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In accordance with Section 7.0 of EPA's final guidance, "A Guide to Preparing Superfund Proposed Plans, Records of Decision, and Other Remedy Selection Decision Documents,"EPA 540-R-98-031,July 1999, the changes in cover materials and areal dimensions of the cover are significant post-ROD changes that must be addressed through the ESD process. Further, the AB cover is augmented by institutional controls, which are also significant changes. According to Section 2.1 of the Draft Final RAR, the ESD for DSERTS 67 addressed the revised cleanup standards, the addition of institutional controls, and the replacement of the planned asphalt cover with an AB cover. There is, however, no discussion in the Draft Final RAR that indicates the change in cover size was addressed by the ESD. Please explain how the reduction in size of the DSERTS 67 cover will be documented through the Post-ROD change process. 4. The Executive Summary indicates the DDCE"was initiated to further assess the nature and extent of contamination at DSERTS 67 and to define the lateral extents [sic] of the AB cover." Based on the information regarding the DDCE in Section 1.3 and Figure 2-3, however,it is not clear that the nature and lateral extent of contamination have been defined at DSERTS 67. Section 1.3 indicates that manganese exceeded the cleanup level of 812.5 mg/kg at sample locations SL0014 and SL0016 (846 mg/kg and 2090 mg/kg, respectively). Figure 2-3 indicates that SL0014 is located along the northern boundary of the AB cover and SL0016 is located outside the AB cover. Since manganese concentrations at SL0014 and SL0016 exceeded the cleanup standard, clarify whether additional sampling was performed to delineate the bounds of high manganese concentration surrounding each sampling location. This additional sampling should have been performed in order to determine the location of the northern boundary,of the AB cover in the area of SL0014, as well as the extension of the AB cover to the northwest over the area of SL0016. Please revise the RAR to clarify whether additional sampling was performed to fine tune the nature and extent of manganese contamination in the areas surrounding SL0014 and SL0016. As discussed previously in the Specific Comment 3 on the Draft RAR, at least two other soil samples (SS086 and SS087) had contaminant concentrations exceeding the ESD's revised cleanup standards. These two samples were collected at locations outside and northwest of the AB cover. SS086 had 89.3 mg/kg arsenic and 26,000 mg/kg manganese, while SS087 had 13,700 mg/kg of manganese. Please revise the RAR to explain why the area represented by these two previous sampling locations was not included in the area of AB cover. 5. The Draft Final RAR provides the Technical Memorandum regarding the Apatite Mineralization Bench-Scale Pilot Test (see Appendix B), which was used to justify the asphalt cover as the ROD-selected remedial design. However, the same degree of backup 2