NC0069841_Report_20240113 (2)

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UNION
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December 11, 2023
Mr. Michael Montebello
NPDES Program Branch Chief
Division of Water Resources
Water Quality Permitting Section - NPDES
1617 Mail Service Center
Raleigh, North Carolina 27699-1611
Re: Division of Water Resources (DWR) Modeling Report Review dated 10/25/23
Crooked Creek Water Reclamation Facility
NDPES Permit No. NC0069841
Dear Mr. Montebello:
We have received your Modeling Report Review correspondence with respect to Union County's
Request for Speculative Limits for the new Crooked Creek Water Reclamation Facility (CCWRF)
submitted on January 4, 2023. After careful review of the information and considerations in your
letter with our consultants Black & Veatch and Tetra Tech, we would like to request a meeting with
the appropriate Division of Water Resources (DWR) staff to discuss your considerations, our
thoughts, and discuss the path forward.
A few of our initial thoughts for the discussion include:
• We are unfamiliar with the "natural condition study and evaluation" referred to in your
letter and would like to discuss.
We would like to discuss your considerations for why the modeling should be based on
physical properties of the stream from approximately seven years ago as you feel it would
be reasonable to assume those conditions will return in time. We haven't seen any return in
the two recent field assessments in recent years, nor have indications it may return so
would like to discuss that assumption.
• We understand your thoughts regarding the reaeration factor and our consultant would like
to discuss the rationale utilized to clarify their approach and discuss.
We would like to discuss the outfall location recommendation you provided and discuss our
thoughts on the current location. While further downstream may appear to predict higher
DO in Crooked Creek, we also understand the importance of water quality in the Rocky
River equally as much as water quality in Crooked Creek. An outfall location further
upstream allows for more assimilation of bioavailable phosphorus and nitrogen by tree
roots, rooted vegetation, and substrate microorganisms.
Union County Water
500 North Main Street, Suite 600
Monroe, NC 28112
T 704.296.4210
unioncountync.gov/water

There are also siting considerations we can discuss that could require an extended outfall
for a downstream discharge which poses additional potential environmental impacts and
long-term maintenance.
Upon your concurrence, Union County Water and our consultants will meet with you at your offices
at your earliest convenience. Please feel free to contact us or coordinate a meeting through our
Planning and Resource Management Director, Aubrey Lofton. Her contact information is below:
Aubrey Lofton
Union County Water
Planning and Resource Management Director
Phone: [phone]
Email: aubrey.lofton@unioncoun , nc.gov
Kindest Regards,
.lan Matthews
County Manager
Enclosure
cc: Union County Water
Hyong Yi - Administrator, hyong.yi@unioncoun , nc.gov
John Shutak - Engineering Division Manager, john.shutak@unioncoun . nc.gov
Aubrey Lofton - Planning and Resources Management Director,
aubrey.lofton@unioncoun , nc.gov
Chris Clark - Operations Director, [e-mail]
Black & Veatch
Kent Lackey, [e-mail]
Chris deBarbadillo, [e-mail]
Tedderfarm Consulting
Steve Tedder, tedderfarmconsulting(a gmail.com
DWR
Pam Behm, [e-mail]
Adugna Kebede, [e-mail]
Bongghi Hong, [e-mail]
Doug Dowden, [e-mail]
Kristin Litzenberger, [e-mail]
Nick Coco, [e-mail]
Nora Deamer, [e-mail]
Michelle Raquet, [e-mail]
Julie Grzyb, [e-mail]
MRO
Andrew Pitner, [e-mail]
Roberto Scheller, [e-mail]
unioncountync.gov/water

DocuSign Envelope ID: 075FFFOD-DDA1-4BC5-B601-A6BA5CF9A589
ROY COOPER
Governor
ELIZABETH S. BISER
Secretary
RICHARD E. ROGERS, JR.
Director
Brian Matthews, County Manager
Planning & Resource Management Director
500 N. Main St., Suite 70
Monroe, NC 28112
Dear Mr. Matthews:
NORTH CAROLINA
Environmental Quality
October 24, 2023
Subject: Modeling Report Review
Crooked Creek WRF
NPDES Permit No. NCO069841
Union County
Yadkin -Pee Dee River Basin
At the request of the NPDES Permitting Branch, the Modeling and Assessment Branch (MAB) staff reviewed the
Crooked Creek report and associated modeling files, provided in March 2023 by Union County. This request was
based upon Union County's proposal to build a facility, Crooked Creek WRF (CCWRF) with proposed discharge
to North Fork Crooked Creek approximately 3.5 miles downstream of the existing Crooked Creek #2 WRF
(CC2WRF).
On July 13, 2021, DWR provided speculative limits for a new facility, Lower Crooked Creek WRF (LCCWRF),
discharging close to Crooked Creek's confluence with Rocky River.
Below are considerations pertaining to Union County's new request (building CCWRF), of which both permitting
and the Planning Section have concerns with the impacts to Crooked Creek compared to the previous alternative
of discharging closer to the confluence with the Rocky River. These considerations are based upon the data
provided by Union County.
One significant issue is that the predicted dissolved oxygen (DO) downstream of the proposed CCWRF
falls below 5 mg/L. According to the modeling report, the minimum summertime DO between the South
Fork Crooked Creek confluence and the Highway 601 crossing (referred to as "Old Debris Dams") was
predicted to be 3.9 mg/L under the CCWRF's maximum permitted discharge scenario (we have additional
concerns with this model estimate discussed below). Originally the predicted DO stays above 5 mg/L
downstream of the approved LCCWRF speculative limits until Crooked Creek's confluence with Rocky
River. The updated report proposes to evaluate the revised discharge impact based on House Bill 219 (i.e.,
not changing the dissolved oxygen concentration by more than 0.10 mg/L). However, the waterbody is
not classified as a swamp nor has there been a natural condition study and evaluation.
2. Several changes were made to the QUAL2K model from the version used for the LCCWRF approval.
According to the report, debris dams above Highway 601 are "no longer present, likely washed out in
major stormflow events". The model was recalibrated to reflect this change: channel bed slope was
increased from 0.0006 to 0.001, and Manning's roughness coefficient was decreased from 0.6 to 0.45. If it
takes major washout events to clear the debris, it would be reasonable to assume that the previously
sluggish conditions will return with time. The version used for the LCCWRF approval is as valid as the
North Carolina Department of Environmzntal Quality I Division of Water Resources
512 North Salisbury Street 1 1617 Mail Service Center I Raleigh. North Carolina 27699-1617
;ARO INA Qprllly, 919.707.9000
Oeparlment of FnHrombntal

