NC0074772_More Information (Received)_20200117

Dilution Modeling Report
for
Diamond Head WWTP
Prepared by
Jerry K. Snyder, P.E., DEE, DWRE
for
Aqua North Carolina, Inc.
January 2020
D/ 17 tZD Jerry K. Snyder, P.E.
Date Typed Name
Pense No. PE032686E

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
TABLE OF CONTENTS
EXECUTIVE SUMMARY 1
1.0 INTRODUCTION 1
1.1 BACKGROUND 1
1.2 DESCRIPTION OF EXISTING OUTFALL 2
1.3 PURPOSE OF DILUTION MODELING STUDY 2
2.0 MODELING APPROACH 5
2.1 MODELING OBJECTIVES 5
2.2 MODELED CONDITIONS 5
2.3 INPUT DATA 6
3.0 MODEL RESULTS 12
4.0 SUMMARY AND RECOMMENDATIONS 14
5.0 REFERENCES 16
6.0 ATTACHMENTS 17
LIST OF TABLES
1 Discharge Limits for Diamond Head WWTP NPDES Permit # NC0074772 1
2 Outfall Pipe Configuration 2
3 CORMIX Model Scenarios 6
4 Measured Data for Lake Norman and Diamond Head 7
5 Water Density Calculations 7
6 Zone of Initial Dilution (ZID) Calculation 9
7 Diamond Head CORMIX Input Data 10
8 Water Quality Criteria 9
9 Input Concentrations and Water Quality Criteria 11
10 Dilution and Distance Required to Meet Water Quality Criteria 15
11 Dilution Achieved at the Zone of Initial Dilution (ZID) Distance 15
LIST OF FIGURES
1 Facility Location Map 3
2 Outfall Pipe Construction Drawing 4
3 Plan View of Plume from Diamond Head Outfall 8
4 Dilution vs. Distance from the Outfall at Diamond Head 12
5 In -Stream Waste Concentration along Plume Centerline — Diamond Head 13
i

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
LIST OF ATTACHMENTS:
1 CORMIX Input and Output Files
ii

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
EXECUTIVE SUMMARY
The mixing behavior of the Diamond Head WWTP discharge into Lake Norman was simulated using the
CORMIX model. Three discharge constituents were modeled, chloride, copper, and zinc. A generic
simulation was also performed that could be applied to any constituent in the discharge. The simulations
indicated that significant mixing and dilution occurred within a short distance of the outfall. A zone of
initial dilution (ZID) was calculated as 4.50 meters based on the outfall configuration. The ZID is an initial
mixing area within a short distance from the outfall. A dilution factor of 10.0 was achieved at the ZID. This
dilution allowed the most stringent water quality criteria for chloride, copper, and zinc to be met within the
ZID when the discharge concentrations were at or below the future daily maximum concentrations for
chloride, copper, and zinc. However, the dilution was not sufficient to allow the maximum measured
concentration of copper to be met within the ZID.
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 # NC0074772
Parameter
Monthly Average
Units
Daily Maximum
Units
Flow'
0.0731
MGD3
Total Chloride2
230
mg/L4
250
mg/L4
Total Copper2
7.88
ug/L5
10.47
ug/L5
Total Zinc2
125.7
ug/L5
125.7
ug/L5
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
5. ug/L is micrograms per liter

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
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.
Table 2 Outfall Pine Configuration
Diamond Head
Location
Lake Norman
Orientation of pipe
Horizontal 2' 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 anticipated 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. The future 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."
One objective of the study was to establish effluent dilution credits for total chloride, total copper, and total
zinc. This study determined the IWC at various distances from the end of the discharge pipe. The distance
where the permitted concentrations are met was determined as an objective of this dilution study. The
distances from the end of the discharge pipe where the permitted concentrations are met are the basis for a
recommended dilution credit. The dilution credit is 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. That short distance is called the zone of initial dilution (ZID). Dilution credits may be developed
and applied to other constituents as well.

