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low- Report: Groundwater-quality Monitoring—May 30,2001: 7500 West Eleventh Street, Tracy, CA. Page 6 Ethyl benzene EPA Method 8020 Total Xylene Isomers EPA Method 8020 f , Fuel Oxygenates* EPA Method 8260A * Analyses were made for the fuel oxygenates tertiary-Butyl alcohol (TBA), Methyl-tertiary butyl ether (MTBE), Di-isopropyl ether (DIPE), Ethyl ' tertiary-butyl ether (ETBE), and tertiary-Amyl methyl ether(TAME). Chromalab is certified to perform the specified analyses by the California Department of Health Services (DHS). The results of the analyses of samples of groundwater are presented in Table 2, which also includes the results of analyses of groundwater samples recovered from the previous sampling rounds. By inspection of the data in Table 2, it can be seen that the lateral and vertical distribution of components of fuel hydrocarbons found on May 30, 2001 in the subsurface beneath the 7500 West Eleventh Street site is compatible with the interpretation made from the data obtained from the site characterization program conducted in April and May 2000. That interpretation is shown graphically on Figures 2, 3, 4 and 5, which show, in plan view and sectional views along section lines A-A', B-B' and C-C', respectively, the locations and geometry of a primary and secondary plume of diesel and gasoline 1 affecting the subsurface. JI Comparing results of analyses of samples of groundwater recovered on May 30, 2001 with those from November 2000, it can be seen that the groundwater samples from monitoring wells MW-1, MW-2 and MW-5, which are to the south and up-gradient of the plume and to the west of the plume,remain free of any traces of analytes of concern. In the case of MW-4, which is located a short distance down-gradient of the former locations of the underground storage tanks on the subject property, analysis of the groundwater sample recovered on May 30, 2001 showed it to be free of any contaminants of concern except for a low concentration of MTBE, at 280 µg/L. Diesel, gasoline and benzene, toluene, ethyl benzene and total xylene isomers (the BTEX ';. compounds), together with the fuel oxygenates TBA and MTBE continue to be present in the groundwater in monitoring well MW-3, which is located immediately down-gradient from the area where the fueling station's pump islands had been located and where affected soil was excavated from the subsurface. However, the concentrations of those analytes were noticeably lower than had been the case in November 2000, with the r concentration of diesel having fallen from 1,300 pg/L to 660 µg/L and the concentration of gasoline having fallen from 3,300 µg/L to 2,600 µg/L, thus continuing a downward sic f t •