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r <br /> Geofogica[Tecfinics Inc. <br /> 2741 River Road <br /> Moi e;to,California 95351 <br /> (209)538- 424IFax#538-5852 <br /> Vertical Definition Work Plan <br /> Valentine <br /> (Castle Motors) <br /> 2315 N Eldorado St. <br /> Stockton, CA <br /> Project No.: 723.2 <br /> August 23, 2000 <br /> 1.0 INTRODUCTION <br /> On October 4, 1999, Geological Technics Inc. (GTI) submitted an Additional Site <br /> Characterization Report which documented the installation of a deep, discretely screened <br /> monitoring well and a deeper soil boring at the site (see Figure 1). Analytical data shows <br /> the presence of gasoline range petroleum hydrocarbons in the soil and groundwater to a <br /> depth of at least 110 feet bgs. <br /> In a letter dated August 1, 2000, Mr. Jeff Wong of SJC PHS/EHD issued a letter directing <br /> that a work plan for the investigation of the vertical definition of the plume be submitted by <br /> August 25, 2000. This work plan addresses that directive. <br /> 2.0 PROPOSED INVESTIGATION <br /> The purpose of this investigation is to further define the vertical extent of groundwater <br /> impacts and site lithology. To accomplish this goal, GTI proposes to install a single <br /> borehole/well, MW-201, to a targeted depth of 150 feet below grade surface. Quarterly <br /> groundwater monitoring of the existing 7 monitoring wells and the new well is proposed for <br /> a one-year period of time. <br /> See Figure 2: Site Map for monitoring well locations. <br /> 2.1 Borehole Drilling <br /> In an effort to define the vertical extent of the plume, GTI proposes to install a deep, <br /> exploratory borehole to approximately 150 feet below grade. The boring will be drilled <br /> using a mud rotary drill rig:to combat the heaving sands that were encountered during the <br /> drilling of MW-101. During the drilling of the previous monitoring wells at the site, <br /> heaving sands became a problem starting at 70 feet bgs. <br />