DocuSign Envelope ID: 075FFFOD-DDA1-4BC5-B601-A6BA5CF9A589
recalibrated model without any active management plan in place. Setting these two parameters back to
their original values, the predicted minimum summertime DO in the debris dam area under the CCWRF's
maximum permitted discharge scenario would become 3.0 mg/L instead of 3.9 mg/L as cited above.
The report states that, when running the CCWRF discharge scenarios, all model inputs except for the
meteorological and boundary conditions were held constant from the recalibrated model. However, upon
examination of the modeling files it was found that reaeration values were entered manually during the
scenario runs, overriding the reaeration calculated by the recalibrated model. As a result, the CCWRF
discharge scenarios are running with reaeration rates about 2 times higher than what would have been
otherwise. The validity of this approach could not be determined since no documentation was provided in
the report. Once a model is calibrated, it is unconventional to alter model formulations during the scenario
evaluation phase, especially for sensitive parameters like reaeration. (The approved LCCWRF scenario
runs were made based on the reaeration rates calculated by the model.) Without manually overriding the
reaeration values, the predicted minimum summertime DO in the debris dam area under the CCWRF's
maximum permitted discharge scenario would become 0.7 mg/L to 2.2 mg/L depending on the debris
condition.
4. One of the issues examined during the review process was whether the construction of CCWRF can be
viewed as an expansion of the existing CC2WRF. One could ask if replacing CC2WRF with CCWRF
would result in a net increase of the stream DO under the critical condition. However, constructing
CCWRF (and consolidating wasteflow from CC2WRF) appears to make the predicted DO in the debris
dam area lower. One reason could be that, because CC2WRF is further upstream from the debris dam
area, the oxygen consuming substances in the wastewater would have more time to be processed before
they flow past the South Fork Crooked Creek tributary. Based upon the information provided the
proposed CCWRF location appears too close to this area for stream processing to happen on the way.
We recommend that Union County evaluate the option of moving the outfall closer to the confluence with the
Rocky River (as was proposed and already given speculative limits for LCCWRF). This location would alleviate
the concerns expressed above with both model scenarios and the physical characteristics of Crooked Creek.
Regardless of the result of this analysis, before any speculative limits can be provided, the final version of the
Rocky River model is needed. The final model is necessary to run scenarios to ensure that the discharge changes
in Crooked Creek do not further impact water quality conditions in Rocky River.
Please let us know if you have any questions regarding these comments. Should you have any questions, please
feel free to contact Derek Denard at [phone] / derek.denard n,deq.nc.gov or Doug Dowden at (919) 707-
3605 / doug.dowdenAdeq.nc.gov.
Respectfully,
DocuSigned by:
Eam. N�
1A64531431644FE...
Michael Montebello
NPDES Program Branch Chief
cc: NPDES Files [Laserfiche]
Union Couty / Brian Matthews[[e-mail]]; Aubrey Lofton[[e-mail]]
Andrew Neff [[e-mail]]; Hyong Yi, A [[e-mail]];
John Shutak [e-mail]]
Black & Veatch / Kent Lackey [[e-mail]]; Morgan Young [[e-mail]]
Tedderfarm Consulting / Steve Tedder[[e-mail]]
DWR / Pam Behm [pamela.behm@ deq.nc.gov]; Adugna Kebede [[e-mail]];
Bongghi Hong [[e-mail]]; Doug Dowden [doug.dowden@ deq.nc.gov];
Kristin Litzenberger[[e-mail]]; Nick Coco [[e-mail]];
Nora Deamer [[e-mail]]; Michelle Raquet [[e-mail]]
MRO / Andrew Pitner [[e-mail]]; Roberto Scheller [[e-mail]]
North Carolina Department orEm ironmental Quality I Division of Water Resources
D E Q�� 512 North Salisbury Street 1 1617 Mail Service Center I Raleigh, North Carolina 27699-1611
nxrn aaacx.iru 919.707.9000
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