ARCHIVED REPORTS XR0003442 - Laserfiche WebLink

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Ms Marla D Guensler . Exxon Company, U S A August 20, I997 Page 3 Soil Sample Analytical Results The soil samples collected at 5 and 10 feet bsg on May 8, 1997, were submitted to Sequoia Analytical laboratory (a California-certified laboratory), for analysis of BTEX using EPA Method 8020, TPPH as gasoline using EPA Method 8015 Modified, and volatile organics using EPA Method 8240 Analytical results reported concentrations to be below the laboratory detection limits for all analytes Soil sample analytical results are summanzed in Table I and a copy of the laboratory analytical report with chain-of-custody documentation is included in Enclosure D SVE Well Installation The SVE well VEW-3 was constructed using 2 inch diameter, flush-threaded, Schedule 40 PVC casing The well was screened with 0 02 inch wide slotted screen extending from 3 feet bsg to the total depth of the boring (10 feet bsg) The annular space in the SVE well was filled with No 3 Lonestar sand from 0 5 feet above the well screen to the maximum depth of the well A 0 5 foot thick bentonite seal was placed above the filter pack The depth of the previously installed below grade piping coincided with the top of the bentonite seal as a result, San Joaquin County waived the grouting of the annular space above the seal under the condition that the seal be hydrated to a point where it would ihold standing water for 10 minutes Construction details for the SVE well (VEW-3) are included in Enclosure C Ground Water Table Elevation Flow Direction and Hydraulic Gradient Depth to ground water was measured in monitoring wells MW-1 through MW-8, on May 30, 1997 Depths to ground water in the wells ranged from 7 12 (MW-5)to 9 92 (MW-2) feet below the top of the well casings Cumulative ground water table measurements are presented in Table 2 A ground water table contour map, constructed from the ground water elevations recorded on May 30, 1997, is included as Figure 3 Based on the ground water table contours, the ground water flow direction is to the northeast, across the site, with an average hydraulic gradient of less than 0 01 Ground Water Sampling Analytical Results Ground water samples collected from monitoring wells MW-1 through MW-8 on May 30, 1997, were submitted to Sequoia Analytical for analysis of BTEX and methyl tertiary butyl ether (MTBE) using EPA Method 8020, and TPPH as gasoline using EPA Method 8015 Modified Concentrations of BTEX and TPPH as gasoline were not reported above the laboratory's limits of detection in the samples collected from monitoring wells MW-1, MW-2, and MW-4 through MW-8 Ground water sample collected from monitoring well MW-3 contained benzene at a concentration of 23 micrograms per liter (�tg/L) and TPPH as gasoline at 74 µg/L Detectable concentrations of MTBE were reported in monitoring wells MW-1 through MW-4, MW-6, and MW-8 The detectable levels of MTBE ranged from 5 0 µg/L (MW-2) to 170 Ftg/L (MW-1) A dissolved benzene concentration map using the May 30, 1997, analytical results is presented as Figure 6 Cumulative analytical results are