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M µ 11 Appendix A - Historical Background River City Petroleum and Connell Motor Lift Truck Page 9 of 14 • Benzene, toluene, ethylbenzene and total xylenes were detected in the soil samples at maximum concentrations of 58 mg/kg, 230 mg/kg, 71 mg/kg and 360 mg/kg,respectively, in the sample from VW14-45 and 62 mg/kg, 330 mg/kg, 120 mg/kg and 550 mg/kg, respectively, in the sample from VW15-45 • TBA was detected in four soil samples with a maximum concentration of 160 micrograms per kilogram (µg/kg), in sample VW13-45, all other detections were above 50 µg/kg • 1,2-DCA was detected in twelve soil samples at a maxnrium concentration of 810 µg/kg,in sample VW14-55 June and July 2005 - Installation of Ground Water Monitoring Wells • Eleven groundwater monitoring wells(MW-38 through MW-48)were installed on between 21 June and 07 July 2005, developed on 11, 12 and 13 July 2005 and surveyed on 12 July 2005 Screen was installed monitoring well MW-41 from approximately 40 feet to 60 feet bsg, in monitoring well MW-38, MW-40, MW-43, MW-46 and MW-47 from approximately 90 feet to 100 feet bsg, and in monitoring well MW-39 MW-42, MW-44, MW-45 and MW-45 from approximately 140 feet to 150 feet bsg with blank casing extended IDto the surface • Only 1,2-DCA was detected in the new set of well installed and in a total of twenty four ground water samples collected from six of the designated hydrogeologic units across the site,the highest concentration of 1,2-DCA was detected in well MW-39(HU6)at 250 µg/1 • The lateral extent of the dissolved 1,2-DCA has not been defined The shallow limit of the dissolved 1,2-DCA plume is defined within the monitoring well network,however, 1,2-DCA concentrations were observed in the newly installed wells to increase with depth across the hydrologic units down-gradient of the former UST release (west) GROUND WATER DEPTH, FLOW DIRECTION AND GRADIENT According to the map titled Lues OfEgual Depth Of Water Wells-Fall 1996, published by the San Joaquin County Flood Control and Water Conservation District,the estimated depth to ground water at the property is approximately 50 to 60 feet below surface grade (bsg) The prevailing ground water flow direction in eastern Stockton is generally northeast, although flow directions may vary locally and seasonably According to current monitoring well information,the ground water table near the site occurs at approximately 50 feet bsg The seasonal fluctuation of the ground water table has been between 35 feet and 60 feet bsg The ground water flow direction at the site has been primarily northeast,however,variability in the flow direction has shown western and northwestern directions, with a typical gradient of 0 001 ft/ft or greater Advanced GeoEnvnronmental,Me