NC0046728_Speculative Limits_20070823

NPDES DOCUI4ENT :MCANNINO COVER :SHEET
NPDES Permit:
NC0046728
Mooresville / Rocky River WWTP
Document Type:
Permit Issuance
Wasteload Allocation
Authorization to Construct (AtC)
Permit Modification
Complete File - Historical
Engineering Alternatives (EAA)
Plan of Action
Instream Assessment (67b)
Speculative Limits
Environmental Assessment (EA)
Permit
History
Document Date:
August 23, 2007
This document is printed on reuse paper - ignore any
coriternt on the reverse side

Michael F. Easley, Govemor
State of North Carolina
William G. Ross, Jr., Secretary
Department of Environment and Natural Resources
Coleen H. Sullins, Director
Division of Water Quality
August 23, 2007
The Honorable Bill Thunberg, Mayor
Town of Mooresville
P.O. Box 878
Mooresville, North Carolina 28115
Subject: Speculative Effluent Limits
Rocky River WWTP/ Proposed Lake
Norman Discharge
Reference NPDES Permit #NC0046728
Iredell County
Dear Mayor Thunberg:
This letter is in response to your request for speculative effluent limits for a proposed discharge of 19
MGD of wastewater to Lake Norman. Currently the Town of Mooresville's Rocky River WWTP
discharges 5.2 MGD of wastewater to Dye Branch in the Yadkin River Basin.
Receiving Stream/Lake. Lake Norman is classified as a WS-IV Sr B CA waterbody in the Catawba
River Basin. The Lake is considered oligotrophic which indicates low biological production related
to very low concentrations of available nutrients. Oligotrophic lakes in North Carolina are generally
found in the mountain region or undisturbed (natural) watersheds and have very good water
quality. DWQ's evaluation of the water quality model provided by the Town's consultant indicates
that Lake Norman at Highway 150 is the best option for the discharge point. Other locations in the
Lake were reviewed by DWQ and found not to be feasible. The Highway 150 discharge location
would have the least adverse impact of all the options presented by the Town's consultant.
Speculative Limits. Based on this information, speculative effluent limits for the proposed discharge
of 19 MGD to Lake Norman are presented in Table 1. The speculative limits for the discharge to
Lake Norman are for the Town's maximum requested flow of 19 MGD. Prior to application for the
NPDES permit (and preferably within the Town's Environmental Assessment), the allocation of
discharge flows between the proposed Lake Norman and the existing Rocky River WWTP's Dye
Branch discharge locations should be determined (if the existing discharge point is under
consideration). The Division cannot proceed forward with a proposed permit until the City has
determined the discharge flow into Lake Norman. As stated in DWQ's letter dated June 28, 2006,
Dye Branch is listed as impaired for aquatic life based on biological integrity in NC's 2006 303(d)
Impaired Streams List. Because of the impact of any increased discharge to Dye Branch, this should
be considered as permitted flows are determined. The Town (and/or its consultants) should have
ongoing discussions with DWQ regarding any increases of wasteflow to Dye Branch.
A complete evaluation of these limits and monitoring frequencies, in addition to monitoring
requirements for metals and other toxicants, will be addressed upon receipt of a formal NPDES
permit request.
1617 Mail Service Center, Raleigh, North Carolina 27699-1617 Telephone [phone] FAX [phone]
512 N. Salisbury Street, Raleigh, North Carolina 27604 On the Internet at http://h2o.enr.state.nc.us/
An Equal Opportunity/Affirmative Action Employer
N°97-thCarolina
Ntzturally

TABLE 1. Speculative Limits for Rocky River WWTP, proposed Lake Norman discharge location
Effluent Characteristic
Effluent Limitations
Monthly Average
Weekly Average
Daily Maximum
Flow
19 MGD
BOD5, Summer
5 mg/L
7.5 mg/L
BOD5, Winter
10 mg/L
15 mg/L
TSS
30 mg/L
45 mg/L
NH3 as N, Summer
1.0 mg/L
3.0 mg/L
_
NH3 as N, Winter
2.0 mg/L
6.0 mg/L
Dissolved Oxygen
6.0 mg/L
28 u /1
Fecal coliform (geometric mean)
200/100 ml
400/100 ml
immTRC
Total Phosphorus
1 mg/L
Total Nitrogen
monitoring
Acute Toxicity Pass/Fail
(Quarterly test)
90%
Monitoring within Lake Norman will also be required to ensure that the WQ model predictions
were accurate, and to ensure the discharge does not create adverse conditions in the Lake in the
future. Mooresville will be required to monitor upstream and downstream of the proposed outfall
for total phosphorus, total nitrogen and chlorophyll a. The lakes sampling procedure is online at
DWQ's website. Please contact Dianne Reid of the Environmental Sciences Section at 919-733-6510
ext. 213 for specific questions on lake sampling. At this time, DWQ would recommend sampling at
minimum above the discharge (outside of the influence of the discharge) and below the discharge at
the approximate Lake location where all 3 counties (Iredell, Catawba and Lincoln) converge.
The depth of the discharge within the lake, as well as the potential for a diffuser, should be
evaluated to facilitate optimal mixing. This issue is complex and needs to have input from
navigational sources as well as Wildlife Resource agencies. At this time, the NPDES Program will
not require a diffuser, but we recommend that this be evaluated and documented within the Town's
Environment Assessment (EA).
Nutrients. A review of the WQ model provided by the Town's consultants predicts that a total
phosphorus limit of 1 mg/1 will protect the water quality standard for chlorophyll a.. However, the
Division encourages the Town to be proactive and evaluate the feasibility of achieving total
phosphorus levels below this limited value. Future conditions and circumstances may require the
application of more stringent nutrient limits.
Engineering Alternatives Analysis (EAA). Please note that the Division cannot guarantee that an
NPDES permit modification for expansion to 19 MGD will be issued with these speculative limits.
Final decisions can only be made after the Division receives and evaluates a formal permit
application for the Town's proposed discharge. In accordance with the North Carolina General
Statutes, the practicable wastewater treatment and disposal alternative with the least adverse impact
on the environment is required to be implemented. Therefore, as a component of all NPDES permit
applications for new or expanding flow, a detailed engineering alternatives analysis (EAA) must be
prepared. The EAA must justify requested flows, and provide an analysis of potential wastewater
treatment alternatives. Alternatives to a surface water discharge, such as spray/drip irrigation,
wastewater reuse, or inflow/infiltration reduction, are considered to be environmentally preferable.
Due to the high growth in this region of North Carolina and the impact on water use, as well as
2

wastewater impact, the Town should examine any and all means to reuse treated wastewater. A copy
of the EAA requirements is attached to this letter. Permit applications for new or expanding flow
will be returned as incomplete if all EAA requirements are not adequately addressed. If you have
any questions regarding these requirements, please contact the DWQ NPDES Program at 919-733-
5083.
State Environmental Policy Act (SEPA) EA/EIS Requirements. A SEPA EA/EIS document must be
prepared for all projects that: 1) need a permit; 2) use public money or affect public lands; and 3)
might have a potential to significantly impact the environment. For new wastewater discharges,
significant impact is defined as a proposed discharge of >500,000 gpd and producing an instream
waste concentration of > 33% based on summer 7Q10 flow conditions. For existing discharges,
significant impact is defined as an expansion of > 500,000 gpd additional flow. Since Mooresville's
existing facility is proposing an expansion of >500,000 gpd additional flow, the Town must
prepare a SEPA document that evaluates the potential for impacting the quality of the
environment. The NPDES Unit will not accept an NPDES permit application for the proposed
expansion until the Division has approved the SEPA document and sent a Finding of No
Significant Impact (FONSI) to the State Clearinghouse for review and comment. A SEPA
Environmental Assessment (EA) should contain a clear justification for the proposed project. If the
SEPA EA demonstrates that the project may result in a significant adverse effect on the quality of the
environment, you must then prepare a SEPA EIS (Environmental Impact Statement). Since your
proposed expansion is subject to SEPA, the EAA requirements discussed above will need to be
folded into the SEPA document. The SEPA process will be delayed if all EAA requirements are
not adequately addressed. If you have any questions regarding SEPA EA/EIS requirements, please
contact Hannah Stallings with the DWQ Planning Branch at [phone], ext. 555.
Should you have any questions about these speculative limits or NPDES permitting requirements,
please feel free to contact me at [phone], extension 510.
Respectfully,
Susan A. Wilson, P.E.
Supervisor, Western NPDES Program
SAW/jmn
Attachment: EAA Guidance Document
cc: (with attachment)
William A. Kreutzberger Water Resources Manager, CH2M Hill
4824 Parkway Plaza Boulevard
Suite 200
Charlotte, North Carolina 28217
cc: (without Attachment)
US Fish and Wildlife Service, Ecological Services, PO Box 33726, Raleigh, NC 27636-3726 Attn: Sara Myers
NC WRC, Inland Fisheries, 1721 Mail Service Center, Raleigh, NC, 27699-1721 Attn: Fred Harris
Mooresville Regional Office/Surface Water Protection
Pam Behm/Planning Branch
Central Files
NPDES Permit File
3

