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Site Background Information: Vanco Truck&Auto laza Page 5 of 6 Hydrogeologic Unit 6 (HU6)• HU6 extends from 7 . feet to 82 feet bsg:and is composed of silty sand to sand type soils. Hydraulic conductiv ties for HU6 generally range between 1 X10-2 and5.0 cm/& HU6 is characterized by very Ic w pore pressures, and-is classified as a flow unit, Hydrogeologic Unit 7 (HU7)- Extending from 82 fec t to total depth of the boring (100 feet bsg); HU7 is composed primarily of stiff; fine-grain d clayey silts; silty.clays, and clay. A thin, cemented sand is encountered•-at,approxima ely 94 t.ifeet to 95 feet bsg: Hydraulic conductivity generally ranges between 1 x 10 V. and, 1 X 10715 cm/s for.clays, silts, and stiff; fine-grained soils. HU7 is characterized by varyi ig -pore pressures ranging between moderate and very high and is identified.as a confi ing layer. I SITE CONCEPTUAL MODEL Based on the data collected,to date from soil boring installation and sampling, AGE has developed a site conceptual model for the release, migration, and.distribution of,the contaminants in the subsurface as described,belo : I The site surface is essentially flat land thatis dev loped as a truck and,auto plaza, The majority of•the ground surface is covered by an phalt:or-concrete cap. In general; a clayey silt layer extending from surface grade to al proximately 30 feet-bsg underlies the assessed portion of:the property(vadose zone & F U1): Beneath the clayey silt layer,is a fine-grained layer consisting of silty sand to fine w nd (HU2), which is encountered from approximately 30 feet to 38-feet-bsg. HU2 has th a characteristics of.an aquifer, or the water table. Beneath the silty sand to sand-layer are alternating layers of stiff, fine-grained soils and sandy soils. The stiff-fine-grained layers act as nfining layers, retarding the vertical migration of contaminarnts. The sandy layers teas migratory flow units, allowing contaminants to migrate vertically and laterally aw, y from the source. During site assessment activities in July andAugu t 2004�and July 2005, saturated soil, or the capillary fringe,was first encountered at aper ximately 25 feet to 30 feet bsg:Based on information from quarterly monitoring events performed by AGE, ground water flow is generally toward the northeast. However, this may be greatly modified by local recharge and discharge patterns. Site assessment activities to date defined tw areas where soil is impacted by concentrations of petroleum hydrocarbons. Thi i maximum petroleum hydrocarbon concentrations were detected in pilot soil borings MI V4.and MW-6 at depths of-15 feet and 35 feet bsg, respectively(TPH-d: 2,600 mg/kg and ,500 mg/kg). Until the monitoring well installation conducted in July 2005, the maximum petroleum hydrocarbon concentration Advanced GceEeviroamenlsk Inc.