NC0069841_Basis for Speculative Limits Tech Memo_20221117

TETRA TECH 4000 Park Drive,suite 200•PO Box 14409
Research Triangle Park, NC 27709
Tel [phone]•Fax [phone]
MEMORANDUM
To: Aubrey Lofton (Union County) Date: November 17, 2022
Andrew Neff(Union County)
Cc: Kent Lackey (Black&Veatch) Subject: Basis for Speculative Limits for
the Proposed Crooked Creek
From: Trevor Clements, Hillary Yonce Water Reclamation Facility
1.0 INTRODUCTION
This technical modeling memorandum is intended to support the Union County Water(UCW) plan to
construct a new wastewater reclamation facility (WRF) that would discharge effluent to North Fork
Crooked Creek, referred to herein as the Crooked Creek WRF (CCWRF). Assimilative capacity of the
receiving water was assessed using an existing Crooked Creek QUAL2K model that was calibrated and
corroborated (Tetra Tech, 2019a), with development and documentation reviewed and approved by the
North Carolina Division of Water Resources (DWR, 2019). Union County first applied the Crooked Creek
QUAL2K model to support the County's request for interim effluent limits for the Grassy Branch facility
(NPDES Permit No. NC0085812) under a Special Order by Consent (SOC) along with modified final
permit limits to reflect plant improvements (Tetra Tech, 2019b). Union County has further directed that the
model be applied to develop a speculative wasteload allocation for a proposed new facility to be located
immediately downstream of Ridge Road, approximately 3.5 miles downstream of the existing Crooked
Creek#2 (CC2)WRF discharge (National Pollutant Discharge Elimination System [NPDES] Permit No.
NC0069841) (Figure 1).
Union County proposes to construct the CCWRF in stages based on two increasing flow tiers over time:
• Stage 1: effluent discharge limit 6.0 MGD
• Stage 2: effluent discharge limit 12.0 MGD
With this staged approach, Union County will also be consolidating wasteflow from CC2 WRF as well.
The proposed CCWRF outfall location is approximately 2.7 miles upstream of the confluence of the North
and South Forks of Crooked Creek.
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
Rocky River
Grassy
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Proposed Crooked Creek WRF
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Q Existing Outfall
Proposed Outfall
Crooked Creek Watershed N 0 r 2 4 River/Stream
TETRA TECH Existing and Proposed Outfalls Kdemeters
NAo_1ea�s�aiepia�e Nonn_ca�oo�a rips_�zoo_reai A 0 1 2 Nliles Q Watershed Boundary
Map DotlucsE t1-tit-30]3.N Yoiwe
Figure 1. Crooked Creek Watershed with Existing and Proposed Facility Outfall Locations.
2.0 REFINEMENT OF • •
The existing QUAL21K model for Crooked Creek was calibrated and corroborated based on existing
conditions observed during summer 2016 and approved by DWR in 2019. Since that time, additional field
work was conducted to further confirm the veracity of the model to simulate updated existing conditions in
2022, particularly in the vicinity of the debris dams previously documented upstream of Highway 601.
During late summer 2021, a field crew walked approximately 3.5 miles from Lawyers Road to Highway
601 and found that the previously observed and modeled large debris dams above Highway 601 were no
longer present, likely washed out in major stormflow events. The following summer in 2022, a synoptic
survey of dissolved oxygen (DO) concentrations and flow velocity measurements were conducted along
that same stretch to verify the improvements to water quality every 1000 feet. Additionally, DO
measurements were conducted at every road crossing (eleven stations in total)twice during the summer,
and flow measurements were made at key sites. Observations were conducted under reasonably dry,
low-flow conditions based on tracking local flow and weather data, June 13 —September 27, 2022. All
data collected along Crooked Creek during summer 2022 are provided in Appendix A.
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
Field measurements from summer 2022 were compared both to the 2016 observations and to the
calibrated model results to ensure reasonable accuracy in simulation of updated existing conditions. Flow
conditions during field survey were lower in 2022 than in 2016, so the data were very useful for evaluating
existing water quality profiles in Crooked Creek.
It was apparent that the physical channel changes that occurred since 2016 upstream of Highway 601
resulted in a small but noticeable improvement in water quality. Two model refinements were conducted
to best simulate existing conditions and prepare the model for scenario application of the CCWRF
discharge. The hydraulic parameterization was refined for the model reach from South Fork Crooked
Creek and Highway 601 to capture the observed improvement through that stretch. Because DO
concentrations were higher along this reach but still show signs of low-velocity zones, channel bed slope
was increased from 0.0006 to 0.0010, and Manning's roughness coefficient was changed from 0.60 to
0.45, changes which represent about 50% improvement in DO concentrations in that region, capturing the
observed data range. Additionally, the existing model reach from the CC2 discharge to the South Fork
Crooked Creek confluence was split into two reaches at the location of the new proposed CCWRF
discharge location for model application scenarios. Model results prior to recalibration of this reach are
shown in Figure 2 with black lines, while model results after recalibration of this reach are shown with red
lines, all relative to summer 2022 observations from before noon (open blue circles), and after noon (solid
blue circles).
Rocky River 10
Hemby WWTP CC2 WWTP SF CCTrib Grassy WWT j O Confluence
i I
O 1 Old Debris Dams ��_---�—_—_--_-- 8
/ .� I • Q 0 q�,y/ . 6
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Distance from outlet(miles)
O 2022 Data AM • 2022 Data PM —Simulated Mean-Updated
———Simulated Min/Max-Updated —Simulated Mean ———Simulated Min/Max
Figure 2. Crooked Creek QUAL2K calibrated model results for DO relative to summer 2022 observations,
with and without modification of the old debris dam reach.
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
3.0 QUAL2K MODEL ' ' •
North Carolina Water Quality Regulations (15A NCAC 02B .0206) specify that water quality standards
related to oxygen-consuming wastes be protected using the minimum average flow for a period of seven
consecutive days that has an average recurrence of once in ten years (7Q10 flow). NC regulations (15A
NCAC 02B .0404) also provide for seasonal variation for the discharge of oxygen-consuming wastes, with
the summer period defined as April through October and winter period as November through March.
Additionally, all existing permitted wasteload allocations (WLAs) must be accounted for to evaluate
available assimilative capacity for a speculative WLA for the proposed CCWRF.
Set-up of the refined calibrated Crooked Creek QUAL21K model for evaluating impacts under seasonal
critical conditions for a speculative WLA is documented below.
