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I ' Mr Ron Rowe • December 3, 1997 ' Groundwater samples were submitted under proper chain of custody control to West Laboratory of Davis, California Samples were analyzed in accordance with United States Environmental Protection Agency (USEPA) guidelines for total petroleum hydrocarbons- gasoline (TPH-G)using USEPA Method modified 8015, and benzene, toluene, ' ethylbenzene, and total xylenes (BTEX) compounds and methyl-t-butyl ether(MTBE) using USEPA Method 8020/602 Samples were also analyzed for tertiary butyl alcohol (TBA), MTBE, di-isopropyl ether (DIPE), ethel tertiary butyl ether (ETBE), and tertiary amyl methyl ether(TAME) using USEPA Method 8260, in accordance with the new SJCEHD's guidance dated September 25, 1997 ' QUARTERLY MONITORING RESULTS ' Groundwater elevation data, recent petroleum hydrocarbon analytical data, and historic analytical data are contained in the following sections Groundwater Elevation Data Groundwater elevations measured in facility monitoring wells on October 23, 1997 (summarized in Table 1), ranged from minus (-)28 97 to--29 73 feet MSL Groundwater levels in the wells decreased approximately 1 58 to 1 81 feet from the previous monitoring event in July 1997 As shown in Figure 3, the groundwater flow direction is easterly at a gradient of about 2 1 x 10-3 foot per foot, which is consistent with historic trends (summarized in Table 2) ' Petroleum Hydrocarbon Analytical Data ' Certified laboratory reports and chain-of-custody documentation are presented in Appendix C Current TPH-G, BTEX, and MTBE results are presented in Table 3 TBA, MTBE, DIPE, ETBE, and TAME results are presented in Table 4 Historic quarterly monitoring analytical data is listed in Table 5 Historic tabulation and graphical presentations for TPH-G and benzene are presented in Table 6 and Table 7, respectively Figure 4 and Figure 5 illustrate current TPH-G and benzene concentrations in groundwater 1 PSH was not observed in any of the monitoring wells The highest TPH-G and BTEX concentrations were detected in samples collected from monitoring well MW-1 Lower ' TPH-G and BTEX concentrations were measured in samples collected from monitoring wells MW-7, MW-10, and MW-12 Petroleum concentrations were not detected in samples collected from monitoring wells MW-2, MW-3, MW-4, MW-5, MW-8, MW-11, and MW-13 As illustrated in the Table 6 and Table 7 historic graphical presentations, TPH-G and benzene concentrations are generally trending lower The TPH-G and benzene plumes in 1