NC0085812_Grassy Branch QUALK2K model_20200807

Strickland, Bev
From: Behm, Pamela
Sent: Friday, August 7, 2020 12:17 PM
To: Hill, David A
Cc: Basinger, Corey; Hennessy, John; Denard, Derek; Scheller, Roberto; Montebello,
Michael J; Kebede, Adugna; Hong, Bongghi
Subject: Re: Grassy Branch QUALK2K model
Attachments: Rocky River discussion.docx
David,
Please see attached. It is important that we consider the Rocky River holistically. We have some concerns
given that we have not seen this level of interest in expansions to one waterbody in such a short amount of
time from different municipalities. What is not being addressed is any analysis of the increase in nutrient
loading to this waterbody based on these expansions, which is already experiencing some of the highest
nutrient concentrations in the basin. This is not being done because we don't have nutrient water quality
standards. It is expected down the road (no idea on timeframe) that we will have nutrient limits in place when
the NCDP process gets to flowing waters. I would think it would be prudent for all of these discharges to
include the need for future nutrient removal in their long term planning and designs for new facilities.
The attached describes all of the current expansion requests, a description of the current models available and
finally, modeling recommendations we would make to evaluate a new Crooked Creek facility.
Thanks,
Pam
From: Hill, David A <[e-mail]>
Sent: Monday, July 27, 2020 4:57 PM
To: Behm, Pamela <[e-mail]>
Cc: Basinger, Corey <[e-mail]>; Hennessy, John <[e-mail]>; Denard, Derek
<[e-mail]>; Scheller, Roberto <[e-mail]>; Montebello, Michael J
<[e-mail]>
Subject: Grassy Branch QUALK2K model
Hello Pam,
Union County is looking into an additional option while they pursue the SOC for the Grassy Branch plant that
your unit reviewed the QUAL2K for. They are considering building a new regional plant that will take the flow
from Grassy Branch and the Crooked Creek plant upstream of it thereby replacing both of those plants. Details
are vague at the moment but it looks like the new discharge would be on Crooked Creek near the Grassy
Branch plant. Our question is, do you think the existing model they have would be 'easily' modifiable to
account for this new discharge scenario? Crooked Creek is roughly 12 miles above my best guess of where the
discharge will be so my biggest concern is will that increase BODu loading to the Rocky River and will the
model need to be extended into the Rocky? If it needs extended, would the Mallard/Muddy Creek QUAL2K be

able to model the increased loading where Crooked Creek enters the Rocky with minimal modification? This
option would also require the county to make a quick decision on purchasing property on which to build the
new plant so our other question, and assuming the county/consultants can get their ducks lined up fast
enough with changing the model, how long would your unit take to review the new model?
Thanks,
David Hill
Environmental Specialist II
"Email preferred during this State of Emergency"
NC DEQ / Division of Water Resources / Water Quality Permitting
NPDES Industrial Permitting, Wastewater Branch
919 707 3612 office
919 707 9000 main office
david.hilla-ncdenr.gov
Physical Address: 512 North Salisbury St.,Raleigh, NC, 27604
Mailing Address: 1617 Mail Service Center, Raleigh, INC, 27699-1617
Email correspondence to and from this address is subject to the
North Carolina Public Records Law and may be disclosed to third parties.

Rocky River (Yadkin RB) — 2020 NPDES Summary
Recent requests for new and expanding wastewater plants along Rocky River (Yadkin):
1. Mallard Creek WRF from 12 MGD to 16 MGD (first discharges to Mallard Creek)
2. Muddy Creek WWTP from 0.3 MGD to 1 MGD
3. Grassy Branch WWTP from 0.05 MGD to 0.12 MGD (first discharges to Crooked Creek)
4. A new wastewater treatment facility discharging to Crooked Creek (being considered but no
official request submitted yet)
5. West Stanly WWTP planning an expansion from 0.9 MGD (discharging to Rocky River near Long
Creek confluence)
6. City of Locust is currently sending its wastewater to West Stanly WWTP but looking for an
alternative (i.e., direct discharge to Rocky River)
Models developed for the Rocky River and tributaries include:
Rocky River QUAL21K Model
DWR currently has a QUAL21K model simulating dissolved oxygen (DO) in Rocky River, developed
for Charlotte Water per Mallard Creek WRF expansion request. Some relevant river milepoints in the
model are (from the downstream end):
• Mallard Creek: 54.6 mi
• Muddy Creek: 30.0 mi
• Crooked Creek: 23.8 mi
• Long Creek: 8.2 mi
• Lane Creek (most downstream tributary): 0.2 mi
Because the model was developed to simulate Mallard Creek WRF expansion scenarios, there appears
to be relatively higher degree of confidence in the upstream areas. Model uncertainty may increase as it
gets closer to the downstream areas. Some factors potentially contributing to the downstream
uncertainty are:
The current model may not include all the wastewater plants in the downstream area. For
example, West Stanly WWTP, which discharges to the Rocky River around the confluence with
Long Creek, is not explicitly included in the model.
The downstream end of the model is not the end of Rocky River (i.e., Rocky River -Pee Dee River
confluence). The model ends at about 0.2 miles downstream from the Lane Creek confluence,
where the USGS station 02126000 is located. At about 2 miles downstream from the Lane Creek
confluence, there is an ambient monitoring station (Q9120000) that is not covered by the
current QUAL21K model.
Crooked Creek QUAL21K Model
The Division of Water Resources (DWR) Modeling and Assessment Branch completed review of the
Crooked Creek QUAL21K modeling study in September 2019. Union County Public Works is currently in
the process of submitting an SOC application for the Grassy Branch WWTP located 6.7 miles upstream of
Crooked Creek's confluence with Rocky River (Figure 1). Data collected from three field trips in the
summer of 2016 were used for the calibration and corroboration of the model, along with other sources

