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California Regional Water Quality Control Board <br /> Central Valley Region ,J <br /> Steven T.Butler,Chair Gray Davis <br /> Winston H.Hickox Governor <br /> Secretaryjor Sacramento Main Office <br /> Environmental - internet Address: http:/Iw .s b.ca.gov/- gcb5 <br /> Protection 3443 Routier Road,Suite A,Sacramento,California 95827-3003 <br /> Phone(916)255-3000•FAX(916)255-3015 <br /> TO: Wendy Cohen, Chief FROM: Joseph Mello <br /> Site Cleanup Unit Associate Engineering Geologist <br /> Site Cleanup Unit <br /> DATE: 6 October 1999 SIGNA <br /> SUBJECT: DRAFT REMEDIAL INVESTIGATION REPOR YNCOLN CENTER, <br /> STOCKTON, SAN JOAQUIN COUNTY <br /> I reviewed the 20 August 1999 Draft Remedial Investigation Report, Lincoln Center, Stockton, <br /> California (Draft RI Report) submitted by LFR Levine Fricke (LFR) for the Lincoln Center <br /> Environmental Remediation Trust. I have the following comments. <br /> GENERAL COMMENTS <br /> 1. The Draft RI Report states that dense nonaqueous phase liquid(DNAPL) has not been observed in <br /> groundwater samples from the site. However, it is not likely that a specific DNAPL investigation <br /> (i.e., obtaining and chemically enhancing groundwater samples obtained at the base of the aquifer) <br /> was ever conducted. According to DNAPL Site Evaluation (U.S. Environmental Protection Agency, <br /> 1993),DNAPL is inferred in groundwater samples detected at greater than 10 percent of effective <br /> solubility limits and highly suggested at concentrations greater than one percent of effective <br /> solubility limits. Based on concentrations of tetrachloroethene (PCE) greater than 50 percent of <br /> effective solubility limits,DNAPL can be inferred at the site even if it has not been observed. <br /> Additionally, since a specific DNAPL investigation has not been conducted at the site,references to <br /> the lack of observed DNAPL should be eliminated in the Final RI Report. <br /> 2. Figures and text in the Draft RI Report do not address the inferred or suggested areas of DNAPL <br /> impact. Since the ultimate remediation method will need to address DNAPL, its inferred and <br /> suggested occurrence and distribution need to be discussed and mapped in the Final RI Report. <br /> Maps should be prepared for both vertical and lateral DNAPL distribution. <br /> 3. Groundwater extraction wells are on the downgradient side of the site along Pacific Avenue. The <br /> inferred DNAPL area bisects the site along Benjamin Holt Drive. Continued extraction of <br /> groundwater, since it is not focused on the DNAPL pools,may exacerbate spread of contamination <br /> at the site. Discontinuation of extraction would minimize further spread of DNAPL pools,but would <br /> eliminate the containment function the system is currently providing and would not reverse pool <br /> spread that may have already occurred. Focused groundwater extraction or treatment in the inferred <br /> and suspected DNAPL areas needs to be implemented to minimize further migration of DNAPL <br /> pools. <br /> California Environmental Protection Agency <br /> Ca Recycled Paper _ <br />