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i.. PROPOSED WORK PLAN FOR PRETANK CLOSURE SITE ASSESSMENT Shell Service Station $725 Tracy Boulevard,Tracy California Delta Project No.40-69-012 Page S are believed to be single-walled and of steel construction. The fiberglass tanks were placed in the same location as the steel tanks that were removed. A waste oil tank of unknown size was removed from the site in 1985. The location of the previous waste oil tank is unknown at this time. 2.3 Previous Subsurface Investi ative Activities Prior to tank replacement activities in 1985, Shell contracted J. H. Kleinfelder & Associates to drill four test soil borings in the vicinity of the underground storage tanks. The soil borings were drilled to a depth ranging from 11.5 to 16.5 feet below the surface; approximate locations are illustrated in the Kleinfelder report presented in Appendix A. In the course of their 1985 investigation, Kleinfelder collected soil samples for classification and screening with a trace gas analyzer (believed to be an OVA). In general, Kleinfleder characterized the natural soils at the site as sand and silt. Water was encountered in boring 13-1 at a depth of approximately 11.5 feet. Gasoline hydrocarbons(presumed) were detected using a trace gas analyzer in borings B-4, B-2, and B-1 at a depth of approximately 10 feet or roughly corresponding to the bottom of the tanks and just above the detected water level. Samples collected from greater depth (i.e., below the water table) did not contain petroleum hydrocarbon constituents. Petroleum hydrocarbon constituents were not found in any of the soil i.. samples screened from boring B-3. Refer to Appendix A for boring locations. Following removal of the steel tanks in 1985,soil samples were collected by Canonie Engineers, Inc., y from below the three tanks. In addition, water samples were collected from the bottom of the excavation. The results are included in the analytical report prepared by Canonie Engineers +j (Appendix B). Samples were analyzed for total extractable hydrocarbons, benzene, toluenes, xylenes, ethylene dibromide, and organo-lead. In summary, soil samples indicated a TPH range of nondetectable (at 1 ppm) to 40 ppm in soils, and from not detected to 0.7 ppm in water. Organo- lead, ethylene dibromide, benzene, and toluene were below detectable levels in all soil samples analyzed. Xylenes were detected in the water sample at a concentration of 66 parts per billion(ppb) and in one soil sample at a concentration of 1.2 ppb. The depth represented by these samples is not known.