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S � � r� A S S O C I A T E S I N C . i REMEDIAL ALTERNATNES -- GROUND WATER ATC evaluated four remedial alternatives to further,reduce petroleum hydrocarbons in the ground water beneath the Subject Property. The alternatives includ' pump and treat, air sparging, natural attenuation and enhanced natural attenuation. i LPump and Treat This remedial approach involves pumping of.ground water to the Lsurface for treatment. It would require the installation of additional four-inch diameter extraction wells. Prior to installation of the extraction wells, aquifer testing using existing monitoring wells would be conducted to determine aquifer characteristics. The 1 results would be used to determine the most affective pumping rate, capture zone, draw down, and design of the extraction wells. A variable speed electrical. pump would be placed in each extraction well. Ground water would be placed in a surface holding tank prior to treatment. The ground water would then be pumped through dual 1,000-pound activated carbon vessels to remove gasoline hydrocarbons. The discharge from the first carbon vessel would be periodically analyzed to-establish carbon breakthrough. Treated water would be discharged into the sanitary sewer system if allowed'by the City of Stockton. If the City of Stockton will not issue a discharge permit, the extracted water would be disposed of off-site at a liquid recycling facility. Air Sparging This remedial approach'�for accelerated cleanup involves injecting air into the ground water table. An air compressor capable of delivering 10 cubic feet per minute (cfm) at 20 pounds per square inch (psi) would be utilized to inject air into the ground water table. The:injected air serves two purposes: 1) removing gasoline hydrocarbons from the saturated soil and ground water by air stripping, and 2) providing increased oxygen to the ground water to promote bacterial action to degrade the hydrocarbons. ATC would need to install a soil vapor extraction(SVE) system to remove the stripped hydrocarbons from above the water table. a In addition to the air sparging wells, the three existing two-inch-diameter vapor extraction wells would be utilized in order to ensure the capture of the hydrocarbons stripped from the saturated zone. All of the wells would be plumbed to the treatment system area. The two-inch-diameter vapor extraction wells would be plumbed into the vapor extraction manifold. The air sparging wells would be manifolded into an industrial duty air compressor. Solenoid valves and timers would be used to cycle the compressed air between the air sparging wells to prevent preferential air channeling and to maximize the efficiency of the system. A series of filters would be used to prevent any contaminants in the compressed air stream from,impacting the ground water. Water samples would be collected and analyzed from the existing ground water monitoring wells to evaluate the effectiveness of the treatment system. Dissolved oxygen and pressure readings would be measured in all of the ground water monitoring wells to provide an indication of the radial influence of the air sparging wells. In addition, vapor concentrations of the influent to the extraction system would be monitored monthly. The SVE system wouldbe operated to remove the hydrocarbons being stripped from the saturated zone by the air sparging system. An estimated 1,000 to 2,000 pounds of carbon would be required for six months of system operation. Vapor samples would be obtained from the SVE system during operation to chart the remediation Diesel Performance January 5,2004 ATC Project Number 5462577 Page 6