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' 30 August 2004 AGE-NC Project No 99-0592 ' Page 9 of 13 ' lateral extent and having similar hydrologic characteristics (i e hydraulic conductivity, transmissivity, etc ) over Its vertical and horizontal extent A `flow unit' may be defined as a hydrological 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 ' The model presented is interpretational The 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 approximately 64 feet bsg, the depth to the ground water table The vadose zone is predominantly fine grained material from surface grade to 57 feet bsg The zone is characterized by a moderate friction ratio and generally low pore pressures ' Hydrological Unit 1 (HU1), at the top of the current saturated zone, extends from 60 feet to approximately 67 feet bsg and is comprised predominantly of sand, grading from silty sand to ' gravelly sand This interval is characterized by low pore pressures Hydrological Unit 2 (HU2) extends from 67 feet to approximately 72 feet bsg and is composed ' primarily of silt and some sandy silt HU2 is characterized by varying pore pressures ranging between moderately low and high Hydrological Unit 3 (HU3) extends from 72 feet to 77 feet bsg, HU3 is composed of stiff fine-grained material A sample was attempted at 73 feet bsg to identify it better,but the screen from ' the ground water sample taken above that depth was sampled instead HU3 is characterized by generally high pore pressure, dropping in proximity to the contact with HU4 Hydrological Unit 4(HU4)extends from 77 feet to 85 feet bsg and is composed of sandy silt to sand to a gravelly sand HU4 is characterized by low pore pressure and friction ratio, and may be classified as a significant flow unit Hydrological Unit 5 (HU5) extends from 85 feet to 100 feet bsg or total depth, 1FfU5 is composed of clayey silt and silt with some stiff fine grained material HU5 is characterized by generally low ' to moderate pore pressures Hydrological units are depicted in cross sectional view A-A' (Figure 4) ' Advanced GeoEnvironmental,Inc