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s SUPPLEMENTAL INFORMATION REPORT OF WASTE DISCHARGE 8200 N. HIGHWAY 99, STOCKTON, CA A. Wastewater Treatment System and Characteristics 1. On January 28, 1998, three 8,000-gallon gasoline underground storage tanks (USTs). dispenser pumps, and associated piping were removed from the property. Obvious contamination was noted during UST removal operations and soil samples collected from beneath the removed USTs and pump island revealed significant levels of petroleum hydrocarbon constituents. Subsequent investigations have determined that gasoline hydrocarbon constituents. including MTBE, have been detected in groundwater beneath the site at elevated levels as a result of operation of a retail gasoline service station at the site. 2. This interim remedial action will consist of groundwater extraction, treatment, and discharge to the ground surface. The system will consist of four major components: 1) extraction well. 2) a treatment system, 3) a conveyance system to the treatment system, and 4) discharge area. The existing 4-inch diameter well (MW1) will be utilized as the groundwater extraction well. Contaminated groundwater will be pumped from well MW I through subgrade piping to the treatment system. Conveyance piping will be double-contained, consisting of buried 4" diameter, schedule 40 PVC with internal flexible tubing. BackfloXV prevention will be incorporated into the system. Extracted groundwater will be processed through two 2,000-pound granular activated carbon (GAC) units, which will be configured in series. The treatment system will be fitted with a manifold constructed of PVC piping. which will allow Ground Zero to configure either GAC unit as the primary unit. Sample ports will be located between all vessels to allow detection of potential contaminant break through and to obtain samples immediately prior to discharge. The submersible pump and any necessary process water pumps will be controlled by PumpTec or similar controllers. Pump controls will be operated through a control switch, which will detect any decrease in amperage when water levels drop below the pre-set levels and shut down the system. A general schematic diagram of the GAC interim groundwater treatment system is presented on Figure 1, attached. Treated effluent will be discharged to the ground surface via surface sprinkler(s) after the effluent has been verified non-detect by laboratory analyses. 3. A water supply well is located on-site approximately 200 feet east of the former USTs. In addition, an estimated 50 to 70 private domestic water wells are located within 0.5 miles of the site. An aerial photograph showing a 0.5-mile radius from the site is presented on Figure 2. An unlined drainage ditch is located across Foppiano, appoximately 90 feet south of the former USTs. A partial USGS topographic map is presented on Figure 3. 4. A site map showing the location of the facility, MTBE plume, extraction well, monitoring wells, treatment system, disposal facility, and site boundary is presented on Figure 4. 5. The anticipated average flow for the initial remediation system is 1-2 gallons per minute (gpm), xvith a maximum anticipated flow of 3-4 gpm.