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Appendix A - Site Conceptual Model FORMER CONNELL MOTOR LIFT TRUCK/RIVER CITY PETROLEUM 2211 North Wilson Way, Stockton, California To date, the vertical and lateral extent of soil and ground water contamination has been generally defined, except for low concentrations of the solvent 1,2-dichloroethene (1,2-DCA) The CVRWQCB Staff concurred that the concentrations of 1,2-DCA detected at the stoddard investigation site appear to be contributed by the former RIVER CITY PETROLEUM UST release IThe scope of work includes the installation, operation and maintenance of a soil vapor extraction system for the treatment of the vadose zone contamination, both hydrocarbons and additives ' Additional site assessment of the dissolved 1,2-DCA, laterally surrounding the know lateral distribution Generally the ground water investigation should be directed west of the former USTs and north and south of the monitoring wells in the building The vertical assessment of 1,2-DCA ' should be conducted in the former UST area, southwest of the former UST area, and north/south of the current well network The exact placement of multi-level monitoring will have to be decided at a later iteration,based on an evaluation of the data to be collected Most likely additional multi-level ' wells will be placed north and west of the building,within the southern portion of the building based on the know distribution of the 1,2-DCA, in an attempt to encompass the know 1,2-DCA ' distribution SITE DESCRIPTION 1 The site is predominately level, at an elevation of approximately 20 feet above mean sea level Approximately 90%of the surface of the site is covered by asphalt, concrete or structures Six main ' building complexes are located on the site Parcel No 117-150-031 is occupied by the Rev-a-Lon Barber Shop, Connell Truck Tire Service, James Poulk Auto Body and Paint, Lift Truck Services, Cherokee Trailer Sales and formerly by River City Petroleum Company ' GROUND WATER DEPTH, FLOW DIRECTION AND GRADIENT ' According to the map titled Lines Of Equal 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 groundwater ' 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 55 feet bsg The seasonal fluctuation of the ground water table has been tbetween 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 to 0 001 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 1