ARCHIVED REPORTS XR0009904 - Laserfiche WebLink

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Corrective Action Plan Page 7 extend from beneath the paving down to a depth of some 12 to 14 ft and penetrates into the deeper strata composed of loose sands Based on the results of analyses of soil samples and olfactory indicators noted on the boring logs, it appears that the total depth to which the soil has been contaminated in the Lvicinity of Well ULT 9 may have been locally influenced by excavations that were made to install the sanitary-sewer lateral that serves the property (refer to Figure 2 for location) In bonngs at distance from this area, the maximum depth at which the presence of components of gasoline was signaled by sample analyses or olfactory indicators was 14 ft or less As stated, the interpretations of the estimated maximum extent of soil contamination shown on Figures 7 and 8 are believed to be conservative Because the specific gravity of hydrocarbon fuels is less than 1 0, when leaking gasoline reaches groundwater it floats and then spreads by lateral dissemination over the water table Thus, the highest concentrations of components of hydrocarbon fuels in the soil are expected to be present in a zone within a short distance above and below the water table This interpretation is supported by the data shown on Figures 3 and 4 that note the presence, or lack thereof, of olfactory indicators or analytically detectable components of hydrocarbon fuels in soil samples recovered from the subsurface The data summarized on Figures 3 and 4 indicates that the soil is free of contamination beneath the 152 East 11th Street site in the zone between the ground surface and the first occurrence of affected soil dust above the water table This is consistent with the known mechanism by which gasoline that has leaked from underground storage tanks is disseminated through the subsurface However, if there were any sources of leakage at, or close to, the ground surface, there may be local areas where contaminated soil is present at higher elevations than indicated on Figures 7 and 8 This is suspected to be the case in the vicinity of the canopy structure located on the East 11 th Street frontage of the property (see Figure 2 for location) This was the location of the dispensing-pump island when the site was an active service station Contamination of shallow soils due to spillage and leaks from points in piping are commonly found at such locations Based on available records, it appears that the condition of shallow soils around the former location of the pump island was not explored at the time the storage tanks were removed and the piping that connected the tanks to the pumps may still be buried in the subsurface REMEDIATION STRATEGY To develop the original corrective action plan for the subject site (Ref 14), the applicability of alternate remedial technologies was studied in the context of the site- specific geotechnical, hydrogeologic, groundwater-quality, construction engineering, and site infrastructure and usage parameters and the interactions between them The principal constraints that affect the choice of remedial technologies for this site are the adverse subsurface conditions in terms of the stability of excavations and the potential