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Gcolo&tcaI T"haics Inc. Additional Site Characterization Work Plan Page 2 Project No. 724.2 March 8,2005 south of MW-5. Wells MW-7 and MW-107 werelaced a tely 15 feet cast of the former UST field. A discretely screened deep well, MW-104 ,was aPlaced adjacent to the former dispenser island on the western portion of the site. The installation of these wells "~ completed the definition of the soil plume, as soil samples from these borings did not contain detectable contamination. It appears that the soil plume is defined by: • MW-3 and MW-5 to the north and northwest U MW-2, MW-6 and MW-106 to the east Q MW-1 to the south MW-4 is interpreted to be on the edge of the soil plume on the west under Grant Street The shallow groundwater plume is evident in well MW-4 and defined laterally to the east (down gradient) by MW-5, MW-6 and MW-7. The presence of TPH-G contamination in intermediate wells MW-106 and MW-107 suggests that a submerged plume is being sourced by residual soil contamination beneath the present water table (at approximately 38 feet below surface in December 2003). It is noted that the screened intervals of these wells (55- 60 feet bgs) are placed near the elevation of the groundwater table in 1992 — approximately 54 feet bgs. In our March 18, 2002 "Risk Evaluation & Appendix B Closure-Checklist" work plan, Geological Technics Inc. (GTI) proposed performing contaminant mass estimate calculations and limited fate and transport calculations. This work plan was submitted to the San Joaquin County Environmental Health Department (SJC/EHD) and is necessary to receive site closure concurrence from the Regional Water Quality Control Board. In their letter correspondence dated April 24, 2002, the SJC/EHD denied GTI's work plan and directed that a work plan for �• additional plume definition be submitted. Geological Technics Inc. (GTI) submitted our June 27, 2002 "Additional Site Characterization Work Plan - Monitoring Well Installation" work plan to meet the SJC/EHD directive. The work plan proposed the installation of four sets of off-site monitoring wells to define the lateral extent of the contamination. V In their letter correspondence dated September 3, 2002, the SJC/EHD reviewed GTI's work plan and made several recommendations. SJC/EHD wanted changes to proposed wel locations and screened intervals. We responded by submitting a work plan addendum October 3, 2002 that incorporated their comments and addressed the changes desired SJC/EHD. SJC/EHD approved the addendum in their October 23, 2002 letter. completed the field work on December 15 - 23, 2003 and submitted our April 19 "Additional Site Characterization Report" addressing the soil and groundwater investi `r The SJC/EHD indicated their desire to consider the site for closure in t' correspondence dated November 24, 2004. In our 'Td Quarter 2003 C