Modeling Report for Diamond Head WWTP — NPDES #NCOO74772 January 2020
Figure 1 Facility Location Map
Outfall 001
Lat 35° 33' 52 '
Long 80 ° 51' 58"
(Takc discharge)
AQUA North Carohina
Diamond Head Subdivision WWTP
ReetYrinit rcaiii Lax NCrniin[RamCIVCRI ind!I
kllPalo tirr�inoid= r 1A151 iireem CIBSS I V: El: (A
Iola Grid'Quad: Ely E.Mnaesvillle, Fj ; Ca iwie River
!itF hails_ 11 .0q-3: ilur. 03054L07
approximate location
Facility
Location
noL �o 4IL
North rth J
L NPDES Permit NC(071772
Iredell Coca

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
Figure 2 Outfall Pipe Construction Drawing

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
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, copper, and zinc in the discharged water
as the plume mixes with ambient water. Although total chloride, copper, and 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 MODELED CONDITIONS
The simulations were accomplished using a well -established and accepted hydrodynamic model, Cornell
Mixing Zone Expert System (CORMIX). The CORMIX model was used to simulate the plume behavior of
the existing discharge under existing conditions. The model was used to develop a steady-state
concentration profile along the discharge plume centerline. The locations and distances from the end of the
outfall pipe where the permitted total chloride, copper, and zinc concentrations are met were determined. A
total of four simulations were performed representing total chloride, total copper, total zinc and a generic
(generalized) parameter. Since the pumps cycle on an off with the treated effluent level in the pump tank, a
single instantaneous pumping rate was used in the model to represent the discharge flow rate because the
instantaneous pumping rate while the pumps are on will remain the same. This reflects the actual mixing
behavior at the outfall pipe while the discharge is active. 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 discharge rate while the pump is operating will remain the same.
Three specific model runs were made for total chloride, copper, and zinc. These parameter -specific
simulations account for the background concentration of total chloride, copper, and zinc in the ambient
environment. The generalized plume simulation assumed 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. The permitted daily maximum concentration was used as input to the
CORMIX model.

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
Table 3 CORMIX Model Scenarios
Discharge
Flow 1
Modeled
Constituent
Discharge
Concentration2
Units
(gpm)
40
Total Chloride
250
mg/L
40
Total Copper
10.47
ug/L
40
Total Zinc
125.7
ug/L
40
Generalized
Parameter
100
1. The instantaneous pumping rate was used for all
scenarios.
2. Before adjustment for background concentrations.
2.3 INPUT DATA
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 utilizes data on the discharge
configuration and flow rate, 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
(CORMIX1), submerged multi -port diffusers (CORMIX2), and buoyant surface discharges (CORMIX3).
The CORMIX1 module was used for this study. The data requirements for the CORMIX model and the
sources of those data are listed in Table 4 below.
Adjustments for Background Concentrations
CORMIX models the concentrations of constituents in water, no matter which units of measure are used, as the
concentrations above background. Therefore, if there is a non -zero background (ambient) concentration of any
modeled constituent, that background concentration is subtracted from the discharge concentration and the water
quality criterion as well. For interpretation of the calculated model output concentrations, the background
concentrations are added to the predicted plume concentrations. When a background concentration is present, the
dilution factors (S) calculated by the model are the ratio of the adjusted discharge concentration to the adjusted water
quality criterion.
In addition to the four model scenarios listed in Table 3 above, one additional scenario was run. This represented the
maximum copper concentration measured on October 17, 2018. Additional water samples were collected on October
17, 2018 and analyzed for use in this dilution modeling study. These are listed in Table 4 below.

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
Table 4 Measured Data for Lake Norman and Diamond Head October 17, 2018
Measurement Location
Parameter
Value
Units
Effluent
Temperature
23
°C
Effluent
Total Dissolved Solids
445
mg/L
Effluent
Chloride
96
mg/L
Effluent
Copper
27
ug/L
Effluent
Zinc
91
ug/L
Upstream
Temperature
23
°C
Upstream
Total Dissolved Solids
32
mg/L
Upstream
Chloride
6.0
mg/L
Upstream
Copper
<5
ug/L
Upstream
Zinc
12
ug/L
Downstream
Temperature
23
°C
Downstream
Total Dissolved Solids
31
mg/L
Downstream
Chloride
6.25
mg/L
Downstream
Copper
<5
ug/L
Downstream
Zinc
<10
ug/L
Water Density Calculations
The behavior of the discharge plume modeled in CORMIX is affected by the energy (velocity) of the discharged jet
and the relative density of the discharged water and the receiving water. The densities used for the Diamond Head
discharge and Lake Norman were calculated from the measured total dissolved solids (TDS) concentration and
temperatures measured on October 17, 2018. The calculated water densities are summarized in Table 5 below.
Table 5 Diamond Head Water Densities
Total Dissolved
Solids, TDS
Temperature
J.
Density
mg/L
°C
kg/m3
Discharge
445
23
997.879
Lake Norman
32
23
997.566
1. Density was calculated from Sea Water Equation of State
online calculator, http://fermi.jhuapl.edu/denscalc.html.
Discharge Rate
The discharge rate was calculated from the measured time required for the discharge pump to draw down a holding
tank between the upper and lower set points on the tank. The 92-inch diameter tank was drawn down 1.25 feet in 5
minutes. This resulted from a pumping rate of 87 gallons per minute (gpm); 0.125 million gallons per day (mgd).
Initial model runs indicated that this flow rate created a coherent jet with a high velocity at the end of the pipe which
resists initial mixing with the ambient water resulting in a dilution factor, S, of 6.5 at a ZID distance of 4.50 meters
from the end of pipe. A dilution factor of 6.5 was not sufficient to achieve the water quality criterion for zinc within
the ZID. Exploratory model runs indicated that lowering the discharge rate, and exit velocity of the jet, allowed more
rapid mixing with the ambient water. By reducing the discharge rate by about half allowed more rapid mixing. Aqua

