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Jeff Whitworth • -2- • 14 September 2007 <br /> t Shell Stockton Terminal <br /> The WP-FS presents an evaluation of four remedial alternatives "for reducing groundwater <br /> petroleum constituent concentrations in localized areas ("hot spots') off." Shell identifies <br /> three source areas (SAs) to be targeted for remediation: SA-1 (near Tank 14 and the former <br /> rail car off-loading area), SA-2 (near the truck loading rack), and SA-3 (former unlined holding <br /> pond near MW-2 and MW-13R). The evaluated remedial technologies include soil excavation, <br /> soil vapor extraction with air sparging (SVE/AS), groundwater extraction, and dual phase <br /> extraction (DPE). Shell's specific remedial objectives are to "remove hydrocarbon mass from <br /> the most heavily impacted soil and groundwater within the identified source areas, mitigate <br /> further hydrocarbon migration in soil and groundwater, continue the groundwater monitoring <br /> program to monitor water quality and plume stability, and establish a contingency plan to <br /> expedite or enhance remediation, if future monitoring indicates unanticipated plume <br /> migration." <br /> Based on the evaluation, Shell determined that DPE presents the most cost-effective option at <br /> an estimated total cost of $490,000 over a three-year operation period. Shell states that pilot <br /> testing of the DPE technology would be needed in one of the three SAs to determine technical <br /> feasibility, effectiveness and full-scale design criteria. The WP-FS assumes the installation of <br /> a total of 16 DPE wells in the three SAs and an assumed 25-foot radius of influence (ROI). For <br /> disposal of treated groundwater, Shell states it will consider two options: discharge to the <br /> sanitary sewer and discharge to land under the Regional Water Board's General Order No. <br /> R5-2003-0044. The WP-FS states that permeability testing will be needed to determine the <br /> feasibility of land discharge. For sewer discharge, the treatment system must be able to <br /> address previous problems with TBA concentrations and the methane lower explosive limit. <br /> For groundwater cleanup levels, Shell proposes that the Regional Water Board grant an <br /> exception to the default municipal (MUN) designation for groundwater underlying the Site and <br /> use the San Francisco Bay Regional Water Board's (Region 2) Environmental Screening <br /> Levels (ESLs) instead of the Central Valley Region's water quality objectives. For soil cleanup <br /> levels, Shell proposes to use Region 2's ESLs or a site-specific human health risk assessment <br /> (HHRA). <br /> Our comments are presented below. <br /> 1. Shell based its selection of DPE over the other three remedial alternatives primarily on <br /> economic feasibility. However, Regional Water Board staff could not compare the costs of <br /> the excavation and SVE/AS options because Table A-Remedial Alternative Comparison in <br /> the FS did not include total costs for these options. We cannot adequately evaluate the <br /> remedial alternatives in the absence of a complete cost comparison. Table A needs to be <br /> revised to include costs for the excavation and SVE/AS options. <br /> 2. Shell proposes to remediate only the most heavily contaminated soil and groundwater in <br /> only three localized SAs referred to as "hot spots." We do not concur with this proposed <br /> cleanup objective. Shell has stated but not demonstrated that cleanup at the Site is <br /> technically or economically infeasible. The FS must be revised to include site-wide <br /> groundwater cleanup as the remedial objective. <br /> 3. The WP-FS does not specify whether pilot testing will be conducted in one or multiple SAs. <br /> The WP-FS provided an estimate of $25,000 for the cost of conducting a pilot test in one <br />