NC0085812_SOC (application),_20200109

Union County
500 N Main St
Monroe NC 28112
T. 704-283-3500
www.unioncountync.gov
December 30, 2019
JAN 0 9 2920
Ms. Julie Grzyb
Supervisor, Complex Permitting Unit NCp�(�pWRINPDES
N.C. Department of Environmental Quality
Division of Water Resources, Water Quality Section
1617 Mail Service Center
Raleigh, NC 27699-1617
RE: Union County Public Works — Grassy Branch Wastewater Treatment Plant
NPDES Permit No. NCO085812
Application for Special Order by Consent
Dear Ms. Grzyb,
We have enclosed one original and two copies of the completed and executed application form
and required attachments for a Special Order by Consent (SOC) for the Grassy Branch
Wastewater Treatment Plant (WWTP), National Pollutant Discharge Elimination System
(NPDES) Permit NC0085812. We have enclosed the following documents:
1. Application for SOC to include the following attachments:
a. Attachment III —Additional Flow or Flow Reallocation
b. Attachment IV — Necessity Narrative
c. Attachment V — Engineer's Certification
d. Attachment VI — Predicted Compliance Schedule
e. Attachment VI — Fund Sources Identification
2. SOC Pre -Application Certification
3. Non-refundable $400 fee
The County has worked diligently to manage the potential for compliance issues at the Grassy
Branch WWTP. We have been actively involved in reduction of infiltration and inflow (1&1) in the
collection system and we continue to operate and maintain the Grassy Branch WWTP to the
best of our ability with the existing infrastructure. We believe that the majority of the Notice of
Violations (NOVs) are attributed to record rainfall in the region. However, we acknowledge that
over -allocation of sewer connections to the Grassy Branch WWTP has contributed to and
intensified the compliance issues. Therefore, we respectfully request a permanent additional
flow allocation as part of the SOC. Our engineer, Hazen and Sawyer, recommends a permanent

increase in the design maximum month flow from 0.05 mgd to 0.120 mgd.
We appreciate the time and effort of the NPDES Complex Permitting Unit to review our
application for the SOC. Please do not hesitate to contact us if you have any questions.
Sincerely,
William M. Watson,
County Manager
Enclosures
cc: Corey Basinger, DWR Regional Office, Water Resources Supervisor
Andrew Neff, PE, Union County Public Works, Water and Wastewater Division Director
Scott Honeycutt, Engineering Director
John Shutak, CIP Manager
Hyong Yi, Union County Public Works, Public Works Administrator
Jim Struve, PE, Hazen and Sawyer
Bart Farmer, Water reclamation Superintendent
Ott
.CO
H CAR
Page 2

Union County, NC
Grassy Branch WWTP
NPDES Permit No. NC0085812
Application for Special Order by Consent
Table of Contents
Tab A.
Application Form for Special Order by Consent (SOC)
Tab B.
Attachment III - Additional Flow or Flow Reallocation
Tab C.
Attachment IV - Necessity Narrative
Tab D.
Attachment V - Engineer's Certification
i. Attachment A — Crooked Creek QUAL2K Model Development (Tetra Tech)
ii. Attachment B — Crooked Creek QUAL2K Model Application for Grassy Branch
VVVUTP (Tetra Tech)
Tab E. Attachment VI - Predicted Compliance Schedule
Tab F. Attachment VI1 - Funding Sources Identification
Tab G. SOC Pre -Application Certification

STATE OF NORTH CAROLINA
DEPARTMENT OF ENVIRONMENT AND NATURAL RESOURCES
DIVISION OF WATER RESOURCES
APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC)
I. PERMIT RELATED INFORMATION:
1. Applicant (corporation, individual, or other): Union Count � Public Works
2. Print or Type Owner's or Signing Official's Name and Title:
William M. Watson. County Manager
3. Facility Name (as shown on Permit): Grass • Branch Wastewater Treatment Plant
4. Owner Phone: [phone] (or
5. Owner Email: Mark. Watson a unioncountvnc. ov
4. Application Date: June 28.2019
5. NPDES Permit No. (if applicable): _ NCO085812
6. Name of the specific wastewater treatment facility (if different f om 13. above):
Same
II. PRE -APPLICATION MEETING:
Prior to submitting this completed application form, applicants must meet with the appropriate
regional office staff to discuss whether or not an SOC is appropriate for this situation. Please
note the date this meeting occurred and who represented the pernlittee:
Representative: Corer Basinger Date: Mav 2 2019
III. ADDITIONAL FLOW OR FLOW REALLOCATION:
In . accordance with NCGS 143-215.67(b), only facilities owned by a unit of government may
request additional flow. Refer to Attachment III
Additional flow may be allowed under an SOC only in specific circumstances. These
circumstances may include eliminating discharges that are not compliant with an NPDES or
Non -discharge permit. These circumstances do not include failure to perform proper
maintenance of treatment systems, collection systems or disposal systems. When requesting
additional flow, the facility must include its justification and supporting documentation.

If the requested additional flow is non -domestic, the facility must be able to demonstrate the
ability to effectively treat the waste and dispose of residuals. The applicant must provide a
detailed analysis of the constituents in the proposed non -domestic wastewater.
The total domestic additional flow requested: 120.000 gallons per day.
The total non -domestic additional flow requested: 0 gallons per day.
The total additional flow (sum of the above): 120.000 gallons per day.
Please attach a detailed description or project listing of the proposed allocation for additional
flow, with an explanation of how flow quantities were estimated. Further, any additional flow
requested must be justified by a complete analysis, by the permittee, that additional flow will not
adversely impact wastewater collection/treatment facilities or surface waters.
IV. NECESSITY NARRATIVE:
Please attach a narrative providing a detailed explanation of the circumstances retarding the
necessity of the proposed SOC. Include the following issues: Refer to Attachment IV
• Existing and/or unavoidable future violations(s) of permit conditions or limits(s),
• The existing treatment process and any process modifications that have been made to
date to ensure optimum performance of existing facilities,
• Collection system rehabilitation work completed or scheduled (including dates),
• Coordination with industrial users regarding their discharges or pretreatment facilities.
Identify any non -compliant significant industrial users and measure(s) proposed or
already taken to bring the pretreatment facilities back into compliance. If any industrial
facilities are currently under consent agreements, please attach these agreements,
• Date and outcome of last Industrial Waste Survey,
• Whether or not the facility is acting as a regional facility receiving wastewater from other
municipalities having independent pretreatment programs.
V. CERTIFICATION:
The applicant must submit a report prepared by an independent professional with expertise in
wastewater treatment. This report must address the following: Refer to Attachment V
• An evaluation of existing treatment units, operational procedures and recommendations
as to how the efficiencies of these facilities can be maximized. The person in charge of
such evaluation must sign this document.
• A certification that these facilities could not be operated in a manner that would achieve
compliance with final permit limits. The person making such determination must sign
this certification.
• The effluent limits that the facility could be expected to meet if operated at their
maximum efficiency during the term of the requested SOC (be sure to consider interim
construction phases).
• Any other actions taken to correct problems prior to requesting the SOC.
2

NO
VI. PREDICTED COMPLIANCE SCHEDULE:
The applicant must submit a detailed listing of activities along with time frames that are
necessary to bring the facility into compliance. This schedule should include milestone dates for
be innin 11, construction. ending construction. and achieving final compliance at a minimum. In
determining the milestone dates, the following should be considered:
Refer to Attachment VI
• Time for submitting plans, specifications and appropriate engineering reports to DWR for
review and approval.
• Occurrence of major construction activities that are likely to affect facility performance
(units out of service, diversion of flows, etc.) to include a plan of action to minimize
impacts to surface waters.
• Infiltration/Inflow work, if necessary.
• Industrial users achieving compliance with their pretreatment permits if applicable.
• Toxicity Reduction Evaluations (TRE), if necessary.
VII. FUNDING SOURCES IDENTIFICATION:
The applicant must list the sources of funds utilized to complete the work needed to bring the
facility into compliance. Possible funding sources include but are not limited to loan
commitments, bonds, letters of credit, block grants and cash reserves. The applicant must show
that the funds are available, or can be secured in time to meet the schedule outlined as part of this
application.
Refer to Attachment VII
If funding is not available at the beginning of the SOC process, the permittee must submit a copy
of all funding applications to ensure that all efforts are being made to secure such funds.
Note: A copy of the application should be sufficient to demonstrate timeliness unless regional
office has reason to request all information associated with securing funding.
THE DIVISION OF WATER RESOURCES WILL NOT ACCEPT THIS APPLICATION
PACKAGE UNLESS ALL OF THE APPLICABLE ITEMS ARE INCLUDED WITH THE
SUBMITTAL.
Reyuired Items:
a. One original and two copies of the completed and appropriately executed application
form, along with all required attachments.
If the SOC is for a City / Town, the person signing the SOC must be a ranking
elected official or other duly authorized employee.
If the SOC is for a Corporation / Company / Industry / Other, the person signing
the SOC must be a principal executive officer of at least the level of vice-
president, or his duly authorized representative.
If the SOC is for a School District, the person signing the SOC must be the
Superintendent of Schools or other duly authorized employee.

Note: Reference to signatory requirements in SOCs may be found in the North
Carolina Administrative Code [T15A NCAC 2H .1206(a)(3)].
b. The non-refundable Special Order by Consent (SOC) processing fee of $400.00. A
check must be made payable to The Department of Environment and Natural
Resources.
c. An evaluation report prepared by an independent consultant with expertise in
wastewater. (in triplicate)
APPLICANT'S CERTIFICATION:
(NO MO IFICATIONTO THIS CERTIFICATIONISACCEPTABLE)
1, (NOW
���� �+� 4 WAT5dyl,— ,attest this application for a Special Order by
Consent (SOC) has been reviewed by me and is accurate and complete to the best of my
knowledge. I understand if all required parts of this application are not completed and if all
required supporting information and attachments are not included, this application package may
be returned as incomplete. (Please be advised that the return of this application does not prevent
DWR from collecting all outstanding penalties upon request). Furthermore, I attest by my
signature that I fully understand that an upfront penalty, which may satisfy as a full
settlement of outstanding violations, may be imposed. {Note: Reference to upfront penalties
in Special Orders by Consent may be found in the North Carolina Administrative Code [T15A
NCAC 2H .1206(c)(3)].}
0/` Date
Signature of Signing Official
William M. Watson CoLinty Man a er
Printed Name of Signing Official
THE COMPLETED APPLICATION PACKAGE, INCLUDING THE ORIGINAL AND TWO
COPIES OF ALL SUPPORTING INFORMATION AND MATERIALS, SHOULD BE SENT
TO THE FOLLOWING ADDRESS:
NORTH CAROLINA DIVISION OF WATER RESOURCES
POINT SOURCE BRANCH
1617 MAIL SERVICE CENTER
RALEIGH, NORTH CAROLINA 27699-1617
IF THIS APPLICATION IS FOR A NON -DISCHARGE SYSTEM, THEN SEND TO:
NORTH CAROLINA DIVISION OF WATER QUALITY
AQUIFER PROTECTION SECTION
1636 MAIL SERVICE CENTER
RALEIGH, NORTH CAROLINA 27699-1636

STATE OF NORTH CAROLINA
DEPARTMENT OF ENVIRONMENTAL QUALITY
DIVISION OF WATER RESOURES
APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
III. Additional Flow or Flow Reallocation
1. Background
Union County owns and operates the Grassy Branch WWTP and associated collection system
infrastructure. The WWTP is permitted to discharge 0.05 mgd of treated effluent into Crooked Creek via
NPDES permit NC0085812. The collection system consists of approximately 31,000 feet of gravity sewer,
123 manholes, and two wastewater pump stations. The Loxdale Pump Station pumps 21,400 gpd and the
Unionville Pump Station pumps 10,245 gpd. The Grassy Branch WWTP receives only domestic
wastewater. The WWTP serves three schools, two residential subdivisions, and several private parcels,
summarized as follows:
• Piedmont High School (1,363 students)
• Piedmont Middle School (1,018 students)
• Unionville Elementary School (701 students)
• Loxdale Subdivision (52 homes)
• Smithfield Subdivision (62 homes)
• Private parcels (12 homes)
2. Summary of Flow Issues
The County has received Notice of Violations (NOVs) for flow, five-day biochemical oxygen demand
(BOD5), ammonia (NH3-N), fecal coliform, total suspended solids (TSS), and pH over the last several
years. The Grassy Branch WWTP NOVs are summarized in Table III-1. The County has attributed the
majority of the NOVs to record rainfall events in the region; however, over -allocation of sewer connections
to the Grassy Branch WWTP has contributed to and intensified the compliance issues (refer to Section 5
of this attachment). Figure III-1 provides an illustration of the Grassy Branch WWTP flow and recorded
rainfall. The data demonstrates that the design flow capacity is exceeded during rain events. Influent flow
peaks have exceeded a ratio of 7 to 1 (e.g., peaking factors greater than 7) compared to the design
capacity of the WWTP. Additionally, record rainfall was recorded in the region in 2018 through May 2019
Figure III-2 provides the monthly rainfall in the region from January 2015 through August 2019. The
average monthly rainfall in the region is approximately four inches.

APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
III. Additional Flow or Flow Reallocation
Table III-1: Summary of Notice of Violations for Grassy Branch WWTP
Permit Violation
Flow
BOD5
BOD5
NH3-N
NH3-N
TSS
(monthly
(weekly
(monthly
(weekly
(monthly
Fecal
(weekly
Date
average)
averaaw
average)
average)
average}
Coliform
average) pH
1 /31 /2018
0.058
2/3/2018
23
1,500
2/28/2018
0.07
220
3/3/2018
6,971
3/17/2018
3/31 /2018
27.1
3/31 /2018
20.3
16.3
6/2/2018
13.2
2,949
10/6/2018
440
10/13/2018
570
10/20/2018
810
10/31/2018
0.056
11 /10/2018
1,200
11 /17/2018
6,000
11 /30/2018
0.088
12/11 /2018
9.97
12/15/2018
7,200
12/22/2018
16.1
560
12/29/2018
17
6,000
12/31 /2018
0.106
4.86
1,448
1 /5/2019
737
1/12/2019
23.3
1 /31 /2019
0.10
2/28/2019
0.07
4/6/2019
193
6,000
177
4/13/2019
14.6
6.05
4/30/2019
0.065
24.8
2.05

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APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
III. Additional Flow or Flow Reallocation
3. Summary of Infiltration and inflow (W) Reduction Efforts
The County has actively been involved in the reduction of infiltration and inflow (I&I) in the collection
system. A Phase 1 1&1 study was commissioned in 2016 to broadly determine problem areas. A Phase 2
study in 2017 focused on repair efforts readily identified in the Phase 1 study. The Phase 2 study also
included wet weather monitoring. In 2018, Phase 3 efforts included confirming the effectiveness of
previous repair efforts, extensive closed-circuit television (CCTV) review of the entire collection system,
and the continuation of repair efforts. Phase 4 of the I&I reduction effort was initiated in January 2019.
This phase consists of a review of dry and wet weather data and patterns and on -going inspection of the
collection system.
As of January 2019, the entire Grassy Branch collection system has been surveyed by CCTV. As of
May 2019, 42 manholes have been grouted and 48 inflow collectors installed. Table III-2 provides a
summary of the maintenance data for the I&I reduction effort from 2014 to present, including investigative
man hours and quantity of repaired infrastructure (e.g., manholes, laterals, etc.). Table III-3 provides a
detailed summary and timeline of the County's I&I reduction efforts.
Table III-2: Summary of I&I Effort Maintenance Data
2014
2015
2016
2017
2018
2019
Man Hours Investigating
960
1080
960
480
1512
1152
Man Hours Repairing
360
48
0
72
1152
192
Footage Cleaned
0
0
10,181
425
10,146
CCTV Footage
160
40
10,181
160
16,273
14,627
Hours Smoke Testing
24
20
36
36
37
32
Smoke Test Footage
14,745
7,283
4,235
4,570
15,308
8,368
Manholes Repaired
3
0
0
0
42
3
Lateral Repaired
6
4
0
4
25
8
Cleanouts Repaired
6
4
0
4
17
8
Inflow Dishes Installed
0
0
0
0
53
0
5/10

APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
lll. Additional Flow or Flow Reallocation
Table III-3: Grassy Branch WWTP Basin Detailed I&I Abatement Timeline
March 2016 — Flow monitoring conducted by Frazier Engineering (90 day study)
• Identified 5 key locations within the trunk sewer to install A/V flow meters.
• Meters removed June 2016.
June 2016 — Results from flow monitoring study delivered
• Identified significant I&I in upstream private system from Piedmont Middle and High school campuses.
September 2016 — Issued NOV to Union County Public Schools (UCPS) for violation of the UCPW
Sewer Use Ordinance
• NOV issued a 90 day deadline to repair deficiencies; no response.
• January 3, 2017 — Issued follow-up correspondence to UCPS.
• January 6, 2017 — UCPS issues statement of repair completion by January 17.
• January 26, 2017 — UCPS declares work is complete and UCPW may re -inspect.
• February 27, 2017 and March 22, 2017 —Issued correspondence to inform UCPS of outstanding repairs
identified during smoke test re -inspection. UCPS declared that funding was not available during their fiscal year
but that funds were identified the following FY with a project specifically designed for I&I abatement per the
NOV.
• July 18, 2017 — UCPS issued Notice to Proceed to their contractor with completion date of August 2017.
• August 9, 2017 — UCPW and UCPS conducted post -smoke test re -inspection. Found a number of deficiencies
still exist. August 14, 2017 — Re -inspection showed all repairs had been made satisfactorily.
October 2017 — Phase 2 Flow Monitoring — Follow-up (90 day study)
• Frazier Engineering installed 5 A/V flow meters in exact locations from previous study to determine
effectiveness of repairs and identify other areas requiring attention.
• Meters removed January 2018.
February 2018 — Results from flow monitoring study delivered
• Identified other significant I&I areas in the trunk sewer upstream of the WWTP.
April 2018 — Began in-house I&I efforts based on flow monitoring results
• Conducted I&I search during numerous late night rain events. Plugged line segments between manholes to
identify I&I entry points.
o Any line segment identified as an I&I entry point was inspected via CCTV.
■ CCTV inspection identified a defective tap which was repaired.
• Repair was made and re -inspected via CCTV to affirm the repair.
• Conducted 35 manhole inspections from GB WWTP to Smithfield subdivision connection.
o Identified 5 manholes with defects.
o All manholes repaired utilizing chemical grout injection, hydraulic cement, and ring/cover and inflow dishes
where needed.
May 2018 — Flow monitoring follow up — Frazier Engineering (90 day study)
• Monitor area limited to "micro -monitor" most significant contributor of I&I determined by previous study.
May 2018 -- I&I efforts in branch sewers in Loxdale and Smithfield subdivision
• Efforts include smoke tests, MH inspections, and CCTV all services and connections.

APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
III. Additional Flow or Flow Reallocation
Table III-3: Grassy Branch WWTP Basin Detailed I&I Abatement Timeline
o Loxdale area
• 3 manholes were identified for repairs — Repaired by chemical grout injection and hydraulic cement.
■ 4 cleanouts were repaired.
■ 13 inflow dishes installed.
o Smithfield area
■ 4 manholes were identified for repairs — Repaired by chemical grout injection and hydraulic cement.
• Installed 31 inflow dishes.
June 2018 — Grassy Branch Trunk Sewer
• All manholes in the Grassy Branch trunk sewer (outfall) were inspected.
o Installed inflow dishes and verified all MH's were sealed and secured from WWTP to the most upstream
point of the system. There were no visible leaks above ground.
October 2018 — Continuation of I&I efforts in branch sewers in Loxdale subdivision and Grassy Branch
Trunk Sewer
• Efforts include smoke tests, manhole inspections, and CCTV all services and connections.
o No visible detection as a result of test in customer clean -outs.
• Inspection of Grassy Branch trunk sewer did not indicate significant issues, only replacing missing bolts in
manhole covers.
November 2018 — I&I efforts from Clontz Long Road to Grassy Branch WWTP
• CCTV survey along Clontz Long Road to Grassy Branch WWTP.
o A small leak was discovered and repaired at a manhole along the route.
• Survey was not completed along entire route.
December 2018 — Continuation of I&I efforts from Clontz Road to Grassy Branch WWTP, Loxdale
Subdivision, and Smithfield
• CCTV crew continued survey along Clontz Road. Efforts stopped due to a large rain event, which prohibited
cameras from being deployed.
• The Loxdale subdivision survey discovered one leaking sewer lateral that was repaired and one manhole
grouted.
• CCTV crew conducted mainline survey in Smithfield, ties in to the main trunk line to Grassy Branch WWTP
o No visible detection was reported.
2019 — Phase 4 of I&I Efforts
• Entire collection system has been surveyed by CCTV.
o 42 manholes have been grouted and 48 inflow collectors installed.
• Ongoing inspections demonstrated repair work needed in several areas.
• County staff continues plug testing during rain events.
Page

APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
III. Additional Flow or Flow Reallocation
The County is not able to quantify a specific reduction in influent flow as a result of the on -going I&I
reduction efforts. However, the County's I&I reduction efforts have resulted in a slight decrease in the
peaking factors at the Grassy Branch WWTP. Table III-4 summarizes the annual average, maximum
month, maximum 7-day, and maximum day peaking factors (PF) from 2015 through 2018. In 2018, the
maximum day peaking factor was 6.72 compared to 7.76 in 2015 prior to I&I reduction efforts.
Table III-4: Summary of Historical Influent Peaking Factors
Parameter 2015 2016 2017 2018
Maximum month peaking 1.94 1.65 1.74 1.91
factor
Maximum week (7-day) 2.98 3.44 2.70 2.72
peaking factor
Maximum day peaking 7.76 7.00 6.74 6.72
factor
4. WWTP Process Modifications
Union County has been actively evaluating process changes at the WWTP to minimize NOVs. Staff has
taken several precautionary measures in anticipation of high flow events, as follows:
• Bypassing of tertiary filters during wet weather events.
• Increased monitoring of WWTP to include frequent visits during a wet weather event and constant
monitoring of telemetry via supervisory control and data acquisition (SCADA).
• Control of air input to aeration basins to retain suspended solids:
o Shutting down of all compressors except one.
o Reducing remaining compressor to 30 Hz.
o Shutting down all aerator drop legs except the first set.
Additional process changes will not resolve the permit violations. County staff has made all of the feasible
process changes and implemented the appropriate operational strategies in an on -going effort to resolve
the compliance issues.
5. Additional Flow Request
The historical data indicate the influent flows that exceed the permitted design capacity of the Grassy
Branch WWTP have resulted in final effluent permit violations for flow, conventional pollutants, and
bacterial pollutants (refer to Attachment to SOC Application IV. Necessity Narrative). The County has
attributed the majority of the NOVs to record rainfall events in the region. However, the County also
acknowledges that more sewer connections have been allocated to the Grassy Branch WWTP than
available capacity.

APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
III. Additional Flow or Flow Reallocation
Hazen recommends a permanent increase in the design maximum month flow from 0.05 mgd to
0.120 mgd. The flow increase is associated with the existing domestic flow discharging to the WWTP, the
maximum student capacity of the three schools, new connections in the Smithfield subdivision to fulfill
contractual obligations, and private parcel connections along the main sewer line to the plant. The
Loxdale subdivision has reached the maximum dwelling units for the subdivision. The anticipated planned
flow was established using the average day wastewater flow rates published in 15A NCAC 02T .0114
(Wastewater Design Flow Rates). The anticipated planned flow was added to the annual average flow to
the WWTP.
A maximum month peaking factor of 1.7 was applied to the annual average flow, which results in a
maximum month design flow of 0.120 mgd. The peaking factor of 1.7 is the median peaking factor of the
2014 through August 2019 data set. Figure 111-3 provides an illustration of the average day and maximum
month flows at the WWTP from January 2014 through August 2019 and associated peaking factors. The
maximum month peaking factors are significantly higher than what is typical for larger treatment facilities.
Table III-5 summarizes the proposed design annual average and maximum month flow.
Table III-5: Summary of Methods Used to Calculate Proposed Maximum Month Design Flow
Current
-Dwelling Unit / School Flow,.qpid
Anticipated
Planned Flow, qpd
Total Flow, Peaking
gpd Factor 9
Piedmont High School ----
1,953 1,2,3
---- ----
(1,363 students)
Piedmont Middle School ----
04
(1,018 students)
I
I
Unionville Elementary School ----
04
---- ----
(701 students)
I
I
Loxdale Subdivision (52 lots) ----
05
I ---- ----
Smithfield Subdivision (70 lots) ---- I
1,800 1.6 I
---- ----
Private parcels ---- I
11,5201,' I
---- ----
Annual average flow 53,360 I
15,270 I
68,630 ----
Maximum month flow 8 ---- I
---- I
120,000 1.7
Maximum week (7-day) flow ---- I
---- I
201,000 3.0
Maximum day flow ----
----
469,000 7.0
' Per 15A NCAC 02T .0114 — Wastewater Design Flow Rates.
2 15 gpd / student for average day school flow rate converted to an annual average flow (e.g., school in session
180 days per year).
3 High school is currently 84 % enrolled. Maximum capacity is 1, 600 students per Union County Public Schools.
4 The middle and elementary schools are. at maximum enrollment.
5 The Loxdale subdivision is built out to a maximum of 52 homes.
6 The Smithfield subdivision currently contains five vacant lots. Vacant lots were counted as three bedrooms for
planning purposes.
Private parcels currently contain 12 dwelling units. Approximately 32 vacant lots are available and were
counted as three bedrooms for planning purposes.
s Rounded to the nearest 10, 000 gallons.
9 The maximum month peaking factor is based on the median peaking factor of the January 2014 through
August 2019 data set.