3.1 SIMULATING CRITICAL CONDITIONS
3.1.1 Low Flow Statistics
The United States Geological Survey(USGS) provided 7Q10 estimates for multiple locations in Crooked
Creek based on a watershed drainage area relationship of 0.001 cubic feet per square mile (cfsm)
derived from the nearby Richardson Creek and Crooked Creek monitoring data (USGS, September 2019
via email correspondence with Curtis Weaver; based on Weaver and Fine 2003; 2012). The USGS winter
7Q10 estimate was one order of magnitude greater, at 0.01 cfsm. The 7Q10 flow estimates at Highway
601 and NC Highway 218 are 0.037 cfs and 0.044 cfs respectively for summer, and 0.371 cfs and 0.444
cfs respectively for winter. Applying this drainage-area based 7Q10 relationship, flow was calculated at
the model boundary inputs for the Crooked Creek QUAL21K model
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
Table 1). Based on the tributary inflows and the two instream estimates provided by USGS, a simple flow
balance equation was used to estimate the amount of flow entering the stream via diffuse baseflow
(Figure 3).
The drainage area at the proposed new outfall location immediately downstream of Ridge Road is 15.4
square miles, which was used to calculate the following low-flow statistics at that location, as confirmed
by USGS (August 2022 via email correspondence with Curtis Weaver; Appendix B):
• Annual 7Q10 low-flow discharges: average 0.02 cfs, median 0.00 cfs (zero 7Q10)
• Annual 30Q2 low-flow discharges: average 0.25 cfs, median 0.23 cfs (non-zero 30Q2)
• Winter 7Q10 low-flow discharges: average 0.15 cfs, median 0.14 cfs
• Annual 7Q2 low-flow discharges: average 0.11 cfs, median 0.14 cfs
• Average annual discharge discharges: average 13.7 cfs, median 13.9 cfs
Based on these statistically derived flow conditions, Crooked Creek is considered to have a zero 7Q10
flow condition, and a non-zero 30Q2 flow condition. The NPDES permitting policy as documented in the
NC DWR 1999 "Zero Flow Policy" indicates that new discharges under these specific flow conditions are
subject to unique regulations for effluent limitations, discussed further in Section 4.0.
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
Table 1. Estimated 7Q10 flow tabulated for boundary conditions of Crooked Creek.
Drainage Area Summer7Q10 Winter 7Q1
Boundary Condition (Mi2) Flow(cfs) Flow(cfs)
Headwater 7.4 0.007 0.074
South Fork Crooked Creek (SF CC)tributary 18.4 0.018 0.184
Grassy Branch tributary 3.8 0.004 0.038
Diffuse Flow 1: Headwaters to Highway 601 N/A 0.011 0.113
Diffuse Flow 2: Highway 601 to NC Highway 218 N/A 0.004 0.035
Diffuse Flow 3: NC Highway 218 to Outlet N/A 0.006 0.059
Headwater Inflow
Summer 7Q10:0.007 cfs
Winter 7Q10:0.074 cfs
Diffuse Inflow 1
�— Summer 7Q10:0.011 cfs
SF CC Tributary Winter 7Q10:0.113 cfs
Summer 7Q10:0.018 cfs
Winter 7Q10:0.184 cfs
Highway 601 instream flow
Summer 7Q10:0.037 cfs
Winter 7Q10:0.371 cfs
Grassy Branch Tributary Diffuse Inflow 2
Summer 7Q10:0.004 cfs f Summer 7Q10:0.004 cfs
Winter 7Q10:0.038 cfs Winter 7Q10:0.035 cfs
NC Highway 218 instream flow
Summer 7Q10:0.044 cfs
Winter 7Q10:0.444 cfs
Diffuse Inflow 3
�—Outlet instream flow Summer 7Q10:0.006 cfs
Summer 7Q10:0.050 cfs Winter 7Q10:0059 cfs
Winter 7Q10:0.503 cfs
Figure 3. Crooked Creek QUAL2K model 7Q10 flow balance schematic diagram.
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
3.1.2 Modified Seasonal Inputs
The summer and winter periods are identified (per 15A NCAC 02B .0404) in the existing permit as April 1
to October 31, and November 1 to March 31 respectively. The seasonal critical conditions simulation for
summer and winter involved the following key difference relative to the calibration model:
• Modification of simulation date based on warmest summer month or warmest winter month for
water temperature, and associated meteorological inputs modified based on new simulation date
• Modification of boundary conditions (headwaters and tributaries) based on:
o Flows to represent critical seasonal 7Q10 conditions instream
o Water temperature to represent critically warm summer or winter conditions
o DO concentrations to represent median DO saturation observed during critically warm
summer or winter conditions
• Diffuse inflow conditions were parameterized identically to the headwater boundary conditions
All other model inputs were held constant from the calibration model for the summer critical conditions
simulation. For the winter critical condition simulation, stream shade conditions were decreased by half
from 70 percent to 35 percent relative to summer conditions to simulate the impact of winter leaf-fall.
Warmest summer water temperatures occur in July based on instream water quality data sampling
conducted by the Yadkin Pee Dee River Basin Association (YPDRBA) at four sites along Crooked Creek.
To parameterize the boundary conditions (headwater, diffuse flow, and tributary inflow), a statistical
analysis was conducted on observed instream data measured immediately upstream of the Hemby Acres
WWTP. This upstream location is the only water quality sampling site in the basin which is not influenced
by an upstream effluent discharge. The 75th percentile water temperature of all measurements at this
location (2014—2019) during the month of July was 25.0 °C. The median DO saturation observed during
all July measurements of both temperature and DO at this location was 58 percent. Applying 58 percent
DO saturation to the water temperature of 25.0 °C results in a boundary condition DO concentration of 4.8
mg/L, which was rounded up to 5.0 mg/L to be applied to the headwaters, diffuse, and tributary inflows as
representative of these inputs likely being at the water quality standard under natural conditions.
QUAL2K requires assignment of a simulation date to support meteorological conditions. The 751h
percentile water temperature of 25.0 °C is similar to the average water temperatures observed in July
2015, so the summer critical simulation date was selected as July 15, 2015. Model inputs for hourly air
and dew point temperatures were pulled from this new simulation date from the same gage as was used
for the calibration and corroboration model setup (KNCUNION2 at Campobello Drive). Average air and
dew point temperatures on July 15, 2015, were 29.9°C (85.8 IF) and 19.3 °C (66.7 IF) respectively.
Critical winter conditions for water temperature were estimated for boundary conditions using the period
of record of instream YPDRBA water quality data. On average, the warmest winter water temperatures
occur in the month of November. Water temperature inputs for boundary conditions (headwaters,
tributaries, and diffuse inflow)were developed based on the 75th percentile of all observed water
temperature results in the period of record for the instream water quality sampling site located
immediately upstream of Hemby Acres WWTP. The result of this analysis is 13.4 IC, which was applied
to all winter critical condition boundary inputs. The median DO saturation observed during all November
measurements of both temperature and DO was 67 percent. Applying 67 percent DO saturation to the
water temperature of 13.4 °C results in a boundary condition DO concentration of 7.0 mg/L.
