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Preliminary Subsurface Investigation <br /> City of Stockton, former Western Pacific Railroad Property, Stockton, CA <br /> May 27, 1992 <br /> W0601.1D <br /> The sites identified by the computer records search to be an environmental concern are listed <br /> on Table 1. Details of the records review and an explanation of the types of site and <br /> ' information contained in the lists above are included in Appendix B. These site determinations <br /> were made as a result of file searches and windshield surveys. Upgradient site releases are only <br /> ' of great significance if contaminants have migrated via the groundwater to the subject property. <br /> ' 3.0 SITE GEOLOGY AND HYDROGEOLOGY <br /> The site is situated on level terrain comprised of Quaternary-Recent alluvial sediments and fill <br /> ' materials. The site is primarily underlain by silt and clay with zones of silty sand. The fill <br /> materials have reportedly included municipal solid waste as well as dredged material from the <br /> ' channel. Depth to water is approximately 28 feet below grade (Well Logs, Appendix C). The <br /> groundwater flow direction is westerly (Figure 2). <br /> 3.1 Local Groundwater Conditions <br /> ' A review of data from the California Department of Water Resources (DWR), Regional Water <br /> ' Quality Control Board (RWQCB), United States Geological Survey (USGS), and the San Joaquin <br /> County Flood Control District (SJCFCD) was undertaken in order to characterize the water <br /> quality and hydrologic setting in the Stockton area. <br /> An investigation conducted by DWR (1967) during the mid-1960's indicated that the <br /> groundwater supply in the greater Stockton area was being slowly infringed upon by the poor <br /> quality waters underlying the Delta. The poor quality waters seemed to be migrating from the <br /> west at a rate governed by certain constant geologic parameters and variable hydraulic <br /> parameters, including increased pumping east of Stockton. Appendix D, Figure D-1 shows a <br /> comparison of the chloride content of select wells against time and distance from an arbitrary <br /> baseline (300 parts per million) for the years 1953 and 1963. The largest separation between <br /> R041392.SAv 4 <br />