ARCHIVED REPORTS XR0009911 - Laserfiche WebLink

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Groundwater Quality Monitoring - 152 East 11th Street, Tracy Page 5 The results of the analyses are summanzed in Table 3 A Copy of the Certificate of Analysis is attached (Note For convenience of reference, the results of analyses of all groundwater samples that have been recovered during successive sampling rounds from all j of the wells installed for both the 152 and 153 East 11th Street properties are compiled in Table 4 } j Interpretation of Results The geotechnical and geochemical data from the investigations reported herein and data from available records of previous investigations conducted on the 152 and 153 East l lth Street properties have been synthesized and used as the basis for an interpretation of the 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 November 15th , 1995 Compared to conditions when depths to groundwater were last measured on February 17th, 1995 (during the regional wet season) the water table has fallen approximately one foot The direction of groundwater flow remains to the northwest and its gradient (approximately 0 002 ft /ft ) is similar to that measured previously The results of the analyses of the groundwater samples recovered on November 15th 1995 that are presented in Tables 2 and 4 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 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 11 th 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, geochemical 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 down gradient from the point where those tanks and piping were formerly located toward the East 11th Street frontage of the site and has probably migrated some distance northward under the street The 160ug/liter concentration of total petroleum hydrocarbons in the sample recovered from interior well NAV-4 on November 15th , 1995 is significantly lower than the 700jig/liter measured in the sample recovered from that well on February 17th, 1995 . (Refer to Table 4) The concentrations of benzene toluene, ethyl benzene and total xylenes