Based on the critical warm water temperature analysis for the month of November, the simulation date
was selected to be the first of November. The simulation date was selected to be November 1, 2015 as
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
the summer critical condition was also chosen for the year 2015. Meteorological inputs for hourly air and
dew point temperatures were pulled from station KNCUNION2. Average air and dew point temperatures
on November 1, 2015, are 15.5 °C (59.9 IF) and 13.8 °C (56.9 IF) respectively.
3.2 PERMITTED DISCHARGE ASSUMPTIONS
There are three permitted wastewater treatment facility outfalls located along Crooked Creek modeled
explicitly: Hemby Acres WWTP which is operated by Carolina Water Services Inc., and CC2 and Grassy
Branch WWTPs which are both operated by Union County. For model application scenarios, inputs were
based on permitted effluent limits. Calibration model inputs were held constant for non-permitted
constituents (e.g., inorganic and organic phosphorus)for these simulations.
Existing permit limits for the three outfalls along Crooked Creek vary seasonally and by facility for
constituents of DO, five-day biochemical oxygen demand (BOD5), total suspended solids (TSS), and
ammonia (NH3) (Table 2). Proposed permit limits associated with the CCWRF were approximated first to
be equal to those for CC2, and final proposed speculative permit limits are suggested based on modeling
results. As in the calibration and corroboration model setups, TSS is simulated conservatively as
inorganic suspended solids since organic solids are captured through the simulation of BOD5 as ultimate
labile carbonaceous BOD (CBODfast).
For the seasonal simulations, the water temperature associated with each effluent outfall was developed
using the average observed July or November water temperature for 2015. Summer water temperature
inputs for Hemby Acres, CC2, and Grassy Branch were set to 25.9 °C, 26.3 °C, and 25.7°C respectively.
Winter water temperature inputs for the three were set to 14.4 °C, 18.2 °C, and 15.9°C respectively.
Water temperatures associated with CCWRF were set identically to CC2.
Table 2. Existing point source permit limits for water treatment facilities along Crooked Creek.
NPIDES ID Facility Season Flow BOD5 NH3 DO TSS
NCO035041 Hemby Summer 0.3 9 3.0 >_ 5 30
Acres Winter 15 8.0
NCO069841 Crooked Summer 19 5 1.0 6 30
Creek#2 Winter 10 1.9
NCO085812A Grassy Summer 0.12 5 1.0 , 6 30
Branch Winter 10 2.0
A: Note that from a recently approved SOC analysis, Grassy Branch WWTP increased its flow from 0.05 MGD to 0.12
MGD. Associated water chemistry limits are also based on final limits associated with the SOC.
Note that there is one other permitted discharge for groundwater remediation located near the
headwaters of the South Fork Crooked Creek. This permittee (NPDES ID NC0088838)for the Radiator
Specialty Company has a maximum permitted discharge limit of 0.09 MGD and monthly water quality
limits for the effluent are associated with TSS (30 mg/L), with additional daily maximum limits for a
number of pollutants such as tetrachloroethene, vinyl chloride, and dioxane. Although this discharge is
located far upstream along the South Fork Crooked Creek, the point source was included explicitly in the
model at the outlet of South Fork Crooked Creek into the mainstem at permit limits for flow and TSS.
Model parameterization for temperature and DO were set equal to those of the South Fork Crooked
Creek tributary.
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
4.0 MODEL SCENARIOSAND RESULTS
The approved calibration model setup for Crooked Creek was used to simulate critical conditions and
verify whether the proposed CCWRF speculative permit limits meet existing requirements for North
Carolina related to instream water quality. The following rules and regulations are applicable to the
CCWRF model scenarios:
1. Per 15 NCAC 02B.0404, "Water Quality Based Effluent Limitations", speculative effluent limits
must be proposed for both summer and winter discharge periods.
2. Per 15 NCAC 02B.0206 "Flow Design Criteria for Effluent Limitations", seasonal low flow
conditions must be established through consultation with USGS.
3. Per NC DWQ developed "Zero-Flow Policy" (May 12, 1999), new and expanding NPDES
discharges to zero-flow streams (7Q10=0; 30Q2>0), Regulation 2B .0206 sets effluent limitations
at BOD5 at 5.0 mg/L, NH3-N at 2 mg/L, and DO at 6 mg/L unless otherwise determined to be
protective of water quality standards.
4. Per 1990 EPA guidance, NC DWQ developed an "Ammonia Toxicity Policy" (May 12, 1999),
instream ammonia concentrations must not exceed 1.0 mg/L in summer and 1.8 mg/L in winter
downstream of a proposed NPDES discharge under seasonal low flow evaluations.
5. Per House Bill 219 of the General Assembly of North Carolina, effective June 30, 2022, for new
or expanding wastewater discharge facilities, NC DEQ is authorized to allow limited wastewater
discharge to waters with naturally occurring low DO levels. G.S. 143-215.1 was amended to: "For
surface waters of the State that have naturally occurring low dissolved oxygen levels, as
determined by the Department, permitted wastewater discharges to such surface waters shall not
cause a reduction in the dissolved oxygen levels of such surface waters of more than 0.10 mg/1
below the approved modeled in-stream dissolved oxygen level for the surface waters at total
permitted capacity for all discharges to such surface waters."
To meet these policy guidelines in development of speculative limits for DWR approval, critical low-flow
summer and winter scenarios were applied based on the calibrated QUAL2K model of Crooked Creek,
with dischargers simulated at permitted maximum allowable flow and water chemistry effluent limits.
Speculative limits were developed for CCWRF which are protective of instream ammonia toxicity policies,
adhering to the zero-flow policy limitations, and indicate an instream condition which does not negatively
impact existing background low flow conditions by more than 0.10 mg/L (de minimis impact).
To meet these requirements of North Carolina law, both protecting and enhancing existing water
resources, the following model scenario applications were run (Table 3):
• Summer Critical: 7Q10 low flow summer conditions, no treated effluent dischargers
• Winter Critical: 7Q10 low flow winter conditions, no treated effluent dischargers
• Scenario 1: 7Q10 low flow summer conditions, CCWRF at 6.0 MGD flow, CC2 incorporated
• Scenario 2: 7Q10 low flow winter conditions, CCWRF at 6.0 MGD flow, CC2 incorporated
• Scenario 3: 7Q10 low flow summer conditions, CCWRF at 12.0 MGD flow, CC2 incorporated
• Scenario 4: 7Q10 low flow winter conditions, CCWRF at 12.0 MGD flow, CC2 incorporated
Proposed effluent limits for seasonal flow, BOD5, NH3, and DO for all scenarios reflect values which are
equal to or more stringent than those required under the Zero-Flow Policy in North Carolina.
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
Table 3. Proposed speculative permit limits for treated effluent from CCWRF at Ridge Road, discharging
to the North Fork Crooked Creek.
