volume of water percolating the landfill producing leachate. Operating a leachate collection system early as we are currently doing is the most effective means of curtailing contaminant rich leachate loading to the environment. The pumping system proposed would only be operational after the cap is in place and would function as an expensive redundant leachate collection system. The reason these two alternatives result in approximately the same volume of leachate collection is because the existing collection system is in place without the landfill cap (.and therefore under maximum leachate generation conditions) while the pump and treat system leachate estimates are with the landfill cap in place. As described in the response t o Issue 14, the cap is estimated t o reduce leachate generation through infiltration by 99.9 percent. Issue 9: Pumping and treating leachate (Alternative 2B) is more protective of the environment and will achieve water quality standards seven years sooner than the proposed Alternative 2. Although Alternative 2B would take eight months longer to implement than Alternative 2 it is worth the additional cost to achieve standards quicker. -. Res~onse: DEC evaluates the alternatives in accordance with the National Contingency Plan (NCP) criteria described in Section V of this ROD. Both Alternatives 2 and 2B meet the threshold criteria by substantially complying with Applicable or Relevant and Appropriate Requirements (ARARs) and providing overall protection of human health and the environment. While the commenter noted that Alternative 2B is projected to achieve water quality standards in 8 years as opposed to Alternative 2 taking 15 years, in those same 8 years, Alternative 2 would reduce contaminant loadings to the Hudson River by 90 percent (refer. to FS Report, Appendix A, Tables 4 through 10). In addition, by accelerating the capping schedule 2 full years by proceeding with the cap design prior to this ROD, the net environmental benefit is greater than pumping and treating leachate for 8 or even 15 years (refer to FS, Appendix A, Tables 4 and 11). By capping the landfill sooner, two years of chromium (along with other contaminants) loading to the river will be eliminated, which equates to a reduction of 46.7 pounds of chromium discharge to the river. Fifteen years of pumping and treating versus capping alone equates to a reduction of only 36.1 pounds of chromium discharge to the river. Other contaminants would follow this same trend. For t'lese reasons, the DEC believes these two alternatives -*iovide essentially equal long-term effectiveness in protection of the environment. Short-term effectiveness is about the same for these two alternatives with no significant adverse impacts expected under either alternative. While Alternative 2B provides a slightly greater reduction in mobility of leachate contaminants than Alternative 2, it is more difficult to implement due to the added construction and operation of an on-site pretreatment plant and it is significantly greater in cost than Alternative 2. Based on the above, the DEC believes that Alternative 2 provides a better balance between long and short-term effectiveness; reduction of toxicity, mobility, and volume; cost, and implementability than Alternative 2B. Issue 10: If the leachate collection system is unsuccessful in collecting all of the leachate from the landfill, discuss any impacts the leachate which escapes will have on the environment. The benefits of a slurry wall should be reconsidered. Response: Using the leachate collection estimates in the response to Issue 8, it is clear that the leachate collection system in the selected remedy will capture most but not all of the leachate which is estimated to be within the waste mass. The leachate collection system is intended to prevent the direct discharge of leachate to the surrounding surface waters. The remainder of the leachate in the waste mass will travel downward below mean sea level where it will slowly seep out laterally into the subsurface of the Hudson River. Because this process will take place slowly and the Hudson River provides a dilution of approximately 55,000 to 1, landfill leachate loading will have a negligible impact on surface water quality. The landfill has been , leaching significant quantities of leachate into the surrounding environment for 60 years with present estimates of over 55 million gallons per year. Although some quantity of leachate will continue to migrate into the river subsurface approximately 99.9% of the rain and snow melt water will be eliminated from leachate generation by the cap. The landfill leaahate mound (water level within the waste) will be starved of water and will begin to fall as leachate continues to be removed via the collection system. The substrate is not an adequate liner to enhance with a slurry wall and eliminate hydraulic connection with the river discharge system. A slurry wall would only be effective at the CPL in combination with a pump and treat system (Alternative 2B). A slurry wall