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' 1 � <br /> 1 , <br /> } I 4 <br /> �1 <br /> `` 61 28 February 1997 <br /> I AGE-NC Project No 95-0144 , <br /> Page 19'of 20 <br /> } <br /> I I 1 <br /> duration and type of monitoring required Fate and Transport modeling may be used to demonstrate <br /> } ' 'the potential for,hydrocarbons to impact nearby ground water receptors Quarterly ground water <br /> monitoring may also be used to establish a stable and declining ground water plume <br /> } <br /> 1 <br /> ,1 fl <br /> Y <br /> 7 0.' RECOMMENDATIONS FOR REMEDIATION OF HYDROCARBON- <br /> r IMPACTED SOIL <br /> The vertical andllateral extent ofhydrocarbon-impacted soil in the vicinity of former USTs No 1 <br /> 'll and 8 is limited Impacted soil extends to a depth of less than 20 feet bsg Excavation of impacted <br /> soil can easily be accomplished using a backhoe or excavator Small 'volumes of impacted soil may <br /> r ,not be reachable with excavation near UST No 1 However, due to the Iiinited lateral extent, only <br /> ' 1 a small volume of impacted soil would be left in place We estimate the re v s f approximately <br /> I 200 cubic yards of soil in the vicinity of UST No 1 and approximately 750 cubic yards of soil in the <br /> 1 vicinity of UST No 8 Very little overburden soil,would need to be removed in the vzcznity of USTs <br /> No 1 and 8 <br /> 1 II <br /> 1 <br /> Petroleum hydrocarbons were not detected in samples collected in the vicinity of former UST No <br /> ` 2 1 herefore, we recommend no remediation be required in this location <br /> Impacted soil in the vicinity of USTs No 3 through 6 occurs primarily at a depth of 15 to�25 feet <br /> 1 � I <br /> bsg Petroleum hydrocarbons were detected at concentrations as high as 270 ppm in soil samples <br /> collected at a depth,'of 20 feet bsg during the installation of IAS-1 BTE&X concentrations were near <br /> or below detection limits in soil samples collected'in the vicinity of USI s No 3 through 6 since <br /> 1994 Excavation would require the removal of overburden soil Impacted soil also extends toward <br /> 'the south under the building on-site and would not be teachable with excavation Therefore, <br /> ' excavation does not appear to be a viable option for site remediation <br /> h I ' <br /> 1 ' <br /> .1 Only low concentrations of hydrocarbons have been detected in soil samples collected near former <br /> USTs No 3 through 6 Installation of a remedial system would not be cost effective based on the , <br /> possible benefits obtained We iherefore'recommend natu ral attenuation as the remediation method <br /> for soil in the vicinity of former USTs No-3 through 6 g <br /> t <br /> In order to'determine the feasibility of natural attenuation,one boring should be installed near IAS-1 <br /> A soil sample from a depth of 20 feet bsg should be analyzed for bioenumeration'to determine if ' <br /> hydrocarbon-degrading bacteria are naturally present The sample should also be analyzed for <br /> t physicochemical. properties to determine biotoxicity; which might hinder natural degradation <br /> Additional borings should be installed at regular intervals to monitor progress of natural attenuation $ �r <br /> F4 <br /> i Soil remediation methods, estimated durations and associated costs are summarized on Table 9 ,1 <br /> I 1 <br /> j � s <br />