NC0085812_Modification Request_20210511

April 26,2021
Mr. Mike Montebello
Water Quality Permitting Section—NPDES
Division of Water Resources RECEIVED
North Carolina Department of Environmental Quality
1617 Mail Service Center MAY 11 2021
Raleigh,NC, 27699-1617
RE: Union County Public Works NCDEQ/DWR/NPDES
Grassy Branch Water Reclamation Facility
NPDES Permit Renewal, Permit No.NC0085812
Dear Mr. Montebello:
The Union County Public Works Division is permitted to discharge 0.05 million gallons per day(mgd)of
treated effluent from the Grassy Branch Water Reclamation Facility(WRF)to Crooked Creek via North
Carolina National Pollutant Discharge Elimination System(NPDES) Permit NC0085812. 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 for the Grassy Branch WRF over the last
several years. 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 WRF has contributed to and
intensified the compliance issues. The Grassy Branch WRF flow and recorded rainfall 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 Grassy Branch WRF.
To address the on-going violations at Grassy Branch, Union County has executed and submitted the
application form and required attachments to the Department of Environmental Quality(DEQ)Division
of Water Resources(DWR)for a Special Order by Consent(SOC). The Grassy Branch SOC package
requested an increase in design capacity from 0.05 to 0.12 mgd to address the over-allocation of sewer
connections. In response, DWR staff requested that the County's SOC application be amended to include
a National Pollutant Discharge Elimination System (NPDES)permit major modification to support the
County's request for a capacity increase.
The enclosed application is for the major modification of the Grassy Branch WRF NPDES permit. In
accordance with the requirements of federal (40 CFR 122)and state(15A NCAC 2H .0105(3))
regulations, we are submitting three signed copies of the completed application package and associated
attachments and figures.The application package includes the following information:
• NPDES Permit Application—EPA Form 2A(Sections 1 to 6,Table A, and Table B)
• EPA Form 2A Additional Information(Topographic Map, Process Flow Diagram, and Process
Narrative)

• Engineering Alternatives Analysis Technical Memorandum,with associated attachments.
If you have any questions regarding any of the NPDES permit major modification application materials,
please contact Andrew Neff, Water& Wastewater Division Director at(704)296-4215 or
[e-mail].
Sincerely
Hyong
Public Works Admin or
Attachments
cc:
Andrew Neff,P.E., Water& Wastewater Division Director
Bart Farmer, Union County Public Works, Water Reclamation Facilities Superintendent
Alex Latham,Union County Public Works, WRF Supervisor
Mary Sadler, PE, Hazen and Sawyer
Jim Struve, PE, Hazen and Sawyer

' t I
EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
Form U.S.Environmental Protection Agency
2A &EPA Application for NPDES Permit to Discharge Wastewater
NPDES NEW AND EXISTING PUBLICLY OWNED TREATMENT WORKS
SECTION 1.BASIC APPLICATION INFORMATION FOR ALL APPLICANTS(40 CFR 122.21(j)(1)and(9))
1.1 Facility name
Grassy Branch WRF
Mailing address(street or P.O.box)
4600 Goldmine Road
City or town State ZIP code
o Monroe NC 28112
Contact name(first and last) Title Phone number Email address
8 Andrew Neff,P.E. Water and Wastewater Division Director [phone] [e-mail]
Location address(street,route number,or other specific identifier) El Same as mailing address
1629 Old Fish Road (Off NCSR 1610)
L
City or town State ZIP code
Monroe NC 28110
1.2 Is this application for a facility that has yet to commence discharge?
❑ Yes 4 See instructions on data submission ❑✓ No
requirements for new dischargers.
1.3 Is applicant different from entity listed under Item 1.1 above?
❑ Yes ❑✓ No 4 SKIP to Item 1.4.
Applicant name
= Applicant address(street or P.O.box)
0
77.
c City or town State ZIP code
Contact name(first and last) Title Phone number Email address
i a
0.
1.4 Is the applicant the facility's owner,operator,or both?(Check only one response.)
❑ Owner ❑ Operator ✓❑ Both
1.5 To which entity should the NPDES permitting authority send correspondence?(Check only one response.)
El Facility ✓❑ Applicant ❑ Facility and applicant
(they are one and the same)
1.6 Indicate below any existing environmental permits.(Check all that apply and print or type the corresponding permit
w number for each.)
Existing Environmental Permits
❑✓ NPDES(discharges to surface ❑ RCRA(hazardous waste) ❑ UIC(underground injection
water) control)
NC0085812
2 ❑ PSD(air emissions) ❑ Nonattainment program(CAA) ❑ NESHAPs(CAA)
rn
❑ Ocean dumping(MPRSA) ❑ Dredge or fill(CWA Section El Other(specify)
404)
EPA Form 3510-2A(Revised 3-19) Page 1

a
EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
1.7 Provide the collection system information requested below for the treatment works.
Municipality Population Collection System Type Ownership Status
Served Served (indicate percentage)
Union County 129 Homes and no %separate sanitary sewer 0 Own 0 Maintain
-csZ 3 Schools 0 %combined storm and sanitary sewer 0 Own ❑ Maintain
cu 0 Unknown 0 Own ❑ Maintain
co
o %separate sanitary sewer 0 Own 0 Maintain
•@ %combined storm and sanitary sewer 0 Own 0 Maintain
a 0 Unknown 0 Own 0 Maintain
a %separate sanitary sewer 0 Own 0 Maintain
c %combined storm and sanitary sewer D Own 0 Maintain
fc 0 Unknown ❑ Own 0 Maintain
E a; %separate sanitary sewer ❑ Own 0 Maintain
rn %combined storm and sanitary sewer 0 Own 0 Maintain
c 0 Unknown 0 Own 0 Maintain
Total
129 Homes and
°' Population73 3 Schools
c.o Served
Separate Sanitary Sewer System Combined Storm and
Sanitary Sewer
Total percentage of each type of 1o0 % o
sewer line(in miles)
L-' 1.8 Is the treatment works located in Indian Country?
c
o El Yes El No
0
v
1.9 Does the facility discharge to a receiving water that flows through Indian Country?
IS
❑ Yes ✓❑ No
1.10 Provide design and actual flow rates in the designated spaces. Design Flow Rate
am mgd
To
Annual Average Flow Rates(Actual)
U N
< w Two Years Ago Last Year This Year
mi
R 0 0.06 mgd 0.04 mgd 0.05 mgd
(75 Maximum Daily Flow Rates(Actual)
o Two Years Ago Last Year This Year
0.37 mgd 0.30 mgd 0.19 mgd
01.11 Provide the total number of effluent discharge points to waters of the United States by type.
o Total Number of Effluent Discharge Points by Type
a a Combined Sewer Constructed
TTreated Effluent Untreated Effluent Overflows Bypasses Emergency
co C
JCI Overflows
0
1 0 0 0 0
EPA Form 3510-2A(Revised 3-19) Page 2

EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
Outfalls Other Than to Waters of the United States
1.12 Does the POTW discharge wastewater to basins,ponds,or other surface impoundments that do not have outlets for
discharge to waters of the United States?
❑ Yes ❑✓ No 4 SKIP to Item 1.14.
1.13 Provide the location of each surface impoundment and associated discharge information in the table below.
Surface Impoundment Location and Discharge Data
Average Daily Volume Continuous or Intermittent
Location Discharged to Surface (check one)
Impoundment
O Continuous
gpd 0 Intermittent
❑ Continuous
gpd 0 Intermittent
❑ Continuous
gpd 0 Intermittent
2 1.14 Is wastewater applied to land?
❑ Yes ❑✓ No 4 SKIP to Item 1.16.
c 1.15 Provide the land application site and discharge data requested below.
a Land Application Site and Discharge Data
Continuous or
Location Size Average Daily Volume Intermittent
a' Applied (check one)
acres d 0 Continuous
N gp ❑ Intermittent
0
acresgpd 0 Continuous
0 Intermittent
❑ Continuous
acres gpd 0 Intermittent
76 1.16 Is effluent transported to another facility for treatment prior to discharge?
o ❑ Yes ❑✓ No 4 SKIP to Item 1.21.
1.17 Describe the means by which the effluent is transported(e.g.,tank truck,pipe).
1.18 Is the effluent transported by a party other than the applicant?
❑ Yes ElNo 4 SKIP to Item 1.20.
1.19 Provide information on the transporter below.
Transporter Data
Entity name Mailing address(street or P.O.box)
City or town State ZIP code
Contact name(first and last) Title
Phone number Email address
EPA Form 3510-2A(Revised 3-19) Page 3

EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
1.20 In the table below,indicate the name,address,contact information, NPDES number,and average daily flow rate of the
receiving facility.
Receiving Facility Data
- Facility name Mailing address(street or P.O.box)
a
City or town State ZIP code
0
Contact name(first and last) Title
0
Phone number Email address
aNPDES number of receiving facility(if any) 0 None Average daily flow rate mgd
0 1.21 Is the wastewater disposed of in a manner other than those already mentioned in Items 1.14 through 1.21 that do not
have outlets to waters of the United States(e.g.,underground percolation,underground injection)?
❑ Yes No 4 SKIP to Item 1.23.
0
0 1.22 Provide information in the table below on these other disposal methods.
Information on Other Disposal Methods
o Disposal Location of Size of Annual Average Continuous or Intermittent
Method Disposal Site Disposal Site Daily Discharge (check one)
Description Volume
0 Continuous
acres gpd 0 Intermittent
0
0 Continuous
acres gpd ❑ Intermittent
❑ Continuous
acres gpd ❑ Intermittent
1.23 Do you intend to request or renew one or more of the variances authorized at 40 CFR 122.21(n)?(Check all that apply.
o �
Consult with your NPDES permitting authority to determine what information needs to be submitted and when.)
C f ❑ Discharges into marine waters(CWA ❑ Water quality related effluent limitation(CWA Section
413 Section 301(h)) 302(b)(2))
❑✓ Not applicable
1.24 Are any operational or maintenance aspects(related to wastewater treatment and effluent quality)of the treatment works
the responsibility of a contractor?
❑ Yes ElNo+SKIP to Section 2.
1.25 Provide location and contact information for each contractor in addition to a description of the contractor's operational
and maintenance responsibilities.
Contractor Information
Contractor 1 Contractor 2 Contractor 3
= Contractor name
0
(company name)
o Mailing address
(street or P.O.box)
City,state,and ZIP
code
oContact name(first and
last)
Phone number
Email address
Operational and
maintenance
responsibilities of
contractor
EPA Form 3510-2A(Revised 3-19) Page 4

EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
SECTION 2.ADDITIONAL INFORMATION(40 CFR 122.21(j)(1)and(2))
c Outfalls to Waters of the United States
= 2.1 Does the treatment works have a design flow greater than or equal to 0.1 mgd?
•(7) Note:Major mod request to
❑✓ Yes expand from 0.05 to 0.12 mgd ❑ No 4 SKIP to Section 3.
2.2 Provide the treatment works'current average daily volume of inflow Average Daily Volume of Inflow and Infiltration
and infiltration. Not quantifiable, Max day PF 7:1 gpd
Indicate the steps the facility is taking to minimize inflow and infiltration.
The County has actively been involved in the reduction of infiltration and inflow(I&I)in the collection system.A Phase 1 I&I study was commissioned in
t6 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
0 included wet weather monitoring.In 2018,Phase 3 efforts included confirming the effectiveness of previous repair efforts,extensive closed-circuit
c television(CCTV)review of the entire collection system,and the continuation of repair efforts.Phase 4 of the 1&1 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.
2.3 Have you attached a topographic map to this application that contains all the required information?(See instructions for
o specific requirements.)
� cu
o
0 ❑✓ Yes El No
0
E 2.4 Have you attached a process flow diagram or schematic to this application that contains all the required information?
(See instructions for specific requirements.)
0
rr-
�a
❑✓ Yes ❑ No
2.5 Are improvements to the facility scheduled?
✓❑ Yes ❑ No 4 SKIP to Section 3.
Briefly list and describe the scheduled improvements.
0
1 Scheduled improvements for an expansion from 0.05 mgd to 0.12 mgd include larger influent pumps,retrofit of the
existing aeration basin.one additional package secondary treatment train,and new positive displacement blowers.
2 Improvements also include an additional secondary clarifier,a new cloth disk filter,new UV disinfection system and
aerobic digestion improvements.
0
3.
73
to
4.
2.6 Provide scheduled or actual dates of completion for improvements.
Scheduled or Actual Dates of Completion for Improvements
Affected Attainment of
Scheduled Begin End Begin
Outfalls Operational
o Improvement Construction Construction Discharge
a. (from above) (list outf) Level
I (MM/DD/YYYY) (MM/DD/YYYY) (MM/DD/YYYY)
number (MM/DD/YYYY)
a
3 1. 001 10/01/2023 10/01/2025 03/01/2026 03/01/2026
m
2. 001 10/01/2023 10/01/2025 03/01/2026 03/01/2026
3.
4.
2.7 Have appropriate permits/clearances concerning other federal/state requirements been obtained?Briefly explain your
response.
❑ Yes ❑✓ No ❑ None required or applicable
Explanation:
Permits will be obtained prior to construction for the expansion of the facility from 0.05 to 0.12 mgd.
EPA Form 3510-2A(Revised 3-19) Page 5

EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
SECTION 3.INFORMATION ON EFFLUENT DISCHARGES(40 CFR 122.21(j)(3)to(5))
3.1 Provide the following information for each outfall.(Attach additional sheets if you have more than three outfalls.)
Outfall Number o01 Outfall Number Outfall Number
State NC
CountyUnion County
co
0 City or town Monroe
0
s Distance from shore 111ft. ft. ft.
Depth below surface NA ft. ft. ft.
0
Average daily flow rate 0.05 mgd mgd mgd
Latitude 35° 07' 50" N
Longitude 80° 29' 40" W °
3.2 Do any of the outfalls described under Item 3.1 have seasonal or periodic discharges?
❑ Yes El No 4 SKIP to Item 3.4.
d
i 3.3 If so, provide the following information for each applicable outfall.
Outfall Number Outfall Number Outfall Number
Number of times per year
o discharge occurs
ri Average duration of each
`-) discharge(specify units)
Average flow of each
discharge mgd mgd mgd
Months in which discharge
occurs
3.4 Are any of the outfalls listed under Item 3.1 equipped with a diffuser?
❑ Yes 0 No 4 SKIP to Item 3.6.
3.5 Briefly describe the diffuser type at each applicable outfall.
Ct..
Outfall Number Outfall Number Outfall Number
vi 3.6 Does the treatment works discharge or plan to discharge wastewater to waters of the United States from one or more
discharge points?
El Yes ❑ No 4SKIP to Section 6.
EPA Form 3510-2A(Revised 3-19) Page 6

EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
3.7 Provide the receiving water and related information(if known)for each outfall.
Outfall Number 001 Outfall Number Outfall Number
Receiving water name Crooked Creek
Name of watershed,river,
0
or stream system Crooked Creek River Basin
U.S.Soil Conservation
'L
N Service 14-digit watershed 030401050702
o code
41 Name of state
3 management/river basin Yadkin-Pee Dee
a)
U.S.Geological Survey
ru 8-digit hydrologic 03040105
re cataloging unit code
Critical low flow(acute) NA cfs cfs cfs
7Q10(Summer)=
Critical low flow(chronic) 0.004 cfs cfs cfs cfs
Total hardness at critical mg/L of mg/L of mg/L of
low flow NA CaCO3 CaCO3 CaCO3
3.8 Provide the following information describing the treatment provided for discharges from each outfall.
Outfall Number 001 Outfall Number Outfall Number
Highest Level of El Primary 0 Primary 0 Primary
Treatment(check all that ❑ Equivalent to 0 Equivalent to 0 Equivalent to
apply per outfall) secondary secondary secondary
0 Secondary 0 Secondary 0 Secondary
❑ Advanced 0 Advanced 0 Advanced
❑ Other(specify) 0 Other(specify) 0 Other(specify)
c
0
'Q Design Removal Rates by
'� Outfall 001
4)
c BOD5 or CBOD5 96
c
m
E
ai TSS 97 % % %
L
WI Not applicable ® Not applicable ® Not applicable
Phosphorus % % %
VI Not applicable ® Not applicable ® Not applicable
Nitrogen % ova
Other(specify) 0 Not applicable ® Not applicable ® Not applicable
NH3-N 96 %
EPA Form 3510-2A(Revised 3-19) Page 7

EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
3.9 Describe the type of disinfection used for the effluent from each outfall in the table below. If disinfection varies by
season,describe below.
d
The Grassy Branch WRF relies on Ultraviolet disinfection at outfall 001.
0
U
o Outfall Number 001 Outfall Number Outfall Number
a Disinfection type UV
Seasons used Summer and Winter
Dechlorination used? 0 Not applicable ❑ Not applicable El Not applicable
❑ Yes El Yes ❑ Yes
El No El No El No
3.10 Have you completed monitoring for all Table A parameters and attached the results to the application package?
O Yes El No
3.11 Have you conducted any WET tests during the 4.5 years prior to the date of the application on any of the facility's
discharges or on any receiving water near the discharge points?
El Yes ❑✓ No 4 SKIP to Item 3.13.
3.12 Indicate the number of acute and chronic WET tests conducted since the last permit reissuance of the facility's
discharges by outfall number or of the receiving water near the discharge points.
Outfall Number Outfall Number Outfall Number
Acute Chronic Acute Chronic Acute Chronic
Number of tests of discharge
water
Number of tests of receiving
water
3.13 Does the treatment works have a design flow greater than or equal to 0.1 mgd?
❑✓ Yes Note:Major mod request to
c+a expand from 0.05 to 0.12 mgd ElNo 4 SKIP to Item 3.16.
0 3.14 Does the POTW use chlorine for disinfection,use chlorine elsewhere in the treatment process,or otherwise have
reasonable potential to discharge chlorine in its effluent?
d El Yes 4 Complete Table B,including chlorine. ✓❑ No 4 Complete Table B,omitting chlorine.
3.15 Have you completed monitoring for all applicable Table B pollutants and attached the results to this application
CD
package?
❑✓ Yes El No
3.16 Does one or more of the following conditions apply?
• The facility has a design flow greater than or equal to 1 mgd.
• The POTW has an approved pretreatment program or is required to develop such a program.
• The NPDES permitting authority has informed the POTW that it must sample for the parameters in Table C,must
sample other additional parameters(Table D),or submit the results of WET tests for acute or chronic toxicity for
each of its discharge outfalls(Table E).
Yes 4 Complete Tables C, D,and E as
❑ applicable. ElNo 4 SKIP to Section 4.
3.17 Have you completed monitoring for all applicable Table C pollutants and attached the results to this application
package?
❑ Yes El No
3.18 Have you completed monitoring for all applicable Table D pollutants required by your NPDES permitting authority and
attached the results to this application package?
❑ Yes ❑ No additional sampling required by NPDES
permitting authority.
EPA Form 3510-2A(Revised 3-19) Page 8

