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Report:Groundwater-quality Monitoring—July 27,2004: 7500 West Eleventh Street, Tracy,CA. Page 3 When the tanks were removed, it was found that fuel hydrocarbons had leaked from _- underground piping beneath the fuel pump islands of the former fueling station. The L . former locations of the fuel pump islands are also shown on Figure 2. At the same time that the tanks were removed from the site, soil heavily affected by fuel hydrocarbons was excavated from beneath the pump island area and 521.25 tons of that material were disposed off-site at a permitted facility. In addition, some 2,000 gallons of floating product and affected groundwater were removed from the subsurface by pumping from a tank pit into a vacuum truck, which was used to transport it to a permitted recycling facility(Dietz Irrigation 1999a). An initial phase of site characterization work was completed in May 2000. It included the L ? installation of seven groundwater-quality monitoring wells (Nos. MW-1 through MW-7) at the locations shown on Figure 2 and was followed by a series of quarterly rounds of groundwater-quality monitoring. An extended phase of site characterization was initiated j on March 25, 2002; it included the installation of an additional eight groundwater-quality monitoring wells, numbered MW-3A, MW-3B, MW-8 through MW-12, and MW-12A. It a was completed on April 11, 2002, with a round of groundwater sampling and analysis that encompassed all 15 groundwater-quality monitoring wells by then extant on the site (The San Joaquin Company, 2002c). Quarterly groundwater-quality monitoring then continued until April 2004, when seven additional groundwater-quality monitoring wells, numbered MW-13 through MW-19 were installed as part of-a further phase of site characterization. That phase of site characterization was completed by a round of groundwater sampling and analysis on April 30, 2004 (The San Joaquin Company Inc. <= ' 2004a). This present report documents a round of groundwater-quality monitoring that was conducted on July 26 and 27, 2004, utilizing all 22 groundwater-quality monitoring wells that were present on the site by that date, When groundwater was first recovered from groundwater-quality monitoring well MW-7 .: on May 11, 2000, the sample contained moderate concentrations of Total Petroleum Hydrocarbons quantified as diesel (TPHd) and Total Petroleum Hydrocarbons quantified as gasoline (TPHg), with commensurate concentrations of benzene, toluene, ethyl benzene and total xylene isomers (BTEX) and 22 µg/L of methyl-tertiary butyl ether, a 1-.4 fuel oxygenate. Thereafter, the concentration of components of fuel hydrocarbons followed an increasing trend until the analytes of concern exceeded their maximum solubility in water (see Table 2). However, as early as the sampling round performed on November 28, 2000, no MTBE was detected in the samples recovered from Monitoring Well MW-7. It is believed that this does not indicate that, by that time, the groundwater in the vicinity of that well was free of MTBE. Rather, it indicates that the high concentrations of other components of fuel hydrocarbons were such as to raise the method detection limit of the MTBE analysis to a level greater than the concentration of jthat analyte actually present in that groundwater sample. By April 11, 2002, it was clear that floating product was present in the surface of the groundwater in Monitoring Well MW-7, as predicted. It continued to be present at various apparent thicknesses up to 0.58 ft. until an LNAPL-purging program in that well was initiated on .November 8, 2003. As part of the further extension of the site sic