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Site Background Information Waterloo Food & Fuel AGE-NC Project No 99-0559 Page 10 of 11 grained intervals Hydrological Unit 4(HU4)extends from between 85 and 90 feet to 92 feet to approximately 105 feet bsg and consists primarily of sand, gravelly sand, cemented sand and silty sand Pore pressures in this interval are uniformly low This unit should be characterized as a flow unit Hydrological Unit 5 (M5)extends from approximately 105 to the total depth penetrated by all CPT borings(approximately between 125 and 160 feet bsg)except the deepest borings CPT-6 and CPT-7 Clay is the predominant on-site soil type,smaller intervals of stiff,fine-grained soil,silty clay,clayey silt and silt In addition, a thin (approximately 1-foot thick), a laterally discontinuous layer of cemented sand was identified in CPT-1 at 125 feet bsg and a similar-size silty sand was identified in CPT-2 at 155 feet bsg Soil types in HU5 are coarser towards the north and southwest,and include clayey silt, silt, stiff, fine-grained soil and sandy silt, with a finer-gramed, predominantly clay interval at between approximately 125 and 150 feet bsg, a 5-foot thick,laterally discontinuous sand layer was identified,at approximately 140 feet bsg in CPT-7 HU5 is characterized by pore pressure variations from low to moderate pressures, with occasional, moderately high pressures associated with silty and stiff, fine-grained soil Hydrological Unit 6 (HU6) extends from approximately 165 feet bsg to total depth of the deepest CPTs (CPT-6 and CPT-8) and between 165 and 170 feet bsg in multi-level well MW-5 The unit consists of silty sand and gravelly sand and is characterized by a very low pore pressure If laterally continuous beyond CPT-6, CPT-8 and MW-5, this unit should be characterized as a flow unit SITE CONCEPTUAL MODEL Based upon current data collected AGE has prepared the following site conceptual model i • The subsurface lithology is composed dominantly of silty fine sand, sandy silt,clayey silt to silty clay and clay Sigiuficant sand intervals were identified at between 50 and 60 feet bsg, between 90 and 110 feet bsg and between 165 and 170 feet bsg Based on the soil descriptions and CPT hydrologic information (pore pressure), AGE has identified six hydrologic units (HU1 through HU6) • 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 UST fuel dispenser line,at the in-tank turbins Additionally soil samples collected from the product delivery line trenches indicated significant leaks at the dispenser islands • 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 below the UST dispenser area proper Available data is suggestive of a release was Advanced GeoEnvironmentsl,Inc