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4Wt4gXA1 Tecluucs 1XC Page 7 Groundwater Monitonng Report ' Project No 724 2 February 13, 2006 ' 3.0 CONCLUSIONS & RECOMIIMNDATIONS t Based on our interpretation of the data collected over the course of this subsurface investigation, GTI has reached several conclusions These conclusions assume that 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 ' Conclusions 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 Generally the plume has migrated down gradient of the source and is displaced east of the former UST o The highest MTBE concentrations detected in the intermediate and deep aquifers ' were in wells MW -106 (25 lig/1) and MW -209 (8 4 tAg/1), respectively o Water table well MW -7 contains 2 2 ug/]L MTBE o The contaminated shallow, intermediate and deep wells are down gradient from ' the former UST and dispenser locations areas in the predominant groundwater direction to the east o 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 -109 in the intermediate wells, ' and MW -208 in the deep wells, respectively o The presence of 53 ug/1 TPH-G in deep well MW -210 is the first contaminant detection recorded for this well ' r In their correspondence dated September 3, 2002, the San Joaquin County Environmental Health Department (SJC/EHD) identified two LUFT sites (701 E Charter Way and 749 E Charter Way) as being up gradient of the subject site The ' contamination detected in the MW -108/208 location may be partly or entirely originated from an offsite source • 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 low concentrations of TPH-G & MTBE in these wells do ' not warrant an engineered clean up 4 The data shows that a relatively stable, wide spread, low concentration plume of ' petroleum hydrocarbon compounds is 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