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31 January 2013 AGE-NC Project No. 02-0926 Page 4 of 21 make it distinct from surrounding bodies of rock or sediment (Sanders, 1998), or a part of a body of rock that forms a distinct hydrologic unit with respect to the flow of ground water (Maxey, 1964). A 'flow unit' may be defined as a hydrogeologic unit and is characterized by significantly greater hydraulic conductivity values than overlying and underlying units; a flow unit is capable of serving as a preferred migration route, and could potentially allow migration of large contaminant masses over great distances. Based on the CPT results and comparison with soil descriptions from borings advanced on the site, AGE has developed a preliminary subsurface model of the site soil stratigraphy comprised of seven informal zones - a vadose (unsaturated) zone and six hydrologic units. The model presented is interpretational and can be modified as more data is collected. The seven 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 maximum depths of approximately 43 feet bsg, the vadose zone is composed primarily of clay, silt, silty clay, and clayey silt, with discontinuous lenses of sandy sediments encountered at approximately 25 feet and 29 feet bsg. This zone is characterized by low to high pore pressures; local zones of low pore pressure appear to be due to the presence of discontinuous lenses of sandy and silty sediments. HU1 - This zone extends from approximately 43 feet to between 59 feet and 62 feet bsg. An apparently continuous fine sandy layer (consisting of cemented sand and stiff, fine- grained material) is encountered at the top of the zone to depths between 45 feet and 50 feet bsg, underlain by alternating intervals of clayey, silty, and sandy material. This unit is characterized by moderate to high pore pressures; local zones of low pore pressure appear to be due to the presence of thin layers of stiff, fine-grained material. HU2 - HU2 extends from between 59 feet and 62 feet bsg to approximately 70 feet bsg, and consists primarily of clayey silt, silt, and stiff, fine-grained material. Pore pressure within this unit is uniformly low. HU3 - HU3 extends from 70 feet to approximately 73 feet bsg and consists of sand, silty sand, and sandy silt with low pore pressures. This unit may be considered a flow unit. HU4 - HU4 extends from 73 feet bsg to between 80 feet and 82 feet bsg, and consists primarily of clayey silt, silt, and stiff, fine-grained material. Pore pressures within this unit are moderate to high. HU5 - Extending from between 80 feet and 82 feet bsg to approximately 90 feet bsg, this unit consists primarily of interbedded silty and clayey material. Pore pressures range from low to moderately high; local zones of low pore pressure appear to be due to the presence Advanced GeoEnvironmental, Inc.