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Site Background Information K& S Gas & Grocery • Page 5 of 5 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 cm/s) ' Hydrogeologlc Unit 3 (HU3) - HU3 extends from 85 feet to between 95 feet and 100 feet bsg, it consists of predominantly fine-grained material, 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,though moderate to high pore pressures are evident in more clayey intervals, and low pore pressures in stiffer fine-grained intervals ' Hydrogeologic Umt 4(HU4) -HU4 extends from 95 feet to 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) - This unit extends from approximately 120 feet 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 transition to silty clay in the eastern half The lateral variation in soil types is reflected m the pore pressures, which tend to be dominantly low in the western half and • moderate to high in the eastern half of the area H dro polo c Unit 6 (HU6) - This unit extends from approximately 135 feet to 150 feet bsg and ' interval consists predominantly of sand and gravelly sand, and is characterized by very low to low pore pressure ' Hydrogeologic Unit 7(HU7)-Beginning at 150 feet bsg,HU7 is evidenced as 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 of piezometer cone data Proceedings of the ASCE Specialty Conference to Situ 86, Use of In Situ Tests to Geotechnical Engineering, Blacksburg, p 1263-1280 Sanders L L 199$ A manual o teld h ro lo , Prentice-Hall, Inc ,New Jersey, 381 p f1' y dgeo � 1 Advanced GeoEnvironmental,Inc