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STATE OF NORTH CAROLINA
DEPARTMENT OF ENVIRONMENTAL QUALITY
DIVISION OF WATER RESOURES
APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
IV. Necessity Narrative
1. Background
Union County owns and operates the Grassy Branch WWTP and associated collection system
infrastructure. The WWTP is permitted to discharge 0.05 mgd of treated effluent into Crooked Creek via
NPDES permit NC0085812. The Grassy Branch WWTP receives only domestic wastewater. Industrial
users do not discharge to the WWTP. Additionally, the WWTP does not accept influent wastewater from
other municipalities. The WWTP serves three schools, two residential subdivisions, and several private
parcels.
The County has received Notice of Violations (NOVs) for flow, five-day biochemical oxygen demand
(BOD5), ammonia (NH3-N), fecal coliform, total suspended solids (TSS), and pH over the last few years.
The Grassy Branch WWTP NOVs are summarized in Table IV-1. The County has attributed the majority
of the NOVs to record rainfall events in the region. However, over -allocation of sewer connections to the
Grassy Branch WWTP has also contributed to and intensified the compliance issues (refer to Attachment
III. Additional Flow or Flow Reallocation).
Table IVA : Summary of Notice of Violations for Grassy Branch WWTP
Permit Violation
Flow
BOD5
BOD5 NH3-N
NH3-N
TSS
(monthly
(weekly
(monthly (weekly
(monthly
Fecal (weekly
Date
averse)
averac;e
averayej avera;ei_
average)
Coliform average) pH _
1 /31 /2018
0.058
2/3/2018
23
1,500
2/28/2018
0.07
220
3/3/2018
6,971
3/17/2018
3/31 /2018
27.1
3/31 /2018
20.3
16.3
6/2/2018
13.2
2,949
10/6/2018
440
10/13/2018
570
10/20/2018
810
10/31 /2018 0.056

APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
IV. Necessity Narrative
Table IV-1: Summary of Notice of Violations for Grassy Branch WWTP
Permit Violation
Flow
BODs
BODs
NH3-N
NH3-N
TSS
(monthly
(weekly
(monthly
(weekly
(monthly
Fecal
(weekly
Date
averse)
averse)
averse
average)
average)
Coliform
average) pH
11/10/2018
1,200
11 /17/2018
6,000
11 /30/2018
0.088
12/11 /2018
9.97
12/15/2018
7,200
12/22/2018
16.1
560
12/29/2018
17
6,000
12/31 /2018
0.106
4.86
1,448
1 /5/2019
737
1 /12/2019
23.3
1/31/2019
0.10
2/28/2019
0.07
4/6/2019
193
6,000
177
4/13/2019
14.6
6.05
4/30/2019
0.065
24.8
2.05
2. WWTP Process Modifications
Union County has been actively evaluating process changes at the WWTP to minimize NOVs. Staff has
taken several precautionary measures in anticipation of high flow events, as follows:
• Bypassing of tertiary filters during wet weather events.
• Increased monitoring of WWTP to include frequent visits during a wet weather event and
constant monitoring of telemetry via supervisory control and data acquisition (SCADA).
• Control of air input to aeration basins to retain suspended solids:
o Shutting down of all compressors except one.
o Reducing remaining compressor to 30 Hz.
o Shutting down all aerator drop legs except the first set.
Additional process changes will not resolve the permit violations. County staff has made all of the feasible
process changes and implemented the appropriate operational strategies in an on -going effort to resolve
the compliance issues.

APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
IV. Necessity Narrative
3. Collection System Rehabilitation
The County has been actively involved in reduction of infiltration and inflow (I&I) in the collection system.
A Phase 1 1&1 study was commissioned in 2016 to broadly determine problem areas. A Phase 2 study in
2017 focused on repair efforts readily identified in the Phase 1 study. The Phase 2 study also included
wet weather monitoring. In 2018, Phase 3 efforts included confirming the effectiveness of previous repair
efforts, extensive CCTV review of the entire collection system, and the continuation of repair efforts.
Phase 4 of the I&I reduction effort was initiated in January 2019. This phase consists of a review of dry
and wet weather data and patterns and on -going inspection of the collection system.
As of January 2019, the entire Grassy Branch collection system has been surveyed by closed-circuit
television (CCTV). As of May 2019, 42 manholes have been grouted and 48 inflow collectors installed.
Table IV-2 provides a summary of the maintenance data for the I&I reduction effort from 2014 to present,
including investigative man hours and quantity of repaired infrastructure (e.g., manholes, laterals, etc.). A
detailed summary and timeline of the County's I&I reduction efforts is located in Attachment III (Additional
Flow or Flow Reallocation).
Table IV-2: Summary of I&I Effort Maintenance Data
2014
2015
2016
2017
2018
2019
Man Hours Investigating
960
1080
960
480
1512
1152
Man Hours Repairing
360
48
0
72
1152
192
Footage Cleaned
0
0
10,181
425
10,146
CCTV Footage
160
40
10,181
160
16,273
14,627
Hours Smoke Testing
24
20
36
36
37
32
Smoke Test Footage
14,745
7,283
4,235
4,570
15,308
8,368
Manholes Repaired
3
0
0
0
42
3
Lateral Repaired
6
4
0
4
25
8
Cleanouts Repaired
6
4
0
4
17
8
Inflow Dishes Installed
0
0
0
0
53
0
J!9

APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
IV. Necessity Narrative
4. Unavoidable Future Violations
Figures IV-1 through IV-4 compare the final effluent monthly average BOD5, TSS, ammonia, and fecal
coliform concentrations to the WWTP permitted capacity, respectively. The effluent BODS exceedances
have typically occurred during the cold weather months of the year since 2015. Effluent TSS was
exceeded in 2015 and again in April 2019. Weekly and monthly averages for ammonia have been
exceeded, particularly in the colder months. Fecal coliform violations have occurred since 2015
regardless of season.
The historical data indicate influent flows greater than the permitted maximum month design flow results
in final effluent permit violations for flow, BOD5, ammonia, and fecal coliform. Per the evaluation provided
in Attachment III (Additional Flow or Flow Reallocation), the majority of the NOVs are attributed to record
rainfall events in the region. However, it is acknowledged that over -allocation of sewer connections to the
Grassy Branch WWTP has contributed to and intensified the compliance issues. The County's continued
I&I rehabilitation efforts have resulted in a slight reduction in the peaking factors; however, the average
day flow to the WWTP has not significantly decreased. The existing Grassy Branch WWTP treatment
infrastructure will not support compliance with the current effluent permit limits. The violations will
continue to occur without infrastructure improvements.
The WWTP must not receive an NOV during the consent order timeframe. The proposed interim monthly
average effluent limits are provided in Table IV-3. The proposed interim effluent limits do not include a
weekly average limit. It is anticipated that during construction, a weekly average limit will be difficult to
meet and will likely result in NOVs.
The proposed interim limits were developed based on the current performance of the WWTP prior to the
upgrade and improvements to existing infrastructure. Interim limits are proposed for BOD5, TSS,
ammonia, and fecal coliform. Changes are not being proposed for the current effluent permit limit for
dissolved oxygen at 5 mg/L. The justification for the effluent limits for each pollutant are as follows:
• BOD5 — With exception of one data point in March 2015, the WWTP has consistently
achieved a monthly average BOD limit of 30 mg/L in winter and summer months. The
process evaluation confirmed the reliability of the existing secondary treatment process to
meet the proposed monthly average BOD limit of 30 mg/L in winter and summer. The
secondary process is not equipped with the volume or aeration capacity to reliably meet
less than 30 mg/L BOD without raising the risk of a NOV.
TSS —A monthly average of 100 mg/L is proposed as an interim effluent limit. With the
exception of a March 2019 data point, the WWTP has consistently achieved less than
60 mg/L of effluent TSS. However, the calculated hydraulic and solids loading rates to the
existing filters are excessive compared to standard engineering practice. Therefore, the
proposed interim effluent TSS limit of 100 mg/L was established to avoid future NOVs as
a result of limited solids handling and filter capacity at the WWTP.
Ammonia —A monthly average of 20 mg/L and 6 mg/L ammonia is proposed as interim
effluent limits in the winter and summer months, respectively. The historical data
indicates that the WWTP has consistently achieved 20 mg/L in the winter and 6 mg/L in
4/9

APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
IV. Necessity Narrative
the summer. The secondary process is not equipped with the volume or aeration capacity
to reliably meet less than the proposed summer and winter interim limits without
increasing the risk of an NOV during the SOC timeframe.
Fecal coliform — A monthly average limit of 900/100 mL is proposed as in interim effluent
limit for fecal coliform. The existing UV system cannot be further optimized and does not
have the required capacity to meet the proposed maximum month design flow of
0.12 mgd. The highest monthly geometric mean occurred in December 2018 with a result
of approximately 758/100 mL. The capacity of the existing UV system is not sufficient to
meet a weekly average limit or a daily maximum during the SOC timeframe.
• Dissolved oxygen — No changes are proposed for the effluent dissolved oxygen limit of
greater than 5 mg/L.
Table IV-3: Proposed Interim Effluent Limits
Monthly Average Weekly Average
Interim flow, mgd 0.120 ----
BOD5, mg/L (November 1 through March 31) 30
BOD5, mg/L (April 1 through October 31) 30 ----
TSS, mg/L
100
Ammonia, mg/L (November 1 through March 31) 20
Ammonia, mg/L (April 1 through October 31) 6
Fecal coliform, geometric mean / 100 mL 900 ----
Dissolved oxygen, mg/L
>5
The QUAL2K modeling results (Tetra Tech, 2019) support the proposed interim effluent limits. The
calibrated baseline wasteload model demonstrated strong performance results and captured key
dissolved oxygen trends in Crooked Creek. The calibrated QUAL2K model was then used to assess the
impact of the Grassy Branch WWTP expansion flow for both the interim and final proposed effluent limits.
The model demonstrates that there is assimilative capacity for both the interim SOC and final effluent
permit limits. The instream dissolved oxygen standard of 5 mg/L was met in all conditions. The model
results also demonstrated that ammonia toxicity will not be exceeded.
519

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STATE OF NORTH CAROLINA
DEPARTMENT OF ENVIRONMENTAL QUALITY
DIVISION OF WATER RESOURES
APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
V. Engineer Certification

HazenTechnical Me»Iorandum
North Carolina License C-0381
December 3, 2019
To: Union County Department of Public Works
From: Jim Struve, PE, Hazen and Sawyer (Hazen)
Mary Sadler, PE, Hazen
Joe Rolirbacher, PE, Hazen
Michael Parker, PE, Hazen
Amanda Ford, Hazen
►2/3t r+9
Engineer Certification for Grassy Branch
Wastewater Treatment Plant Special Order by
Consent
1. Introduction
This process certification is in support of the Union County Public Works (UCPW) application for a
Special Order by Consent (SOC) for the Grassy Branch Wastewater Treatment Plant (WWTP). This
correspondence is an independent professional report on the status of the Grassy Branch WWTP to meet
the existing National Pollutant Discharge Elimination System (NPDES) permit limits during the period
the WWTP will be operating under the SOC. The following narratives specifically address the SOC
application requirements. It should be noted that all engineering detenninations are supported by a
detailed process evaluation published separately from this signed and sealed certification.
2. Summary of Existing WWTP Infrastructure
The Grassy Branch WWTP is an extended aeration package treatment plant (PTP) constructed by Hydro -
Aerobics Package Wastewater Treatment Systems in 1997. The WWTP is pennitted for a maximum
month design flow of 50,000 gallons per day (gpd), or 0.05 million gallons per day (mgd) to the Crooked
Creek receiving stream, a Class C water. Union County operates the facility NPDES permit NC0085812.
Table 2-1 summarizes the current final effluent permit limits for five-day biochemical oxygen demand
(BODs), total suspended solids (TSS), ammonia (NH3-N), and fecal coliform.
The Grassy Branch WWTP consists of coarse screening, flow equalization, two conventional aeration
basins with coarse bubble diffusers, two secondary clarifiers, a sand filter, and ultraviolet (UV)
disinfection. Waste activated sludge (WAS) is processed in an aerobic digester for volatile solids
reduction. The digested solids are then pumped to a tanker truck and transported to the Crooked Creek
WWTP for further stabilization. Table 2-2 summarizes the design criteria of the existing Grassy Branch
WWTP infrastructure.
Hazen and Sawyer • 9101 Southern Pine Blvd, Suite 250 • Charlotte, NC 28273 • 704.357.3150

Hazen
Table 2-1: Current Final Effluent Permit Limits
Parameter
Monthly
Average
Weekly
Average
BOD5, mg/L (April 1 through October 31)
5
7.5
BOD5, mg/L (November 1 through March 31)
10
15
TSS, mg/L
30
45
Ammonia, mg/L (April 1 through October 31)
2
6
Ammonia, mg/L (November 1 through March 31)
4
12
Fecal coliform, geometric mean / 100 mL
200
400
Dissolved oxygen, mg/L
> 5
Table 2-2: Summary of Design Criteria for Existing Grassy Branch WWTP Infrastructure
Unit Process
Parameter
Design Criteria
Number of pumps
2
Influent Pump Station
Capacity per pump, gpd
129,600
Capacity total, gpd
259,200
Type
Coarse Manual Bar Screen
Influent Screening
Number
1
Opening diameter, inch
2
Number
2
Volume per basin, gallon
7,700
Flow Equalization
Volume total, gallon
15,400
Type of aeration system
Coarse bubble
Number of blowers
2
Flow Equalization
Treatment Aeration System
Type of blowers
Positive displacement
Motor, horsepower (HP)
2
Number
2
Secondary Treatment
Volume per basin, gallon
25,000
C i lortiras•\ itr.iii:l N\a.teN� iirt Irk,,ini:iii I- u i

Hazen
Table 2-2: Summary of Design Criteria for Existing Grassy Branch WWTP Infrastructure
i
Unit Process
Secondary Treatment
Aeration System
Secondary Clarifier
Sand Filter
Sand Filter Aeration
System
Ultraviolet Disinfection
3. Flow Evaluation
Parameter
Volume total, gallon
Hydraulic retention time per basin, hour
Hydraulic retention time total, hour
Type of aeration system
Number of blowers
Type of blowers
Motor, horsepower (HP)
Number of clarifiers
Diameter, feet
Surface area, SF
Number of beds
Area of bed per unit, SF
Area of bed total, SF
Fill material
Number of blowers
Type of blowers
Motor, horsepower (HP)
Number of banks
Number of modules
Number of lamps per module
Design Criteria
50,000
12
24
Coarse bubble
2
Positive displacement
7.5
2
10
78.5
2
18.75
37.5
Anthracite/Sand
2
Positive displacement
3
2
3
2
The historical data indicate that influent flows in excess of the permitted design capacity of the WWTP
have resulted in final effluent permit violations for flow, conventional pollutants, and bacterial pollutants.
The County has attributed the majority of the Notice of Violations (NOVs) to record rainfall events in the
region. The County also acknowledges that more sewer connections have been allocated to the Grassy
Branch WWTP than available capacity.

Hazen
Hazen recommends a permanent increase in the design maximum month flow from 0.05 mgd to
0.120 mgd. The flow increase is associated with the existing domestic flow discharging to the WWTP, the
maximum student capacity of the three schools, new connections in the Smithfield subdivision to fulfill
contractual obligations, and private parcel connections along the main sewer line to the plant. The
Loxdale subdivision has reached the maximum dwelling units for the subdivision. The anticipated
planned flow was established using the average day wastewater flow rates published in 15A NCAC 02T
.0114 (Wastewater Design Flow Rates). The anticipated planned flow was added to the annual average
flow to the WWTP.
A maximum month peaking factor of 1.7 was applied to the annual average flow, which results in a
maximum month design flow of 0.120 mgd. The peaking factor of 1.7 is the median peaking factor of the
2014 through August 2019 data set. The maximum month peaking factors at the Grassy Branch WWTP
are significantly higher than what is typical for larger treatment facilities. Table 3-4 summarizes the
proposed design annual average and maximum month flow.
Table 3-4: Summary of Methods
Used to Calculate
Proposed Maximum
Anticipated
Month Design
Total Flow,
Flow
Current
Peaking
Dwelling Unit / School
Flow,.gpd
Planned Flow, pd
gpd
----
Factor 9
Piedmont High School
----
1,953 1 2.3
____
(1,363 students)
Piedmont Middle School
----
04
(1,018 students)
I
I
Unionville Elementary School
I ----
04
(701 students)
I
I
Loxdale Subdivision (52 lots)
I ----
I 05
Smithfield Subdivision (70 lots)
----
I 1,800 1,6
Private parcels
---- I
11,520 1,7
Annual average flow I
53,360 I
15,270 I
68,630 I
----
Maximum month flow 8 I
---- I
---- I
120,000 I
1.7
Maximum week (7-day) flow I
----
---- I
201,000
3.0
Maximum day flow
----
----
469,000
7.0
Per 15A NCAC 02T .0114 — Wastewater Design Flow Rates.
2 15 gpd /student for average day school flow rate converted to an annual average flow (e.g., school in session
180 days per year).
3 High school is currently 84% enrolled. Maximum capacity is 1, 600 students per Union County Public Schools.
4 The middle and elementary schools are at maximum enrollment.
5 The Loxdale subdivision is built out to a maximum of 52 homes.
6 The Smithfield subdivision currently contains five vacant lots. Vacant lots were counted as three bedrooms for
planning purposes.
Private parcels currently contain 12 dwelling units. Approximately 32 vacant lots are available and were
counted as three bedrooms for planning purposes.
8 Rounded to the nearest 10, 000 gallons.
9 The maximum month peaking factor is based on the median peaking factor of the January 2014 through
August 2019 data set.
, Pl,jnt
4.. 1

Hazen
4. Evaluation and Optimization of Existing Treatment Units
4.1 Historical Influent Characterization Data
Tables 4-1 and 4-2 summarize the maximum month, maximum week (e.g., 7-day), and maximum day
peaking factors (PF) and influent concentrations and loads, respectively. Data was evaluated from 2015
through 2018. Data from the year 2019 does not account for the impact of the seasonal flow variation and
was therefore not included in the analysis. A statistical approach was used for evaluating influent
characterization metrics and peaking factors. The original design influent loads and concentrations for the
WWTP are not known, as the criteria were not provided in the manufacturer's Wastewater Treatment
Systems Operations and Maintenance (O&M) manual. The proposed design concentrations and loads for
the Grassy Branch WWTP improvements project are summarized in Table 4-3.
Table 4-1: Influent Flow and Peaking Factors
Parameter 2015
1 2016
2017
2018
Maximum month peaking factor 1.94
1.65
1.74
1.91
Maximum week (7-day) peaking factor 2.98
3.44
2.70
2.72
Maximum day peaking factor 7.76
7.00
6.74
6.72
Table 4-2: Annual Average Influent Concentrations and Loads
Parameter
2015
2016
2017
2018
BOD5, mg/L
135
185
217
203
BOD5, Ib/d
46
59
69
87
TSS, mg/L
184
325
462
458
TSS, Ib/d
63
98
137
170
NH3-N, mg/L
33
33
27
29
NHS-N, Ib/d
10
11
9
11
_ .. .. ii� ii � (.iPt1�5� f';.:. .II �•�+.. �I n.11lll.'I: I'I.rl'. Yac,� i., I

Parameter
TSS
BODs
TKN
NH3-N
Total
phosphorus
Table 4-3: Proposed Influent Design Concentrations and Loads
Concentration,
Maximum Month
Maximum Week
Maximum Day
m L
Load, Ibld
Peakin Factor
Peak -in Factor
Peakin Factor
250
140
1.2
1.5
2.0
250
140
1.2
1.5
2.0
40
22
1.2
1.5
2.0
26
15
1.2
1.5
2.0
4.2 Influent Pumps
5.0 1 2.8 1 1.2 1 1.5 1 2.0
The existing influent pumps are rated at 130,000 gpd each at 15 feet of total dynamic head (TDH), which
allows for 260,000 gpd with both units in service. The existing pumps cannot be further optimized and do
not have sufficient capacity for the proposed maximum month design flow. Additional pumps will be
needed to provide adequate capacity with redundancy for the proposed improvements.
4.3 Influent Screening
Influent screening is comprised of a manual coarse bar screen designed for a peak hour flow of
150,000 gpd (e.g., 2.5 times the maximum month design flow of 50,000 gpd). The existing bar screen
cannot be further optimized. Additional screening unit(s) are required as the existing screen does not have
adequate capacity to meet the proposed maximum month design flow.
4.4 Flow Equalization
Existing flow equalization consists of two 7,700-gallon basins, or 15,400 gallons total volume. The
existing flow equalization basins cannot be further optimized, as the basins do not provide adequate
hydraulic retention time to attenuate the proposed maximum month design flow. Additional equalization
volume is required as part of the facility improvements.
4.5 Secondary Treatment Train
The secondary treatment process consists of a 50,000 gpd (e.g., two trains in service) conventional
aeration activated sludge process. The PTP is equipped with coarse bubble diffusers and two rotary lobe
positive displacement blowers. The aeration basins were designed to provide a 24-hour hydraulic
retention time at the current maximum month design flow of 0.05 mgd. However, only 15 hours of
hydraulic retention time is provided at current flows. The WAS flow is not measured nor were solids
hauling records available for the determination of the solids retention time (SRT). The positive
displacement blowers and coarse bubble aeration system does not have adequate capacity to treat the

■
existing annual average, maximum month, maximum week, and maximum day loads with one blower out
of service. Based on the available hydraulic, process, and equipment capacity, the secondary process
cannot be further optimized to treat additional flow. New process volume and aeration equipment is
required as part of the facility improvements for the proposed maximum month design flow.
4.6 Secondary Clarifiers
The Grassy Branch WWTP has two 10 foot diameter secondary clarifiers. Each clarifier has a sidewater
depth of 10 feet. The reported historical peak day surface overflow rates (SOR) and surface loading rates
(SLR) are 1,823 gpd/SF and 63 lb/SF, respectively. The calculated overflow and loading rates are
excessive compared to standard engineering best practices. Typical design overflow rates range from
300 to 1,000 gpd/SF. Typical solids loading rates range from 15 to 35 lb/day-SF. The existing secondary
clarifiers are undersized and cannot be further optimized. New secondary clarification capacity is required
for the proposed improvements.
4.7 Tertiary Filtration
The WWTP has two mixed media (anthracite/sand) tertiary filters each with a surface area of 18.75 SF.
The historic peak day hydraulic loading rate and solids loading rate are 7.3 gpm/SF and 3.9 lb/SF,
respectively. The calculated hydraulic and solids loading rates are excessive compared to standard
engineering best practices. Typical filter design hydraulic and solids loading rates are 5 gpd/SF and
3 lb/day-SF, respectively. The existing mixed media filters cannot be further optimized. New filtration
capacity is required for the proposed improvements.
4.8 UV Disinfection
The existing UV disinfection system was installed in the original chlorine contact chamber as a retrofit
project. Routine maintenance is problematic as it requires that UCPW staff remove grating and stand in
the channel. The existing UV system cannot be further optimized and does not have the required capacity
to meet the proposed maximum month design flow. An additional unit(s) will be required to meet the
proposed peak day flow.
4.9 Effluent Flow Measurement
Effluent flow is measured via a discharge weir. The existing weir will require replacement to
accommodate the proposed maximum month design flow.
4.10 Post Aeration
The facility does not have a formal post aeration system. Aeration is achieved through the effluent flow
weir and head drop to the final effluent discharge location. The facility has not had any effluent permit
violations for dissolved oxygen, so it is not anticipated that additional post aeration capacity will be
needed.

Hazen
4.11 Aerobic Digester
The existing aerobic digester equalization consists of two 4,500-gallon basins for 9,000 gallons of total
volume. The aerobic digester is equipped with coarse bubble diffusers connected to the secondary
treatment positive displacement blowers. The aerobically digested solids are pumped out and transported
to the Crooked Creek WWTP for final disposal. Additional aerobic digestion volume will be needed to
accommodate the proposed maximum design flow. The final disposal method will not be altered.
4.12 Operational Procedures
Current operating procedures are consistent with best practices for operation of a wastewater treatment
facility. Housekeeping and maintenance of the facility are excellent for industry standards. No operational
changes are recommended at this time.
5. Specific Requirements of the SOC
5.1 Evaluation of Existing Treatment Units and Operational Procedures
The existing Grassy Branch WWTP does not have adequate process capacity to adequately treat the
current flows and loads and maintain NPDES permit compliance. The WWTP cannot be further
optimized or operated in a manner that achieves compliance with final effluent permit limits. Additional
process units are necessary for compliance with the existing final effluent permit limits.
5.2 Effluent Limits that the Facility Could Be Expected to Meet if Operated at Maximum
Efficiency during the Term of the Requested SOC (Consider Interim Construction Phases)
The historical data indicate that influent flows greater than the permitted maximum month design flow
will result in final effluent permit violations for flow, BODs, TSS, ammonia, and fecal coliforn.
Table 5-1 summarizes the requested interim effluent limits for the Grassy Branch WWTP. The requested
limits are based on the 2015 to August 2019 historical data in conjunction with the process modeling and
WWTP evaluation. It is not anticipated that construction phases will be applicable to the proposed
upgrade project, so tiered interim limits are not provided.
5.3 Effluent Limits after Expansion and Upgrade of WWTP
Speculative limits were informally discussed with the Division of Water Resources (DWR) for the
upgraded and expanded Grassy Branch WWTP during the process of preparing the SOC application
package. DWR responded that a receiving stream model was necessary to assess water quality impacts of
the expanded flow. The County conducted a site -specific QUAL2K model of the Crooked Creek
receiving stream in 2016 and 2017 as part of a broader master planning process. A Final Study Plan was
approved by DWR in July 2016. Site -specific sampling was conducted in August 2016. A draft model
report was submitted to the County in 2017.

