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Mr. Harlin Knoll February 19, 1990 Page 3 Ground Water Management Plan The following is a summary of the ground water management plan Delta has prepared for the installation of the new underground gasoline storage tanks. A Wastewater Discharge Permit for discharge of dewatering system water was issued by the City on December 18, 1989. During the installation of the new storage tanks, it is predicted that ground water will be encountered at 9 to 11 feet below the ground surface. Therefore, the area within the proposed locations of the new underground storage tanks must be dewatered during excavation and tank installation. A hole 20 feet deep and several feet wide will be excavated near the upgradient corner of the proposed excavation. An 18-inch-diameter slotted pipe will be planed in the hole and a gravel pack placed around the pipe. A sump pump will be Iowered to the bottom of the pipe. The pump will be used to dewater the excavation as it is being dug and while the new tanks are being placed. The recovered ground water will be discharged into an aboveground storage tank, passed through a treatment system, and discharged into additional aboveground storage tanks. Delta will collect a water sample from each storage tank (with a minimum of 1 sample per 20,000 gallons of water). As required by the Wastewater Discharge Permit issued by the City, each sample will be analyzed for TPPH and total oil and grease to insure that the maximum concentrations allowed by the City Municipal Code are not exceeded. If a sample collected from a tank exceeds the discharge concentration requirements, modifications will be made to the water treatment system. After modifications have been completed, the water will be passed back through the system and another sample will be analyzed for BTEX, TPPH, and total oil and grease. After the discharge standards have been met, the contents of the tank will be discharged into the sanitary sewer, at a discharge rate not to exceed 50 gpm. We estimate that a maximum volume of 100,000 gallons will be discharged to the City Sanitary Sewer System during the planned excavation and tank replacement activities. Verification Sampling: Storage Tank and Product Line Excavations Following the removal of the existing underground gasoline storage tanks, soil samples will be collected from the sidewalls of the excavation adjacent to both ends of each tank at the soil/ground water interface. The samples will be collected from two feet into the finished excavated surfaces of the sidewalls following the methods recommended on page 13 of the Regional Board Staff Recommendations for Initial Evaluation and Investigation of Underground Tanks. Also, one soil sample will be collected for every 20 linear feet of excavated product distribution line from one foot below the bottom of the trench excavation. In addition, a soil sample will be collected from the sidewall of the excavation for the new underground storage tanks near soil boring SB-10 to verify that petroleum hydrocarbons identified during our pretank closure investigation have been removed. All collected soil samples will be submitted to the mobile on-site analytical laboratory or a 12-hour turnaround local laboratory for analysis of BTEX and TPPH concentrations. If TPPH concentrations exceed 10 ppm or if subjective analysis and PID screening indicate that soil containing petroleum hydrocarbons remain in the soil underlying the site,the excavation will be widened until subjective analysis and PID screening indicate that soil containing petroleum hydrocarbons has been removed. Next, a confirming soil sample will be collected and analyzed for BTEX and TPH concentrations. The necessary excavation work will continue until either TPPH concentration is below 10 ppm or until further excavation