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t ten. n , A Du Pont I3i1>m:encs Page 16 August 10, 1989 Job No,211-71-6 LABORATORY'TESTING Physical Anal nes of Soil Representative sail samples from both the unsaturated zone and saturated zone were selected for grain size analysis, porosity, and permeability tests. The results of these tests were used for classification purposes and were correlated with the field observations to provide a better understanding of the subsurface hydrogeologic conditions. The results of these physical analyses are presented in Appendix B. Chemical Analyses of Soil and Water Chemical laboratory tests were perft-.-,n -1 cn both soil and water samples. As part of the current investigation:, soil and ground-water samples were tested for total petroleum hydrocarbons (as gasoline),benzene, ethylbenzene, toluen;., and xylenes by Trace Analysis Laboratoty in Hayward (see Appendix B). RESULTS AND DISCUSSION Subsurface Soils The exploratory borings and monitorinevel!s revealed that the alluvial scdimants in the area of the k _ Douglas Gas Station are highly fi terbedded and consist of variable amounts of clay,silt,silty sand, and sand. Silty sand is predominant to depths of approximately 10 to 12 feet;this unit is underlain F.. by a sequence of interbedded silts and sands. 'The aquifer(encountered at a depth of approximately 55 feet)consists primarily of silty sand and sand with silt(with localized lenses of sandy silt),which in turn is underlain by sandy clay and clayey sand. For more detail see the Boring Logs and WE�-II: Logs in Appendix A. Laboratory test results show that the permeability of the aquifer materiills ranges from 3.5 X 10' cm/sec. to 4.6 X 10"; the latter value was obtained from a sandy silt? encountered in monitoring well MW-20 at a depth of 61 feet. - Geologic cross sections made through the site (see Plate 2) show the highly interbedded and interfingered nature of the sediments. In general, it appears that the soils contail more sand and silty sand interbeds to the northwest and thicker interbeds of silt to the southeast.'The suosurface soils generally increase in moisture content and consistent'with depth(there is a dramatic increase in soil consistency, reflected by higher blow counts, at a depth of 8 to 12 feet). Information on subsurface soil properties is included in Appendix B and is summarized fit Table C, Summary of Soil.Laboratory_Test_.Results..(Physical.Properties)._._ -._.__ Grou::d Water The most recent static ground-water levels were measured from the monitoring wells at the Douglas. ^_r Gas Staian site on June 19, 1989. EIevations of the monitoring wells(i.e.,ground surface and top r.. of casing) and potentiometric levels are shown in Table D. Ground water was encountered at a f�.