Number NPDES Permit Number FacilityName Form Approved 03/05/19
EPA Identification
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
3.19 Has the POTW conducted either(1)minimum of four quarterly WET tests for one year preceding this permit application
or(2)at least four annual WET tests in the past 4.5 years?
El Yes ❑ No+ Complete tests and Table E and SKIP to
Item 3.26.
3.20 Have you previously submitted the results of the above tests to your NPDES permitting authority?
ID Yes ❑ No 4 Provide results in Table E and SKIP to
Item 3.26.
3.21 Indicate the dates the data were submitted to your NPDES permitting authority and provide a summary of the results.
Date(s)Submitted Summary of Results
(MM/DD/YYYY)
a
c
C
co 3.22 Regardless of how you provided your WET testing data to the NPDES permitting authority,did any of the tests result in
toxicity?
❑ Yes ❑ No 4 SKIP to Item 3.26.
a, 3.23 Describe the cause(s)of the toxicity:
c
a
w
3.24 Has the treatment works conducted a toxicity reduction evaluation?
❑ Yes ❑ No 4 SKIP to Item 3.26.
3.25 Provide details of any toxicity reduction evaluations conducted.
3.26 Have you completed Table E for all applicable outfalls and attached the results to the application package?
El Yes ❑ Not applicable because previously submitted
information to the NPDES •ermittin• authorit .
SECTION 4.INC USTRIAL DISCHARGES AND HAZARDOUS WASTES(40 CFR 122.21(j)(6)and(7))
4.1 Does the POTW receive discharges from Sills or NSCIUs?
❑ Yes ElNo 4 SKIP to Item 4.7.
d 4.2 Indicate the number of SlUs and NSCIUs that discharge to the POTW.
Number of SIUs Number of NSCIUs
U)
0
-a 4.3 Does the POTW have an approved pretreatment program?
_ ❑ Yes ❑ No
4.4 Have you submitted either of the following to the NPDES permitting authority that contains information substantially
identical to that required in Table F:(1)a pretreatment program annual report submitted within one year of the
application or(2)a pretreatment program?
❑ Yes ❑ No 4 SKIP to Item 4.6.
7,6 4.5 Identify the title and date of the annual report or pretreatment program referenced in Item 4.4.SKIP to Item 4.7.
U,
4.6 Have you completed and attached Table F to this application package?
❑ Yes ❑ No
EPA Form 3510-2A(Revised 3-19) Page 9

EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
4.7 Does the POTW receive,or has it been notified that it will receive,by truck,rail,or dedicated pipe,any wastes that are
regulated as RCRA hazardous wastes pursuant to 40 CFR 261?
❑ Yes ❑✓ No 4 SKIP to Item 4.9.
4.8 If yes,provide the following information:
Annual
Hazardous Waste Waste Transport Method Amount of Units
Number (check all that apply) Waste
Received
❑ Truck ❑ Rail
d ❑ Dedicated pipe ❑ Other(specify)
0
❑ Truck ❑ Rail
❑ Dedicated pipe ❑ Other(specify)
tn
0
N ❑ Truck ❑ Rail
❑ Dedicated pipe ❑ Other(specify)
ki 4.9 Does the POTW receive,or has it been notified that it will receive,wastewaters that originate from remedial activities,
including those undertaken pursuant to CERCLA and Sections 3004(7)or 3008(h)of RCRA?
❑ Yes ❑✓ No 4 SKIP to Section 5.
7 4.10 Does the POTW receive(or expect to receive)less than 15 kilograms per month of non-acute hazardous wastes as
c specified in 40 CFR 261.30(d)and 261.33(e)?
❑ Yes 4 SKIP to Section 5. ❑ No
4.11 Have you reported the following information in an attachment to this application:identification and description of the
site(s)or facility(ies)at which the wastewater originates;the identities of the wastewater's hazardous constituents;and
the extent of treatment,if any,the wastewater receives or will receive before entering the POTW?
❑ Yes ❑ No
SECTION 5.COMBINED SEWER OVERFLOWS(40 CFR 122.21(j)(8))
E 5.1 Does the treatment works have a combined sewer system?
a ❑ Yes ❑✓ No 4SKIP to Section 6.
5.2 Have you attached a CSO system map to this application?(See instructions for map requirements.)
Q El Yes El No
5.3 Have you attached a CSO system diagram to this application?(See instructions for diagram requirements.)
❑ Yes ❑ No
EPA Form 3510-2A(Revised 3-19) Page 10

EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
5.4 For each CSO outfall,provide the following information.(Attach additional sheets as necessary.)
CSO Outfall Number CSO Outfall Number CSO Outfall Number
City or town
0
.a State and ZIP code
o
o County
0
Latitude ° II °
0
o ° ° °
Longitude
(...)(1)
Distance from shore ft. ft. ft.
Depth below surface ft. ft. ft.
5.5 Did the POTW monitor any of the following items in the past year for its CSO outfalls?
CSO Outfall Number CSO Outfall Number CSO Outfall Number
Rainfall ❑ Yes ❑ No ❑ Yes ❑ No ❑ Yes ❑ No
rn
c
•`o CSO flow volume ❑ Yes ❑ No ❑ Yes ❑ No ❑ Yes ❑ No
CSO pollutant ❑ Yes ❑ No ❑ Yes El No ❑ Yes ❑ No
o concentrations
cn
(..) Receiving water quality ❑ Yes ❑ No El Yes ❑ No ❑ Yes ❑ No
CSO frequency ❑ Yes ❑ No ❑ Yes ❑ No ❑ Yes ❑ No
Number of storm events ❑ Yes ❑ No ❑ Yes ❑ No ❑ Yes ❑ No
5.6 Provide the following information for each of your CSO outfalls.
CSO Outfall Number CSO Outfall Number CSO Outfall Number
L
as
Number of CSO events in>- events events events
N the past year
c Average duration per hours hours hours
c event 0 Actual or 0 Estimated 0 Actual or 0 Estimated 0 Actual or 0 Estimated
0
Lu million gallons million gallons million gallons
o Average volume per event
c`n., 0 Actual or 0 Estimated 0 Actual or 0 Estimated 0 Actual or 0 Estimated
Minimum rainfall causing inches of rainfall inches of rainfall inches of rainfall
a CSO event in last year 0 Actual or 0 Estimated 0 Actual or 0 Estimated 0 Actual or 0 Estimated
EPA Form 3510-2A(Revised 3-19) Page 11

EPA Identification Number NPDES Permit Number Facility Name Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF OMB No.2040-0004
5.7 Provide the information in the table below for each of your CSO outfalls.
CSO Outfall Number_ CSO Outfall Number CSO Outfall Number
Receiving water name
Name of watershed/
stream system
0 U.S.Soil Conservation 0 Unknown 0 Unknown 0 Unknown
Service 14-digit
watershed code
> (if known)
0 Name of state
ce management/river basin
NU.S.Geological Survey 0 Unknown 0 Unknown 0 Unknown
8-Digit Hydrologic Unit
Code(if known)
Description of known
water quality impacts on
receiving stream by CSO
(see instructions for
exam I les
SECTION 6.CHECKLIST AND CERTIFICATION STATEMENT(40 CFR 122.22(a)and(d))
6.1 In Column 1 below,mark the sections of Form 2A that you have completed and are submitting with your application. For
each section,specify in Column 2 any attachments that you are enclosing to alert the permitting authority.Note that not
all applicants are required to provide attachments.
Column 1 Column 2
Section 1: Basic Application
Information for All Applicants ❑ w/variance request(s) CIw/additional attachments
❑ Section 2:Additional I w/topographic map ✓❑ wl process flow diagram
Information 0 w/additional attachments
❑✓ w/Table A ❑ w/Table D
❑ Section 3:Information on ❑ w/Table B ❑ wl Table E
1` Effluent Discharges
? ❑ w/Table C ❑ wl additional attachments
Section 4:Industrial ❑ w/SIU and NSCIU attachments ❑ wl Table F
V' 0 Discharges and Hazardous
c Wastes ❑ w/additional attachments
o Section 5:Combined Sewer El w/CSO map El w/additional attachments
E ❑ Overflows
a, ❑ w/CSO system diagram
Section 6:Checklist and
N
❑ Certification Statement ❑ w/attachments
Y 6.2 Certification Statement
U
N
bc
I certify under penalty of law that this document and all attachments were prepared under my direction or supervision in
accordance with a system designed to assure that qualified personnel properly gather and evaluate the information
submitted. Based on my inquiry of the person or persons who manage the system,or those persons directly responsible
for gathering the information,the information submitted is,to the best of my knowledge and belief,true,accurate,and
complete.I am aware that there are significant penalties for submitting false information,including the possibility of fine
and imprisonment for knowing violations.
Name(print or type first and last name) Official title
Water and Wastewater Division
Andrew Neff,P.E. Director
GI
Signatur Date signed
tt.;
#4.44— it,4 4 14
41/-t.2_/-4,Q./
EPA Form 3510-2A(Revised 3-19) Page 12

1
EPA Identification Number NPDES Permit Number Facility Name Outfall Number Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF 001 OMB No.2040-0004
TABLE A.EFFLUENT PARAMETERS FOR ALL POTWS
Maximum Daily Discharge Average Daily Discharge Analytical ML or MDL
Pollutant Number of Methods (include
Value Units Value Units Sam•les units)
Biochemical oxygen demand
o ML
o BODE or❑CBOD5 193 mg/L 5.47 mg/L 161 SM 5210B <2 2 MDL
resort one
0 ML
Fecal coliform 12,500 MPN/100mL 339 MPN/100mL 174 SM 9222D <1 0 MDL
mgd n flow rate 0.05 mg d 0.05 N/A '., ,
pH(minimum) 6.20 su
pH(maximum) 8.95 su
Temperature(winter) 20.80 C 12.69 C 98
Temperature(summer) 27.50 C 20.77 C 151
12 ML
Total suspended solids(TSS) 177 mg/L 6.29 mg/L 156 SM 2540D <2.6 O MDL
1 Sampling shall be conducted according to sufficiently sensitive test procedures(i.e.,methods)approved under 40 CFR 136 for the analysis of pollutants or pollutant parameters or
required under 40 CFR chapter I,subchapter N or O.See instructions and 40 CFR 122.21(e)(3).
EPA Form 3510-2A(Revised 3-19) Page 13

This page intentionally left blank.

EPA Identification Number NPDES Permit Number Facility Name Outfall Number Form Approved 03/05/19
110009720506 NC0085812 Grassy Branch WRF 001 OMB No.2040-0004
TABLE B.EFFLUENT PARAMETERS FOR ALL POTWS WITH A FLOW EQUAL TO OR GREATER THAN 0.1 MGD
Maximum Daily Discharge Average Daily Discharge Analytical ML or MDL
Pollutant Number of Methods include units
Value Units Value Units Samples Methods (
)
0 ML
Ammonia(as N) 17.0 mg/L 0.81 mg/L 159 SM 4500NH3 0.10 0 MDL
Chlorine ❑ML
NA mg/L NA mg/L NA NA NA
(total residual,TRC)2 ❑MDL
0 ML
Dissolved oxygen 13.20 mg/L 8.94 mg/L 279 SM 45000G 0.10 0 MDL
0 ML
Nitrate/nitrite NA mg/L NA mg/L NA NA NA 0 MDL
ML
Kjeldahl nitrogen NA mg/L NA mg/L NA NA NA ❑❑MDL
0 ML
Oil and grease NA mg/L NA mg/L NA NA NA ❑MDL
0 ML
Phosphorus NA mg/L NA mg/L NA NA NA 0 MDL
ML
Total dissolved solids NA mg/L NA mg/L NA NA NA 0 MDL
1 Sampling shall be conducted according to sufficiently sensitive test procedures(i.e.,methods)approved under 40 CFR 136 for the analysis of pollutants or pollutant parameters or
required under 40 CFR chapter I,subchapter N or 0.See instructions and 40 CFR 122.21(e)(3).
2 Facilities that do not use chlorine for disinfection,do not use chlorine elsewhere in the treatment process,and have no reasonable potential to discharge chlorine in their effluent are not
required to report data for chlorine.
EPA Form 3510-2A(Revised 3-19) Page 15

This page intentionally left blank.

Lead and Copper Rule Revisions Summary
Y
The final draft revisions to the Lead and Copper Rule have been distributed to public water systems. There
have been extensive changes to the rules and compliance is expected to start in January 2024. There have
been some delays at the federal level that may push the compliance starting period to September 2024.
We identified the need for assistance to ensure we comply with the new rules, as some of the changes are
very complex and subjective.
• With that in mind, operations has budgeted for consultation in our FY22 operating budget to help
guide us through the steps and processes that will need to be implemented to ensure compliance
with the rule before it begins in 2024. We will look for the consultant to help us form the best plan
for system service line inventory, service line replacement program, and a "find and fix"policy.
Below is a summary of the most critical changes to the rule and what it will mean for us. It does not include
a complete plan to address each requirement. I believe we would task the consultant with structuring a plan
in the order of importance and the best way to implement it once the consultant has been selected.
Tap Sampling Guidance
Significant changes have been made to lead and copper tap sampling procedures with the LCRR. The EPA
has revised the sample pool tier structure. Any system with enough lead service lines in their system to fill
the sample pool will be required to sample all lead service lines.
• Our sample pool will be adjusted to include any "known lead service line" customers that are
identified during our work before the rule is implemented.
There have also been some sampling changes. Rather than sampling the 1st liter for both lead and copper
at the selected sample pool sites, utilities are now required to sample the 1st liter for copper and the 5th
liter for lead at locations with lead service lines. Additional changes, such as using only wide mouth bottles
and no pre-flushing, are also included in the new rule.
• We will review our monitoring SOP and make changes as needed for the collection of lead samples
per the new rule.
Lead Service Line - Revised Definition
Lead Service Lines
A pipe is considered a lead service line (LSL) if a portion is made of lead, which connects the water main
to the building inlet. An LSL can be owned by the water system, the property owner, or both.
If the only lead on a service line is a lead gooseneck, pigtail or connector, it is not considered an LSL.
Galvanized Service Lines
A galvanized service line is now considered an LSL if it is currently or was formerly downstream of an LSL
or a service line of unknown material due to the tendency of galvanized to capture lead from upstream
sources and release it back into the water if the pipes are disturbed or if the water quality changes. This is
being called a "galvanized requiring replacement". For sampling tier selection, a galvanized service line is
a Tier 3 sampling site and not an LSL (Tier 1 and Tier 2).
Based on clarification from the EPA, galvanized requiring replacement(Tier 3 sites) should be sampled at
the 1st liter for lead rather than the 5th liter although the text is ambiguous on this. Further clarification has
been requested from the EPA and this section will be updated once received.

Lead and Copper Rule Revisions Summary
• We will need to monitor this change and adjust our sampling SOP based on the final rule. I
believe we will write a new SOP, only for lead and copper sampling to address new sampling
protocols and the requirements for monitoring any sites that exceed the action level as noted in
this document below.
Clarification was provided by the EPA that a galvanized service line downstream of a lead gooseneck is
not considered an LSL. If a system encounters a lead gooseneck, it must replace it (or offer to replace it if
the gooseneck is privately owned). A system does not need to replace utility-owned galvanized service
lines nor offer to replace privately-owned galvanized service lines downstream of lead goosenecks when
the goosenecks are removed. However, a system does need to offer to replace a galvanized service line
if it is currently, or was formerly, downstream of an LSL.
• We do not believe. nor have we ever found a lead service line in our system. If that remains the
case, after a full system inspection, this will greatly limit our exposure for a line replacement
program.
Unknown Service Lines
A service line of unknown material, or lead status unknown service line, means a service line that has not
been verified as non-lead. It is not necessary to physically verify all materials. Other means of verification
will be approved by the states (e.g. records indicating installation after a local, state or federal lead ban).
Until the service line can be verified as non-lead, it will count towards the total number of LSLs in the
service line material inventory.
• Note: All service line materials will need to be identified regardless if they have been ruled non-
lead by dating or other means.
a After dating and records search, a plan will be needed to identify material for remainder
service lines. Some data is already available from information collected by meter
services. Additional data can be collected by staff as they interact with our water
connections.
Important note on disturbance!
If a system causes a disturbance to an LSL, galvanized requiring replacement or lead status unknown
service line, it must provide a point-of-use filter that is certified to NSF 53 standards with a 6-month supply
of replacement cartridges along with information about elevated lead levels and flushing instructions to
the customer. A disturbance includes a full LSL replacement, a partial LSL replacement, removal of a
gooseneck, a meter replacement or anything else requiring the service to be shut down or bypassed
temporarily.
• If needed, the average cost for lead filtering water pitcher is about$40. This would include the
water pitcher with filter and one replacement filter.
Water Quality Parameter(WQP) Monitoring
Collect one sample every 2 weeks at all entry points to the system and collect two samples per monitoring
period at all WQP sampling sites at the standard number of sampling sites (See CFR 141.87(a)(ii)(2)).
Monitoring period shall be every 6 months until the state designates optimal corrosion control treatment.
Although WQP sampling data can be grandfathered in, the lead tap samples during the same period would
need to be collected per the new provisions in the LCRR for the data to count.
If CCT is modified, continue sampling every 6 months until your state specifies new WQP values for optimal
corrosion control.

