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WESTERN 1386 EAST$EAMER STREET <br /> GEO-ENGINEERS WOODLAND CA 95776-6003 <br /> CALIF.CONTRACTOR#5!3857 (530) 668-5300,FAX(530)662-0273 <br /> REGISTERED GEOLOGISTS we9c@mother.com <br /> d� D <br /> March 5, 2003 MAR 112003 <br /> r-NVIRONMENT HEALTH <br /> Mr. Shawn Hart PERMIT/SERVICES <br /> San Joaquin County <br /> Department of Public Works <br /> 1810 E. Hazelton Ave. <br /> Stockton, CA 95201 <br /> Dear Mr. Hart: <br /> 1 <br /> The following information is provided as documentation of Western Geo-Engineers' <br /> (WEGE) investigation and remediation of an unauthorized release of groundwater <br /> contaminated with gasoline to the storm drain system in the vicinity of 1876 Country <br /> Club Blvd. Stockton,California. <br /> Description of the Unauthorized Release <br /> The unauthorized release to the storm drain occurred between 2:00 AM and 10:30 AM on <br /> Tuesday, February 25, 2003 when groundwater that was being pumped from an open r <br /> excavation at the site overtopped a 21,665 gallon capacity Baker tank. The tank was <br /> being used to temporarily store pumped groundwater on site prior to treatment of the <br /> groundwater through carbon canisters and eventual disposal to the sanitary sewer <br /> system. The discharge to the sewer was conducted under a discharge permit issued by <br /> the City of Stockton. <br /> WEGE re-initiated the pumping of groundwater from the open excavation at the northern <br /> portion of the site on Friday, February 21, 2003 at 3:00 PM in anticipation of the <br /> continued excavation of gasoline contamianted soil from the site that was scheduled to <br /> i occur during the week of February 24 —28, 2003. The WEGE technician adjusted the <br /> pumping rate of water from the excavation to the Baker tank to 4 gallons per minute prior <br /> to leaving the site. The technician noted that the sump pump, which discharged water <br /> from the base of the Baker tank to the carbon cannisters and sewer, was.pumping at a rate J <br /> of approximately 10 gallons per minute. Thus, the potential discharge rate from the Baker <br /> tank to the sewer system exceeded the potential inflow to the tank from the open <br /> excavation.. The sump pump at the base of the tank was controlled by a low water float <br /> switch attached to the pump which prevented further discharge from the tank when the <br /> water level in the tank dropped to within 1.4 feet of its base. At this level, the Baker <br /> Tank contained 1,484 gallons of water and possessed a capacity for 20,181 additional <br /> gallons of water before it was overtopped. <br /> r <br />