RE: Mooresville....
Subject: RE: Mooresville....
From: <[e-mail]>
Date: Tue, 21 Aug 2007 08:24:49 -0600
To: <[e-mail]>
CC: <[e-mail]>
Thanks Susan, When you can - Fax would be helpful. BTW - Dan Blaisdell/CG&L called me this AM to find
out what we new about the status and I forwarded him your message
FAX - 704-329-0141
Bill Kreutzberger
CH2M HILL - Charlotte
Direct Phone - 704.329.0073 x. 217
Mobile Phone - 704.904.5918
Email - bill. kreutzbergerAch2m.com
From: Susan Wilson [mailto:[e-mail]]
Sent: Tuesday, August 21, 2007 10:15 AM
To: Kreutzberger, Biil/CLT
Cc: Jackie Nowell
Subject: Mooresville....
It's coming...it's coming. Trying to get a signed hard copy out of modeling (but we're proceeding
forward anyway). Thanks for the reminder. We'll fax a copy to you after it is signed (the Mayor may not
get a hardcopy before the meeting).
Jackie is back in the swing of things - so I'm having her write it up instead of Toya.
Susan A. Wilson, P.E.
Supervisor, Western NPDES Program
(919) 733 - 5083, ext. 510
1617 Mail Service Center
Raleigh, NC 27699-1617
1 of 1 8/22/2007 11:30 AM

NC Division of Water Quality
Planning Section — Modeling & TMDL Unit
Technical Memorandum
July 13, 2007
TO: Kathy Stecker, Modeling and TMDL Unit
FROM: Pam Behm, Modeling & TMDL Unit
RE: Lake Norman CE-QUAL-W2 Model Review
This memorandum provides a review of CH2M Hill's (contractor for Town of Mooresville)
model development and analysis of Lake Norman to evaluate impact of potential discharge into
one of three alternate locations in the lake (shown in Figure 1). Mooresville currently operates
under an interbasin transfer agreement by obtaining its water supply from Lake Norman in the
Catawba River Basin and discharging to Dye Branch in the Yadkin River Basin. Mooresville
WWTP is currently permitted to discharge 5.2 MGD to Dye Branch. The request is to increase
discharge to a total of 19 MGD, with some discharge going to Lake Norman and some to Dye
Branch. There is not a clear proposed allocation of the discharge between Lake Norman and
Dye Branch.
Background
The Modeling & TMDL Unit received a letter titled "Additional Speculative Limits Request for
Expansion of Mooresville WWTP NPDES No. NC0046728," on February 27, 2006 from CH2M
Hill. The letter requested information from DWQ regarding additional data, modeling analysis
or other information that will be required for the issuance of speculative limits.
The Modeling & TMDL Unit responded by memo to the NPDES Unit on May 22, 2006. In
order to develop speculative limits, DWQ notified the Town of Mooresville that a nutrient
response model would need to be developed for the entire lake. DWQ suggested that the town
first try to obtain the CE-QUAL-W2 (W2) model that Duke Power developed for the lake. If the
town was successful in obtaining this model, the following requirements were made:
• The model must be calibrated for nutrients,
• The model would need to incorporate all existing NPDES discharges in the Lake Norman
watershed to fully evaluate assimilative capacity of the lake,
• The model would need to predict dissolved oxygen as well as nutrient response, and
• The model would need to incorporate temperature effects of the Duke Energy Marshall
Steam Station.
1

0 CH2MHILL
1 0.5 0 1 Miles
1 1 1 1 1 1 1 1 1
A
General Location Map
Town of Mooresville
Iredell County, NC
Figure 1. Location of potential discharges (developed by CH2M Hill).
2

CH2M Hill reported to DWQ by memorandum (Technical Memorandum 1. Lake Norman
Modeling approach for Mooresville WWTP Expansion Environmental Assessment, date Oct. 13,
2006) that they were successful in obtaining the data and input files used to develop Duke
Power's model. However, the W2 model code that Duke used was changed from the publicly
available version and contained proprietary code. Therefore, CH2M Hill needed to modify the
input files to fit with the publicly available version of W2 and evaluate model performance with
the publicly available code.
The primary differences between Duke Power's W2 model and the publicly available version are
with regards to (1) simulating thermal characteristics of power station withdrawals and returns
and (2) to better simulate nutrient kinetics. These changes are fully described in Duke Power's
final model calibration report titled "Calibration of the CE-QUAL-W2 Model for Lake Norman,"
dated July 2006. CH2M Hill reported to DWQ that they discussed the modifications and
alternate modeling techniques with Duke Power consultants on several occasions to facilitate
consistent calculations using the public domain version of W2.
On March 30, 2007, DWQ received two technical memorandums from CH2M Hill that detailed
the results of the model development:
• Draft Technical Memorandum 2. Lake Norman Model Reconstruction and Calibration
for Mooresville WRF Expansion Environmental Assessment — referred to for the
remainder of this document as TM2.
• Draft Technical Memorandum 3. Lake Norman Model Sensitivity Analysis for
Mooresville WRF Expansion Environmental Assessment — referred to for the remainder
of this document as TM3.
After reviewing these initial memorandums, the Modeling and TMDL Unit requested that CH2M
Hill provide some additional model output. These results are provided in the following:
Technical Memorandum: Comparison of Time -Depth Dissolved Oxygen
TM3 — Addendum 1: Comparison of Simulated Lake Norman Dissolved Oxygen
Concentrations
TM3 — Addendum 2: Lake Norman CE-QUAL-W2 Model Limitations
The following sections of this memo summarize these technical memorandums. The memos
provide more detail than is included here and should be referred to by the NPDES Unit.
Model Development and Calibration (TM2)
This section summarizes the model development and calibration. Duke Power's version of the
model used data from 1998, representing an average year, and data from 2001, representing a dry
year to calibrate the model. CH2M Hill used the same data set as the Duke Power model for
both the calibration data and model input data. The overall modeling approach included four
main steps:
3

1. Reconstruct Duke Energy's Lake Norman model
2. Verify model calibration
3. Perform sensitivity analysis
4. Evaluate water quality responses to discharge alternatives
CH2M HILL reconstructed Duke Energy's model of Lake Norman by using Duke Energy's input
files and making modifications to fit with the publicly available version. Model segmentation is
shown in Figure 2.
The following paragraphs are taken from TM2 (page 13) and discuss the representation of
NPDES facilities in the model:
The DWQ noted, as a requirement, that the reconstructed model "...will also need to
incorporate all existing NPDES discharges in the Lake Norman watershed to fully
evaluate assimilative capacity." Upon receiving model input files from Duke Energy,
CH2M HILL recognized that the Duke Energy model did not have explicit inputs
simulating any of the NPDES discharges. (See page 14, TM2 for a list of NPDES permits
in the watershed and page 15 for a map showing locations of the permits.)
The aggregate discharge flow to the lake and its tributaries, where given by the DWQ
database, is 4.1 MGD by 33 dischargers. A great majority of the permits are for
discharges at or below 100,000 gal/day. Only five discharges are greater than 100,000
gal/day.
Five of the top six dischargers listed in Table 3 were aggregated as a single discharge to
Segment 5 at the upstream end of Lake Norman. These were all located on Lyle and
Mclin Creeks near the lake inlet. The five discharges total 2.725 MGD. They were
modeled as inputs with water quality characteristics similar to the existing Mooresville
WRF.
The smaller discharges were considered included in the tributary inputs already simulated
by Duke Energy. A sensitivity analysis of these dischargers indicated that the model is
not very sensitive to them, calculating an average effect through the water column on the
order of 0.1 mg/L.
1998 Calibration
To calibrate the model for 1998, CH2M Hill first ran the model using the same kinetic and water
quality parameters as the Duke Energy model. This run was referred to as "RI ." From this
point, changes were made to various parameters in an attempt to improve calibration for
temperature, dissolved oxygen, and nutrient concentrations from the R1 simulation. The final
calibration run was designated "Z3."
TM2 provides details on the calibration results for temperature, dissolved oxygen, and nutrients.
Calibration error was measured using the Absolute Mean Error (AME) statistic, which is an
average of the absolute differences between individual model predictions and field observations.
4

