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LFR Inc. 2.2.1 Groundwater Investigations in the Vicinity of the Bank of Stockton Background information, including site history, previous investigations, and contaminant nature and extent, is presented in LFR's "Interim Source Area Remedial Investigation Report, Lincoln Center, Stockton, California" ("Interim Investigation Report"), dated May 22, 1998, and in the "Remedial Investigation Report, Lincoln Center, Stockton, California," dated December 10, 1999. As discussed in the Interim Investigation Report, monitoring wells MW-108A, MW-205B, and MW-0301C were previously constructed to further characterize the lateral extent of Hazardous Substance- affected groundwater immediately downgradient from the area of Lincoln Center where the highest concentrations of Hazardous Substances have been detected in groundwater. These wells were installed on the eastern side of the Pacific Avenue frontage road, near the Bank of Stockton (Figure 2). During the drilling of these three wells, a coarse- grained sand interval was encountered at approximately 82 to 100 feet bgs within the lower A-zone aquitard interval that typically separates the A zone from the B zone. This interval was encountered at this approximate depth only at this location and was not observed in nearby borings. At nearby well locations MW-020B, MW-021B, MW- 030C, MW-203B-1,2,3, MW-200B, MW-20113, and MW-204B, intervals of clays, silts, or sands less than 1 foot in thickness were encountered at this approximate depth interval. The coarse-grained sand interval encountered at this depth interval is considered anomalous to the lower A zone and the B zone, and appears to also be a significant migration pathway for the movement of Hazardous Substances within both A- and B-zone groundwater to the east of Pacific Avenue. A historical summary of the analytical results of Hazardous Substances detected in groundwater samples collected from monitoring wells at the Site is presented in Table 1. Time-concentration graphs for wells located in the vicinity of the Bank of Stockton (wells MW-108A, MW-205B, and MW-301C) are presented in Appendix A. Analytical results from groundwater samples collected from A-zone groundwater monitoring well MW-108A between 1997 and 2006 indicate relatively static concentrations of PCE, averaging over 3,000 µg/l, and minimal transformation of PCE to cis-1,2-DCE, which has been detected at concentrations averaging less than 50 µg/l. Conversely, analytical results from groundwater samples collected from monitoring well MW-205B (screened from approximately 85 to 100 feet bgs) indicate increased transformation of PCE to cis-1,2-DCE at concentrations averaging over 1,000µg/1 since December 2001. This total change in Hazardous Substances in well MW-205B indicates that the degradation of the Hazardous Substances within the B zone is likely complete through vinyl chloride even though it is not being detected in the groundwater samples by the analytical laboratory. Analytical results from groundwater samples collected from monitoring well MW-301C indicate that groundwater in the C-zone aquifer is generally at or below the laboratory detection limit. Due to the static PCE concentrations observed in the A zone and the transformation of the PCE within the B-zone aquifer to degradation products within the vicinity of the Bank of Stockton, additional actions are warranted for the remediation of Hazardous Substances within the A zone in the vicinity of the Bank of Stockton. Page 6 wp-PhV_IRASep07-Final-06750.dm:lfr