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DISCO PROPERTY,STOCKTON,CALIFORNIA <br /> Addendum <br /> Workplan for Additional Investigation Disco Property <br /> Stockton, California <br /> June1998 <br /> The April 1997"Workplan for Additional Investigation—Disco Property" (Attachment A to <br /> this addendum) proposed three activities to delineate the vertical and horizontal extent of <br /> hydrocarbon constituents in soil and groundwater,as summarized in Table 1. That <br /> workplan is modified by this addendum requested in the San Joaquin County Public Health <br /> Service/Environmental Health Division(PHS/EHD) letter dated October 14, 1997.This <br /> addendum adds additional investigations to the 1997 workplan and modifies previously <br /> identified activities,including deletion of those that have been completed since the original <br /> workplan submittal, such as the well survey update. A proposed schedule for these <br /> activities is included in Attachment B to this workplan addendum. <br /> Additional Activities <br /> Two activities will be conducted prior to undertaking the soil boring and monitoring well <br /> installation described in the 1997 Workplan: <br /> • Cone Penetrometer (CPT)testing and <br /> • Expedited groundwater screening <br /> These activities will provide additional lithologic and groundwater data for refining the <br /> location and depth of potential future soil borings and monitoring wells. <br /> CPT Logging <br /> CPT testing and data interpretation will be performed to provide lithologic data that is <br /> more detailed and extends to greater depths than is currently available.CPT logging will be <br /> performed in the approximate locations shown on Figure 1A.The locations were selected to <br /> provide data at approximately 100 foot centers within the probable area of hydrocarbon <br /> impacted groundwater as estimated from existing well monitoring data. Available locations <br /> for CPT testing south of the Disco property are limited by Highway 4. CPT lithologic <br /> logging will be performed to the maximum depth achievable up to 150 feet bgs. Blow count <br /> measurements during previous soil sampling activities at the Disco property indicate that <br /> strata exist that may limit the depth to which a CPT can be advanced. <br /> Expedited Groundwater Screening <br /> The groundwater screening activities described in the 1997 Workplan to be performed <br /> during soil boring activities will be replaced by groundwater screening performed prior to <br /> drilling. To provide preliminary data on the vertical extent of hydrocarbon constituents in <br /> groundwater, groundwater grab samples will be obtained using a Hydropunch or similar <br /> I <br />