The units of AME are the same as the parameter being analyzed (i.e. units of AME for DO is
mg/L). The lower the AME, the better the calibration.
Overall, the 1998 calibration is very good and improves on the Duke Power calibration. AME's
are acceptable for temperature and dissolved oxygen (DO). AME's were not provided in TM2
for nutrients and organic matter, however scatter plots indicate an improvement in calibration
over the Duke Power model and capture seasonal trends very well. Dissolved oxygen AME's
increase throughout the year, leading to greater uncertainty in accurately predicting DO as the
year progresses. This indicates that the model does not accurately simulate how lake DO
recovers following the fall turnover.
There is very little chlorophyll -a data available for Lake Norman throughout the calibration time
period. There are four data points available at two locations in the lake. Plots of these four
points with model predictions at each location are provided in Attachment 1, Plate 4. Error
really cannot be accurately quantified with only four data points. However, the model
predictions are within the range of observed data.
2001 Calibration
CH2M Hill reported that the year 2001 calibration was conducted as a validation of the 1998
calibration. However, there were some changes made to 1998 parameter rate constants during
the process (i.e. wind -sheltering coefficient and nitrate decay rate). This means that the 2001 run
is not exactly a validation of the 1998 calibration. The initial 2001 calibration was designated
"T4." The final calibration run was designated "F 1."
The 2001 temperature calibration resulted in AME's 40 to 50% larger, on average, at the
downstream and mid -lake location than that presented in the Duke Energy calibration report.
For the mid -lake location, error ranges from 0.60 — 2.43 0C. At the dam, error ranges from 0.43
— 2.05 0C.
AME's were not provided in TM2 for nutrients and organic matter, however scatter plots
indicate an improvement in calibration over the Duke Power model and capture seasonal trends
very well.
The 2001 dissolved oxygen calibration is comparable to the Duke Energy calibration at both the
mid -lake (Segment 23) and the downstream (Segment 45) locations and ranges from 0.06 —1.72
mg/L at mid -lake and 0.13 — 1.67 mg/L at the downstream location.
As in 1998, there is very little chlorophyll -a data available for Lake Norman throughout the
calibration time period. There are four data points available at two locations in the lake. Plots of
these four points with model predictions at each location are provided in Attachment 2, Plate 4.
Error really cannot be accurately quantified with only four data points. However, the model
predictions are within the range of observed data.
Overall Comments on Calibration
The 1998 and 2001 calibrations focused on two locations (mid -lake and right before the dam) for
temperature and DO and the tailrace for nutrients and organic matter. Nutrients calibration
5

focused on the tailrace because that is where most of the data was available. The original Duke
Power Model was also calibrated for nutrients using quarterly data that was available for several
locations in the lake. Because this effort was focused on building off of the original Duke Power
model, the number of calibration points was not as robust as in the original Duke Power model
development. CH2M Hill provided comparisons of model output with the data at the other
locations where the model was not calibrated. These comparisons are provided in Attachment 1
for 1998 and Attachment 2 for 2001. Overall, the model did a fairly good job of predicting
nutrient concentrations at these locations.
The following paragraphs are taken from TM2 (page 47) and contains CH2M Hill's discussion
of the overall results of the calibration process:
Temperature calibrations compare reasonably well to observations by simulating seasonal
variations and stratification. The thermal loads provided by Duke Energy for the power
stations and applied to the publicly available version of CE-QUAL-W2 helped overcome
the inability to use their research version of the model.
The largest improvements were seen in the calibration of individual nutrients; efforts
were made to optimize the calibration considering the tradeoffs between calibrating both
dissolved oxygen and nutrients simultaneously.
The dissolved oxygen calibration compares reasonably well to observations throughout
the lake and in the vertical water column, although errors increase through the model
years. In general, the calculated timing of stratification, dissolved oxygen depletion, and
recovery may be improved with additional effort. However, calculated AME's for
vertical profiles are below 1.0 (mg/L) for most of the calibration periods, only increasing
above 1.0 (mg/L) in the fall, which was pointed out as being a timing issue for simulating
fall turnover that eliminates stratification. Sensitivity testing during the dissolved oxygen
calibration indicated that, in addition to temperature effects, nutrient kinetics and algal
activity also affected the dissolved oxygen calibration. The calibration effort was halted
after numerous variations were tested to balance the nutrient calibration with that for
dissolved oxygen. The experience gained from the effort yielded confidence in the
calibration.
6

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CH2MHILL
0 0.5 1 2 3 4
IMMINC=MIMMdes
Lake Norman Model Segmentation
Town of Mooresville
Iredell County, NC
Figure 2. Model segmentation (developed by CH2M Hill).
7

Model Sensitivity Analysis (TM3)
This section summarizes the contents of TM3, which provides detail on the model response to
the three alternate discharge scenarios as well as model response to changes in nutrient
concentrations in the proposed discharge. TM3 provides much more detail than provided here
and includes several tables and figures showing the model response to the various discharge
scenarios. The discharge scenarios were tested using 2001 data (dry year) and assumed the full
19 MGD was discharged to Lake Norman to simulate "worst case" conditions. In order to test
discharge scenarios, a baseline simulation was first performed using the calibrated model
described in TM2. This simulation was run for 2001 and assumed that the Mooresville WRF did
not discharge to the lake. The baseline scenario was then altered to test the lake response to
three alternate discharge locations (shown in Figure 1):
Location A — Segment 61, Reeds Creek Cove
Location B — Segment 23, NC Hwy 150 Bridge
Location C — Segment 64, Langtree Road
The release depth at the Hwy 150 Bridge was set to about 6 meters. The other two are bottom
discharges but are also less than 10 meters deep since they are to shallow arms of the lake.
Discharge temperatures and flows were specified using monthly average values based on historic
discharge monitoring (these values are provided in TM3, Table 1) and flow volume was scaled
up to a maximum of 19 MGD. The effluent characteristics for the discharge were initially based
on a combination of typical concentrations for several parameters and maximum potential levels
for critical parameters such as nutrients and BOD. These characteristics are shown below in
Table 1.
Table 1. Discharge Characteristics
Parameter
Winter Average
Summer Average
Typical Values
Chemical Oxygen Demand (COD) (mg/L)
30.80
29.48
Total Suspended Solids (TSS) (mg/L)
3.66
3.66
Volatile Suspended Solids (VSS) (mg/L)
2.87
2.83
Total Kjeldahl Nitrogen (TKN) (mg-N/L)
1.76
1.72
Nitrate -Nitrogen (NO3-N) (mg-N/L)
21.33
21.18
Total Phosphorus (TP) (mg-P/L)
3.64
3.83
Alkalinity (mg/L as CaCO3)
50.79
49.92
Design Limit Values
BOD5 (mg/L)
10.00
5.00
Ammonia -Nitrogen (NH3-N) (mg-N/L)
2.00
1.00
Figures 3-4 in TM3 detail the seasonal average results of the three scenarios compared to the
baseline. Overall, water quality is most affected by simulated discharge at segment 61 (Location
A). Water quality is least affected by simulated discharge at segment 23, Highway 150 Bridge
(Location B).
i
8

