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• Work Plan Ranch Market 23569 South Santa Fe Road Riverbank, California Site Description and Background The site is located at the southeastern intersection of Santa Fe Road and Henry Road in Riverbank,California(Figure 1). For surface improvements,there is one single story brick building. The remainder of the site is covered with asphalt. Previously the site was operated as a gasoline commercial refueling station. Currently the site is being used as a mini market(Figure 2). On May 20, 1991,Semco removed three underground storage tanks,two one thousand and one five hundred gallon,which were located in the front of the building. The analytical results from the laboratory indicated the presence of petroleum hydrocarbon in the soil at the bottom of the tanks. High concentration of petroleum was detected in the soils and ground water samples collected during the January 23, 1998 site investigation. o e of Work San Joaquin County, in their letter of April 15, 1998 has requested the definition of lateral and vertical extent of soil and groundwater contamination at the subject site. Therefore,we propose to drill four monitoring wells,as shown in Figure 2. One of the wells will be drilled adjacent to the soil boring B-1 and the other locations have been selected to define the edge of the plume and lateral extent of the-contamination. • The wells will be drilled to a depth of forty feet, as shown in Figure 3. The present water table is located at approximately thirty feet below the surface. Undisturbed soil samples at five feet intervals will be collected with a California split-spoon sampler. To evaluate the amount of dissolved constituents that may have impacted the water,groundwater samples will be collected. Fifteen feet of 0.02 slotted two inch PVC casing will be placed below the water table and five feet will be placed above it. Number three sand will be placed opposite the slotted hydrated bentonite seal to prevent the cement seal from entering the sand, and above the bentonite the annulus will be sealed with neat cement slurry. The casing will be capped with a locking cap and the well will be sealed with a traffic box cemented to the surface. For more details, please see the Quality Assurance/Quality Control section of this report. The soil and water samples will be tested as follows: ITEM DETECTION LIMITS Soil BTEX-EPA 8020 Benzene .005 ppm Toluene .005 ppm Ethyl Benzene .005 ppm Each Xylene .005 ppm TPH Soils-D.O.H.S./Luft Manual as gasoline 1.0 ppm Water BTEX-EPA 602 Benzene 0.5 ppb Toluene 0.5 ppb Ethyl Benzene 0.5 ppb Each Xylene 0.5 ppb TPH Watcr-D.O.H.S./Luft Manual as gasoline 50.0 ppb •