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BUR April 27, 2006 001-06750-05-323 Ms. Marie T. McCrink, P.G., C.HG. G°3ECOWED Associate Engineering Geologist California Regional Water Quality Control Board f.7.41 LOG6 Central Valley Region 11020 Sun Center Drive, Suite 200 ENVIR MI!TSER/SERVICES HEALTH PERMIT/SERVICES Rancho Cordova, California 95650-6114 Subject: Work Plan to Conduct a Focused Membrane Interface Probe Investigation, Lincoln Center, Stockton, California Dear Ms. McCrink: This work plan presents the scope of work to conduct a focused membrane interface probe (MIP) investigation at Lincoln Center, located in Stockton, California ("the Site"). This investigation is performed voluntarily in support of a pilot study to evaluate enhanced bioremediation of groundwater in the vicinity of the Bank of Stockton. The purpose of the focused MIP investigation is to aid in the design of an effective lactate delivery system by assessing the extent of higher- concentration chlorinated solvents in this vicinity. 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," dated May 22, 1998, and in the "Remedial Investigation Report," dated December 10, 1999. As discussed in the Interim Investigation Report, monitoring wells MW-108A, MW-205B, and MW-0301C were constructed to further characterize the lateral extent of Hazardous Substance-affected groundwater immediately downgradient from the areas of Lincoln Center where the highest concentrations of Hazardous Substances have been detected in A-zone groundwater. These wells were installed on the eastern side of the Pacific Avenue frontage road, near the Bank of Stockton (Figure 1). During the drilling of these three wells, a coarse-grained sand interval was encountered at approximately 92 to 100 feet below ground surface (bgs) within the B zone. This interval was encountered at this approximate depth only at this location in the B zone. At well locations MW-020B, MW-021B, MW-030C, MW-203B-1,2,3, MW-200B, MW-201B, 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 B zone. Analytical results for groundwater samples collected from monitoring wells MW-108A and MW-205B from 1997 to 2005 indicate static concentrations of tetrachloroethene (PCE; Figures 2 and 3). Analytical results for groundwater samples collected from monitoring well MW-301C indicate that groundwater in the C-zone aquifer is generally at or below the laboratory detection 1900 Powell Street, 12th Floor, Emeryville, California 94608-1827-(510)652-4500-fax(510)652-2246• www.1fr.com