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
NC personnel were able to reliably throttle the discharge rate from Diamond Head to 40 gpm. Therefore, the pump
discharge rate used in the model was 40 gpm.
Downstream Velocity
The downstream velocity was calculated from the relative drainage areas at Cowan's Ford Dam (1,790 square miles,
s.mi.) and the Catawba River at the discharge location 10.1 s.mi.) and the average annual flow at the dam (1,726
mgd) based on five years of daily discharge data. The calculated average annual flow along the Catawba River at
Pine Run is 9.7 mgd (15.0 cfs). The cross -sectional area of the Catawba River at the discharge location was measured
from Google Earth and a U.S.G.S. Quadrangle map (Mooresville, NC, 7.5-minute quadrangle, 2016) as 5,044 square
feet, s.f. The calculated downstream velocity is 0.003 feet per second, fps.
Diffuser Configuration
The outfall for Diamond Head is a 4-inch diameter ductile iron (DI) pipe with a deflector plate diffuser at the end of
the pipe. For input to CORMIX, the outfall was described as a 0.33-foot diameter circular outfall with a vertical
angle of 45°. The outfall pipe is located 2 feet above the channel bottom.
Outfall Pipe Orientation
The diffuser is perpendicular to the direction of the Catawba River. The origin for the coordinate system for model
output is at pipe opening. The coordinates are oriented as follows. The downstream direction of flow is the positive
X direction. The opposite river bank is the positive Y direction, and straight up from the bottom is the positive Z
direction. The discharge is pointed in the positive Y direction and the plume is weakly deflected in the X direction, to
the left, by the small downstream velocity. Figure 3 shows the dimensions of the plume originating from the diffuser
pipe. The origin of the graph is at the end of the outfall pipe.
Figure 3 Plan View of Plume Trajectory for Diamond Head Outfall
Plan View of Plume Trajectory
Diamond Head Outfall
Ab%
2
1.5 1 0.5 0
-0.5 -1
Distance Downstream from 0utfall, Meters
Plan View of Trajectory Right Edge Plume Left Edge Plume
10
m
8
0
6
2
4
aw
ire
2 0
V
0 4
d
V
m
0

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
Zone of Initial Dilution (ZID)
The ZID is a limited area around a discharge pipe or outfall where the water quality criteria for toxic constituents
may be exceeded as long as the criteria are met at the edge of this limited zone and the limited nature of the ZID
allows for passage of aquatic life around the zone. The dimensions of the ZID can be calculated as the minimum of 5
x ambient depth or 50 x discharge length scale (DLS). The DLS is defined as the square root of the area of the
discharge. The ZID for the diffuser is 14.77 feet (4.50 meters). Table 6 below shows the calculation of the ZID
distance for Diamond Head.
Table 6 Zone of Initial Dilution Calculations
Pipe
Diameter
Area
Discharge
Length
Scale, DLS
50 x DLS
Avg.
Depth at
Discharge
5 x Depth
Zone of
Initial
Dilution,
ZID
Zone of
Initial
Dilution,
ZID
(in.)
(s.f.)
(ft.)
(ft.)
(ft.)
(ft.)
(ft.)
(m)
Diamond Head
4
0.09
0.30
14.77
26.00
130.00
14.77
4.50
Table 7 below lists the input values used in the generalized model scenario.
Water Quality Criteria and Background Concentrations
Lake Norman is classified as WS III/B water uses. Class WS III is a water supply classification and B is for primary
contact recreation. In addition, there are chronic and acute limits that apply to freshwater aquatic life. Table 8 below
lists the water quality criteria for chloride copper and zinc for Lake Norman. The minimum of all the water quality
criterion for chloride, copper, and zinc was selected as the limiting criterion.
Table 8 Water Quality Criteria
FW Aquatic
Parameter
Units
B
WS III
Chronic
Acute
Background
Chloride
mg/L
N/A
250
230
230
6
Copper'
ug/L
N/A
N/A
1.97
2.53
0
Zinc2
ug/L
N/A
N/A
26.32
26.11
12
1. A hardness value of 17 mg/L as CaCO3 was used to calculate the criterion
for copper.
2. A hardness value of 17 mg/L as CaCO3 was used to calculate the criterion
for zinc.
3. The lowest Water Quality Criterion was used as the critical criterion.
The input concentrations for chloride, copper, and zinc adjusted for background concentrations are listed in Table 9
below. Table 9 shows the maximum daily permit limits, the minimum water quality criteria, the ambient
concentrations, and the adjusted discharge and criteria concentrations.

