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NOW S.00 �. Site Background Information: Sarale Farms Page 4 of 5 HYDROGEOLOGiC MODEL Based on the CPT results and comparison with soil descriptions from borings previously advanced on the site, AGE has developed a preliminary subsurface model of the site soil stratigraphy comprised of six informal zones - a vadose (unsaturated) zone and five hydrogeologic units. `. Hydrogeologic units maybe defined as distinctive vertical intervals of soil with a significant lateral extent and having similar hydrologic characteristics(i.e. hydraulic conductivity, transmissivity, etc.) over its vertical and horizontal extents. A `flow unit' may be defined as a hydrogeologic unit �• characterized by significantly greater hydraulic conductivity values than the 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 and will be modified as more data is collected. The six vertical zones identified are as follows(depths are approximate and can vary by several feet across Lo the site): Vadose Zone - Extending from surface grade to approximately 5 feet bsg (average depth to the `' ground water table), the uppermost 4 feet is generally comprised of clayey peat, underlain by predominantly fine-grained sediment (clayey silt and silty clay) from 4 feet to 5 feet bsg. Hydrologic Unit 1 (HU1) - At the top of the current saturated zone, HUI extends from approximately 5 feet bsg to between 20 feet and 22 feet bsg and is comprised primarily of fine- grained sediments (silt, clayey silt, and silty clay). Pore pressure is low throughout the zone. Hydrologic Unit 2 (HU2) - HU2 extends from 20 feet to between 33 feet and 35 feet bsg on the south and west portions of the site and 22 feet to 40 feet bsg to the north and east; the zone is composed primarily of fine-grained sandy sediments (sand and silty sand) sandwiched between approximately l-foot thick layers of silt and/or sandy silt. This unit exhibits Iow pore pressures and may be considered a flow unit. Hydrologic Unit 3(HU3)-Extending from the base of HU2 to between 46 feet and 48 feet bsg,HU3 �., consists of clay,clayey silt,and silty clay exhibiting moderate to high pore pressures.This unit may act as a confining layer. Hydrologic Unit 4(HU4)-HU4 consists of three,approximately 8-to 10-foot thick layers of sandy sediments (sand, silty sand, sandy silt, and cemented sand) separated by thinner (approximately 1 foot to 3 feet thick)layers of fine-grained material(clay, silty clay, silt,and clayey silt). This zone is characterized by generally low pore pressure, except for moderate to high-pressure peaks associated with intervals of less permeable sediments; this unit may be considered a flow unit. Hydrologic Unit 5 (HU5) -Extending from the base of HU4 to the total depth of the borings, HU5 consists primarily of interbedded silty and clayey material(silty clay,clayey silt,and silt).This zone Advanced CeoRnvironmental,Inc. Up