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HomeMy WebLinkAboutNC0004987_Responses to Comments_20210422Responses to Comments for Marshall Steam Station 04/22/2021 Comments from SELC 1) Comment: Add Treatment System Performance Standard and More Effective Monitoring Response: The optimization requirement will be incorporated into the permit, but without the numeric quarterly limit for Selenium since the Marshall treatment system is relatively new and we don't have the long-term performance data for this system. Numeric limit was included in the Belews Major Modification because Duke has gained experience in operating the system over several years and is capable of reliably achieving prescribed quarterly average limit of 12 µg/L for Selenium. The proposed monitoring frequencies of Quarterly are consistent with the similar Duke permits and sufficient to evaluate compliance with the permit limit. It is necessary to emphasize that this is an Internal Outfall and wastewater will be subject to an additional treatment in the Lined Retention Basin. Comparison of the monitoring frequencies for internal and external outfalls is not appropriate. 2) Comment: Add Reopener Clause Response: The Reopener Clause will be added. 3) Comment: Require treatment technology -based limits for Outfall 002 Response: The Technology -based limits are already incorporated into the permit. The effluent limitations in the permit are established in accordance with the existing federal and state rules and regulations. EPA has recently updated 40 CFR 423 and after reviewing parameters of concern established TBELs for several of these parameters. The EPA decided that TBELs for all parameters of concern are not necessary because "Effluent limits and monitoring for all pollutants of concern is not necessary to ensure that the pollutants are adequately controlled because many of the pollutants originate from similar sources, have similar treatabilities, and are removed by similar mechanisms. Because of this, it may be sufficient to establish effluent limits for one pollutant as a surrogate or indicator pollutant that ensures the removal of other pollutants of concern."