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25 March 2002 AGE-NC Project No 97-0326 ' Page 4 of 9 ' 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 and will 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 30 feet bsg,the depth to the water table The vadose zone is predominantly fine grained(silt and clay), with an approximately 60-foot wide and up to 8- foot thick sand lense at the western half of the site Hydrological Unit 1 (HUI), at the top of the current saturated zone, extends from 30 feet to ' approximately 70 feet bsg It is comprised primarily of fine-grained sediment characterized by low to very low pore pressure from 30 to 40 feet bsg, increasing to generally moderate pore pressures ' from 40 to approximately 60 feet bsg, then decreasing to low to very low pore pressures from 60 to 70 feet bsg Hydrological Unit 2 (HU2) extends from 70 feet to approximately 85 feet bsg, consists of a 7 feet fine-grained interval overlying an approximately 4-foot, laterally continuous sand unit The zone is characterized by very low to low pore pressure ' Hydrological Unit 3 (HU3)extends from 85 feet to between 95 and 100 feet bsg,it is predominantly fine grained except for two thin cemented sand lenses (each approximately 1 foot thick) at the ' western edge of the survey area This zone is characterized by variable pore pressures, apparently moderate to high pore pressures in clayey intervals and low pore pressures in undifferentiated, stiff fine-grained Intervals ' Hydrological Unit 4(HU4)extends from between 95 and 100 feet to approximately 120 feet bsg and consists of approximately 10 feet of fine-grained sediment overlying approximately 10 feet of sand, ' the lower half of the sand interval is gravelly sand HU4 is characterized by very low to low pore pressure ' Hydrological Unit 5 (HU5) extends from approximately 120 to approximately 135 feet bsg It is a predominantly fine-grained interval, silts and a 2-foot thick sand lense predominate in the western ' half of the survey area,whereas clayey silts predominate in the eastern half The lateral variation in soil types is reflected in the pore pressures, which tend to be dominantly low in the western half and moderate to high in the eastern half of the area, therefore HU5 can be characterized by a lateral ' boundary or transition zone Advanced GeoEnvironmental,Inc