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4 19 July 1996 <br /> . <br /> NO FURTHER 2 ACTION RECOMMENDATION �# F <br /> 7-ELEVEN,.9 110 THORNTON ROAD - - •. <br /> STOCKTON, sAN JOAQUIN COUNTY <br /> Groumd Water Emiction and Remediation <br /> The ground water extraction and treatment system operated between <br /> as installed.May PumpinglO fMW4 <br /> 8r <br /> Hand bailing morn MW4 began in May.198two d days <br /> started <br /> PW1. and PW3 was added. By early <br /> started in July 1986.'5 In December 1986, pumping <br /> 1988, ground water levels had-dropped-and ground water extraction from the monitorvery ing weals and <br /> pumping wells had become inefficient• In Separate April base hydrocagbonser �were recoveround water ed, and extracted <br /> installed and operated until lair s Sep P <br /> in and discharged to the City sewer. Approximately 1.6 <br /> ground water was treated by air stripping <br /> million gallons of contaminated ground water were extracted and treated with the recovery of 780 <br /> gallons of free product. <br /> Sad Vapor Exaction and Remedhition <br /> ary 1987 to January 1991. S <br /> The soil vapor extraction and treatment system operateacfrom lsu n i 90, after ground water oil <br /> vapors were.initiaily extracted from the four vapor extrtion wea water elevation, the vapor extraction system <br /> extraction became impractical due to the drop in grted air <br /> was expanded to include three monitoring wells, e oris and the clean air wasdischarged,ound wa:ter recovery well. to the <br /> and vapors were treated with carbon to remo e p <br /> atmosphere. An estimated 576 gallons of petroleum hydrocarbons were recovered'. a ` <br /> UUrmlerground Tank Excavation ` were excavated. Soil samples from <br /> In 1991, the three underground tanks and the associated piping <br /> able levels odepth of 2.5sFe O+ne soil sample from under the <br /> the tank pits contained low to nondetect <br /> product lines-contained up to 2100 ppm a de gasoline at p y <br /> S <br /> Coa&nmdaan Samp1 }, <br /> Periodic ground water sampling frorimi"June 1986 <br /> contaminationa6 n numerous wells to no detectable <br /> from free product in several wells and dissolved e in MWl• In March 1996, ground water samples <br /> concentration in any wells except for 0.8 pp however, none was detected. Sixteen <br /> were also analyzed;for Methyl Tert-Butyl Ether (MTBE), <br /> confirmation borings were drilled in 1993 and 1995 to determine the Moline atnt of oaldepth of 20 Eeet, <br /> remaining. soil contamination was fo bat 35 Eee'in one �.n A soil?vapo 600 r extraction test was conducted , <br /> ; <br /> 160 ppb gasoline at 25 feet, 8 pp <br /> 1994 to evaluate residual contamination.-The test revealed the continued presence of hydrocarbon <br /> contamination at a removal rate of 0.29 pounds of gasoline per day. _ <br /> oline.in ound.water, SOII C0ntaminStlons and <br /> Based on the continued presence of dissolved gas $r <br /> vapors, the remaining volume of contaminated soil was estimated to be 450 cubic Yards <br /> hydrocarbon p , <br /> roximatel �0-gallons of gasoline. <br /> contann91app Y <br /> L <br /> SHE ClOSLae k aggressive and comprehensive, no contamination is.found in the <br /> - <br /> Because the cleanup at this site was aggr ground water contamination remain on site, and the soil <br /> domestic well: low levels of dissolved we recommend concurrence <br /> contamination remaining is no longer a significant thregat.to water queer action. " <br /> with San Joaquin Couriv letter of'12 March 1996, re uiring.aio_f <br />