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! Site Background Information Vanco Truck &Auto Plaza Page 3 of 6 analyzed Analytical results of soil and grab ground water samples are summarized in Tables 1 and 2 of this appendix STRATIGRAPHY In general, light brown to orange brown, fine-grained soil consisting of clayey silt to silty clay was encountered from surface grade to 25 feet bsg,characteristically,the material had low plasticity and toughness with a dry to slightly moist moisture content Brownish-gray or brown,moist to saturated, poorly graded sandy silt to fine sand was encountered between 25 feet and 35 feet bsg A sandy silt to silt was encountered at approximately 35 feet to 40 feet bsg From 40 feet bsg to total depth, the stratigraphy is dominated by alternating layers of silty sand or silt and clayey silts to clay layers The layers vary in thickness from approximately 5 feet to 15 feet HYDROGEOLOGIC MODEL • Based on the 05 August 2004 CPT results, AGE developed a preliminary subsurface model of the site sediment stratigraphycomprised of eight informal zones a vadose(unsaturated)zone and seven hydrogeologic units Hydrogeologic,orhydrostratigraphic,units(HUs)are defined as a body of rock or sediment that has hydrogeologic characteristics (i e hydraulic conductivity, pore pressure, etc ) that make it distinct from surrounding bodies of rock or sediment(Sanders, 1998),or a part of a body of rock that forms a distinct hydrologic unit with respect to the flow of ground water(Maxey, 1964) A`flow unit'may be defined as a hydrogeologic unit characterized by significantly greater hydraulic conductivity values than overlying and underlying units, a flow unit is capable of serving as a preferred migration route,and could potentially allow migration of large contaminant masses over great distances The model presented is interpretational and will be modified as more data is collected The eight vertical zones are)Identified as follows(depths are approximate and can vary by several feet across the site) Vadose/First Water Zone-This zone extends from surface grade to approximately 20 feet bsg Static water is at 20 feet bsg in the monitoring wells, however, the first saturated soil samples were collected at 30 feet bsg This indicates that the water table is confined by the overlying fine-grained materials This zone is characterized by moderate pore pressures Hydrogeologic Unit i (HU 1) - Extending from 20 feet to approximately 30 feet bsg, HU 1 is comprised predominantly of sandy silt,clayey silt,and silt Dominant hydraulic conductivities,based Advanced GeoEnvironmental,Inc