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soil and groundwater cleanup standards have been attained (per 27 <br /> CCR, Section 20410) , " this does not apply to the above listed <br /> sites, because the in-place soil contaminants of concern are <br /> currently not impacting groundwater. (SWMU 33 may be an <br /> exception. ) Also, the decision flow chart for groundwater <br /> monitoring in Appendix E does not address this concern. All <br /> sites listed above would probably end up being monitored once a <br /> year (which is acceptable) . However, there are no criteria for <br /> determining when to stop this annual monitoring. For example, <br /> how would one determine if performance monitoring is needed at <br /> the above five sites for the next five years or the next 50 <br /> years? <br /> For SWMU 7, Section 9.7.3 . 8. states "Annual sampling for four <br /> years will identify any groundwater impacts. " It is not clear <br /> why four years of annual sampling is considered adequate. Has <br /> vadose zone modeling demonstrated that the maximum impact to <br /> groundwater is expected to occur within this time frame? <br /> Please revise Section 9.1 to include an additional paragraph <br /> which addresses these concerns. This new paragraph should <br /> describe steps for determining when performance monitoring can be <br /> discontinued. Such steps may include additional soil sampling <br /> for DI WET analyses and additional vadose zone modeling to assess <br /> contaminant leaching potential . The paragraph should <br /> specifically reference the above five sites, and any other sites <br /> which fit this category. <br /> ADDITIONAL DETAILED COMMENTS <br /> 7 . [Declaration, Section D.S, Statutory Determinations, page D-1] <br /> Per EPA' s ROD guidance (Interim Final, October 1989, Section <br /> 6 . 2 . 5. 1 and EPA's Record of Decision Checklist) , if the remedy <br /> does not meet the statutory preference for treatment as a <br /> principle element, then a statement should be made to this <br /> effect, followed by a summary rationale. Three sites do not meet <br /> the statutory preference for treatment: SWMU 7 (Institutional <br /> Controls) , Drum Storage Area/Building 30 (Institutional <br /> Controls) , and the Northern Depot Area (asphalt cover) . As a <br /> result, the following statement should be added to Section D. 5 : <br /> "However, because treatment of the principle threats of the sites <br /> was not found to be practicable, this remedy does not satisfy the <br /> statutory preference for treatment as a principle element. " <br /> Additionally, the rationale for selecting Institutional Controls <br /> or asphalt cover for these should be briefly summarized. <br /> A-6 <br />