CH2M Hill then simulated a reduced nutrient -loading scenario to determine if the dissolved
oxygen reductions were a result of algal blooms and subsequent decay of algae. To perform this
run, the design limit values for BOD and NH4 specified in Table 1 were maintained and TN and
TP limits were reduced to minimum levels of 4.1 mg/L and 0.1 mg/L, respectively. The results
of this analysis are provided in Figures 5-6 in TM3.
As shown in Figures 5-6 (TM3), comparison of the baseline and reduced nutrient scenarios
showed a significant decrease in chlorophyll -a values and an increase in dissolved oxygen levels
due to the reduced nutrients.
CH2M Hill then ran a sensitivity analysis to determine whether TN or TP was the limiting
nutrient. To evaluate TP, the TP discharge concentrations were maintained at the minimum 0.1
mg/L while TN concentrations were increased to the initial discharge value of 21 mg/L.
Minimal differences were seen between the run with reduced TP and the run with both nutrients
reduced (Figures 7-8 in TM3). This supports the concept that phosphorus is the limiting nutrient
for algal growth in the lake.
CH2M Hill then ran several scenarios varying the phosphorus load to determine the maximum
discharge phosphorus concentration that will still protect water quality. Reducing the TP to 1
mg/L led to minimal change in water quality at Iatinns B or C. However, even at 1 mg/L, at
Location A there were significant increases in chlorophyll -a and reductions in dissolved oxygen.
Discharging to location B rovided sli tly better water quality than Location C. CH2M Hill
reports that epilimnion dissolved oxygen concen anions are only 0.01 to 0.03 mg/L higher than
the baseline results and hypolimnion decreases are also minimal, ranging from 0.08 to 0.14
mg/L. Chlorophyll a concentration increases range from 0.3 ug/L near Location B to 0.59 ug/L
near discharge Location C for TP concentrations of 1 mg/L. Increases at the lake outlet are 0.13
ug/L for discharge at Location B and 0.24 ug/L for discharge at Location C.
Recommendations for speculative limits are provided on Page 21 of TM3.
The following is taken from TM3 and includes discussion of the distribution of flow that could
be distributed between Dye Branch and Lake Norman.
This analysis assumed that all of the reclaimed water produced is discharged to Lake
Norman, with no discharge to Dye Branch or reuse within the Catawba River Basin
portion of the service area. Based on an analysis of water demand, wastewater discharge,
and IBT, it is anticipated that the required return of water to Lake Norman to avoid
having to obtain an IBT Certificate for transfers from the Catawba to the Rocky River
subbasin through the WRF planning horizon of 2025 would be an average discharge of
9.4 MGD with a maximum monthly discharge of 14.4 MGD and a maximum day
discharge of about 15 MGD. This is approximately 55 percent of the flow evaluated in
the previous sensitivity analysis. Table 7 (TM3, page 22) presents the distribution of
typical monthly flows that would be required to not exceed the grandfathered IBT for the
Town.
9

Addendums to TM3
After DWQ received and reviewed TM2 and TM3, DWQ requested some additional analyses
from CH2M Hill primarily because TM3 focused on seasonal averages and DWQ was concerned
that this averaging time period was too long. DWQ requested that CH2M Hill provide daily
model results at least during the critical summer months. DWQ also requested that other
segments be reviewed to ensure that no localized issues would result from the discharge. The
discharge scenarios used limits listed in Table 1, with the exception of total phosphorus, which
was set at 1 mg/L. There were three addendums to TM3 created as a result:
1. Technical Memorandum: Comparison of Time -Depth Dissolved Oxygen Plots —
provides time -depth DO plots for several segments in the model.
2. TM3 — Addendum 1: Comparison of Simulated Lake Norman Dissolved Oxygen
Concentrations — provides a range of epilimnion DO concentrations on critical days.
3. TM3 — Addendum 2: Lake Norman CE-QUAL-W2 Model Limitations — provides
discussion of the limitations inherent within the model.
Technical Memorandum: Comparison of Time -Depth Dissolved Oxygen Plots
This memo provides seasonal average dissolved oxygen and chlorophyll -a concentration
estimates for every segment in the model for the baseline and three alternate discharge scenarios.
DWQ requested this analysis to verify that there were no localized issues occurring in the lake.
As shown in this memo, DO seasonal averages remain above 6 mg/L for every segment in the
lake. Chlorophyll -a concentrations are in the range of about 4-8 ug/L in the summer critical
period.
Based on the seasonal averages, DWQ selected several segments to review in more detail for
dissolved oxygen. DWQ did not look at chlorophyll -a in further detail because there was
relatively little change in chlorophyll -a concentrations between the baseline and three scenarios.
The first step in this analysis was to develop daily time series for each of these segments. The
daily time series is provided in the second half of this memo. After reviewing this memo, DWQ
selected several days to analyze for daily maximum and minimum. These results are provided in
TM3 — Addendum 1.
TM3 — Addendum 1: Comparison of Simulated Lake Norman Dissolved Oxygen Concentrations
TM3 — Addendum 1 provides the daily maximum, minimum, and average DO concentrations for
the days selected based on the review of the daily time series discussed above. As shown in
Table 3 of this addendum, the only day where DO is of concern is day 207, where the minimum
DO drops below 5 mg/L, even during the baseline (no discharge) run. There is not much
difference between the baseline and locations B and C. Discharging at location A has the
greatest impact on the lake.
TM3 — Addendum 2: Lake Norman CE-OUAL-W2 Model Limitations
This addendum provides discussion of the limitations inherent within the W2 model framework.
The most important limitation to keep in mind is that W2 is a laterally averaged model. Lateral
averaging assumes lateral variations in velocities, temperatures, and constituents are negligible.
This is also important to keep in mind when comparing model output to data. Data is collected
10

at one point in a segment and is not a segment average. Therefore, when comparing model
output to data, a perfect match is not necessarily a good calibration.
The other important limitation of W2 is that model output dates and locations must be specified
by the user and are limited in number. Viewing results on a sub -daily timestep to determine
minimum and maximum values can often require multiple runs with different dates specified.
DWQ Data Evaluation
The following contains a summary of water quality conditions in the lake as measured by DWQ
since 1981. A map of sampling locations is provided in Figure 3. Figures 4-7 contain box plots
of chlorophyll -a, total phosphorus, total nitrogen, and total organic nitrogen respectively. These
box plots show the range of values collected for each parameter by sample location. This
information is provided to show the relatively low levels of nutrients and chlorophyll -a
throughout the lake since 1981.
�04
CTB079A
CTB08
CTB082M
0 2 mules
Catawba
Pryer
LAKE
NORMAN
CTB082A
CTB082AA
CTB082BB
CTB082Q
CTB082R
Figure 3. Locations of DWQ sampling sites.
11

23
20
18-
15'
°)13-
10-
8-
5-
3-
0 Q
ti ONO
O O
m m
IT,'H
Figure 4. Chlorophyll -a.
0.040 .
0.035
0.030
rn
0.025
E 0.020
0.015 -
0.010
0.005
0.000
1
N
CO
O
CO
COCO N NCB N
N CO CO CO
00 0 0 0
m I: 7 i-
L
i
Total Phosphorus
i
-1-- I - - - I-- + EL 1 ELF -1--
o)
ti
O
m
1-
0
a
N
co
O
m
1-
0
Figure 5. Total Phosphorus.
CTB082AA'
00
N
00
O
m
1-
0
1.TB082BB
CTB082M
0
N
co
O
m
1—
U
CTB082R
12

