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California Regional Water Quality Control Boarda <br /> Central Valley Region <br /> Robert Schneider,Chair <br /> Arnold Schwarzenegger <br /> Alan C.Lloyd,Ph.D. `� Governor <br /> Secretaryfor 11020 Sun Center Drive#200 Rancho Cordova,CA 95670-6114 leF <br /> Environmental (916)464-3291•Fax(916)464-4704 <br /> Protection http://wwNv.swrcb.ca.gov/rwgcb5 <br /> J l/. <br /> 14 April 2005 <br /> Mr. Darin Rouse Mr. Phil Johnson SC`p��F <br /> Chevron Products Company Sims-Group Managemekq� Ty <br /> P.O. Box 6004 374 Lincoln Center <br /> San Ramon, CA 94583 Stockton, CA 95207 <br /> REVIEW, CffEVK0NP-#9=6Z7I,-6633PACIFICAVEVUE,STOCKTON, SAN JOA-QUINCOUYTY — <br /> I reviewed the 25 March 2005 Conceptual Site Model(Report), submitted on behalf of Chevron Product <br /> Company (Chevron)by Secor International Inc. (Secor). The Report states that a site conceptual model (SCM) <br /> was prepared "...to identify sources,potential receptors, and routes of exposure." The Report is divided into <br /> sections labeled Setting(Geology, Stratigraphy, Hydrogeology),Site Background and Current Conditions, <br /> Groundwater Monitoring and Sampling,Remediation,Sources of Impacts,Potential Groundwater Receptors, <br /> Groundwater Flow and Transport Modeling, and Conclusions. The Report contains a CD-ROM of Appendices <br /> labeled Historical Soil and Groundwater Analytical Tables,Historical Boring Logs,Fourth Quarter 2004 <br /> Groundwater Monitoring Report, and EDR Radius Map Report. The Report follows the SCM format listed in <br /> CalEPA's California Human Health Screening Levels (CHHSLs). <br /> Chevron 9-6171 is an active service station with Underground Storage Tanks(USTs) located at the above <br /> address. Maximum groundwater concentrations(4`"Quarter 2004)were: Total Petroleum Hydrocarbons as <br /> gasoline, 6,400 micrograms per Liter(gg/L)and Benzene, 0.5 µg/L. MtBE was not detected at the method <br /> detection limit of 2 µg/L. Additional groundwater monitoring for chlorinated solvents, including <br /> tetrachloroethene(PCE) is conducted on Chevron's wells for several drycleaners represented by the <br /> Lincoln Center shopping mall (Lincoln Center), also the property owner of the Chevron station. PCE is <br /> commingled with petroleum hydrocarbons, and groundwater extraction wells operated by Lincoln Center <br /> remediate both chlorinated solvent and petroleum hydrocarbon contaminants by an air sparging/granulated <br /> activated carbon treatment system. Nearby City of Stockton Municipal Supply Wells have been decommissioned <br /> due to PCE contamination. <br /> The Report's Conclusions state, in addition to your site,there are four potential primary sources for hydrocarbons <br /> near Benjamin Holt Drive and Pacific Avenue: Former Norge Cleaning Village(dry cleaners), Former Regal <br /> #603/Exxon#7-0136 service station, Canepa's Carwash, and Shell service station. The Report uses the rationale <br /> that due to the low concentrations of MtBE(0.065 mg/kg)detected in a saturated soil sample, and no MtBE in <br /> unsaturated soil samples "...implies that some, or a majority of the petroleum hydrocarbons detected in <br /> groundwater beneath the Chevron site may not be the result of past activities at the Chevron site." <br /> The Report continues"This assumption is supported by the complex history of groundwater gradient fluctuations <br /> produced by pumping and extraction of groundwater beneath the site by multiple extraction wells in the site <br /> vicinity. " The Report also cites the history of the site(USTs removed and replaced in 1986) and the theoretical <br /> low percentage of MtBE in gasoline dispensed in California before 1992 as supporting evidence for additional <br /> sources at the site. <br /> California Environmental Protection Agency <br /> Cei'Recycled Paper <br />