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14 February 2000 AGE-NC Project No 96-0254 IPage 9 of 10 on the top of each ground water monitoring well casing at the site to the nearest 0 01-foot relative to the San Joaquin County Bench Mark Datum # BM3M-37 The results of the monitoring well survey are contained in Table 1 The surveying report (Baumbach & Piazza) is presented in Appendix C Depth to ground water at the site ranged from 6 97 to 10 70 feet below well casing top The ground I water elevation in each well were calculated from these data The ground water elevations at the site ranged from 26 18 feet to 30 18 feet above mean sea level (msl) The ground water flow direction and gradient were calculated from the well elevation data IContours of the ground water elevation data suggest that the ground water flow was directed toward the north from the former UST area, shifting in the down-gradient direction toward the north- northeast This pattern of ground water flow direction is typical for the area The ground water gradient on 07 December 1999 was calculated to be an average of 0 003 under the former UST area and to be approximately 0 006 north of the site under Toste Road Figure 5 illustrates the contoured ground water elevations as measured on 07 December 1999 4 0. SUMMARY AND CONCLUSIONS The following conclusions were drawn from the results of this investigation The prevailing ground water flow direction at the site is generally north to northeast ' - Significantly impacted ground water was encountered in samples from monitoring wells MW-1A, MW-113, MW-4 and MW-7 with benzene concentrations exceeding the State of I California maximum contaminant level (MCL) of 1 µg/1 Significantly impacted ground water was also encountered in grab water samples from probe bonngs PB4 and PBS MTBE was detected in one well on the site at a concentrations of 8 9 µg/1 - Soil impacted with TPH-g and BTEX was limited to a depth above 24 feet bsg Soil impacted with TPH-g was only encountered at five-feet bsg, located in the down gradient ' direction of former USTs (MW-4), BTEX-impacted soil was detected south of the former dispensers at depths of ten and fifteen feet bsg ' - Soil impacted with petroleum is defined and limited to the site within the area enclosed by soil bonngs PB2, PB3, PBS, PB6 and well MW-6 - Ground water impacted with petroleum is defined and located within the area enclosed by ' wells MW-2, MW-3, MW-5, MW-6 and MW-3 on the Grant Line Road gas station site Figure 4 depicts the estimated areal distribution of impacted ground water containing ' benzene Adtianced GeoEnNronmental Inc 1