Modeling Report for Diamond Head WWTP — NPDES #NCOO74772 January 2020
Table 7 Diamond Head CORMIX Input Data
Module: CORMIX1 Submerged Single Port Discharges
TAB
I INPUT DATA
I UNITS OF MEASURE
Project Tab
Name:
Diamond Head - Lake Norman
Scenario:
Generalized
Ambient Tab
Average Depth:
28
feet
Discharge Depth:
26
feet
Ambient Velocity:
O.i103
feet per second, fps
Bounded/Unbounded
Bounded
VViidth:
236
feet
Manning's n:
U025
Wind Speed:
0
meters/second, m/s
Ambient Density Data
Fresh/Uniform
Water Density:
997.566
kilograms per meter squared, kgjm2
Effluent Tab
Flow Rate:
0.1)576
million gallons per day, MGD
Concentration:
1U0
percent, %
Discharge Density
997.879
kilograms per meter squared, kg/m2
Pollutant Type:
Conservative
Discharge Tab
Nearest Bank:
Left
Distance to nearest bank:
1U0
feet
Port Diameter:
0.33
feet
Vertical Angle Theta (0 )
45
degrees, °
Horizontal Angle Sigma (al:
90
degrees, °
Port Height:
2
feet
Mixing Zone Tab
Toxic/NonToxic
NonToxic
WQStandard
No WQStandard
(for generalized parameter scenario)
Specified Mixing Zone Tab
Mixing Zone Specified
Distance:
4.50
meters
Region of Interest
1000
meters
Grid Intervals for Display
100
No. of Display Steps

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
Table 9 Input Concentrations and Water Quality Criteria Adjusted for Background Concentration
Parameter
Units
Discharge
Concentration
Water
Quality
Criterion
Ambient
Concentration
Discharge
Concentration
above
Background
Water
Quality
Criterion
above
background
Scenario Name
Chloride
mg/L
250.0
230
6.0
244
224
Permitted Chloride
Copper
ug/L
10.47
1.97
0
10.47
1.97
Permitted Copper
Zinc
ug/L
125.7
26.11
12
113.7
14.11
Permitted Zinc
Max. Copper
ug/L
27.0
1.97
0
27
1.97
Highest Measured Copper

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
3.0 MODEL RESULTS
The CORMIX model calculates the mixing of the discharged water with the ambient water and displays a dilution
factor, S, and the instream waste concentration (IWC) at the plume centerline. CORMIX defines the dilution factor,
S, as the discharge concentration divided by the in -stream waste concentration. For example, if the dilution factor is
25, the concentration at the plume centerline is 4 % of the discharge concentration. A plot of the calculated centerline
dilution factors versus distance from the outfall pipe is shown in Figure 4. Note that all output from CORMIX is in
metric units even though it does allow input of English units for most parameter values. Figure 5 is a corresponding
plot of the Instream Waste Concentration (IWC) versus distance from the outfall pipe. Figure 5 is based on the
discharge concentration of 100% and can be applied to any constituent in the discharged water.
Figure 4 Dilution vs. Distance from the Outfall at Diamond Head
14
12
v 10
8
u_
0 6
4
Dilution vs. Y Distance from Outfall
Diamond Head
2
•
0
0
1 2 3 4 5 6
Distance Across River from Outfall, Meters

