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the pumps allow for up to a four minute hiatus interval, after which the pump will reactivate This hiatus mainly allow for water level recharge within the wells The ground water treatment system operates on a batch basis, with a daily total of 14,400 gallons Once the 2,000-gallon holding tank fills,approximately 1,750 gallons of extracted ground water is treated and discharged The discharge of treated water(effluent) to the City of Stockton was adjusted at a flow rate of approximately 15 GPM Grab ground water samples were collected from the influent of each well and the effluent of the treatment system Samples were collected in laboratory-supplied 40-m1 EPA-approved volatile organic analysis (VOA) vials containing 0 5 ml 18% hydrochloric acid as a preservative Effluent samples were collected in the (VOA) vials, 1-liter amber bottles without preservative and 500- milliliter plastic bottles without preservative The samples were analyzed forTPH-g,BTEX,MTBE, Volatile and Semi-volatile compounds (VOC and SVOC), Metals Cd, Cr, Cu, Pb, Ni and Zn in accordance with EPA Method 200 Modified and pH Dissolved hydrocarbon concentrations detected from ground water samples collected at the influent end of the treatment system generally declined over the quarter The concentration of benzene detected in the influent treatment samples was reduced by an average of 70%,during the remediation period GROUND WATER TREATMENT • Between 15 April and 19 September 2003, the ground water extraction and treatment system processed approximately 302,703 gallons of water The total volume of ground water treated as of 30 September 2003 is approximately 2,459,705 gallons, an estimated that approximately 5,700 gallons of water was discharged per day during this time Cumulative totals of 5 69 lbs of benzene and 140 lbs of TPH-g are estimated to have been extracted since ground water treatment began on 02 April 2002 GENERAL OVERVIEW A soil vapor extraction(SVE)/in-situ air-sparging(IAS)system was installed and operated at the site from April 1996 to late June 1999 to remediate hydrocarbon-impacted soil and ground water However, over the course of the SVE remedial action,rising ground water elevation had submerged a significant portion ofcontaminated soil,leaving a greatlyreduced vadose zone addressable by SVE technology and apparently rendering IAS ineffective due to a thicker saturated zone and diminished ability to recover sparged air Areas in the eastern portion of the site and at the northwest corner of the site had not demonstrated a sustained reduction of dissolved hydrocarbons Subsequently a more effective remedial system was required In accordance with EHDICVRWQCB directives and approval,AGE conducted three separate ground water extraction pumping tests in March 2001 Analysis of the ground water extraction data indicted . that ex-situ ground water treatment was feasible,the radius of influence generated by a pumping rate Advanced GeoEnvironmental,Inc