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CHAPTER 3 <br /> ADDITIONAL SITE INVESTIGATION <br /> This chapter discusses field activities conducted at the Site by Brown and Caldwell during <br /> February 1997 and March 1997. The objective of the additional investigation was to install <br /> deeper groundwater monitoring wells near the basin to supplant existing wells which have been <br /> historically dry, and to install one additional groundwater monitoring well downgradient of the <br /> Site to further delineate the extent of chloroform in the shallow water-bearing unit. The work <br /> discussed below was requested by the RWQCB letter dated October 4, 1996. The work was <br /> performed in accordance with Brown and Caldwell's December 4, 1996 plan which was <br /> approved, with minor modifications, by the RWQCB in a letter dated January 9, 1997. Brown <br /> and Caldwell's work plan and the RWQCB's approval letter are included in Appendix A. <br /> Groundwater Monitoring Well Installation <br /> Brown and Caldwell personnel supervised the installation of three groundwater monitoring <br /> Wells (BC-18, BC-19, and BC-20) in the vicinity of the Site between February 4 and 7, 1997. A <br /> fourth Well, BC-21, was not installed upgradient of the Site as proposed. The existing <br /> upgradient Well, BC-6, was determined by Brown and Caldwell to be adequate in location and <br /> depth. Wells BC-18 and BC-19 were installed adjacent to the basin at the north end of the Site. <br /> Well BC-20 was installed in the residential neighborhood north of the Site, at 91 Deerwood Lane <br /> (Figure 1). Prior to initiating the field work, well installation permits were obtained from the San <br /> Joaquin County Public Health Services. An encroachment permit was also obtained from the <br /> City of Tracy for installation of the downgradient well (Appendix B). <br /> Gregg Drilling and Testing, Inc., of Martinez, California (C-57 license number 485165) <br /> performed the well installation. Three soil borings were advanced to between 50 feet and 56 feet <br /> below ground surface (bgs) utilizing a truck-mounted Mobile B-61 drill rig (for Wells BC-19 and <br /> ewopo \m92�2-1sy,Gdm 3-1 <br />