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Subsurface Investigation Report-Tosco(Former BP)Service Station No. 11195 Lathrop,Califomia April 11,2002 The five Geoprobes were all advanced to 12 feet bgs. Soil sampling for lithologic logging was conducted . continuously beginning at 5 feet bgs. Soil samples from selected depths were collected for chemical analysis. The soil samples were handled in accordance with GR Field Methods and Procedures(Appendix A). The GR geologist prepared logs of the borings and screened the samples in the field for the presence of volatile organic compounds. Lithologic and screening data and the depths at which soil and groundwater samples were collected are presented on the boring logs in Appendix B. . 3.2 Groundwater Sampling After groundwater was encountered, probing was halted and grab groundwater samples were collected from each boring with a disposable Teflon bailer. The samples were decanted into the appropriate laboratory- supplied containers, as described in GR's Field Methods and Procedures (Appendix A). 3.3 Borehole Sealing After probing and sampling were completed,the boreholes were sealed with neat cement grout. The grout was placed from the bottom of the boring to approximately one foot bgs with a tremie pipe. The boreholes were finished to surface with quick-set concrete in paved areas or covered by surface soil. Mr.Michael J. Infurna of the PHS-EHD was present at the site and approved the grouting procedures. 3.4 Waste Disposal Drill cuttings were placed in DOT-approved 5-gallon buckets and stored onsite pending disposal. One two part composite sample [Comp-1 (A,B)] was collected from the drill cuttings and submitted to the laboratory for analysis and disposal characterization. The analytical results from the composite soil sample were submitted to Allied Waste's Forward Landfill in Manteca. Upon receiving approval from the landfill,the drill cuttings will be transported to the Forward Landfill by a California-licensed hazardous waste hauler. 3.5 Laboratory Analysis All soil and groundwater samples were submitted to Sequoia Analytical in Walnut Creek California(FLAP #1271). The samples were analyzed for Total Petroleum Hydrocarbons as gasoline(TPHg)by Environmental Protection Agency(EPA)Method 8015 modified,benzene, toluene,ethylbenzene,xylenes(BTEX)and methyl tert-butyl ether (MtBE) by EPA Method 8021. In addition, all groundwater.samples were analyzed for Ethanol, tert-butyl alcohol (TBA), MtBE, di-isopropyl ether (DIPE), ethyl tert-butyl ether (ETBE), 1,2- dichloroethane(1,2 DCA), tert-amyl methyl ether(TAME) and ethylene dibrorrride(EDB)by EPA Method 8260B. The composite soil sample, Comp-1(A,B), was analyzed for TPHg,BTEX and MtBE(EPA Methods 8015M18021)and total lead (EPA Method 601013). Copies of the laboratory analytical reports and chain-of-. custody records are included in Appendix C. 4.0 RESULTS 4.1 Subsurface Conditions Groundwater was encountered during probing at depths ranging from approximately 9.5 to 10 feet bgs. Soil encountered during this investigation consisted primarily of an overlying layer of poorly graded sand from 140193.11-2 5