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_ DIRECTOR <br /> San Joaquin County Donna Heran,REHS 4 <br /> o-Qu•In, Environmental Health Department AsISTA t DIREREHS <br /> CTOR <br /> Lau°.r. c 600 East Main Street <br /> , <br /> Stockton, California 95202-3023 PROGRAM COORDINATOR <br /> �. Carl Borgman,REHS <br /> Mike Huggins,REHS,RDI <br /> REHS <br /> :,. - � • Website: WWW.sjgov.org/ehd Ra>geertrMCCIeallon,REHS <br /> �4:i—.F Phone: (209) 468-3420 <br /> Fax: (209) 464-0138 .teff Carruesco,REHS,RDI <br /> f<asey Foley, REHS <br /> June 19, 2008 <br /> Stephanie Furgal <br /> Chevron Environmental Management Company <br /> 6001 Bollinger Canyon Road Room K2240 <br /> San Ramon, CA 94583 <br /> Subject: Former Unocal #2859 <br /> 1665 Pacific Avenue <br /> Stockton, CA <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed the "Response <br /> to Comments — San Joaquin County EHD" (Response) dated May 22, 2008, prepared by <br /> ARCADIS for the above subject site and provides the following comments. <br /> Arcadis used a trend analysis to calculate a biodegradation constant based on groundwater <br /> sample results from MW 10 from January 2006 to January 2008 and assumed the same <br /> biodegradation rates would continue in the future to calculate dates each analyte would reach <br /> the San Francisco Bay Regional Water Quality Control Board (SFBRWQCB) environmental <br /> screening levels for groundwater. This analysis indicates that water samples from MW 10 will <br /> have a concentration of 100 micrograms per liter (ug/1) of total petroleum hydrocarbons as <br /> gasoline (TPH-g) by June 2030 and a concentration of 1 ug/1 of benzene by April 2027. The <br /> t Response states that further active remediation is not warranted and recommends monitored <br /> natural attenuation. <br /> j The Response states that the ozone sparge system reportedly operated between August 2002 <br /> and December 2005 and uses those dates of operation for deciding to start the trend analysis <br /> from January 2006. Quarterly reports for second, third and fourth quarters of 2005 state that the <br /> system was not operated or shut down. Given the above reason for the start date of the trend <br /> analysis, it should have started with April 2005 water sample concentrations (which increased <br /> from April 2005 to January 2006). Please be advised that the use of SFBRWQCB <br /> environmental screening levels for soil in San Joaquin County is acceptable by the EHD and the <br /> Central Valley Regional Water Quality Control Board (CVRWQCB) but their use as groundwater <br /> j cleanup goals in San Joaquin County is not acceptable. <br /> In letters dated March 26, 2008 and May 13, 2008, the EHD informed you that if it could not be <br /> demonstrated that the contaminant concentrations at this site would meet water quality <br /> objectives in a reasonable time (estimated to be about 10 years) then active remediation must <br /> be performed to expedite the site clean up so it would be completed within that reasonable time <br /> frame. Even with the use of the trend analysis and SFBRWQCB environmental screening levels <br /> in the Response, contaminant concentrations were not projected to be met within a reasonable <br /> time (10 years). <br /> i . <br />