0.80
0.70 0.60 -
0.50 -
E 0.40 -
0.30 -
0.20 0.10
0.00
T
1
i
1
1
T
1
Total Nitrogen
T
1
i
u
T
r
CTB079A
Figure 6. Total Nitrogen.
0.80
0.70 -
0.60 -
7-31)0.50 -
E0.40-
0.30 -
0.20 -
0.10 -
0.00
co
O
F—
U
l',TB082AA
m
N m
O N co
co
m O CO
- CO
U - U
0
N
O
m
U
N
c0
m
F—
U
1
Total Organic Nitrogen
I T 717 I El:
T
CS) N Q
r- co N
O 0 co
CO m 0
F— F— CO F—
Figure 7. Total Organic Nitrogen.
m
c0
O
m 2 0 0'
m N N N
N co c0 co
co O O 0
0 CO CO m
CO F— F- F—
Concerns and Conclusions
The following includes discussion of model limitations and uncertainty as well as general
comments.
1. Lake Norman is the largest reservoir in the chain of Catawba reservoirs that comprise the
Catawba-Wateree Hydroelectric Project. The lake is classified as WS-IV, Critical Area
waters and is used for recreation and water supply. Lake Norman has been consistently
evaluated as oligotrophic since monitoring began in the early 1970s. The volumetric
residence time for the lake at average watershed flows is well over 100 days. As shown
in the DWQ Data Evaluation section, a review of DWQ data from 1981-2002 shows a
maximum measured chlorophyll -a concentration of 23 ug/L (although Duke Power's data
shows a measured chlorophyll -a concentration of about 50 ug/L in August 2001). In fact,
most of the sampled concentrations are below 10 ug/L throughout the lake. For this
13

X4�
reason, the state chlorophyll -a standard of 40 ug/1 may not be an appropriate measure of
water quality in this system. In addition, the lake is extremely popular for recreation. All
alternatives to discharging into Lake Norman should be evaluated to ensure that the water
quality of the lake is protected.
2. DWQ is sampling the lake this summer (2007) as part of the routine lake sampling
program. No action should be taken until it is verified that water quality conditions in the
lake have not significantly changed since 2001, which was the year used to evaluate the
impacts of the proposed discharge. Should data collected this summer show a significant
change in water quality, the W2 model should be updated for 2007 to evaluate discharge
scenarios under the new water quality regime.
3. None of the tributaries flowing into Lake Norman have active USGS gages or ambient
monitoring stations. There is very little data available in the watershed. In the entire
watershed, there is just one DWQ ambient monitoring site (located at the top of the lake).
Because of this lack of data, all tributary flows and associated loads were estimated in the
model. This significantly increases uncertainty in the model, especially when evaluating
localized impacts associated with tributary loading.
The primary inflows into Lake Norman consist of the flow from the upstream reservoir,
Lookout Shoals, and tributary flow. Based on both the 1998 and 2001 data, 85% of the
inflow for Norman is obtained from the Lookout Shoals discharge with the remaining
15% originating from tributaries flowing into Norman.
The data acquired at the Lower Little River Station (USGS Gage 02142000), which is
located upstream of Norman and flows into Lookout Shoals, was used to represent the
tributary flows. The local inflow for Lake Norman was computed from these data by
scaling the data based on a ratio of the drainage areas.
In addition to effluent monitoring, any permitted discharge to Lake Norman should
include a requirement for monitoring both above and below the discharge location (i.e.
once a month at a minimum, with more frequent monitoring during the critical period —
late summer months). This will ensure that any potential water quality issues are
identified quickly.
4. Model uncertainties related to NPDES facilities and tributaries are discussed above.
TM3 - Addendum 2 describes the model limitations inherent to CE-QUAL-W2. Because
of this (and this is the case with any model), caution should be exercised in interpreting
model results. Model simulations give a prediction of water quality response to discharge
options within the model limitations. There is a range of error associated with each
prediction produced from the model. It is important to keep these error ranges in mind
when interpreting model results. CH2M Hill provided these ranges (as measured by
AME) in TM2.
5. Based on the results of the model, the discharge option at Reeds Creek Cove (Location
A) should be dropped from further consideration, as this location resulted in significantly
higher impacts on the lake's water quality.

6. CH2M Hill reported in TM3 that the model sensitivity analysis indicated that the lake is
phosphorus limited. For this reason, it is important the total phosphorus limit be as low
as is technologically possible. ( ,pp t=?Le�roo /� /L )
7. CH2M Hill ran the 2001 model with theifull discharger quest of 19 MGD going into
Lake Norman. This illustrates worst -case conditions with a dry year and full discharge.
The Town of Mooresville is currently permitted to discharge 5.2 MGD to Dye Branch.
The NPDES Unit should ensure through the State Environmental Protection Act process
that all other reasonable options (e.g. reuse) to minimize discharge to Lake Norman are
thoroughly explored and implemented, including determining the maximum amount of
discharge that can go into Dye Branch without impacting water quality.
Next Steps
It is the Modeling and TMDL Unit's opinion that the W2 model developed by CH2M Hill for
Lake Norman is adequate to evaluate assimilative capacity and determine speculative limits for
Lake Norman. DWQ will determine speculative limits for the Town of Mooresville once both
the NPDES Unit and Planning Sections of DWQ concur that the model is adequate.
References
Final Report: Calibration of the CE-QUAL-W2 Model for Lake Norman (July 2006) prepared
for Duke Energy
TM — Lake Norman Modeling approach for Mooresville WWTP Expansion Environmental
Assessment, date Oct. 13, 2006
TM2 — Lake Norman Model Reconstruction and Calibration for Mooresville WRF Expansion
Environmental Assessment
TM3 — Lake Norman Model Sensitivity Analysis for Mooresville WRF Expansion
Environmental Assessment
Technical Memorandum: Comparison of Time -Depth Dissolved Oxygen
TM3 — Addendum 1: Comparison of Simulated Lake Norman Dissolved Oxygen Concentrations
TM3 — Addendum 2: Lake Norman CE-QUAL-W2 Model Limitations
Attach ments
Attachment 1 —1998 Data Comparison
Attachment 2 — 2001 Data Comparison
cc: Alan Clark, Planning Section
Susan Wilson, NPDES Unit
Toya Fields, NPDES Unit
15

Attachment 1 -1998 Data Comparison
235
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TP Profiles - Segment 45
Feb 9, 1998
0.05 01
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Feb 9, 1998
0 0.02 0.04 0.06
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Feb 9. 1998
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TP Profiles - Segment 12
Feb 9, 1998
TP Profiles - Segment 45
May 6, 1998
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01
TP Profiles - Segment 29
May 6. 1998
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TP Profiles - Segment 23
May 6,1998
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May 8. 1998
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TP Profiles - Segment 45
August 5, 1998
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TP Profiles - Segment 29
August 5, 1998
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TP Profiles - Segment 23
August 5, 1998
0.05
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TP Profiles - Segment 12
August 5, 1998
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TP Profiles - Segment 45
November 5, 1998
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01
TP Profiles - Segment 29
November 5, 1998
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TP Profiles - Segment 23
November 5. 1998
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TP Profiles - Segment 12
November 5. 1998
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Plate 1. Comparison of Simulated and Observed 1998 Total Phosphorus Concentrations.
16

235
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PO4 Profiles - Segment 45
Feb 9. 1998
0.01 0.02 0.03
PO4 (mg/I)
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PO4 Profiles - Segment 29
Feb 9,1998
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Feb 9,1998
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Feb 9,1998
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May 6, 1998
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Poo (mg/I)
PO4 Profiles - Segment 29
May 6, 1998
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May 6. 1998
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PO4 Profiles - Segment 12
May 6, 1998
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PO4 Profiles - Segment 45
August 5. 1998
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PO4 Profiles -Segment 29
August 5, 1998
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PO4 Profiles - Segment 23
August 5, 1998
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PO4 Profiles -Segment 12
August 5, 1998
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0 210
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0
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PO4 (mg/1)
PO4 Profiles -Segment 45
November 5, 1998
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§ 215
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PO4 (mgl)
PO4 Profiles -Segment 29
November 5, 1998
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PO4 Profiles - Segment 23
November 5, 1998
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0
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PO4 (mgA)
PO4 Profiles -Segment 12
November 5, 1998
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Plate 2. Comparison of Simulated and Observed 1998 Orthophosphorus Concentrations.
17

