NC0074772_Plan of Action_20180904

NCoU79-71a
MODELING PLAN FOR
DUMOND HEAD W WTP
Prepared by
Jerry K. Snyder, P.E., DEE, DWRE
for
Aqua Nortb Carolina, Inc.
SEP'TEMBER 2018
lif % je1Ty. SIlvder. P.E.
Date Typed Name
Pennsylvania P.E.. License No. PE032666fi

Modeling Plan for Diamond Head WWTP — NPDES #NC0074772 September 2018
TABLE OF CONTENTS
1.0 INTRODUCTION..............................................................................................................I
1.1 BACKGROUND.........................................................................................................1
1.2 DESCRIPTION OF EXISTING OUTFALL...............................................................1
1.3 PURPOSE OF DILUTION MODELING STUDY.....................................................4
2.0 MODELING APPROACH.................................................................................................5
2.1 MODELING OBJECTIVES........................................................................................5
2.2 MODELING APPROACH..........................................................................................5
2.3 INPUT DATA REQUIREMENTS AND SOURCES.................................................6
LIST OF TABLES
1 Discharge Limits for Diamond Head VWVTP NPDES Permit # NCO074772 ................1
2 Outfall Pipe Configuration..............................................................................................4
3 CORMIX Model Scenario..............................................................................................6
4 CORMIX Date Requirements and Sources.....................................................................7
LIST OF FIGURES
1 Facility Location Map.....................................................................................................2
2 Outfall Pipe Construction Drawing.................................................................................3

Modeling Plan for Diamond Head WWTP — NPDES #NC0074772 September 2018
1.0 INTRODUCTION
1.1 BACKGROUND
Aqua North Carolina, Inc. operates the Diamond Head Subdivision Wastewater Treatment Plant
(WWTP) under NPDES Permit NC0074772. The WWTP treats 100% domestic wastewater from
the Diamond Head Subdivision. The WWTP is located at 799 Williamson Road, Mooresville,
Iredell County, North Carolina. The WWTP is permitted to discharge up to 0.0731 million gallons
per day (MGD) with projected expansion to 0.100 MGD. The average discharge flow rate in 2017
was 0.0225 MGD. The future discharge limits for chloride, copper, and zinc are listed in Table 1
below.
Table 1
Discharge Limits for Diamond Head WWTP NPDES Permit #
NCO074772
Parameter
Monthly Average
Units
Daily Maximum
Units
Flow'
0.0731
MGD3
Total
Chloride
230
mg/0
250
mg/L4
Total
Copper2
7.88
ug/L5
10.47
ug/O
Total
Zinc'
125.7
ug/0
125.7
ug/LS
Notes:
1. The anticipated future flow rate is 0.100 MGD.
2. The discharge limits will become effective April 1, 2020.
3. MGD is million gallons per day
4. mg/L is milligrams per liter
S. ug/L is micrograms per liter
1.2 DESCRIPTION OF EXISTING OUTFALL
The WWTP discharges treated domestic wastewater to Lake Norman (Reeds Creek Arm) in the
Catawba River Basin through a permitted outfall pipe. A location map showing the locations of
the facility and the outfall pipe is included as Figure 1 below. Lake Norman is classified as WS-
III & B (Water Supply III and Full Contact Recreation). The outfall is a 4-inch diameter pipe
that ends in the center of Reeds Creek, 100 feet from the shore. A construction drawing
showing the profile of the outfall pipe is included as Figure 2 below. On occasion the
concentration of total copper has exceeded the anticipated permit limit of 7.88 ug/L. The basic
configuration of the outfall is described in Table 2 below.

Modeling Plan for Diamond Head W WTP — NPDES #NC0074772
Figure 1 Facility Location Map
September 2018
\ ` � . � 1 .n✓ �J•: �' 1 '' � �C+1 � � • 11
1 �:;.• Outfall 001
Lai 350 33' 52" G
Lung 80 ° 51' 58"`PBedB Ji
r 1 f,l �� jl)•') (lake discharge) }
r 1
B
AVq'I'P nppmyinu
bl
Williannun Road
AQUA North Carolina
Diamond Head Subdivision WWTP
Facility
Location
ReM.b•31wm Iukc N,.mjg [,r kBmrkj
W.0 Swmm 114751 Slm C4rl N•S IV, B. CA
Oal LL� wale
Sul, Gd&Ou•d: EISSE M.'O NC III", Ow.: Caurke Rno
a u541n-5! flu mow1A1
NPDES Permit NC0074772
North Iredell Count
2