Hazen
Table 5-1: Interim Effluent Permit Limits Request
Parameter Monthly Avera a
Weekly Average
Interim flow, mgd
0.120
----
BOD5, mg/L (November 1 through March 31)
30
----
BOD5, mg/L (April 1 through October 31)
30
----
TSS, mg/L
100
----
Ammonia, mg/L (November 1 through March 31)
20
----
Ammonia, mg/L (April 1 through October 31)
6
----
Fecal coliform, geometric mean / 100 mL
900
----
Dissolved oxygen, mg/L
> 5
The QUAL2K model was updated in late summer 2019 to serve as a baseline wasteload model of existing
conditions in the Crooked Creek receiving stream. The model was submitted to DWR staff for review in
August 2019. A meeting was held with DWR staff on October 1, 2019 to discuss the model calibration,
verification, and performance results. Attachment A of this Engineering Certification provides the
Crooked Creek QUAL2K Model Development Report (Tetra Tech, October 2019). The model
demonstrated strong performance results and captured key dissolved oxygen trends.
Interim and final permit limits were also discussed during the meeting with DWR on October 1, 2019. Per
15A NCAC 02B .0206(d)(1), if the 7Q] 0 receiving stream flow is estimated to be zero and if the 30Q2
flows are estimated to be greater than zero, the minimum flow requirements are a BOD concentration of
5 mg/L, an ammonia concentration of 2 mg/L, and a dissolved oxygen concentration of 6 mg/L. A 1 mg/L
ammonia threshold is typically applied to address ammonia toxicity. Based on the discussion during the
October 1, 2019 meeting with DWR staff, Table 5-2 provides a summary of the anticipated effluent limits
for the upgraded and expanded WWTP. A major NPDES permit modification and an engineering
alternatives analysis will be required for the permanent flow increase.
The calibrated QUAL2K model was then used to assess the impact of the Grassy Branch WWTP
expansion flow for both the interim and final proposed effluent limits. The Crooked Creek Model
Application Report for the Grassy Branch WWTP (Tetra Tech, October 2019) is located in Attachment B.
The model demonstrates that there is assimilative capacity for both the interim SOC and final effluent
permit limits. The instream dissolved oxygen standard of 5 mg/L was met in all conditions. The model
results also demonstrated that ammonia toxicity will not be exceeded.
One of the issues raised by DWR staff during the October 1, 2019 meeting was the impact of the Grassy
Branch WWTP expansion on downstream turbidity impairment in the Rocky River. Significant sources of
turbidity in the Rocky River watershed have been associated with stormwater run-off and sediment
erosion during rain events. The steady state QUAL2K model does simulate output for TSS. Tetra Tech
conducted a statistical analysis of the relationship between TSS and turbidity at four downstream ambient

Is
:-1
water quality sampling sites. Tetra Tech concluded that an expansion of the Grassy Branch WWTP is
unlikely to contribute to the downstream turbidity impairment. The impact of the Grassy Branch WWTP
low effluent flow compared to turbidity contribution from precipitation events is negligible.
Table 5-2: Anticipated Final Effluent Permit Limits for the Upgraded and Expanded WWTP
Parameter
Monthly Average
I Weekl Average
Flow, mgd
0.120
----
BOD5, mg/L (April 1 through October 31)
5
7.5
BOD5, mg/L (November 1 through March 31)
10
15
TSS, mg/L
30
45
Ammonia, mg/L (April 1 through October 31)
1
2
Ammonia, mg/L (November 1 through March 31)
2
g
Fecal coliform, geometric mean / 100 mL
200
400
Dissolved oxygen, mg/L
EXI
5.4 Any Other Actions Taken to Correct Problems Prior to Requesting the SOC
The County has been actively involved in reduction of infiltration and inflow (I&I) in the collection
system. A Phase 1 I&I study was commissioned in 2016 to broadly determine problem areas. A Phase 2
study in 2017 focused on repair efforts readily identified in the Phase I study. The Phase 2 study also
included wet weather monitoring. In 2018, Phase 3 efforts included confirming the effectiveness of
previous repair efforts, extensive closed-circuit television (CCTV) review of the entire collection system,
and the continuation of repair efforts. Phase 4 of the I&I reduction effort started in 2019. This phase
consists of a review of dry and wet weather data and patterns and on -going inspection of the collection
system. As of January 2019, the entire Grassy collection system has been surveyed by CCTV. As of May
2019, 42 manholes have been grouted and 48 inflow collectors installed. County anticipates continuing
I&I efforts in the Grassy Branch WWTP collection system.
Union County has also been actively evaluating process changes at the WWTP to minimize NOVs. Staff
has taken several precautionary measures in anticipation of high flow events, as follows:
• Bypassing of filters.
Increased monitoring of WWTP to include frequent visits during a wet weather event and
constant monitoring of telemetry via SCADA.
• Control of air input to aeration basins to retain suspended solids:
o Shutting down of all compressors except one.
. . . . . . . . .. I I...II i,,._I! 1-I 1' - of , I

Hazen
o Reducing remaining compressor to 30 Hz.
o Shutting down all aerator drop legs except the first set.
6. Summary of Recommendations for Infrastructure Improvements
The historical data indicate the influent flows that exceed the permitted design capacity of the Grassy
Branch WWTP have resulted in final effluent permit violations for flow, conventional pollutants, and
bacterial pollutants. The County has attributed the majority of the NOVs to record rainfall events in the
region. The County also acknowledges that more sewer connections have been allocated to the Grassy
Branch WWTP than available capacity. Hazen recommends a pennanent increase in the design maximum
month flow from 0.05 mgd to 0.120 mgd.
Hazen recommends an expansion of the Grassy Branch WWTP to include the following improvements:
• Larger influent pumps.
• A retrofit of the existing aeration basin coarse bubble diffusers to fine bubble diffuser equipment.
• One additional package secondary treatment train to include volume for flow equalization.
• New positive displacement blowers serving the existing and new aeration basins.
• An additional secondary clarifier.
• A new cloth disk filter.
• A new UV disinfection system.
• Additional volume for aerobic digestion.
It is not anticipated that post aeration equipment will be needed for the plant expansion based on the
current plant performance. Plant hydraulics would be evaluated during detail design. Existing unit
processes will remain in service during construction. It is not anticipated that construction activity will
affect the current facility perfonnance.
i ' . . tIlcl' ' . III,. f' r I ., I I of 1 I

Attachment A: Crooked Creek QUAL2K Model
Development, Tetra Tech, October 15, 2019

Crooked Creek QUAL2K Model
Development
Union County, North Carolina
October 15, 2019
PREPARED FOR
Union County Public Works
500 North Main Street, Suite 500
Monroe, NC 28112
PREPARED BY
Tetra Tech
One Park Drive, Suite 200
PO Box 14409
Research Triangle Park, NC 27709
Pictured: North Fork Crooked Creek (Tetra Tech, 2016)
N
TETRA TECH

(This page was intentionally left blank.)

Crooked Creek QUAL2K Model
October 15, 2019
The Crooked Creek watershed in Union County, North Carolina supports three existing wastewater
treatment plants (WWfPs): Hemby Acres, Crooked Creek #2, and Grassy Branch. These WWTPs
discharge treated effluent directly into Crooked Creek. There are a number of tributaries across the
watershed including the North Fork and South Fork of Crooked Creek, and Grassy Branch which is the
most downstream before the confluence with the Rocky River (Figure 1).
Figure 1. Crooked Creek watershed map
A QUAL2K river water quality model was developed to evaluate the existing conditions along Crooked
Creek. The baseline model of existing conditions along Crooked Creek was built, calibrated, and
corroborated using monitoring data collected during the summer of 2016. Monitoring results and other
criteria were used to break the modeled receiving stream into six model stream reaches (Figure 2).
® TETRA TECH
ES-1

Crooked Creek QUAL2K Mode!
October 15, 2019
® TETRA TECH
Crooked Creek Watershed
QUAL21K Model Segmentation
!VAQ„+eea SwePvne Nvm, G�Nev rlv&_77op,ca,n
� itldKMf OSO]-ZOl®. MYuce
Figure 2. Crooked Creek QUAL2K model reach segmentation
Rocky River
River/Stream
QWatershed Boundary
A strong model calibration result was achieved for DO (Figure 3). The model simulation of daily average
DO concentration captured key trends along the stream longitudinally, particularly in accounting for
diurnal variation. A model corroboration simulation also demonstrated a similarly strong model
performance (Figure 4). Sensitivity analyses revealed that the model was most sensitive to assumptions
for sediment oxygen demand and reaeration, but results were relatively robust given strong assumptions
based on good monitoring data.
O-M TETRA TECH ES-2

Crooked Creek QUAL2K Mode!
October 15, 2019
I--1-- I - _--2 ------ - I - — --- 3-------- I — 4------ I ---------- —------ 5---------- —------ I _-- - ---------- -- 6------------_----__-
Hemby CC#2 SFCC HWY Grassy WWTP, 12
WWTP WWTP confluence 601 Grassy Branch confluence
Beaver
Dams � 10
-=T------- 8
• ---- •
i @ r • 00 0 • f • 6
1 4D�...0....``, .,._ O r• it • •• - �- __• - • ---------------
� O •
1O I. s O _ •` ---� 4
00
+ O + �'
- - '• 2
0
20 15 10 5
Distance from outlet (miles)
• YPDRBA Pant Data n Obs Long Data (AM) Trip 1 Obg long Data (PM) Trip 1
o Obs Long Data (AM) Trip 2 • Obs Long Data (PM) Trip 2 Simulated Mean
- - - - Simulated Min/Max Observed Sonde Data — WQS: 5.0 mg/l
DO Saturation
Figure 3. Simulated and observed DO along Crooked Creek (calibration)
2---------- I ------------- 3 --- - -- I ---4-- - I--------
Hemby CC#2 SFCC HWY
WWTP WWTP confluence 601
Beaver
Dams
--- I------------------------6 - -
Grassy WWTP.
Grassy Branch confluence
- ------ I • -----------------------
•
n =•
L=j
O.- - - - - -------- - - - - --
• 'f
20 15 10 5
Distance from outlet (miles)
• YPDRBA Pant Data O Obs Long Data (AM) • Otas Long Data (PM)
—SimuiatedMean - - -- Simulated Min/Max Observed Sonde Data
--- WQS: 5.0 mg/l DO Saturation
Figure 4- Simulated and observed DO along Crooked Creek (corroboration)
0
0
12
10
8 E
4
2
0
o�
E
c
O
}
0
0
NTETRA TECH ES-3

Crooked Creek QUAL2K Model
October 15, 2019
TABLE OF CONTENTS
1.0 INTRODUCTION.....................................................................................................................................1
2.0 SUMMARY OF AVAILABLE DATA
3
.......................................................................................................
2.1 Goose and Crooked Creeks LWP..................................................................................................
3
2.2 Permitted Point Source Monitoring..................................................................................................
3
2.3 YPDRBA (Coalition) Instream Sampling..........................................................................................
5
2.4 Tetra Tech Sampling.......................................................................................................................
5
2.5 HEC-RAS Modeling Efforts...........................................................................................................
6
2.6 Goose and Crooked Creek LSPC Model........................................................................................
6
3.0 QUAL2K MODEL SETUP......................................................................................................................
8
3.1 Model Documentation......................................................................................................................
8
3.2 Model Date Selection.......................................................................................................................
8
3.3 Model Segmentation.........................................................................................................................8
3.4 Reach Hydraulics.......................................................................................................................
10
3.5 Meteorological Inputs, Light and Heat.........................................................................................
12
3.5.1 Hourly Inputs............................................................................................................... .....
12
3.5.2 Light and Heat Inputs...........................................................................................................
14
3.6 Carbonaceous Biochemical Oxygen Demand Simulation............................................................
15
3.7 Boundary Conditions.....................................................................................................................
15
3.7.1 Headwaters.........................................................................................................................
15
3.7.2 Point Source Flows and Water Quality...............................................................................
19
3.7.3 Tributary Flows and Water Quality......................................................................................
22
3.8 Reach Water Quality Parameters ................................................................................................
23
4.0 MODEL CALIBRATION AND CORROBORATION.............................................................................26
4.1 Hydrology Calibration.....................................................................................................................
26
4.2 Water Temperature Calibration .............................................
27
4.3 Water Quality Calibration..............................................................................................................
28
4.4 Model Corroboration Results....................................................................................................
29
4.4.1 Water Temperature Corroboration................................................................................. ...29
4.4.2 Water Quality Corroboration...............................................................................................
30
5.0 MODEL SENSITIVITY..........................................................................................................................31
6.0 REFERENCES......................................................................................................................................34
LN TETRA ECH 1

Crooked Creek QUAL2K Model October 15, 2019
CA Stream Hydrology Measurements................................................................................................. 43
C.2 Nutrient Sampling........................................................................................................................ 44
C.3 Longitudinal Dissolved Oxygen ...................................................................................................48
CA Diurnal Dissolved Oxygen.......................................................................................................... 60
LIST OF TABLES
Table 1.
Existing permit limits for the wastewater treatment plants located along Crooked Creek .............
5
Table 2.
Reach segmentation for Crooked Creek QUAL21K model..............................................................
9
Table 3.
Reach hydraulic model setup inputs...........................................................................................11
Table 4.
Meteorological inputs data source summary ...............................................................................12
Table 5.
Hourly inputs for air temperature, dew point temperature, and cloud cover................................13
Table 6.
Light and heat model setup inputs................................................................................................14
Table 7.
USGS flow conditions in adjacent Goose Creek watershed (flows in cfs)....................................16
Table 8.
Headwater water quality initial model inputs (calibration model).................................................18
Table 9.
Headwater water quality initial model inputs (corroboration model).............................................19
Table 10.
Point source flow and water quality inputs (calibration period)..................................................20
Table 11.
Point source flow and water quality inputs (corroboration period) .............................................
21
Table 12.
Tributary flow and water quality inputs (calibration model).........................................................22
Table 13.
Tributary flow and water quality inputs (corroboration model)....................................................23
Table 14.
Model inputs for bottom algae coverage....................................................................................
24
Table 15.
Crooked Creek QUAL2K model sensitivity test runs................................................................
31
Table 16.
Crooked Creek QUAL21K model sensitivity test run results.......................................................
33
LIST OF FIGURES
Figure 1.
Crooked Creek watershed map.................................................................................................. 1
Figure 2.
Crooked Creek QUAL21K model reach segmentation................................................................. 2
Figure 3.
Simulated and observed DO along Crooked Creek (calibration) ................................................ 3
Figure 4.
Simulated and observed DO along Crooked Creek (corroboration) ............................................. 3
Figure 5.
Crooked Creek watershed location map...................................................................................... 2
Figure 6.
Crooked Creek watershed elevation and reach map....................................................................2
Figure 7.
Crooked Creek point source discharge locations and YPDRBA water quality sampling sites...... 4
® TETRA TECH 2

Crooked Creek QUAL2K Model
October 15, 2019
Figure 8. LSPC model extent and subbasins for the Goose and Crooked Creek watersheds.......
Figure 9. Crooked Creek QUAL2K model reach segmentation......................................................
Figure 10. Crooked Creek summer 2016 cross sectional surveys by Tetra Tech ..........................
Figure 11. Crooked Creek channel bottom width measured from summer 2016 cross sections ...
Figure 12. Crooked Creek stream discharge estimates..................................................................
Figure 13. Simulated and site -estimated flows for Crooked Creek model extent (calibration).......
Figure 14. Simulated and observed water temperature along Crooked Creek (calibration) ...........
Figure 15. Simulated and observed DO along Crooked Creek (calibration) ...................................
Figure 16. Simulated and observed water temperature along Crooked Creek (corroboration).......
Figure 17. Simulated and observed DO along Crooked Creek (corroboration) ...............................
Figure 18. Sensitivity test results (runs 1 and 2): bottom algae coverage and SOD rate .................
Figure 19. Sensitivity test results (runs 3, 4, and 5): Manning's n, shade, and headwater flow......
Figure 20. Sensitivity test results (run 6): reaeration model selection .............................................
7
.28
29
30
30
32
32
33
® TETRA TECH

Crooked Creek is a Class C waterway, with the South Fork, North Fork, and Crooked Creek downstream
of the confluence all listed as Category 5 impaired waterways for turbidity and ecological/biological
integrity (NC DENR, 2016). The Crooked Creek watershed is located largely in Union County, North
Carolina with a small fraction of land in the headwaters located in Mecklenburg County. The watershed is
on the southeastern extent of the Charlotte metropolitan area, immediately east of the City of Matthews.
The North Fork and South Forks of Crooked Creek join north of the City of Monroe, then flow eastward as
Crooked Creek until the confluence with Rocky River in the Yadkin Pee Dee River Basin (Figure 5). The
Crooked Creek drainage area is about 50 square miles, and the mainstem of the creek currently receives
effluent from three permitted wastewater treatment plants (WWTPs): Hemby Acres, Crooked Creek #2,
and Grassy Branch.
Elevation across the watershed ranges from 406 — 794 feet (124 — 242 meters) (Figure 6). The North
Fork Crooked Creek is approximately 11.6 miles long, South Fork Crooked Creek is 13.9 miles long,
Crooked Creek south of the confluence is 12.2 miles long, and the Grassy Branch tributary is 3.0 miles
long. There are also several small unnamed tributaries within the watershed.
In order to simulate existing conditions along Crooked Creek, a QUAL2K model was set up, calibrated
and corroborated based on data collected in 2016. QUAL2K is a one-dimensional steady-state river water
quality model frequently used for simulating DO (Chapra et al., 2012). QUAL2K assumes a well -mixed
stream channel (both vertically and laterally), and employs a diel, or 24-hour period, heat budget which
can be used to model DO on an hourly basis. Model calibration and corroboration used data collected
during August and September 2016, along with supplemental data from other sources. This report details
data sources, QUAL2K model setup, calibration, corroboration, and sensitivity analyses.
Q'TETRA TECH

Crooked Creek QUAL2K Model
October 15, 2019
I
North olina
Mecklenburg
County Rocky River
r i Stanly
Il
J County Crooked Creek
South ;Ca olina
Union
County
North Fork
Crooked Creek -
"� 1
� Grassy Branch
t - -
-, Legend
r• ,rl • South Fork Stream/River
- Crooked Creek
• �! v _ Highway
1
Interstate
® Watershed Boundary
Crooked Creek watershed N o o.7s 4s s County Boundary
TETRA TEf.N s� �ICNometers
w A o o.7s s a State Boundary
Milec
Figure 5. Crooked Creek watershed location map
Crooked Creek
Mecklenburg
County
Union
County
'North Fork Crooked Creek �
0
River
Stanly
County
Legend
South Fork Crooked Creek
River/Stream
Watershed Boundary
0 County Boundary
Elevation (feet)
High: 794
Crooked Creek Watershed (rr�
N o e.s 4 z Low: 406 � rETaw TEOt Digital Elevation Model v+
0 e.75 1.5 3
Figure 6. Crooked Creek watershed elevation and reach map
QTETRA TECH 2

Crooked Creek QUAL2K Model
October 15, 2019
The available data related to flow and water quality in the Crooked Creek watershed prior to the summer
of 2016 was relatively limited, therefore field work was conducted by Tetra Tech to provide directly
applicable data required for QUAL2K model setup, calibration, and corroboration. Note that there are no
USGS or other flow gaging stations present within the Crooked Creek watershed. Available data for
Crooked Creek which is relevant to QUAL2K model development is provided below
2.1 GOOSE AND CROOKED CREEKS LWP
In 2008, the North Carolina Ecosystem Enhancement Program (NCEEP, now referred to as DMS which
stands for Division of Mitigation Services) began development of a local watershed plan (LWP) for the
Goose and Crooked Creek watersheds. The LWP involved preliminary characterization of the watersheds
starting in 2008 and a more detailed watershed assessment starting in 2010. The LWP (Tetra Tech,
2012a) focused on:
• Determining the functional status of aquatic systems in the watershed.
• Identifying key stressors and their sources impacting water quality, habitat, and hydrology.
• Determining where management to address sources and stressors is most needed.
• Identifying potential management opportunities and key assets of the watershed.
Data collection and analysis associated with the LWP were used to inform channel characterization. For
example, there was extensive documentation associated with the channel bed materials, presence of
snags and logs in the streambed, and anecdotal evidence informs decision making in the model such as
the high instream Manning's n roughness values.
2.2 PERMITTED POINT SOURCE MONITORING
There are three point sources present within the Crooked Creek watershed which are permitted through
the National Pollutant Discharge Elimination System (NPDES). Hemby Acres WWTP (NPDES ID:
NC0035041, permitted discharge 0.3 MGD) and Grassy Branch WWTP (NPDES ID: NC0085812,
permitted discharge 0.05 MGD) are minor point sources, whereas Crooked Creek #2 WWTP (NPDES ID:
NC0069841, permitted discharge 1.9 MGD) is classified as a major point source (Figure 7). Effluent
discharge and instream monitoring data collected for these facilities was used to support model setup and
calibration is presented in Appendix A.
Carolina Water Service Inc., which owns and operates the Hemby Acres WWTP located on the North
Fork of Crooked Creek, conducts instream water quality sampling immediately upstream and downstream
of the effluent discharge location. Sampling at these locations approximately 200 feet upstream and 200
feet downstream of the outfall has been collected on a weekly basis since 2014 and consists of
temperature, DO, and fecal coliform bacteria. Carolina Water Service, Inc. also reports treated effluent
flow and water quality data associated with their permitted discharge: flow reported daily, while water
temperature, pH, five-day biochemical oxygen demand (BOD5), ammonia (NH3), DO, and total suspended
solids (TSS) are reported weekly.
aTETRA TECH

Crooked Creek QUAL2K Model
October 15, 2019
North Fork
Crooked Creek
Hemby Acres WWTP
(NC0035041)
r
08386000
SR 1520
Croo*ed Creea
Grassy Branch 08388900
WWV(NC0085812) G SR 1601
Crooked Creek —�
WWTP #2
(NC0069841)
08386200
SR 1514
r
South Rork
Crooked Creek
Crooked Creek Watershed
N o os i 2
�.—.J TETRA TECH Coalition Water Quality Sampling mwc=�KTometas
v;s_apn2_sukwx_nam_cww Iuma_.w Mites
uro wmK� a, oz »re M--
Legend
Rocky River
Stanly
1 County
08388000
@NC218
Grassy Branch
4 WWTP Discharge Site
Coalition Chemistry Station
River/Stream
® Watershed Boundary
County Boundary
Figure 7. Crooked Creek point source discharge locations and YPDRBA water quality sampling sites
Union County owns and operates the other two NPDES-permitted dischargers located along Crooked
Creek: major discharger Crooked Creek #2 WWTP and minor discharger Grassy Branch WWTP. Treated
effluent flow is reported daily for both dischargers. Water temperature and pH are reported daily for
weekdays only at both sites. BODs, NH3, DO, and TSS are reported weekly for Grassy Branch and daily
on weekdays for Crooked Creek #2. Chemical oxygen demand (COD) is reported monthly for both sites,
and total nitrogen (TN), total phosphorus (TP), and hardness are reported monthly for Crooked Creek #2.
Note that effluent sampling for Crooked Creek #2 occurs prior to entering a pipe that carries the effluent
from the plant to the discharge location. The distance between the plant sampling point and the pipe
outfall is approximately 2.5 miles, which raised concerns that DO depletion could occur during transit
through the closed system. Tetra Tech's sampling of the effluent, however, showed that DO
concentrations in the effluent leaving the pipe were similar to those recorded at the entrance to the pipe.
The NPDES permit limits for the existing outfalls within the Crooked Creek watershed are detailed in
Table 1.
aTETRA TECH
4

Crooked Creek QUAL2K Model
October 15, 2019
Table 1. Existing permit limits for the wastewater treatment plants located along Crooked Creek.
NPDES ID Facility Name Permitted Allowable Flows and Concentrations (Summer)
Flow (MGD) BOD5 (mg/1) NH3-N (mg/1) DO (mg/1) TSS (mg/1)
NCO069841 Crooked 1.9 5.0 2.0 >_ 6.0 30.0
Creek #2
NCO085812 Grassy Branch 0.05 5.0 2.0 _> 5.0 30.0
There is one additional permitted discharge located in the watershed, Radiator Specialty Company
(NPDES ID NC0088838) which discharges near the headwaters of the South Fork Crooked Creek. This
permit is associated with groundwater remediation and has a maximum allowable discharge of 0.09
MGD. This discharge is not simulated directly in the Crooked Creek QUAL21K model, however it is
captured indirectly through the model inputs associated with the downstream end of the South Fork
Crooked Creek.
2.3 YPDRBA (COALITION) INSTREAM SAMPLING
There are four Coalition water quality sampling sites in the Crooked Creek watershed which are
monitored by the Yadkin Pee Dee River Basin Association (YPDRBA). Of these four sites, two are located
on the North Fork Crooked Creek (Q8386000, Q8386200), one is located on Crooked Creek below the
confluence of the North and South Forks (Q8388900), and one is located below the confluence of Grassy
Branch (Q8388000) (Figure 7). All four sites monitor temperature (temp), pH, DO, and total nitrogen (TN)
approximately monthly, and Site Q8388000 also measures other nutrient data on a monthly basis since
2.013 including nitrate and nitrite (NOX), ammonia (NH3), and total Kjeldahl nitrogen (TKN). These
Coalition sites also monitor turbidity, fecal coliform bacteria, conductivity, and total suspended solids
(TSS) on a monthly basis. These data were used to support model calibration to instream conditions
along Crooked Creek and are presented in Appendix B. Note that sampling at site Q8388900 was
discontinued during 2013.
2.4 TETRA TECH SAMPLING
During the late summer of 2016, hydraulic and water quality sampling was performed by Tetra Tech on
three separate field trips: August 15-19, August 31-September 2, and September 13-16. Sampling efforts
included surveying 20 cross sections along Crooked Creek, estimating flow velocity and discharge, and
generating a log of hydraulic information related to the creek. Water quality sampling on all three trips
involved longitudinal DO sampling by probe, deployment of multi -day sondes for diurnal DO and water
temperature fluctuation measurements, and grab sampling for water quality analyses for oxygen -related
and nutrient -related constituents. The longitudinal samples included direct sampling of the effluent
discharges, and a few small tributaries. The 2016 summer sampling results provided key data for model
parameterization and calibration (Appendix C).
NTETRA TECH 5

Crooked Creek QUAL2K Model
October 15, 2019
-N 2.5 HEC-RAS MODELING EFFORTS
Two flow models have been created for the Crooked Creek watershed using the Hydrologic Engineering
Center River Analysis System (HEC-RAS) model developed by the US Army Corps of Engineers
(USACE, 2016). HEC-RAS models are used by hydraulic engineers for channel flow and stage analysis
for floodplain determination, typically using design storm events. The combined HEC-RAS models cover
the full extent of Crooked Creek, Grassy Branch, and the North and South Forks. Although HEC-RAS
models are largely developed and applied for high -flow flood condition modeling, certain components of
the models may be useful for low flow steady-state analysis, such as calibration of reach hydraulic
parameters and constraining hydraulic parameterization.
The HEC models in the Crooked Creek watershed covered all of the mainstem and major tributaries.
Most of the HEC-RAS models were obtained from the NC Floodplain Mapping Program — Geospatial and
Technology Management Dept. Several HEC-RAS models for portions of the Crooked Creek mainstem
were provided by Union County. The HEC-RAS models comprise both "Limited Detail Study" and
"Detailed Study" flood models. The "limited detail' models predict flood delineations for the 100-year
storm event using cross section geometry developed from LIDAR data. The "detailed" models are much
more rigorous than "limited detail" studies because they determine specific channel profiles, bridge and
culvert opening geometry, and floodplain characteristics using traditional field surveys. The "detailed
study" model also includes flood profiles for the 10-, 25-, and 50-year storm events.
2.6 GOOSE AND CROOKED CREEK LSPC MODEL
A model was developed to simulate hydrology and water quality in the Goose and Crooked Creek
watersheds in support of watershed planning conducted by NCEEP, Centralina Council of Governments
and North Carolina Division of Water Quality (Tetra Tech, 2012b). This effort involved simulating these
two adjacent drainages using the Loading Simulation Program C++ (LSPC) watershed model to represent
existing conditions (Tetra Tech, 2009a). The LSPC model, a continuous watershed model with a 1-D
stream channel representation, was parameterized based on hydrologic soil groups, land slope
characteristics, and land use/land cover across the two basins. Hydrology was calibrated to observed
streamflow at multiple locations within the Goose Creek watershed. Although there are no flow monitoring
stations within the Crooked Creek basin (and no direct hydrology calibration), the geology and soils of
Crooked Creek are similar to Goose Creek. As a result, model hydrology predictions are likely reasonable
across a range of flows. Water quality calibration was performed for both creeks by comparing simulated
pollutant concentrations and loads to observed values.
1-R-t TETRA TECH 6

