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i Site Background Information AGE-NC Project No 97-0326 Page 4 of 5 ' Representatives of AGE performed an area reconnaissance for visible potential receptors within a 2,000-foot radius of the above referenced site A representative number of residences and commercial establishments were queried regarding their water source, rincluding a residence on 1642 South California Street which may still have a domestic well (no one answered the door) AGE representatives did not locate any well receptor sites within ' the 2,000-foot radius However,ground water monitoring wells were found,these wells were presumably in use for local ground water investigation Additional information is provided in the AGE-prepared Sensitive Receptor Survey, dated 19 ' December 2000 ' HYDROGEOLOGICAL MODEL Based on the additional soil information acquired during this investigation, AGE modified the ' subsurface model of the site soil stratigraphy to include eight informal zones,a vadose(unsaturated) zone and seven hydrogeologic units A hydrogeologic or hydrostratigraphic unit (HU) may be defined as a body of rock or sediment that has hydrogeologic characteristics that make it distinct ' from surrounding bodies of rock or sediment(Sanders, 1998), or a part of a body of rock that forms a distinct hydrologic unit with respect to the flow of groundwater(Maxey, 1964) A`flow umt' may ' be defined as a hydrogeologic unit and is characterized by sigmficantly 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 and will be modified as more data are collected,hydraulic ' data were piezeocone (CPT) measurements 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 35 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 ' H dro eolo is Unit 1 HU1 at the to of the current saturated zone, extends from 35 feet to Y g g ( )� P approximately 70 feet bsg It is comprised primarily of fine-grained sediment characterized by low ' to very low pore pressure from 35 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 Hydrogeologic Unit 2 (HU2) extends from 70 feet to approximately 85 feet bsg, consists of a ' laterally-continuous sand layer of apparent variable thickness The zone is characterized by very low Advanced GeoEnvironmental,Inc I