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N N Site Background Information : Stallworth Auto Sales Page 9 of 11 (unsaturated ) zone and ten hydrogeologic units ; the model presented is interpretational and may be modified as additional data is collected . The eleven vertical zones identified are as follows (depths are approximate and can vary by several feet across the site) : Vadose Zone - Extending from surface grade to 31 feet bsg , the average depth to the ground water table . The vadose zone is predominately coarse grained (sand and silty sand ) from surface grade to 10 feet bsg , with fine material (silt and clay) and some coarser grained materials inferred from 10 feet bsg to the surface of the water table. Hydrogeologic Unit 1 ( HU1 ) - At the top of the current saturated zone, HU1 extends from 31 feet to between 49 feet and 55 feet bsg and is comprised primarily of silt and clay with discontinuous sand lenses and is characterized on the CPT logs by low to moderate pore pressures . Hydrogeologic Unit 2 (HU2) - extends from between 49 feet and 55 feet to 60 feet bsg . HU2 is characterized by silty sand interbedded with thinner silt and clay layers with moderately low to moderate pore pressures . Hydrogeologic Unit 3 ( HU3) - extends from 60 feet to 63 feet bsg ; HU3 is a sand to silty sand layer characterized by very low pore pressure . Hydrogeologic Unit 4 (HU4) - extends from 63 feet to 127 feet bsg ; HU4 consists primarily of silts and clays with some discontinuous layers of sand to sandy silt. The unit is characterized by low to moderate pore pressure . Hydrogeologic Unit 5 (HU5) - extends from 127 feet to 131 feet bsg ; HU5 consists of sand to silty sand , characterized by very low pore pressure . Hydrogeologic Unit 6 (HU6) - extends from 131 feet to 161 feet bsg ; the unit is predominately silt and clay with laterally discontinuous sands to sandy silts ; HU6 is characterized by low to moderate pore pressure. Hydrogeologic Unit 7 (HU7) - extends from 161 feet to 177 feet bsg ; the unit is characterized by a thick sand interval on the eastern edge of the site which appears to transition to interbedded stiff fine grained soil , clays and silts towards the west. Pore pressures in HU7 range between low pressures in the sand interval to moderately low to moderate in the finer-grained soils. Hydrogeologic Unit 8 ( HU8 ) - extends from 177 feet to 190 feet bsg ; HU8 consists primarily of silt and clay; the unit is characterized by moderately low to moderate pore pressures. Hydrogeologic Unit 9 (HU9) - extends from 190 feet to 195 feet bsg ; the unit is a silty sand to sandy silt layer characterized by low and some moderate pore pressures . Advanced GeoEnvironmental, Ine.