Lead and Copper Rule Revisions Summary
Parameters to sample shall include pH and alkalinity. If a corrosion inhibitor is used for corrosion control,
sampling is also required for the inhibitor residual (i.e. orthophosphate or silica). Confirm with your state if
any other parameters are required for your system.
Additional WQP sites may need to be added under the Find and Fix provisions. WQP sites are added near
any individual tap water samples above 15 tag/L up to a maximum of double the standard WQP sites.
Systems with 90 th Percentile Lead Below 10 pg/L
The first year once the LCRR is effective (January 2024), all systems with LSLs will be required to sample
every 6 months at the standard number of sites for lead and copper. As of now, it is unclear if systems
without LSLs will be required to go on 6-month monitoring or continue with their current monitoring
frequency. This will likely be determined by each state and will depend on if your system's previous tap
sampling can be said to have met the new sampling site selection, procedures and requirements in the
LCRR.
• Union County is presently on a reduced monitoring program that requires sampling every three
years. These samples are taken from June to September, but this will change with the new rule.
We are required to take 50 samples every three years but would have to take 100 samples
should we return to normal monitoring. If we cannot rule out lead service lines in the system, we
will need to take 100 samples every six months beginning with the new rule.
If our system does not exceed the lead trigger level of 10 pg/L and the copper action level of 1.3 mg/L
with the new sampling requirements for two consecutive 6-month monitoring periods, our system may
reduce monitoring frequency to annual monitoring at the standard number of sites for lead and the
reduced number of sites for copper. Systems must maintain water quality within the optimal water quality
parameters (OWQPs) during this same period and receive a written determination from the state
approving annual monitoring based on the state's review of monitoring, treatment and other relevant
information.
To qualify for triennial monitoring (every three years) as a large system, our system's 90th percentile for
lead must be at or below 5 pg/L and 90th percentile for copper at or below 0.65 mg/L for two consecutive
6-month monitoring periods with the new sampling requirements. Systems must maintain water quality
within the OWQPs during this same period and receive a written determination from the state approving
triennial monitoring based on the state's review of monitoring, treatment and other relevant information.
If at any point in the future our system adds a new source or long-term change in treatment, our system
will be required to go back to 6-month monitoring at the standard number of sites for lead and copper
unless the state determines the addition of the new source or treatment does not have an impact on
corrosion control treatment (New Yadkin Plant).
• We will most likely be on the standard monitoring schedule when the Yadkin Plant goes online.
We can work towards a reduced monitoring plan once we have an inventory of our system
completed.
• Below are the results of our last two cycles of lead testing.
2019 Lead Results
LEAD SAMPLES
90th Percentile Level = ND
No. Location3 Tier/Target Lead mg/I No. Location4 Tier/Target Lead mg/I

CI 0 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 000 ,-1 m m E 0 0 0 0 0
Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z O O 0 0 0 "a Z Z Z Z Z
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01 CO NI lD N .m-1 ,-I N if) Ln N d' al N 00 IJ) J � 1 N COLi) N O1 In N 01 Ln m CO N LO I..0
J J J J -I r1 I-1 c-I J J J _I J J J -1 <-1 i--1 _.1 J 1-1 J J IN J -JD N a--, J J _JD JN -JD -JD
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J N 00 01 0 ,--I N M ‘Zr Lh J N CO al 0 c-1 N m Cr 1n J f� 00 a1 O a1 O J N 00 Ol 0
N N N N m M M M M M M M M M ‘Zr d' Cr .Zr d' ct d d d' d' u1 Z N N N N M
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0 0 0 0 0 0 0 0 0 0 0 0 Cl 0 0 0 Cl 0 Cl Cl 0 0 0 0 0 E 0 0 0 0 0
Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z Z O -0 Z Z Z Z Z
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co c-I c-1 1-1 c-1 c-1 c-I c-1 c-1 i-1 N N N N N Ni
J

Lead and Copper Rule Revisions Summary
6 L99 1 ND 31 L43 1 ND
7 L73 1 ND 32 L76 1 ND
8 L69 1 ND 33 L95 1 ND
9 L101 1 ND 34 L04 1 ND
10 L90 1 ND 35 L96 1 ND
11 L79 1 ND 36 L67 1 ND
12 L88 1 ND 37 L93 1 ND
13 L45 1 ND 38 L55 1 ND
14 L23 1 ND 39 L57 1 ND
15 L17 1 ND 40 L49 1 ND
16 L38 1 ND 41 L87 1 0.0038
17 L22 1 ND 42 L54 1 0.0042
18 L89 1 ND 43 L20 1 0.0046
19 L64 1 ND 44 L51 1 0.0054
20 131 1 ND 45 L66 1 0.0064
21 L94 1 ND 46 L85 1 0.0064
22 L78 1 ND 47 L59 1 0.013
23 L40 1 ND 48 L58 1 0.017
24 L50 1 ND 49 L74 1 0.42
25 L81 1 ND 50 L24 1 0.44
Corrosion Control Treatment(CCT)
Monitoring has shown that we have done a great job with our system's corrosion control! It is unclear at
this time if our system's status will carry over with the LCRR. We suspect that if our tap sampling site
selection and procedures do not exactly align with the new requirements for sampling, our system will be
required to go on 6-month monitoring.
If we are not confident that our system's 90th percentile will consistently be below 5 pg/L with the new
sampling requirements, we may want to consider conducting a corrosion control treatment (CCT) study.
Currently we believe the system can maintain this level but additional testing will need to be performed
based on the new sampling techniques.
• We will need to work with our treatment superintendent and the CRWTP manager to better
understand if improvements can be made to CCT.
Inventory Requirements and Lead Service Line Replacement for All Systems
• Service Material Inventory
All systems are required to compile a service line material inventory (including both utility-owned
and privately-owned sides of the service line) by January 2024 or demonstrate absence of LSLs.
Any galvanized service lines that are, or were formerly, downstream of an LSL, or"galvanized
requiring replacement," are required to be included in the overall count of LSLs for eventual
replacement. Services with unknown materials that may be lead will be classified as "lead status
unknown service lines" and will also count towards the total number of LSLs in the system until
they are verified. Update inventory annually or triennially, based on sampling frequency, with any
replacements and/or verifications. If your system supplies over 50,000 people, you are required to

Lead and Copper Rule Revisions Summary
publish the inventory online. If your system supplies less than 50,000 people, it is not required to
be online but it must be available to the public on request.
All systems must notify customers who have service lines categorized as lead, galvanized
requiring replacement, or lead status unknown within 30 days of completing the inventory and
then on an annual basis. The EPA has specific guidelines in the rule for what information needs
to be included in the notification.
• To begin our service line inventory, we will immediately start working with our GIS team
to identify homes and businesses that were built before 1978. This will automatically label
those connections as ""Lead Status Unknown."We can then determine the best
approach on how to identify them individually. All services newer than 1978 will still need
to be identified as plastic or copper. Most of these can be determined by records and
county specifications over the years.
• Schools— We will partner with our school system to lay out a plan for monitoring both the
supply side of their service as well as within the schools. Once we have a plan, we will
begin performing non-compliance sampling to build a data base that will be needed for
the new rule This should help both us and the school system to be prepared for future
requirements
• Daycares— We will need to compile a list of daycares for monitoring, which can be
furnished by environmental health. We will then begin sampling these sites and
conducting an inventory of their service lines in advance of the new lead rule.
• LSL Replacement Program Plan
If you find that your system has LSLs based on your inventory, all systems with LSLs must also
prepare a Lead Service Line Replacement Program by January 2024. The plan must include:
o A strategy for determining "lead status unknown" service lines
o Procedures to conduct full LSL replacements
o Communication strategies
o A recommended LSL replacement goal rate in the event of a lead trigger level
exceedance (for systems over 10,000 persons)
o Flushing procedures
o LSL prioritization strategies
o Funding strategies including ways to accommodate customers that are unable to pay for
the replacement of their portion on their own
o If our inventory yields any LSL's, we will need to create the replacement plan. If needed, I
believe this task would go to our consultant for development.
Find and Fix
When an individual sample exceeds the lead action level, customers must be notified within 3 days of
receiving the results. A utility must perform a "Find and Fix" for all individual samples exceeding 15 pg/L
{ of lead by conducting the following:
1. Corrosion Control Treatment Assessment—Within 5 days of receiving the results, conduct
additional WQP monitoring at a sample site on the same size water main and within a half mile of

•
Lead and Copper Rule Revisions Summary
the residence with the sample exceeding 15 pg/L. If a new WQP location is added, it should be
incorporated into future WQP monitoring. The number of WQP sites may continue to increase
with individual samples exceeding 15 pg/L until your system's number of WQP sites is double the
standard number of sites for your size. Small systems without corrosion control treatment may
have 14 days to collect the sample.
2. Site Assessment—Within 30 days of receiving results, collect a follow-up sample at the location
exceeding 15 pg/L.
o For a lead service line, a different sample volume or sample collection procedures may
be used to assess the source of elevated lead levels.
o For a service line that is not lead, collect 1 liter first draw sample after 6+ hours of
stagnation.
o Results must be submitted to the state but will not be used for the 90th percentile
calculation.
o If access is denied for resampling, document customer refusal or nonresponse after two
attempts to obtain the follow-up sample.
3. Investigate the high lead value and determine needed corrective action.
o Determine if either localized or centralized adjustment of corrosion control treatment are
needed or if other distribution system actions are necessary(such as flushing to reduce
water age).
Since our system does not yet have optimal corrosion control treatment, treatment reoptimization
recommendations to the state are not required to be provided.

i
Union County Public Works
Grassy Branch WRF
NPDES Permit No. NC0085812
Outfall 001
Form 2A Additional Information
B.2 Topographic Map
Refer to Figure 1 for the topographic map.
B.3 Process Flow Schematic or Diagram
Refer to Figures 2-1 and Figure 2-2 for process flow schematics at 0.05 and 0.12 mgd,
respectively.
Overview
The Grassy Branch Water Reclamation Facility(Grassy Branch WRF) is an extended aeration
package treatment plant (PTP)constructed by Hydro-Aerobics Package Wastewater Treatment
Systems in 1997.The facility design flow is 50,000 gallons per day(gpd).
Influent Pumping& Headworks
The existing influent pump station consist of two pumps rated at 130,000 gpd each at 15 feet of
total dynamic head (TDH).The pumps operate in a duty/standby service.The influent screening
is comprised of a manual coarse bar screen designed for 150,000 gpd (2.5 times the maximum
month design flow of 50,000 gpd).The existing equalization basins have a combined volume of
15,400 gallons. Coarse bubble diffusers and two, 2-horsepower(HP) rotary lobe positive
displacement(PD) blowers provide aeration and mixing in the equalization basins.
The proposed expansion to 0.12 mgd will include an additional manual coarse bar screen and
equalization basin to provide for additional treatment capacity at the Grassy Branch WRF.
Secondary Treatment Process
The existing secondary treatment process consists of two, 25,000-gallon extended aeration
basins with coarse bubble diffusers.Air is supplied by two, 7.5-HP rotary lobe PD blowers.The
blowers are controlled via variable frequency drives (VFD).The aeration system is a single run of
coarse bubble diffusers located along the entire length of one wall in each aeration basin.The
location of the diffusers provides a spiral roll flow pattern for complete mixing within the basin.
Lime slurry(30%) provides supplemental alkalinity. RAS flow is estimated at 100%of the plant
flow,which is corroborated by the Hydro-Aerobics Package Wastewater Treatment Systems
Operations and Maintenance (O&M) manual. WAS is stored in a 9,000-gallon aerated holding
tank.The holding tank has coarse bubble diffusers connected to the secondary treatment
aeration system PD blowers. Solids are pumped out and transported to the Crooked Creek WRF
for stabilization and ultimate disposal.The flow from each aeration basin combines in the MLSS

Union County Public Works
Grassy Branch WRF
NPDES Permit No. NC0085812
Outfall 001
distribution box prior to entering the secondary clarifiers. The Grassy Branch WRF has two, 10-
foot diameter secondary clarifiers.
The proposed expansion to 0.12 mgd will include an additional aeration basin and secondary
clarifier to provide for additional capacity at the treatment facility.
Filtration and Disinfection
The Grassy Branch WRF has two mixed media (anthracite/sand)tertiary filters with a surface
area of 18.75 square feet(SF) each (37.5 SF total). Prior to discharge into Crooked Creek,
secondary effluent is disinfected via UV disinfection technology.The UV system was installed in
the original chlorine contact chamber as a retrofit.
The proposed expansion of the Grassy Branch WRF includes the addition of a new cloth media
disk-type filter.The existing sand filters will be utilized as a standby, redundant unit.
Additionally,a new UV disinfection system is proposed which would allow for one duty and one
standby unit to meet peak daily flows.

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State Grid/Quad: Stanfield N e14IS-9G1,,, Figure 1 : Topographic Map
G17NW di
Receiving Stream: Crooked Creek H F.. y° ,=Q Union County Public Works
Stream Class: C c?.? •o�
Drainage Basin: Yadkin Pee Dee Grassy Branch WRF
Sub-basin: 03-07-12
Latitude: 35°07' 50" N NPDES Permit NC0085812
HazenLongitude: 80° 29' 40" W _ Union County, NC

30% Lime Slurry
Q=0.05 ' Q=0.10
n -of
k:
Influent Pump
Station (2 pumps) Manual Coarse y
EQ Basins(2) Aeration Basins (2) Secondary
Bar Screen (1) Clarifiers(2)
Q=0.05 mgd
RAS
RAS/WAS PTP
4
Q
\ 4;. ,� =0.05 mgd
Crooked Creek WAS
UV Disinfection Anthracite/Sand Q=0.002 mgd
Tertiary Filters(2)
•
Transported to Crooked Aerated Holding
Creek WRF for Stabilization Tank(1)
Figure 2-1:
Process Flow Diagram
Grassy Branch WRF
Existing: 0.05 mgd
NPDES Permit NC0085812

30% Lime Slurry
4(.. e
Q= 0.12 Q=0.24 -
7 mgd mgd
yr
Influent Pump
Station (2 pumps) Manual Coarse Secondary
EQ Basin (3) Aeration Basins (3)
Bar Screen (2) Clarifiers (3)
Q=0.12 mgd ® 0
RAS
RAS/WAS PTP
.o I I, 4 S,.. Q=0.12 mgd
.,•----..t-.-.,.. 4----- '"'.s...:.,,,....,, ., . 11111, 1, I4, l''. 4---- 4,01 4
)
.."..0
Crooked Creek
WAS
UV Disinfection Disc Filter(1) Q=0.004 mgd
•
0111/111
ihi,_41110"
11i
Transported to Crooked Aerated Holding
Creek WRF for Stabilization Tank (3)
Figure 2-2:
Process Flow Diagram
Grassy Branch WRF
Expansion: 0.12 mgd
NPDES Permit NC0085812

