NC0065102_Comments_20231013

CARY
UTILITIES
October 6, 2023
Mr. Nick Coco, PE
Department of Environmental Quality
Division of Water Resources
NPDES Municipal Permitting Unit
1617 Mail Service Center
Raleigh, NC 27699-1617
RECEIVED
OCT 13 2023
NCDEQ/DWR/NPDES
Subject: South Cary WRF Draft NPDES Permit (NC0065102) Comments
Dear Mr. Coco:
On September 12, 2023, Cary received the draft NPDES permit for the South Cary Water
Reclamation Facility (NC0065102). We appreciate the opportunity to review the draft permit, fact
sheet, and associated reasonable potential analyses (RPA). Cary respectfully submits the
following comments and requests for modification of the proposed draft permit.
NPDES Permit Cover Letter
1. Total Residual Chlorine (TRC) limits and monitoring requirement (not listed on cover
letter), referenced in Section A.(1.)(a.) on pg. 3 of 15, in Footnote 5 on pg. 4 of 15, in
Section A.(2.)(a.) on pg. 5 of 15, and in Footnote 5 on pg. 6 of 15.
Request: Remove TRC monitoring as chlorine addition is not listed or permitted for effluent
disinfection. Cary will continue to maintain a redundant UV disinfection system, spare parts,
service support, and emergency backup generators for our existing and approved method
for effluent disinfection. If chlorine addition is required with a future permit modification,
chlorine monitoring language can be added.
2. Special condition to monitor effluent PFAS (511 bullet point, pg. 1).
Request: Cary requests NC Division of Water Resources (NCDWR) acknowledge the role
of the State of North Carolina approval processes for laboratory procedures prior to
requiring reporting of PFAS sampling results.
3. Certification of Compliance When a Permit Limit is Set At or Below ML (Minimum Levels)
has been removed from the permit. (81h bullet point, pg. 1).
Request 1: This item is referenced as Special Condition A.(10.) but should be referenced as
Special Condition A.(7.) in the existing permit.
Request 2: We would like to request that this ML language remain in the permit as in
previous permits. We request this clarification for PQL be immediately available for
reference in the current permit.

Part I, A.(1.) Effluent Limitations and Monitoring Requirements f12.8 MGDI (Page 3 & 4 of 15)
1. Total Residual Chlorine (TRC) limits, monitoring requirement, and Footnote 5.
Request: Remove TRC monitoring requirements and footnote 5 as chlorine addition is not
listed or permitted for use in the effluent stream. If chlorine addition is required with a future
permit modification, chlorine monitoring language can be added.
2. Footnote 4: "Twice per week sampling must occur on any two non-consecutive days
during the calendar week. "
Request: Please confirm that week's consisting of holidays will not require two non-
consecutive day sampling if holiday prevents it.
3. Footnote 10: "See Special Condition A.(8.)."
Request: Revise language to reference "Special Condition A.(9.)."
4. Footnote 12: Effluent Pollutant Scan monitoring requirement.
Request: Remove TRC as a monitoring requirement as chlorine disinfection is not approved
or used for disinfection.
5. Conductivity limits and monitoring requirement.
Request: Remove conductivity monitoring requirements. Fact Sheet 4. — Instream Data
Summary (page 4 of 14). Instream Data Summary indicates:
"As the South Cary WRF does not receive industrial wastewater from a Significant Industrial
User, conductivity monitoring is not required. Review of conductivity data from the
downstream monitoring stations indicates that conductivity is slightly higher at the nearest
downstream monitoring station than the two further stations. An LNBA station, J4690000,
exists upstream of the discharge above Sunset Lake. While the lake may influence
parameters, conductivity at LNBA Station J4690000 was used as a general indicator of
upstream conductivity. Review of conductivity data reported at J4690000 demonstrated an
average conductivity of 234 umhos/cm, ranging from 79 umhos/cm to 436 umhos/cm. As
the conductivity above the lake appears to reflect the conductivity below the discharge,
instream conductivity has not been added at this time."
Upstream conductivity (J4690000) monitoring indicates higher average and maximum
values as downstream conductivity monitoring (J4868000, J4980000, and J5000000). New
monitoring requirements in Fact Sheet 10. — Monitoring Requirements indicates:
"While the facility does not have any Significant Industrial Users, effluent conductivity
monitoring has been added to track potential influence on the receiving stream which has
observed high levels of ambient conductivity. Effluent conductivity monitoring is to be
conducted daily in accordance with 15A NCAC 02B .0508."
The new effluent conductivity monitoring requirement overlooks instream observations and the
NCDWR statement in Fact Sheet 4. Instream Data Summary - "As the conductivity above the
lake appears to reflect the conductivity below the discharge...". Instream monitoring data does
not indicate or suggest that the South Cary WRF effluent negatively influences conductivity in
the stream and daily monitoring requirements are not warranted. Upstream data shows that
conductivity in Middle Creek is influenced by upstream contributions and prior to the South
Cary WRF effluent discharge, daily effluent conductivity monitoring requirements is an
arbitrary application of 15A NCAC 02B .0508 and should not be required.
C-.RY

