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ATTACHMENT A <br /> EPA COMMENTS <br /> DDRW-TRACY <br /> SITE-WIDE COMPREHENSIVE ROD <br /> DECEMBER 1997 <br /> GENERAL COMMENTS <br /> 1. [SWMU 4 Ecological Risk Concerns: Response to EPA General <br /> Comment Nos. G1 and G6 of October 15, 1997; Section 6 .6 . 5 .4; <br /> Section 9. 7. 1. 11 through 9.7. 1. 15] Many issues pertaining to <br /> ecological risk at SWMU 4 continue to be unresolved. <br /> a. Since risk-based cleanup levels concentrations have not been <br /> finalized, it appears inappropriate to state, in Section <br /> 9 .7. 1 . 13, that excavation will be to a depth of <br /> approximately 3 inches (2, 500 cy) . It is not clear why <br /> DDJC-Tracy continues to use the 3-inch excavation <br /> assumption. Perhaps DDJC-Tracy' s continued use of this <br /> assumption relates to the planned installation of geofabric <br /> and clean backfill following the excavation. As stated in <br /> Section 9 . 7. 1. 13, this geofabric and backfill are intended <br /> to "isolate subsurface soils form ecological receptors . " Is <br /> DDJC-Tracy relying on this fabric and backfill to be an <br /> integral part of the remedy to prevent birds from feeding <br /> below this barrier? If so, is DDJC-Tracy implying that <br /> after removal of 3 inches of sediment, any soil which <br /> remains above the risk-based cleanup level is acceptable to <br /> leave behind, because the geofabric and fill will act as an <br /> impenetrable barrier to feeding birds? If this is DDJC- <br /> Tracy's position, this needs to be clearly stated and <br /> additional documentation is needed to justify why such a <br /> barrier is indeed effective, and thus, why cleanup to the <br /> risk-based level is not necessary below the barrier. <br /> In contrast, if this can not be justified, or if this is not <br /> DDJC-Tracy's position, it is unclear what value the <br /> geofabric will provide to the remedy. Since if all sediment <br /> must be removed to the risk-based cleanup level anyway, all <br /> sediment below the geofabric should be "clean" , while newly <br /> deposited sediment above the geofabric may contain some <br /> contamination from runoff. Thus, the geofabric would not <br /> "isolate subsurface soils from ecological receptors. " <br /> Instead, it would only isolate ecological receptors from <br /> "clean" underlying sediment. Additionally, if the geofabric <br /> A-1 <br />