Hazen and Sawyer
Hazen 4011 WestChase Suit
e
Blvd, 500
Raleigh, NC 27607•919.833.7152
Firm License No.C-0381
TECHNICAL MEMORANDUM
To: Copes: RECEIVED
Andrew Neff, PE Jim Struve, PE
Water and Wastewater Division Director MAY 1 12021
Union County Public Works
From:
NCDEQ/DwR/NPDES
Mary Sadler, PE
Anthony Young, El
Date:
April 2021
Subject:
Engineering Alternatives Analysis to Support Major NPDES Modification Request
Grassy Branch WRF Expansion from 0.05 mgd to 0.120 mgd
Special Order by Consent Application
1. Introduction
Union County is located on the border of South Carolina approximately 15 miles southeast of Charlotte
and is home to fourteen municipalities. Union County Public Works (UCPW) is responsible for the
management, operation and maintenance of the wastewater collection and treatment system for
unincorporated Union County and all County municipalities except for the City of Monroe and the Town of
Marshville. The County's wastewater system is comprised of five conventional activated sludge
wastewater reclamation facilities (WRF)with a combined rated treatment capacity of 9.65 million gallons
per day(mgd).
The Grassy Branch WRF is one of the five treatment facilities that Union County owns and operates. The
WRF was constructed in 1997 by a developer and since acquired by Union County. The Grassy Branch
WRF is permitted to discharge 0.05 mgd of treated effluent into Crooked Creek via NPDES permit
NC0085812. The Grassy Branch collection system consists of approximately 31,000 feet of gravity sewer,
123 manholes, and two wastewater pump stations. The Loxdale Pump Station has a capacity of
21,400 gpd and the Unionville Pump Station has a capacity of 10,245 gpd. The Grassy Branch WRF
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 for the Grassy Branch
WRF over the last several years. 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 WRF has
contributed to and intensified the compliance issues. Grassy Branch WRF flow and recorded rainfall 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
WRF.
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To address the on-going violations at Grassy Branch, Union County has executed and submitted the
application form and required attachments to the Department of Environmental Quality (DEQ) Division of
Water Resources (DWR)for a Special Order byConsent(SOC). GrassyBranch SOC package
p ( ) p 9
requested an increase in design capacity from 0.05 to 0.12 mgd to address the over-allocation of sewer
connections. In response, DWR staff requested that the County's SOC application be amended to include
a National Pollutant Discharge Elimination System (NPDES) permit major modification to support the
County's request for a capacity increase. Per DWR Guidance, this Technical Memorandum provides the
Engineering Alternative Analysis (EAA)to support the capacity increase request at the Grassy Branch
WRF.
2. Need for Project
Historical data indicates that influent flows greater than the permitted design capacity of the Grassy
Branch WRF have resulted in final effluent permit violations for flow, conventional pollutants, and bacterial
pollutants. The County has attributed many 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 WRF than
available capacity. The Grassy Branch WRF receives domestic wastewater from a defined service area.
The WRF serves three schools, two residential subdivisions, and 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 lots)
• Smithfield Subdivision (70 lots, five of which are vacant)
• Private parcels (12 homes)
A permanent increase in the design maximum month flow from 0.05 mgd to 0.120 mgd is required at the
Grassy Branch WRF. This flow increase is associated with the existing domestic flow discharging to the
WRF, the maximum student capacity of the three schools, new connections in the Smithfield subdivision to
fulfill contractual obligations (five lots), and private parcel connections along the main sewer line to the
WRF. 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 WRF.
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 WRF are
significantly higher than what is typical for larger treatment facilities. Table 2-1 summarizes the proposed
design annual average and maximum month flow.
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Table 2-1: Summary of Methods Used to Calculate Proposed Maximum Month Design Flow
Current Anticipated Total Flow, Peaking
Dwelling Unit/School Flow, gpd Planned Flow, gpd gpd Factor 9
Piedmont High School ---- 1,953 1,2,3 __--
(1,363 students)
Piedmont Middle School ---- 0' ---- -
(1,018 students)
Unionville Elementary School ---- 0" ---- ----
(701 students)
Loxdale Subdivision (52 lots) ---- 0 5 ---- ----
Smithfield Subdivision (70 lots) ---- 1,800 1'6 ---- ----
Private parcels ---- 11,520 1'7 ---- ----
Annual average flow 53,360 15,270 68,630 ----
Maximum month flow 8 ---- ---- 120,000 1.7
Maximum week (7-day)flow ---- ---- 201,000 3.0
Maximum day flow ---- ---- 469,000 7.0
I 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.
7 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.
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3. Alternatives Analysis
Six wastewater capacity alternatives were evaluated to address the Grassy Branch WRF expansion from
0.05 mgd to 0.12 mgd. This alternatives analysis addresses the additional 0.07 mgd of capacity that will be
required to meet the needs of the Grassy Branch service area. The alternatives that were considered in
this analysis include the following:
• No action
• Infiltration and inflow(MI) reduction
• Connection to other publicly-owned treatment works (POTWs)
• Land application
• Non-conjunctive reuse
• Expand the Grassy Branch WRF and surface water discharge to Crooked Creek
Opinion of probable project costs were prepared for the applicable alternatives. Cost opinions were
prepared in accordance with the guidelines of the Association for the Advancement of Cost Engineering
(AACE) International for a Class 4 level of estimation. A Class 4 estimate is prepared based on
information developed during a feasibility phase. The expected accuracy range for a Class 4 level of
estimation is +50 percent to—30 percent. Cost opinions include contingency, mobilization, bonds and
insurance, and general conditions. For the total present worth evaluation, a time period of 20 years was
used and a discount rate of 2.3 percent per EPA 2020 Discount Rates Circular A-94. Piping, electrical, and
structural infrastructure was assumed to have a life of 40 years. Mechanical equipment was assumed to
have a life of 20 years.
3.1 No Action
The no-action alternative consists of the County not constructing the necessary wastewater treatment
capacity to address the over-allocation of flow in the Grassy Branch service area. Based on historical data
from the County, influent flows that exceed the permitted design capacity of the Grassy Branch WRF will
continue to result in final effluent permit violations for flow, conventional pollutants, and bacterial
pollutants. The Grassy Branch WRF does not have the capacity to treat the increase in flow without an
increase in infrastructure capacity. Therefore, this alternative was eliminated from further consideration.
3.2 Infiltration and Inflow Reduction
The County has actively been involved in the 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 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.
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As of January 2019, the entire Grassy Branch collection system has been surveyed by CCTV. Table 3-1
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 3-1: Summary of I&I Effort Maintenance Data
2014 2015 2016 2017 2018 2019
Man Hours 960 1080 960 480 1512 1152
Investigating
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
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 WRF. Table 3-2 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.
The County has committed to the continuation of I&I efforts in the Grassy Branch WRF collection system.
The additional 0.07 mgd of capacity needed to address growth in the planning area cannot be accounted
for in I&I reduction efforts. Therefore, the Ill reduction alternative has been eliminated from further
consideration as a stand-alone alternative to the proposed capacity increase.
1
Table 3-2: Summary of Historical Influent Peaking Factors
Parameter 2015 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
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3.3 Connection to Other Publicly-Owned Treatment Works
Connection to other publicly-owned treatment works (POTWs)was evaluated as an alternative to an
expansion of the Grassy Branch WRF. Wastewater treatment facilities in the proximity of a five-mile radius
of the Grassy Branch WRF include the Old Sycamore WRF, the Tallwood WRF, and the Crooked Creek
WRF. All three treatment facilities are owned and operated by Union County. Union County's Twelve Mile
Creek Water Reclamation Facility is approximately 20 miles from the Grassy Branch WRF. A fifth
treatment facility in the proximity of the Grassy Branch WRF is the City of Monroe WWTP. The Monroe
WWTP has a permitted capacity of 10.4 mgd and is approximately 10 miles from the Grassy Branch WRF.
Figure 3-1 illustrates the location of the five wastewater treatment facilities in Union County relative to the
Grassy Branch service area.
Table 3-3 summarizes the treatment facility, permitted discharge, average day flow, percent of capacity
remaining, and the estimated distance from the Grassy Branch WRF for the five identified wastewater
treatment facilities. The closest treatment facility within a five-mile radius of the Grassy Branch WRF is the
Tallwood WRF, which is owned and operated by Union County. Similar to the Grassy Branch WRF, the
Tallwood WRF has a defined service area (e.g., a residential community). The Tallwood WRF does not
have capacity to accommodate the additional Grassy Branch flow. The remaining treatment facilities are
outside the five-mile radius of the Grassy Branch sewershed. Furthermore, the City of Monroe is currently
in the initial planning phase for an expansion of the Monroe WWTP. The City has requested speculative
limits from DWR to initiate the expansion process. Flows to the Monroe WWTP are approaching
70 percent of the permitted capacity.
Table 3-3: Summary of Publicly Owned Treatment Works in Proximity to the Grassy Branch WRF
Percent of
Municipality/ Capacity with Estimated
Wastewater NPDES Average Day 0.07 mgd Distance
Service Treatment Permitted (Maximum Day) Grassy from Grassy
Provider Facility Discharge' Flow 2 Branch WRF Branch WRF
Union County Old Sycamore 0.15 mgd 0.046 mgd 77% 6.6 miles
WRF1
Union County Tallwood WRF 0.05 mgd 0.038 mgd > 100% 5.1 miles
(0.17 mgd)
Union County Crooked 1.9 mgd 1.132 mgd 60% 9.0 miles
Creek WRF (3.3 mgd)
Union County Twelve Mile 7.5 mgd 5.4 mgd 73% 19.9 miles
Creek WRF (10.94 mgd)
City of Monroe Monroe 10.4 mgd 6.94 mgd 67% 9.5 miles
WWTP (16.6 mgd)
Old Sycamore Creek WRF is permitted as a land application system via non-discharge permit WQ0011928.
2 Data from 2019 and 2020 Local Water Supply Plans.
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Connection to neighboring POTWs has been removed from consideration as a viable alternative to an
expansion of the Grassy Branch WRF. The majority of the identified wastewater treatment facilities are
outside of a five-mile radius from the Grassy Branch WRF. This alternative would require extensive
conveyance infrastructure, resulting in elevated capital and operation and maintenance (O&M) costs. The
most proximate treatment facility to the Grassy Branch WRF does not have available treatment capacity
for the Grassy Branch sewershed.
3.4 Land Application
Land application of wastewater effluent was evaluated as a discharge alternative to an expansion of the
Grassy Branch WRF. Land application systems include individual or community onsite subsurface
systems, drip irrigation, and spray irrigation. Land application systems generally do not require advanced
secondary treatment processes prior to irrigation per North Carolina Administrative Code (NCAC)
15A 02T, Waste Not Discharged to Surface Water. Typically, only preliminary treatment is used. Land
application systems also do not facilitate other options for effluent disposal, such as reuse or high-rate
infiltration. Secondary effluent limits for land application include BOD5 and total suspended solids (TSS)
less than 30 mg/L, ammonia less than 15 mg/L, and fecal coliform less than 200 colonies/100 ml. Influent
pumping, screening, and equalization for the additional 0.07 mgd to be land applied would be located on
the treatment plant site.
Suitable property for disposal of land application effluent must be acquired to dispose of the additional
0.07 mgd. A conservative land application rate of 1 inch per acre per week was selected based on similar
systems in North Carolina and published criteria (EPA, 2006). Including land for a storage pond, wetlands,
buffers, and access roads, Union County would need to acquire a minimum of 32 acres of land for effluent
disposal of 0.07 mgd. Figure 3-2 illustrates the properties evaluated based on size, zoning classification,
and proximity to the treatment plant. The closest suitable land application site with sufficient available land
was approximately 1 mile from the Grassy Branch WRF. The identified plot is approximately 52 acres with
a zoning designation of RA 40. Detailed investigations were not performed to determine the suitability of
the land for application or the availability of the property.
Research suggests that land application of secondary treated effluent may reduce the porosity of soil
(i.e., clogging) and the infiltration rate over time (Clanton and Slack 1987). Therefore, more land may be
required to dispose of the same quantity of effluent as the system ages. Additionally, land application
systems do not maximize the value and service of the property due in part to the large buffer areas that
are required.
Table 3-4 summarizes the total present worth for the land application disposal alternative. Costs include
land acquisition, spray field infrastructure, effluent pumping, conveyance, and preliminary treatment at the
Grassy Branch WRF. The total present worth for this alternative is approximately$7,720,000. Attachment
A provides the design, capital cost, and O&M cost calculations for the land application alternative.
The land application alternative has been removed from consideration for several reasons. This alternative
is not as economically feasible as the selected alternative. The total present worth cost is approximately
$2 million higher than the selected alternative. Additionally, Union County would be responsible for
operating two separate wastewater treatment systems, which is an increase in annual O&M cost.
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Furthermore, the County would anticipate negative public perception of siting a land application system in
primarily residential areas. Site security will also pose a concern.
Table 3-4: Present Worth Analysis for Land Application
Capital Annual Useful Life, Salvage
Cost''2 08,1111 Cost 2,4 Years 5'6 Amount'
Land application capital cost:
Land acquisition $394,000 $56,700 ---- $394,000
Spray field infrastructure $525,000 ---- 20 $0
Access roads $581,000 ---- 20 $0
Storage pond $221,000 ---- 40 $110,500
Storage pond liner $69,000 ---- 20 $0
Pump station at WRF $238,000 ---- 40 $119,000
Pump station at land $164,500 40 $82,250
application site
Effluent force main $187,000 ---- 40 $93,500
Monitoring wells $150,000 40 $75,000
Fencing $138,000 ---- 20 $0
Capital cost for Grassy $720,000 $168,000 33.2 $286,000
Branch WRF expansion
Engineering/Legal/ $1,500,000 ---- ---- ----
Construction
Total $4,888,000 $224,700 ---- $1,160,000
Total Present Worth of O&M $3,570,000
Total Present Worth of Salvage $736,000
Total Present Worth $7,720,000
All costs in 2021 dollars.
2 Construction subtotal includes contingency, contractor's general conditions, bonds, insurance, overhead, and
profit(25% +20%).
3 Time period of 20 years with an interest rate of 2.3%(EPA 2020 Discount Rates Circular A-94).
4 Grassy Branch WRF O&M cost based on annual Grassy Branch Operating Budget.
5 Grassy Branch WRF salvage amount calculated assuming 66%structural life and 34%mechanical life.
6 Useful life assumes a piping, electrical, and structural life of 40 years and a mechanical life of 20 years.
Land assumed to have a 100%salvage value.
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3.5 Non-Conjunctive Reuse
In addition to land application, a non-conjunctive reuse system was evaluated as a discharge alternative
for the expansion of the Grassy Branch WRF. Reuse is the beneficial reuse of tertiary treated wastewater
effluent. DWR defines non-conjunctive reuse as a wastewater treatment system that relies on reclaimed
water uses to account for all the generated wastewater(i.e., zero direct discharge to surface water).
Design criteria for reclaimed water systems in which an irrigation system is required to meet the needs of
the facility are more stringent than for land application systems. Per NCAC 15A 02T, Waste Not
Discharged to Surface Waters, effluent criteria for reclaimed water systems include BOD5 less than
10 mg/L, TSS less than 5 mg/L, ammonia less than 4 mg/L, fecal coliform less than 14 colonies/100 ml,
and a maximum turbidity of 10 NTU.
This alternative involves the development of a non-conjunctive reuse system to land apply the 0.07 mgd of
expanded treated effluent from the Grassy Branch WRF onto suitable land within a 5-mile radius of the
treatment plant. This alternative would require the expansion of the Grassy Branch WRF as well as
additional disinfection to meet reclaimed water standards. Treated effluent would be pumped from the
Grassy Branch WRF to a storage pond at the reuse application site. Refer to Figure 3-2 for a general
location of a potential dedicated spray irrigation site. In addition to treatment design criteria, NCAC 15A
02T provides design criteria for distribution lines and reclaimed water utilization. Setback requirements for
irrigation and utilization areas are less stringent than for land application systems. The required setbacks
for treatment and storage facilities in reclaimed water systems are identical to those for land application
systems.
Production of reuse quality effluent allows a greater range of options for land application other than a
dedicated land application site. These effluent disposal options include golf courses, residential lawns,
parks and school grounds, athletic fields (e.g., soccer, baseball, football), irrigation of crops, and industrial
uses(such as cooling and wash down water). Additionally, beneficial reuse is considered by many
communities as a supplement to the NPDES discharge, particularly to offset potable water demand in the
hot summer months. Water reuse systems in North Carolina are generally landscape irrigation-based
systems that experience high demands during the hot, dry summer season and little to no demands during
the cool,wet winter season.
A cost-effective reduction of a surface water discharge requires commercial and industrial users on a year-
round basis. Ideally, reuse options could help to offset high potable water demands during the spring and
summer seasons when residential irrigation and other demands peak. However, potential reuse demand
within a 2-mile radius of the plant is low, with limited reuse water applications near the plant.
• No potential irrigation sites (golf courses, residential lawns, etc.)were identified within a
2-mile radius of the plant.
• No significant industrial users (SIUs) or agricultural reuse opportunities exist near the
treatment plant.
• Plant effluent quality will generally meet reuse requirements for monthly average and
daily maximum BOD5, TSS, and ammonia limits. Additional disinfection would be required
to meet reclaimed water fecal coliform standards.
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Table 3-5 summarizes the total present worth for the non-conjunctive reuse disposal alternative. Costs
include land acquisition, spray field infrastructure, effluent pumping and force main, sitework and
expansion of the Grassy Branch WRF. The total present worth for this effluent disposal option is
approximately$8,550,000. The capital and total present worth costs are 166% higher than the cost of the
selected alternative. Attachment B provides the design, capital cost, and O&M cost calculations for the
non-conjunctive reuse alternative.
The non-conjunctive reuse water was removed from consideration as a viable alternative. The extreme
seasonal variation in non-potable water demand requires a dedicated property(s)for spray irrigation. Site
security, additional operation and maintenance costs associated with a second treatment system, and high
capital costs are inherent to this alternative. Similar to the land application alternative, the County would
anticipate opposition from the public regarding a use of land inconsistent with the surrounding residential
area.
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Table 3-5: Present Worth Analysis for Non-Conjunctive Reuse System
Capital Annual Useful Life, Salvage
Cost''2 O&M Cost3 4 years 5'6 Amount'
Land application capital cost:
Land acquisition $394,000 $57,700 ---- $394,000
Spray field infrastructure $525,000 ---- 20 $0
Access roads $581,000 ---- 40 $290,500
Storage pond $47,000 ---- 40 $23,500
Storage pond liner $17,000 ---- 20 $0
Pump station at WRF $238,000 ---- 40 $119,000
Pump station at land $164,500 ---- 40 $82,250
application site
Effluent force main $187,000 ---- 40 $93,500
Monitoring wells $150,000 ---- 40 $75,000
Fencing $138,000 ---- 20 $0
Chlorine disinfection at WRF $130,000 ---- 20 $0
Capital cost for Grassy $2,100,000 $168,000 33.2 $834,940
Branch WRF expansion
Engineering/Legal/ $1,500,000 ---- ---- ----
Construction
Total $6,172,000 $225,700 ---- $1,913,000
Total Present Worth of O&M $3,590,000
Total Present Worth of Salvage $1,214,000
Total Present Worth $8,550,000
'All costs in 2021 dollars.
2 Construction subtotal includes contingency, contractor's general conditions, bonds, insurance, overhead, and
profit(25% +20%).
3 Time period of 20 years with an interest rate of 2.3%(EPA 2020 Discount Rates Circular A-94).
'Grassy Branch WRF O&M cost based on annual Grassy Branch Operating Budget.
5 Grassy Branch WRF salvage amount calculated assuming 66%structural life and 34%mechanical life.
5 Useful life assumes a piping, electrical, and structural life of 40 years and a mechanical life of 20 years.
'Land assumed to have a 100%salvage value.
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3.6 Expand the Grassy Branch WRF and Surface Water Discharge to Crooked Creek
(Selected Alternative)
The expansion of Union County's Grassy Branch WRF from 0.05 mgd to 0.12 mgd was identified as the
most favorable project alternative to accommodate the flows in the Grassy Branch service area. No
additional land will be required for this project alternative as all modifications will be restricted to plant
property. This alternative has been selected by Union County to be the most technically feasible, the most
economical, and the most protective of water quality in the receiving stream.
An expansion of the Grassy Branch WRF requires infrastructure improvements necessary to achieve a
rated plant capacity of 0.12 mgd and meet the speculative effluent limits. The facility consists of a
conventional activated sludge process for CBOD5 removal, nitrification, and phosphorus removal. The
facility consists of screening, flow equalization, aeration basins, secondary clarification, tertiary filtration,
UV disinfection, and post aeration. BioWin°process modeling indicates that modifying the existing plant
processes will be successful in achieving permitted effluent limits. The improvements required to meet the
speculative permit limits are summarized as follows:
• 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 detailed design. Existing unit
processes will remain in service during construction. It is not anticipated that construction activity will affect
the current facility performance.
The expansion of the Grassy Branch WRF and a surface water discharge to Crooked Creek was identified
to be the most technically feasible, the most economical, and the most protective of water quality in
Crooked Creek. Table 3-6 summarizes the total present worth for this selected alternative. The net present
worth for the selected alternative is approximately$5,140,000. This alternative allows the County to
leverage the existing assets on the Grassy Branch WRF site.
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Table 3-6: Present Worth Analysis for Expanding Union County's Grassy Branch WRF
Capital Annual Useful Life, Salvage
Cost 1,2 O&M Cost 3,4 years 5,6 Amount'
Capital Cost for Grassy Branch $2,100,000 $168,000 33.2 $834,940
WRF Expansion
Engineering /Legal/ $900,000 ---- ---- ----
Construction
Total $3,000,000 $168,000 ---- $835,000
Total Present Worth of O&M $2,670,000
Total Present Worth of Salvage $530,000
Total Present Worth $5,140,000
All costs in 2021 dollars.
2 Construction subtotal includes contingency, contractor's general conditions, bonds, insurance, overhead, and
profit(25% +20%).
3 Time period of 20 years with an interest rate of 2.3%(EPA 2020 Discount Rates Circular A-94).
4 Grassy Branch WRF O&M cost based on annual Grassy Branch Operating Budget.
5 Grassy Branch WRF salvage amount calculated assuming 66%structural life and 34%mechanical life.
6 Useful life assumes a piping, electrical, and structural life of 40 years and a mechanical life of 20 years.
Land assumed to have a 100%salvage value.
3.6.1 Water Quality Modeling to Support Expanded Surface Water Discharge
Speculative limits were informally discussed with the Division of Water Resources (DWR)for the upgraded
and expanded Grassy Branch WRF 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.
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 C provides the Crooked Creek QUAL2K Model
Development Report(Tetra Tech, October 2019). The model demonstrated strong performance results
and captured key dissolved oxygen trends.
The calibrated QUAL2K model was then used to assess the impact of the Grassy Branch WRF 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 D. The model
demonstrates that there is assimilative capacity for the final effluent permit limits. Table 3-7 provides a
summary of the anticipated final effluent permit limits. The instream dissolved oxygen standard of 5 mg/L
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was met in all conditions. The model results also demonstrated that ammonia toxicity will not be
exceeded.
Table 3-7: Anticipated Final Effluent Permit Limits for the Upgraded and Expanded WRF
Parameter Monthly Average Weekly 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 6
Fecal coliform, geometric mean / 100 mL 200 400
Dissolved oxygen, mg/L > 6
One of the issues raised by DWR staff during the October 1, 2019 meeting was the impact of the Grassy
Branch WRF 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 water
quality sampling sites. Tetra Tech concluded that an expansion of the Grassy Branch WRF is unlikely to
contribute to the downstream turbidity impairment. The impact of the Grassy Branch WRF low effluent flow
compared to turbidity contribution from precipitation events is negligible.
4. Summary
An expansion of the surface water discharge to Crooked Creek was selected as the preferred alternative.
A surface water discharge results in the least economic impact to the County. This alternative also
leverages the existing assets on the Grassy Branch WRF site. The water quality modeling results indicate
that assimilative capacity is available in Crooked Creek for the increased discharge.
Page 14/17

Hazen
5. References
Association for the Advancement of Cost Engineering (AACE) International. 2005. Cost Estimate
Classification System—As Applied in Engineering, Procurement, and Construction for the Process
Industries, TCM Framework: 7.3—Cost Estimating and Budgeting. (Recommended Practice No. 18R-97).
Black &Veatch. December 2011. Final Comprehensive Water&Wastewater Master Plan; Population,
Water Demand, &Wastewater Flow Projections for Union County, NC.
Clanton, C.J. and Slack, D.C. 1987. Hydraulic Properties of Soils as Affected by Surface Application of
Wastewater. Transactions of the ASAE—American Society of Agricultural Engineers. V. 30(3) p. 683-687.
May/June 1987.
Hazen and Sawyer. 2019. Engineer's Certification, Grassy Branch Wastewater Treatment Plant Special
Order by Consent Application Package. Prepared for Union County Public Works.
Hazen and Sawyer. 2018. Technical Memorandums for Facility Process Improvements for Twelve Mile
Creek Water Reclamation Facility, Crooked Creek Wastewater Treatment Plant, Old Sycamore Creek
Wastewater Treatment Plant, and Tallwood Wastewater Treatment Plant. Prepared for Union County
Public Works.
Monroe, City of. 2019. Local Water Supply Plan. Submitted to Division of Water Resources.
Union County. October 2013. National Pollutant Discharge Elimination System Permit for the Grassy
Branch Wastewater Treatment Plant, NC0085812. Issued by the North Carolina Department of North
Carolina Department of Environmental Quality Division of Water Resources.
North Carolina Department of Environment and Natural Resources (DENR). September 2006. North
Carolina Administrative Code, Title 15A, Waste Not Discharged to Surface Waters. Division of Water
Quality, Environmental Management Commission Raleigh, NC.
Tetra Tech. October 2019. Crooked Creek QUAL2K Model Development Report. Prepared for Union
County Public Works Department and Hazen and Sawyer.
Tetra Tech. October 2019. Crooked Creek Model Application Report for the Grassy Branch WWTP.
Prepared for Union County Public Works Department and Hazen and Sawyer.
Union County. January 2020. Grassy Branch Wastewater Treatment Plant Special Order by Consent
Application Package.
Union County Public Works. 2020. Local Water Supply Plan. Submitted to Division of Water Resources.
United States Environmental Protection Agency(EPA). September 2006. Process Design Manual—Land
Treatment of Municipal Wastewater Effluents. EPA/625/R-06/016. Office of Research and Development,
Cincinnati, Ohio.
Page 15/17