Scenario Season Scenario Flow Condition BOD5(mg/L) NH3 (mg/L) DO (mg/L)
1 Summer 6.0 MGD with CC2 incorporated 5.0 1.0 6.0
2 Winter 6.0 MGD with CC2 incorporated 5.0 1.8 6.0
3 Summer 12.0 MGD with CC2 incorporated 5.0 1.0 6.0
4 Winter 12.0 MGD with CC2 incorporated 5.0 1.8 6.0
4.1 INSTREAM DISSOLVED OXYGEN RESULTS
Results for both summer and winter seasonal scenarios for flow limits of 6.0 and 12.0 MGD indicate that
the proposed outfall location with associated speculative limits improve water quality conditions instream
relative to the anoxic conditions present and expected in a zero-flow 7Q10 stream (Figure 4, Figure 5).
DO concentrations are predicted to be low in the upper portion of Crooked Creek under the most critical
seasonal conditions due to extreme low flow and physical channel configuration. Similar to impacts of the
currently permitted CC2 discharge, the proposed CCWRF outfall improves instream water quality with a
pulse of treated wastewater at flow volumes high enough to potentially support aquatic ecosystems.
10
Grassy
Grassy Trib 9
Hemby CC2 Proposed SFCC WWT
WWTP WWTP Outfall Trib Old Debris Dams 1
8
1 1 � 7 _
6 u-
E
-----------------------------------50-rg,L O
------------------------- ----------- 5 0
c
4 a,
1 3
I�
a I 2
N
> L C
4. 1
Y O q I \ Z
y y I! -
0
30 25 20 15 10 5 0
Distance from outlet(km)
----WQ$&0 mgA —Summer 6 MGD — —Summer No Outfalls
Summer 12 MGD Upstream of Proposed Outfall
Figure 4. Crooked Creek QUAL2K model results for summer CCWRF scenarios
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
10
Grass,V
CC2 T•ib 9
Hemby WWTP Proposed SFCC — —
WWTP Outfall Trib Old Debris Dams
8
1 1 11
6 E
------------------------------------50 mg/L5 00
C
4
I� 3
I� 2
� I 00
O ~ 1
30 25 20 15 10 5 0
Distance from outlet(km)
----WQ5 5.0 mo —Winter 6 MGD — -Winter No Outfalls
Winter 12 MGD -Upstream of Proposed Outfall
Figure 5. Crooked Creek QUAL2K model results for winter CCWRF scenarios.
4.2 INSTREAM AMMONIA TOXICITY RESULTS
When effluent flows dominate instream conditions, there can be a concern for aquatic life relative to
ammonia toxicity. For low-flow streams, DWR has set forth a policy that ammonia toxicity is defined as
instream concentrations from ammonia exceeding 1.0 mg/L in summer, and 1.8 mg/L in winter. For all
model application scenarios, ammonia toxicity guidelines are not exceeded downstream of the CCWRF
discharge (Table 4).
Table 4. Simulated instream maximum ammonia concentration downstream of CCWRF.
downstreamScenario Scenario Description NH3 maximum
CCWRF (mg/L)
1 Summer; CCWRF at 6.0 MGD with CC2 0.96
incorporated
2 Winter; CCWRF at 6.0 MGD with CC2 1.73
incorporated
3 Summer; CCWRF at 12.0 MGD with CC2 0.98
incorporated
4 Winter; CCWRF at 12.0 MGD with CC2 1.76
incorporated
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Memorandum- Basis for Speculative Limits for Proposed CCWRF November 17, 2022
4.3 RESULTS AT CONFLUENCE WITH ROCKY RIVER
Model predictions of water quality parameters related to oxygen-demanding pollutants and nutrients at
the confluence with the Rocky River (the mouth of Crooked Creek) are provided in Table 5 for both 6.0
and 12.0 MGD flow conditions for CCWRF.
Table 5. Crooked Creek model results at confluence with Rocky River for various flow scenarios.
ConditionsExisting Critical Interim Critical .
QUAL2K Model Conditions (CCWRF 6.0 MGD) (CCWRF 12.0 MGD)
Outputs at
Outlet Summer Winter Summer Winter
Flow(m3/s) 0.01 0.02 0.29 0.30 0.55 0.56
Temperature(°C) 25.20 15.70 25.39 15.85 25.43 15.98
DO(mg/L) 0.00 0.43 7.05 8.26 7.39 8.57
CBODu (mg/L) 40.09 17.59 3.91 2.87 2.17 2.76
NH4(mg/L) 0.01 0.00 0.06 0.07 0.06 0.19
Organic N (mg/L) 0.05 0.08 0.15 0.15 0.10 0.14
NO3(mg/L) 0.00 0.00 10.64 17.02 15.23 20.94
Organic P (mg/L) 0.01 0.01 0.02 0.06 0.02 0.09
Inorganic P(mg/L) 0.00 0.00 1.30 1.34 2.10 2.10
5.0 CONCLUSION
Based on the application of the approved calibrated QUAL2K model, water quality conditions in Crooked
Creek are improved with the addition of the new proposed facility CCWRF immediately downstream of
Ridge Road. The recommended speculative limits include annual BOD5 and DO limits of 5.0 mg/L and 6.0
mg/L respectively, with seasonally variable NH3 limit of 1.0 mg/L in summer and 1.8 mg/L in winter. While
the instream DO water quality standard cannot be maintained in all locations downstream of the
discharge, there is assimilative capacity prior to the confluence with Rocky River, and the added
discharge improves background zero-flow 7Q10 conditions significantly. It is recommended that Union
County request in writing for speculative limits for CCWRF using this memo as justification.
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Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
6.0 RESOURCES
General Assembly of North Carolina. Session 2021. House Bill 219 (Ratified Bill) "Authorize DEQ to Allow
Limited Wastewater Discharge to Waters with Naturally Occurring Low Dissolved Oxygen Levels".
Amendment to General Statute 143-215.1.
https://www.ncleg.gov/Sessions/2021/Bills/House/PDF/H219v4.pdf
North Carolina Administrative Code. Readopted Effective 5/1/2020. 15A NCAC 02B .0404 Water Quality
Based Effluent Limitations. http://reports.oah.state.nc.us/ncac/title%2015a%20-
%20environ mental%20quality/chapter%2002%20-
%20environmental%20management/subchapter%20b/subchapter%20b%20rules.pdf
North Carolina Administrative Code. Readopted Effective 11/1/2019. 15A NCAC 02B .0206 Flow Design
Criteria for Effluent Limitations. http://re ports.oah.state.nc.us/ncac/title%2015a%20-
%20environmental%20guality/chapter%2002%20-
%20environmental%20management/subchapter%20b/subchapter%20b%20rules.pdf
North Carolina Division of Water Quality. Dated 5/12/1999 and 7/10/2009. Ammonia Toxicity Policy.
https://deg.nc.gov/waste-management/dwm/sf/i hs/guidance/am mon iatoxicity-200907l 0-dwq-swp-
npdes/download
North Carolina Division of Water Quality. Dated 5/12/1999 and 7/10/2009. Zero-Flow Policy.
https://files.nc.gov/ncdeg/Water%20Quality/Surface%20Water°/o20Protection/N PDES/GUI DANCE/ZeroFl
ow-20090710-DWQ-SWP-N PDES.doc
Tetra Tech. 2019a. Crooked Creek QUAL2K Model Development; Union County, North Carolina.
