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Site Background Information: Vanco Track &Auto Plaza Page 3 of 6 110 mg/kg,0.017 mg/kg,and 0.037 mg/kg,respecti ely.A total of three grab groundwater samples were collected from soil boring CPT-1. No ronstituents of concern were detected at or above laboratory detection limits in the grab C round water samples analyzed. On 29 July.2005, three additional shallow ground ater monitoring wells (MW-4, MW-5, and MW-6)were installed at,the site. Pilot borings W-41hrough MW-6 were completed as ground ;water monitoring wells of,the same designations using 2-inch diameter polyvinylchloride(PVC)casing with a 0.010-inch slotted screen installed from 15 feet to 35 feet bsg: TPWg was detected in the soil samples Ilected from boring MW-4 at 15 feet bsg(MW4=15)and at 35 feet bsg(MW4-35)at cone 3ntrations of 46 mg/kg and 230 mg/kg, respectively; TPHig also was detected in soil samples MW&30 and MW6-35 at concentrations of�34�,mg/kg:and 38 mg/kg, resp ctively. TPH=d was detected in soil samples MW415,MW4-20,MW4-35,MW6-30 and MW6-35 at-a maximum concentration of 2,600 Mg/kgin sample MW4=15. MTBE was detected in samples MW4120 and MW4-25 at-coneentrations of 0.016 mg/kg and 0.017 mg/kg respectively. 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=grain d soil consisting,of clayey silt to silty clay was encountered from surface grade to 25 feet bsgs characteristically,the material had low plasticity and toughness with a dry to slightly moistmoistUre 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 stratigraphy comprised of,eight,informal zones: a vadose (unsaturated)zone and seven hydrogeologic units Hydrogeologic, or hydrostratigraphic, units (HUs) are defined as a body of rock or sediment that, has hydrogeologic characteristics (i.e. hydraulic conductivity, pore pr ssure, 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 Advanced GeoEnvironmental,Inc.