• K
_ 9 _
A
Tallwood Estates WRF 1y- .
(2/ (0.05mgd) ®.._._ 'a
`
r
,� Grassy Branch WRF f,
160 f01de Sycamore WRF (Existing 0.05 mgd; Proposed 0.12 mgd)
_._.,. (0.15 mgd) ®
t
olk
la Ilk /1 t , \•
\ioit
IIP
/ 0
"-- I 1111104*
Crooked Creek WRF *f
1(1.9 mgd) N '
1 -\ ,111‘ ,
// f /
;85vow /' S,
i 0
11104'‘ II
1;lc-41*
otlPooli436\4tat:/fr.fc:llklhik.latllIllIllift
City of Monroe WWTP
(10.4 mgd)
0 Al
Twelvemile Creek WRFi
(7.5 mgd) ;
Legend
Q Existing Water Reclamation Facility Property 1 1 Union County Boundary
"`.t Sanitary Sewer Pipe Primary Road
C ) 5-Mile Radius of Grassy Branch t Major Waterway
MI Grassy Branch Parcel Major Waterbody
Grassy Branch WRF Sewershed
N
Figure 3-1: UCPW Existing Facilities Service Area
w
-4fr...E
Grassy Branch WRF Major NPDES Modification
Union County, NC
1 inch equals 5 miles Jo N ,e<,ti
Miles Hazen
0 2.5 5 10 „,.*°••

Cabarrus County _, _
Mecklenburg — — Stanly County
•
County ♦
4 I triti I I III I Ilik
/ 41644/ ♦
Union /
County / 0 •
/ i� lNk* •
/
A ?f::7 41Ikk ‘
/ 4C) PD' Grassy Branch WRF Ihrl
cV `
/ 1
,1,,%,
ir CI:4A\
Cg,
.A.I"lL0
l;v0i ai li4= ;
1
c
i0 tI
N1
, cp ,
� o
11
c ,
0 ,
zt,„:„ 4(, 4i /
♦cp g ei /
d '''''' '''''g'''':: :::•
r_,..,-,_./
, 0
.... u
19, L I
Legend
us Selected Parcel g
'
17 Parcels-40+acres with no structure
- Grassy Branch WRF
Illlll O Grassy Branch WRF Sewershed
r_, 5-Mile Radius of Grassy Branch
-\_-)
Major Waterway )
(TJ County Boundary (/
n
Figure 3-2: Location of Potential Land Application Sites
W Grassy Branch WRF Major NPDES Modification
Union County, NC
1 inch equals 1 mile
M ,,
Hazen
Miles
0 0.5 1 2 - -

Hazen
Attachment A: Design, Capital Cost, and
Operation and Maintenance Cost Calculations for
Land Application Alternative

Land Application Calculations for 0.07 mgd Plant Flow
DESIGN FLOWRATE: 0.070 mgd Note:Proposed Grassy Branch design maximum month flow from 0.05 mgd to 0.12 mgd
LAND REQUIRED:
Area for Average Daily Flow(A, )(Land Application)
Loading Rate: 52.0 in/ac-yr
Loading Rate: I 1.00 tin/ac-week
Land Required(Equation): Flow(mad)•365 days/yr
Loadingrate in/ac`r '27,154 gal/ac'in
Land Required: acres
Offsite Storage Pond Area Required(Asp)(Treated Water)
Storage Capacity: I 30 Idays Estimate
Storage Volume Required: 280,729 ft^3 Design Flow(mgd)'Storage Capacity(days)/7.48 gal/f03
Assume Depth for Pond: 8 feet
•
Precipitation Allowance: -1 feet
Freeboard: -2 feet
Water Depth: 5 feet
Storage Pond Area: acres Storage Volume/(Water Depth'43560 f02/ac)
Land Required for Application+Land required for Storage 19 acres
Allowance for Buffer Yards and Access Roads
Percentage of Wetted Area: 35% Based on past projects,actual parcels unknown
6.8 acres
Allowance for Circumventing Wetlands and Unusable Land Due to Topo
Percentage of Wetted Area: 25% Based on past projects,actual parcels unknown
4.8 acres
Total Land Required:
Parcel Acreage Available I 52.0 'acres Based on GIS
CAPITAL COST CALCULATIONS
Capital Cost for Land:
Total Land Required: 52 acres ATOT0L
Estimated Land Cost: IBMII=111$/acre Average land value found using GIS
Capital Cost for Land: Total Land Requirement'Estimated Land Cost
Capital Cost of Land Application System(Spray Irrigation Infrastructure):
Land required for application: 18 acres AWETTED
Estimated Cost for Spray Field: I $15,500 I Original Value
ENR Index 2000: 6221 I
ENR Index 2020: 11466
Estimated Cost for Spray Field: $29,000 Includes pipe manifolds and valves,clearing,site lighting,etc.
Cost for Spray Field:
Cost of Access Roads:
Road Width= 9 feet
Gravel Thickness= 3 inches
Road Length= 5 miles
Road Length= 26,400 feet
Road surface area= 26,400 yd02 Width'Length/9 ft"2/yd"2
Prepare sub-base= 15 $/yd"2 Estimate
3/4"Stone Base-3"thick= 7 $/yd"2 Estimate
Total Cost= 22.00 $/yd^2
Cost of Roads= Road Surface Area•Total Cost
Cost of Storage Pond:
Pond Depth= 8 feet Earthwork Volumes:Assume 1/2 depth is excavated and this material is used to create berm.
Pond Area= 1.3 acres
Clear&Grub Area= 1.3 acres Entire Pond Area
Excavation Volume= 8,318 yd"3 1/2 Total Depth'Pond Area•43560 ft^2/ac/27 ft^3/yd^3
Compaction Volume= 8,318 yd"3 1/2 Total Depth'Pond Area'43560 ft^2/ac/27 ft"3/yd03)
Clear&Grub Unit Cost=I $10,000 IS/acre Hazen estimate
$12,889
Excavation Unit Cost=I $18 I$/yd^3 Hazen estimate
= $149,722
Compaction Unit Cost=I $7.00 I$/yd^3 Hazen estimate
$58,225
Total Earthwork Cost=
Cost of Pond Liner
Storage pond volume= 280,729 ft"3
Storage pond area= 35,091 ft02
Required Liner for Pond Width and Depth= 49,303 ft"2 Add twice the depth and extra 2 feet for edges to both the length and the width
Cost of pond liner= $1.40 $/ft02 From pond liner provider websites(Firestone Pond Guard)with labor for installation,shipping,etc.
Total Liner Cost=
Cost of Pump Station at VWJTP(to Pump Land App Site)
Flow= 0.175 mgd 0.70 gpd x 2.5 PF
Sitework,subgrade,concrete= $30,000 Includes labor and installation
Mechanical= $110,000 Includes labor and installation
Electrical= $33,000 Includes labor and installation
Materials and Labor Escalation= $15,000
Contractor O&P,contingency,bonds,etc.= $50,000
New Pump Station at W WTP=
Cost of Pump Station at Land App Site
Page 1

Sdework,subgrade,concrete= $25,000 Includes labor and installation
Mechanical= $75,000 Includes labor and installation
Electrical= $22,500 Includes labor and installation
Materials and Labor Escalation= $12,000
Contractor O&P,contingency,bonds,etc.= $30,000
New pump station at land application site=
Cost of Force Main: Determine Pipeline Size&headloss(Using Hazen-Williams Eq.):
Flow= 0.175 mgd 0.07 mgd x 2.5 peak=0.175 mgd
Diameter= 4 inch One Force Main to Land Application Site
Length= 0.74 miles
Length= 3,900 feet
Hazen-Williams C=I 110 j
Velocity= 3.1 ft/s
headloss= 58 feet
Static Heads 30 Ifeet
Total Head Loss 88 feet
Total Length of Pipe= _ 3,900 feet
Cost of DIP= 48 1$/ft ($12/In-diameter foot)
Total Cost of Force Main=
Cost of Monitoring Wells:
Assume: -Need one(1)upgradient and three(3)downgradient wells at each spray field
and lagoon/storage pond site 3 Isprayfields at 6 acres per sprayfield
-Depth of well to be 20 feet
No.of wells= 15
Cost per well= $10,000
Total Monitoring system cost=
Cost of Fencing:
•
Unit Cost of Fencing= 23 $/LF installed
Length of Fence= 6,000 feet Estimate based o n acres
Cost of Fence= $138,000
ANNUAL O&M COSTS:
Spray Head Replacement
Anor= 788,209 ff2
Radius of Spray=I 25 Ifeet Based on past projects
• Area of Spray= 1963 ft2
#of heads= 410 spray heads
Percent per year replacement=I 10% Based on past projects
• Replacement per year= 41 spray heads
Cost per spray head= ®'
Annual Replacement cost=
Control Valve Replacement
Control Valves per acre= 2 valves/acre Based on past projects
Unit cost for control valve= 500 $/valve Based on past projects
Control valve replacement interval= 0.2 years Based on past projects
Annual Replacement cost=
Spray Head and Control Valve Labor Costs
Labor per hour= $/hr Based on past projects
Labor per year= ®' hours Based on past projects;52 hour for 3x the heads
Annual Labor= $/year
Lawn Mowing
Labor= 1.5 hrs/acre
Labor per hour= 32 $/hr
Cost per acre mowing= 48 5/acre
No.of times mowed per year= 0 times/yr Once per week warm months,twice monthly colder months
Mowing Cost= $yr
Pump Station at WWTP
Peak Flow= 0.175 mgd Assume equalization,peaking factor of 2.5
Pipe Diameter= 4 inches
Force Main Length= 3,900 feet
Hazen-Willams C= 110
Velocity= 3.10 ft/sec
Headloss= 57.83 feet
Static head= 30 feet
Total Headloss= 87.83 feet
Midpoint Flow= 60.8 gpm Power costs based on mid-point of design flow.
Total Dynaminc Head= 88 feet
Pump Efficiency=( 65%
Pump Motor Power= 2.1 HP Total operating horsepower
Electrical Cost=I $0.070 ($/kw-h
Annual Power= 13,521 kwh/year
Power Cost=-$/year
Page 2

Pond and Pump Station Maintenance
$/gal= r r $/1,000 gal/day Power(site pump station,lights,etc.),pond inspection and
Total= maintenance(e.g.,algae control,etc.)
TOTAL ANNUAL O&M COSTS
SUMMARY-CAPITAL COSTS: SUMMARY-ANNUAL O&M COSTS:
Land Acquisition $394,000 Spray Head Replacement $1,000
Spray Field Infrastructure $525,000 Control Valve Replacement $3,620
Access Roads $581,000 Spray Head and Control Valve Labor Costs $400
Storage Pond $221,000 Lawn Mowing $38,000
Storage Pond Liner $69,000 Pump Station at WWTP $900
Pump Station at WWTP $238,000 Pond and Pump Station Maintenance $12,800
Pump Station at Land Application Site $164,500
Effluent Distribution Force Main $187,000
Monitoring Wells $150,000
Fencing $138,000
Total Cost Total Cost
Page 3

Hazen
Attachment B: Design, Capital Cost, and
Operation and Maintenance Cost Calculations for
Non-Conjunctive Reuse Alternative

Reuse Calculations for 0.07 mgd Plant Flow
'Closest Golf Course is Charlotte National Golf Club.7.5 miles away
DESIGN FLOWRATE: I 0.070 Imgd Note:Proposed Grassy Branch design maximum month flow from 0.05 mgd to 0.12 mgd
LAND REQUIRED:
Area for Average Daily Flow(Arer)(Reuse)
Loading Rate: 52.0 in/ac-yr
Loading Rate: I 1.00 Iin/ac-week
Land Required(Equation): Flow(mgd)'365 days/yr
Loadin rate in/ac'r•27,154 gal/ac'in
Land Required: acres
Offsite Storage Pond Area Required(Asp)(Treated Water)
Storage Capacity: I 5 'days 25%of design Bow plus 5-day reject storage
Storage Volume Required: 46,952 f1^3 Design Flow(mgd)•Storage Capacity(days)/7.48 gal/ft"3
Assume Depth for Pond: 6 feel
Precipitation Allowance: -1 feet
Freeboard: -2 feet
Water Depth: 3 feet
Storage Pond Area: acres Storage Volume/(Water Depth•43560 ft"2/ac)
Land Required for Application+Land required for Storage
18 acres
Allowance for Buffer Yards and Access Roads
Percentage of Wetted Area: 15% Based on past projects,actual parcels unknown
2.8 acres
Allowance for Circumventing Wetlands and Unusable Land Due to Topo
Percentage of Wetted Area: 20% Based on past projects.actual parcels unknown
3.7 acres
Total Land Required: acres
Parcel Acreage Available I 52.0 'acres Based on GIS
CAPITAL COST CALCULATIONS
Cost for Land:
Total Land Required: 52.0 acres Aroru
Estimated Land Cost: IIIMEEMI=8/acre Average land value found using GIS
Capital Cost for Land: Total Land Requirement•Estimated Land Cost
Cost of Land Application System(Spray Irrigation Infrastructure):
Land required for application: 18 acres AwET,Eo
Estimated Cost for Spray Field: I $15,500 Original Value
ENR Index 2000 6221
ENR Index 2020 11466
Estimated Cost for Spray Field $29,000 Includes pipe manifolds and valves,clearing,see lighting,etc.
Cost for Spray Field:
Cost of Access Roads:
Road Width= 9 feet
Gravel Thickness= 3 inches
Road Length= 5 miles
Road Length= 26,400 feel
Road surface area= 26,400 yd"2 Width*Length/9 ft"2/yd^2
Prepare sub-base= 15 $/yd"2 Estimate
3/4"Stone Base-3"thick= 7 $/yd"2 Estimate
Total Cost= 22.00 $/yd"2
Cost of Roads= Road Surface Area•Total Cost
Cost of Storage Pond
Pond Depth= 6 feet Earthwork Volumes:Assume 1/2 depth is excavated and this material is used to create berm.
Pond Area= 0.4 acres
Clear 8 Grub Area= 0.4 acres Entire Pond Area
Excavation Volume= 1,739 yd"3 1/2 Total Depth•Pond Area•43,560 ft^2/ac/27 ft^3/yd"3
Compaction Volume= 1,739 yd"3 1/2 Total Depth•Pond Area•43,560 ft"2/ac/27 ft"3/yd"3
Clear 8 Grub Unit Cost=I $10.000 IS/acre Hazen estimate
$3,593
Excavation Unit Cost= $18 I$/ytl^3 Hazen estimate
$31,301
Compaction Unit Cost=I $7.00 l$/yd^3 Hazen estimate
$12,173
Total Earthwork Cost=
Cost of Pond Liner
Storage pond volume= 46,952 ft"3
Storage pond area= 7,825 ft"2
Required Liner for Pond Width and Depth= 11,938 ft"2 Added 20%contingency in area to account for unknown see issues.
Cost of pond liner= $1.40 $/ft"2 From pond liner provider webshes(Firestone Pond Guard)with labor for installation,shipping,etc.
Total Liner Cost=
Cost of Pump Station at WWTP to Pump Land App Site
Flow= 0.175 mgd 0.70 gpd x 2.5 PF
Silework,subgrade,concrete= $30,000 Includes labor and installation
Mechanical= $110,000 Includes labor and installation
Electrical= $33,000 Includes labor and installation
Materials and Labor Escalation= $15,000
Contractor O8P,contingency,bonds,etc._ $50,000
New Pump Station at WWTP=
Page 1

Cost of Pump Station at Land App Site
Sitework,subgrade,concrete= $25,000 Includes labor and installation
Mechanical= $75,000 Includes labor and installation
Electrical= $22,500 Includes labor and installation
Materials and Labor Escalation= $12,000
Contractor O8P,contingency,bonds,etc.= $30,000
New pump station at land application site=
Cost of Force Main: Determine Pipeline Size 8 headloss(Using Hazen-Williams Eq.):
Flow= 0.175 mgd (0.07 mgd x 2.5 peak=0.175 mgd)
Diameter= 4 inch One Force Main to Land Application Site
Length= 0.74 miles
Length= 3,900 feet
Hazen-Williams C=I 110
Velocity= 3.1 ft/s
headloss= 58 feet
Asumed Static Head' 30 I feet
Total Head Loss 88 feet
Total Length of Pipe= 3,900 feet
Cost of DIP=I 48 J$/ft($12/in-diameter foot)
Total Cost of Force Main=
Cost of Monitoring Wells
Assume: -Need one(1)upgradient and three(3)downgradient wells at each Tay field
and lagoon/storage pond site 3 Jsprayfields at6 acres per sprayfield
-Depth of well to be 20'
No.of wells= 15
Cost per well= $10,000
Total Monitoring system cost=
Cost of Chlorine Disinfection at WWTP
Liquid Cl2 Feed Pump Quantity= 2 Duty,spare pumps
Unit Cost= $30,000
Total liquid feed pump cost= $80,000 With installation and pump enclosure
Storage Tank-NaOCI= 1 —I
Unit Cost= $50,000 JI
Storage Tank Cost= $50,000 Installed cost(concrete pad,containment,etc.)
Misc.Valves/Instruments Quantity= 1 Lump sum
Unit Cost= $20,000
Misc.Valves/Instruments cost= $20,000 Installed cost
Total Chlorination System Cost=
Cost of Fencing:
Unit Cost of Fencing= 23 H$/LF installed
Length of Fence= 6,000 feet Estimate based o n acres
Cost of Fence= $138,000
ANNUAL O&M COSTS:
Spray Head Replacement
A = 788,209 flu
Radius of Spray=I 25 Ifeet Based on past projects
Area of Spray= 1963 ttr
#of heads= 410 spray heads
Percent per year replacement=I 10% I Based on past projects
Replacement per year= 41 spray heads
Cost per spray head=
Annual Replacement cost=
Control Valve Replacement
Control Valves per acre= 2 valves/acre Based on past projects
Unit cost for control valve= 500 $/valve Based on past projects
Control valve replacement interval= 0.2 years Based on past projects
Annual Replacement cost=
Spray Head and Control Valve Labor Costs
Labor per hour= 20 $/hr Based on past projects
Labor per year= 20 hours Based on past projects;52 hour for 3x the heads
Annual Labor= $/year
Lawn Mowing
Labor 1.5 hrs/acre
Labor per hour= 32 $/hr
Cost per acre mowing= 48 $/acre
No.of times mowed per year=0 times/yr Once per week warm months,twice monthly colder months
Mowing Cost= $/yr
Pump Station at WWTP Site
Peak Flow= 0.175 mgd Assume equalization,peaking factor of 2.5
Pipe Diameter= 4 inches
Force Main Length= 3,900 feet
Hazen-Willams C= 110
Velocity= 3.1 ft/sec
Headloss= 58 feet
Static head= 30 feet
Total Headloss= 87.83 feet
Midpoint Flow= 60.8 gpm Power costs based on mid-point of design flow.
Total Dynaminc Head= 88 feet
Pump Efficiency=I 65% I
Pump Motor Power= 2.08 HP Total operating horsepower
Electrical Cost=I $0.070 I$/kw-h
Annual Power= 13,521 kwh/year
Power Cost= $/year
Page 2

Pond and Pump Station Maintenance
$/gal= $0.500 $/1,000 gal/day power(site pump station,lights,etc.),pond inspection and
Total= maintenance(e.g.,algae control,etc.)
O&M Cost for Chlorine Feed
Cl2 Dose=l 6 Ippm Max dose
Required lb/day C12= 8.78 lb/day CI With 2.5 peak
Delivered Concentration= 5.000 %
Density of NaOCI at Selected Conc.= 1.040 lb CVgal
Required gal/day as Delivered Cl:= 8 gal CI,/day
Volume Delivered at Selected Conc.=I 4,000 Igal
Concentration at End Use= 5 %
Required gal/day as Actual Cl:= 8 gal Clu/day
Days Storage=I 30 (days
Total Storage Vol.Req'd= 253 gallons
Total Storage Vol.Req'd= 4,000 gallons Based on delivery volume
Number of Tanks=I 1 I
Volume per Tank= 4,000 gallons
Tank Height=I 10 Ifeet
Tank Diameter= 7 feet
$/gal=I $0.65 Igal
Required gal/day= 8 gal Cy day
253 gal/month
3,031 gal/year
Cost per Year of Hypochlorite= $2,000 $/year
Total Chlorination O&M Cost= Divided by two to take the mid-point value for O&M cost(use 0.035 mgd instead of 0.07 mgd)
TOTAL ANNUAL O&M COSTS
SUMMARY-CAPITAL COSTS: SUMMARY-ANNUAL O&M COSTS:
Land Acquisition $394,000 Spray Head Replacement $1,000
Spray Field Infrastructure $525,000 Control Valve Replacement $3,620
Access Roads $581,000 Spray Head and Control Valve Labor Costs $400
Storage Pond $47,000 Lawn Mowing $38,000
Storage Pond Liner $17,000 Pump Station at W WTP Site $900
Pump Station at W WTP $238,000 Pond and Pump Station Maintenance $12,800
Pump Station at Land Application Site $164,500 Chlorine Disinfection $1.000
Effluent Distribution Force Main $187,000
Monitoring Wells $150,000
Chlorine Disinfection $130,000
Fencin. $138 000
Annual O&M Cost
Page 3

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

Crooked Creek QUAL2K Model
Development
Union County, North Carolina
October 15, 2019
PREPARED FOR PREPARED BY
Union County Public Works Tetra Tech
500 North Main Street, Suite 500 One Park Drive, Suite 200
Monroe, NC 28112 PO Box 14409
Research Triangle Park, NC 27709
,s
•�`• _FY -,,jf yq�
h '�. } D N S ro. •
AN --er
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•
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Pictured:North Fork Crooked Creek(Tetra Tech, 2016)
TETRA TECH

(This page was intentionally left blank.)

