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Geola,qica(Techuucs Inc Page 5 <br /> ' Groundwater Monitoring Report <br /> Project No 724 2 <br /> May l4,2002 <br /> ' MT - - <br /> BE was detected in intermediate wells MW 106 and MW 107 utilizing EPA Method <br /> ' 8020 The levels detected are consistent with those detected in past events utilizing <br /> EPA Method 8260 <br /> ' The shallow groundwater plume is evident in well MW-4 and defined laterally to the east <br /> (down gradient) by MW-5, MW-6 and MW-7 This situation is illustrated in Figure 6 — <br /> Water Table Well Benzene Concentrations Figure 7 --- Intermediate Well Benzene <br /> Concentrations & Figure 8 — Intermediate Well MTBE Concentrations suggest that a <br /> significant plume does not exist below the water table The presence of TPH-G <br /> contamination in well MW-106 and MW-107 suggests that a submerged plume is being <br /> ' sourced by residual soil contamination beneath the present water table It is noted that the <br /> screened intervals of these wells (55-60 feet bgs) are placed near the elevation of the <br /> groundwater table in 1992 —approximately 54 feet bgs <br /> As indicated in Figure 9 -- MW-2 TPH-G vs GW Elevation, with the exception of June 20, <br /> 1997, contaminant concentrations have been stable in down gradient well MW-2 <br />' Oxidation/Reduction Potential (ORP) measurements (Table S) indicate that only well MW- <br /> 6 <br /> has a positive value The negative ORP values observed in the rest of the wells show that <br /> they are either within the core of the contamination plume or are in the reaction/depletion <br /> shadow down gradient of the plume <br /> 3.0 CONCLUSIONS & RECOMMENDATIONS <br />' The contamination plume as observed from these wells is stable and does not appear to be <br /> sourcing a significant off site plume In GTI's opinion the levels of contamination present <br />' do not warrant an engineered clean up But in their correspondence dated April 24, 2002, <br /> the San Joaquin. County Environmental Health Department (SJC/EHD) directed the <br /> submittal of a work plan for additional lateral plume definition GTI will prepare a work <br />' plan to meet the requirements of the SJC/EHD <br /> We also recommend that a well construction spreadsheet be prepared and attached to the <br />' next report This and a geologic cross section will help interpret the site conditions and <br /> establish a site conceptual model <br /> 1 <br />