ARCHIVED REPORTS XR0009916 - Laserfiche WebLink

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Groundwater Quality Monitoring - 152 East 1 lth Street, Tracy Page 5 The results of the analyses are summarized 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 of the wells installed for both the 152 and 153 East l lth Street properties are compiled in Table 4 ) 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 11th 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 September 3rd 1994 Compared to conditions when depths to groundwater were last measured on February 25th 1994 (during the regional wet season) the water table has fallen some 1 2 to 1 5 feet and is approximately 0 6 feet lower than was the case in at the end of the dry season in the previous year (October 1993) The latter finding is interpreted to be related to the drought conditions that have been affecting the region However, as has been noted in earlier reports, seasonal and longer duration changes in groundwater elevations are relatively small at this site The direction of groundwater flow remains to the northwest and its gradient (approximately 0 003 ft /ft ) is similar to that measured previously The results of the analyses of the groundwater samples recovered on September 3rd 1994 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 ,r 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, geochemucal 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 1 lth Street property has moved downgradient 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