Crooked Creek QUAL2K Model October 15, 2019
EXECUTIVE SUMMARY
The Crooked Creek watershed in Union County, North Carolina supports three existing wastewater
treatment plants (WWTPs): 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).
c
I._._ Rocky River
----_1 Stanly
' (
North Carolina
= County
Crooked Creek
t
1 Grassy BrPanch
WWT Sil%
South Carolina
t - North Fork411%10#11fil.
/ Crooked Creek
F
Hemby Acres i
�
veo
�/ w w coked Creek#2
IV
VWYTP
�Illr. ! Grassy Branch
lik ,. % J
sr tr.... _ v.,....«.
South Fork Legend
' 111)111* 4 1
Crooked Creek
Existing WWTP Outfall
tr
•
FE! River/Stream
- Highway
Crooked Creek Watershed N o o s e 2 - Watershed Boundary
C TETRA TECH WvVTP Outfalls v Wlometers
w n `sew n n y M n o 0 5 i 2Ft G5 County Boundary
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 Model October 15, 2019
Rocky River
Grassy Branch WWTP
` crooked Creek
Hemby Acres WWTP
Crooked Creek WWTP#2. r
c
ta�
a
Gtyy�
North Fork Crooked Creek
Ctee � � Legend
.... GLOP A WWTP Discharge
f0 Large Beaver Dam
5�J
River/Stream
OWatershed Boundary
Model Reach
Reach,
arm.e Reach 2
Reach 3
neem Ree<h
Crooked Creek Watershed N 0 05 t 2
It TETRA TECH QUAL2K Model Segmentation A oKAometers Reath Reach s
MA�_w3 swr.»_haa�c«oe._r iva,lrou<<� 0 O S t 2 ..< Rea e
.aro wmaueasar.mlc.R rax. OMiles
Figure 2. Crooked Creek QUAL2K model reach segmentation
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.
'fi-I TETRA TECH ES-2

Crooked Creek QUAL2K Model October 15, 2019
1-1-1 -2 —I— -3I-—4—I- ----5---- I--- 6--- I 12
Hemby CC#2 • SFCC HWY Grassy WWTP,
WWTP WWTP confluence 601 Grassy Branch confluence
Beaver I 10
I
I I Dams
' ----Jew.a 8 orb
• E
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• YPDRBA Point Data 0 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/I
DO Saturation
Figure 3. Simulated and observed DO along Crooked Creek (calibration)
1--3.--1---2 I 3-----I— -4 I— —— 5 — --I --— —---6-- 112
Hemby CC#2 SFCC HWY Grassy WWTP,
WWTP WWTP confluence 601 Grassy Branch confluence
Beaver
I I Dams --- 1 10
1 i - --•1
_• • • 8
, --- ---1
I
• I o • c
•
OD
---' '` ��'• t9 LPaa
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Distance from outlet(miles)
• YPDRBA Point Data 0 Obs Long Data(AM) • Obs Long Data(PM)
-Simulated Mean ----Simulated Min/Max Observed Sonde Data
WQS:5.0 mg/I DO Saturation
Figure 4. Simulated and observed DO along Crooked Creek (corroboration)
®TETRA 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
foil TETRA TECH 1

Crooked Creek QUAL2K Model October 15, 2019
C.1 Stream Hydrology Measurements 43
C.2 Nutrient Sampling 44
C.3 Longitudinal Dissolved Oxygen 48
C.4 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 QUAL2K 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 QUAL2K model sensitivity test run results 33
LIST OF FIGURES
Figure 1. Crooked Creek watershed map 1
Figure 2. Crooked Creek QUAL2K 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
OTETRA TECH 2

Crooked Creek QUAL2K Model October 15, 2019
Figure 8. LSPC model extent and subbasins for the Goose and Crooked Creek watersheds 7
Figure 9. Crooked Creek QUAL2K model reach segmentation 9
Figure 10. Crooked Creek summer 2016 cross sectional surveys by Tetra Tech 10
Figure 11. Crooked Creek channel bottom width measured from summer 2016 cross sections 11
Figure 12. Crooked Creek stream discharge estimates 16
Figure 13. Simulated and site-estimated flows for Crooked Creek model extent (calibration) 27
Figure 14. Simulated and observed water temperature along Crooked Creek (calibration) 28
Figure 15. Simulated and observed DO along Crooked Creek (calibration) 29
Figure 16. Simulated and observed water temperature along Crooked Creek (corroboration) 30
Figure 17. Simulated and observed DO along Crooked Creek (corroboration) 30
Figure 18. Sensitivity test results (runs 1 and 2): bottom algae coverage and SOD rate 32
Figure 19. Sensitivity test results (runs 3, 4, and 5): Manning's n, shade, and headwater flow 32
Figure 20. Sensitivity test results (run 6): reaeration model selection 33
®TETRA TECH 3

1.0 INTRODUCTION
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.
nTETRA TECH 1

Crooked Creek QUAL2K Model October 15, 2019
1 I
North Carolina
Mecklenburg
• County Rocky River
AA Stanly
County
Crooked Creek
Ai
South Carolina
aik
Union
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- c /� North Fork
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ilit 4
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South Fork_14010.1107.-
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- Highway
. - Interstate
OWatershed Boundary
Crooked Creek Watershed N o 0.75 is I County Boundary
aTETRA TECH O141ortfe+erf
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Figure 5. Crooked Creek watershed location map
li
.Rocky River
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j North Fork Crooked Creek . etir
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,'. River/Stream
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Elevation(feet)
High 794
1111.
IIMMIRMI
Crooked Creek Watershed
N o os+ 2 Low 406
®TETRA TECH Digital Elevation Model A a----„, ',7---
Figure 6. Crooked Creek watershed elevation and reach map
[.]TETRA TECH 2

Crooked Creek QUAL2K Model October 15, 2019
2.0 SUMMARY OF AVAILABLE DATA
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.
®TETRA TECH 3

Crooked Creek QUAL2K Model October 15, 2019
soar. Rocky River
.i Stanly
County
'y Crooked Creek
Grassy Branch 08388900
North Fork WWTP(NC0085812) @ SR 1601
lltiP I I lit
'‘ Crooked Creek .84J\ 4Ø8
„......7...„... ...,,,40.
Grassy Branch
%is
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South Fork
Crooked Creek Legend
I.
WWTP Discharge Site
",, A Coalition Chemistry Station
\1,� River/Stream
Crooked Creek Watershed N 0 0 5 , 2 Watershed Boundary
®TETRA TECH Coalition Water Quality Sampling k vK4om.t°"
0 0.5 1 2 County Boundary
V.C.. ..e.la'wJ• r mow r4� root .........Mass
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. BODE, 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.
®TETRA TECH 4

Crooked Creek QUAL2K Model October 15, 2019
Table 1. Existing permit limits for the wastewater treatment plants located along Crooked Creek.
Permitted Allowable Flows and Concentrations (Summer)
NPDES ID Facility Name
Flow (MGD) BOD5(mg/I) NH3-N (mg/I) DO (mg/I) TSS (mg/I)
NC0035041 Hemby Acres 0.3 9.0 3.0 >_ 5.0 30.0
NC0069841 Crooked 1.9 5.0 2.0 >_ 6.0 30.0
Creek#2
NC0085812 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 isassociated with groundwater remediation and has a maximum allowable discharge of 0.09
er i9
P
MGD. This discharge is not simulated directly in the Crooked Creek QUAL2K 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
2013 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).
®TETRA TECH 5

Crooked Creek QUAL2K Model October 15, 2019
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.
®TETRA TECH 6

Crooked Creek QUAL2K Model October 15, 2019
ietik'
'--'- '- ''' ' ilt-APOik. 7' -A
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V, Q LSPC Model Subbasin
\ =Crooked Creek Watershed
Crooked Creek Watershed N o o s, 2 IIIIGoose Creek Watershed
O TE1MATECH LSPC Model Extent vxe«nn : County
A o o e z Boundary
Figure 8. LSPC model extent and subbasins for the Goose and Crooked Creek watersheds
0 TETRA TECH 7

Crooked Creek QUAL2K Model October 15, 2019
3.0 QUAL2K MODEL SETUP
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: QUAL2K version 2.12b1. 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).
3.2 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 bycomparing the simulated and observed results
p 9 p P 9
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 significant hydrologic differences than
downstream of the dams, reflected in channel geometry, flow velocity, and observed DO concentrations.
QTETRA 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
Reach Upstream Downstream
Reach Description Length, Elevation, Elevation,
mi (km) ft (m) ft(m)
1 Headwaters to Hemby Bridge WWTP 0.88 (1.42) 623 (190) 617 (188)
2 Hemby Bridge WWTP to Crooked Creek#2 2.80 (4.50) 617 (188) 587 (179)
WWTP
3 Crooked Creek#2 WWTP to South Fork 3.75 (6.03) 587 (179) 558 (170)
Crooked Creek (SFCC) confluence
4 South Fork Crooked Creek (SFCC)to end of 1.61 (2.59) 558 (170) 551 (168)
two large beaver dams
5 End of beaver dams, crossing Highway 601, to 5.21 (8.39) 551 (168) 502 (153)
Grassy Branch WWTP
6 Grassy Branch WWTP to Rocky River 6.72 (10.82) 502 (153) 410 (125)
Rocky River
Crooked Creek
Grassy Branch WWTP
Hemby WWTP
Northh Fork Crooked Creek.
Crooked Creek WWTP#2
Grassy Branch
•
Legend
• WWTP Discharge
Large Beaver Dam
South Fork Crooked Creek River Stream
QWatershed Boundary
Model Reach
Crooked Creek Watershed N e 05 r 2
®TETRA TECH QUAL2K Model Segmentation .=.K10Tttef* -{L
0 os t 2 „s
r.o rawww�.ew MO.�^ owks
Figure 9. Crooked Creek QUAL2K model reach segmentation
®TETRA TECH 9

Crooked Creek QUAL2K Model October 15, 2019
3.4 REACH HYDRAULICS
Stream hydraulics were simulated using the Manning's Formula method within QUAL2K. 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.
,`Rocky River
M� f
r, Crooked Creek
, Aolie,01#
North Fork Crooked Creek,
0 Grassy Branch <
/
"'" -- Legend
e.
Cross Section Site
South Fork Crooked Creek River/Stream
OWatershed Boundary
\. Model Reach
.....� Reach 1
�.•..Reach 2
aS Reach I
-Reach.
Crooked Creek Watershed N o 05 1 2 ..... .Reach 5
®TETRA TECH 2016 Survey Cross Sections OKnometers
0 0.5 1 2 Reach 6
Figure 10. Crooked Creek summer 2016 cross sectional surveys by Tetra Tech
®TETRA TECH 1 0

Crooked Creek QUAL2K Model October 15, 2019
30
y=0.9833x+1.764
R2=0.7034
a 25 •
• •
20 •!• •Reach 1(no data)
ro
• •..••" •Reach 2(5 sites)
0 15
• •Reach 3(3 sites)
o • •
m a 10 •Reach 4(No Data)
• • •
c 0 •Reach 5 6 sites)
to
5
I •Reach 6(6 sites)
Z
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 Location Shorthand Channel Manning's Bottom Width, Side
Bed Slope n ft(m) Slopes
1 HW to Hemby WWTP 0.0014 0.1 2.17 (0.66) 4.37
2 Hemby WWTP to CC#2 WWTP 0.0010 0.1 4.00 (1.22) 4.71
3 CC#2 WWTP to SFCC 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) 6.51
6 Grassy WWTP to outlet 0.0020 0.1 19.11 (5.83) 7.55
®TETRA TECH 11

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 °F (28.4 °C)with a daily range between minimum and maximum air temperatures of
15.95 °F (8.86 °C). Average air temperature as developed for model corroboration was 86.0 °F (24.6 °C)
with a daily range between minimum and maximum air temperatures of 18.0 °F (10.0 °C).
Table 4. Meteorological inputs data source summary
Parameter Processing Note
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.
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Crooked Creek QUAL2K Model October 15, 2019
Table 5. Hourly inputs for air temperature, dew point temperature, and cloud cover
Calibration Model Corroboration Model
Hour Air Temp Dew Point Cloud Air Temp Dew Point Cloud
(°F) Temp (°F) Cover(%) (°F) Temp (°F) Cover(%)
1 78.75 68.42 0.00% 72.67 66.00 0.00%
2 77.75 67.90 0.00% 71.33 65.00 0.00%
3 76.81 68.13 0.00% 70.17 64.17 0.00%
4 76.20 68.00 0.00% 69.33 64.00 41.67%
5 75.56 68.00 0.00% 69.00 63.50 45.83%
6 74.90 68.00 0.00% 68.00 63.00 50.00%
7 74.30 67.50 0.00% 68.00 63.00 93.75%
8 77.60 70.80 0.00% 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
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 QUAL2K 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
Parameter(units) Model Input Note
Light Parameters
Photosynthetically Available Radiation 0.47 Light parameters initialized based on
Background light extinction (/m) 0.2 QUAL2K example file.
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 QUAL2K
Atmospheric turbidity coefficient 2 Default value suggested by QUAL2K
Manual
Atmospheric longwave emissivity model Brutsaert This equation tends to allow for warmer
water temperatures to be achieved
Wind speed function for evaporation and Brady- Default wind speed function for QUAL2K
air convention Graves-Geyer
Sediment Heat Parameters
Sediment thermal thickness (cm) 20 Model default suggestions from QUAL2K
Sediment thermal diffusivity (cm2/s) 0.005 manual. Default suggestion for sediment
thermal thickness of 10 cm was modified
Sediment density(g/cm3) 1.6 to 20 cm given the observed presence of
Sediment heat capacity(cal/g °C) 0.4 thicker sediment along the channel.
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Crooked Creek QUAL2K Model October 15, 2019
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 QUAL2K 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 (CBODultimate)for simulation in QUAL2K in order
to approximate the slow or fast CBOD concentration after some fifty days of decomposition. For slow
CBODuitimate simulation in the model the Phelps equation below may be employed, as detailed in the
QUAL2K manual (Chapra et al., 2012):
CBOD5
slow CBODuitimate =
1 —e(-k1x5)
Note that for the equation above, ki is the rate of oxidation for CBOD which the QUAL2K manual
suggests can range from 0.05—0.3/d. For slow CBODuitimate in the model, 0.05/d will be used, and for
fast CBODuitimate, 0.3/d will be used in the model environment.
As mentioned above, WWTP effluent was modeled as fast CBODuitimate, 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 BOD5
In summary, boundary conditions for headwaters and tributaries were simulated as slow CBOD pools
estimated based on in-stream CBOD5 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:CBODultimate.
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
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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 distancc a crude 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
•
6 y=0.1713x+1.2151
R2=0.8221
u 5
•Reach 1(No Data)
s 4 • . •Reach 2(2 sites)
•Reach 3(2 sites)
0 •
3 • •Reach 4(No Data)
E y .• • •Reach 5(3 sites)
•v
"' 2 •.••.j •Reach 6(1 site)
1 •Outliers(Reach 3,6)
•
0
0 5 10 15 20
Distance from headwaters (miles)
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)
USGS gage Minimum Maximum Average Flow on Flow on Flow on
Flow, 2016 Flow, 2016 Flow, 2016 8/16/2016 8/31/2016 8/14/2016
0212467451 0.38 98.44 4.46 0.61 0.38 0.48
0212467595 0.62 158.78 7.01 0.94 0.78 0.79
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 cms).
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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 CBODuitimate 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/I), 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:
CBODS
CBODuitimate =
1 —e(—k,x5)
mg
mg
• slow CBOD at headwaters = 1 —e(_005/d)xs) = 4.52 I
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Crooked Creek QUAL2K Model October 15, 2019
Table 8. Headwater water quality initial model inputs (calibration model)
Parameter Model Input 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 Hemby WWTP samples on
8/18/16 (4.43 mg/I) and 8/30/16 (4.32 mg/I)
Slow CBOD (mg/L) 4.52 Refractory pool of CBOD calculated based on instream
Fast CBOD (mg/L) 0 CBODS measurements from WQ Grab Site#1 on Trips
1 and
Organic Nitrogen (pg/L) 508 Calculated as the difference between Trip 1 and Trip 2
observed TKN and NH3 for WQ Grab Site#1; non-
detects set to half of the detection limit.
NH4-Nitrogen (pg/L) 25 Ammonia was not detected in the headwaters from WQ
Grab Site#1 from Trips 1 and 2, therefore the
headwaters were set to half of the detection limit.
NO3-Nitrogen (pg/L) 280 Average of observed NOX at WQ Grab Site#1, Trips 1
and 2.
Inorganic Phosphorus (pg/L) 95 Observed PO4 from WQ Grab Site#1 was used from
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 BOD5:CBODuItimate.When DMR-reported concentrations for any given parameter were listed as
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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)
Parameter Hemby Acres Crooked Creek Grassy Branch
WWTP #2 WWTP' WWTP
Discharge Information
NPDES Permit ID NC0035041 NC0069841 NC0085812
Permit Class Minor Major Minor
NPDES Permitted Flow(MGD) 0.3 1.9 0.05
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] 0.0018 [0.04]
Water Temperature (°F) 78.1 79.9 78.3
Dissolved Oxygen (mg/L) 6.5 7.6 7.7
Slow CBOD (mg/L) 0 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)
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 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 CBODuibmate 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
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)
Hemby Acres Crooked Creek Grassy Branch
Parameter WWTP #2 WWTP1 WWTP
Model Inputs based on DMR Data (September 2016 Averages)
Location (km), distance from outlet 32.48 27.81 10.82
Inflow(m3/s), [MGD] 0.0039 [0.09] 0.0381 [0.87] 0.0018 [0.04]
Water Temperature (°F) 75.6 75.6 76.3
Dissolved Oxygen (mg/L) 6.8 8.0 7.6
Slow CBOD (mg/L) 0 0 0
Fast CBOD2 (mg/L) 11.80 4.08 2.00
Inorganic Suspended Solids 1.25 4.71 1.27
(mg/L)
Ammonia Nitrogen (pgN/L) 50.00 57.06 255.56
pH 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 CBODultimate 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 PO4
5Alkalinity 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
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
CBODuuimateand estimated the same way as the headwaters.
Table 12. Tributary flow and water quality inputs (calibration model)
Grassy
Parameter SFCC Branch Data Source Information
Inflow, ft3/s (m3/s) 1.06 0.32 Estimated by water balance as the difference between
(0.03) (0.009) instream flow estimates which are not accounted for by point
source flows.
Water Temperature, (°F) 81.86 74.48 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.
Conductivity(pmhos) 252 252 No available data, assumed same as headwaters
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/I) 100 100 No available data, assume model default
Phytoplankton (ug/I) 0 0 No available data, assumed zero
pH 7.35 6.23 pH estimates are based on probe sampling conducted on
Trip 1 for SFCC and Grassy Branch.
Slow CBOD (mg/L) 4.52 23.73 Average measured CBOD5 from Trips 1 and 2 was used to
Fast CBOD (mg/L) 0 0 approximate slow CBOD as described in the text. Observed
CBOD5 along Grassy Branch was noticeably high.
Ammonia N (pgN/L) 478 25 NH3 and NOX data are averages of observed data from
Organic N (pgN/L) 1,073 435 Trips 1 and 2 at WQ Site#9 (SFCC) and WQ Site#13
(Grassy Branch). Organic N was calculated as the
Nitrate+Nitrite N (pgN/L) 2,865 1,600 difference between observed TKN and NH3 data.
Organic P (pgP/L) 380 98 Organic P was calculated as the difference between
Inorganic P (pgP/L) 245 72 observed TP and PO4 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)
Grassy
Parameter SFCC Branch Data Source Information
Inflow, ft3/s (m3/s) 1.06 0.32 Estimated to be the same as during the calibration period.
(0.03) (0.009)
Water Temperature (°F) 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/I) 100 100 No available data, assume model default
Phytoplankton (ug/I) 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
Organic N (pgN/L) 630 705 Site#9 (SFCC) and WQ 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
Inorganic P (pgP/L) 92 72 observed TP and PO4 from Trip 3.
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
23
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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/I. 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
Bottom Algae Coverage
Reach
Calibration Corroboration
1 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.
0
TETRA TECH 24