Prepared for Union County Public Works, Monroe, NC.
Tetra Tech. 2019b. Crooked Creek QUAL21K Model Application for Grassy Branch WWTP. Prepared for
Union County Public Works, Monroe, NC.
USGS, September 2019 and August 2022 email correspondence with Curtis Weaver, South Atlantic
Water Science Center, Raleigh, NC.
Weaver, J.C., and Fine, J.M. Published 2003, Revised 2012. Low-flow characteristics and profiles for the
Rocky River in the Yadkin-Pee Dee River basin, North Carolina, through 2002: U.S. Geological Survey
Water-Resources Investigations Report 03-4147, 47 p.
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Memorandum- Basis for Speculative Limits for Proposed CCWRF November 17, 2022
APPENDIX . DATA OBSERVATIONS SUMMER 2022
Summary of summer 2022 monitoring data collected along Crooked Creek.
Table 6. Summary of summer 2022 field monitoring data for Crooked Creek, upstream to downstream.
Distance from Date Time D• D• Flow Velocity
Crooked-601 11.0 8/9/2022 10:50 AM 62.0 5.09 - -
Crooked-601 11.0 8/24/2022 10:59 AM 38.6 3.33 - -
Crooked-601 11.0 9/14/2022 3:52 PM 56.6 4.87 - -
Crooked-601 11.0 9/27/2022 1:43 PM 68.4 6.4 2.35 0.059
Crooked-Brief 3.8 6/13/2022 1:33 PM 83.8 6.78 0.77 0.17
Crooked-Brief 3.8 6/20/2022 1:10 PM 85.0 7.46 3.82 0.55
Crooked-Brief 3.8 7/26/2022 11:34 AM 88.8 7.19 4.27 0.32
Crooked-Brief 3.8 7/27/2022 8:45 AM 82.8 6.80 4.36 0.26
Crooked-Brief 3.8 8/4/2022 9:36 AM 80.5 6.59 3.18 0.23
Crooked-Brief 3.8 8/11/2022 11:28 AM 1 107.7 8.88 3.42 0.24
Crooked-Brief 3.8 8/15/2022 1:14 PM 97.1 8.20 0.72 0.06
Crooked-Brief 3.8 8/16/2022 8:37 AM 84.10 7.25 22.81 0.76
Crooked-Brief 3.8 8/24/2022 12:21 PM 86 7.3 2.14 0.1964
Crooked-Brief 1 3.8 8/30/2022 9:46 AM 57.2 4.90 0.63 0.07
Crooked-Brief 3.8 9/14/2022 4:53 PM 85.5 7.43 - -
Crooked-NC218 6.4 8/24/2022 11:34 AM 69 5.91 0.67 0.0549
Crooked N-Fairview 18.3 8/9/2022 9:05 AM 70.5 5.84 - -
CrookedN-Fairview 18.3 8/24/2022 9:40 AM 30.5 2.64 - -
Crooked N-Fairview 18.3 9/14/2022 2:14 PM 40.9 3.59 - -
CrookedN-Idlewild 19.5 8/9/2022 8:48 AM 86.4 7.14 - -
CrookedN-Idlewild 19.5 8/24/2022 9:23 AM 56.7 4.88 - -
CrookedN-Idlewild 19.5 9/14/2022 1:54 PM 63.1 5.55 - -
CrookedN-Lawyers 14.0 8/9/2022 10:24 AM 85.8 7.01 - -
Crooked N-Lawyers 14.0 8/24/2022 10:39 AM 62.5 5.34 - -
CrookedN-Lawyers 14.0 9/14/2022 3:35 PM 69.3 6.03 - -
CrookedN-Lawyers 14.0 9/19/2022 9:04 AM 68.4 6.18 2.17 0.165
Crooked N-Lawyers 14.0 9/27/2022 9:30 AM 84.9 8.12 1.94 0.218
OTETRA TECH 14

Memorandum- Basis for Speculative Limits for Proposed CCWRF November 17, 2022
Distance from . • • Fl
_A
CrookedN-Ridge 15.0 8/9/2022 9:58 AM 77.3 6.35 9.45 0.1716
CrookedN-Ridge 15.0 8/24/2022 10:12 AM 44.2 3.76 0.92 0.0255
CrookedN-Ridge 15.0 9/14/2022 3:15 PM 47.8 4.15 5.27 0.1397
CrookedN-RRR 15.7 8/9/2022 9:22 AM 83.5 6.84 - -
CrookedN-RRR 15.7 8/24/2022 9:54 AM 62.3 5.3 - -
CrookedN-RRR 15.7 9/14/2022 2:28 PM 71.2 6.08 - -
Crooked N-Stevens 22.7 8/9/2022 8:21 AM 90.4 7.57 0.32 0.0583
CrookedN-Stevens 22.7 8/24/2022 9:03 AM 55.9 4.94 0.03 0.0069
Crooked N-Stevens 22.7 9/14/2022 1:17 PM 61.4 5.51 0.12 0.024
Crooked-Sikes 4.6 8/24/2022 12:07 PM 47.7 4 - -
Crooked-Sikes 4.6 9/14/2022 4:38 PM 61.4 5.35 - -
Crooked-Un ion Brief 7.6 8/24/2022 11:13 AM 64.1 5.5 - -
Crooked-Un ion Brief 7.6 9/14/2022 4:10 PM 80.7 6.97 - -
Station 1 i 13.8 1 9/19/2022 9:30 AM 60.5 5.46 - 0.129
Station 2 i 13.6 9/19/2022 9:49 AM 73.3 i 6.61 - 0.096
Station 3 13.4 9/19/2022 10:13 AM 50.2 4.54 - 0.078
Station 4 13.3 9/19/2022 10:37 AM 54.2 4.84 - 0.011
Station 5 13.1 9/19/2022 11:05 AM 61.4 5.45 - 0.185
Station 6 12.9 9/19/2022 11:28 AM 65.7 5.84 - 0.096
Station 7 12.7 9/19/2022 11:50 AM 53.1 4.77 - 0.063
Station 8 12.5 9/19/2022 12:07 PM 34.4 3.08 - 0.048
Station 9 12.3 9/19/2022 12:26 PM 45.2 4.03 - 0.131
Station 10 12.1 9/27/2022 11:00 AM 55.8 5.3 - 0.165
Station 11 11.9 9/27/2022 11:23 AM 62.1 5.91 - 0.131
Station 12 11.7 9/27/2022 11:40 AM 58.9 5.63 - 0.040
Station 13 i 11.6 9/27/2022 12:06 PM 55.7 5.35 - 0.081
Station 14 11.4 9/27/2022 12:22 PM 48.3 4.64 - 0.054
Station 15 11.2 9/27/2022 12:39 PM 65.2 6.16 - 0.104
Station 16 11.0 9/27/2022 1:00 PM 70.7 6.6 - 0.417
OTETRA TECH 15

Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
LOW FLOW • •
Images of email correspondence with USGS in collaboration with NC DWR on low flow statistics for
Crooked Creek (6-page email thread).
