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C, I [ i Site Background Information: Vanco Truck&Auto Plaza Page 3 of 6 analyzed. On 29 July 2005, three additional shallow ground water monitoring wells (MW-4, MW-5, and MW-6) were installed at the site. Pilot borings MW-4 1hrough MW-6 were completed as ground ! water monitoring wells of the same designations using 2-inch diameter polyvinylchloride (PVC) casing with a 0.0 10-inch slotted screen installed from 15 feet to 35 feet bsg.TPH-g was detected in the soil samples collected from boring MW-4 at 15 feet b g(MW4-15)and at 35 feet bsg(MW4-35) I at concentrations of46 mg/kg and 230 mg/kg,respective y;TPH-g also was detected in soil samples MW6-30 and MW6-35 at concentrations of 34 mg/kg and 38 mg/kg, respectively. TPH-d was j detected in soil samples MW4-15, MW4-20, MW4-3 , MW6-30, and MW6-35 at a maximum concentration of 2,600 mg/kg in sample MW4-15. MT E was detected in samples MW4-20 and MW4-25 at concentrations of 0.016 mg/kg and 0.017 g,respectively. I Analytical results of soil and grab ground water samples are summarized in Tables I and 2 of this appendix. STRATIGRAPHY In general,light brown to orange brown,fine-grained so 1 consisting of clayey silt to silty clay was encountered from surface grade to 25 feet bsg;characteri tically,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 b -ween 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 sai id 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 develo ed a preliminary subsurface model of the site sediment stratigraphy comprised ofeight informal zo es:a vadose(unsaturated)zone and seven hydrogeologic units.Hydrogeologic,or hydrostratigraph c,units(HUs)are defined as abody ofrock or sediment that has hydrogeologic characteristics(i.e.I ydraulic conductivity,pore pressure, etc.) that make it distinct from surrounding bodies ofrock or s iment(Sanders,1998),or apart 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 char icterized by significantly greater hydraulic conductivity values than overlying and underlying uni ; a flow unit is capable of serving as a preferred migration route,and could potentially allow migration of large contaminant masses over great distances. Admneed Geo£nvironmental,Ine.