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Ms. Margaret Lagorio,SJCEHD February 2,2009 Work Plan for Collection of Soil Gas Data Joe's Travel Plaza, 15600 S.Harlan Road Lathrop,California Page 2 According to Mr. Dhoot, the subject site has operated as a motor fuel dispensing facility since 1954. Several generations of underground storage tanks (USTs) and aboveground storage tanks (ASTs) have been installed at the site during the subsequent years. Currently, there are three gasoline USTs (12,000, 10,000, and 4,000 gallons) and one diesel UST (4,000 gallons) that supply the automobile dispenser islands, and four 10,000-gallon diesel ASTs that supply the heavy truck dispensers. The current station configuration is shown on Figure 2. BREIF SUMMARY OF PREVIOUS ENVIRONMENTAL WORK Environmental investigations at the site began in January 1997, when petroleum-hydrocarbon impact was identified during removal and replacement of USTs. Since that time, more than sixty (60) vertical soil borings have been drilled at the property and in surrounding areas to evaluate the lateral and vertical extent of soil and groundwater impact beneath the site. Of these borings, twenty-two borings were converted to permanent groundwater monitoring wells screened across three intervals of water-bearing strata beneath the site. Evaluation of potential remedial alternatives for the site (in the form of dual-phase extraction [DPE] pilot testing and groundwater pump testing) was performed at the site in June 2004 and December 2005. Quarterly groundwater monitoring and sampling was initiated in February 2000; and is currently ongoing. A summary of well construction details is included as Table 1. Historical groundwater monitoring and sampling data are included as Tables 2 and 3. GEOLOGY Based on available historic soil boring logs, soil beneath the site and surrounding areas is generally fine-grained (predominantly silty clays, clayey silts, and clays, and minor intervals of silts, sandy silts, and material classified by cone penetration test [CPT] as "stiff fine grained") to the total depth explored of 100 feet below ground surface(bgs). Three laterally extensive sand strata(identified as Sands A, B, and C herein) have been encountered within the fine-grained sequence, along with several thin laterally restricted sand bodies. Sand A is encountered approximately 5 to 8 feet bgs, and is approximately 3 to 10 feet thick. Sand B is encountered at depths between 25 and 35 feet bgs, and is approximately 7 to 18 feet thick. Sand B appears to extend north to south across the entire site vicinity, but may be limited laterally to the southwest. Sand C is encountered at depths between 50 and 65 feet bgs, and is approximately 15 to >25 feet thick. Geologic cross-sections illustrating interpreted stratigraphic relationships beneath the site vicinity are included as Figures 3 and 4. HYDROGEOLOGY Fifteen groundwater monitoring wells (MW-1 through MW-7, MW-9, MW-10, MW-11, MW-14A, MW-15A, MWO-1, MWO-2, MWO-3) have been screened to depths of about 20 feet bgs to monitor groundwater occurrence and quality in Sand A. In addition, one well K:Uoe's Truck Plaza\Work Plans\Work Plan for Collection of Soil Gas Data 2-2-09.doc