NC0004987_Correspondence_20210519 (3)

Responses 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."