NC0004979_Other Agency Documents_20210728 (2)

Responses to Comments for Allen Steam Station
07/01/2021
Comments from SELC
1) Comment: DEQ's Application of the Early Retirement Exemption Is Premature
Response: Early retirement exemption has been postponed and earlier FGD
limits have been re -instated until Duke submits the Notice of Planned
Participation.
2) Comment: Treatment System Performance Standard and More Effective
Monitoring
Response: The existing monitoring frequency is sufficient to evaluate
performance of the treatment systems. Comparison with Outfall 002 is
inappropriate since Outfall 002 discharges interstitial coal ash water that has
higher concentration of the pollutants. On the contrary, Outfall 006 discharges
from the basin that does not contain coal ash and Outfall 005 is an internal
outfall.
3) Comment: DEQ Should Not Remove the Permit's ELG Reopener Clause
Response: The re -opener clause will be added to the permit.
4) Comment: Require technology -based effluent 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."
5) Comment: Conditions A. (21.) and A. (22.)
Response: During Major Modification only a portion of the permit is re -opened
and modified, the rest of the permit remains intact. Therefore, language in the
special conditions did not change. In addition, the permit expires on July 31,
2023 and hypothetical extension of the 3.5 years compliance schedule would be
beyond this date, which makes such an extension invalid.
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6) Comment: Compliance Boundary Map
Response: The compliance boundary map is not changing. During Major
Modification only a portion of the permit is re -opened and modified, the rest of
the permit remains intact. Therefore, maps are typically not included, unless
modification includes changes to the maps.
Comments from a citizen
Problem # 1 - proposed permit allows for unlimited discharges of elements such as
mercury and arsenic.
Response: The need for water quality based effluent permit limits is determined based
on the results of the reasonable potential analysis (RPA). The RPA procedure utilized
by the Division is conducted in accordance with the EPA's regulation (40 CFR
122.44(d)(1)). When the permitting authority determines, using procedures in
paragraph (d) (1) (ii) of this section, that a discharge causes, has the reasonable
potential to cause, or contributes to an in -stream excursion above the allowable
ambient concentration of a State numeric criteria within a State water quality
standard for an individual pollutant, the permit must contain effluent limits for that
pollutant. Permit limits are added only if the results of the RPA indicate the potential
for exceeding the water quality standards, and are not arbitrarily assigned. However,
absence of permit limits does not allow the facility to violate instream water quality
standards.
Problem #2 - proposed permit does not require monitoring for elements typically seen
around coal ash sites.
Response: Coal ash basins typically contain Arsenic, Selenium, Mercury, Zinc, Copper,
Bromide, Cadmium, and Lead. The permit contains a requirement to monitor all these
contaminants.
In addition, the need for toxicant limits and monitoring is based upon a demonstration
of reasonable potential to exceed water quality standards, a statistical evaluation that
is conducted during every permit renewal utilizing the most recent effluent data for
each outfall. The RPA is conducted in accordance with 40 CFR 122.44 (d) (i). The NC
RPA procedure utilizes the following: 1) 95% Confidence Level/95% Probability; 2)
assumption of zero background; 3) use of 1/2 detection limit for "less than" values; and
4) stream flows used for dilution consideration based on 15A NCAC 2B.0206. Effective
April 6, 2016, NC began implementation of dissolved metals criteria in the RPA
process in accordance with guidance titled NPDES Implementation of Instream
Dissolved Metals Standards, dated June 10, 2016.
A reasonable potential analysis was conducted on effluent toxicant data provided by
the facility in the permit application. Pollutants of concern included toxicants with
positive detections and associated water quality standards/criteria. Based on this
analysis, the following permitting actions are proposed for this permit:
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No Limit or Monitoring: The following parameters will not receive a limit or monitoring,
since they did not demonstrate reasonable potential to exceed applicable water quality
standards/criteria and the maximum predicted concentration was <50% of the
allowable concentration: Beryllium, Chromium III, Chromium VI, Molybdenum,
Aluminum, and Boron.
Problem #3 - proposed permit allows for water to be discharged at a high temperature.
This can contribute to water loss and can harm aquatic life.
Response: The facility has a 316(a) variance that allows discharges of the heated
effluent. The variance requires extensive biological monitoring of the receiving stream.
The facility also must submit Balanced and Indigenous Population (BIP) study during
each permit renewal to demonstrate existence of healthy aquatic community. The last
BIP study submitted by Duke demonstrated that Balanced and Indigenous population
exists in the receiving stream, the DWR biologists agreed with this conclusion.
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