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05 August 1999 AGE-NC Project No 96-0254 Page 3 of 4 concentrations of 200 micrograms per liter(µg/1), 3,400µg11 and 57 µg/1 , respectively TPH d was ' detected in the samples collected from wells MW-lA and MW-1B at concentrations of 68 µg/1 and 130µg/1 Benzene was detected in samples collected from wells MW-IA , MW-1B, MW-2A, MW- 2B,MW-5 and MWW-6 at concentrations of 16µg11, 740µg/l, 1 5 µg/1, 0 72 µg/l 0 93 µg/l and 12 I µg11, respectively The sample from MW-3 did not contain detectable concentrations of benzene Toluene and xylenes were detected in all well samples at concentrations as high as 400 µ.g11 (toluene,MW-1B) and 220µg/1 (xylene, MW-1B) Ethylbenzene was not detected in wells MW-2B Iand MW-3 MTBE was detected in MW-1B at a concentration of 13 µg11 AGE believes that the low concentrations of various BTEX compounds detected in ground water Isamples collected from monitoring wells MW-2A, MW-2B,MW-3,MW-5 and MW-6 are the result of cross contamination of the samples, probably due to purging the wells with a new type of hose that resisted decontamination procedures None of the affected wells have had detectable concentrations of the analytes during the previous four ground water monitoring events, and each newly detected analyte had similar concentrations in the five wells AGE anticipates that the I analytical results from samples collected from the monitoring wells during the next monitoring event will be similar to the results for the first four monitoring events lie AGE believes that the detected concentrations of the analytes in samples from MW-1 A and MW-1 B are fairly representative of actual aquifer conditions as the concentrations detected are significantly higher than the suspected cross-contamination concentrations, and the two wells were the last wells ' purged and sampled Laboratory results of ground water samples analyzed for petroleum hydrocarbons are summarized Iin Table 2 and 3 The laboratory reports (MAI Laboratory ID 13996 to 14502), QA/QC reports and chain-of-custody forms are included in Appendix B 4.0. SUMMARY AND CONCLUSIONS The following conclusions were drawn from the results of this investigation • Ground wvater at the site was encountered at a depth of approximately 7 to 8 feet bsg The prevailing ground water flow direction at the site is generally northward • Significantly impacted ground water was encountered in samples from monitoring wells IMW-lA and MW-1B, with benzene concentrations exceeding the State of California maximum contaminant level (MCL) of l ppb • BTEX compounds detected in ground water samples collected from monitoring wells MW- 2A, MW-2B, MW-3, MW-5 and MW-6 are believed to be the result of cross-contamination and may not be representative of aquifer conditions in the areas of these wells Adi anced CeoEnN iron mental Inc