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i i . Site Background Information I AGE-NC Protect No 97-0326 Page 5 of 5 tto low pore pressures, however, a pore-pressure dissipation test conducted at CPT-4 suggests that the hydraulic conductivity is low in this sand interval (between 2x 10-5 and 4x 10"' centimeters per ' second) Hydrogeologic 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 more clayey intervals and low pore pressures in stiffer ' fine-grained Intervals Hydrogeologic 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 Hydrogeologic 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 in the western half of the ' survey area transitions to silty clay 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 ' Hydrogeologic Unit 6 HU6 extends from approximately 135 feet to 150 feet bsg This interval { ) pp consists dominantly of sand and gravelly sand and is characterized by very low to low pore pressure 1 Hydrogeologic Unit 7 (HU7), 150 feet bsg, is a black clay recovered at total depth in wells MW-8 ' and MW-9 ' REFERENCES Maxey, G B , 1964, Hydrostratigraphic units Journal of Hydrology, v 2, pp 124-129 Robertson,P K , Campanella,R G , Gillespie,D and Greig,J , 1986, Use ofpiezometer cone data Proceedings of the ASCE Specialty Conference in Situ 86, Use of In Situ Tests to Geotechnical Engineering, Blacksburg, p 1263-1280 Sanders, L L , 1998,A manual of field hydrogeology, Prentice-Hall, Inc ,New Jersey, 381 p 1 Advanced GeoEnvuonmental,Inc 1