Yonce, Hillary
From: Weaver,John C<)[e-mail]>
Sent Monday,Auqust 8,2022 4:30 PM
To: Yonce,Hillary
Cc: Albertin,Klaus R Clements,Trevor,Weaver,John C
Subject RE:(REVISED 7Q10 DISCHARGES)USGS response to DWR USGS Low Flows request x
2019-26(dated 2019/09/1 1)for Crooked Creek Union County._Re:[EXTERNAL]Low-
Flow Request-Approved&Sent to USGS
^ CAUTION:This email originated from an extemaI sender.Verify the source before opening links or attachments,m
Hillary,
A quick scan of the 8 index sites used for the September 2019 estimates indicates 7 of the sites were low-flow
characteristics published in the 2003 Rocky River basin-wide low-flow report,and 1 of the index sites was a continuous-
record streamgage published in the 2015 USGS statewide low-flow report SIR 2015-5001. Given both these publications
preceded the 2019 low-flow request,the statistics from the two reports would still represent the most recently
published low-flow statistics that are the primary basis for completing responses to low-flow requests.
Given the above,my immediate reaction is to counsel that you should proceed forward using the low-flow yields that
were provided via email to you on September 25,2019(email thread below]. I did a quick basin delineation using
Stream5tats and confirmed the drainage area of 1SA sgmi for the location coordinates you provided in your previous
email.
If the same index sites and low-flow yields are applied to the point of interest with a drainage area of 15.4 sgmi,then
the following estimated low-flow discharges would be provided:
Annual 7Q10 low-flow discharges=_>from 0 to 0.085 cfs(average about 0.02 cfs,median about 0 cfs)4 rounded to
zero flow
Annual 30Q2 low-flow discharges=_>from 0 to 0.51 cfs(average about 0.25 cfs,median about 0.23 cfs)
Winter 7Q10 low-flow discharges=_>from 0 to 0.34 cfs(average about 0.15 cfs,median about 0.14 cfs)
Annual 7Q2 low-flow,discharges==>from 0 to 0.22 cfs(average about 0.11 cfs,median about 0.14 cfs)
Average annual discharge discharges==>from 11.1 to 15.4 cfs(average about 13.7 cfs,median about 13.9 cfs)
The above values highlighted using red font are the median values from the low-flow yields and would be the final set of
estimated low-flow characteristics that would be provided in response to an updated request.
Hope this information is helpful.
Thank you.
Curtis Weaver
3.Curtis Weaver,Hydrologist,PC Cmai1:icweaven`usas.oav
USGS South Atlantic Water Science Center Online:httos.-!iwww.usos-aov/centers/sa-water
North Carolina-South Carolina-Gecrgja
3916 Sunset Ridge Road
Ratergh,NC 27607
Phone:[phone] // Fax:[phone]
OTETRA TECH 16

Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
From:Yonce,Hillary<[e-mail]>
Sent:Monday.August 8,2022 2:40 PM
To:Weaver,John C<[e-mail]>
Cc:Albertin,Klaus P<[e-mail]>,-Clements,Trevor<[e-mail]>
Subject:RE:(REVISED 7Q10 DISCHARGES)USGS response to DWR USGS Low Flows request k 2019-26(dated
2019/D9/11)for Crooked Creek Union County...Re:(EXTERNAL]Low-Flow Request-Approved&Sent to USGS
Hello Curtis and Klaus,
I want to request a follow-up to this existing low-flow request for Crooked Creek in Union County lout let me know if this
should be sent via a new web portal request).I appreciate the updated statistics you provided in September 2019,
however Union County was not able to move forward at that time-so we would appreciate an update to those existing
calculations and/or verification that those statistical calculations hold true.Your previous calculations,literature,and
references are included in the email thread below,we hope to use these low-flow statistics as applied to an updated
location in the watershed,just downstream of the Ridge Road crossing on North Fork Crooked Creek.
StreamStats indicate the drainage area at this point(35.10261870607441,-80.S7001829147337)to be approximately
15.4 square miles.In September 2019,your updated analysis included the following area-based stats for the watershed:
• Annual 7010 low-flow yields=_>from 0 to 0.006 cfsm(average at 0.001,median about 0 cfsm)
• Annual 3002 low-flow yields=_>from 0 to 0.03 dsm(average about 0.02 cfsm.median about 0.015 dsm)
• Winter 7010 low-flow yields=_>from 0 to 0.02 cfsm(both average and median about 0-01 cfsm)
• Annual 702 law-flow yields=_>from 0 to about 0.015 cfsm(both average and medan about 0.01 cfsm)
• Average annual discharge yields==>from 0.72 to 1 dsm(both average and median about 0.9 cfsm)
If these statistics still hold true based on your review of the data,please let me know,as we would apply these calculations to
the approximate 15.4 square mile drainage area below Ridge Road on North Fork Crooked Creek to estimate the following-
• Av idyr Aiuiuel 70101uw-rlvw yiteM—0.02 ulti
• Average Annual 3002 low-flow yield=_>0.31 cfs
• Average W inter 7010 law-flow yield=_>0.15 cis
• Average Annual 702 low-flow yield =_>0.15 cis
• Average annual discharge yield =_>13.86 cis
Thank you for your time.Curtis-and 6 you would like to receive this request via the web portal please just let me know_
Hillary
llftry VatiM•PM I Professional Hydrologist.Environmental Scientist
Pronouns:she,her,hers
Direct#1(919)485-207`71 Business+l(919)485-8278 1 Mobile+l(919)605-0291 1 F a,[phone] hillaU gnncPr@tPrfatech cnm
Tatra Toth I LeodkV wfdh Science-I WTR
4Do0 Park Drive,Suite 200,Durham,NC 2 7703 1 PO Box 14409.Durham,NC 27709 1 tetratech.com
This message,including any ortochertcvrts,may include privilegtA confidential and/or insideWovmotion.Any distribution or use of tbis
communication by anyone odhw than the intended recipient is suictfy pwhibded aid may be unlawhAL flyou are not the intended recipient.please
,a.,-M,inq to this message and then delete it from your system.
