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extended Plume Definition:-7500 W 11 rh St., Tracy,CA. Page 12 r Previous interpretations of the hydrostratigraphy of the Navarra Site as illustrated by cross- sections along lines A-A' through C-C' were generated based on the logs of bonngs and monitoring wells drilled at the site through April 2002 (The San Joaquin Company 2002c). Additional stratigraphic data from the new borings and wells drilled in April 2004 permitted detail of those sections to be enhanced and the additional cross-sections D-D' through F-F' to be generated. Required revisions of sections A-A' through C-C' due to availability of the new data were minimal and the hydrostratigraphy revealed in the new cross-sections D-D' through F-F' confirm the hydrostratigraphic and contaminant transport characteristics of the site that was previously interpreted based on a synthesis of the data from the boring logs, groundwater elevational and geochemical data available prior to the additional site characterization work that is described in this report. data from the new borings confirms SJC's earlier It is particularly notable that stratigraphicg interpretation (The San Joaquin Company 2002x) that the orientation of the long axis of the primary plume -of affected groundwater emanating from the 7500 West Eleventh Street property is associated with a zone of the subsurface that runs approximately north-northeast from the area around the pump islands of the former truck fueling station on the subject property and from there across West Eleventh Street at least as far north as Carmelo Avenue in the area of the subsurface that is beneath and close to South Chrisman Road. Within that zone, there are significant deposits of sand and silt and, in some instances, such as is seen in the well logs of floating product Monitoring Wells MWFP-2 and MWFP-5 and of groundwater-quality Monitoring Wells MW-17, MW-19 and MW-9, the sand deposits include gravels, while in .others, there are distinct gravel lenses included within the stratigraphic sections. To the west of that zone, there are relatively few permeable sediments, or, where such are present, they are separated from it by zones where the strata to the depth explored are predominantly low-permeability clayey soils. See, for example, the L hydrostratigraphy shown on section D-D' (Figure 6) and section E-E' (Figure 7). Further to the north, as seen in hydrostratigraphic section F-F' (Figure 8), the high permeability facies extend further west than is the case in the more southerly areas. The hydrostratigraphic interpretation described above is supported by the groundwater ' contour map shown on Figure 9, which, as is described in Section 4.10.1, was constructed by the depth to groundwater measurements made in the array of monitoring wells on April 30, 2004. The contours have a distinct pattern that indicates the presence of a relatively high- permeability zone that extends down-gradient from Monitoring Well MW-3 in the direction of MWFP-1 and MW-7 and, while becoming less distinct, from there north-northeastward in a down-gradient direction. Similarly, the distribution of analytes of concern in the groundwater at the locations of the individual wells that comprise the total groundwater- quality monitoring array, supports the interpretation that contaminants were transported down-gradient within a relatively permeable zone along the axis of the plume, but that their } lateral dispersion was rather narrowly restricted in areas to the west and east of that axis. Based on the synthesis of the hydrostratigraphic, groundwater contour and geochemical data obtained through completion of the site characterization data described in this report, following is a summary interpretation of the dominant features of the site's hydrostratigraphy. SJC