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Geologccal TeckxuslKc Page 7 Groundwater Monaonng Report Project No 724 2 May 17, 2004 elevation changes for the past 10 years in down gradient well MW-2 The well did not contain petroleum hydrocarbon contaminants above the laboratory reporting limits for the ' first time since June 24, 1993 3.0 CONCLUSIONS & RECOMMENDATIONS Based on our interpretation of the data collected over the course of this subsurface investigation, GTI have reached several conclusions These conclusions are based on the ' premise that the data we considered, although incomplete, are representative of actual site conditions We acknowledge that there may be undiscovered conditions, which would upon their consideration, change our interpretation and thus our conclusions r Our recommendations are based on our knowledge of site conditions, and on the state and limitations of subsurface investigative technology Conclusions e This report details the initial sampling event of the nine new wells installed in December 2003 and the existing ten wells The groundwater plume does not display a typical "core" but exhibits,wide variations in contaminant concentration in both vertical and lateral planes as shown in Figures 6 - 12 The highest MTBE concentrations detected in the shallow, interinediate and deep aquifer were in wells MW-7 (3 8 ug/1), MW-106 (10 9 ug/1) and MW-209 (8 1 ug/1), respectively These ' wells are in line from the former UST and dispenser locations areas to the east in the predominant groundwater direction In contrast, the highest TPH-G & Benzene concentrations were detected to the northeast of the site in wells MW-108 and MW- 208 e In its correspondence dated September 3, 2002, the San Joaquin County Environmental Health Department (SJC/EHD) identified two LUFT sites (701 and ' 749 E Charter Way) up gradient of the subject site The contamination detected in the MW-1081208 location may be from an offsite source The rationale for this conclusion is that the TPH-G contaminant found in this well does not corroborate with the MTBE plume that seems to be migrating down gradient in a east-southeast direction, not in an east-northeasterly direction - • Geological Technics Inc (GTI) intended to produce mass balance calculations for groundwater plume But the spatial variation in contaminant concentrations and possibility of a co-mingled plume from the off site sources would make an estimate ' arbitrary at this point in time o The SJC/EHD also stated in their above letter that a sandy interval at 70 — 80 b could be acting as lateral conduit for contaminant migration The presence of ' contamination in deep wells MW-208 and MW-209 support this theory, however GTI still suggests that the levels do not warrant an engineered clean up