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7-Eleven/Stockton <br /> May 1990 5 <br /> It (PW-2) has never been used as a pumping well. A deeper, <br /> 12-inch-diameter recovery well (PW-3) was installed on-site to <br /> replace the 4-inch-diameter monitoring well, MW-4, which had been <br /> used as an interim on-site recovery well. <br /> Also, during October and November of 1986, three additional <br /> monitoring wells MW-lo through MW-12 were installed off site to <br /> obtain further dissolved-plume definition. Underground piping <br /> was connected to MW-12 in order to allow it to be used, as a <br /> pumping well to intercept dissolved hydrocarbons in the event <br /> that migration was detected approaching the Tomato Growers <br /> Association (TMG) domestic well. This well (MW-12) has not been <br /> used as a .pumping well to date. <br /> Initially, the groundwater recovered by pumping was treated <br /> f by carbon adsorption <br /> prior to being discharged to the City of <br /> Stockton sanitary sewer system. In February 1987, the carbon <br /> filtration system was replaced by an air-stripping tower. ' <br /> Additional work conducted in February. 1987 included. the <br /> installation of two new monitoring wells (MW-13 and b1W-14).. The <br /> monitoring well locations were selected to evaluate the origin of <br /> sporadic hydrocarbon contamination detected in samples from <br /> domestic wells which are located upgradient of the site. work in <br /> February 1987 also included the installation and activation..of a <br /> soil-vent remediation system. The soil-vent system was installed <br /> to address the adsorbed and vapor phases of contamination in the <br /> vadose-zone soils. This system consists of four vapor- <br /> extraction. points connected to a high-vacuum blower and <br /> manifolded to a.vapor--phase, .activated-carbon adsorption..system. <br /> GROUND"ATEN <br /> TECHSOLOGI:INC. <br /> 1�i <br />