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0 <br /> 5. Section 4.1.2.2,Page 4-2: It is unclear why additional step-out excavations were not <br /> performed after the final round of sampling showed concentrations of contaminants <br /> exceeding cleanup standards. The Remedial Action Objective (RAO) for SY;W 8 based <br /> on the ROD was to "remove all known soil with contaminant concentrations above <br /> cleanup standards", which is therefore protective of human health and the environment. <br /> The text does not provide an explanation on why the excavation was backfilled prior to <br /> removing all known contamination. Please provide an explanation on why additional <br /> step-out excavations were not conducted and why the excavation was backfilled prior to <br /> defining the lateral extent of contamination. <br /> 6. Section 4.2,Page 4-2: There is no discussion of the remaining threat to human health <br /> from the pesticides left in the soil above ROD cleanup levels. Please add a new section to <br /> explain why it is protective of human health. <br /> 7. Section 5.2.1, Page 5-2: The following statements are not entirely correct and should be <br /> reworded: "A Soil Vapor Extraction (SVE) well would preferentially draw vapor from <br /> the "looser" backfill material, rather than the native material originally targeted in the <br /> ROD. It should be noted that the only contaminant reported above ROD cleanup <br /> standards during final excavation confirmation sampling would not be remediated by <br /> SVE." First, the text needs to acknowledge that a sheet piling or other subsurface <br /> structure could be installed to reduce possible preferential flow from the fill material <br /> during SVE operation. Second, bioventing, at reduced flow rate compared to traditional <br /> SVE, might be effective in treating the total petroleum hydrocarbon (TPH) contaminated <br /> area without affecting the excavation area. Also, the text needs to acknowledge that a <br /> laboratory TPH measurement actually represents many petroleum hydrocarbons. Some of <br /> the petroleum hydrocarbons that are included in a TPH scan are volatile enough to be <br /> removed by SVE, others are not. Overall, the proposal to remove SVE from the proposed <br /> remedy does not include enough supporting rationale. This section needs to describe the <br /> nature and extent of contamination left in place, including a discussion of the <br /> uncertainties in the data set and explore the possibility of using bioventing instead of <br /> traditional SVE to address the TPH contamination. Bioventing could enhance bacterial <br /> activity in the site soils, potentially breaking down some of the longer chain hydrocarbons <br /> that cannot be removed by traditional SVE. <br /> 8. Section 6.2.4,Page 6-2: The text does not provide an explanation of why the grass area <br /> in the northwestern portion of DSERTS 67 was not covered with gravel. It appears that <br /> the majority of the site (approximately 88%) is covered, but does not explain why the <br /> remaining grass areas were not covered with the AB cover or gravel. Please provide an <br /> explanation in the text on when and why it was decided not to cover the grass areas. <br /> 3 <br />