Crooked Creek QUAL2K Mode!
October 15, 2019
h 114
116 101
t1:
7 IDd <02
t1n tDs
S�
113 145
112 h (,. ' 201
21; tP7 tD8 204' 2d2
106
107 205
i 1fi^ / 215 I.1 212
2t3 2D6
21d
i11 ZTD
2il i
IDS —
Legend
LSPC Model Reach
200 LSPC Model Sutbasin
Crooked Creek Watershed
Crooked Creek Watershed ry o o e t z Goose Creek Watershed
j� LSPC Model Extent a vxlom.w•
mar w `1 ohs 1 r County Boundary
Figure 8. LSPC model extent and subbasins for the Goose and Crooked Creek watersheds
® TETRA TECH
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Crooked Creek QUAL2K Model
October 15, 2019
3.1 MODEL DOCUMENTATION
The most recent version of the QUAL2K model available at the time of this report was used for modeling
Crooked Creek: QUAL21K version 2.12bl. QUAL2K is a river and stream water quality model that is
intended to represent a modernized version of the QUAL2E model (Brown and Barnwell, 1987). QUAL2K
was developed at Tufts University and has been funded partly by the United States Environmental
Protection Agency (Chapra et al., 2012).
f.2 MODEL DATE SELECTION
The QUAL2K model is set up to run for a specific date, and information about latitude, longitude, and time
zone are used to inform solar energy forcing. Based on the summer 2016 sampling, the QUAL2K model
for Crooked Creek was setup and calibrated to a date in August which best represented the first two
sampling trips. The model was corroborated as well by comparing the simulated and observed results
associated with the third sampling trip in September. The first and second trips to the Crooked Creek area
for data collection were August 15 —19, and August 31 — September 2. Grab samples were taken on
those sampling efforts for the most part on August 16 and August 31 respectively. A date chosen
approximately halfway between those two dates was identified to use as the model calibration date
(August 24, 2016). The model corroboration date was chosen as the grab sampling date of September
14, 2016 during the third sampling field trip which was September 13 — September 16.
There is reasonable justification for combining the first and second field trips into a single calibration
period based on known flow and atmospheric conditions. An analysis of flow gages in the adjacent
watershed of Goose Creek, as well as an analysis of local air temperatures suggest that conditions on the
August 16 and 31 were sufficiently alike to support combining data associated with those two trips for a
single steady state model calibration run. Average air temperature on 8/16 and 8/31 were 84.6 °F (29.2
°C) and 79.4 °F (26.3 °C) respectively. The two USGS flow gages along Goose Creek (0212467451 and
0212467595) both observed streamflow conditions between 0.4 and 0.9 cfs on August 16th and 31st
Flows at these gages experienced average annual flows in 2016 on the order of 7.0 and 4.4 cfs
respectively, so conditions were considered sufficiently similar and relatively low during the two August
dates compared to the annual statistics.
3.3 MODEL SEGMENTATION
The extent of the Crooked Creek QUAL2K model is defined as upstream of the Hemby Bridge WWTP on
the North Fork, running 21.0 miles (33.8 kilometers) to the outlet at Rocky River. The total modeled
distance is subdivided into "reaches" which themselves are made up of 0. 1 -kilometer computational
"elements". In general reach divisions represent areas of approximately similar hydraulic conditions. For
Crooked Creek, the 6 segmented reaches largely reflect key points of interest in the watershed such as
WWTP discharges or tributary inflows. The reach located downstream from the South Fork Crooked
Creek (SFCC) confluence is segmented at a large beaver dam above Highway 601 because this stretch
is particularly obstructed and sluggish due a series of large beaver/debris dams. This reach between
SFCC and the end of the beaver dams above Highway 601 has significanthydrologic differences than
downstream of the dams, reflected in channel geometry, flow velocity, and observed DO concentrations.
® TETRA TECH 8

Crooked Creek QUAL2K Model
October 15. 2019
Hydraulic parameterization for each model reach was based on GIS-based spatial analyses of
NHDPlusV2 flowlines, a 3-meter resolution digital elevation model (DEM) obtained from the USDA Data
Gateway, and field data from surveys conducted in August and September 2016. Table 2 and Figure 6
summarize the reach segmentation for the Crooked Creek QUAL2K model which were used for model
setup and did not vary between calibration and corroboration model setups.
Table 2. Reach segmentation for Crooked Creek QUAL2K model
1
Headwaters to Hemby Bridge VVVVTP
0.88 (1.42)
2.80 (4.50)
3.75 (6.03)
623 (190)
617 (188)
587 (179)
617 (188)
587 (179)
558 (170)
2
Hemby Bridge VVVVTP to Crooked Creek #2
VVVVTP
3
Crooked Creek #2 VVVVTP to South Fork
Crooked Creek (SFCC) confluence
4
South Fork Crooked Creek (SFCC) to end of
two large beaver dams
1.61 (2.59)
558 (170)
551 (168)
5
End of beaver dams, crossing Highway 601, to
Grassy Branch VVVVTP
5.21 (8.39)
551 (168)
502 (153)
502 (153)
410 (125)
6
r
Grassy Branch VVWTP to Rocky River 6.72 (10.82)
Crooked Creek
Grassy BranchWWTP,, P
f Hemby Acres
North fork Crooked Creek=
f
Crooked Creek WWTP #2•
1
y�
\ f_1
Fork Crooked Creek
IockyRiver
GrassyBranch
Legend
WWTP Discharge
t. Large Beaver Dam
River/Stream
OWatershed Boundary
Model Reach
�e R—h t
R h ^
Rauh3
R—h I
®
CrN a o�=
Looked Creek Watershed TETRA TECH QUAL2K Model Segmentation Kiii@ s
xw �ca� srnwt,.« han c,ro�..ros.azw =«� A 0 0.5 1�2Miks �r Roxh s
erevarcouaic�sair na�ro�s '
Figure 9. Crooked Creek QUAL2K model reach segmentation
NTETRA TECH
I

Crooked Creek QUAL2K Model
October 15, 2019
1-, 3.4 REACH HYDRAULICS
Stream hydraulics were simulated using the Manning's Formula method within QUAL21K. Model inputs
related to Manning's Formula may vary for each reach and are represented as average conditions based
on the 2016 field survey cross sectional data (Figure 10). There were 20 locations surveyed during
summer 2016, and channel geometry characteristics are used to approximate average conditions for
each model reach. There is a strong relationship between increasing channel bottom width and distance
from the headwaters, reflecting the corresponding increase in drainage area and flow; therefore, the
average distance of each reach from the headwaters was used to approximate channel bottom width
(Figure 11). Surface and bottom channel widths were used to estimate average channel side slopes for
each reach by assuming trapezoidal area.
1
rooked Creek Watershed N 0 0.5 1 2
1'p.tTETAATECH 2COZ Survey Cross Sections A vKaaratars
0 0.5 1 2
s�iswrv>w ram_cm�_cics 3za_r.n �7llMiies
�➢emtluc.tl 116Xr5:.HHrMIw
Legend
Q Gross Section
— River/Stream
QWatershed
Model Reach
Reach t
Site
Boundary
s Reach 2
Reach 3
......i Reach 4
® Reach 5
+.r Reach 6
Figure 10. Crooked Creek summer 2016 cross sectional surveys by Tetra Tech
QTETRA TECH
10

Crooked Creek QUAL2K Model
October 15, 2019
30
y = 0.9833x+ 1.764
v 25 R2 = 0.7034
v + •
- s 20 • Reach 1(no data)
• Reach 2 (5 sites)
0 15
c # Reach 3 (3 sites)
m • •
10 • *Re ac h 4 (No Data)
� a•
Reach 5 (6 sites)
� 5
`-' • Reach 6 (6 sites)
0
0 5 10 15 20
Distance from headwaters (miles)
Figure 11. Crooked Creek channel bottom width measured from summer 2016 cross sections
For reach hydraulics, bottom channel widths were estimated based on the regression presented in Figure
11. Channel side slopes were estimated using surface and bottom channel widths and an average depth
of 1 foot (0.32 meters). Bottom widths were generally small, and since water depths were shallow along
the entire Crooked Creek, side slopes are high.
Channel bed slope is calculated as the difference in upstream and downstream elevation divided by the
reach length (refer to Table 1 for raw data). Manning's n (roughness coefficient) can range from about
0.025 - 0.150 for natural streams (Chow, 1959). Manning's n may be subject to alteration during model
calibration because channel roughness is heavily influenced by pool -riffle structures, debris, and
obstructions (Beven et al., 1979). Manning's n was initialized for all reaches as 0.1 which indicates
"mountain streams with boulders" since there is significant data suggesting high debris content and
irregular channel bottoms along the entire stream (Chow, 1959). Manning's n was the only reach
hydraulic parameter adjusted during model calibration.
Table 3. Reach hydraulic model setup inputs
Reach
1
Location Shorthand
HW to Hemby WWTP
Channel Manning's
SlopeBed
0.0014 0.1
Bottom Width,
2.17 (0.66)
Side
Slopes
4.37
2
Hemby WWTP to CC#2 WWTP
CC#2 WWTP to SFCC
0.0010 0.1
4.00 (1.22)
4.71
3
0.0015 0.1
7.43 (2.26)
5.35
4
SFCC to Beaver Dams
0.0006 0.1
10.50 (3.20)
5.93
5
Beaver Dams to Grassy WWTP
0.0014 0.1
13.58 (4.14)
19.11 (5.83)
6.51
7.55
6
Grassy WWTP to outlet
0.0020 0.1
® TETRA TECH

Crooked Creek QUAL2K Model
October 15, 2019
3.5 METEOROLOGICAL INPUTS, LIGHT AND HEAT
3.5.1 Hourly Inputs
Metrological inputs to the QUAL2K model include air temperature, dew point temperature, wind speed,
cloud cover percentage, and percent of solar radiation blocked by stream shade. Hourly meteorological
data are available through the Weather Underground (www.wunderground.com) for sites near Crooked
Creek. The "Campobello Drive" site in Unionville, North Carolina (KNCUNION2) is located near Crooked
Creek and was identified as the best source of hourly meteorological inputs for the QUAL2K model. For
development of each meteorological input, see Table 4. Average air temperature as developed for model
calibration was 83.1 OF (28.4 °C) with a daily range between minimum and maximum air temperatures of
15.95 OF (8.86 °C). Average air temperature as developed for model corroboration was 86.0 OF (24.6 °C)
with a daily range between minimum and maximum air temperatures of 18.0 OF (10.0 °C).
Table 4. Meteorological inputs data source summary
Air Hourly air temperatures (dry bulb temperatures) were calculated as hourly averages of
Temperature data from the KNCUNION2 site on 8/16/2016 and 8/31/2016 for the calibration model.
Hourly air temperature from the same station was used from 9/14/2016 for the
corroboration model. Inputs did not vary by reach.
Dew Point Hourly dew point temperatures were calculated as hourly averages of data from the
Temperature KNCUNION2 site on 8/16/2016 and 8/31/2016 for the calibration model. Hourly dew
point temperatures from the same station was used from 9/14/2016 for the
corroboration model. Inputs did not vary by reach.
Wind Speed
Hourly wind speed was available from the KNCUNION2 site, however the riparian
vegetation and channel incision shelters the stream so significantly (as observed
during field trips) that wind was assumed to be negligible to the stream for both
calibration and corroboration models. Inputs were set to zero for all hours at all
reaches.
Cloud Cover Hourly cloud cover were calculated as hourly averages of data on 8/16/2016 and
8/31/2016 from the closest regional airport (Monroe Airport, station ID: KEQY). Hourly
cloud cover from the same station was used from 9/14/2016 for the corroboration
model. Inputs did not vary by reach.
Shade A single shade percentage of 70% is applied to all hours and all reaches as an
average daily approximation for both calibration and corroboration models. Note that
Crooked Creek is highly shaded, with much of the stream completely sheltered by
vegetation such that the channel cannot be identified through aerial imagery.
NTETRA TECH 12

Crooked Creek QUAL2K Model
October 15, 2019
Table 5. Hourly inputs for air temperature, dew point temperature, and cloud cover
Hour
=��
Calibration
Air Temp
(°F)
Model
Dew Point Cloud
Temp (°F) Cover (%)
I oil
Corroboration
Air Temp
(°F)
Model
Dew Point
Temp (°F)
Cloud
Cover (%)
of
No =I
to
I Ill.
I fill
7
74.30
67.50
0.00%
68.00
63.00
93.75%
8
77.60
70.80
0.0007.
68.17
63.33
100.00%
9
81.55
72.25
0.00%
70.00
65.50
100.00%
10
85.50
73.70
31.25%
72.67
68.33
100.00%
11
86.00
74.40
37.50%
75.83
71.33
91.67%
12
88.10
75.80
62.50%
78.00
72.67
25.00%
13
89.60
76.00
50.00%
79.83
73.00
0.00%
14
90.00
75.62
62.50%
81.60
72.40
0.00%
15
89.67
74.80
50.00%
84.00
70.83
0.00%
16
90.25
74.25
0.00%
85.50
70.00
0.00%
17
89.83
74.33
12.50%
86.00
70.00
0.00%
18
89.67
74.33
0.00%
86.00
68.00
50.00%
19
89.38
73.88
0.00%
84.40
69.00
0.00%
20
87.60
72.40
0.00%
82.20
68.20
0.00%
21
84.58
70.90
0.00%
79.33
67.00
0.00%
22
82.20
69.90
0.00%
77.25
67.00
0.00%
23
80.46
69.16
0.00%
75.60
67.00
0.00%
24
79.13
69.00
0.00%
74.60
66.40
0.00%
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Crooked Creek QUAL2K Model
October 15, 2019
__N 3.5.2 Light and Heat Inputs
Several parameters related to light and heat functions can be adjusted for a given QUAL2K model. For
model setup, solar inputs are calculated within the model based on latitude, time zone, and Julian day.
Based on these inputs for Crooked Creek on 8/24/2016, sunrise and sunset were calculated within the
model to be at 6:48 AM and 7:58 PM, which were externally verified through the North Carolina Wildlife
Resources Commission, which publicly documents sunrise and sunset times across North Carolina
(www.NCWildLife. org). Sunrise and sunset times for the corroboration model on 9/14/2016 were
calculated in the model as 7:04 AM and 7:29 PM respectively.
Most light and heat parameters were estimated based on suggested values from the QUAL21K manual.
There are a number of options for modeling atmospheric attenuation of solar energy, atmospheric
longwave emissivity, and wind speed function for evaporation and air convection/conduction, and
sediment heat parameters (Table 6).
Table 6. Light and heat model setup inputs
Photosynthetically Available Radiation
0.47
Light parameters initialized based on
QUAL2K example file.
Background light extinction (/m)
0.2
Linear chlorophyll light extinction (/m)
0.0088
Nonlinear chlorophyll light extinction (/m)
0.054
ISS light extinction (/m)
0.052
Detritus light extinction (/m)
0.174
Model Parameters
Atmospheric attenuation model for solar
Bras
Default atmospheric formula for QUAL21K
Atmospheric turbidity coefficient
2
Default value suggested by QUAL21K
Manual
Atmospheric I ngwave emissivity model
Brutsaert
This equation tends to allow for warmer
water temperatures to be achieved
Wind speed function for evaporation and
air convention
Brady-
Graves -Geyer
Default wind speed function for QUAL2K
Sediment Heat Parameters
Sediment thermal thickness (cm)
20
Model default suggestions from QUAL2K
manual. Default suggestion for sediment
thermal thickness of 10 cm was modified
to 20 cm given the observed presence of
thicker sediment along the channel.
Sediment thermal diffusivity (cm2/s)
0.005
_
1.6
Sediment density (g/cm3)
Sediment heat capacity (cal/g °C)
0.4
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Crooked Creek QUAL2K Model
October 15, 2019
--'s 3.6 CARBONACEOUS BIOCHEMICAL OXYGEN DEMAND SIMULATION
The QUAL2K model simulates instream chemical biological oxygen demand (CBOD) as two different
pools: fast CBOD which is rapidly oxidized and labile in nature, and slow CBOD which is slowly oxidized
and refractory in nature. For the QUAL21K model of Crooked Creek, fast CBOD was used to simulate the
presence of oxygen -demanding substances in WWTP effluent, while slow CBOD was used to simulate
the presence of instream background decay of organic matter such as leaf litter. The QUAL2K manual
suggests that when modeling slow and fast CBOD separately, to keep the distinct pools apart by setting
the CBOD hydrolysis rate to zero, so that choice was made for the Crooked Creek model.
Incubation time for BOD or CBOD measurements in laboratories is typically short-term for five days,
reporting the results as BOD5 or CBOD5 respectively. These five-day concentrations of BOD and CBOD
must be converted to the ultimate concentration of CBOD (CBODuitimate) for simulation in QUAL2K in order
to approximate the slow or fast CBOD concentration after some fifty days of decomposition. For slow
CBODultimate simulation in the model the Phelps equation below may be employed, as detailed in the
QUAL2K manual (Chapra et al., 2012):
slow CBOD _ CBODS
uirtmate — 1 — e(_klxs)
Note that for the equation above, kt is the rate of oxidation for CBOD which the QUAL21K manual
suggests can range from 0.05 — 0.3 /d. For slow CBODuitlmate in the model, 0.05 /d will be used, and for
fast CBODultimate, 0.3 /d will be used in the model environment.
As mentioned above, WWTP effluent was modeled as fast CBODultimate, which was based on Discharge
Monitoring Report (DMR) data reported as BOD5 concentrations. The original QUAL-II model (NCASI,
1985) internally converted 5-day BOD to ultimate CBOD using a ratio of 1.46 and was not user -specified
(EPA, 1985). Studies have shown that rates can vary significantly from low ratios for domestic wastewater
to very high ratios (e.g., 30) for pulp and paper waste (EPA, 1985). Leo, et al. (1984) summarized the
results for numerous facilities that showed the ratios for secondary to advanced secondary averages from
slightly below to slightly above 2. In the absence of specific lab studies on the existing County plant
effluent BOD5 to CBODultimate ratio, a factor of 2 was assumed:
fast CBODuitimate = 2 x BOD,
In summary, boundary conditions for headwaters and tributaries were simulated as slow CBOD pools
estimated based on in -stream C130D5 sampling and Phelps first -order reaction equation, while boundary
conditions for effluent point sources were simulated as fast CBOD pools estimated based on DMR BOD5
sampling and a ratio of 2:1 for BOD5:CBODuitimate.
3.7 BOUNDARY CONDITIONS
3.7.1 Headwaters
3.7.1.1 Headwater Flows
Of the twenty stream cross -sections surveyed during summer 2016, ten were paired with velocity
measurements to estimate instantaneous streamflow. Stream velocity during each of three separate
sampling trips was so low that a propeller -driven Global Water FP111 Flow Probe velocity meter with a
lower measurement limit 0.3 ft/s (0.1 m/s) was not able to provide an estimate (i.e., velocity was too low to
OTETRA TECH
15

Crooked Creek QUAL2K Model
October 15, 2019
move the propeller to measure velocity). Therefore, at these ten sites, an orange was timed to float a
specific distancecrude but reasonable way to estimate average channel velocity. Stream discharge
was subsequently approximated at these ten sites by multiplying the estimated flow velocity by cross -
sectional area (Figure 12). This estimation was conducted using a linear regression of eight of the sites,
as two were deemed to be probable outliers and may reflect error in methodology.
7
A
v 5
'0 3
W
M
E
1
0
■
■
0 5 10 15
Distance from headwaters (miles)
y = 0.1713x+1.2151
Rz = 0.8221
■ Reach 1(No Data)
■ Reach 2 (2 sites)
Reach 3 (2 sites)
• Reach 4 (No Data)
* Reach 5 (3 sites)
0, Reach 6 (1 site)
■ Outliers (Reach .3, 6)
•
20
Figure 12. Crooked Creek stream discharge estimates
Although there are no flow gages located along Crooked Creek, flow gages in the adjacent Goose Creek
watershed during the summer 2016 sampling period revealed that reasonably similar low -flow conditions
were present during all three sampling trips. Streamflow conditions at USGS gages 0212467451 (Goose
Creek at SR1524 near Indian Trail) and 0212467595 (Goose Creek at SR1525 near Indian Trail) were
reported to be similarly low during all summer sampling trips in Crooked Creek (Table 7). Based on the
limited flow data in -hand and the low -flow conditions in the adjacent Goose Creek, it is assumed that flow
conditions were reasonably similar across all three sampling trips to use the same flow boundary
conditions during calibration and corroboration model periods.
Table 7. USGS flow conditions in adjacent Goose Creek watershed (flows in cfs)
It is possible to use the relationship between discharge and distance from the headwaters to approximate
flows at the headwaters. As seen in Figure 12 and using the linear regression, the best estimate of
headwater flow conditions during the entire summer sampling period of 2016 is 1.215 cfs (0.034 cros).
® TETRA TECH
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Crooked Creek QUAL2K Model
October 15, 2019
3.7.1.2 Headwater Water Quality
Water quality conditions at the headwaters to be assumed for model calibration and corroboration periods
were developed from the sampling sites located upstream of the Hemby Acres WWTP. Water
temperature and DO were observed by Carolina Water Services Inc. upstream of the WWTP on a weekly
basis. For the calibration period, the average of conditions from the weeks of the associated trips 1 and 2
were used to generate average headwater conditions for water temperature and DO, while grab sample
site #1 results were averaged for trip 1 and trip 2 for all other applicable constituents. For the
corroboration period, average conditions used during field trip 3 as sampled upstream of Hemby Acres
WWTP were used in tandem with grab sampling at site #1. Headwater water quality inputs for model
initialization for the calibration period and corroboration period are detailed in Table 8 and Table 9
respectively. Headwater boundary conditions specified for the calibration and corroboration periods are
not subject to change although they vary between the two periods based on instream data. Within the
model, the downstream extent was not a prescribed boundary.
For the simulation of CBODwtimate at the headwaters, the entire pool was estimated to be slow CBOD
because upstream of this point does not include any effluent sources. Modeled slow CBOD is
approximated as a function of observed CBOD5 at WQ Grab Site #1 and the slow decay rate detailed in
Section 3.6 of 0.05 /d. Measurements of CBOD5 at Site #1 on field trips 1, 2, and 3 were all non -detects
(detection limit of 2 mg/1), therefore estimates of instream CBOD5 were set to half the detection limit for
the calculation of ultimate slow CBOD to use for model input for both calibration and corroboration:
CBOD _ CBODS
intimate — 1 — e(_k,x5)
mg
slow CBOD at headwaters — 1 l — 4.52 mg
1 — e(-0.057)x5) -
I, t TETRA TECH 17

Crooked Creek QUAL2K Model October 15, 2019
„ N Table 8. Headwater water quality initial model inputs (calibration model)
ModelI Parameter Data Source
Water Temperature (°F) 74.8 Average of upstream of Hemby WWTP samples on
8/18/16 (76.3 °F) and 8/30/16 (73.4 °F)
Conductivity (pmhos) 252 Unknown at headwaters, set to average result of all
downstream sondes from Trip 2 (no data from Trip 1)
Inorganic Solids (mg/L) 0 Unknown at headwaters, assume zero
Dissolved Oxygen (mg/L) 4.38 Average of upstream of FFemby WWTP samples on
8/18/16 (4.43 mg/1) and 8/30/16 (4.32 mg/1)
Slow CBOD (mg/L) 4.52
Refractory pool of CBOD calculated based on instream
CBOD5 measurements from WQ Grab Site #1 on Trips
1 and 2 1
Calculated as the difference between Trip 1 and Trip 2 l
Fast CBOD (mg/L) 0
Organic Nitrogen (pg/L) 508
observed TKN and NHa for WQ Grab Site #1; non -
detects set to half of the detection limit.
Ammonia was not detected in the headwaters from WQ
NH4-Nitrogen (pg/L) 25
Grab Site #1 from Trips 1 and 2, therefore the
headwaters were set to half of the detection limit.
Average of observed NOX at WQ Grab Site #1, Trips 1
NO3-Nitrogen (pg/L) 280
and 2.
Observed PO4 from WQ Grab Site #1 was used from
Inorganic Phosphorus (pg/L) 95
Trip 2. The observation from Trip 1 was not used as it
was flagged for quality control exceedances.
Organic Phosphorus (pg/L) 16
Difference between Trip 1 and Trip 2 observed TP and
PO4 for WQ Grab Site #1, excluding flagged PO4
sample.
Alkalinity (mg/L) 100
Unknown at headwaters, use model default
Phytoplankton (mg/L) 0
Unknown at headwaters, assume zero
pH 7
Unknown at headwaters, use model default
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Crooked Creek QUAL2K Model
October 15, 2019
Table 9. Headwater water quality initial model inputs (corroboration model)
Parameter Model Input Data Source
Water Temperature (°F) 71.8 Observed upstream of Hemby WWTP samples on
9/12/16
Conductivity (pmhos)
311
Unknown at headwaters, set to average result of all
downstream sondes from Trip 3
Inorganic Solids (mg/L)
0
Unknown at headwaters, assume zero
Dissolved Oxygen (mg/L)
3.63
Observed upstream of Hemby WWTP samples on
9/12/16
Slow CBOD (mg/L)
4.52
Refractory pool of CBOD calculated based on instream
Fast CBOD (mg/L)
0
CBOD5 measurements from WQ Grab Site #1 on Trip 3
Organic Nitrogen (pg/L)
680
Calculated as the difference between Trip 3 observed
TKN and NH3 for WQ Grab Site #1; non -detects set to
half of the detection limit.
NH4-Nitrogen (pg/L)
50
Ammonia was not detected in the headwaters from WQ
Grab Site #1 from Trip 3, therefore the headwaters were
set to half of the detection limit.
NO3-Nitrogen (pg/L)
77
Observed NOX at WQ Grab Site #1 from Trip 3
Inorganic Phosphorus (pg/L)
51
Observed PO4 from WQ Grab Site #1 from Trip 3
Organic Phosphorus (pg/L)
69
Difference between.Trip 3 observed TP and PO4 for WQ
Grab Site #1
Alkalinity (mg/L)
100
Unknown at headwaters, use model default
Phytoplankton (mg/L)
0
Unknown at headwaters, assume zero
pH
7
Unknown at headwaters, use model default
3.7.2 Point Source Flows and Water Quality
The three permitted wastewater treatment plant effluent dischargers along Crooked Creek were modeled
explicitly: Hemby Acres WWTP which is operated by Carolina Water Services Inc., and Crooked Creek #2
WWTP and Grassy Branch WWTP which are both operated by Union County.
For the most part, point source model inputs for flow and water quality were based on average conditions
for August (calibration model) and average conditions for September (corroboration model) based on
Discharge Monitoring Report (DMR) data. For parameters not available through DMR monitoring,
concentrations were estimated based on grab samples from the discharge pipe outfalls from trips 1, 2,
and 3 (Table 10, Table 11). DMR reports show that discharge flows and water quality did not vary widely
across August and September.
As detailed in Section 3.6, effluent fast CBOD pools estimated based on DMR BOD5 sampling and a ratio
of 2;1 for BODS:CBODultimate. When DMR-reported concentrations for any given parameter were listed as
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19

