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• • Mr.Brian Taylor <br /> N) November 9, 2007 <br /> CONESTOGA-ROVERS <br /> &ASSOCIATES <br /> the extent of impacted soil is discovered to be larger than anticipated and is near/underneath structures <br /> (considered very likely). The cost-effectiveness (and overall technical effectiveness) of excavation is <br /> compromised if the structures and impacted soils are left in place. Additionally, excavation activities <br /> will have an adverse impact to the local/regional economy (via revenue loss and job losses). Many <br /> of the variables of this remedial alternative can not be quantified at this time to generate an <br /> accurate cost estimate, but enough is known to suggest that the costs (to both Shell and the local <br /> economy) of excavation would be excessive. Therefore, based on limited implementability and cost, <br /> CRA does not recommend soil excavation." <br /> Consequently, based on this discussion, there are too many uncertainties to generate a meaningful cost <br /> estimate for excavation. However, the cost to remediate this site by excavation will be orders of <br /> magnitude greater than the other remedial alternatives evaluated. <br /> As presented in the FS, "SVE, with appropriate wells, is assumed to be effective and feasible in reducing <br /> hydrocarbon impacted vadose zone soils based on past SVE activities. However, full remediation is <br /> unlikely due to low permeability areas and inability to access large portions of impacted areas due to on- <br /> going Terminal operations. AS is considered infeasible given site-specific hydrogeologic conditions <br /> (generally low permeability silts and clays). SVE limitations have been identified in remediating <br /> hydrocarbons in saturated soils. Therefore, CRA does not recommend that SVE/AS be implemented <br /> as a remedial alternative for the site." <br /> The FS concluded SVE/AS to be technically infeasible, therefore it is not considered a remedial option; <br /> potential implementation costs are irrelevant. <br /> Page 2, Item 2: "Shell proposes to remediate only the most heavily contaminated soil and groundwater <br /> in only three localized SAs referred to as "hot spots." We do not concur with this proposed cleanup <br /> objective. Shell has stated but not demonstrated that cleanup at the Site is technically or economically <br /> infeasible. The FS must be revised to include site-wide groundwater cleanup as the remedial objective." <br /> Response: As presented in the FS, "The FS presented below evaluates remedial alternatives for reducing <br /> groundwater petroleum constituent concentrations in localized areas ("hot spots") only. It is Shell's <br /> technical opinion that attainment of the RWQCB Basin Plan water quality objectives on a site-wide basis <br /> is considered to be technically and/or economically infeasible given site-specific hydrogeologic <br /> conditions, which generally consist of low permeability silts and clays and the absence of laterally <br /> continuous saturated coarse-grained layers." <br /> 1729 2 <br /> Worldwide Engineering, Environmental, Construction, and IT Services <br />