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_ sd10 field investigation was conducted under the direct supervision of Russell Juncal, California Registered y Geologist No. 3864, and Nora H. Kataoka, California Registered Civil Engineer No. 38322. E a 4.0 Subsurface Conditions ,. 4.1 Field Inspection The soils encountered during drilling consisted ,.� predominantly of silty clays and clayey silts, with shallow intervals of poorly graded sands to 29.0 feet, "he maximum depth explored. A cross sectional view {A-A' } o.": the soil stratigraphy as shown, on Figure 3 is depicted on Figure 5. Hydrocarbon odors were noted in soil boring SB1 in the interval between S and 11 feet below grade. Field inspection did not record the presence of hydrocarbon vapors or visual s staining of soils typically associated with hydrocarbon contamination in well borings MWl through MV4. The only sample to register a reading on the PID was the 10 foot sample from SB1 (6.2 ppm) . The depth to first groundwater beneath the site was recorded to be approximately 10 feet below grade. Depth to water r' measurements for monitorings conducted in October and IY November 198^ are presented in Table 1. Groundwater gradient maps were prepared using the Kriyging method (Figures 6, 7, and 8). The gradient maps for the three t monitorings show a consistent north to northeasterly groundwater flow at a one percent gradient. As such, both wells M42 and MW3 are down gradient from the former diesel tants pit. 4.2 Laboratory Analysis - Soil The laboratory analysis of ra.mo_.es collected at 10.0 feet in the soil and well borings did not record the presence of STEX above the 0.02 ppm method detection limit. The 10 foot sample from soil boring SB1 recorded 378 ppm TPH-D. The TPH-D concentrations were not detected above the 10.0 ppm detection limit in any of the well boring samples. ri Laboratory test results fo; these samples are summarized in Table 2. Laboratory data sheets, chain of custody forms and i laboratory quality control data are presented in Appendix V. [a 4.3 Laboratory Analysis - Groundwater The laboratory analysis of the groundwater sample collected from wells MW1 through MW4 did not record the presence of BTEX above the 0.3 ppb method detection limit. The TPH-D ---- --- ------ - - -- ----- concentration was-not-detected-above—the---30:0--ppb--detection--_,.._.____.._..-----.._-_-----...-------_ ----:—._.—_-.. limit in any of these four wells. Concentrations of fecal % ,; coliform were detected above the 2.2 MPN (most prcLable 4