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.
nTETRA TECH 25

Crooked Creek QUAL2K Model October 15, 2019
4.0 MODEL CALIBRATION AND CORROBORATION
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 cms) respectively.
TETRA TECH 26

Crooked Creek QUAL2K Model October 15, 2019
SFCC HWY 4.5
confluence 601 •
I CC#2 4.0
WWTP • j
3.5
3.0
Hemby • •
Grassy WWTP,W ;n
WTP • Grassy Branch confluence 2.52.0 0
I •
• L_
• 1.5
J
1.0
0.5
0.0
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.
®TETRA TECH 27

Crooked Creek QUAL2K Model October 15, 2019
1-1 I-------2---____I- 3-- -I--4--I 5— -- -- --I 6— — -- --
90
•
LI 1 70
Beaver HWY 60 A,Dams 601
50
Hemby CC#2 SFCC Grassy WWTP. 40 E
WWTP WWTP confluence Grassy Branch confluence
30 01
m
20
10
0
20 15 10 5 0
Distance from outlet(miles)
Simulated Mean Temp ---- Simulated Min/Max Temp Observed Sonde Data
• YPDRBA Point Data 0 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
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
®TETRA TECH 28

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.
I-1--I-----2 I ---3 I---4-_—I--- — -5 - -- -I- - __ _-6 _ _-I 12
Hemby CC#2 • SFCC HWY Grassy WWTP.
WWTP WWTP confluence 601 Grassy Branch confluence
Beaver 10
1 I Dams I
• E
-------• r ° •• •• • c
' `s • • ••/ . ----------i - -� • d ° • • to
, • • •
'
i' e ' • • � G 0• °---' O • i_ • v
_
` __ 2
,--, yam ,
o,
0
20 15 10 5 0
Distance from outlet(miles)
• YPDRBA Point Data 0 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 -W05:5.0 mg/I
DO Saturation
Figure 15. Simulated and observed DO along Crooked Creek (calibration)
4.4 MODEL CORROBORATION RESULTS
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.
®TETRA TECH 29

Crooked Creek QUAL2K Model October 15, 2019
I--1--1 -2 I----3-------I-----4 I— — ——5---------I 6 I
90
80
tr.
60 w
Beaver HWY 50
Dams 601 •
40 6
F
Hemby CC#2 SFCC Grassy WWTP, 30
WTP WTP confluence Grassy Branch confluence 3
W W
20
10
0
20 15 10 5 0
Distance from outlet(miles)
Simulated Mean Temp ---- Simulated Min/Max Temp -Observed Sonde Data
• YPDRBA Pant Data 0 Obs Long data(AM) • Obs long data(PM)
Figure 16. Simulated and observed water temperature along Crooked Creek (corroboration)
4.4.2 Water Quality Corroboration
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.
I—1—I-------2 I 3— —I--4--I------------5 — I—---_ — —6---------I
Hemby CC#2 SFCC HWY Grassy WWTP. 12
WWTP WWTP confluence 601 Grassy Branch confluence
Beaver
Dams I 10
i' aa. _------. • s
a i
• / ):‘..42.,Th "c"
r B r
• ` • 1 a
a O
2
aas
0
20 15 10 5 0
Distance from outlet(miles)
• YPDRBA Point Data 0 Obs Long Data(AM) • Obs Long Data(PM)
-Simulated Mean ----Simulated Min/Max Observed Sonde Data
WQS:5.0 mg/I ----DO Saturation
Figure 17. Simulated and observed DO along Crooked Creek (corroboration)
®TETRA TECH 30

Crooked Creek QUAL2K Model October 15, 2019
5.0 MODEL SENSITIVITY
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
Model Run Details
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 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 QUAL2K
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 Thackston-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
I-1-I 2 I 3 I-4--1 5 I— 6 —I 8
Hemby CC#2 SFCC HWY GrassyWWTP.
WTP 1
W P confluence 601 Grassy Branch confluence 7 "Q
iBeaver
Dams _ ''' S
t \ . -- - --- 5 >
' , ---
0
\ / , , .-
` 4 la
•\ f \ \ I I ,��
\ ` '% `� III/ o
\ +/ 3
♦`. - ``\ III/ H
... \ `..III 2 0
• \ l! C
\ `,, ffl
\\ / 1 '3)
2
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 I 3 I-4—I 5 I— -6 —I 8
Hemby CC#2 SFCC HWY Grassy WWTP.
WWT• P P confluence 601 Grassy Branch confluence 7 `a
Beaver
°a 1 __
r"1-1 _ 6 C
11 ,.ww.zs�.,l
:._:�sa... it��-"'M:'► 5 A
tt��r e . 4
.� ,_' \ ,` I I Q I/ 2
/ C
\-./ ra
1 fu
2
0
20 15 10 5 0
Distance from outlet(miles)
Calibrated Model ---- Sensitivity 3:Manning's n
---- Sensitivity 4:Shade Sensitivity 5:Headwater Flow
Figure 19. Sensitivity test results (runs 3, 4, and 5): Manning's n, shade, and headwater flow
®TETRA TECH 32

Crooked Creek QUAL2K Model October 15, 2019
I-1-I 2 I 3 1-4—I 5 I— 6 —1 8
Hemby CC#2 SFCC HWY GrassyWWTP. _ 7
WWTP P confluence Gr .Vic r.&lance- 45
�� _ Beaver ��, ��' • E
n � �__�!':;-- '-_-� Dams / 6
. 1 r-I-1 i 0)
r r
1 2 6
t @
• r 1 (i)
0
20 15 10 5 0
Distance from outlet(miles)
Calibrated Model(Tsivoglou-Neal) --- - Sensitivity 6a:O'Connor Dobbins
- - -- Sensitivity 6b:Churchill ---- Sensitivity 6c:Owens 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
Model Run Details Difference in Mean DO Relative Percent
(mg/I) 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%
Sensitivity 6 Reaeration Model Variations 1.1 24%
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.
®TETRA TECH 33

Crooked Creek QUAL2K Model October 15, 2019
6.0 REFERENCES
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.
1 1 TETRA TECH 34

Crooked Creek QUAL2K Model October 15, 2019
APPENDIX A: PERMITTED POINT SOURCE DATA
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)
Flow Temp BOD5 NH3 TSS DO COD TN TP Hardness Alkalinity
Date (MGD) (°F) pH (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I)
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
8/8/16 0.89 79.7 7.3 <2 3.3 <2.5 7.6
8/9/16 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
8/14/16 0.75
8/15/16 0.79 82.0 7.5 2.9 <.1 2.5 7.7
8/16/16 0.82 81.5 7.6 <2 <.1 <2.5 7.9
8/17/16 0.80 81.1 7.5 <2 <.1 <2.5 8.0 85
8/18/16 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
8/23/16 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
®TETRA TECH 35

Crooked Creek QUAL2K Model October 15, 2019
Date Flow Temp H BOD5 NH3 TSS DO COD TN TP Hardness Alkalinity
(MGD) (°F) p (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I)
8/27/16 0.81
8/28/16 0.94
8/29/16 0.90 79.0 7.1 2.5 <.1 4.3 80
8/30/16 0.81 78.8 7.1 <2 <.1 2.7 8.0
8/31/16 0.77 80.1 7.1 <2 <.1 <2.6 7.9 38
9/1/16 0.78 78.4 7.2 <2 <.1 <2.5 8.0
9/2/16 0.86 80.6 6.8 7.8
9/3/16 1.85
9/4/16 0.91
9/5/16 0.75 77.0 6.9 7.3
9/6/16 0.79 76.1 7.3 <2 <.1 <2.5 8.2
1 9/7/16 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
9/15/16 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
9/19/16 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
9/30/16 0.87 77.0 7.3 <2 <.1 <2.5 7.7
®TETRA TECH 36

Crooked Creek QUAL2K Model October 15, 2019
Table A-2. DMR data from August and September 2016: Grassy Branch VWVTP (NC0085812)
Flow Temp GODS NH3 TSS DO COD Alkalinity
Date (MGD) (°F) pH (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I)
8/1/16 0.01 80.6 7.1
8/2/16 0.05 75.2 7.3 2.4 0.32 2.7 7.75 30 59
8/3/16 0.03 75.2 7.1
8/4/16 0.03 77.0 7.5
8/5/16 0.02 77.0 7.5
8/6/16 0.32
8/7/16 0.02
8/8/16 0.07 77.0 7.8
8/9/16 0.11 77.0 7.8
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
8/12/16 0.03 78.8 7.7
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 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
®TETRA TECH 37

Crooked Creek QUAL2K Model October 15, 2019
Flow Temp BOD5 NH3 TSS DO COD Alkalinity
Date (MGD) (°F) pH (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I)
8/30/16 0.03 77.0 6.9 3.4 3.3 5.6 7.88
8/31/16 0.03 77.0 6.6
9/1/16 0.04 78.8 6.9 <2 1.2 <2.5 7.52 59
9/2/16 0.03 78.8 7.1
9/3/16 0.10
9/4/16 0.03
9/5/16 0.02 77.0 7.4
9/6/16 0.04 78.8 7.4
9/7/16 0.03 77.0 6.8 <2 <.1 <2.6 7.98 74
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
9/14/16 0.03 77.0 6.6 <2 0.46 <2.5 7.16 62
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
Flow Temp BOD5 NH3 TSS DO COD Alkalinity
Date (MGD) (°F) pH (mg/I) (mg/I) (mg/I) (mg/I) (mg/I) (mg/I)
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)
Flow Temp BOD5 NH3 TSS DO
Date
(MGD) (°F) p (mg/I) (mg/I) (mg/I) (mg/I)
8/1/16 0.06 80.4 7.0 6.72
8/2/16 0.08
8/3/16 0.09 79.0 7.3 2.3 <0.1 <2.5 7.38
8/4/16 0.09
8/5/16 0.08
8/6/16 0.13
8/7/16 0.08
8/8/16 0.07
8/9/16 0.10
8/10/16 0.10 79.5 8.0
8/11/16 0.10 78.6 7.6 4.6 <0.1 <2.5 6.73
8/12/16 0.09
8/13/16 0.10
8/14/16 0.10
8/15/16 0.06
8/16/16 0.09 76.8 6.8 5.84
8/17/16 0.09
8/18/16 0.08 80.2 7.7 <2 <0.1 <2.5 6.5
8/19/16 0.10
8/20/16 0.08
8/21/16 0.09
8/22/16 0.12
8/23/16 0.07 76.3 7.8 5.31
8/24/16 0.09
TETRA TECH 39
1

Crooked Creek QUAL2K Model October 15, 2019
Flow Temp BOD5 NH3 TSS DO
Date (MGD) (°F) pH (mg/I) (mg/I) (mg/I) (mg/I)
8/25/16 0.07 75.6 7.3 <2 <0.1 <2.5 6.65
8/26/16 0.09
8/27/16 0.14
8/28/16 0.06
8/29/16 0.09
8/30/16 0.09 75.6 8.1 12 <0.1 <2.5 6.62
8/31/16 0.11
9/1/16 0.07 76.8 7.6 6.2
9/2/16 0.10
9/3/16 0.18
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 0.09
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

QUAL2K Model October 15, 2019
Crooked Creek
Flow Temp BOD5 NH3 TSS DO
Date (MGD) (°F) pH (mg/I) (mg/I) (mg/I) (mg/I)
9/24/16 0.08
9/25/16 0.08
9/26/16 0.08
9/27/16 0.04 75.7 7.1 7.33
9/28/16 0.20 75.4 7.2 4.5 <0.1 <2.5 7.12
9/29/16 0.07
9/30/16 0.09
Table A-4. Instream DMR water quality data upstream and downstream of Hemby Acres WWTP,August
and September 2016
Temperature (°F) Dissolved Oxygen (mg/I)
Date
Upstream Downstream Upstream Downstream
8/3/16 74.8 75.4 4.72 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
9/28/16 68.2 69.8 4.22 4.98
TETRA TECH 41

Crooked Creek QUAL2K Model October 15, 2019
APPENDIX B: YPDRBA COALITION DATA
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
Sampling Site
Parameter Date* Q8386000 (NFCC Q8386200 (NFCC Q8388000 (CC
at SR 1520) at SR1514) at NC 218)
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/I) 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/I)
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/I)
9/13/2016 No Data No Data 0.08
TKN as N (mg/I) 9/13/2016 No Data No Data 0.8
8/9/2016 No Data No Data 1.74
NOX as N (mg/I)
9/13/2016 No Data No Data 2.49
TP (mg/I) 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
0
TETRA TECH 42

Crooked Creek QUAL2K Model October 15, 2019
APPENDIX C: TETRA TECH 2016 SAMPLING DATA
C.1 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
Distance from Sample Point Width (ft) Velocity Maximum Site-Estimated
Headwaters (km) ID (ft/s) Depth (ft) Flow(cfs)
2.21 8 16 No Data 1.1 No Data
2.92 13 13 0.30 0.5 1.54
5.15 26 18 0.15 0.9 1.63
5.58 33 10 No Data 0.6 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
23.33 119 38 No Data 1.1 No Data
25.28 160 38.5 0.18 1.0 4.11
26.34 120 28.5 No Data 1.1 No Data
27.59 121 26.5 No Data 1.2 No Data
27.79 122 30 No Data 1.8 No Data
29.23 182 35 0.03 1.1 0.84
-1 TETRA TECH 43

Crooked Creek QUAL2K Model October 15, 2019
C.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 (BOD5), 5-day
carbonaceous biochemical oxygen demand (CBOD5), 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).
ra
13 14 15
a - 12 tkillit4
.. ,
2 :
4,,,
, okisr i 3 4
5 6 7 8
s
'Note:Site 9 was sampled further upstream 1
�'�F ion South Fork Crooked Creek during the €
- I second and third samping efforts i
e...„, „Iliki°.
Legend
1
, ..„ , • Grab Sample Site
• WWTP Discharge
9
Crooked Creek Watershed N 0 0.5 1 2 NHD HiRes Flowline
®TETRA TECH Water Quality Grab Samples �Ki1OrnE0"rs
NA D'OWsue. Fl� <.w A 0 0.5 1 2 Watershed Boundary
.1,M.,.ma.+e w w�.cw Mlles
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/I)
BODE CBOD5
ID Location Note
1 2 3 1 2 3
1 US of Hemby discharge 1.40* 1.20* 4.10 1.10* 1.20* 0.60*
2 Hemby WWTP discharge 0.70* 2.60 1.40* 0.70* 3.20 2.10
3 Indian Trail Fairview Rd 1.30* 2.00* 1.50* 0.80* 1.60* 1.60*
4 Crooked Creek#2 discharge 1.50* 0.70* 2.20 0.80* 0.50* 1.50*
5 US of CC#2 WWTP discharge 1.50* 1.30* 1.40* 1.00* 1.20* 1.90*
6 Old Farm Bridge crossing 1.60* 1.00* 0.90* 1.40* 0.60* 0.30*
7 DS 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 9.00 8.10 0.90* 3.00 7.50 1.10*
14 Hwy 218 crossing 1.10* 0.60* 0.90* 0.00* 0.80* 0.60*
15 US of Brief Rd 1.00* 0.70* 1.10* 0.50* 0.70* 0.40*
*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
TETRA TECH 45

Crooked Creek QUAL2K Model October 15, 2019
Table C-3. Nitrogen species results (units mg/I)
Location NH3-N NO2+NO3-N TKN TN
ID Note
1 2 3 1 2 3 1 2 3 1 2 3
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
VWVfP
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 0.00* 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 mg/I.
OTETRA TECH 46

Crooked Creek QUAL2K Model October 15, 2019
Table C-4. Phosphorus species results (units mg/I)
PO4-P TP
ID Location Note
1 2 3 1 2 3
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 2.10 0.50 0.47 0.47 0.57
4 Crooked Creek#2 discharge 2.90 4.60 4.80 2.50 4.80 6.10
5 US of CC#2 WWTP discharge 0.31 1.10 0.16 0.24 0.23 0.36
6 Old Farm Bridge crossing 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 SF Crooked Creek 0.34 0.15 0.09 1.10 0.15 0.19
10 DS 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 PO4-P:0.050 mg/I, TP: 0.050 mg/I.
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.
?Ifiti
/�
.
_ ""-) ail
\ --, '''.'", 4
‘711--'
'''' P µ .Y� : 11.6 rl
46 r°, .. ,.....,. .
.... g .M-- Legend
• WWT'P Discharge
V A Large Beaver Dam
NHD HiRes Flowline
it t Watershed Boundary
I DO(mg/L)
, . <4.0
4.0-5.0
Crooked Creek Watershed • 5.0
I")TETRA TECH Longitudinal DO Sampling(8/15-8/19) N o o.50Kilometers
WO,..,vsy.. es..i . e Ca*r� e r A o os t z No Data
6.26/6.aauaom,w iF612*mF. Mites
Figure C-2. Instream longitudinal dissolved oxygen measurements (8/15/16-8/19/16)
®TETRA TECH 48