Crooked Creek QUAL2K Model
October 15, 2019
below detection limit, the concentration was assumed to be half of the detection limit for the purposes of
calculating average effluent concentrations.
Table 10. Point source flow and water quality inputs (calibration period)
LDischarge Information
NPDES Permit ID NCO035041 NCO069841 NCO085812
Permit Class Minor Major Minor
NPDES Permitted Flow (MGD) 0.3 1.9 0.05
�i Model Inputs based on DMR data (August 2016 Averages)
Location (km), distance from outlet
32.48
27.81
10.82
Inflow (m3/s), [MGD]
0.0039 [0.09]
0.0364 [0.83]
79.9
7.6
0.0018 [0.04]
Water Temperature (OF)
78.1
78.3
Dissolved Oxygen (mg/L)
6.5
7.7
0
Slow CBOD (mg/L)
0
0
Fast CBOD2 (mg/L)
8.36
2.38
3.60
Inorganic Suspended Solids (mg/L)
1.25
1.56
2.46
Ammonia Nitrogen (pgN/L)
50
940
640
pH
7.5
7.3
7.3
Model Inputs based on summer grab sampling data (Trips 1 and 2 Averages) I
Corresponding Grab Sample ID
#2
#4
#12
Organic Nitrogen (pgN/L)3
565
1,100
825
Nitrate+ Nitrite Nitrogen (pgN/L)
38,000
28,450
39,000
Organic Phosphorus (pgP/L)4
800
2,000
1,150
Inorganic Phosphorus (pgP/L)
3,300
2,700
1,850
Specific Conductance (pmhos)6
641
628
837
Phytoplankton (ug/L)
No Data, assume 0
Alkalinity (mg/L)
86.05 73.4 1
98.6
'Measurements were observed at the entrance of the pipe. DO measurements at the end of the pipe suggest that water quality does
not change significantly through the pipe.
2Measured and reported BOD5 was converted to fast CBOD,,,,R,a,e as described in the text with 1:2 ratio.
3Organic nitrogen was not measured directly, but calculated as the difference between measured TKN and NH3
°Organic phosphorus was not measured directly, but calculated as the difference between measured TP and PO4
5Alkalinity was not measured at Hemby Acres, so it was approximated as the average the other two dischargers
6Conductance measured from Trip 3 (used for calibration and corroboration models)
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Crooked Creek QUAL2K Model
October 15, 2019
� Table 11. Point source flow and water quality inputs (corroboration period)
Model Inputs based on DMR Data (September 2016 Averages)
Location (km), distance from outlet
32.48
27.81
10.82
Inflow (mNs), [MGD]
0.0039 [0.09]
0.0381 [0.87]
75.6
0.0018 [0.04]
76.3
Water Temperature (OF)
75.6
Dissolved Oxygen (mg/L)
6.8
8.0
7.6
Slow CBOD (mg/L)
0
0
0
Fast CBOD2 (mg/L)
11.80
1.25
4.08
4.71
2.00
1.27
Inorganic Suspended Solids
(mg/L)
rAmmonia Nitrogen (pgN/L)
50.00
57.06
255.56
7.3
7.1
7.1
Model Inputs based on summer grab sampling data (Trip 3)
Corresponding Grab Sample ID
#2
#4
#12
Organic Nitrogen (pgN/L)3
1075
1875
100
Nitrate+ Nitrite Nitrogen (pgN/L)
25100
33900
53300
Organic Phosphorus (pgP/L)4
1600
1300
200
Inorganic Phosphorus (pgP/L)
4000
4800
4500
Specific Conductance (pmhos)
641
628
837
Phytoplankton (ug/L)
No Data, assume 0
Alkalinity (mg/L)
64.65 37.7 91.4
'Measurements were observed at the entrance of the pipe. DO measurements at the end of the pipe suggest that water quality does
not change significantly through the pipe.
2Measured and reported BOD5 was converted to fast CBODu,t,mate as described in the text with 1:2 ratio.
'Organic nitrogen was not measured directly, but calculated as the difference between measured TKN and NH3
"Organic phosphorus was not measured directly, but calculated as the difference between measured TP and POa
'Alkalinity was not measured at Hemby Acres, so it was approximated as the average the other two dischargers
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Crooked Creek QUAL2K Model
October 15, 2019
­N 3.7.3 Tributary Flows and Water Quality
Model inputs for flow and water quality for the South Fork Crooked Creek and Grassy Branch tributaries
contributing to the Crooked Creek mainstem were developed based on a combination of observed data,
water balance calculations, and best professional judgement. Streamflow was estimated at several points
along Crooked Creek based on cross-section surveys paired with velocity measurements. By combining
the observed streamflow information with the reported point source discharge data, the relative
contributions of each modeled tributary can be estimated using a water balance assuming no other losses
due to evaporation and groundwater seepage. For tributary inflows, CBOD is modeled as slow
CBODwtimate and estimated the same way as the headwaters.
Table 12. Tributary flow and water quality inputs (calibration model)
Inflow, ft3/s (m3/s) 1.06 1 0.32 Estimated by water balance as the difference between
(0.03) 1 (0.009) instream flow estimates which are not accounted for by point
source flows.
Water Temperature, (OF) I 81.86 74.48
Conductivity (pmhos)
252
252
ISS (mg/L)
0
0
Dissolved Oxygen
(mg/L)
2.47
2.67
Alkalinity (mg/1)
100
100
Phytoplankton (ug/1)
0
0
pH
7.35
6.23
Slow CBOD (mg/L) 4.52 23.73
Fast CBOD (mg/L) 0 0
Ammonia N (pgN/L)
478
25
Organic N (pgN/L)
1,073
435
Nitrate+Nitrite N (pgN/L)
2,865
1,600
Organic P (pgP/L)
380
98
Inorganic P (pgP/L)
245
72
Water temperature is based on probe sampling conducted
on Trip 1 for SFCC and Grassy Branch. Note that Grassy
Branch is cooler because it is largely groundwater -fed.
No available data, assumed same as headwaters
No available data, assumed zero
DO estimates are based on probe sampling conducted on
Trip 1 for SFCC and Grassy Branch.
No available data, assume model default
No available data, assumed zero
pH estimates are based on probe sampling conducted on
Trip 1 for SFCC and Grassy Branch.
Average measured CBOD5 from Trips 1 and 2 was used to
approximate slow CBOD as described in the text. Observed
CBOD.5 along Grassy Branch was noticeably high.
NH3 and NOX data are averages of observed data from
Trips 1 and 2 at WQ Site #9 (SFCC) and WQ Site #13
(Grassy Branch). Organic N was calculated as the
difference between observed TKN and NH3 data.
Organic P was calculated as the difference between '
observed TP and POa during Trips 1 and 2 for SFCC (WQ
Site #9). Model inputs for Grassy Branch are from Trip 3
only because of a lab issue with P-species data from Trips 1
and 2 (WQ Site #13).
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Crooked Creek QUAL2K Model
October 15, 2019
Table 13. Tributary flow and water quality inputs (corroboration model)
Inflow, ft3/s (m3/s)
1.06
(0.03)
0.32
(0.009)
Estimated to be the same as during the calibration period.
Water Temperature (OF)
71.6
76.8
Water temperature is based on probe sampling conducted
on Trip 3 for SFCC and Grassy Branch.
Conductivity (pmhos)
102
263
Estimates are based on probe sampling conducted on Trip 3
for SFCC and Grassy Branch.
ISS (mg/L)
0
0
No available data, assumed zero
Dissolved Oxygen
2.47
2.67
DO estimates are based on probe sampling conducted on
(mg/L)
Trip 1 for SFCC and Grassy Branch.
Alkalinity (mg/1) 100 100 No available data, assume model default
Phytoplankton (ug/1) 0 0 No available data, assumed zero
pH 5.95 7.51 pH estimates are based on probe sampling conducted on
Trip 3 for SFCC and Grassy Branch.
Slow CBOD (mg/L)
9.49
4.52
Measured CBOD5 from Trip 3 was used to approximate slow
Fast CBOD (mg/L)
0
0
CBOD as described in the text.
Ammonia N (pgN/L)
110
25
NH3 and NOX data are observed data from Trip 3 at WQ J
Organic N (NgN/L)
630
705
Site #9 (SFCC) and WO Site #13 (Grassy Branch). Organic
N was calculated as the difference between observed TKN
Nitrate+Nitrite N (pgN/L)
5
610
and NH3 data.
Organic P (pgP/L)
98
98
Organic P was calculated as the difference between
92
72
observed TP and PO4 from Trip 3.
Inorganic P (pgP/L)
3.8 REACH WATER QUALITY PARAMETERS
Modeled water quality parameters that can vary by reach include sediment oxygen demand (SOD) rates;
prescribed nutrient flux rates from sediment; channel reaeration rates; nutrient hydrolysis and settling
rates; phytoplankton growth, respiration, and death rates; and bottom algae coverage, growth, respiration,
and death rates. If not otherwise specified for a given reach, water quality parameterization was tabulated
using default values and suggested ranges of model inputs.
Model inputs related to reaeration, SOD, bottom algae, and phytoplankton can have large influence on
average DO and the diurnal range of DO. The DO sondes were used to identify the diurnal variation in
DO observed at specific points along Crooked Creek. DO sondes were used to identify the relative impact
of bottom algae (surrogate for macrophyte growth) along Crooked Creek based on observed diel DO
variation. During the first field sampling trip, DO sondes were placed upstream and downstream of the
Crooked Creek #2 discharge and near the crossing of Highway 601 During the second trip, DO sondes
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Crooked Creek QUAL2K Model
October 15, 2019
were placed at the Highway 601 crossing, at the Brief Road crossing, and at the State Road 1601
crossing. All six sondes experienced a diurnal DO variation between 1.18 and 2.53 mg/l. Diurnal DO
fluctuations are due to photosynthetic processes of biota which are light and temperature dependent. The
relatively low diurnal fluctuations in DO observed along Crooked Creek suggest that algae play a
relatively minor role in the system. Bed coverage of algae was parameterized for the calibration and
corroboration models as a forcing function, such that inputs varied between the two models based on
observed algal conditions and diel DO variation between the two simulation periods (Table 14). The
magnitude of daily minimum and maximum DO are controlled by the streambed coverage of bottom algae
as an aggregate term for all macrophyte growth exerting photosynthetic processes within the water
column. For the calibration model, reach 1 was parameterized with 25% bottom algae coverage, while all
other reaches were set to 50% coverage. Between the field sampling work in August and September,
there was additional algal growth observed, such that reach parameterization for bottom algae coverage
was increased for the corroboration model run. For this model run, reach 1 was parameterized with 50%
bottom algae coverage, while reaches 2, 3, 4, and 6 were set to 75% coverage. Reach 5 was increased
further to 95% bottom algae coverage due to the presence of increased algae and multiple DO
observation points measured at supersaturation in this reach.
Table 14. Model inputs for bottom algae coverage
1
Bottom Algae
CorroborationReach
Calibration
25% 50%
2
50%
75%
3
50%
75%
4
50%
75%
5
50%
95%
6
50%
75%
Average instream DO concentrations are sensitive to SOD, which is the consumption of DO at the soil -
water interface. SOD is simulated in QUAL2K as both a rate of oxygen consumption as well as a percent
coverage of the channel bottom. SOD was not measured along Crooked Creek, so the model was
initialized based on the observed range measured in another North Carolina Piedmont -area stream: Rich
Fork Creek near High Point (Tetra Tech, 2009b). SOD estimates associated with Rich Fork Creek were
also used in the modeling effort associated with Twelve Mile Creek in Union County (Tetra Tech, 2009c).
SOD was measured with in situ chambers at a number of locations along Rich Fork Creek, both upstream
and downstream of an existing WWTP. The observed range of SOD along Rich Fork Creek was 0.067 —
0.213 g/ft2/d (0.721 — 2.293 g/m2/d), with the lowest values generally being recorded upstream of the
WWTP discharge. The Crooked Creek model was initialized with instream SOD coverage set to 100% at
a rate of 0.067 g/ft2/d (0.721 g/m2/d) for all reaches. This SOD rate was adjusted during calibration adjust
simulated DO concentrations to mimic longitudinal profiles. Note that the North Carolina Division of Water
Quality has measured SOD across the state periodically and the observed range for the Upper Cape Fear
River watershed was approximately 0.4 — 2.5 g/m2/d, which provided a constraining range during model
calibration.
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Crooked Creek QUAL2K Model
October 15, 2019
Channel reaeration is the natural input of oxygen to a waterbody through the transfer of atmospheric
oxygen into the water column at the air -water interface. Rates of reaeration are typically higher for
shallow, fast moving streams, and lower for slow, deep streams. Although reaeration was not measured
directly in Crooked Creek, anecdotal evidence and observed reaeration from the Rich Fork Creek project
was used to confine and inform the Crooked Creek model setup. Rich Fork Creek had observed
reaeration rates of 0.32/d in low -velocity pooled areas of the stream, and 1.85 /d in free -flowing sections
of the stream with observed flows on the order of 27 cfs. The Tsivoglou-Neal reaeration formula was
identified as likely appropriate for Crooked Creek as it computes reaeration based on mean water velocity
and channel slope and is appropriate for low flow streams where flow ranges 1 — 15 cfs, and the average
field -estimated flow along Crooked Creek is about 2.5 cfs (Tsivoglou and Neal, 1976).
For model setup, initial assumptions for reach parameters related to nutrient processing, settling rates,
and decay were held at model default values and were adjusted during calibration as -needed.
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Crooked Creek QUAL2K Mode!
October 15, 2019
Model calibration involves comparing how well model simulations match observed data. Model calibration
is designed to ensure that the model is adequately and appropriately representing the system in order to
answer the study questions. The model must be able to provide credible representations of the movement
of water, and the DO and BOD interactions within the stream representing steady state conditions.
Corroboration is applied using a different time period to confirm that model calibration is robust, provide
additional evaluation of model performance, and to guard against over -fitting to the calibration data.
The QUAL2K model for Crooked Creek will be calibrated to an average of data collected during the first
two sampling trips in August 2016. The corroboration period for the model will be focused on the middle
of September during the third and final summer sampling trip. Physical properties related to stream flow
and atmospheric inputs may be subject to change during the model corroboration period. The model will
be set up for these conditions using available data and calibrated to reproduce observed DO.
4.1 HYDROLOGY CALIBRATION
Reach hydraulics were calibrated in order to approximate observed and estimated conditions of flow,
depth, and velocity along Crooked Creek during the summer sampling trips. Manning's n was the key
calibration parameter that was adjusted to capture site -estimated flow dynamics since the measured
cross -sections were considered reasonable enough to approximate channel shapes. The calibrated reach
hydraulic inputs were to alter Manning's n to 0.3 for all reaches except Reach 4 (sluggish, pooled beaver
dam reach) which had a roughness coefficient of 0.6.
Travel time for the full extent of Crooked Creek was estimated by the model to be just over six days, and
model results of flow along the mainstem compared to observations may be seen in Figure 13. Along the
entire reach, simulated stream velocity ranged from 0.07 - 0.16 ft/s (0.02 — 0.05 m/s) (observed range
was 0.13 — 0.39 ft/s [0.04 — 0.12 m/s]), and simulated water depth ranged from 0.89 — 2.13 ft (0.27 — 0.65
m) (observed range was 0.49 — 2.10 ft [0.15 — 0.64 m]). Upstream and downstream streamflow along
Crooked Creek were simulated to be 1.06 and 4.24 cfs (0.03 and 0.12 cros) respectively
DTETRA TECH
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Crooked Creek QUAL2K Mode!
October 15, 2019
SFCC
HWY
4.5
confluence
601
1
!
4.0
CC#2
WWTP
f 3.5
I3.0
Hemby
Grassy WWTP.
WWTP
Grassy Branch confluence 2.5
U
2.0
2
LL
2.5
1.0
0.5
20 15 10 5 0
Distance from outlet (miles)
Field -Estimated Flow -Simulated Flow: Calibration Model
Figure 13. Simulated and site -estimated flows for Crooked Creek model extent (calibration)
4.2 WATER TEMPERATURE CALIBRATION
In general, the parameters which control water temperature are channel geometry, meteorological inputs,
stream shading, atmospheric heat models, and sediment heat parameters. Initialized parameterization
related to sediment thermal properties, stream shading, and heat models captured the observed water
temperature data reasonably well.
The simulated minimum, maximum, and average water temperature are shown in Figure 14 in
comparison with observed water temperature from the YPDRBA in August, longitudinal sampling along
the entire extent from sampling trips 1 and 2, and the range of temperatures observed at the sonde
locations from trips 1 and 2 as well (Figure 14). Moving from upstream to downstream, it is possible to
see that the majority of morning sampling (open circles) fall below the mean simulated water temperature
line, while the majority of afternoon sampling (closed circles) fall above the mean simulated water
temperature line. The spread of observed temperature data is largely captured by the diel range
simulated by the model as seen in the dashed lines below. In general the sonde data which represents
the observed range of data over several days at a given point (red vertical lines) are skewed low relative
to the longitudinal sampling (points) due to the fact that these sondes were submerged along the stream
bed which is anticipated to be cooler and more well -insulated to daily fluctuations than the water closer to
the surface.
.., 27

Crooked Creek QUAL2K Model
October 15, 2019
1--1--1 ----- --z-- - -I--- --------- 3---------- 1----4----- I -- - --- s--------- --------I
1
90
--- s+ -.- •------- �-1 -
._ --* --i%►-----------------a Sf too
-�_--- J---_-�- r �'t-_____ _r-------------------
Sea ver
HWY
Dams 601
Hemby CC#2 SFCC Grassy WWTP,
WWTP WWTP confluence Grassy Branch confluence
20 15 10 5
Distance from outlet (miles)
— Simulated Mean Temp - - - - Simulated Min/Max Tentp Observed Sonde Data
• YPDRBA Point Data O Obs Long Data (AM) Trip 1 Obs Long Data (PM) Trip 1
O Obs long data (AM): trip 2 • Obs long data (PM) trip 2
Figure 14. Simulated and observed water temperature along Crooked Creek (calibration)
4.3 WATER QUALITY CALIBRATION
70
aB
60 �
so
m
i✓
40 E
30
3
20
10
0
0
The primary focus of water quality calibration was related to DO concentrations along Crooked Creek.
The key parameters which control average DO concentrations were identified to be SOD rate and
channel reaeration. The magnitude of diel DO variation is controlled by the streambed coverage of bottom
algae. Reaeration rates were simulated using the Tsivoglou-Neal model, and were estimated as 0.4 - 3.3
/d, with an average reaeration rate of 2.3 /d. The lowest reaeration rate occurred in the model along the
sluggish beaver -dammed Reach 4.
SOD rates were used as a calibration parameter, constrained by the range of observed SOD in the Upper
Cape Fear River basin from NC DWQ of 0.4 - 2.5 g/m2/d. Calibrated SOD rates ranged from 1.0 - 2.2
g/m2/d in the calibrated model, such that reach 1 was assigned 1.0 g/m2/d, while all other reaches were
assigned 2.2 g/m2/d to best approximate average instream DO conditions.
The simulated minimum, maximum, and average DO are shown in Figure 15 in comparison with observed
DO from the YPDRBA in August, longitudinal sampling along the entire extent from sampling trips 1 and
2, and the range of DO observed at the sonde locations from trips 1 and 2 as well. Annotations on the plot
below reveal key features along the mainstem such as point source and tributary inflows which may have
significant impacts on in -stream DO concentration. From upstream to downstream, it is possible to the
see the increase in DO due to the Hemby WWTP discharge, then a decline in DO downstream due to the
BOD decay from the effluent. The DO spike at the end of Reach 2 is due to the CC#2 outfall, and the DO
decline downstream is smaller downstream relative to downstream of Hemby because of the difference in
BOD loading to the stream. The SFCC tributary has low DO, and the DO along the sluggish and dammed
Reach 4 causes a precipitous drop in oxygen along that reach. The recovery in DO downstream of the
beaver dams and Highway 601 is due to the combined impacts of higher slopes, less in -stream BOD, and
the impact of the Grassy Branch WWTP is relatively small as Crooked Creek flows down to Rocky River.
The range of daily DO concentrations observed along Crooked Creek is captured reasonably well by the
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Crooked Creek QUAL2K Model
October 15, 2019
calibration model, with DO at the downstream end estimated to be about 6 mg/I at the Rocky River
confluence.
1--1--1------ 2----- ----- I-------------3---------- I -- 4-- -- I ---........-- 5------------------- I --- ----------- -------- 6----.----------
Hemby CC#2 SFCC HWY Grassy WWTP,
WWTP WWTP confluence 601 Grassy Branch confluence
Beaver
Dams
• ________� r O • • •
Q 000
96
C- 1, O O LSD 0--------------------------
r
•1 • r
12
10
0
20 15 1.0 0
Distance from outlet (miles)
• YPDRBA Point Data O Obs Long Data (AM) Trip 1 • Obg Song Data (PM) Trip 1
O Obs Long Data (AM) Trip 2 • Obs Long Data (PM) Trip 2 Simulated Mean
- - - - Simulated MinjMax Observed Sonde Data WQS: 5.0 mg/l
DO Saturation
Figure 15. Simulated and observed DO along Crooked Creek (calibration)
4.4 MODEL CORROBORATION RESULTS
O
Model corroboration is conducted in order to verify the simulation and parameterization achieved during
model calibration reasonably approximates stream conditions during different stream conditions. Although
overall stream hydrology is held constant between the calibration and corroboration periods, significant
model changes were made for the corroboration regarding the following parameters: model run date,
meteorological inputs (air temperature, dew point temperature, and cloud coverage), tributary and
headwater chemistry, and point source flow and water chemistry. All other model parameters related to
channel geometry, flows, shading, SOD, and reaeration were held constant for the corroboration model
run.
4.4.1 Water Temperature Corroboration
In general, the water temperature was reasonably well simulated during the model corroboration period.
The downstream water temperature from near the end of Reach 5 and into Reach 6 was observed much
warmer than the model predicted, but the water temperatures are reasonably well approximated for
Reaches 1 through most of Reach 5.
The simulated minimum, maximum, and average water temperature are shown in Figure 16 in
comparison with observed water temperature from the YPDRBA in September, longitudinal sampling
along the entire extent from sampling trip 3, and the range of temperatures observed at the sonde
locations from trips 3 as well.
NTETRA TECH
29

Crooked Creek QUAL2K Model
October 15, 2019
-4-----1-- ---- -- --------- 5-- - ---- - -- I --------- -------------- 6--------- -------------- 1
90
�t'-'------- .-- ----
-i--- - - - a- _ -----
---------- •---- ----- - I - - - - - - - - ------
8U
-•----------- -------------
---------------------------------------------------
70
60 d
I
Beaver HWY
so
Dams 601
2
40 F
Heml CC#2
SFCC
Grassy WWTP,
30
WTP WTP
WW
confluence
Grassy Branch confluence
20
20 15
Simulated Mean Temp
O YPDRBA Point Data
10
Distance from outlet (miles)
- - - - Simulated Min/Max Temp
O Obs Long data (AM)
5
Observed Sonde Data
• Obs long data (PM)
Figure 16. Simulated and observed water temperature along Crooked Creek (corroboration)
4.4.2 Water Quality Corroboration
0
10
0
The simulated minimum, maximum, and average DO during the corroboration period are shown in Figure
17 to reasonably approximate observed DO relative to DO from the YPDRBA in September, longitudinal
sampling from sampling trip 3, and the range of DO observed at the sonde locations from trip 3.
1--1-- I --- ----- 2--- ----- 1 w- ----s----------- I ----- 4------ I ---------------- ------- - ------ --------
6---- - --- — - I
Hemby CC#2 SFCC HWY Grassy WWTP, 12
WWTP WWTP confluence 601 Grassy Branch confluence
Beaver
1 Dams I 10
-----------� ------------------- _
•• • • $
r• • r r
r r r O ellas
_r
r A �
---------"--'-- 4
i
o
r� .• r _ - v
----- , - -'1 g
• ,
o
r
0
20 is 10 0
Distance from outlet (rniles)
• YPDRBA Pant Data O Obs Long Data (AM) • Obs Long Data (PM)
—Simulated Mean - - - - Simulat.dMin/Max Obsened Sonde Data
— WQS: 5.0 rng/I DOSaturation
Figure 17. Simulated and observed DO along Crooked Creek (corroboration)
I jmot TETR4, T -• 30

Crooked Creek QUAL2K Model
October 15, 2019
A series of sensitivity analyses were conducted in order to provide an increased understanding of
uncertainty associated with key model parameters. The relative impact of several model parameters were
gauged in order to test the model sensitivity to changes in: bottom algae coverage, SOD rate, Manning's
n, percent shade, headwater flow rate, and the selected reaeration model (Table 15). Each parameter
was tweaked by +25% and -25% with the exception of the reaeration model, for which other formulas
were selected in each successive run.
Table 15. Crooked Creek QUAL2K model sensitivity test runs
Calibration
Representative summer conditions for setting up sensitivity analyses
Sensitivity 1
Bottom Algae +/- 25%
Sensitivity 2
SOD Rate +/- 25%
Sensitivity 3
Manning's n +/- 25%
Sensitivity 4 Shade +/- 25%
Sensitivity 5 Headwater Flow +/- 25%
Sensitivity 6 j Reaeration Models: O'Connor -Dobbins, Churchill, Owens -Gibbs, Thackston -Dawson
The results from the six sensitivity tests reveal the relative impact each of the tested parameters has on
the simulated mean dissolved oxygen concentrations along the extent of the Crooked Creek QUAL21K
model. Sensitivity tests 1 and 2 involve a 25% change in bottom algae coverage and SOD rate
respectively. These scenarios reveal that the model is more sensitive to SOD rate than bottom algae
coverage by impacting mean DO on the order of 16% and 5% respectively (Figure 18). Sensitivity tests 3,
4, and 5 involve a 25% change in Manning's n, shade, and headwater flow respectively. These scenarios
reveal the impact to mean DO to be relatively small, on the order of 4-5% for these three tests (Figure
19). Sensitivity test 6 involved testing model sensitivity to reaeration model selection (Figure 20). Of the
four reaeration models selected, the impact on mean DO was as follows, from greatest to least: Owens -
Gibbs (35%), O'Connor -Dobbins (31%), Churchill (19%), and Thacksto n -Dawson (11%). Both Owens -
Gibbs and O'Connor -Dobbins reaeration models predicted a positive impact on mean DO, while Churchill
and Thackston-Dawson reaeration models predicted a negative impact on mean DO relative to the
calibration model which used the reaeration model of Tsivoglou-Neal. In general, both Churchill and
O'Connor -Dobbins models are only appropriate for streams with depths greater than 1.6 feet (0.5 meters)
which is greater than the observed depths in Crooked Creek. The Owens -Gibbs formula overestimates
reaeration significantly (similar to O'Connor -Dobbins), likely because Owens -Gibbs assumes high
reaeration with low depth, even when velocities are small, but as seen visually along Crooked Creek, low
velocities can lead to pooling and stagnation with limited reaeration occurring. The Thackston -Dawson
formula responds similarly to the selected model of Tsivoglou-Neal, however it consistently underpredicts
instream DO by about 0.5 mg/I. The Tsivoglou-Neal formula remains the best fit to the observed data
during both the calibration and corroboration periods (Thackston and Dawson, 2001). The overall results
are summarized in Table 16.
® TETRA TECH 31