Part I A.(2.) Effluent Limitations and Monitoring Requirements [16.0 MGDI (Pape 5 & 6 of 15)
1. Total Residual Chlorine (TRC) limits, monitoring requirement, and Footnote 5.
Request: Remove TRC monitoring requirements and footnote 5 as chlorine addition is not
listed or permitted for use in the effluent stream. If chlorine addition is required with a future
permit modification, chlorine monitoring language can be added.
2. Footnote 4: "Twice per week sampling must occur on any two non-consecutive days
during the calendar week. "
Request: Please confirm that week's consisting of holidays will not require two non-
consecutive day sampling if holiday prevents it.
3. Footnote 10: "See Special Condition A.(8.)."
Request: Revise language to reference "Special Condition A.(9.)."
4. Footnote 12: Effluent Pollutant Scan monitoring requirement.
Request: Remove TRC as a monitoring requirement as chlorine disinfection is not approved
or used for disinfection.
5. Conductivity limits and monitoring requirement.
Request: Remove conductivity monitoring requirements. See comment above for Part I,
A. (1.) - #5.
Part I, A.(3.) Instream Monitoring Requirements (Pape 6 of 15)
1. Table header language: "Beginning on the effective date of this permit and lasting until
lasting until permit expiration, the Permittee shall perform instream sampling upstream
and downstream of Outfall 001 as specified below:"
Request: Remove duplicate language "lasting until."
2. Footnote 1 sentence: "Instream sampling requirements fGF are provisionally waived in
light of the permittee's participation in the Lower Neuse River Basins Association
(LNBA). "
Request: Remove the word "for" from the referenced sentence in Footnote 1.
3. Table and Footnote 1: Measurement frequency
Request: Please clarify the measurement schedule which is referenced as monthly in the
table and 3/week and 1/week in footnote 1.
Part I, A.(5.) Additional Monitoring Requirements for Permit Renewal (Page 8 of 15)
1. (a.) Effluent Pollutant Scans Chlorine (total residual, TRC) monitoring requirement.
Request: Remove TRC as a monitoring requirement. Chlorine disinfection is not approved
or used for disinfection at South Cary WRF.
CA RY UTILITIES

