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Site Background Information: Den's Auto Repair Page 7 of 8 Hydrologic Unit 2 (HU2) - Extends from 45 feet to approximately 90 feet bsg and is composed dominantly of stiff,fine-grained soil,clayey silt,silt and lesser amounts of clay.HU2 is characterized by varying pore pressures ranging between moderate and high. Hydrologic Unit3(HU3)-Extends from 90 feet bsg to total depth;HU3 is composed of interbedded stiff, fine-grained soil, silty and gravelly sand, clayey silt and silty clay from 90 feet bsg to approximately 110 feet bsg and sand, silty sand and gravelly sand from 110 feet bsg to total depth. HU3 is characterized by generally low pore pressures, and may be classified as a flow unit. SITE CONCEPTUAL CONTAMINATION MODEL Based upon current data collected AGE has prepared the following site conceptual model: 1 • The subsurface lithology is composed dominantly of silty fine sand,sandy silt,clayey silt to ql,)d silty clay and clay.The upper two hydrologic units are comprised of silt and clay��95 Significant sand intervals were identified at between 70 feet and 75 feet bsg,betwe 90 andfeet bsg, �/p 100 feet bsg and 105 f�et bsg, and at 110 feet bsg. Based on the soil descriptions and CPT hydrologic information (pore pressure), AGE has identified three hydrologic units (HU1 through HU3). • A release of petroleum hydrocarbons (TPH-g) and benzene, toluene, ethyl benzene and xylenes (BTEX)compounds and fuel additives(MTBE)was documented to have occurred from fuel UST area. Petroleum hydrocarbons were detected in the soil samples collected from below the former UST area,while the most significant concentrations of hydrocarbons and MTBE were detected at the are of well MW-1A. • Hydrocarbon-impacted soil was present in the vadose zone below the former UST location, within saturated zone in the locations of the newly installed well MW-1, and distributed in the capillary zone. • Soil encountered at 35 feet bsg in the boring established for well MW-1 was not impacted by detectable concentrations of petroleum hydrocarbons,while soil at depths between 43 and 70 feet bsg were impacted by petroleum hydrocarbons. The impacted soil encountered between 43 and 70 feet bsg in MW-1 appears to be part of a significan u ndefine lum'�",'� possible associated with the former dispenser island more than 20 feet southe s eewwWt • Impacted soil encountered in the former UST cluster may extend,at depth,to the MW-I ar but the lower hydrocarbon concentrations in the former UST cluster suggest otherwise No soil contamination was encountered in boring B2,which extended only to 35 feet bsg. • The petroleum hydrocarbons then dissolved into the ground water at the former UST area. If analytical results from well MW-1 are considered to be the signature of an on-site source, then the groundwater would have flowed west while the water table was a 50 to 55eet bsg i?.S f J rl ' Advanced GeoEnviron mental,Inc. G� /r7]tJl 31