© m N r lease consider the environment before printing.Read more
OTETRA TECH 17

Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
OTETRA TECH
From:Weaver,John<icweaverCa usgs.Rov>
Sent:Wednesday,September 2S,2019 9:48 AM
To:Yonce,Hillary<Hillary.YonceCatetratech.com>
Cc:DWR USGS Low Flows<[e-mail]>;Albertin,Klaus P<[e-mail];Grzyb,Julie
<[e-mail]>;Hill,David A<david.hill@ncdenrsov>;Kebede,Adugna<[e-mail]>;Fine,
Jason M<jmfine usgs.gov>;Fransen,Tom<[e-mail]>;Linwood Peele<linwood.peele@ncdenr.¢ov>;
Clements,Trevor<[e-mail]>;Steve Tedder<[e-mail]>;John C
Weaver<[e-mail]>
Subject:(REVISED 7Q10 DISCHARGES)USGS response to DWR USGS Low Flows request ri 2019-26(dated 2019/09/11)
for Crooked Creek Union County...Re:[EXTERNAL)Low-Flow Request-Approved&Sent to USGS
Q CAUTION:This entail otginated from an external sender.Verify the source before opening links or attachments Q
Ms.Yonce,
In response to your follow-up inquiry about the lbw-flow characteristics for two locations on Crooked Creek(at U.S Highway 601 and NC
Highway 21SI in the vicinity of Fairview in northern union County,the following information is provided_
listorical background(prior to May 2016)
A check of the lav-fla+r files here at the USGS South Atlantic Water Science Center I Raleigh office)indicates previous low-flow
determinations for these points of interest. The 7010 discharge was estimated at 0.01 cfs in 1970 for Crooked Creek at
Fairview(station id 02124766 drainage area 36 9 sgmi.at Highway 601). A 7010 discharge was estimated at zero flow in
January 1988 for Crooked Creek at NC 218 near Fairview Istation id 0212476690,drainage area 43-9 sgmi I. The low-flow files
also indicate estimated 7010 discharges(completed in 1988 and 2001)at zero flow for two other locations on Crooked Creek
above and below the points of interests Istation id's 02124763 and 0212476725).
The USGS has records of miscellaneous measurements at two locations on Crooked Creek. Four miscellaneous
measurements were collected at the partial-record station at Highway 601 in the 1954. 1961.and 1964 water years(including
one measurement at zero flow)- One mrscellaneous measurement was obtained in the 2002 water year at Crooked Creek at SR
1547 near Fairview Istation id 0212476710 drainage area 47 3 sgmi)- While the number of available measurements at each of
these sites is insufficient to permit a low-flow determination based on measured data.the historical occurrence of a zero-flow
measurement at the Highway 601 site prov9des support ar little!o no potential for sustained base fl(yxs along this reach of
Crooked Creek
In the absence of sole-specific discharge records sufficient for a low-flow analysis.estimates of low-flow characteristics at
ungaged locations are determined by assessing a range in the low-flow yields lexp(essed as flow per square mile drainage area.
or cfsm)at nearby sites where estimates have been determined.
For streams in Union County,low-flow characteristics published by the USGS are provided in the following reports:
111 The first rs a statewide report completed in the early 1990's It is USGS Water-Supply Paper 2403.'Low-flow characteristics
of streams in North Carolina'(Giese and hlason. 1993). An online version of the report is available
athttp:,pubs.usas.gov'wsp 2403,'repor!.pdf. The report provides the low-flow characteristics(based on data through 1988)via
regional relations and at-site values for sites with drainage basins between 1 and 400 sgmi and not considered or known to be
affected by regulation and-or diversions
121 The second is a basin-wide report for the Rocky River basin published in 2003. It is USGS Water-Resources Investigations
Report 034147.'Low-Flow Characteristics and Profiles for the Rocky River in the Yadkin-Pee Dee River Basin,North Carolina,
3
OTETRA TECH 18

Memorandum- Basis for Speculative Limits for Proposed CCWRF November 17, 2022
through 2002"(Weaver and Fine,2003)_ An online version of the report is available
through http i pubs.usgs gov1wn,wrF034147.'. The report provides the low-flow characteristics(based on data through 2002)for
continuous-reoord gaging stations and partial-record sites within the Rocky River basin. The report also provides low-flow
discharge profiles(7010,3002.winter 7010,and 702)for the Rocky River from its headwaters in Mecklenburg County to its
mouth.
(3)The turd is a statewide report recently published in March 2015- It is USGS Scientific Investigations Report 20t5-5001.
'Low-flaw characteristics and flow-cluration statistics for selectedUSGS continuous-reoord streamgaging stations in North
Carolina through 2012'(Weaver.2015). The report is available online at httpaipubs.usgs.gov.,sir12015 5001i. The report
provides updated low-flow characteristics and flaw-duration statistics for 266 active(as of 2012 water year)and discontinued
streamgages across the state where a minimum a(10 climatic years discharge records were available for flow analyses
A basin delineation completed using the online USGS StreamStats application for North Carolina
(https lstreamstals usgs.gov+ss)indicates the drainage area for Crooked Creek at U.S.Highway 601 (35.12886,-80.53687
NAD83)is 3T 1 sgmi. A basin delineation completed using the online USGS StreamStats application for North Carolina
(httpsl streamstats usgs.goy,ss)indicates the drainage area for Crooked Creek at N.C.Highway 218(35.13310.-80.48964
NAD83)is 44.4 sgmi.
