ARCHIVED REPORTS XR0010073 - Laserfiche WebLink

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r� Regional lithologic lateral and vertical variation are present in the shallow aquifer strata and underlying confining strata, which are typical for river and floodplain deposits in this portion of the San Joaquin Valley (see Geologic Cross Section, Figure 2) While regional lateral and vertical variation are present in the aquifer and confining strata, these strata as a whole form the aquifer stratigraphy between about 10- to 24-feet The underlying confining strata display some lateral lithologic variations and were not observed to yield water However, given the lateral lithologic variation, and as mentioned above, it is possible that these strata leak (up or down) vertical gradients In our opinion, on the basis of these observations, both aquifer strata and the underlying confining strata are interpreted to have some lateral extent underlying the immediate site vicinity Chemical Analysis A total of thirty-nine (39) soil samples and eleven reconnaissance groundwater samples were analyzed at Chromalab, Inc a State certified analytical laboratory from the exploratory borings These samples were tested for the following, Total Petroleum Hydrocarbons as Gasoline (TPHG) and Diesel (TPHD), Benzene (B), Toluene (T), Ethylbenzene (E) and Xylene (X), Methyl-tert-butyl-ether (MTBE) and fuel oxygenates, using EPA Methods 3510/8015, 8020, 8240 and 8260 The results are tabulated and • presented in the attached Tables I and 2 below Discussion Soil Chemical Data The site assessment revealed that low concentrations of highly degraded contaminants were present in the capillary fringe at PB-17 (advanced through the edge of the former UST pit), at P13-15, 16 and 19 (immediately downgradient of the former UST pit) at PB- 10 and PB-18 near MW-9, and at PB-13 near MW-3 Other capillary fringe samples showed that contaminants were not detected Intermediate depth soil samples also showed that contaminants were not detected with the exception of PB-14-4 at 22 feet where 0 014 parts per billion (ppb) of Xylene were detected Contaminants were not detected in the deepest soil samples at PB-12-5 at 26 feet and PB-13-5 at 26 feet MTBE and oxygenates were not detected in any soil sample Soil samples collected at the 25-26 foot depths in PB-13, 18 and 19 showed that contaminants were not detected (see Tables 1 and 2) Reconnaissance Groundwater Chemical Data Four reconnaissance groundwater samples were collected on April 25, 2001, and all contained various concentrations of TPHG and BTEX contaminants (see Table 2) The highest concentrations observed from the April 25, 2000 bonngs were at PB-1 l (31,000 ppb TPHG and 170 ppb Benzene) and at PB-13 (21,000 ppb TPHG and 160 ppb . Benzene) MTBE and oxygenates were not detected in any groundwater sample (see Table 3) Page 6