Crooked Creek QUAL2K Model
October 15, 2019
�. 1--1-8
Hemby CC#2 SFCC HWY GrassyWWTP.
WWTP nA/TP confluence .601 GrassyBrranchconfluence 7 0�
1 Beaver . _ ,—■ "'------------
Dams
6
-------- - - - - -- 40
►■� a ' '• 5 x
■ r ■
. ►► ++r%,
.r ► 5�, `I Ir Q
►►'t If 2 C
+ err rr
0
20 15 10 5 0
Distance from outlet (miles)
Calibrated Model - - - - Sensitivity 1: Bottom Algae - - - - Sensitivity 2: SOD Rate
Figure 18. Sensitivity test results (runs 1 and 2): bottom algae coverage and SOD rate
1-1- I---2------
l -
Hemby
CC#2
WW
P
IrP
---I —4---I —
SFCC
confluence 601
f Beaver
i Dams
Grassy W WTP,
Grassy Branch confluence
20 15 10 5 0
Distance from outlet (miles)
Calibrated Model - - - - Sensitivity 3: Manning's n
- - - - Sensitivity 4: Shade ------- Sensitivity 5: Headwater Flotvf
8
7 -,,b
E
W
5
x
O
4 -a
v
3 O
Ln
2
c
0
Figure 19. Sensitivity test results (runs 3, 4, and 5): Manning's n, shade, and headwater flow
NTETRA TECH
32

Crooked Creek QUAL2K Model October 15, 2019
1-1-1 ----------- ( g
Hemby CC42 SFCC HWY GrassyWWTP.
WWTP -- P asSy� n
- -confluence 60 - - - -Girrlcv tiluence_ - - - - - - - 7
Beaver - -
'�- Dams
- X
5 x
O
4 a
a
3 0
2 p
1 a
0
20 15 10 5 0
Distance from outlet (miles)
Calibrated Model (Tsi voglou -Neal) Sensitivity 6a: O'Connor Dobbins
Sensitivity 6b: Churchill - - - Sensitivity 6c: Ovrens Gibbs
- - - - Sensitivity 6d: Thackson-Dawson
Figure 20. Sensitivity test results (run 6): reaeration model selection
Table 16. Crooked Creek QUAL2K model sensitivity test run results
Average Absolute Average Absolute
..efRun Details Difference in Mean DO Relative Percent
Difference on Mean DO
Calibration Baseline N/A N/A
Sensitivity 1 Bottom Algae +/- 25%
0.2
5%
Sensitivity 2 SOD Rate +/- 25%
0.8
16%
Sensitivity 3 Manning's n +/- 25%
0.2
4%
Sensitivity 4 Shade +/- 25%
0.2
5%
Sensitivity 5 Headwater Flow +/- 25%
0.2
4%
24%
Sensitivity 6 Reaeration Model Variations
1.1
The selection of the reaeration formula can result in the largest single absolute error, however there is
reasonably good knowledge that the selected model of Tsivoglou-Neal is the most appropriate choice.
The next parameter which the model is quite sensitive to is SOD, which had an average absolute relative
percent difference on mean DO of 16%. Since neither reaeration nor SOD were measured directly along
Crooked Creek, the interaction between those two parameters are likely the greatest source of
uncertainty within the model environment, although estimates for both were established based on
reasonable approximations.
33

Crooked Creek QUAL2K Model
October 15, 2019
Beven, K.J., Gilman, K., and Newson, M. 1979. Flow and flow routing in upland channel networks. Hydrol.
Sci. Bull. 24:43-69.
Brown, L. C. and T. O. Barnwell, Jr., 1987. The enhanced stream water quality models QUAL2E and
QUAL2E-UNCAS: Documentation and User Manual. Tufts University and US EPA, Athens, Georgia.
Chapra, S.C., G.J. Pelletier, H. Tao. 2012. QUAL2K: A Modeling Framework for Simulating River and
Stream Water Quality, Version 2.12: Documentation and User's Manual. Civil and Environmental
Engineering Dept., Tufts University, Medford, MA.
Chow, V.T. 1959. Open -channel hydraulics: New York, McGraw-Hill, 680 p.
EPA. 1985. Rates, Constants, and Kinetics Formulations in Surface Water Quality Modeling (Second
Edition). EPA/600/3-85/040.
Leo, WM, RV Thomann, TW Gallaher. 1984. Before and after case studies: comparisons of water quality
following municipal treatment plant improvements. EPA 430/9-007. Office of Water, Program Operations,
U.S. Environmental Protection Agency, Washington, DC.
National Service Center for Environmental Publications (NCASI). 1985. Computer program
documentation for the enhanced stream water quality model QUAL2E. EPA/600/3-85.
North Carolina Department of Natural Resources (NC DENR). 2016. 2016 303(d) Listing Methodology.
Tetra Tech. 2009a. Loading Simulation Program in C++ (LSPC) Version 3.1 User's Manual. Fairfax, VA.
Tetra Tech. 2009b. Hydrology and Hydraulic Modeling Report for Rich Fork Creek, NC. Prepared for City
of High Point and Hazen & Sawyer. Prepared by Tetra Tech.
Tetra Tech. 2012a. Goose and Crooked Creek Local Watershed Plan (LWP). Prepared for North Carolina
Ecosystem Enhancement Program (NCEEP). Prepared by Tetra Tech.
Tetra Tech. 2012b. Goose Creek and Crooked Creek Watersheds:'Model Development and Calibration
(LSPC Model). Prepared for Centralina Council of Governments and North Carolina Division of Water
Quality. Prepared by Tetra Tech.
Tetra Tech. 2012c. QUAL2 Model Update for Twelve Mile Creek below the Union County WWTP.
Prepared for Union County Public Works Department and Hazen & Sawyer. Prepared by Tetra Tech.
Thackston, E.L., and J.W. Dawson. 2001. Recalibration of a reaeration equation. Journal of
Environmental Engineering, ASCE, 127(4), 317-321.
Tsivoglou, E. C., L.A. Neal. 1976. Tracer Measurement of Reaeration. III. Predicting the Reaeration
Capacity of Inland Streams. Journal of the Water Pollution Control Federation, 48(12):2669-2689.
United States Army Corps of Engineers (USACE). 2016. HEC-RAS River Analysis System User's
Manual. Davis, California.
Weaver, J.C., and J.M. Fine. 2003. Low -Flow Characteristics and Profiles for the Rocky River in the
Yadkin -Pee Dee River Basin, North Carolina, through 2002. USGS Water -Resources Investigations
Report 03-4147
E '.1 T Ee. 34

Crooked Creek QUAL2K Model
October 15, 2019
Included here are the treated effluent flow and water quality data associated with the permitted point
sources in the Crooked Creek watershed for August and September 2016 (Table A-1, Table A-2, and
Table A-3). Note that parameters such as chemical oxygen demand (COD), TN, TP, and hardness were
measured only once per month at some sites. Also reported by Carolina Water Services, Inc. are
instream water quality conditions immediately upstream and downstream of the Hemby Acres WWTP
which were used for headwater condition parameterization and instream calibration (Table A-4).
Table A-1. DMR data from August and September 2016: Crooked Creek #2 WWTP (NC0069841)
8/1/16 0.71
80.4
7.5
<2
<.1
<2.5
7.8
8/2/16 0.86
78.8
7.3
<2
0.91
<2.5
7.8
8/3/16 0.85
78.8
7.4
<2
0.92
<2.5
7.6
88
8/4/16 0.79
78.8
7.4
<2
1.0
<2.5
7.7
8/5/16 0.80
77.4
7.3
<2
0.87
<2.6
5.5
8/6/16 0.92
8/7/16 0.81
r8/8/10.89
79.7
7.3
<2
3.3
<2.5
7.6
0.95
79.3
7.3
<2
4.7
<2.5
7.6
8/10/16 0.91
80.2
7.2
<2
3.5
<2.6
7.4 33 6.4 3.3 74
91
8/11/16 1.11
80.2
7.4
2.2
7.6
8/12/16 0.87
82.4
7.2
6.8
8/13/16 0.26
8114/16 0.75
8/15/16 0.79
82.0
7.5
2.9
<.1
2.5
7.7
8116/16 0.82
81.5
7.6
<2
<A
<2.5
7.9
8/17/16 0.80
81.1
7.5
<2
<.1
<2.5
8.0
85
8118/16 0.85
80.8
7.3
7.8
8/19/16 0.95
80.6
7.0
7.4
8/20/16 0.89
8/21 /16 0.84
8/22/16 0.80
80.6
7.3
<2
<.1
<2.5
7.9
8123/16 0.82
78.8
7.3
<2
<.1
<2.5
7.9
8/24/16 0.76
77.9
7.3
<2
<.1
<2.5
8.0
65
8/25/16 0.77
77.5
7.3
<2
<.1
<2.5
8.1
8/26/16 0.81
80.6
6.7
<2.5
7.2
QTETRA TECH
35

Crooked Creek QUAL2K Model October 15, 2019
Date Flow Temp
(MGD) (°F)
pH
BODS
(Mg/1)
NH3 TSS DO COD
Img/l) (mg/1) (mg/1) (mg/l)
TN TP
(mg/1) (Mg/1)
Hardness Alkalinity
(mg/1) (mg/1)
®�®®_--®__-__
®®_■__
_____
==-■--____
®®mm-®_____
=W®mmm®=_____
9/7/16 1 0.89
76.6
7.2
<2
<.1
3.9
8.0
9/8/16 0.81
77.4
7.2
2.7
<.1
6.5
7.9 27 30.35 4.8 150
52
9/9/16 0.78
77.7
7.2
5.2
<.1
10.4
8.0
9/10/16 0.78
9/11/16 0.78
9/12/16 0.80
77.7
7.1
6.8
0.11
19
8.0
9/13/16 0.89
76.8
7.1
2.4
<.1
8.4
8.1
9/14/16 0.79
77.5
7.0
2.0
<.1
7.6
7.9
34
9115/16 0.79
77.5
7.0
8.0
9/16/16 0.78
78.8
6.4
2.6
<.1
6.6
7.9
9/17/16 0.76
9/18/16 0.80
9119/16 0.81
78.6
6.4
<2
0.11
4.6
7.9
9/20/16 0.81
77.5
6.8
<2
<.1
3.0
8.0
9/21/16 0.82
75.4
7.2
<2
<_1
<2.6
8.2
27
9/22/16 0.88
75.2
7.2
<2
<.1
<2.6
8.3
9/23/16 1.07
75.9
6.4
7.9
9/24/16 0.89
9/25/16 0.86
9/26/16 0.96
76.6
7.4
<2
<.1
<2.6
8.2
9/27/16 0.89
75.9
7.6
8.3
9/28/16 0.95
76.8
7.3
3
<.1
<2.5
8.1
9/29/16 0.84
76.1
7.3
<2
<.1
<2.5
8.2
9130/16 0.87
77.0
7.3
<2
<.1
<2.5
7.7
aTETRA TECH
36

Crooked Creek QUAL2K Model October 15, 2019
Table A-2. DMR data from August and September 2016: Grassy Branch WWTP (NC0085812)
Date Flaw Temp
(MGD) (OF)
P H
BOD5 NH3
(mg/1) (mg/l)
TSS
(Mg/1)
DO COD
(mg/1) (mg/1)
Alkalinity
(mg/1)
8/10/16
0.04
78.8
7.8
8/11/16
0.03
78.8
7.2 <2 <.1 <2.6 7.95 87
R117/1F
n n-i
7R A
77
8/13/16
0.18
8/14/16
0.02
8/15/16
0.02
82.4
7.7
8/16/16
0.02
80.6
7.6 <2 <.1 <2.6 7.04 96
8/17/16
0.02
80.6
7.2
8/18/16
0.02
82.4
7.3
8/19/16
0.04
78.8
7.5
8/20/16
0.03
8/21 / 16
0.02
8/22/16
0.02
1 78.8
7.2
8/23/16
0.02
77.0
7.0 <2 <.1 2.6 8.25 131
8/24/16
0.02
77.0
7.0
8/25/16
0.03
77.0
7.0 2 <.1 <2.5 7.3 120
8/26/16
0.03
78.8
7.3
8/27/16
0.02
8/28/16
0.03
8/29/16
0.03
78.8
7.0
DTETRA TECH 37

Crooked Creek QUAL2K Model
October 15, 2019
Date
Flow
(MGD)
Temp
(*F)
pH
BODs
(mg/1)
NH3
(mg/1)
TSS
(mg/1)
DO
(mg/l)
COD Alkalinity
(mg/1) (mg/l)
9/8/16
0.04
75.2
6.7 <2 <.1 <2.5 7.38 67
9/9/16
0.03
77.0
6.9
9/10/16
0.03
9/11/16
0.02
9/12/16
0.02
78.8
7.0
9/13/16
0.03
77.0
6.3 <2 0.34 <2.5 7.19 19 38
Q/1All R
fl M
77 r%
R F 7 n AR ) A 7 1a cz-)
9/15/16
0.04
75.2
6.8
9/16/16
0.04
77.0
7.3
9/17/16
0.03
9/18/16
0.02
9/19/16
0.02
77.0
7.7
9/20/16
0.04
75.2
7.6
9/21 /16
0.03
73.4
7.1 <2 <.1 <2.5 8.35 164
9/22/16
0.04
73.4
7.1 <2 <.1 <2.6 7.49 176
9/23/16
0.05
75.2
7.0
9/24/16
0.05
9/25/16
0.02
9/26/16
0.04
77.0
7.7
9/27/16
0.05
73.4
6.7
9/28/16
0.10
77.5
7.8
® TETRA TECH 38

Crooked Creek QUAL2K Model
October 15, 2019
9/29/16 0.03 74.5 7.2 <2 ' <.1 <2.5 + 8.34
9/30/16 0.04 74.5 7.3 <2 <.1 <2.6 7.35
Table A-3. DMR data from August and September 2016: Hemby Acres WWTP (NC0035041)
IMMMMI
ENINEIM
=I
MEN
ENEEN
OUNNEEN
INNEE
I MIMMENEEN
MEN
EN
NINE
NO
==ENNE
=MMENIIE
NO
MEN
® TETRA TECH 39

Crooked Creek QUAL2K Model
October 15, 2019
Date
Flow
(MGD)
Temp
(T) pH
BOD5
(mg/1)
NH3 TSS DO
(mg/1) (mg/1) (mg/1)
V. 1 V
9/4/16
0.08
9/5/16
0.09
9/6/16
0.06
73.9
7.0
6.55
9/7/16
0.09
9/8/16
0.08
74.5
7.0 11
<0.1 <2.5 6.1
9/9/16
0.08
9/10/16
0.11
9/11/16
0.08
75.2
7.2
7.01
9/12/16
0.07
76.1
8.2 4.9
<0.1 <2.5 7.21
9/13/16
00.9
9/14/16
0.10
9/15/16
0.07
9/16/16
0.09
9/17/16
0.09
9/18/16
0.08
9/19/16
0.11
9/20/16
0.09 75.9 7.4 6.61
9/21/16
0.08
9/22/16
0.10 76.6 7.3 3.2 <0.1 <2.5 6.87
9/23/16
0.10
TETRA TECH
40

Crooked Creek QUAL2K Model
October 15, 2019
Date
Flow
(MGD)
=ENI
Temp
(OF)
p H
BOD5
(mg/l)
NH3
(mg/1)
TSS
(mg/1)
EN
DO
(mg/1)
Table A-4. Instream DMR water quality data upstream and downstream of Hemby Acres WWTP, August
and September 2016
Date
8/3/16
Upstream
74.8
(OF)
Downstream
75.4
Dissolved
Upstream
4.72
OxygenTemperature
Downstream
5.03
8/11/16
73.8
75.2
4.57
5.03
8/18/16
76.3
76.8
4.43
4.96
8/25/16
73.6
75.0
3.33
4.01
8/30/16
73.4
75.0
4.32
4.91
9/8/16
71.6
73.2
4.01
4.59
9/12/16
71.8
73.2
3.63
4.97
9/22/16
73.9
76.3
3.65
4.01
F9/28/161
68.2 1
69.8
4.22
4.98
NTETRA TECH
41

Crooked Creek QUAL2K Model
October 15, 2019
Water quality sampling conducted by the Yadkin Pee Dee River Basin Association (Coalition) during
August and September of 2016 may be relevant to use for model calibration and corroboration (Table B-1).
Table B-1. Coalition water quality data of -interest from August and September 2016
8/9/2016
77.2
77.2
78.8
Water Temperature (°F)
8/30/2016
76.6
76.8
76.5
9/13/2016
73.6
73.8
74.8
8/9/2016
5.8
5.8
6.3
Dissolved Oxygen (mg/1)
8/30/2016
5.7
5.8
6.4
9/13/2016
5.5
5.7
6.5
8/9/2016
6.6
6.6
6.8
pH (s.u.)
8/30/2016
6.6
6.6
6.9
9/13/2016
6.6
6.6
6.8
8/9/2016
263
289
162
Conductivity (umhos/cm)
8/30/2016
393
372
219
9/13/2016
248
229
179
8/9/2016
310
270
166
Fecal Coliform (#/100m1)
9/13/2016
300
250
162
8/9/2016
No Data
No Data
9.1
Suspended Residue (mg/1)
9/13/2016
No Data
No Data
20
8/9/2016
16
20
16
Turbidity (NTU)
9/13/2016
21
11
11
8/9/2016
No Data
No Data
0.1
Ammonia as N (mg/1)
9/13/2016
No Data
No Data
0.08
TKN as N (mg/1)
9/13/2016
No Data
No Data
0.8
8/9/2016
No Data
No Data
1.74
NOX as N (mg/1)
9/13/2016
No Data
No Data
2.49
TP (mg/1)
9/13/2016
No Data
No Data
0.76
"Note: some samples were taken 1 day before or after the reported date listed in this table
® TETRA TECH
42

Crooked Creek QUAL2K Model
October 15, 2019
--,A
CA STREAM HYDROLOGY MEASUREMENTS
Twenty cross -sections were measured during the 2016 summer sampling effort (Table C-1).
Table C-1. Measured reach properties, summer 2016
2.21
8
13
16
13
No Data
0.30
1.1
No Data
2.92
0.5
0.9
0.6
1.54
1.63
No Data
5.15 26 18 0.15
5.58 33 10 No Data
5.93
3
No Data
No Data
No Data
No Data
6.20
35
19
0.22
2.1
6.25
10.43
61
14
0.26
1.1
2.23
12.45
75
17
0.30
0.8
2.83
14.63
87
23
0.40
0.5
3.29
15.68
1
27
No Data
0.2
No Data
18.71
252
16.5
0.28
0.8
2.42
21.26
117
41.5
No Data
0.6
No Data
22.09
138
24
0.33
1.0
3.61
22.90
118
40.6
No Data
1.6
No Data
23.33
25.28
26.34
27.59
119
160
120
121
38
38.5
28.5
26.5
No Data
0.18
No Data
No Data
1.1
1.0
1.1
1.2
No Data
4.11
No Data
No Data
27.79
122
30
No Data
1.8
No Data
29.23
182
35
0.03
1.1
0.84
OTETRA TECH
43

Crooked Creek QUAL2K Model
October 15, 2019
G.2 NUTRIENT SAMPLING
Grab samples were analyzed for water quality constituents along Crooked Creek during each sampling
effort. Fifteen samples were taken from the main stem, tributaries, and wastewater treatment plant
discharge sites during each sampling trip (Figure C-1). Water quality analyses were conducted by Pace
Analytical laboratory for the following parameters: 5-day biochemical oxygen demand (BODS), 5-day
carbonaceous biochemical oxygen demand (CBODS), ammonia (NH3), nitrate and nitrite (NO2+NO3),
phosphate (PO4), total Kjeldahl nitrogen (TKN), total nitrogen (TN), and total phosphorus (TP).
For a number of laboratory samples, the measured parameter was found to be below the level of
detection (LOD). The laboratory equipment did produce a numerical result below the LOD which has
been included and flagged as such. Although these results are below the LOD, the numbers seem
reasonable and may be relevant to include in modeling efforts with an increased level of uncertainty
associated with the exact concentrations. The results from all grab samples have been compiled by
sampling location, parameter, and trip (Table C-1, Table C-2, and Table C-3).
1 2 3
.4
...r I 5
f
Crooked Creek Watershed
® TETRA TECH
Water Quality Grab Samples
NAp 1B8] Slesr�W. NbM C.mfY FlI'S.3S0, =.r.
wa �xa vmxie N nmw�
12
11
10
5
9*
7 8 l
N o 0.5 1 z
A OKil—ter.
0 0.5 1 2
Miles
'Note: Site 9 was sampled further upstream
Ion South Fork Crooked Creek during the
second and third sampling efforts
Legend
Grab Sample Site
■ WWTP Discharge
NHD HiRes Flowline
Watershed Boundary
Figure C-1 Water quality grab sample locations
® TETRA TECH
44

Crooked Creek QUAL2K Model
October 15, 2019
Table C-2. BOD/CBOD results (units mg/1)
■
1
Location Note
US of Hemby discharge
1.40*
eoo-
1.20*
4.10
1.10*
:•D
1.20*
1
0.60*
2
Hemby WWTP discharge
0.70*
2.60
1.40*
0.70*
3.20
2.10
3
4
Indian Trail Fairview Rd
Crooked Creek #2 discharge
1.30*
1.50*
2.00*
0.70*
1.50*
2.20
0.80*
0.80*
1.60*
0.50*
1.60*
1.50*
5
6
US of CC#2 WWTP discharge
Old Farm Bridge crossing
1.50*
1.60*
1.30*
1.00*
1.40*
0.90*
1.00*
1.40*
1.20*
0.60*
1.90*
0.30*
7
IDS of Rocky River Rd
1.50*
0.50*
1.20*
1.00*
0.95*
0.50*
8
Ridge Road crossing
1.50*
0.60*
3.50
0.80*
0.90*
0.90*
9
SF Crooked Creek
1.40*
2.00
0.80*
0.90*
1.20*
2.10
10
DS of debris dams
1.40*
0.70*
0.90*
1.10*
0.90*
0.30*
11
Brief Rd crossing
1.40*
1.30*
0.70*
0.90*
1.20*
0.50*
12
Grassy Branch WWTP discharge
0.70*
1.10*
1.70*
0.20*
1.10*
0.10*
13
Grassy Branch Tributary
Hwy 218 crossing
US of Brief Rd
9.00
1.10*
1.00*
8.10
0.60*
0.70*
0.90*
0.90*
1.10*
3.00
0.00*
0.50*
7.50
0.80*
0.70*
1.10*
0.60*
0.40*
14
15
*reflects the numerical result reported from lab analysis although result is below reporting limit
Report limit for BOD5: 2.0 mg/I, CBOD5: 2.0 mg/I
NTETRA TECH
45

Crooked Creek QUAL2K Model
October 15, 2019
Table C-3.
Nitrogen species results
(units mg/1)
• •
ID Location
Note
1 US of
0.08*
0.03*
0.02*
0.34
0.22
0.08
0.46*
0.94
0.73
0.81
1.20
0.80
Hemby
discharge
2 Hemby
0.02*
0.05*
0.02*
33.70
42.30
25.10
0.98
0.00*
1.10
34.70
42.30
26.30
WWTP
discharge
3 Indian Trail
0.00*
0.07*
0.08*
6.50
3.20
5.40
0.79
0.54
0.98
7.30
3.70
6.30
Fairview Rd
4 Crooked
0.00*
0.02*
0.00*
24.00
32.90
33.90
1.20
1.10
1.90
25.10
33.90
35.80
Creek #2
discharge
5 US of CC#2
0.09*
0.08*
0.15
2.30
0.51
0.70
0.53
0.69
1.40
2.80
1.20
2.10
WWTP
discharge
6 Old Farm
0.12
0.05*
0.04*
10.80
20.50
28.90
1.00
1.30
1.50
11.80
21.80
30.50
Bridge
crossing
7 DS of Rocky
0.02*
0.05*
0.04*
11.70
23.30
24.10
1.20
0.63
1.50
12.90
23.90
25.50
River Rd
8 Ridge Road
0.03*
0.05*
0.03*
10.30
16.40
33.20
1.20
1.10
1.10
11.40
17.40
34.30
crossing
9 SF Crooked
0.07*
0.93
0.11
5.60
0.13
0.00*
1.50
1.60
0.74
7.10
1.70
0.74
Creek
10 DS of debris
0.08*
0.07*
0.13
0.46
1.50
8.40
0.92
0.56
1.20
1.40
2.00
9.60
dams
11 Brief Rd
MCI
0.02"
0.01"
0.34
2.90
0.67
0.67
0.73
0.75
1.00
3.70
1.40
crossing
12 Grassy
0.01*
0.44
0.03*
34.00
44.00
53.30
1.30
0.84
0.00*
35.30
44.80
53.30
Branch
WWTP
discharge
13 Grassy
0.00*
0.02*
0.02*
1.50
1.70
0.61
0.79
0.25*
0.73
2.30
1.90
1.30
Branch
Tributary
14 Hwy 218
0.02*
0.07*
0.02*
1.20
3.80
2.50
0.44*
0.70
0.56
1.60
4.50
3.10
crossing
15 US of Brief
0.01 *
0.03*
0.00*
0.55
13.80
0.89
0.47*
0.72
0.46*
1.00
14.50
1.30
Rd
reflects non -detect, numerical
result reported
Reporting limit for NH3-N: 0.10 mg/I, NO2+NO3-N:
0.020
mg/I,
TKN: 0.50
mg/I,
TN: 0.12
rng/I.
DTETRA TECH
46

