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Quarterly Report - 152 East 11th Street, Tracy Page 5 . Total Xylenes EPA Method 8020 The results of the analyses are summarized in Table 2 Copies of the Certificates of Analysis are attached (Note For convenience of reference, the results of analyses of all groundwater samples that have been recovered during successive sampling rounds from all of the wells installed for both the 152 and 153 East 11th Street properties are compiled in Table 4 ) INTERPRETATION OF RESULTS The geotechnical and geochemlcal data from the investigations reported herein and data from available records of previous investigations conducted on the 152 and 153 East 11th Street properties have been synthesized and used as the basis for an interpretation of the lateral and vertical extent to which the subsurface has been affected by hydrocarbons released at the 152 East Street site This interpretation is presented in the form of the plan view on Figure 2 The groundwater-table contours shown on Figure 2 reflect the data gathered on October 13th 1993 Compared to conditions when depths to groundwater were last measured on July 8th, 1993, the water table has dropped some 0 2 to 0 3 feet However, the direction of groundwater flow remains to the northwest and its gradient (approximately 0 003 . ft /ft ) is similar to that observed previously The analyses of the groundwater samples recovered on October 13th support earlier interpretations of the distribution of hydrocarbons in the subsurface that are shown on Figure 2 Analysis of groundwater from sampled wells around the perimeter of the plume confirm that these areas remain unaffected by detectable traces of hydrocarbon fuel components Concentrations of hydrocarbons in the sample from interior well NAV-4 are significantly lower than those reported previously (ref Table 4) The concentration of Total Petroleum Hydrocarbons quantified as gasoline had fallen to 570 pg/Liter compared to 3,800 pg/Liter measured in a sample recovered from this well on January 20th 1993 with corresponding reductions in the measured concentrations of the other analytes It is important to understand that the interpretations shown on Figures 2 are not intended to precisely define the exact boundaries of hydrocarbon fuel components affecting the subsurface Specifically, they should not be used for reaching a conclusion as to whether or not groundwater affected by hydrocarbons that may have been released into the subsurface on the 152 E 11th Street site has, or has not, coalesced with fuel components released into the subsurface on the Beacon Station site However, when taken together with the previously available data, the geotechnical, geochemlcal and hydrological data reported herein support an interpretation that gasoline that leaked from underground tanks, or the associated piping, that were on the 152 East 11th Street property has moved • downgradient from the point where those tanks and piping were formerly located toward