Part I, A.(9.) PFAS Monitoring Requirement (Pape 11 of 15)
Request: Cary requests NCDWR acknowledge the role of the State of North Carolina
approval processes for laboratory procedures prior to requiring reporting of PFAS sampling
results.
Fact Sheet, 4. Instream Data Summary (Page 3 & 4 of 14)
1. Summarization of instream data and what instream monitoring will be proposed for this
permit action (third paragraph).
Request: Take into account and include upstream stations LNBA Station J4690000, for
Conductivity.
2. Summarization of instream data and what instream monitoring will be proposed for this
permit action (first paragraph below Table 2). "As no upstream data were available, no
statistical analysis comparing upstream and downstream monitoring results was
conducted."
Request: We would like clarification concerning this statement, because there are upstream
monitoring locations.
3. Summarization of instream data and what instream monitoring will be proposed for this
permit action (fourth paragraph below Table 2). Review and discussion of conductivity
data from downstream monitoring stations.
Request: We would like clarification concerning this statement.
Fact Sheet, 6. Water Quality -Based Effluent Limitations (WQBELs) — Ammonia and Total
Residual Chlorine Limitations (Page 6 of 14)
1. Description of any proposed changed to ammonia and/or TRC limits for this permit
renewal sentence: "However, in the event of an emergency where chlorination is required
as a backup or temporary means of disinfection at the facility, a TRC limit and monitoring
requirement have been added to the permit based on the review of the attached WLA
spreadsheet. "
Comment: The SCWRF is not designed or approved to use chlorine for disinfection. Cary will
continue to maintain a dual -fully redundant ultra -violet (UV) disinfection system, spare parts,
service support, and emergency backup generators for our existing and approved method for
effluent disinfection. If chlorine addition is required with a future permit modification, chlorine
monitoring language can be added.
Fact Sheet, 6. Water Quality -Based Effluent Limitations (WQBELs) — Reasonable Potential
Analysis (RPA) for Toxicants (Page 6 of 14)
1. Table 3. Mercury Effluent Data Summary
Request: Several of the numbers in the table are incorrect. Please correct the numbers as
shown in the table below. Several sample results were deemed inaccurate and resampled.

The inaccurate data was replaced. It appears the table shown includes the original data, not
the corrected data.
Table 3. Mercury Effluent Data Summary
2019
1 2020
2021
2022
2023
# of Samples
4
4
4
4
2
Annual Average Conc. Ng/L
0
1.20
0
1.35
0.56
Maximum Conc. Ng/L
0
1.79
0
2.09
1.12
TBEL, ng/L
47
WQBEL, ng/L
12.2 @12.8 MGD and 12.1 @ 16.0 MGD
Fact Sheet, 6. Water Quality -Based Effluent Limitations (WQBELs) - Other TMDL/Nutrient
Management Strategy Considerations (Pape 8 of 14)
1. Other TMDL/Nutrient Management Strategy Considerations — Nitrogen.
Request: Please correct all typos to reflect the correct Total Nitrogen allocation of 180,211
Ibs/year.
Comment: Cary's South Cary WRF has a permitted total nitrogen load of 180,211
pounds/year and is based on our current 12.8 MGD capacity needs. Both the future hydraulic
capacity and nitrogen allocation is very important for Cary's future growth projections. The
South Cary WRF total nitrogen allocation is in accordance with the NC Neuse Nutrient
Strategy and the Neuse River Compliance Association co-permittee NPDES Permit
NC000001. Cary's total nitrogen allocation is finite and even with our WRF currently meeting
and exceeding the limits of technology for nitrogen removal, any reduction would be very
detrimental. Any proposed reduction in future hydraulic capacity, transportation factor
calculation, or nitrogen allocation is extremely important for Cary and likewise any point source
discharger in the Neuse River Basin subject to the Neuse Nutrient Strategy.
Fact Sheet, 6. Water Quality -Based Effluent Limitations (WQBELs) - Other WQBEL
Considerations (Page 9 of 14)
1, Other WQBEL Considerations - In the middle of the paragraph, where the sampling points
are listed, the sentence reads, "The Town has conducted sampling of the South Cary WRF
influent headworks (influent + recycled flow), Mixed Liquor Suspended Solids (MLSS),
pellets, and solids, and post -filtration."
Request: Revise the sentence so that it reads as follows, "The Town has conducted sampling
of the South Cary WRF influent headworks (influent + recycled flow), Mixed Liquor Suspended
Solids (MLSS), pellets, and Gravity Belt Thickener (GBT) solids, and post -filtration."
Remove the word "and", and insert the words, "Gravity Belt Thickener (GBT)".
Thank you for the opportunity to review and provide comments on the South Cary WRF draft
NPDES permit renewal. If there are any questions regarding these comments, please feel free
to contact Mr. Jarrod Buchanan, South Cary WRF Plant Manager at 919-779-0697
([e-mail]).
CARP! UTILITIES

Sincerely,
mie Revels, P.E.
Utilities Director
Cc: Josh Cummings, SCWRF Facilities Operation Supervisor, ORC
Donald Smith, Wastewater Collections Program Manager
Jarrod Buchanan, PE, SCWRF Manager
Corrie Bondar, PE, Assistant Utilities Director
CARY