Low flow determinations September 2019
Inspection of the second and third above-referenced reports indicates the presence of nine(9)nearby selected USGS
partial-record sites(6)and continuous-record streamgages(3)in both the Crooked Creek and Richardson Creek basins in
general vicinity of the point of interest where low-flow characteristics were published. Among these 9 sites,the low-
flow discharge yields for the indicated flow statistics are as follows:
(REVISED see comments below)Annual 7010 lax-flow yields=_>from 0 to 0.006 cfsm(average at 0-001,median about 0
dsm)
Annual 3002 low-flow yields=_>from 0 to 0.03 dsm(average about 0.02 dsm.median about 0.015 cfsm)
Winter 7010 low-flaw yields=_>from 0 to 0.02 dsm(both average and median about 0.01 cfsm)
Annual 702 lair-flax yields=_>from 0 to about 0.015 cfsm(both average and median about 0.01 dsm)
Average annual discharge yields=_>from 0.72 to 1 dsm(both average and median about 0 9 dsml
(1)Crooked Creek at Fairview(station id 02124766,StreamStats drainage area 37.1 sgmi,at U.S.Highway 601)
Application of the above ranges in low-flax yields results to the drainage area(37.1 sgmi)for this first point of interest results in
the following estimated low-flow discharges:
(REVISED see comments below)Annual 7010 discharges=_>from 0 to 0.22 cfs(average about 0.04 ds.median at 0 cfs)
Annual 3002 discharges=_>from 0 to about 1.1 ds(average 0.74 cfs,median about 0.55 cfs)
Winter 7010 discharges=>from 0 to 0.74 cfs(average and median about 0.4 ds)
Annual 702 discharges=>from 0 to about 0.55 cfs(average and median about 0.4 cfs)
Average annual discharge=_>from 26.7 to 37.1 cfs(both average and median 33.4 cfs)
(2�Crooked Creek at N.C_Highway 218 Istation id 0212476690,StreamStats drainage area 44.4 sgmi.at N_C.Highway
218)
Application of the above ranges in law-flax yields results to the drainage area(44.4 sgmi)for this second point of interest results
in the following estimated low-flow discharges:
(REVISED see comments below)Annual 7010 discharges=_>from 0 to 0.27 cfs(average about 0.04 ds,median at 0 cfs)
Annual 3002 discharges=_-'rom 0 to about 1.3 ids(average 0.89 cfs,median 0.67 cfs)
Winter 7010 discharges=_>from 0 to 089 cfs(both average and median about 0.4 di
Annual 702 discharges=_>from 0 to 0.67 cis(both average and median about 0.4 cis)
4
OTETRA TECH 19

Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
.Average annual discharge==>from about 32 to 44.4 cfs(both average and median abou'40 cfs)
For the record...,-omments concerning the revised 7010 discharges(reproduced from separate email transmission sent
to Ms-Yonce on September 19.2019):
'In response to the May 2016 request.the 7010 discharges for the two Crooked Creek locations were estimated based on use
of 9 index sites(7 partial-record sites,2 continuous-record streamgages)in the nearby Richardson Creek basin located in
central eastern Union County(to the south and east of the Crooked Creek basin in northwest Union County). Explanation of
use of the Richardson Creek basin for the May 2016 determinations was attributed to the same underlying geologic zone
beneath both basins(email from USGS dated May 26,2016).
In reviewing your[Ms. Yonce]email dated 09,103.2019 requesting additional low-flow characteristics for these two locations,d
was noted that a USGS partial-record site(station id 02125482,drainage area 153 sgmiI was inadvertently used in the May
2016 determinations. As the low-flow characteristics for this site are recognized as being affected by upstream flow diversions
(footnote'm'on page 23 in VVeaver and Fine 2013'I.today's review indicates the low-flow characteristics at this index site
should have not been used in the May 2016 determinations
Further review of the remaining 8 index sites in the Richardson Creek basin used for the previous 7010 determinations now
raises questions about the inclusion of a second USGS partial-record site on Richardson Creek(station id 02125310,drainage
area 89 sgmi.at Secondary Road 1006 upstream from Stewarts Creek I. As this site rs also located downstream from the
wastewater treatment plant,some of the discharge records(25 miscellaneous measurements during 1953.54,1956-59, 1970-
74. 1976-77 water years)at this location may also be affected by diversions due to the upstream WWTP operations. Further
investigabon into the time line of the WWTP relative to the drscharge records may be warranted.
Removal of these two partial-record sites from the group of index sites will result in substantialry lower(if not zero flow)annual
7010 discharges Given it's been several years since the May 2016 determinations,I regret the inconvenience these revised
7010 estimates may cause. However,my review today strongty suggests this revision needs to be completed to strengthen the
technical basis for these estimates. Please note this revision does not affect the ability to provide the winter 7010,annual
3002,annual 702.and average annual discharge estimates I will proceed with the revised 7010 discharges as well as
estimation of the remaining streamflow statistics.
I will re-iterate a statement made in the May 2016 response. As stated.'however,because of the high number of nearby sites
with zero-flow 7Q 10 low-flow yields and the limited amount of discharge records a variable for Crooked Creek.it must be noted
that caution is appropriate in the use of these estimates. it's very possible the above average 7Q10 discharge estimates for
each point of interest may be too high. But again.this can only be resolved with the collection of new discharge records for
Crooked GreeK- At besL estimation of low-now Characteristics In this area of Norn Carolina is challenging due to the limped
discharge records available for analysis. This situation further re-enforces the need for future data collection for streams in this
area.'
Please note:
11)The estimated flows are provided in units of cubic feet per second(cfs).
12)The information provided in this message is based on a preliminary assessment and considered provisional,subject to revision pendinc
collection of future data and further analyses.
These provisional streamflow statistics are provided via the DWA USGS Low Flows cooperative agreement between USGS and the N.C.
Department of Environmental Quality,Division of Water Resources.
Hope this information is helpful.
Thank you.
Curtis Weaver
J.Curtis Weaver,Hydrologist_PE Email:jcweaverousgs.gov
USGS South Atlantic Water Science Center Online:httm,11www.ugyyyov/centers/sa-water
North Carolina-South Carolina-Georgia
3916 Sunset Ridge Road
Raleigh,NC 27607
Phone:[phone] // fax:[phone]
OTETRA TECH 20

Memorandum— Basis for Speculative Limits for Proposed CCWRF November 17, 2022
On Wed,Sep 11,2019 at 12:38 PM Fransen,Tom ctom.fransentSncdenr.gov>wrote:
Your request has been approved and sent to USGS.
Request for USGS to provide low-flow statistics.
Request details:
Request ID:26
Date of request:9/11/2019 3-0SA0 PM
Requestor.HillaryYonce
Phone Number:919-485-2077
Program:
Email: (anonymous)
Agency:A Consultant or DEQ for a Counsultant
Have you spoken with someone from DWR?:
Reason for request:Not specified
Whom did you speak with?:
Local Government:
Consultanting Company/Organization:Tetra Tech
Contact Name:Hillary Yonce
Contact Phone Number:919ASS-2077
Contact Email:Hillary.Yonce@tetratech.00m
Reason for request:Not specified
Permit Number:
Public Water Supply ID:
Site Information-
River/Stream:Crooked Creek(two locations--at U.S.Highway 601 and NC Highway 218)
Latitude-Longitude:0.000000 Other location Information:In vicinity of Fairview in northern Union County
Statistics being requested:["7Q10-Winter","30Q2%"7Q2","Average Annual"]
Other information:This is a follow up to a May 2016 low-flow request in which I provided 7Q10 estimates for two points
of interest on Crooked Creek in Union County.
Follow-up email dated 09/03/2019 received by JCWeaver(USGS)from Hillary Yonce(Tetra Tech).
This low-flow request entered by JCWeaver(USGS)on D9/11/2019 based on information supplied by the requester.
Approved by:Grzyb,Julie([e-mail])
Comments-
6
OTETRA TECH 21