(DMR, AMS, etc.). The work is generally of high quality. Most of the parameter choices are backed up by
the data or otherwise justified. No inconsistency was found between the report and model contents.
The reported simulation results suggest, and are supported by field measurements, that DO may be
under severe depletion around and upstream of Beaver Dams area (Figure 1). It appears safe to assume
that there is no or little assimilative capacity left from the headwaters of North Fork Crooked Creek
(upstream of the South Fork confluence) down to the Highway 601 crossing. DO in Crooked Creek starts
to recover from the Highway 601 area and becomes around 6 mg/L when discharged to Rocky River. The
water quality condition at the end of Crooked Creek, and its potential impact downstream of Rocky
River confluence, will need to be carefully considered in the subsequent scenario analyses.
Again, these simulations are based on surveys made in the summer of 2016. Of particular concern is that
critical condition was not yet assessed in this work, and no model run was made under the permitted (as
opposed to actual) discharges. Simulated flow at the Crooked Creek -Rocky River confluence was about 4
cfs. Subtracting point source contributions, the natural flow might have been around 2.5 cfs at the time
of field surveys. It represents a low -flow condition, though still higher than the critical 7Q10 condition
(about 0.2 cfs, or as low as 0 cfs, as estimated by USGS).
Also as a reminder, the Complex Permitting Branch asked to include NCO088838 (Radiator Specialty
Company) in the model, a groundwater remediation system permitted at 0.09 MGD discharging to an
unnamed tributary of South Fork Crooked Creek.
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Crooked Creek QUALM Dissolved Oxygen Simulations
(Based on Actual Discharges)
d
N V
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v N O m
Q U U O
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V j OD
O 2
—Calibration Run (8/24/2016)
Beaver Dams —Corroboration Run (9/14/2016)
DO Standard
21 18 15 12 9 6 3
River Mile
Figure 1. Crooked Creek dissolved oxygen simulation results. Wastewater discharges used in the
simulations were obtained from DMR data: Hemby Acres WWTP at 0.09 MGD (permitted at 0.3 MGD);
Crooked Creek #2 WWTP at 0.83 MGD (calibration run) or 0.87 MGD (corroboration run) (permitted at
1.9 MGD); Grassy Branch WWTP at 0.04 MGD (permitted at 0.05 MGD).
PA
C

Evaluation of Proposed New WWTP Discha
A proposed new WWTP is under consideration by Union County that would discharge into Crooked
Creek. This plant would combine the existing Grassy Branch and Crooked Creek WWTPs and take them
offline. The Modeling and Assessment Branch has been asked to comment on what would be needed to
evaluate the impacts of the proposed facility.
Both the Crooked Creek and Rocky River Qual2K models will need to be modified by the discharger's
consultant. The Modeling and Assessment Branch should be sent a modeling plan for evaluation prior
to the project to ensure all concerns will be addressed. This will greatly improve the review turnaround
time by the Modeling and Assessment Branch.
For Crooked Creek Qual2K:
The model needs to include NC0088838 (Radiator Specialty Company) as discussed above.
Model scenarios will need to be developed to compare the current discharges and the
proposed new discharge under 7Q10 conditions at full permitted loading. Of particular
interest is an analysis of any resulting increases in loading to the Rocky River.
For Rocky River Qual2K:
1. Due to Crooked Creek entering the Rocky River approximately 24 miles upstream of the
model endpoint, it is not likely that the model will need to be extended further downstream
for this analysis.
2. A model scenario will need to be run to incorporate the change in loading that is expected
from the new discharge and the distance until DO recovers and returns to upstream
conditions.
3. All direct discharges need to be included at either full permitted flow or at the requested
expansion requests shown above for Mallard and Muddy Creeks WWTPs. West Stanley
WWTP Outfall 002 needs to be incorporated into the model as discussed above.