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4Q Extended Site Characterization Report. 7500 West Eleventh Street, Tracy, CA. Page 4 ` the location of Monitoring Well MW-10 would be detected by situating a monitoring well on, or close to the principal axis of the plume of affected groundwater (The San Joaquin Company 2001 e, p. 8). Consequently SJC was very concerned that elimination of the well at the selected location would risk failure to detect the northern extension of the plume of affected groundwater in that area (The San Joaquin Company Inc, 2001 b). The issue was resolved with the assistance of the RWQCB (Hartzell 2001), who recognized the importance of a groundwater-quality monitoring well located at the position of Well ij MW-10 on Figure 2, and by the Navarras obtaining authorization from the USTCF to complete an additional well (Well MW-9 on Figure 2) at the location requested by the SJCEHD (The San.Joaquin Company Inc 2001 a). ._ The fieldwork required to implement the extended site characterization program was initiated on March 25, 2002 with the drilling of the additional exploratory borings and the installation of the additional groundwater-quality monitoring wells. It was completed on April 11, 2002 with a round of groundwater sampling and analysis that encompassed all k_ 15 groundwater-quality monitoring wells by then extant on the site. r=; In the following sections, the complete history of the site from the time that the underground storage tanks were removed through the round of groundwater sampling conducted on April 11, 2002 is summarized, together with a detailed record of the work performed to implement the extended site characterization program. Logs of all 16 exploratory borings that have been drilled on the site and of the 15 installed groundwater- quality monitoring wells are included as Appendix A. The documentation in this report also includes tables that record the -results of analyses of all of soil samples recovered from beneath the site, the depths to groundwater measured in all wells, and the results of the analyses of samples of groundwater recovered from all wells and borings on the site. In addition to providing a convenient and comprehensive database, the information f provided permits the reader to make an independent evaluation of the hydrogeological and geochemical data without the need to rely on SJC's interpretations, conclusions and =1 recommendations. i-:-1 E =:J i, l i SJC i