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On the basis of the laboratory analyses, it is recommended the soil cuttings stored in <br /> drums on-site be transported by manifest to a Class II landfill for disposal <br /> At this time, it is recommended that a quarterly groundwater monitoring program be <br /> initiated to monitor the groundwater at the site Further resampling of the monitoring <br /> wells should confirm the analytical results obtained from this sampling event and <br /> provide information on the nature of the groundwater and contaminate flow <br /> Based upon the results of this investigation, three alternative courses of action are <br /> presented to address the remediation of petroleum hydrocarbon impacted soil no <br /> action, in-situ vapor extraction, and excavation and disposal <br /> The no action alternative is appropriate if the concentrations present a low risk to <br /> health and the environment as prescribed by federal, state, and local regulations. This <br /> site presents high risk of continued leaching to groundwater and concentrations are in <br /> excess of maximum contaminant levels (MCL's) for benzene The no action alternative <br /> is not recommended for this site <br /> Excavating the contaminated plume is a second option This alternative is the most <br /> effective approach in removing sods impacted with hydrocarbons It can, however, be <br /> a very costly approach ($100 per cubic yard) The quantities to be excavated and <br /> removed may be as high as 1 ,900 cubic yards at this site, for an estimated cost of <br /> • $189,000 Due to the proximity of the impacted soils over groundwater, the volume of <br /> soil to be removed, and the presence of underground and surface facilities at the site, <br /> this alternative is not considered practical In addition, excavation near the service <br /> budding may weaken the integnty of the footings and foundation, adding to the cost for <br /> shoring the budding <br /> It is the opinion of AquaGeosciences, Inc that another alternative for remediation is in- <br /> situ vapor extraction either by thermal oxidation or internal combustion As a variation <br /> to vapor extraction, AGI recommends conducting an in-situ air sparging test Based on <br /> the test results, air sparging of the groundwater may be conducted in combination with <br /> the soil vapor extraction <br /> 10 0 LIMITATIONS <br /> AGI performed this investigation in accordance with the generally accepted standards <br /> of care which exist in Central California at this time It should be recognized that <br /> definition and evaluation of geologic conditions is a difficult and inexact science <br /> Judgments leading to conclusions and recommendations are generally based on <br /> limited knowledge of subsurface conditions present No warranty expressed or <br /> implied, is made <br /> 17 of 17 <br />