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Advanced GeoEnvironmental, Inc. =- 06 November 2002 AGE Project No. 95-0173 Mr. Jeff Wong NOV 4 2002 San Joaquin County Environmental Health Department ENVINiNIAENT HEALTH 304 East Weber Avenue, Third Floor PERMIT/SERVICES Stockton, CA 95202 SUBJECT: Revisions to Work Plan Addendum, dated 29 April 2002 CALIFORNIA FUELS CARDLOCK STATION 2402 Pacific Avenue, Stockton CA Dear Mr. Wong: A work plan addendum was submitted by Advanced GeoEnvironmental, Inc. (AGE) to the San Joaquin County Environmental Health Department(SJCEHD)on 29 April 2002;the scope of work included installation of one ground water extraction well, screened between 30 and 60 feet below surface grade (bsg), and performance of a ground water aquifer pumping test. However, based on a meeting between AGE and the SJCEHD on 19 July 2002, the SJCEHD decided that revisions to the Work Plan Addendum were necessary prior to their approval. Therefore,this revised work plan addendum is being submitted to address the concerns of the SJCEHD. The location of the site is illustrated in Figure 1. A plan of the site is illustrated on Figure 2. Between 11 April 2000 and present(approximately 2'/4 years),a soil vapor extraction(SVE)system has been in continuous operation at the site to remediate petroleum-impacted soil at depths between 15 feet and 30 feet bsg(vadose zone). Since the start-up date, AGE estimates that the total volume of hydrocarbons extracted from the vadose zone utilizing SVE technology was approximately 1,348 gallons (Table 1). From the start-up date to present, the average SVE influent total petroleum hydrocarbon(TPH-g)concentrations have decreased from approximately 2,200 micrograms per liter (µg/1) to 548 gg/l, or a 75 percent decrease (Table 1). Therefore, SVE appears to be effective in removing petroleum mass in the vadose zone. At the same time, an in-situ air sparging system (IAS) has been in continuous operation at the site to address petroleum-impacted ground water at depths between 25 and 38 feet bsg, subsequently identified as Hydrologic Unit 1.Analytical results of ground water samples from on-site monitoring wells suggest that the IAS system has been moderately effective in reducing the overall mass of dissolved petroleum plume in Hydrologic Unit 1 (Table 2). 837 Shaw Road,Stockton,California 95215 Telephone(209)467-1006 FAX(209)467-1118