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7 i Work Plan Addendum - February 2009 CALIFORNIA FUELS CARDLOCK STATION 2402 Pacific Avenue, Stockton, California 1.0. INTRODUCTION At the request of Mr.David Atwater of Van De Pal Enterprises Inc.,Advanced GeoEnvironmental, Inc(AGE)has prepared this work plan addendum for advancing three remediation confirmation soil borings,for conducting a soil vapor survey(vapor intrusion investigation),and for conducting a soil vapor extraction(SVE)rebound test at the site located at 2402 Pacific Avenue, Stockton,California (site). This work plan addendum was prepared in accordance with a San Joaquin County Environmental Health Department (EHD) letter directive (Appendix A), dated 12 January 2009. The purpose of the.SVE_rebound test and the confirmation soil borings are to evaluate the SVE remedial progress at the site. The purpose of the soil vapor investigation is to satisfy a Regional Water Quality Control Board (CVRWQCB) requirement to evaluate Environmental Screening Levels(ESLs),California Human Health Screening Levels(CHHSLs)and potential vapor intrusion into buildings prior to closure consideration. A summary of previous investigation for this site was included as Appendix A in Quarterly Report- 3' Quarter 2008, dated 25 October 2008.The location of the site is illustrated on Figure 1. A plan of the site is illustrated on Figure 2.This work plan addendum has been prepared in accordance with CVRWQCB guidelines for the investigation of underground storage tanks (UST) sites. 2.0. SCOPE OF WORK Due to shallow petroleum-impacted soil documented at the site during UST removal activities (March 1996) and during previous drilling activities (July 1996-November 1997), the EHD has directed by letter(Appendix A; dated 12 January 2009) that the threat of potential vapor intrusion into buildings on the site should be investigated. Therefore, AGE is proposing to drill and sample � \ two soil vapor borings(B-11 and B-12)to characterize potential soil vapor intrusion. The proposed boring locations for B-11 and B-12 were based on Figure 3, which depicts total petroleum hydrocarbon-gasoline(TPH-g)concentrations previously detected in shallow soil samples collected z� between 15 feet 6a4�xrM" Between April 2000 and November 2006,an SVE and in-situ air sparging(IAS)remediation system h was continuously operated at the site; during this remediation period, an estimated 13,582 pounds (equivalent to 2,172 gallons) of petroleum hydrocarbons`was removed from impacted soil and ground water.However,due to declining SVE concentrations encountered from the SVE remediation system, SVE and 1AS remediation operations were suspended at the site in November 2006. w Confirmation soil samples and performance of an SVE rebound response test are now warranted ayt�w this time. Therefore,AGE is proposing to collect confirmation soil samples to depths of 40 feet bs4g from proposed boring locations B-11, B-12 and B-13. Additionally, AGE is proposing to conduct .art ks-'73I T— U�- 4:'u4 ky'- _V Advanced GeoEnvironmental,Inc.