Vi
_ I -. i - - �r/a- li"i�ii� li .'�Sa wu . 1 i -1. '.. .-......�. ' !� 1►-_1 1 _�-i--••! + }' � • � _ i � `I 1i i � ! I ! { i
lS711 -t_-. .� - - _. _—.i... . ._. -.� •T" f 1 i �.:_:• - 1 .r.1. � � I �a-4-.-.�._..1 -i ` 1 1 I t i 1 � I I �
• t-•
_ _- 1 - i ' • +. _ . ?'� jj'� � f I L l -1-: j � - I � � 1 . - 1. ? i_ i � � �- � ' i I + j
:��wrews� _. 1•r t. .� y•al • }p 1 1 • s 1 1 j
�aeaw wt_ .. � L •-YT' /"ram', �1 ��f 1 ( j ! I ,
�. ---i. r1 , f i i I ►
um no
mar
1 — -
{ MtLuntm ItU 3R I= TD l-TT---► f
-� • I fv:Z MW 6 VAX= W?I
Imo_ HM_��
Ij
\ : Y'v
I.T
C�

Modeling Plan for Diamond Head WWTP — NPDES #NC0074772 September 2018
Table 2 Outfall Pipe Configuration
Diamond Head
Location
Lake Norman
Orientation of pipe
Horizontal T above bottom
Distance from Shore, feet
100
Diameter, inches
4
Diffuser
Deflector Plate
Material
Ductile Iron
Easement Width, feet
20-25
1.3 PURPOSE OF DILUTION MODELING STUDY
In 2017 the Facility exceeded its monthly average limit for the concentration of total copper in
September and December. The measurements of TOTAL copper in September and December
were 10 ug/L and 9 ug/L respectively while the Monthly Average limit for copper is 7.88 ug/L.
It should be noted that both of these measurements were lower that the Daily Maximum limit of
10.47 ug/L. Since only one measurement was taken during each month, that value represented
both the Monthly Average and the Daily Maximum reported value.
The latest NPDES permit renewal effective June 1, 2018 requires a Study Plan and
recommendations for dilution modeling. "The plan shall recommend steps needed to establish in
instream waste concentration (IWC) at the point of discharge. "
The study will establish effluent dilution credits for total chloride, total copper, and total zinc.
The objective will be to determine the IWC at various distances from the end of the discharge
pipe. The distance where the permitted concentrations are met will be determined as an objective
of this dilution study. This will be the basis for a recommended dilution credit. The dilution credit
will be an allowance of end -of -pipe concentrations greater than the permit value as long as the
permitted concentrations are achieved within a short distance from the end of the pipe. Dilution
credits may be developed and applied to other constituents as well.
4

Modeling Plan for Diamond Head WWTP — NPDES #NC0074772 September 2018
2.0 MODELING APPROACH
2.1 MODELING OBJECTIVES
The objective of the modeling study is to simulate the behavior of the discharge plume from the
outfall. The simulation will allow evaluation of the IWC of total chloride, total copper, and total
zinc in the discharged water as the plume mixes with ambient water. Although total chloride,
total copper, and total zinc are the main constituents of interest in this study, the simulation
results will be general and could be applied to any constituent in the discharged water.
2.2 MODELING APPROACH
The simulations will be accomplished using a well -established and accepted hydrodynamic
model. The modeling approach consists of the following tasks:
Task 1 Compile and Evaluate Data.
The data required for modeling will be obtained from existing sources as much as possible. This
includes Discharge Monitoring Reports (DMRs), previous dilution and wasteload allocation
calculations, outfall construction plans, and Duke Energy, who operates Lake Norman.
Task 2 Perform Parameter -Specific and Generalized Simulations.
The CORMIX model will be used to simulate the plume behavior of the existing discharge
under existing conditions. The model will be used to develop a steady-state concentration
profile along the discharge plume centerline. The location and distance from the end of the
outfall pipe where the permitted total chloride, total copper, and total zinc concentrations are
met will be determined. A total of four simulations will be performed. Since the pumps cycle on
an off with the treated effluent level in the pump tank, the instantaneous pumping rate will be
used in the model. This will reflect the actual mixing behavior at the outfall pipe. The
instantaneous pumping rate is independent of the flow rate passing through the treatment plant.
If the average daily flow to the plant changes, the pumps cycle more or less frequently, but the
instantaneous pumping rate while the pumps are on will remain the same. Specific model runs
will be made for total chloride, total copper, and total zinc. The parameter -specific simulations
will account for the background concentration of total chloride, total copper, and total zinc in
the ambient environment. The generalized plume simulation will assume 100% as the discharge
concentration and 0% in the background concentration. The results of the generalized
simulation can be used to calculate the IWC of any constituent in the discharged water by
multiplying the model -predicted percentage concentration in the plume by the concentration of
that constituent at the end of the pipe. The four model scenarios are summarized in Table 3
below.

