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Ms Margaret Lagroio August 11,2004 Subsurface Assessment Report Project No 2033-15600-01 Joe's Truck Plaza, 15600 South Harlan Road,Lathrop,CA Page 7 samples from well boring MW-7 were analyzed for total petroleum hydrocarbons as gasoline (TPHG) and diesel (TPHD) using USEPA Method SW8015B DHS/LUFT Manual, and for benzene, toluene, ethylbenzene, and total xylenes (BTEX), methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), di-isopropyl ether (DIPE), tertiary amyl methyl ether (TAME), tertiary butyl alcohol (TBA), 1,2-dichloroethane (1,2-DCA), ethylene dibromide (EDB), methanol, and ethanol using USEPA Method SW8260B Soil analytical results are summarized in Table 1 and groundwater analytical results are summarized in Table 2 Certified Analytical Reports with chain-of-custody records are presented in Appendix F FINDINGS Site Geology and Hydrogeology Stratus utilized the logs of the CPT borings to construct cross-sections depicting the stratigraphic relationships beneath the study area (Figures 3, 4, and 5) Soils beneath the study area consist primarily of fine-grained material (predominantly silty clay, clayey silt, and clay, with minor amounts of silt, sandy silt, and material classified by CPT as "stiff fine grained") to the total depth explored of 100 feet bgs Three laterally extensive sand strata (identified as Sand A, Sand B, and Sand C on the cross-sections) were encountered within this fine-grained unit, along with several thin, laterally restricted sand bodies Sands A, B, and C do not appear to be stratigraphically connected Sand A is encountered approximately 5 to 8 feet bgs, and is approximately 3 to 10 feet thick Sand A appears to extend laterally across the entire study area A thin stratum of silty material was encountered within Sand A at boring CPT-2 All of the existing groundwater monitoring wells, except MWO-1X, are installed across this sand zone Sand B is encountered at depths between 25 and 35 feet bgs, and is approximately 7 to 18 feet thick This stratum may also be laterally continuous In Cross-Sections B-B' (Figure 4) and C-C' (Figure 5), Sand B appears to extend north to south across the entire study area However, Cross-Section A-A' (Figure 3) suggests that Sand B may be limited laterally to the southwest Several thin strata of silty material were encountered within Sand B Sand C is encountered at depths between 50 and 65 feet bgs This stratum is approximately 15 to greater than 25 feet thick, and appears to be laterally extensive beneath the entire study area Several thin strata of silty material were encountered within Sand C Based on discussions with SJCEHD personnel, this sandy stratum may extend as far as Sharpe Army Depot, approximately one mile northeast of the subject site P Voe's Truck Plaza\Reports\CPT report 08-2004 doc