Crooked Creek QUAL2K Model October 15, 2019
,i
/
_ ,.,....,A
P , „ ,
,..... \ ..
()) '
, �
0 _._
Legend
WWTP Discharge
A Large Beaver Dam
---- NHD HiRes Flowline
QWatershed Boundary
DO(mg/L)
\ • <4.0
4 4.0-5.0
11 Crooked Creek Watershed N 0 0.5 1 2 • >5.0
NE]TETRA TECH Longitudinal DO Sampling(8/31-9/2) A OK0ometers
J F�,s �� 0 0.5 1 z No Data
n:w, �,,.:cs+>m�e,7-"''-' 0msMiles
Figure C-3. Instream longitudinal dissolved oxygen measurements (8/31/16-9/2/16)
[lb]TETRA TECH 49

Crooked Creek QUAL2K Model October 15, 2019
1
/. Wfi
1
,..,..... 4 4 i
,....:
, ,
.....
, Ao.
....titil44., Legend
..- . WWTP Discharge
Large Beaver Dam
Y NHD HiRes Flowline
QWatershed Boundary
,:, DO(mg/L)
• <4.0
`! 4.0-5.0
( Crooked Creek Watershed N 0 05 1 2 • >5.0
`n]TETRA TECH Longitudinal DO Sampling(9/13-9/16) --Kilometers
J ��..u,s ... A 0 05 t No No Data
ri-w�m�.0 w.i�zoia,one..
Figure C-4. Instream longitudinal dissolved oxygen measurements (9/13/16-9/16/16)
[it)TETRA TECH 50

Crooked Creek QUAL2K Model October 15, 2019
Table C-5. Longitudinal data from trip 1 (August 15-19, 2016)
ID Latitude(N) Longitude(W) Date Time pH DO(mg/I) DO(%Sat) Temp(°F)
1 35.1074 80.63715 8/15 17:48 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 4.13 51.2 79.0
8 35.10617 80.6272 8/16 8:40 7.14 4.03 49.1 78.3
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 8/16 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 35.09602 80.60497 8/16 1:13 6.81 2.29 29.4 80.8
32 35.0961 80.60487 8/16 1:19 7.24 5.22 64.5 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 35.09652 80.59822 8/16 14:38 7.38 5.2 66.2 81.5
®TETRA TECH 51

Crooked Creek QUAL2K Model October 15, 2019
ID Latitude(N) Longitude(W) Date Time pH DO(mg/I) DO(%Sat) Temp(°F)
36 35.09743 80.59677 8/16 15:16 7.31 5.13 64.9 81.7
38 35.09833 80.59464 8/16 15:33 7.37 3.89 49.1 81.1
39 35.0989 80.59364 8/16 15:47 7.28 3.25 39.9 80.8
41 35.09908 80.59235 8/16 16:00 7.27 3.57 44.9 80.8
43 35.10103 80.58817 8/16 16:22 8.66 11.64 152.3 85.3
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 7.29 3.85 48.2 79.9
48 35.10303 80.57883 8/17 8:43 7.48 5.53 69.8 80.2
50 35.10158 80.57745 8/17 9:00 7.47 4.48 56.8 80.1
52 35.10235 80.57418 8/17 9:14 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 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 80.56769 8/17 10:36 7.31 4.64 58.5 80.8
60 35.10611 80.56563 8/17 10:54 7.38 3.77 46.1 79.9
61 35.10641 80.56356 8/17 11:32 7.33 3.91 48.8 79.9
62 35.1075 80.56329 8/17 11:48 7.4 4.01 50.2 79.7
63 35.10954 80.56135 8/17 12:13 7.28 5.28 65 78.6
64 35.11013 80.55966 8/17 12:28 7.41 5.13 64.4 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 Latitude(N) Longitude(W) Date Time pH DO(mg/I) DO(%Sat) Temp(°F)
74 35.11223 80.54912 8/17 14:23 7.34 3.52 45 81.5
76 35.11278 80.54745 8/17 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 35.12245 80.54194 8/18 10:59 6.95 0.82 10.2 78.4
87 35.12229 80.54069 8/18 11:21 7.04 4.43 54.5 79.0
90 35.12278 80.53825 8/18 11:38 7.12 3.64 43.2 78.1
92 35.12492 80.53868 8/18 11:57 7.07 2.78 34 77.7
94 35.12695 80.53902 8/18 12:13 7.06 3.13 38.7 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 13:02 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

1
Crooked Creek QUAL2K Model October 15, 2019
ID Latitude(N) Longitude(W) Date Time pH DO(mg/I) DO(%Sat) Temp(°F)
110 35.13382 80.51204 8/18 15:58 7.49 4.65 59 81.5
111 35.13643 80.5126 8/18 16:12 7.69 4.56 58 81.7
112 35.13899 80.51417 8/18 16:24 7.55 4.09 51.7 81.3
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 Latitude(N) Longitude (W) Date Time pH DO(mg/I) DO(%Sat) Temp(°F)
120 35.14462 80.47173 8/31 15:02 7.57 6.33 77.4 77.7
121 35.13301 80.4896 8/31 15:26 7.5 7.37 89.1 76.6
122 35.13091 80.49409 8/31 15:49 6.78 7.87 95 76.6
123 35.13112 80.49418 8/31 16:06 7.28 7.29 87.9 76.5
124 35.13121 80.49426 8/31 16:12 7.79 5.03 61.2 77.7
125 35.13803 80.50548 8/31 17:14 7.46 5.17 61.8 76.3
126 35.12832 80.53928 8/31 17:39 6.9 4.26 51.1 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 35.09506 80.60077 8/31 19:26 6.78 1.87 22.2 74.8
133 35.10788 80.61561 8/31 19:46 6.8 3 35.9 75.9
134 no data no data 8/31 20:10 7.63 8 98 78.1
135 no data no data 8/31 20:13 7.55 5.9 70.2 75.4
0 TETRA TECH 54

Crooked Creek QUAL2K Model October 15, 2019
ID Latitude(N) Longitude(W) Date Time pH DO(mg/I) DO(%Sat) Temp(°F)
136 35.13803 80.50533 9/1 8:13 7.29 4.66 55 74.1
137 35.13571 80.5023 9/1 8:30 7.42 5.59 65.4 73.9
138 35.13332 80.50132 9/1 8:42 7.33 5.79 67.8 73.6
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 35.13165 80.49204 9/1 10:14 7.28 4.65 54.6 73.9
148 35.13233 80.4902 9/1 10:26 7.34 4.96 58.7 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 35.13813 80.49062 9/1 11:00 7.45 5.52 65.3 74.7
154 35.13709 80.48772 9/1 11:20 7.63 7.24 86.2 75.4
156 35.13804 80.4855 9/1 11:36 7.6 6.72 79.5 74.7
158 35.14062 80.48538 9/1 12:00 7.54 7.43 87.6 74.5
159 35.14259 80.48672 9/1 12:09 7.44 4.66 54.8 74.1
160 35.14266 80.48602 9/1 12:18 7.42 5.99 71.3 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 80.48367 9/1 13:39 7.47 7.42 91.7 78.6
167 35.14518 80.48033 9/1 13:50 7.24 5.8 69.7 76.3
®TETRA TECH 55

Crooked Creek QUAL2K Model October 15, 2019
ID Latitude(N) Longitude(W) Date Time pH DO(mg/I) DO(%Sat) Temp(°F)
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 35.14809 80.46889 9/1 16:23 7.62 7.55 95.5 81.3
178 35.1466 80.46709 9/1 4:32 7.6 7.23 89.5 79.2
180 35.14716 80.46584 9/1 16:44 7.66 6.45 80.8 80.4
181 35.14845 80.46641 9/1 16:48 7.6 6.7 83 79.2
182 35.15091 80.46693 9/1 16:57 7.66 6.14 76.5 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 35.15005 80.45959 9/1 17:57 7.91 6.67 82 78.4
189 35.14981 80.45807 9/1 18:10 7.89 5.28 64.9 78.4
Table C-7. Longitudinal data from trip 3 (September 13-16, 2016)
Specific
Latitude Longitude Turbidity DO DO Temp
ID Date Time pH Conductivity
(N) (W) (NTU) (mg/I) (%Sat) (°F)
(uS/cm)
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
Specific
ID Latitude Longitude Date Time Turbidity pH DO oDO Temp
(N) (W) (NTU) (mg/I) (/oSat) Conductivity (°F)
(uS/cm)
199 35.10886 80.54678 9/14 9:40 13.3 6.61 0.28 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 80.54707 9/14 10:36 12.6 7.09 5.62 65.6 498 73.4
204 35.11332 80.54606 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 9/14 11:20 19.9 7.07 3.44 40.4 459 73.8
207 35.11754 80.54533 9/14 11:29 33.1 7.02 2.51 29.4 420 73.8
208 35.11809 80.54537 9/14 11:38 28.2 7.02 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 9/14 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 9/14 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
0
TETRA TECH 57

r
Crooked Creek QUAL2K Model October 15, 2019
Specific
ID Latitude Longitude Date Time Turbidity pH DO DO Conductivity Temp
(N) (W) (NTU) (mg/I) (%Sat) (uSlcm) ( F)
225 35.12815 80.53922 9/14 14:24 21.4 7.31 4.73 55.7 333
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 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
®TETRA TECH 58

Crooked Creek QUAL2K Model October 15, 2019
Specific
ID Latitude Longitude Date Time Turbidity pH DO Conductivity Temp
(N) (W) (NTU) (mg/I) (%Sat) (uSlcm) ( F)
250 35.13532 80.523 9/15 9:30 22.5 7.38 6.29 72.8 237 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 9/15 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 9/15 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
263 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
0
TETRA TECH 59

Crooked Creek QUAL2K Model October 15, 2019
Specific
Latitude Longitude Turbidity DO DO Temp
ID (N) (W) Date Time (NTU) pH (mgll) (%Sat) Conductivity (oF)
(uS/cm)
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 35.13115 80.49435 9/15 14:23 11.9 7.58 5.73 65.8 166 72.5
284 35.13125 80.4938 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 Site Average DO Minimum DO Maximum DO DO Range
1 DS of CC#2 4.46 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 Brief Rd 4.97 4.11 6.28 2.17
(8/31-9/2)
SR 1601 4.52 3.30 5.83 2.53
®TETRA TECH 60

Crooked Creek QUAL2K Model October 15, 2019
Trip Site Average DO Minimum DO Maximum DO DO Range
HWY 601 3.47 2.82 5.01 2.19
3 Brief Rd 3.93 3.30 4.94 1.64
(9/13-9/16)
N Rocky River 4.89 3.54 6.70 3.16
Rd
SR 1601 4.67 3.33 6.33 3.00
Brief Road
° 0 SR 1601
HWY 601 041411 ,
.
.+
DS of CC#2 "
"' US of CC#2 Rocky River Rd r
%IS 7) ,
:4141 ' un...,.
' Legend
Sonde Location(8/13-8/19)
. Sonde Location(8/31-9/2)
A. Sonde Location(9/13-9/16)
\', ■ WWTP Discharge
(� Crooked Creek WatershedNHD HiRes Flowline
l'til TETRA TECH Dissolved Oxygen Sonde Sites N 0 os 1 Q 2 Kilometers
l —1 A 0 os 1 2M e EJ Watershed Boundary
Nopecl':d...Ma µme
Figure C-5. Dissolved oxygen monitoring sonde sites (all trips)
't TETRA TECH 61

Crooked Creek QUAL2K Model October 15, 2019
8
7
6
5
E
O
0 4 I', _
441
O 3
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
•Trip 1:US of CC#2 •Trip 1:DS from CC#2 •Trip 1:HWY 601
Figure C-6. Diurnal dissolved oxygen concentrations (8/15-8/19), gray areas are night(7pm-7am)
8
7
•
6
•
• ti
"a5 ;" , • . •
E • •• ' y,
o • • r •
• am N •
••. • •
4
C _
N
O b,
2
1 r y
8/31 16:49 8/31 21:37 9/12:25 9/17:13 9/112:01 9/1 16:49 9/121:37 9/2 2:25 9/2 7:1.3
•Trip 2:Brief Rd •Trip 2:SR 1601 •Trip 2:HWY 601
Figure C-7. Diurnal dissolved oxygen concentrations (8/31-9/2), gray areas are night (7pm-7am)
®TETRA TECH 62

Crooked Creek QUAL2K Model October 15, 2019
7
•
6
•• 4104-411100
5 • • ••
4 silipt
+ !11,
O
2
1
0
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
•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)
®TETRA TECH 63

Hazen
Attachment D: Crooked Creek Model Application
for Grassy Branch Wastewater Treatment Plant,
Tetra Tech, October 15, 2019

Crooked Creek QUAL2K Model Application
for Grassy Branch WWTP
Union County, North Carolina
December 4, 2019
PREPARED FOR PREPARED BY
Union County Public Works Tetra Tech
500 North Main Street, Suite 500 One Park Drive, Suite 200
Monroe, NC 28112 PO Box 14409
Research Triangle Park, NC 27709 1t.,fi f
. ., .. ., , ' ., '‘. :•-',4,14:::i.,;*,*. ,;',.......t,1",'!'r''.-,.4."4, . . .0
if
.._ _ . .-_ - ,,- -. 1 . ..4,:.. ....,
_ . ...4f, I..
Pictured:North Fork Crooked Creek(Tetra Tech, 2016)
Nb)
TETRA TECH

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TABLE OF CONTENTS
1.0 INTRODUCTION 1
2.0 QUAL2K 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 lnstream 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 WWTP (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 QUAL2K 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
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Crooked Creek Model Application for Grassy Branch WWTP-Union County December 4, 2019
1.0 INTRODUCTION
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.
1 Tetra Tech. 2019. Crooked Creek QUAL2K Model Development; Union County, North Carolina.
Prepared for Union County Public Works, Monroe, NC.
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Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
Rocky River
i Crooked Creek
Grassy Branch WWTP
Mp" Hemby Acres WWTP
North Fork Crooked Creek.
Crooked Creek WWTP#2
.».
Grassy Branch
Legend
*NW
• WWTP Discharge
A Large Beaver Darn
\\J / South Fork Crooked Creek — River/Stream
QWatershed Boundary
Model Reach
•taaa� Reach I
arr Reach 2
,•`y - Reach
Reach 4
Crooked Creek Watershed N 0 05 t 2 Reach
(it)TETRA TECH QUAL2K Model Segmentation v kilometers
ioe_s a,a Nea ceae._rws_uoa r.« 0 0 5 1 2Miles .e".e. Reach 6
4Mpproa.t-G>46]Ot]HNctel••
Figure 1. Crooked Creek watershed location map, model segmentation, and WWTP discharge sites.
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Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
2.0 QUAL2K MODEL APPLICATION SET-UP
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 Summer 7Q10 Winter 7Q10
Boundary Condition 2
(mi ) Flow (cfs) Flow(cfs)
Headwater 7.4 0.007 0.074
South Fork Crooked Creek (SF CC) tributary 18.4 0.018 0.184
Grassy Branch tributary 3.8 0.004 0.038
Diffuse Flow 1: Headwaters to Highway 601 N/A 0.011 0.113
Diffuse Flow 2: Highway 601 to NC Highway 218 N/A 0.004 0.035
Diffuse Flow 3: NC Highway 218 to Outlet N/A 0.006 0.059
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Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
Headwater Inflow
Summer 7Q10:0.007 cfs
Winter 7010:0.074 cfs
Diffuse Inflow 1
► 4-- 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 4 Summer 7Q10:0.004 cfs
Winter 7Q10:0.038 cfs ► Winter 7Q10:0.035 cfs
NC Highway 218 instream flow
Summer 7Q10:0.044 cfs
Winter 7Q10:0.444 cfs
Diffuse Inflow 3
Outlet instream flow Summer 7Q10:0.006 cfs
Summer 7Q10:0.050 cfs Winter 7Q10:0.059 cfs
Winter 7Q10:0.503 cfs
Figure 2. Crooked Creek QUAL2K model 7010 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
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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/I 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°F) and 19.3 °C (66.7 °F)
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 75th 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/I.
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 °F) and 13.8°C (56.9
°F) 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 BOD5 NH3 DO TSS (mg/I)
(MGD) (mg/I) (mg/I) (mg/I)
Hemby Summer 9 3
NC0035041 Acres 0.3 5 30
Winter 15 8
Crooked Summer 5 2
NC0069841 Creek#2 1.9 >-6 30
Winter 10 4
Grassy Summer 5 2
NC0085812 Branch 0.05 5 30
Winter 10 4
Table 3. Proposed SOC and final effluent permit limits for Grassy Branch WWTP (NC0085812).
5 NH3 DO
Permit Note Season Flow (MGD) �mgD/I) (mg/I) (m9 1) TSS (mg/I)
Summer 6
Interim SOC Limits 0.12 30 >- 5 100
Winter 20
Summer 5 1
Final Limits 0.12 >_ 6 30
Winter 10 2
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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.
Facility Summer Water Temperature (°C), Winter Water Temperature (°C),
Average July 2015 Average November 2015
Hemby Acres 25.9 14.4
Crooked Creek#2 26.3 18.2
Grassy Branch 25.7 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/I), 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.
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Crooked Creek QUAL2K Model Application for Grassy Branch WWTP-Union County December 4, 2019
3.0 MODIFIED DISCHARGE CONDITIONS SCENARIO RESULTS
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/I DO.
Table 5. Crooked Creek QUAL2K model scenarios results for summer and winter critical conditions.
DO minimum DO at Crooked
Scenario Scenario Description downstream of Grassy Creek outlet
Branch WWTP (mg/I) (mg/I)
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
Hemby CC#2 SFCC Beaver Trib 9.00
WWTP WWTP Trib Dams Grassy
1 1 1 1 w PTV a:0
6.00
--- i 5.00
I �
4.00 2
3.00
2.00
1.00
30.00 25.00 20.00 15.00 10.00 5.00 0.00
Distance from outlet(km)
----MIS -Summer-Interim SOC Limits -Summer-Final Permit Limits -Winter-Interim SOC Limits -Winter-Anal Permit limits
Figure 3. Crooked Creek QUAL2K model scenario results for summer and winter.
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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.
Baseline DO minimum Bottom DO minimum DS
Scenario Scenario Description DS of Grassy Branch Algae of Grassy Branch
WWTP (mg/I) Coverage WWTP (mg/I)
Critical summer conditions, 60% 5.55
Grassy Branch at interim
1 SOC limits, other outfalls at 5.39
permit limits 40% 5.22
Critical summer conditions, 60% 5.71
2 Grassy Branch at future 5.53
permit limits, other outfalls at 40% 5.34
permit limits
Critical winter conditions, 60% 5.92
3 Grassy Branch at interim 5.66
SOC limits, other outfalls at
permit limits 40% 5.38
Critical winter conditions, 60% 6.03
Grassy Branch at future
4 permit limits, other outfalls at 5.76 40% 5.48
permit limits
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/I in summer, and 1.8 mg/I in winter. As shown below, for all model
application scenarios, ammonia toxicity is not exceeded (Table 7).
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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.
Maximum NH3 NH3 at Crooked
Scenario Scenario Description downstream of Grassy Creek outlet
Branch WWTP (mg/I) (mg/I)
Critical summer conditions, Grassy
1 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.
Maximum TSS TSS at Crooked
Scenario Scenario Description downstream of Grassy Creek outlet
Branch WWTP(mg/I) (mg/I)
Critical summer conditions, Grassy
1 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 Q8388000, TSS measurements range from 15—224
mg/I, which suggests that turbidity violations are not observed when TSS measurements are below 15
mg/I. 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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