Chuck Miller, USA Petroleum Corp Jim Barton, RWQCB s lenvironmenta112591210003-Stockton%Quarily�3QR-2004 doc 3