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Remediation Report - 152 East 11 th Street, Tracy, California Page 4 additional wells groundwater-quality monitoring wells - making a total of eight - were installed for the Navarras to futher investigate the characteristics of the contanunation that had been found affecting the subsurface beneath their property and beneath adjacent land (Refs 7 and 8) Ultramar performed no futher investigations of the release of hydrocarbon fuels that had affected the Beacon station at 153 East 11th Street The locations of the groundwater-monitoring wells installed for the Navarras, which have been designated NAV, are also shown on Figure 2 Data from Site Investigations and Groundwater-quality Monitoring The investigation of the distribution and concentrations of components of gasoline in the subsurface beneath the 152 East lith Street site and the adjacent streets and private property progressed in stages The results from each stage were reported to the CRWQCB and, when that agency was assigned the role of lead agency, to the SJCPHS As data was obtained and evaluated, it was used to plan subsequent stages of investigation, establish a groundwater-quality monitoring program (Ref 8) and develop a corrective action plan (CAP) Where applicable, the results of the investigations performed for the subject property (i e 152 East 1 lth Street) were supplemented by available data from investigations performed for the Beacon station at 153 East 1 lth Street (Refs 6, 7, 9, 10, 12, 15, 16 and 19) 5 The results of analyses of soil and groundwater samples recovered from the wells installed lip for the Navarras and available information from the wells installed for Ulramar were used to establish the elevation of the groundwater table and the direction and gradient of groundwater flow and to evaluate the extent and characteristics of contamination in the subsurface (Ref 9) Groundwater pumping tests to evaluate the hydrogeologic properties of the soils beneath their property were also conducted for the Navarras at the direction of the SJCPHS (Ref 11) For convenience of reference, the results of analyses of all soil samples recovered from the well installation borings, the groundwater elevations computed from depths to , r groundwater measured in and results of analyses of samples of groundwater recovered from the wells installed for both the 152 and 153 East Street sites have been compiled in Tables Al, A2 and A3, respectively, in Appendix A Logs of the wells installed for the Navarra's and the available logs of the wells installed for Ultramar are presented in Appendix B GEOLOGY AND HYDROGEOLOGY The subject property and the surrounding area are situated on level terrain on the distal, northern slope of an alluvial fan The underlying alluvial sediments are of Quaternary to Recent age Soils beneath the site include clays, silty clays, sandy clays, clays with gravel, sands, silty sands and sands with gravel These clastic materials are distributed in a complex lenticular 1