Crooked Creek QUAL2K Model
October 15, 2019
Table C-4. Phosphorus species results (units mg/1)
1
US of Hemby discharge
0.13
0.10
0.05
0.06
0.16
0.12
2
Hemby WWTP discharge
1.80
4.80
4.00
3.20
5.00
5.60
3
Indian Trail Fairview Rd
0.54
2.90
0.31
2.10
4.60
1.10
0.50
4.80
0.16
0.47
2.50
0.24
0.47
4.80
0.23
0.57
6.10
0.36
4
Crooked Creek #2 discharge
5
US of CC#2 WWTP discharge
Old Farm Bridge crossing
6
1.20
2.90
4.10
1.20
2.70
4.50
7
DS of Rocky River Rd
1.30
3.30
3.60
1.20
3.00
3.90
8
Ridge Road crossing
0.32
2.40
3.60
1.10
2.20
4.00
9 TSF
Crooked Creek
0.34
0.15
0.09
1.10
0.15
0.19
10
IDS of debris dams
0.23
2.10
1.10
0.84
0.53
1.10
11
Brief Rd crossing
0.86
2.70
0.43
0.72
0.66
0.65
12
Grassy Branch WWTP discharge
0.30
3.40
4.50
2.70
3.30
4.70
13
Grassy Branch Tributary
0.20
0.26
0.07
0.19
0.12
0.17
14
Hwy 218 crossing
0.16
1.00
0.74
0.75
0.86
0.80
15
US of Brief Rd
0.14
1.90
0.75
0.66
1.60
0.61
Reporting limit for POa-P: 0.050 mg/l, TP: 0.050 mg/l.
® TETRA TECH 47

Crooked Creek QUAL2K Model
October 15, 2019
C.3 LONGITUDINAL DISSOLVED OXYGEN
Dissolved Oxygen was monitored using a hand-held probe every several hundred meters along the
extent of Crooked Creek on each sampling effort to some degree. The results of the raw DO readings at
each location sampled from each trip are seen below (Figure C-2, Figure C-3, Figure C-4, Table C-5,
Table C-6, Table C-7). Note that these results have not been temperature -corrected. Frequently sampled
alongside dissolved oxygen concentration were: pH, dissolved oxygen saturation, water temperature,
turbidity, and specific conductivity.
Crooked Creek Watershed N 0 0.5 1 2
Q TETRA TECH Longitudinal DO Sampling (8/15-8/l, mmm=�Kilomelers
wu �oea 3zom F.e 0 0.5 1 2
ex—-- H-h— A I Miles
"- Legend
WWTP Discharge
Large Beaver Dam
NHD HiRes Flowline
Watershed Boundary
r
DO (mg/L)
• <4.0
4.0 - 5.0
>5.0
No Data
Figure C-2. Instream longitudinal dissolved oxygen measurements (8/15/16-8/19/16)
QTETRA TECH 48

Crooked Creek QUAL2K Model
r
,r
r
r
w...
• .� -ate
Crooked Creek Watershed
® TETRA TECH Longitudinal DO Sampling (8/31-9/2)
NPl] 190.1 S41�i'ane IYmI� C�iaw FINS 3Jip FwF
Wr. praNmeq OP11201a. rf NCFa4n
October 15, 2019
Legend
WWTP Discharge
Large Beaver Dam
NHD HiRes Flowline
Watershed Boundary
DO (mg/L)
e <4.0
4.0 - 5.0
N 0 0.5 t 2 • >5.0
AvlGlcmeters
0 0.5 t z No Data
� Miles
Figure C-3. Instream longitudinal dissolved oxygen measurements (8/31/16-9/2/16)
NTETRA TECH 49

Crooked Creek QUAL2K Model
October 15, 2019
Jxi.w.
Legend
WWTP Discharge
Large Beaver Dam
NHD HiRes Flowline
Watershed Boundary
DO (mg/L)
• <4.0
4.0 - 5.0
Crooked Creek Watershed N 0 0.5 1 2 s >5.0
D TETRA TECH Longitudinal DO Sampling (9/13-9/16) oKilometers
—, 'm 31e1Wbnn !-' -- .n woe FM 0 0.5 1 2 No Data
uxa mo .m-iizaie..- - �i Miles
Figure C-4. Instream longitudinal dissolved oxygen measurements (9/13/16-9/16/16)
® TFTRA TECH 50

Crooked Creek QUAL2K Model
October 15, 2019
Table C-5. Longitudinal data from trip 1 (August 15-19, 2016)
ID
1
Latitude (N) Longitude (W)
35.1074 80.63715
Date
8/15
Time
17:48
PH
6.29
■• .•
No Data 58.9
79.2
2
35.10429
80.63447
8/15
18:18
6.84
No Data 68.8
80.1
4
35.10346
80.62941
8/15
18:30
6.91
No Data 62
79.5
5
35.10547
80.62941
8/16
8:02
6.95
3.18 39.2
78.3
6
35.10545
80.62855
8/16
8:22
6.99
7.14
4.13
4.03
51.2
49.1
79.0
78.3
8 35.10617 80.6272 8/16 8:40
10
35.10659
80.62418
8/16
9:14
7.13
5.07
61.6
77.5
13
35.10786
80.62229
8/16
9:34
7.1
4.67
55.9
77.4
15
35.10893
80.62077
8/16
10:06
7.18
4.79
58.3
77.4
18
35.109
80.61813
8/16
10:40
7.21
4.68
57.5
77.7
19
35.1076
80.61507
8/16
11:01
7.04
2.97
36.3
78.1
20
35.10626
80.6144
8/16
11:13
7.12
3.65
44.7
78.1
21
35.1044
80.61324
8/16
11:27
7.22
3.15
38.8
78.1
22
35.10303
80.61198
8/16
11:41
7.09
4.5
55.1
78.1
24
35.10164
80.61172
8116
11:51
7.12
4.53
55.3
77.9
25
35.10003
80.6083
8/16
12:11
7.09
4.78
58.4
77.9
26
35.09868
80.60705
8/16
12:25
7.17
4.43
54.2
77.9
28
35.0975
80.60536
8/16
12:58
7.12
3.13
38.4
78.3
30
35.09652
80.60519
8/16
13:05
7.1
3.24
39.9
78.8
31
32
35.09602
35.0961
80.60497
80.60487
8/16
8/16
1:13 6.81
1:19 7.24
2.29
5.22
29.4
64.5
80.8
79.3
33
35.09645
80.6043
8/16
13:32 7.09
5.11
63.4
79.5
34
35.09502
80.60084
8/16
14:02 7.02
2.62
32.3
79.2
35 J
35.09652
80.59822
8/16
14:38 7.38
5.2
66.2
81.5
�'p. Y-
?EC,
51

Crooked Creek QUAL2K Model
October 15, 2019
• Date Time
36 35.09743 80.59677 8/16 7.167
38 35.09833 80.59464 8/16 15:33
39 35.0989 80.59364 8/16 15:47
pH
7.31
.•
5.13
.•
64.9
81.7
7.37
3.89
49.1
81.1
7.28
7.27
8.66
3.25
3.57
11.64
39.9
44.9
152.3
80.8
80.8
85.3
41 35.09908
80.59235
8/16
16:00
43 35.10103
80.58817
8/16
16:22
45 35.10244 80.58469
8/16
16:48
7.93
7.2
90.4
83.3
46 35.10362 80.58096
8/17 8:28
8/17 8:43
7.29
7.48
3.85
5.53
48.2
69.8
79.9
80.2
48 35.10303 80.57883
50 35.10158 80.57745
8/17 9:00 7.47 4.48 56.8 80.1
52 35.10235 80.57418
8/17 914 7.44 4.42 55.1 79.7
53 35.10264 80.57316
8/17 9:32 7.38 4.34 54.3 79.5
54 f 35.10268 80.57128
8/17 9:53 7.28 4.44 55.3 79.7
56 35.10316 80.56911
8/17 10:15 7.31 2.39 29.9 79.7
58 35.10502
60 35.10611
80.56769
80.56563
1 8/17
8117
10:36
10:54
7.31
7.38
4.64
3.77
58.5
46.1
80.8
79.9
61 35.10641
80.56356
8/17
11:32
7.33
3.91
48.8
79.9
62 35.1075
63 35.10954
64 35.11013
80.56329
80.56135
80.55966
8/17
8/17
8/17
11:48
12:13
12:28
7.4
7.28
7.41
4.01
5.28
5.13
50.2
65
64.4
79.7
78.6
80.4
65 35.1108
80.55741
8/17
12:42
7.77
8.08
102.9
82.6
66 35.11146
80.55566
8/17
12:55
7.63
5.03
63
80.4
67 35.11067
80.55408
8/17
13:10
7.4
4.46
56.8
81.7
69 35.11141
80.55309
8/17
13:27
7.36
2.99
37.8
81.1
71 35.11172
80.5519
8/17
13:41
7.33
3
38
81.3
72 35.11196
80.55107
8/17
13:56
7.34
3.21
40.3
80.8
® TETRA TECH
52

Crooked Creek QUAL2K Model
October 15. 2019
ID
74
Latitude (N)
35.11223
Longitude (W)
80.54912
80.54745
Date
8/17
8/17
Time
14:23
pH
7.34
.•
3.52
.•
45
-
81.5
76 35.11278
14:57 7.33
3.9
49.5
81.7
77
35.11274
80.54661
8/17
15:08
7.35
2.47
31.5
81.9
78
35.11441
80.54568
8/17
15:35
7.16
1.22
15.1
79.5
79
35.11661
80.54506
8/17
15:55
7.14
1.1
13.7
79.7
80
35.11855
80.54276
8/17
16:16
7.11
1.9
23.3
80.8
82
35.14477
80.4716
8/18
8:34
7.15
4.27
51.9
77.4
83
35.1331
80.48961
8/18
8:49
7.26
5.3
54.7
77.9
84
35.13116
80.49425
8/18
9:07
7.34
3.7
44.8
76.6
85
35.13099
80.49411
8/18
9:14
6.68
2.78
32.9
74.5
86
87
90
92
94
35.12245
35.12229
35.12278
35.12492
35.12695
80.54194
80.54069
80.53825
80.53868
80.53902
8/18
8/18
8/18
8/18
8/18
10:59
11:21
11:38
11:57
12:13
6.95
7.04
7.12
7.07
7.06
0.82
4.43
3.64
2.78
3.13
10.2
54.5
43.2
34
38.7
78.4
79.0
78.1
77.7
78.3
95
35.12815
80.53928
8/18
12:23
7.02
2.87
35.2
78.1
96
35.12911
80.53567
8/18
12:38
7.05
3.02
37.3
78.6
97
35.12745
80.53224
8/18
1102
7.05
2.69
32.9
78.8
99
35.12849
80.53107
8/18
13:14
7.2
5.12
63.7
79.7
101
35.12836
80.52878
8/18
13:48
7.3
4.86
60.3
79.5
102
35.12998
80.5269
8/18
14:00
7.35
6.7
83.9
80.4
105
35.13273
80.52562
8/18
14:21
7.48
5.1
63.7
79.9
106
35.1348
80.5248
8/18
14:42
7.29
4.51
56.6
80.2
108
35.13543
80.51939
8/18
15:06
7.62
5.9
76
81.9
109
35.13492
80.51781
8/18
15:37
7.45
6.58
82.5
80.4
® TETRA TECH
53

Crooked Creek QUAL2K Model
October 15, 2019
110
35.13382
80.51204
Date
8/18
8/18
8/18
Time
15:58
16:12
16:24
pH
7.49
7.69
7.55
.•
4.65
4.56
4.09
.•
59 81.5
58 81.7
51.7 81.3
111
35.13643
80.5126
112
35.13899
80.51417
113
35.13919
80.51332
8/18
16:34
7.45
5.07
65.2
81.1
114
35.13871
80.51076
8/18
16:42
7.61
5.52
69.8
81.7
115
35.13842
80.50713
8/18
16:50
7.68
5.81
73.4
81.3
116
35.13825
80.50588
8/18
16:56
7.35
5.3
66.5
79.3
Table C-6. Longitudinal data from trip 2 (August 31-September 2, 2016)
ID
120
121
Latitude (N)
35.14462
35.13301
Longitude (W)
80.47173
80.4896
Date
8/31
8/31
Time
15:02
15:26
pH
7.57
7.5
.•
6.33
7.37
.•
77.4
89.1
77.7
76.6
122
35.13091
80.49409
8/31
15:49
6.78
7.87
95
76.6
123
124
35.13112
35.13121
80.49418
80.49426
8/31
8/31
16:06
16:12
7.28
7.79
7.29
5.03
87.9
61.2
76.5
77.7
125
126
35.13803
35.12832
80.50548
80.53928
8/31
8/31
17:14
17:39
7.46
6.9
5.17
4.26
61.8
51.1
76.3
76.1
127
no data
no data
8/31
18:00
6.62
0.82
9.7
74.3
128
35.10136
80.57244
8/31
18:19
7.07
5.47
66.7
77.7
129
35.10238
80.5838
8/31
18:32
7.18
7.17
88.7
79.2
130
35.09903
80.59232
8/31
18:50
6.98
4.52
54.8
77.2
131
35.0961
80.59836
8/31
19:10
7.27
7.67
95.4
79.2
132
133
134
35.09506
35.10788
no data
80.60077
80.61561
no data
8/31
8/31
8/31
19:26
19:46
20:10
6.78
6.8
7.63
1.87
3
8
22.2
35.9
98
74.8
75.9
78.1
135
no data
no data
8/31
20:13
7.55
5.9
70.2
75.4
® TETRA TECH
54

Crooked Creek QUAL2K Model
October 15. 2019
136
Date
35.13803 80.50533 9/1
Time
8:13
8:30
pH
7.29
7.42
.• ..
4.66 55
5.59 65.4
74.1
137
35.13571 80.5023
9/1
73.9
73.6
138
35.13332 80.50132
9/1
8:42
7.33
5.79
67.8
139
35.13187
80.49962
9/1
9:15
7.45
5.9
68.3
73.6
140 35.13139
80.49867
9/1
9:23
7.39
6.51
76.1
73.4
141
35.13094
80.49665
9/1
9:41
7.47
6.45
75.5
73.8
142
35.13089
80.49506
9/1
9:50
7.43
6.81
79.7
73.6
143
35.13116
80.49414
9/1
9:57
7.31
7.35
87.5
75.2
144
35.13094
80.49404
9/1
10:01
6.23
2.67
30.7
71.1
145
35.13134
80.49369
9/1
10:05
7.34
5.87
68.7
73.8
146
148
35.13165
35.13233
80.49204
80.4902
9/1
9/1
10:14
10:26
7.28
7.34
4.65
4.96
54.6
58.7
73.9
74.3
149
35.13306
80.48958
9/1
10:35
7.38
6
70.8
74.7
150
35.1341
80.48951
9/1
10:41
7.47
6.12
72.3
74.7
151
35.13606
80.48993
9/1
10:50
7.35
6.02
70.9
74.3
152
154
156
158
159
160
35.13813
35.13709
35.13804
35.14062
35.14259
35.14266
80.49062
80.48772
80.4855
80.48538
80.48672
80.48602
9/1
9/1
9/1
9/1
9/1
9/1
11:00
1120
11:36
12:00
12:09
12:18
7.45
7.63
7.6
7.54
7.44
7.42
5.52
7.24
6.72
7.43
4.66
5.99
65.3
86.2
79.5
87.6
54.8
71.3
74.7
75.4
74.7
74.5
74.1
75.2
161
35.14226
80.48444
9/1
12:49
7.23
5.01
60.1
75.9
163
35.14281
80.4832
9/1
13:20 7.26
6.56
79.3
76.8
165 35.1444
167 35.14518
�"n.. TETRA TECH
80.48367
80.48033
9/1
9/1
13:39 7.47
13:50 7.24
7.42
5.8
91.7
69.7
78.6
76.3
55

Crooked Creek QUAL2K Model
October 15, 2019
168
35.14437
80.47944
9/1
14:00
7.4
6.17
75.5
78.1
169
35.14214
80.47688
9/1
14:12
7.3
4.67
56.3
77.4
171
35.14138
80.47367
9/1
14:30
7.57
8.05
99.7
79.2
172
35.14304
80.47221
9/1
14:37
7.71
7.87
97.5
79.2
173
35.14477
80.47175
9/1
14:50
7.71
6.54
81.3
79.5
174
35.14561
80.4708
9/1
16:04
7.85
6.37
80.2
80.8
176
35.14824
80.46992
9/1
16:15
7.54
7.77
98.4
81.3
177
178
180
181
182
35.14809
35.1466
35.14716
35.14845
35.15091
80.46889
80.46709
80.46584
80.46641
80.46693
9/1
9/1
9/1
9/1
9/1
16:23
4:32
16:44
16:48
16:57
7.62
7.6
7.66
7.6
7.66
7.55
7.23
6.45
6.7
6.14
95.5
89.5
80.8
83
76.5
81.3
79.2
80.4
79.2
79.9
183
35.15145
80.46413
9/1
17:23
7.75
6.47
80.7
79.9
185
35.14817
80.46246
9/1
17:35
7.85
7.65
94.8
79.2
187
35.14616
80.46063
9/1
17:46
7.8
6.98
86
78.8
188
1 15005
189 35.14981
80.45959
80.45807
9/1
9/1
17:57
18:10
7.91
7.89
6.67
5.28
82
64.9
78.4
78.4
Table C-7. Longitudinal data from trip 3 (September 13-16, 2016)
LongitudeLatitude
Turbidity
.•
..
Specific Temp
Conductivity
194
35.14474
80.47161
9/14
7:20
6.4
6.53
6.23
71
159 71.1
195
35.13801
80.50545
9/14
7:46
7.4
6.07
6.27
71.6
169.1
71.4
196
35.10223
80.58383
9/14
8:20
10.1
6.48
4.69
54.7
531
73.4
197
35.10636
80.54846
9/14
9:20
11.8
5.95
0.57
6.5
102.2
71.6
198
35.10777
80.548
9/14
9:26
65
6.39
0.09
1.1
103
71.8
® TETRA TECH 56

Crooked Creek QUAL2K Model
October 15, 2019
LongitudeLatitude
Date
199 35.10886 80.54678 9/14
Time
9:40
..
(NTU)
13.3
pH
6.61
.•
(mg/1)
0.28
.• Specific Temp
(%Sat) Conductivity C
3.3 105.1 71.2
200 35.11024
80.54744
9/14
10:02
43
6.59
0.05
0.6
136
71.6
201
35.11235
80.54677
9/14
10:19
10.3
6.79
0.29
3.4
102
71.1
203
35.11274
35.11332
80.54707
80.54606
9/14
10:36
12.6
7.09
5.62
65.6
498
73.4
204
9/14
10:50
11.7
7.16
4.99
58.3
499
73.4
205
35.11466
80.54564
9/14
11:03
15.9
7.17
4.3
50.4
489
73.8
206
35.11606
80.54512 9114
11:20
19.9
7.07
3.44
40.4
459
420
73.8
73.8
207 35.11754 80.54533 9/14 11:29 33.1 7.02 2.51 29.4
208
35.11809
80.54537
1 9/14
11:38
28.2
7.02
1 3.25
37.9
398
73.6
209
35.11847
80.54442
9/14
11:47
14.5
7.05
3.27
38.2
406
73.4
210
35.11859
80.5431
9/14
11:58
12.7
7.05
3.07
36
402
73.8
211
35.11815
80.54212
9114
12:13
25.4
7.03
3.25
38.6
396
74.3
212
35.11897
80.54178
9/14
12:22
17.4
7.15
3.76
44.1
391
73.8
213
35.12085
80.54262
9/14
12:56
11.2
7.09
2.95
34.3
384
73.0
214
35.12205
80.54395
9/14
13:05
12
7.01
2.98
35
379
73.8
215
35.12263
80.54272
9/14
13:10
39.9
6.98
2.07
24.3
353
73.0
216
35.1223
80.542
9114
13:14
42.6
6.91
1.67
19.5
337
73.0
217
35.12228
80.54147
9/14
13:23
90
7.02
5.07
59.7
334
74.5
218
35.12233
80.54047
9/14
13:29
29
7.16
5.7
67.5
332
74.8
219
35.1226
80.53941
9/14
13:35
20.9
7.21
6.08
72.2
331
75.0
220
35.12211
80.5386
9/14
13:40
48
7.25
6.14
72.3
331
74.3
221
35.12314
80.5385
9/14
13:50
12.4
7.2
5.58
65.6
333
73.9
222
35.1237
80.53819
9/14
13:57
25.5
7.23
5.76
67.9
335
74.3
223
35.12588
80.53824
9/14
14:08
21.5
7.19
5.15
60.1
344
73.4
224
35.12732
80.53961
9/14
14:18
17.8
7.28
4.98
58.6
339
74.3
NIFTRA TECH 57

Crooked Creek QUAL2K Model
October 15, 2019
225
35.12815
LongitudeLatitude
80.53922
Date
9/14
Time
14:24
..
(NTU)
21.4
pH
7.31
DO
(mg/1)
4.73
DO
(%Sat)
55.7
Specific
Conductivity
333
Temp
('F)
74.1
226
35.12886
80.53698
9/14
14:30
26.4
7.28
4.61
54.1
314
74.1
227
35.13293
80.48951
9/14
15:12
4.5
7.71
8.14
99.3
188
77.7
228
35.13092
80.49402
9/14
15:24
0.1
7.51
18.9
229
263
76.8
229
35.13119
80.49428
9/14
15:31
0.8
7.56
7.8
94.3
837
76.6
230
no data
no data
9/14
16:02
6.9
7.54
7.05
85.1
575
76.5
231
35.09909
80.59237
9/14
16:17
5.6
7.14
5.58
66.8
5.79
75.9
232
35.09612
80.59837
9/14
16:42
3
7.18
7.75
94.7
628
77.7
233
35.09518
80.60079
9/14
16:51
49
7.28
1.63
18.7
198
72.1
234
35.10787
80.61551
9/14
17:07
43.3
7.22
2.68
31.1
274
72.7
235
35.1042
80.63397
9/14
17:19
0.4
7.06
8.16
98.1
641
76.1
236
35.10434
1 80.63426
9/14
17:24
54.4
7.29
2.92
33.6
125
72.1
237
35.1288
80.537
9/15
7:30
14.9
7.47
4.44
51.2
330
72.1
238
35.12906
80.53555
9/15
7:38
11.6
7.29
4.31
49.6
332
72.0
239
35.12732
80.53225
9/15
7:48
12.2
7.2
3.54
41
313
72.5
240
35.12809
80.53156
9/15
7:56
8.5
7.19
3.55
40.9
299
72.1
241
35.12933
80.5312
9/15
8:04
4.5
7.33
5.86
67
294
71.4
242
35.1295
80.53051
9/15
8:09
23.4
7.37
5.89
67.2
293
71.2
243
35.12904
80.52917
9/15
8:15
16.9
7.35
5.36
61.2
291
71.4
244
35.1277
80.52801
9/15
8:24
8.5
7.35
5.09
58.6
291
72.1
245
35.12745
80.52695
9/15
8:34
8.5
7.34
5.14
59.3
279
72.5
246
35.1299
80.52703
9/15
8:48
10.1
7.41
6.18
70.6
274
71.4
247
35.13115
80.52707
9/15
8:56
5.1
7.44
6.29
71.7
271
71.1
248
35.13271
80.5256
9/15
9:03
4.8
7.43
5.71
65.6
266
71.8
249
35.13482
80.52454
9/15
9:10
10.2
7.33
4.98
57.7
238
72.9
sTETRA TECH 58

Crooked Creek QUAL2K Model
October 15, 2019
250
35.13532
LongitudeLatitude
80.523
Date
9/15
Time
9:30
..
(NTU)
22.5
PH
7.38
.•
(mg/1)
6.29
.•
(%Sat)
72.8
Specific
Conductivity
237
Temp
ff)
72.7
251
35.13454
80.52183
9/15
9:41
18.3
7.47
6.72
77.4
234
72.3
252
35.13451
80.52116
9/15
10:00
10.6
7.46
6.45
74.1
233
72.0
253
35.13541
80.51936
9/15
10:20
5
7.55
6.41
73.2
231
71.4
254
35.13516
80.51765
9/15
10:25
14.1
7.43
5.36
61.6
229
71.8
255
35.13304
80.51588
9/15
10:35
11.9
7.5
5.56
64.6
213
72.9
256
35.13282
80.51525
9115
10:40
10.4
7.41
5.48
63.5
210
72.9
257
35.1327
80.51311
9/15
10:52
9.7
7.4
5.2
60.4
206
73.0
258
no data
no data
9/15
10:58
7.9
7.67
6.01
69.6
205
72.7
259
35.13502
80.51162
9/15
11:17
10.9
7.34
5.77
66.8
199
72.7
260
35.13643
80.51194
9/15
11:23
no data
7.73
6.99
80.7
198
72.5
261
35.13703
80.51332
9115
11:31
10.2
7.48
6.62
76.2
197
72.1
262
35.13924
80.51406
9/15
11:43
10.3
7.33
4.65
54
185
73.0
r263
35.13919
80.5123
9/15
11:53
8.5
7.52
6.23
72.5
185
73.2
264 no data no data 9/15 11:55 7.4 7.45 6.45 75.1 186 73.0
265
no data
no data
9/15
11:58
14.9
7.43
6.74
78.8
183
73.6
266
35.13913
80.51331
9/15
12:02
16.8
7.29
6.03
70.7
183
73.9
267
35.13929
80.51405
9/15
12:06
43.1
7.36
5.96
70.1
184
74.1
268
35.13933
80.51427
9/15
12:09
12.5
7.3
4.92
57.4
185
73.4
269
35.13878
80.51134
9/15
12:40
10.9
7.89
6.82
79.8
183
73.8
270
35.13878
80.51134
9/15
12:45
4.8
7.28
3.12
36.3
154
72.7
271
no data
no data
9/15
12:52
4
7.57
7.05
82.2
175
73.2
272
35.13826
80.51035
9/15
12:54
5.9
7.6
7.31
86.2
183
74.3
273
35.13817
80.50831
9/15
13:06
17.2
7.63
7.65
89.2
180
73.4
274
35.13847
80.50727
9/15
13:11
6.5
7.66
7.93
92.6
180
73.6
® TETRA TECH 59