Modeling Plan for Diamond Head WWTP — NPDES #NC0074772 September 2018
Table 3 CORNUIX Model Scenarios
Discharge
Modeled
Discharge
Flow 1
Constituent
Concentration
Units
(gpm)
Total
87
Chloride
250
ug/L
Total
87
Copper
10.47
ug/L
87
Total Zinc
125.7
ug/L
Generalized
87
Parameter
100
%
1. The instantaneous pumping rate will be used for all
scenarios.
Task 3 Prepare a Written Report of Findings.
The results of the CORMIX simulations will be summarized and presented in a written report.
The report will present the model input data and results of the simulations. The results from all
simulations will include a presentation of the IWCs at various distances from the end of the
discharge pipe.
2.3 INPUT DATA REQUIREMENTS AND SOURCES
The CORMIX model is a hydrodynamic computer code that simulates the behavior of hydraulic
plume or "jets" in various ambient environments. It has been applied extensively to model or
simulate the behavior of water discharges into lakes and stream environments. The model
calculates utilizes data on the discharge configuration, ambient environment, and relative
densities between the ambient water and the discharged water. The CORMIX model has
separate modules to simulate submerged single -port discharges (CORMIX 1), submerged multi -
port diffusers (CORMIX2), and buoyant surface discharges (CORMIX3). The CORMIXI
module will be used for this study. The data requirements for the CORMIX model and the
sources of those data are listed in Table 4 below.

Modeling Plan for Diamond Head WWTP — NPDES #NC0074772 September 2018
Table 4 CORMEK Data Requirements and Sources
Category
Parameter
Source of Data
Discharge Data
Flow Rate
Measured Flow Rate While Pumps Are On
Discharge Data
Temperature
Discharge Monitoring Reports (DMRs)
Discharge Data
Total Dissolved Solids
Discharge Monitoring Reports (DMRs)
Discharge Data
Density
Calculated from Temperature and Total
Dissolved Solids
Discharge Data
Velocity
Calculated from Flow Rate and Pipe Diameter
Discharge
Configuration
Pipe Diameter
Construction Drawings
Discharge
Configuration
Deflector Plate
Construction Drawings
Discharge
Configuration
Location, Distance from
Shore
Construction Drawings
Discharge
Configuration
Direction/Orientation of
Pipe
Construction Drawings
Discharge
Configuration
Copper Concentration
Discharge Monitoring Reports (DMRs)
Ambient Data
Depth
Construction Drawings
Ambient Data
Temperature
Sample Collection
Ambient Data
Total Dissolved Solids
Sample Collection
Ambient Data
Density
Calculated from Temperature and Total
Dissolved Solids
Ambient Data
Total Chloride
Concentration
Sample Collection
Ambient Data
Total Copper
Concentration
Sample Collection
Ambient Data
Total Zinc Concentration
I Sample Collection

Rodriguez, Teresa
From: Rodriguez, Teresa
Sent: Thursday, October 4, 2018 3:44 PM
To: Berger, Amanda A
Subject: Re: [External] Diamondhead & Harbor Estates Cormix Modeling Plans
Amanda, the Division agrees with the proposed modeling plans for Harbor Estates and Diamond Head. When
you submit the final report please submit all the model runs input and output files. The PDF documents
include the figures for the outfall configurations, but these are not legible, could you submit a paper copy of
the figures with your final report.
Thanks,
Teresa
From: Berger, Amanda A <[e-mail]>
Sent: Friday, September 28, 2018 4:13:00 PM
To: Rodriguez, Teresa
Subject: [External] Diamondhead & Harbor Estates Cormix Modeling Plans
Hi Teresa,
I hope all is well.
Attached for your review and approval are the Cormix modeling plans for Diamondhead (NC0074772) and
Harbor Estates (NC006386O).
If you have any questions or concerns, please do not hesitate to contact me.
Best regards,
1 • A
Amanda Berger
Manager, Environmental Compliance
Aqua North Carolina
202 MacKenan Court, Cary NC 27511
0:919-653-6965 M:910-773-0406
000