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
Figure 5 In -Stream Waste Concentration along Plume Centerline — Diamond Head
Plume Centerline Concentration, %
100 •
90
80
70
60
50
40
30
20
10
0
0
Concentration vs. Y Distance from Outfall
Diamond Head
1 2 3 4
Distance Across River from Outfall, Meters
5
6
Parameter -Specific Model Results
Three parameter -specific scenarios were run showing calculated in -stream concentrations of chloride, copper, and
zinc. One additional scenario was run using the maximum copper concentration measured in the discharge. Since
CORMIX evaluates excess concentration (i.e., concentrations above background levels, if present) the discharge
concentrations and water quality criteria were both reduced by the measured background levels of chloride and zinc
for input to the model. For interpretation of the model output, the background concentrations are added to the results.
Note that there was no copper measured in the background water sample.
The results of the parameter -specific scenarios are summarized on Table 10. The CORMIX model calculated that the
rapid mixing within the ZID results in mixed concentrations of chloride, copper, and zinc concentrations that are all
less than the most sensitive water quality criteria.
The worst -case scenario is for a discharge concentration of copper at 27 ug/L which is the maximum copper
concentration measured at the outfall and exceeds the proposed daily permit limit of 10.47 ug/L. For this case, the
water quality criterion for copper of 1.97 ug/L would be met 6.46 meters from the outfall pipe at a dilution ratio of
13.7.

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
4.0 SUMMARY AND RECOMMENDATIONS
The calculated centerline dilutions and concentrations at the ZID distance of 4.50 meters are summarized in Table 11
for five scenarios. The results of the dilution modeling, which included the angled plate diffuser and a discharge flow
rate of 40 gpm, show that the future discharge limits on chloride and copper are both met within the ZID distance
from the outfall.
The calculation of the ZID distance of 4.50 meters was presented in Table 6 based on the minimum criterion of
50*DLS. This method for calculating a ZID is recognized by the USEPA, Environmental Regulators, and is
referenced in the CORMIX user's manual. Table 11 demonstrates that a dilution factor of 10.0 is achieved at a ZID
distance of 4.50 meters from the outfall. At this dilution, the water quality criteria for chloride, copper, and zinc are
met when the discharged concentrations are at or below the future daily maximum permitted concentration. The last
column in Table 11 is a possible dilution credit which is a percent increase in the permit limit in the discharge
concentration that will still allow the most stringent water quality criteria to be achieved within the ZID. It is
included to demonstrate the factor of safety built into the future discharge limits.
The maximum copper concentration meets the water quality criterion o 1.97 ug/L at 6.46 meters from the end of the
outfall pipe with a dilution of 13.7. The existing outfall configuration does not meet a dilution factor of 13.7 within
the ZID of 4.50 m.

Modeling Report for Diamond Head WWTP - NPDES #NC0074772 January 2020
Table 10 Dilution Required to Meet Water Quality Criteria and Distance from Outfall Pipe
Discharge
Concentration
Minimum
Water
Quality
Criterion
Distance
in the X
Direction
Distance
in the Y
Direction
Distance
in the Z
Direction
Dilution
Factor
Predicted
Centerline
Concentration
Including
Background
Parameter
Units
Meters
Meters
Meters
S
Chloride
mg/L
250
230
0.00
0.43
1.04
1.0
236
Copper
ug/L
10.47
1.97
0.05
2.74
2.42
5.3
1.97
Zinc
ug/L
125.7
26.11
0.10
4.01
1.82
7.9
38.1
Max. Copper
ug/L
27
1.97
0.44
6.46
0.00
13.7
1.97
Table 11 Dilution Achieved at the Zone of Initial Dilution Distance of 4.50 meters - Diamond Head
Discharge
Concentration
Minimum
Water
Quality
Criterion
Distance
in the X
Direction
Distance
in the Y
Direction
Distance
in the Z
Direction
Dilution
Factor
Predicted
Centerline
Concentration
Including
Background
Possible
Dilution
Credit above
Permit Limit
Parameter
Units
Meters
Meters
Meters
S
Chloride
mg/L
250
230
0.13
4.50
1.18
10.0
30.4
86.8%
Copper
ug/L
10.47
1.97
0.13
4.50
1.18
10.0
1.05
46.7%
Zinc
ug/L
125.7
26.11
0.13
4.50
1.18
10.0
23.40
10.4%
Max. Copper
ug/L
27
1.97
0.13
4.50
1.18
10.0
2.71
-37.6%
Gereric
%
100
N/A
0.13
4.50
1.18
10.0
10.0

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
5.0 REFERENCES
1. Mixing Zones in North Carolina July 23, 1999.
2. Technical Support Document for Water -quality Based Toxics Control, pp. 71-72 (EPA/505/2-90-
001 March 1991).
3. User's Manual for CORMIX: A Hydrodynamic Mixing Zone Model and Decision Support
System for Pollutant Discharges into Surface Waters. G.H. Jirka, R.L. Doneker, and S. W. Hinton
September 1996.

Modeling Report for Diamond Head WWTP — NPDES #NC0074772 January 2020
6.0 ATTACHMENTS
CORMIX Model Input and Output Files in Electronic Form Provided by E-mail