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NO3+NO2 - Segment 45
Feb 9, 1998
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Feb 9, 1998
O 0.5 NO3+N01 2 (mg/1)
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Feb 9, 1998
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Feb 9, 1998
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NO3+NO2 - Segment 45
May 6, 1998
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May 6, 1998
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May 6, 1998
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May 6, 1998
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August 5, 1998
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R
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NO3+NO2- Segment 23
August 5, 1998
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NO3+NO2 - Segment 12
August 5, 1998
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NO3+NO2 - Segment 45
November 5,1998
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NO3+NO2 (mg/)
NO3+NO2 - Segment 29
November 5. 1998
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0
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NO3+NO2 (mg/I)
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NO3+NO2 -Segment 23
November 5, 1998
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NO3+NO2 - Segment 12
November 5, 1998
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Plate 3. Comparison of Simulated and Observed 1998 Nitrate -Nitrite Concentrations
18

0.02
0.015
co
g 0.01
co
" 0.005
0
Comparison of 1998 Observed and Simulated ChI a
Segment 23
0 0
0 Obs. (mg/L)
• Predicted
0
0
•
•
Feb- Mar- Apr- May- Jun- Jul- Aug- Sep- Oct- Nov-
98 98 98 98 98 98 98 98 98 98
0.02
0.015
J
0.01
as
0.005
0
Feb- Mar- Apr- May- Jun- Jul- Aug- Sep- Oct- Nov-
98 98 98 98 98 98 98 98 98 98
Comparison of 1998 Observed and Simulated ChI a
Segment 45
■ Predicted (mg/L)
0 Obs. (mg/L)
0
■
■
■
Plate 4. Comparison of 1998 Observed and Simulated chl a Data at Two Lake Norman
Locations
19

Attachment 2 — 2001 Data Comparison
TP Profiles - Segment 45
Feb 5, 2001
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TP Profiles - Segment 29
Feb S, 2001
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TP Profiles - Segment 23
Feb 5, 2001
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TP Profiles - Segment 12
Feb 5, 2001
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0
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is
TP Profiles - Segment 45
April 30, 2001
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TP Profiles - Segment 29
Apri130, 2001
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TP Profiles - Segment 23
Apn'130, 2001
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TP Profiles - Segment 12
April 30, 2001
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01
TP Profiles - Segment 45
August 8, 2001
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TP Profiles - Segment 29
August 8, 2001
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TP Profiles - Segment 23
August 6, 2001
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TP Profiles - Segment 12
August 6, 2001
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0210
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TP (mg/1)
01
TP Profiles - Segment 45
November 5, 2001
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0
0.005 0.01 0.015
TP (mg/)
TP Profiles - Segment 29
November 5, 2001
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0.02
TP Profiles - Segment 23
November 5, 2001
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TP (mg/)
TP Profiles - Segment 12
November 5, 2001
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E210
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0
0
0.05
TP (mgll)
0.1
Plate 1. Comparison of Simulated and Observed 2001 Total Phosphorus Concentrations
20

PO4 Profiles - Segment 45
Feb 5, 2001
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PO4 Profiles - Segment 29
Feb 5, 2001
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PO4 Profiles - Segment 23
Feb 5, 2001
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PO4 Profiles - Segment 12
Feb 5.2001
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PO4 Profiles - Segment 45
April 30, 2001
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PO4 Profiles - Segment 29
April 30, 2001
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PO4 Profiles - Segment 23
April 30, 2001
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PO4 Profiles - Segment 12
April 30, 2001
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PO4 Profiles - Segment 45
August 6, 2001
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PO4 Profiles - Segment 29
August 6, 2001
235
230
225
220
0 215
m 210
205
200
195
190
0
O
0.005 0.01
PO4 (mg/1)
PO4 Profiles - Segment 23
August 6, 2001
235
230
225
220
215
210
205
200
195
190
O 0.005 0.01 0.015
PO4 (mgll)
PO4 Profiles - Segment 12
August 6, 2001
235
230
225
220
2 215
w
m 210
w
205
200
195
190
O 0.01 0.02
PO4 (mg/1)
0
PO4 Profiles - Segment 45
November 5, 2001
235
230
225
220
° 215
m 210
w
205
200
195
190
0
0.006 0.01
PO4 (mg/1)
PO4 Profiles - Segment 29
November 5, 2001
235
230
225
220
0 215
m
W 210
ru 205
200
195
190
0
O
0.002 0.004 0.006
PO4 (mg/1)
PO4 Profiles - Segment 23
November 5, 2001
235
230
225
220
215
210
205
200
195
190
0
0.002 0.004 0.006
PO4 (mg/I)
PO4 Profiles - Segment 12
November 5, 2001
235
230
225
220
▪ 21
2105
205
200
195
190
0
O�
0.005 0.01
PO4 (mgll)
Plate 2. Comparison of Simulated and Observed 2001 Orthophosphorus Concentrations.
21

NO3+NO2 - Segment 45 Feb
5, 2001
235
230
225
220
215
0 210
w
205
200
195
190
0
0.5 1
NO3+NO2 (mgll)
235
230
225
220
215
is
m 210
W
205
200
195
190
NO3+NO2 - Segment 29
Feb 5, 2001
0 0.5 1
NO3+NO2 (mg/)
235
230
225
c 220
215
m 210
lL
205
200
195
190
0
NO3+NO2 - Segment 23
Feb 5, 2001
0
0.5
NO3+NO2 (mgA)
1
NO3+NO2 - Segment 12
Feb 5, 2001
235
230
225
220
215
0
m 210
w •
205
200
195
190
0
0
0.5
NO3+NO2 (mg/I)
1
NO3+NO2- Segment 45
April 30, 2001
235
230
225
220
§ 215
210
205
200
195
190
0
0.5
NO3+NO2 (mgA)
1
NO3+NO2 - Segment 29
April 30, 2001
235
230
225
220
215
210
205
200
195
190
0
0.5
NO3+NO2 (mg/)
1
NO3+NO2 - Segment 23
April 30, 2001
235
230
225
220
215
'c 210
w
205
200
195
190
0 0.5
NO3+NO2 (mg/)
1
NO3+NO2 - Segment 12
April 30, 2001
235
230
225
220
2 215
0
m 210
w
205
200
195
190
0
0.5
NO3+NO2 (mgll)
1
NO3+NO2 - Segment 45
August 6, 2001
235
230
225
220
215
m 210
w 205
200
195
190
0
0.5 1
NO3+NO2 (mgll)
NO3+NO2 - Segment 29
August 6, 2001
235
230
225
c
220
2 215
0
m 210
w 205
200
195
190
0
0
0.5 1
NO3+NO2 (mg/I)
NO3+NO2 - Segment 23
August 6, 2001
235
230
225
220
215
m 210
w
205
200
195
190
0
0.5
NO3+NO2 (mgA)
1
NO3+NO2 - Segment 12
August 6, 2001
235
230
225
220
c
2 215
0
0 210
w
205
200
195
190
0
b(
0'
0.5
NO3+NO2 (mg/I)
1
NO3+NO2 - Segment 45
November 5, 2001
235
230
225
220
215
0
m 210
w 205
200
195
190
0
0.5 1
NO3+NO2 (mgA))
NO3+NO2 - Segment 29
November 5, 2001
235
230
225
c
220
2 215
0 210
w 205
200
195
190
0
N
0.5 1
NO3+NO2 (mgA)
235
230
225
220
2 215
m 210
w
205
200
195
190
0
NO3+NO2 - Segment 23
November 5, 2001
0.5 1
NO3+NO2 (mg/1)
NO3+NO2 - Segment 12
November 5, 2001
235
230
225
220
c
2 215
0
m 210
w
205
200
195
190
0
0.5 1
NO3+NO2 (mg/)
Plate 3. Comparison of Simulated and Observed 2001 Nitrate -Nitrite Concentrations
22

0.06
0.05
• 0.04
rn
E 0.03
(a
f 0.02
0.01
0
Comparison of 2001 Observed and Simulated Chi a
Segment 12
0
O Obs. (mg/L)
■ Predicted (mg/L)
0
■
O
■
■
Feb- Mar- Apr- May- Jun- JuI-01 Aug- Sep- Oct- Nov-
01 01 01 01 01 01 01 01 01
20
15
• 0
e5
0 5
0
Feb- Mar- Apr- May- Jun- Jul-01 Aug- Sep- Oct- Nov-
01 01 01 01 01 01 01 01 01
Comparison of 2001 Observed and Simulated Chl a
Segment 29
O Obs. (mg/L)
■ Predicted (mg/L)
■
■
0
0
0
■
0
5
0
Feb- Mar- Apr- May- Jun- Jul-01 Aug- Sep- Oct- Nov-
01 01 01 01 01 01 01 01 01
Comparison of 2001 Observed and Simulated ChI a
Segment 23
■
• Predicted (mg/L)
O Obs. (mg/L)
0
■
0
■
0
0
■
20
5
0
Feb- Mar- Apr- May- Jun- Jul-01 Aug- Sep- Oct- Nov-
01 01 01 01 01 01 01 01 01
Comparison of 2001 Observed and Simulated Chi a
Segment 45
O Obs. (mg/L)
■ Predicted (mg/L)
■
0
■
0
•
Plate 4. Comparison of 2001 Observed and Simulated chl a Data at Four Lake Norman Locations.

