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' 4.0 RESULTS OF INVESTIGATION ' 4.1 Soil Subsurface soils at the site consist of silty sands and sands with lenses of clayey sands interbedded From surface to approximately 20 feet bgs, the sands are micaceous and fine to medium grained From 20 feet bgs to approximately 30 feet bgs, interbedded lenses of reddish brown to dark grey clayey sands exist Organic material, such as root casts, and some caliche 1 zones are encountered throughout Moisture content increased with depth from 30 feet with first water typically encountered at approximately 37 feet bgs Appendix C - Soil Boring Logs present a graphical as well as written account of the subsurface lithology for all borings drilled ' at the site Analytical results for soil samples submitted from the first phase of drilling activities, October 1990, reported nondetectable levels of BTEX and concentrations of TPH-D ranging from 1 9 milligrams per kilogram (mg/kg) or parts per million (ppm) to 110 mg/kg TPH-D was only reported in four of the samples submitted to the laboratory ' The sample reporting 110 mg/kg TPH-D was from boring B-2Y at the termination depth of the boring and was collected at the direction of a representative of the San Joaquin County ' DHS/EHD Thus sample consisted of asphalt chips with some native soils All other soil samples reported concentrations of TPH-D of 1 9 to 3 2 mg/kg Analytical results for the soil samples submitted from the second phase of drilling activities, May 1993, reported nondetectable concentrations of TPH-D and BTEX ' All laboratory analytical reports and chain of custody documentation are included as Appendix F-Laboratory Reports and Chain-of-Custody Documentation for Soil Samples Table 2 presents ' analytical results for soil samples in a tabular form 4.2 Ground Water Ground water was found to generally flow to the south - southwest with a gentle gradient Ground water elevation maps for all reporting periods to date are included as Appendix G - Historical Ground Water Elevation Maps Table 3 presents historical ground water elevation data in a tabular form ' Ground water samples submitted for laboratory analysis indicate that TPH-D was detected in two wells, MW-1 and MW-4, in isolated events Samples collected from well MW-1 in May and July 1993 reported concentrations of TPH-D of 950 and 200 micrograms per liter(µg/L) or parts ' per billion (ppb) However, a duplicate sample collected from well MW-1 in May of 1993 reported nondetectable concentrations of TPH-D for this well ' Benzene was detected in one sample from well MW-2 in August 1991 at a concentration of 1 3 µg/L Benzene has not been detected in any other sample collected at the site since November 1990 1 F%9351861CL.OSURE RPT 9 Environmental Science&Engineering,Inc