the waste stream entering the SPT, none of the projected STP effluent (discharge) concentrations would exceed the Permit Action Level. For the metals of concern, the projected plant effluent/SPDES Permit Action Level in pounds per day are as follows: copper (1.48/8.4) nickel (1.4713.9) zinc (4.115.3). Subsequent to this engineering evaluation the Westchester County Department of Public works prepared a report titled, 'Effect of Croton Point Leachate on the Ossining WWTP." Table 2 of this report provides the following actual discharge rates in pounds per day: copper 1.47, nickel <1.83, and zinc <1.83. The contribution of these metals from the leachate in pounds per day are: copper <0.02, nickel 0.15, and zinc <0.80. ("<" means that compound was below the detection limit and is less than the number shown). The sludge from the Ossining STP is presently incinerated. Since metals from the CPL leachate will end up in the STP sludge, the impact of those metals on sludge disposal was also evaluated by the County's consultant prior to sending the leachate to the Ossining STP. That evaluation demonstrated that the metals content of the sludge would be within the current limits for incineration of the sludge. That evaluation also demonstrated that with or without the leachate metals loading to the sludge, the pro~osed USEPA standard for nickel would be exceeded (refer to Westchester County Department of Public Works Report "Effect of Croton Landfill Leachate on the Ossining WWTP," Appendix B, Table 3). If the proposed USEPA standard for nickel is promulgated, the STP would have to upgrade its treatment system regardless of whether the leachate is sent. As part of the operation and maintenance plan, the leachate will be sampled monthly (at the landfill before it enters the sanitary sewer) for the first few years after capping. This data will be evaluated to determine if any changes in leachate quality would warrant pretreatment of the leachate prior to discharge to the sanitary sewer. Also, if regulations change and pretreatment requirements become more stringent and warrant pretreatment, then on-site pretreatment of the leachate will be implemented. Issue 8: What type(s) of on-site treatment would be necessary to implement alternative 2B? How much leachate would actually be removed by Alternative 2 versus Alternative ZB? Res~onse: On-site treatment of leachate was not as clearly defined as the other alternatives in the Feasibility Study (FS), however, the FS does present Alternative 2B: containment with pump and treat, which includes treatment of the leachate. Page 8-5 of the FS also refers the reader to Appendices A and F for further discussion of the pump and treat component of Alternative 2B. DEC carefully reviewed the assumptions used by the County's consultant and the calibration of the groundwater model (Appendix A of the FS presents those results). Based on DEC1s experience with mathematical groundwater models the analysis by the Countyts consultant is reasonable. Although it does not provide details about leachate treatment, Appendix F does identify the processes needed to pretreat the,leachate under active pumping conditions. Those processes would include a chromium reduction system, aeration tank, a first and second stage precipitation system, filtration, neutralization, and a granular activated carbon system. Most metals would end up in a sludge which would require thickeners, a filter press, and sludge disposal. It was assumed that the sludge would be disposed of as a non-hazardous waste (similar to sewage treatment plant sludge). Based on DEC1s experience the leachate treatment system described above would provide adequate treatment of the leachate prior to discharge. It is estimated that Alternative 2B would remove 129 million gallons of leachate over a 15 year period. Based on actual flows recorded to date and projected leachate collection rates it is estimated that in the 15 years beginning April 1992 (when the leachate transfer system began operation), Alternative 2 will remove 127 million gallons of leachate for treatment. The Countyrs decision, with the DEC1s approval, to begin leachate collection and off-site treatment prior to this Record of Decision has resulted in approximately the same volume removal of leachate as pumping and treating leachate for 15 years. High bulk volumes of leachate are currently forming as rain and snow melt water percolate the landfill. The cap will cut the 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