Crooked Creek QUAL2K Model
October 15, 2019
ID
275
no data
no data
..
9/15
13:22
11.9
7.52
7.1
82.4
178
72.9
276
no data
no data
9/15
13:28
7.1
7.39
5.82
68.6
174
74.3
277
35.13634
80.5026
9/15
13:39
10.7
7.82
8.13
97.4
171
76.1
278
35.13442
80.5015
9/15
13:46
13.1
7.84
8.56
102.1
169
75.7
279
35.13269
80.50138
9/15
13:57
7.1
7.88
8.94
108.3
167
77.2
280
35.13197
80.49989
9/15
14:02
6.6
7.89
8.5
101.7
166
75.9
281
35.13145
80.4984
9/15
14:10
9.3
7.7
8.1
95.6
166
74.5
282
35.1309
80.49506
9/15
14:19
8.6
7.87
8.91
107.1
164
76.3
283
284
35.13115
35.13125
80.49435
80.4938
9/15
14:23
11.9
7.58
5.73
65.8
166
72.5
9/15 14:26 16 7.72 8.82 105.4 253 75.7
285
35.13105
80.49401
9/15
14:29
0.1
7.63
16.7
197
269
74.7
286
35.13116
80.4942
9/15
14:32
1.9
7.54
7.84
94.5
790
76.3
C.4 DIURNAL DISSOLVED OXYGEN
Daily cycles of dissolved oxygen concentration can vary due to temperature, macrophyte productivity, and
changes in point sources. Diurnal DO was measured using long-term sondes for multiple days at a
number of locations along Crooked Creek at ten-minute intervals. The sampling locations for each trip are
shown in Figure C-5, with overall statistics reported in Table C-8. Timeseries results of all results for all
sites (not temperature -corrected) are seen in Figure C-6, Figure C-7, and Figure C-8.
Table C-8. Dissolved oxygen sonde result statistics (units are mg/L)
Trip
1
Site
DS of CC#2
Average .•
4.46
Minimum .• Maximum D• .O Range
3.60 5.12 1.52
(8/13-8/19)
HWY 601
3.15
2.54
3.72
1.18
US of CC#2
2.03
1.01
3.25
2.24
2
(8/31-9/2)
Brief Rd
4.97
4.11
6.28
2.17
SR 1601
4.52
3.30
5.83
2.53
® TETRA TECH
.1

Crooked Creek QUAL2K Model
October 15, 2019
Trip
Site Average DO
HWY 601 3.47
Minimum DO
2.82
Maximum DO
5.01
DO Range
2.19
3
(9/13-9/16)
Brief Rd 3.93
N Rocky River 4.89
Rd
SR 1601 4.67
3.30
4.94
1.64
3.54
6.70
3.16
3.33
6.33
3.00
Figure C-5. Dissolved oxygen monitoring sonde sites (all trips)
NTETRA TECH
61

Crooked Creek QUAL2K Model
October 15, 2019
8
7
6
5
E
O
4
d
v
y
O
3
2 r •
r
1
0
8/15/16 13:00 8/16/16 1:00 8/16/16 13:00 8/17/16 1:00 8/17/16 13:00 8/18/16 1:00
6 Trip 1: US of CC#2 0 Trip 1: DS from CC#2 *Trip 1: H WY 601
Figure C-6. Diurnal dissolved oxygen concentrations (8/15-8/19), gray areas are night (7pm-7am)
8
7
f
6
5
O
0 4
a
7
H
O 3
2
1
0
8/31 16:49 8/31 21:37 9/12:25 9/17:13 9/112:01 9/116:49 9/121:37 9/2 2:25 9/2 7:13
■ Trip 2: Brief Rd r Trip 2: SR 1601 *Trip 2: HtM' 601
Figure C-7. Diurnal dissolved oxygen concentrations (8/31-9/2), gray areas are night (7pm-7am)
NTETRA TECH 62

Crooked Creek QUAL2K Model
October 15, 2019
7
i
6 ~ v
E •
O
0 4 v
m
Vf
= 3
O
2
1
■
1
9/14 7:00 9/14 11:48 9/14 16:36 9/14 21:24 9/15 2:12 9/15 7:00 9/15 11:48 9/15 16:36
a Trip 3: Brief Rd • Trip 3: N Rocky River Rd •Trip 3: SR 1601
Figure C-8. Diurnal dissolved oxygen concentrations (9/13-9/16), gray areas are night (7pm-7am)
63

Attachment B: Crooked Creek Model ►4pplication
for Grassy Branch Wastewater Treatment Plant,
Tetra Tech, October 15, 2019
(Note: Report was revised per comments from Division of Water
Resources per meeting on October 9, 2019)

Crooked Creek QUAL2K Model Application
for Grassy Branch WWTP
Union County, North Carolina
December 4, 2019
PREPARED FOR
Union County Public Works
500 North Main Street, Suite 500
Monroe, NC 28112
PREPARED BY
Tetra Tech
One Park Drive, Suite 200
PO Box 14409
Research Triangle Park, NC 27709
Pictured: North Fork Crooked Creek (Tetra Tech, 2016)
N
TETRA TECH

(This page was intentionally left blank.)

TABLE OF CONTENTS
1.0 INTRODUCTION.....................................................................................................................................1
2.0 QUAL21K MODEL APPLICATION SET-UP............................................................................................
3
2.1 Simulating Critical Conditions..........................................................................................................
3
2.1.1 Critical Low Flow Statistics....................................................................................................
3
2.1.2 Modified Seasonal Inputs...............................................................................................
...... 4
2.1.3 Permitted Discharge Assumptions..........................................................................................
6
3.0 MODIFIED DISCHARGE CONDITIONS SCENARIO RESULTS
..........................................................8
3.1 Model Application Sensitivity Testing.............................................................................................
9
3.2 Instream Ammonia Toxicity.............................................................................................................
9
3.3 Instream TSS and Turbidity..........................................................................................................
10
LIST OF TABLES
Table 1.
Estimated 7Q10 flow tabulated for boundary conditions of Crooked Creek ..................................
3
Table 2.
Existing point source permit limits for water treatment facilities along Crooked Creek .................
6
Table 3.
Proposed SOC and final effluent permit limits for Grassy Branch VWVTP (NC0085812)...............
6
Table 4.
Effluent water temperature for seasonal simulations......................................................................
7
Table 5.
Crooked Creek QUAL2K model scenarios results for summer and winter critical conditions........
8
Table 6.
Crooked Creek QUAL2K model scenarios sensitivity testing.........................................................
9
Table 7.
Crooked Creek QUAL2K model application scenario results for ammonia toxicity ......................10
Table 8.
Crooked Creek QUAL21K model application scenario results for instream TSS concentration....11
LIST OF FIGURES
Figure 1, Crooked Creek watershed location map, model segmentation, and WWTP discharge sites....... 2
Figure 2. Crooked Creek QUAL2K model 7Q10 flow balance schematic diagram ..................................... 4
Figure 3. Crooked Creek QUAL2K model scenario results for summer and winter .................................. 8
® TETRA TECH

Crooked Creek Model Application for Grassy Branch WWTP-Union County December 4, 2019
This technical modeling memo is intended to accompany Union County's request for receiving a Special
Order by Consent (SOC) from the North Carolina Division of Water Resources for the Grassy Branch
Wastewater Treatment Plant (WWTP). The facility (NPDES Permit No. NC0085812) discharges into
Crooked Creek approximately seven river miles upstream of the confluence with the Rocky River in the
Yadkin -Pee Dee River Basin. The Grassy Branch WWTP has exhibited periodic noncompliance with
existing effluent NPDES permit limits. The County is seeking interim limits under the SOC and this memo
summarizes our findings of a modeling assessment performed to evaluate potential impacts on the
receiving waters of the proposed interim limits.
A QUAL2K model for Crooked Creek was used for the modeling assessment. The model was calibrated
and corroborated based on data collected in 2016 (Tetra Tech, 20191). The QUAL2K model development
report and corresponding Excel files were submitted to the North Carolina Division of Water Resources
(DWR) on August 12-13, 2019 and verbal approved was received in -person from DWR staff on October
1, 2019. For this SOC modeling analysis, the calibrated QUAL2K model was setup to simulate seasonally
critical conditions and maximum permitted effluent discharges for all treatment facilities located along
Crooked Creek. This report details the QUAL2K model application and SOC scenario analysis.
Tetra Tech. 2019. Crooked Creek QUAL2K Model Development; Union County, North Carolina.
Prepared for Union County Public Works, Monroe, NC.
® TETRA TECH

Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
f'r HembyAcresWWTP
North Fork Crooked CreE
Crooked Creek WWTP #2,
W _ I
s�
iocky River
Crooked Creek
Grassy Branch WWTP
j��jj��� t
OIJ
Grassy Branch '
Legend
WWTP Discharge
Large Beaver Dam
River/Stream
QWatershed Boundary
Model Reach
Raach t
Raach 2
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aaaaaaa� Raach4
Crooked Creek watershed N 0 0.5 1 2
(� TETRA rEC6 QUAC3L2K Model Segmentation oKibmeters IIJ *-c^+w Raschs
l=J KADJ SuN— C— Lim 3Mp F N 0 0.5 1 2 Roach 6
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Fork Crooked Creek
Figure 1. Crooked Creek watershed location map, model segmentation, and WWTP discharge sites
OTETRA TECH 2

Crooked Creek QUAL21< Model Application for Grassy Branch WWTP-Union County December 4, 2019
North Carolina Water Quality Regulations (15A NCAC 02B .0206) specifies 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). Additionally, the NC
regulations (15A NCAC 02B .0404) 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. Set-up of the Crooked Creek QUAL2K model for evaluating impacts under seasonal critical
conditions is documented below.
2.1 SIMULATING CRITICAL CONDITIONS
2.1.1 Critical Low Flow Statistics
There are very limited flow gage records within the Crooked Creek watershed. Curtis Weaver of USGS
provided 7Q10 estimates for the watershed based on a 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). A winter 7Q10 estimate was also provided by Mr.
Weaver as one order of magnitude greater, at 0.01 cfsm. Mr. Weaver provided 7Q10 flow estimates
based on drainage area at Highway 601 and NC Highway 218 of 0.037 cfs and 0.0.044 cfs respectively
for summer, and 0.371 cfs and 0.444 cfs respectively for winter. Applying this 7Q10 relationship, flow was
calculated at the model boundary inputs for the Crooked Creek QUAL2K model (Table 1). Based on the
tributary inflows and the two instream estimates provided by Mr. Weaver, a simple flow balance equation
was used to determine the amount of flow which must enter the stream via diffuse baseflow as well
(Table 1; Figure 2).
Table 1. Estimated 7Q10 flow tabulated for boundary conditions of Crooked Creek.
Drainage Area
Boundary Condition (Mi2)
Headwater 7.4
Summer e
Flow (cfs)
0.007
Flow (cfs
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
0.006
0.035
0.059
Diffuse Flow 3: NC Highway 218 to Outlet N/A
OTETRA TECH

Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
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 Summer 7Q10: 0.004 cfs
Winter 7Q10:0.038 cfs - ---1► I 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 f Summer 7Q10: 0.006 cfs
Summer 7Q10: 0.050 cfs Winter 7Q10: 0.059 cfs
Winter 7Q10: 0.503 cfs
Figure 2. Crooked Creek QUAL2K model 7Q10 flow balance schematic diagram.
2.1.2 Modified Seasonal Inputs
2.1.2.1 Summer Critical Conditions
The summer period is identified (per 15A NCAC 02B .0404) in the existing permit as April 1 to October
31. The summer critical conditions model for Crooked Creek is based primarily on the calibration model.
Key differences from the calibration model include:
• Modification of simulation date based on warmest summer month for water temperature
o Meteorological inputs modified based on new simulation date
Modification of boundary conditions (headwaters and tributaries)
o Flows to represent critical 7Q10 conditions instream (see Table 1)
o Water temperature to represent critically warm summer conditions
o DO concentrations to represent median DO saturation observed during critically warm
summer 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.
The warmest summer water temperatures were found to occur in the month of 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
aTETRA TECH
4

Crooked Creek QUAL2K Model Application for Grassy Branch WWTP—Union County December 4, 2019
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%.
Applying this 58% DO saturation to the water temperature of 25.0 °C results in a boundary condition DO
concentration of 4.8 mg/l applied to the headwaters, diffuse, and tributary inflows.
QUAL2K requires assignment of a simulation date to support meteorological conditions. The 75th
percentile water temperature of 25.0 °C is similar to the average water temperatures observed in July
2015, so the summer critical condition simulation date was selected as July 15, 2015. Meteorological
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 are 29.9 °C (85.8 OF) and 19.3 °C (66.7 OF)
respectively.
2.1.2.2 Winter Critical Conditions
The winter period is identified (per 15A NCAC 02B .0404) in the existing permit as November 1 to March
31. For the winter critical conditions simulation, the following modifications were made relative to the
baseline calibration model:
• Modification of simulation date based on warmest winter month for water temperature
o Meteorological inputs modified based on new simulation date
• Modification of boundary conditions (headwaters and tributaries)
o Flows to represent winter 7Q10 conditions instream (see Table 1)
o Water temperature to represent critically warm winter conditions
o DO concentrations to represent median DO saturation observed during critically warm
winter conditions
• Average shade conditions were decreased by half from 70% to 35% relative to summer
conditions to simulate the impact of assumed winter leaf -fall
• 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.
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 751h percentile of all observed water
temperature results in the POR for the instream water quality sampling site located immediately upstream
of Hemby Acres WWTP. The result of this analysis is 13.4 °C, 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%. Applying this 67% 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 the month of November, the simulation date was
selected to be the first of November. The simulate date was selected to be November 1, 2015 as 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 OF) and 13.8 °C (56.9
OF) respectively-
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Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
2.1.3 Permitted Discharge Assumptions
There are three permitted point sources located along Crooked Creek modeled explicitly: Hemby Acres
WWTP which is operated by Carolina Water Services Inc., Crooked Creek #2 WWTP and Grassy Branch
WWTP which are both operated by Union County. For model application scenarios, inputs were based on
permitted effluent limitations. Calibration model inputs were held constant for non -permitted constituents
(i.e. inorganic and organic phosphorus) for these simulations.
Existing permit limits for the three outfalls along Crooked Creek vary seasonally and by facility (Table 2).
Due to noncompliance with existing permitted limits for the Grassy Branch WWTP Union County is
proposing modified limits for the facility which would reflect an interim SOC period and future final permit
limits, both for higher effluent flow conditions (Table 3). Because of the expansion of flow from the facility
from 0.05 MGD to 0.12 MGD, permit limits associated with ammonia change from existing permit limits of
2 and 4 mg/I for summer and winter to 1 and 3 mg/I respectively, while the year-round permit limit for DO
concentration must stay above 6 mg/I rather than the existing permit limit of 5 mg/I. Discharge Monitoring
Report (DMR) data for Grassy Branch WWTP from 2015 - 2019 includes 184 DO measurements, only 3
of which are below 6 mg/I (2% of samples), so meeting the final permit limit of 6 mg/I for DO should not be
an issue for the facility. On average, the WWTP performs with 96% BOD5 removal, 97% TSS removal,
and 96% NH3 removal based on DMR records.
Similar to the calibration and corroboration model setup, total suspended solids (TSS) is simulated
conservatively as inorganic suspended solids (ISS) since organic solids are captured already through the
simulation of BOD5 as CBODfast in the model.
Table 2. Existing point source permit limits for water treatment facilities along Crooked Creek.
NPDES ID Facility Season Flow BODr, NH3 D•
Hemby Summer 9 3
NC0035041 Acres 0.3 >_ 5 30
Winter 15 8
Crooked Summer
NCO069841 Creek #2 Winter 1
1.9
5
2
? 6
30
10
4
Grassy Summer
NC0085812
Branch Winter
5
0.05 �
10
2
>_ 5
30
4
Table 3. Proposed SOC and final effluent permit limits for Grassy Branch WWTP (NC0085812).
® TETRA TECH 6

Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
For summer and winter simulation periods, the following scenarios were simulated:
1. Critical summer conditions, Grassy Branch at interim SOC limits, other outfalls at permit limits
2. Critical summer conditions, Grassy Branch at final permit limits, other outfalls at permit limits
3. Critical winter conditions, Grassy Branch at interim SOC limits, other outfalls at permit limits
4. Critical winter conditions, Grassy Branch at final permit limits, other outfalls at permit limits
For the seasonal simulations, the water temperature associated with each effluent discharge point source
was developed using the average observed July or November water temperature for 2015 (Table 4).
Table 4. Effluent water temperature for seasonal simulations.
Hemby Acres 1 25.9 f 14.4
Crooked Creek #2 1 26.3 1 18.2 1
Grassy Branch 1 25.7 1 15.9
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/1), with additional daily maximum limits for a number
of pollutants such as tetrachloroethene, vinyl chloride, and dioxane. Although this permitted discharge for
groundwater remediation 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 as
permit limits for flow and TSS. Model parameterization for temperature and DO were set equal to those of
the South Fork Crooked Creek tributary.
® TETRA TECH

Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
Results for both summer and winter seasonal scenarios indicate that there is assimilative capacity for
both interim SOC and final permit limits (Table 5, Figure 3). Although DO concentration is predicted to
drop well below the standard in the upper portion of Crooked Creek under critical summer and winter
conditions due to extreme low flow and physical channel configuration, the Grassy Branch outfall is well
downstream of these locations. The minimum DO concentration downstream of the Grassy Branch
WWTP outfall simulated for both interim SOC and final permit limits is predicted to remain above the
instream WQS of 5.0 mg/l DO.
Table 5. Crooked Creek QUAL2K model scenarios results for summer and winter critical conditions.
Critical summer conditions, Grassy
1 Branch at interim SOC limits, other 5.39 5.89
outfalls at permit limits
Critical summer conditions, Grassy
2 Branch at final permit limits, other outfalls 5.53 5.99
at permit limits
Critical winter conditions, Grassy Branch
3 at interim SOC limits, other outfalls at 5.66 6.99
permit limits
Critical winter conditions, Grassy Branch
4 at final permit limits, other outfalls at 5.76 7.16
permit limits
10.00
Grassy
Fiemb CC#2
y SFCC Beaver Trib 9.00
W WTP WWTP Trib Dams Grassy
1 1 1 1 w�P 8.00
TOO
6.00
E
—------------- --------------------- — ------- --------------- 5.00 C
r
4.00
3.00
1
2.00
"'J
1.00
0.00
30.00 25.00 20.00 15.00 10.0D 5.00 0.00
Distance from outlet (km)
-- -- WQS — Summer -Interim SOC Limits —Summer-Final Permit Limits — Winter -Interim SOC Limits —Winter-Final Permit Limits
Figure 3. Crooked Creek QUAL2K model scenario results for summer and winter.
I'�.I TETRA TECH 8

Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
3.1 MODEL APPLICATION SENSITIVITY TESTING
One area of uncertainty associated with the model application scenarios is related to the level of bottom
algae anticipated for critical summer and winter conditions. As mentioned, the model application
scenarios were run with bottom algae conditions that were simulated for the calibration model period
(bottom algae coverage of 25% for reach 1, and 50% for all other reaches). To test model sensitivity to
this parameter, the model application scenarios were run under conditions that bottom algae coverages
by reach were increased or decreased by 10% (e.g. reach 1 modified to 15% or 35% coverage, and all
other reaches modified to 40% or 60% coverage). Note that on average, this represents a 20 percent
change in parameter values (i.e., 10/50 is 0.2 or 20 percent).
The results of these sensitivity analyses reveal that even under relative model uncertainty on this
parameter, the water quality standard of 5.0 mg/I DO is still met downstream of the Grassy Branch WWTP
discharge for all seasonal and effluent conditions (Table 6).
Table 6. Crooked Creek QUAL2K model scenarios sensitivity testing.
1
Critical summer conditions,
Grassy Branch at interim
SOC limits, other outfalls at
permit limits
5.39
5.53
60%
5.55
40%
5.22
2
Critical summer conditions,
Grassy Branch at future
permit limits, other outfalls at
permit limits
60%
5.71
40%
5.34
3
Critical winter conditions,
Grassy Branch at interim
SOC limits, other outfalls at
permit limits
5.66
60%
5.92
40%
5.38
4
Critical winter conditions,
Grassy Branch at future
permit limits, other outfalls at
permit limits
5.76
60%
6.03
40%
5.48
3.2 INSTREAM AMMONIA TOXICITY
When effluent flows dominate instream conditions, there can be a concern about 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/I in winter. As shown below, for all model
application scenarios, ammonia toxicity is not exceeded (Table 7).
® TETRA TECH
p

Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
Table 7. Crooked Creek QUAL2K model application scenario results for ammonia toxicity.
Critical summer conditions, Grassy
Branch at interim SOC limits, other 0.34 0.06
outfalls at permit limits
Critical summer conditions, Grassy
2 Branch at final permit limits, other outfalls 0.11 0.06
at permit limits
Critical winter conditions, Grassy Branch
3 at interim SOC limits, other outfalls at 1.00 0.04
permit limits
Critical winter conditions, Grassy Branch
4 at final permit limits, other outfalls at 0.21 0.03
permit limits
3.3 INSTREAM TSS AND TURBIDITY
Turbidity is a measure of water clarity or cloudiness, and the water quality standard in North Carolina for
Class C waters is a maximum of 50 Nephelometric Turbidity Units (NTU)2. Although Crooked Creek and
its tributaries are not impaired for turbidity, Crooked Creek discharges into the Rocky River which is
impaired for turbidity. Key sources of turbidity in the Rocky River watershed have been identified as
largely related to stormwater runoff and erosive land use practices which cause sediment wash -off during
precipitation events3.
Generally, high instream turbidity measurements are associated with precipitation events rather than low -
flow conditions which are simulated in this critical conditions QUAL2K model scenario. Model output for
TSS can provide some insight into the assimilation of particulate matter instream under low -flow
conditions, however the true impact of turbidity instream cannot be captured by this steady-state critical
conditions model simulation (Table 8). There are not explicit TSS water quality standards for North
Carolina Class C waterways.
2 NC DWR. 2019. NC 15A NCAC 02B Water Quality Standards for Surface Waters.
3 NC DWQ. 2008. Yadkin -Pee Dee River Basin Plan: Rocky River HUC 03040105.
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Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
Table 8. Crooked Creek QUAL2K model application scenario results for instream TSS concentration.
Critical summer conditions, Grassy
Branch at interim SOC limits, other 14.50 9.26
outfalls at permit limits
Critical summer conditions, Grassy
2 Branch at final permit limits, other outfalls 11.10 8.20
at permit limits
Critical winter conditions, Grassy Branch
3 at interim SOC limits, other outfalls at 11.65 6.08
permit limits
Critical winter conditions, Grassy Branch
4 at final permit limits, other outfalls at 8.56 5.02
permit limits
Turbidity has been measured along Crooked Creek at the four instream YPDRBA sampling sites since
1998. Of the total 913 turbidity measurements, 124 measurements exceed the water quality standard of
>-50 NTU, which is 14% of all samples from July 1998 through July 2019. For the period of record at each
sampling location, the median turbidity measurement ranges from 14 - 16 NTU, the average ranges from
26 - 30 NTU, and the maximum measurements range from 298 - 360 NTU.
Paired sampling data of TSS and turbidity are available at YPDRBA site Q8388000 downstream of the
Grassy Branch WWTP and tributary on Crooked Creek. The 71 paired samples at this site suggest a
generally linear relationship between TSS and turbidity concentrations when analyzed directly, however
the relationship is skewed by only 7 paired results for which turbidity results are -> 50 NTU. When the
paired data is transformed using a natural logarithm, the R-squared value for the entire dataset is 0.4, and
when turbidity data less than 50 NTU is considered, the R-squared value drops to 0.1.
When turbidity measurements are > 50 NTU at site 08388000, TSS measurements range from 15 - 224
mg/I, which suggests that turbidity violations are not observed when TSS measurements are below 15
mg/l. Although the relationship between turbidity and TSS is weak at this location, simulation results and
existing instream data suggest that there is reason to believe that the Grassy Branch WWTP interim SOC
and final permit limits will not contribute to turbidity water quality problems during low flow periods. The
impact of these permit limits on high flow events are similarly unlikely to contribute to stream turbidity
degradation due to the relatively low effluent flow associated with the Grassy Branch WWTP facility
relative to instream flows.
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11

STATE OF NORTH CAROLINA
DEPARTMENT OF ENVIRONMENTAL QUALITY
DIVISION OF WATER RESOURES
APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
VI. Predicted Compliance Schedule
Union County intends to accomplish the following tasks and milestones for the recommended upgrades to
the Grassy Branch Wastewater Treatment Plant (WWTP), as follows:
Milestone
Months from Estimated Date from
Notice to Proceed Notice to Proceed'
Submit Contract Documents for 18 months July 2021
regulatory approval for Grassy Branch
WWTP Upgrade Project
Start construction of Grassy Branch 33 months October 2022
WWTP Upgrade Project upon receiving
approval by applicable regulatory
agencies
Complete construction, start-up and 66 months June 2025
testing of Grassy Branch WWTP
Upgrade Project
I&I Rehabilitation in Grassy Branch basin ---- On -going
Note: Estimated completion dates are dependent on date of Notice to Proceed.
The Grassy Branch WWTP existing infrastructure will remain in service during the construction of the
proposed upgrades. It is not anticipated that construction activity will affect facility performance.

STATE OF NORTH CAROLINA
DEPARTMENT OF ENVIRONMENTAL QUALITY
DIVISION OF WATER RESOURES
APPLICATION FOR A SPECIAL ORDER BY CONSENT (SOC) ATTACHMENT
VII. Funding Sources Identification
Union County intends to fund the recommended improvements and upgrades to the Grassy Branch
Wastewater Treatment Plant (WWTP) as follows:
Imarovement
Upgrades to Grassy Branch WWTP to increase
maximum month design capacity from 0.05 to 0.12 mgd
I&I Reduction Effort in Grassy Branch basin (on -going)
Funding Source
Funding is available in the Union
County Public Works Capital
Improvements Program
Water and Wastewater Operation and
Maintenance funding annually
appropriated by the Board of County
Commissioners

UNION COUNTY
DEPARTMENT OF PUBLIC WORKS
500 North Main Street, Suite 500, Monroe, NC 28112
Phone:[phone] Fax:[phone]
May 16, 2019
Mr. W. Corey Basinger
Regional Supervisor
Water Quality Regional Operations Section
Mooresville Regional Office
610 East Center Ave., Suite 301
Mooresville, NC 28115
Dear Mr. Basinger:
The purpose of this letter is to confirm Union County's interest in pursuing a Special Order of Consent
(SOC) with NCDEQ for flow issues at our Grassy Branch Water Reclamation Facility (WRF). After
meeting with our staff on May 2"d, we have been working on developing the information needed to
make a formal submission for the SOC. Key to this submission is obtaining technical information from
our Engineer who is familiar with the Grassy Branch WRF which will be provided later this month.
Once all the needed information is available, we intend to send you a formal SOC application.
We appreciate both your and your staffs time and effort in helping us move to a solution for the flow
issues at Grassy Branch WRF. Please call me at 704-292-2597 if you need any additional
information.
Sincerely,
Brian Matthews, AICP
Assistant County Manager
cc: Aubrey Lofton, Interim Public Works Administrator
Andrew Neff, Water and Wastewater Division Director
Josh Brooks, Asst. Water and Wastewater Division Director
Bart Farmer, WRF Superintendent
500 North Main St., Suite 600 9 Monroe, NC 28112-4730 • Phone: [phone] • Fax: [phone]