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1 l Appendix A - Historical Background River City Petroleum and Connell Motor Lift Truck Page 10 of 14 One domestic ground water well is located on the property This well is located approximately 350 feet north of the UST release area The well is reportedly screened from approximately 150 feet bsg to the total depth of the water well The well services two buildings on the property Analytical analysis of the water samples collected directly from the well head have been no-detect for the chemicals of concern HYDROGEOLOGICAL MODEL Hydrological units may be defined as significant vertical intervals of sediments having significant lateral extent and having similar hydrologic characteristics (i a hydraulic conductivity, transmissivity, etc) over its vertical and horizontal extent A `flow unit' may be defined as a hydrologic 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 Based on the CPT results, AGE has developed a preliminary site hydrogeologic model comprised of seven informal zones,a vadose(unsaturated)zone and six hydrological units,the model presented is interpretational and will be modified as more data is collected The seven zones are as follows (depths are approximate and can vary by several feet across the site) • These characteristics allowed construction of a site geologic/hydrogeologic model of the vadose zone extending from surface grade to approximately 50 feet bsg or the current water table level which fluctuates with seasonal recharge in the area The hydrologic units defined are informal units and vary considerably based on the direction and content The units are designated to aide in the clarification of flow pathways and to designate migration pathways • The first hydrologic unit from 50 feet or the water table to 75 feet bsg, a second hydrologic unit from 75 feet bsg to 85 feet bsg, and a third hydrologic unit from 85 feet to approximately 100 feet bsg, a fourth hydrologic unit from 100 feet to 110 feet bsg, a fifth hydrologic unit from 110 feet to 145 feet bsg, the sixth hydrologic unit at 145 to 185 feet bsg The second, fourth locally and sixth are presumed to have a greater ground water velocity and therefore may conduct more ground water The seventh hydrologic unit begins vertically at 160 to 185 feet bsg, and extends vertically, unmodified to the depth of the current investigation limits First Quarter 2004 This unit is consistently composed of sand, with gravel locally present i Advanced GeoEnvironmental,Inc