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Remediation Report - 152 East 1 lth Street, Tracy, California Page 14 of the property that are shown on Figure 6 could be readily observed in the field due to discoloration of the soil and were confirmed by analyses of samples recovered from both discolored and apparently unaffected zones in the walls of the excavation The areal distribution of the contanunated soil removed from the subsurface of the site matched almost exactly the distribution that had been predicted from the site characterization studies that preceded the corrective action program The predicted areal limits of the plume of contamination are shown on Figures 2 and 5 Within the excavated area, the actual limits of contamination coincided, for all practical purposes, with the predicted limits NOTE Although the observations made and the data recovered during the remediation work support the predicted distribution of contaminants in the subsurface at off-property locations that is shown on Figure 2, it is important to understand that they may not precisely define the exact boundaries of hydrocarbon fuel components affecting the subsurface beyond the limits of the remedial excavations Specifically, they should not be used for reaching a conclusion as to whether groundwater affected by hydrocarbons released into the subsurface from a source under East l lth Street north of the 152 E l lth Street property boundary has, or has not, coalesced with hydrocarbon fuel components released into the subsurface at the Beacon Station site ) The predicted vertical distribution of contaminated soil also agreed well with that revealed in the remedial excavation and confirmed that the soil affected by the highest concentration of components of gasoline are Iocated under the East 11th Street sidewalk beyond the boundary of the Navarras' property The vertical and lateral limits of contamination in the walls of the remedial excavation developed from observations made when the pit was open, the results of analyses of samples recovered from the walls for total petroleum hydrocarbons that are recorded in Table I and from the geochemicai data that was obtained when the borings made to install the close by groundwater-quality monitoring wells are shown on Figure 6 This distribution is also shown at a larger scale on Figures 3 and 4, where it is superimposed on hydrostratigraphic sections through the 152 East 11th Street property along the section lines AA' and BB' which are located as shown on Figure 2 This observed vertical and distribution of contaminants in the subsurface also agrees well with the distribution predicted in the CAP and its supporting documents The vertical and areal distribution of fuel hydrocarbons shown on Figures 2, 3, 4, 5 and 6 has the classic discus-shaped form taken by gasoline when it leaks from an underground storage tank that is situated with its bottom either below or slightly above a shallow water table The crown of the discus of contaminated soil as it appeared in the north wall of the remedial excavation along the northern boundary of the 152 East 1 lth Street property is shown in Figure 6 Its location coincides precisely with the position at which the, previously described tank fill and vent pipes were discovered when the northern side of the y I