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0 <br /> DDRW-TRACY <br /> CPT INVESTIGATION AT AG-2 <br /> Montgomery Watson, under contract to the US Army Corps of Engineers - Huntsville <br /> Division (CEHND), is currently performing on-going remedial investigation/feasibility <br /> study (RDFS) tasks at Defense Distribution Region West, Tracy, California (DDRW- <br /> Tracy). As part of the these activities, two agricultural wells (AGI and AG2) located in the <br /> Tracy Annex have been abandoned. A third well, AG-3, is scheduled for abandonment in <br /> 1995. <br /> The agricultural wells were about 600 feet deep and were screened over relatively long <br /> intervals. Well abandonment operations were initiated in order to minimize possible <br /> contaminant transport between the major hydrostratigraphic zones through the well casings <br /> and/or associated gravel packs. As part of the original well abandonment effort, <br /> groundwater samples were to be collected within the agricultural wells from the different <br /> hydrostratigraphic zones in order to determine whether the wells had acted as conduits <br /> between the Upper and Lower Tulare aquifers. <br /> During initial evaluatibn of the wells, it was determined that the casing in well AG2 had <br /> collapsed to a depth of 350 feet below ground surface (bgs). Because the collapse was at a <br /> depth within or above the Corcoran Clay, collection of the groundwater sample from the <br /> Lower Tulare Aquifer was not possible. At a subsequent Remedial Project Managers <br /> (RPM) meeting, it was agreed that a replacement monitoring wells screened only within the <br /> Lower Tulare Aquifer would be installed immediately downgradient of AG2. <br /> Subsequently, it has been proposed that depth-specific contaminant profiles would provide <br /> a more thorough understanding of potential vertical migration pathways. <br /> Possible vertical contaminant migration from the Lower Horizon of the Upper Tulare <br /> Aquifer using installation of multiple CPT profiles below the Lower Horizon of the Upper <br /> Tulare Aquifer, with associated depth-specific BAT® groundwater sampling in selected <br /> water-bearing zones <br /> Three pilot CPT locations will be installed in order to identify site stratigraphy immediately <br /> adjacent to AG-2. The CPT profiles will be located around AG-2, including one location <br /> up to 50 feet upgradient, and 2 locations approximately 20 feet and 50 feet downgradient of <br /> the former location of AG-2. From the pilot profiles, sampling zones greater than 2 feet <br /> 1 <br />