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Site Background Information K& S Gas & Grocery ' Page 4 of 5 ' Representatives of AGE performed an area reconnaissance for visible potential receptors within a 2,000-foot radius of the site A representative number of residences and commercial establishments were queried regarding their water source, including 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 activities Additional information is provided in the AGE-prepared Sensitive Receptor Survey, dated ' 19 December 2000 ' HYDROGEOLOGIC MODEL Based on CPT data from February and November 2001 and additional soil information acquired 1 during investigation sctivities,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 ground water(Maxey, 1964) A `flow unit' may be defined as a hydrogeologic unit and is characterized by significantly 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 resented is interpretational and will be modified as more data is collected hydraulic data p � � Y was derived from 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-Extends from surface grade to 35 feet bsg,the depth to the ground water table The ' vadose zone is predommantly 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 ' Hyddrogeologic Unit 1 (HU1) - Starting at the top of the current saturated zone, HU1 extends from 35 feet to approximately 70 feet bsg It is comprised primarily of fine-grained sediment characterized by low to very low pore pressure from 35 feet to 40 feet bsg,increasing to generally moderate pore pressures from 40 feet to approximately 60 feet bsg, then decreasing to low to very low pore pressures from 60 feet to 70 feet bsg Hdrogeologic Unit 2(HU2)-HU2 extends from 70 feet to approximately 85 feet bsg,and consists . of a laterally continuous sand layer of variable thickness The zone is characterized by very low to IAdvanced GeoEnvironmentai,Inc