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AGE-NC Project No. 99-0559 Page 11 of 13 pore pressure spike occasionally occurs at between 60 and 65 feet bsg, generally associated with the silty sand or stiff, fine-grained soil. Hydrological Unit 2 (HU2) extends from approximately 65 to 75 feet bsg. It is composed dominantly of clay, clayey silt, sandy silt, silty sand and stiff, fine-grained soil. Pore pressures ranged from low for clays to moderate for stiff, fine grained soil. Hydrological Unit 3 (HU3) extends from 75 to between 85 and 90 feet bsg and is predominantly stiff, fine-grained soil fine grained sediments, with local occurrences of clay, silty clay, silt and sand. Pore pressure is generally low to moderately low, but can peak to high in portions of the stiff, fine-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 (HU5) 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-grained, 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: The subsurface lithology is composed dominantly of silty fine sand, sandy silt, clayey silt to silty clay and clay. Significant sand intervals were identified at between Advanced GeoEnvironmental, Inc.