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Ge4lagko,7ecltx=fltc. Page 7 Groundwater Monitoring Report Project No 724 2 February 7, 2005 3.0 CONCLUSIONS & RECOMMENDATIONS ' Based on our interpretation of the data collected over the course of this subsurface investigation, GTI has 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 ' Our recommendations are based on our knowledge of site conditions, and on the state and limitations of subsurface investigative technology ' Conclusions • This report details the fourth 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 - 11 The highest MTBE concentrations detected in the intermediate and deep aquifers were in wells MW-106 (15 3 µg/1) and MW-209 (5 9 µg11), respectively None of the water table wells had concentrations above detectable levels The contaminated intermediate and deep wells are in line from the former UST and dispenser locations areas to the east in the predominant groundwater direction In addition, the highest TPH-G concentrations were detected to the east of the site in wells MW-106 and MW-208, and the highest ' Benzene concentrations were detected to the east and northeast in wells MW-106 and MW-108 in the intermediate wells, and MW-208 in the deep wells, respectively • 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) are up gradient of the subject site The contamination detected in the MW-108/208 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 an east-southeast direction, not in an east-northeasterly direction ' • The SJC/EHD also stated in their above letter that a sandy interval at 70 — 80 bgs 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 • The trace Toluene previously detected in well MW-11 indicates that an up gradient source has contributed to the plume beneath the subject site Additional monitoring is needed to confirm this possibility • The data shows that a relatively stable, wide spread, low concentration plume of ' petroleum hydrocarbon compounds are present in the groundwater at this site The deeper TPH-G plume is not defined to the north and the deeper MTBE plume is not defined to the east