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Y� • 440 West Charter Way, Stockton, California December 16, 1993 Texaco Environmental Services Page 5 3.0 SUBSURFACE CONDITIONS Sods encountered during drilling consisted of interbedded clay, silt, and sand A bluish gray Gay was found in all borings at a depths between 39 and 42 feet BGS Groundwater was initially encountered in the bonngs at depths between 37 and 40 feet BGS in semi-confined, clayey silty sand aquifer horizons below the bluish gray clay Detectable concentrations of hydrocarbons exist within the upper silt and sand aquifer and lower clay horizons 3.1 Soil Analytical Results A total of twenty-four sod samples from the borings were submitted to the laboratory for analysis Low concentrations of TPH-G and BTE:X were detected in sod samples collected from MW-14, MW-15, and MW-17 TPH-G concentrations ranged from 1 1 ppm (MW-14-40') to 3 7 ppm (MW-14-45') BTEX concentrations ranged from 006 ppm ethylbenzene (MW-15-45') to 23 ppm benzene (MW-15-45') Soil analytical results are summarized in Table 1 Laboratory analyses . reports and chain-of-custody manifests for soil are included in Appendix C 3 2 Groundwater Analytical Results The analytical results of groundwater samples collected on September 20, 1993 are summarized in Table 2 MW-16 was sampled October 22, 1993 TPH-G concentrations ranged from below method detection limit (<MDL) in MW-16, to 180,000 ppb in MW-5 (Figure 3) Dissolved concentrations of benzene ranged from <MDL in MW-16, to 23,000 ppb in MW-4 (Figure 4) Laboratory analyses reports and chain-of-custody manifests are included in Appendix C 3.3 Groundwater Elevations Groundwater elevations at the site increased an average of 1 02 feet from levels reported the previous quarter The estimated flow direction of the groundwater is toward the east at a gradient of 0 004 (Figure 5) Historical groundwater monitoring data are summarized in Table 3 i 2569suM RP-r GROUNDWATER �r __ TECHNOLOGY