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Site Background Information: Vanco Truck &Auto Raza Page 3 of�6 110 mg/kg,0-.017 mg/kg;and 0.037 mg/kg,respectively.A total of three grab ground water samples were collectedfrom soil boring CPTH,No constituents of concem were detected at or above laboratory detection limits in the grab ground water samples analyzedt 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 I AW-4 through MW-6 were completed, as ground water,. monitoring wells of the same designations using 24nch diameter polyvinylchloride(PVC)casing with a 0:010=inch slo ed screen installed from 15 feet to 35 feet bsg. TPW-g was detected in the soil samples ollected frorn goring MW-4-at45 feet- bsg(MW4,15)and at 35 feet•bsg i MW4y35)at concc intrations of 46 mg/kg and 230 mg/kg,, respectively; TPWg also was detected-in soil amples MW6-30 and' MW6-35 at. concentrations of 34--mg/kg and. 38-,mg/kg; respE ctively. TPH-d.was detected in soil samples MW4=15,MW4-20,MW4-35,MW6-M and MW6-35 ata maximum concentration of 2;600 mg/kg in sample MW4=15. MTBE.was detected in samples MW4=20 and-MW4-25 at concentrations 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 sg;characteristically,the material had low plasticity and toughness with a dry to slightly rT ioist:moisture content- Brownish-gray or brown, moist,to -saturated;=poorly graded sanc y silt-to .fine sand was encountered between 25 feet and 35 feet,bsg. A sandy silt to silt Nas encountered at approximately 35 feet to 40 feet bsg. From 40 feet- bsg:to total de th; 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 r 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'charactenzed by significantly greater hydraulic conductivity values than overlying and underlying units; a flow unit is capable of Advanced GeoEnvlronmentak Inc.