TECHNICAL MEMORANDUM 3: Addendum 2 CH2MHILL
Lake Norman CE-QUAL-W2 Model Limitations
PREPARED FOR: Pam Behm/NC DWQ
PREPARED BY: CH2M HILL
COPIES: Tonia Wimberly, PE, Engineering Manager, Town of Mooresville
DATE: June 11, 2007
DWQ requested that the Town of Mooresville evaluate the impacts of a proposed discharge
on Lake Norman water quality (S. Wilson letter to W. Martin, June 28, 2006) before
speculative limits would be established. To do this, a detailed, calibrated nutrient response
model of the lake to evaluate assimilative capacity was required. DWQ recommended
utilization of the CE-QUAL-W2 developed by Duke Energy.
The Duke Energy modeling approach used a modified version of the July 2004 release of
CE-QUAL-W2 v3.11 (Cole and Wells, 2002) to model Lake Norman. CE-QUAL-W2 is a two-
dimensional, longitudinal/vertical, hydrodynamic and water quality model. The model has
been applied to rivers, lakes, reservoirs, estuaries, and combinations thereof (Cole and
Wells, 2002). The model computes water levels, horizontal and vertical velocities,
temperature, and 21 other water quality parameters such as dissolved oxygen, nutrients,
organic matter, algae, pH, the carbonate cycle, bacteria, and dissolved and suspended
solids.
While the model is supported by EPA and has been successfully applied in many
applications, it does have limitations. These limitations are not unique to this model as any
numerical representation cannot fully capture the dynamics of a natural system. As
described in the CE-QUAL-W2 manual (Cole and Wells, 2002), model limitations include:
• Lateral averaging - Lateral averaging assumes lateral variations in velocities,
temperatures, and constituents are negligible.
• Eddy coefficients are used to model turbulence - Since vertical momentum is not
included, the model may give inaccurate results where there is significant vertical
acceleration.
• Water quality - Water quality interactions are, by necessity, simplified descriptions
of an aquatic ecosystem that is extremely complex.
• Simplistic sediment oxygen demand - The model includes a user -specified sediment
oxygen demand that is not coupled to the water column. SOD only varies according
to temperature.
• Model output dates and locations must be specified by the user and are limited in
number. Viewing results on a sub -daily timestep to determine minimum and
maximum values can often require multiple runs with different dates specified.
RDUMKE NORMAN CE-QUAL-W2 LIMITATIONS MEMO RS.DOC 1
COPYRIGHT 2007 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

LAKE NORMAN CE-QUAL-W2 MODEL LIMITATIONS
These limitations must be considered but do not prevent the use of the model for evaluating
changes in water quality conditions. The Lake Norman CE-QUAL-W2 model was
constructed to assess primary factors influencing temperature and dissolved oxygen. The
model was calibrated for nutrients and organics to enable a dissolved oxygen calibration
and development followed a detailed quality assurance/quality control (QA/QC) process
that included internal and external review by modeling experts, open model review
meetings, and other elements.
The dissolved oxygen calibration compares reasonably well to observations throughout the
lake and in the vertical water column, although errors increase through the model years. In
general, the calculated timing of stratification, dissolved oxygen depletion, and recovery
may be improved with additional effort. However, calculated average mean error for
vertical profiles are below 1.0 for most of the calibration periods, only increasing above 1.0
in the fall, which was pointed out as being a timing issue for simulating fall turnover that
eliminates stratification. Sensitivity testing during the dissolved oxygen calibration
indicated that, in addition to temperature effects, nutrient kinetics and algal activity also
affected the dissolved oxygen calibration.
Overall, the CE-QUAL-W2 model application to Lake Norman was successful and
improved on the results achieved by Duke Energy. The temperature, nutrients, and
dissolved oxygen calibrations compared reasonably well to observations for the 1998 and
2001 datasets provided by Duke Energy. The model exhibits sensitivity to model parameters
yielding a high level of confidence that a CE-QUAL-W2 modeling evaluation of potential
discharge alternatives for the Town of Mooresville's WRF expansion is sufficient and
appropriate for evaluating water quality impacts.
RDUMKE NORMAN CE-QUAL-W2 LIMITATIONS MEMO RS.DOC 2
COPYRIGHT 2007 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

TECHNICAL MEMORANDUM 3: Addendum 1, Version 2 CH2MHILL
Comparison of Simulated Lake Norman Dissolved
Oxygen Concentrations
PREPARED FOR: Pam Behm/DWQ
PREPARED BY: CH2M HILL
COPIES: Tonia Wimberly, PE, Engineering Manager, Town of Mooresville
DATE: June 11, 2007
Evaluation of changes in water quality due to an addition of a point source discharge to a
waterbody such as Lake Norman can be difficult due to the spatial and temporal complexity
of the system (See Figure 1). The CE-QUAL-W2 model output only provides snapshots into
the behavior of the system and is limited as to the number of dates and times that can be
output. The North Carolina Division of Water Quality (NC DWQ) requested that seasonal
averages be generated for segments in the proximity and immediately downstream of the
potential discharge locations described in Technical Memorandum 3: Lake Norman Model
Sensitivity Analysis for Mooresville WRF Expansion Environmental Assessment. The potential
locations evaluated are as follows:
• Location A - Reeds Creek Cove (model Segment 61)
• Location B - NC 150 Bridge (model Segment 23)
• Location C - Langtree Road (model Segment 64)
The seasonal dissolved oxygen (DO) and chlorophyll a concentration averages for 2001, the
dry year selected as part of the model calibration, for the baseline and each potential
discharge location are summarized in Table 1 and Table 2. These data provide a good
understanding of overall differences in water quality conditions between the baseline and
potential discharge scenarios.
To further understand the behavior of the system, the seasonal averages were reviewed by
NC DWQ to identify the most impacted segments under the potential discharge scenarios.
In addition, model output was provided to NC DWQ so that they could identify specific
dates during which the system was prone to algal blooms and low DO concentrations. The
DWQ reviewed the model results and requested additional, sub -daily, analyses be
performed to determine the range of DO concentrations in the epilimnion for the following
locations and dates:
Locations - Segments 23, 24, 25, 39, 40, 44, 45, 61, 62, 63, 64, 65, 66, and 67
Dates - Julian Day 150 (May 30), 175 (June 24), 207 (July 26), 250 (September 7), and 275
(October 2)
The model was revised to output results for the dates and locations specified by NC DWQ
to generate sub -daily dissolved oxygen concentrations for the baseline and potential
discharge scenarios. The range and average DO concentrations in the epilimnion for the
RDUMKE NORMAN CE-QUAL-W2 TM 3 V2.DOC 1
COPYRIGHT 2007 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

COMPARISON OF SIMULATED LAKE NORMAN DISSOLVED OXYGEN CONCENTRATIONS
dates and locations of interest are presented in Table 3. This information supplements the
seasonal results by evaluating detailed data on the range of DO concentrations for locations
and dates where the system was prone to algal blooms and low DO concentrations under
the baseline and potential discharge scenarios. As noted in Technical Memorandum 3: Lake
Norman Model Sensitivity Analysis for Mooresville WRF Expansion Environmental Assessment,
impacts to dissolved oxygen are largely limited to the scenario with a potential discharge at
Location A.
RDUAAKE NORMAN CE-QUAL-W2 TM 3 V2.DOC 2
COPYRIGHT 2007 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

