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Report:Groundwater-quality Monitoring—October 27,2004, 7500 West Eleventh Street, Tracy,CA. Page 1 LO INTRODUCTION This groundwater-quality monitoring report has been prepared for the site of a former fueling station at 7500 West Eleventh Street, Tracy, California (Navarra Site). The - fueling station ceased operation in 1998 and, in December of that year, eight underground fuel tanks were removed from the property. At that time, it was found that soil and groundwater beneath the site were affected by fuel hydrocarbons. A site characterization investigation completed in May 2000 included installation of seven groundwater-quality monitoring wells (The San Joaquin Company 2001d). A second phase of site characterization was conducted in March and April 2002, during which eight additional groundwater-quality monitoring wells were installed (The San Joaquin Company 2002c). A third phase of site characterization was conducted in April 2004, during which seven additional groundwater-quality monitoring wells and five floating product monitoring wells were installed(The San Joaquin Company 2004b). The first round of groundwater-quality sampling and analysis was conducted on May 11, 2000, using the seven wells that were initially installed on the site (The San Joaquin Company 20014). Ten additional rounds of sampling and analysis were conducted between that date and July 30, 2003, with the rounds conducted in April, July and October 2002, and in January and April 2003, involving recovery of groundwater samples from all 15 wells that had been installed at the site by that time (The San Joaquin Company 2001c, 2001b, 2001a, 2002d, 2002c, 2002b, 2002a, 2003e and 2003d). The number of wells sampled for the July 2003, October 2003 and January 2004 monitoring rounds (The San Joaquin Company 2004c, 2003c, 2003b) were reduced at the direction of the San Joaquin County Environmental Health Division(SJCEHD) to the sampling of seven, ten and seven of the 15 groundwater-quality monitoring wells,respectively. The fourteenth monitoring round was conducted on April 21, 22 and 30, 2004, when groundwater samples were recovered from the 15 pre-existing wells and the seven new groundwater-quality monitoring wells installed in that month (The San Joaquin Company 2004b). The fifteenth monitoring round, which included all 22 groundwater-quality monitoring wells, was conducted on July 26-27, 2004 (The San Joaquin Company 2004a), This report documents the sixteenth monitoring round, which was conducted at the 7500 West Eleventh Street site on October 27 and 28, 2004. It includes a compilation of the data obtained from all earlier rounds of groundwater-quality monitoring. In April 2004, a program of testing the quality of water recovered from potable water supply wells in the neighborhood of the Navarra Site was initiated. This report includes the results of the third monitoring round of that program, which was conducted on October 28, 2004. This report also includes records from a program of monitoring the thickness of light non-aqueous phase liquid (LNAPL), present as floating product, in an array of five floating product monitoring wells and three selected groundwater-quality monitoring wells. sic