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Report:Groundwater-quality Monitoring—October 27,2004, 7500 West Eleventh Street, Tracy,CA. Page 3 <br /> tanks and 6 <br /> On December 9, 1998, eight underground fuel storage ,000 linear feet of <br /> associated piping were removed from the property under the permit and oversight of the <br /> l SJCEHD (Dietz Irrigation 1999a). The former locations of the fuel tanks are shown on <br /> Figure 2. <br /> When the tanks were removed, it was found that fuel hydrocarbons had leaked from <br /> underground piping beneath the fuel pump islands of the former fueling station. The <br /> former locations of the fuel pump islands are also shown on Figure.2. At the same time <br /> that the tanks were removed from the site, soil heavily affected by fuel hydrocarbons was i <br /> excavated from beneath the pump island area and 521.25 tons of that material were <br /> disposed off-site at a permitted facility. In addition, some 2,000 gallons of floating <br /> product and affected groundwater were removed from the subsurface by pumping from a <br /> tank pit into a vacuum truck, which was used to transport it to a permitted recycling <br /> facility(Dietz Irrigation 1999a). f <br /> An initial phase of site characterization work was completed in May 2000. It included the <br /> installation of seven groundwater-quality monitoring wells (Nos. MW-1 through MW-7) <br /> at the locations shown on Figure 2 and was followed by a series of quarterly rounds of <br /> groundwater-quality monitoring. An extended phase of site characterization was initiated <br /> F on March 25, 2002; it included the installation of an additional eight groundwater-quality <br /> monitoring wells, numbered MW-3A, MW-3B, MW-8 through MW-12, and MW-12A. It <br /> was completed on April 11, 2002, with a round of groundwater sampling and analysis <br /> that encompassed all 15 groundwater-quality monitoring wells by then extant on the site <br /> (The San Joaquin Company, 2002c). Quarterly groundwater-quality monitoring then <br /> s continued until April 2004, when seven additional groundwater-quality monitoring wells, i <br /> numbered MW-13 through MW-19 were installed as part of a further phase of site <br /> L <br /> characterization. That phase was completed by a round of groundwater sampling and <br /> analysis on April 30, 2004 and another monitoring round was completed on July 27, 2004 <br /> i. (The San Joaquin Company Inc. 2004b, 2004a). This present report documents a round of <br /> groundwater-quality monitoring that was conducted on October 27 and 28, 2004, also <br /> utilizing all 22 groundwater-quality monitoring wells that were resent on the site b that <br /> �' tY g p Y <br /> date. <br /> When groundwater was first recovered from groundwater-quality monitoring well MW-7 <br /> on May 11, 2000, the sample contained moderate concentrations of Total Petroleum <br /> i` <br /> + <br /> Hydrocarbons quantified as diesel (TPHd) and Total Petroleum Hydrocarbons quantified <br /> i <br /> as gasoline (TPHg), with commensurate concentrations of benzene, toluene, ethyl s <br /> E benzene and total xylene isomers (the BTEX compounds) and 22 µg/L of methyl-tertiary <br /> butyl ether (MTBE), a fuel oxygenate. Thereafter, the concentration of components of <br /> fuel hydrocarbons followed an increasing trend until the analytes of concern exceeded <br /> their maximum solubility in water(see Table 2). However, as early as the sampling round <br /> performed on November 28, 2000,no MTBE was detected in the samples recovered from <br /> P p <br /> Monitoring Well MW-7. It is believed that this does not indicate that, by that time, the <br /> a groundwater in the vicinity of that well was free of MTBE. Rather, it indicates that the <br /> high concentrations of other components of fuel hydrocarbons were such as to raise the <br /> 4 method detection limit of the MTBE analysis to a level greater than the concentration of <br /> sic <br />