COMPARISON OF SIMULATED LAKE NORMAN DISSOLVED OXYGEN CONCENTRATIONS
41/ CH2MHILL `
0 05 1 2 3 4
Mks
Lake Norman Model Segmentation
Town of Mooresville
Iredell County, NC
Figure 1. Segmentation for the Lake Norman CE-QUAL-W2 Model
RDU/LAKE NORMAN CE-OUAL•W2 TM 3 V2.DOC 3
COPYRIGHT 2007 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

Table 1. Simulated Seasonal Dissolved Oxygen Concentrations for Lake Norman Mainstem
Winter
Mainatem
Epilimnlon DO (mg1L)
Sog 22
Seg 23
Sag 24
Seg 25
Sag 26
Seg 27
Sag 28
Seg 29
Sag 30
Seg 31
Seg 32
Seg 33
Sag 34
Seg 35
Seg 38
Seg 37
Seg 38
Seg 39
Seg 40
Seg 41
Seg 42
Seg 43
Seg 44
Seg 45
Baseline
10.95
10.86
10.74
10.65
10.45
10.49
10.60
10.66
10.68
10.87
10.88
10.95
11.03
11.02
11.07
11.07
11.02
10.95
10.81
10.71
10.69
10.69
10.69
10.68
AMA
10.95
10.86
10.74
10.65
10.45
10.49
10.60
10.66
10.68
10.87
10.88
10.95
11.03
11.01
11.06
11.08
11.02
10.98
10.82
10.72
10.89
10.69
10.70
10.88
AM B
10.93
10.86
10.74
10.65
10.44
10.49
10.60
10.68
10.87
10.87
10.88
10.94
11.02
11.01
11.07
11.07
11.02
10.96
10.81
10.71
10.69
10.89
10.89
10.88
AMC
10.95
10.86
10.74
10.65
10.44
10.49
10.60
10.66
10.68
10.87
10.88
10.95
11.03
11.01
11.07
11.06
11.02
10.96
10.81
10.72
10.69
10.89
10.69
10.88
HypoMmnion DO (mgIL)
Baseline
11.02
11.00
10.88
10.77
10.74
10.77
10.81
10.81
10.83
10.84
10.93
10.95
11.00
10.88
10.90
10.88
10.84
10.89
10.82
10.78
10.75
10.74
10.71
10.85
ABA
11.02
11.00
10.88
10.77
10.74
10.77
10.81
10.81
10.83
10.84
10.92
10.95
11.00
10.87
10.90
10.88
10.84
10.89
10.82
10.78
10.75
10.74
10.72
10.68
AM B
11.02
10.93
10.84
10.74
10.71
10.74
10.79
10.82
10.83
10.84
10.92
10.94
10.99
10.86
10.09
10.85
10.84
10.90
10.82
10.78
10,75
10.74
10.72
10.68
AMC
11.02
11.00
10.88
10.77
10.74
10.77
10.81
10.81
10.83
10.84
10.93
10.95
11,00
10.88
10.91
10.85
10.83
10.89
10.82
10.77
10.75
10.74
10.72
10.65
Photic zone chl a MA)
Baseline
2.20
2.18
2.18
2.17
2.20
2.14
2.12
2.11
2.11
2.13
2.12
2.13
2.13
2.11
2.12
2.11
2.11
2.11
2.09
2.07
2.08
2.06
2.09
2.10
AMA
2.20
2.18
2.17
2.17
2.20
2.14
2.12
2.11
2.11
2.13
2.12
2.13
2.13
2.11
2.12
2.11
2.11
2.11
2.09
2.07
2.06
2.06
2.09
2.10
AM B
2.21
2.18
2.17
2.17
2.20
2.14
2.11
2.11
2.11
2.13
2.12
2.13
2.13
2.11
2.12
2.11
2.11
2.11
2.09
2.07
2.06
2.08
2.09
2.10
AMC
2.20
2.18
2.17
2.17
2.20
2.14
2.12
2.11
2.11
2.13
2.12
2.13
2.13
2.11
2.12
2.11
2.11
2.11
2.09
2.07
2.08
2.06
2.09
2.10
Spring
Epilimnlon DO (mgrl.)
Seg 22
Seg 23
Sog 24
Seg 25
Seg 26
Scg 27
Sog 28
Sag 29
Seg 30
Seg 31
Sag 32
Seg 33
Seg 34
Sag 35
Seg 36
Seg 37
Seg 38
Seg 39
Seg 40
Seg 41
Seg 42
Son 43
Sag 44
Seg 45
Baseline
8.38
8.41
8.39
8.32
8.21
8.13
8.23
8.35
8.39
8.38
8.42
8.43
8.47
8.43
8.42
8.45
8.53
8.53
8.52
8.51
8.45
8.34
8.12
8.27
AMA
8.34
8.40
8.39
8.31
8.20
8.12
8.22
8.33
8.37
8.37
8.41
8.41
8.46
8.42
8.42
8.46
8.55
8.55
8.54
8.52
8.44
8.32
8.06
8.25
AM B
8.35
8.40
8.39
8.32
8.20
8.12
8.22
8.33
8.38
8.37
8.41
8.42
8.48
8.42
8.41
8.45
8.53
8.53
8.53
8.51
8.44
8.34
8.11
8.27
AMC
8.34
8.40
8.39
8.32
8.20,
8.13
8.22
8.33
8.38
8.37
8.41
8.42
8.46
8.42
8.41
8.45
8.53
8.53
8.53
8.51
8.44
8.33
8.09
8.28
Hypolimnlon DO (mgfl)
Baseline
8.12
8.28
6.28
8.18
8.14
6.14
6.23
6.24
6.34
6.36
6.44
6.48
6.58
8.59
8.59
8.84
6.67
6.83
6.69
6.78
8.77
8.75
8.77
6.85
AMA
5.99
6.13
6.12
6.05
6.02
6.02
6.08
6.09
6.18
8.19
8.27
8.28
8.39
8.39
8.39
6.44
8.47
6.40
6.48
8.53
6.55
8.52
8.55
6.84
AM B
6.03
8.16
8.15
8.07
8.04
8.04
6.11
8.11
8.21
8.22
8.32
6.34
8.46
6.47
8.47
8.53
6.56
6.52
6.58
8.65
8.87
8.64
6.87
6.75
AMC
5.98
6.12
8.10
8.03
8.00
8.00
8.07
8.08
6.17
8.17
8.25
6.25
6.37
8.38
6.37
8.42
8.45
8.41
6.47
6.54
6.58
8.54
8.57
6.88
Photie zone chi a (ug/L)
Baseline
8.13
6.30
8.22
8.10
5.82
5.65
5.78
5.83
5.77
5.88
5.73
5.75
5.79
5.75
5.78
5.88
8.01
5.85
5.78
5.82
5.37
5.05
4.42
4.78
AMA
6.44
6.66
8.81
6.52
6.28
8.13
8.35
6.48
8.47
6.38
8.50
6.83
6.76
6.75
8.87
7.01
7.34
7.37
7.09
8.84
8.35
5.78
4.90
5.37
AM B
8.67
6.85
8.74
8.59
6.28
8.08
6.22
6.29
8.25
6.13
6.18
6.18
8.22
6.16
6.19
8.27
6.41
6.22
6.09
5.93
5.64
5.28
4.59
4.99
AMC
8.43
8.83
8.57
8.45
8.18
6.02
8.20
6.29
6.26
6.17
6.25
6.30
8.36
6.32
6.37
6.47
6.68
6.50
8.33
8.14
5.82
5.42
4.70
5.11
MAME NORsLIN CE4UAL-W2 TM 3 V200C
4
COPYRIGHT 2007 BY C412M HILL INC. • COMPANY CONRDENTA.

COMPARISON OF MISAATED LAKE NORMAN DISSOLVED OXYGEN CONCENTRA110NS
Table 1. Simulated Seasonal Dissolved Oxygen Concentrations for Lake Norman Mainstem (continued)
Summer
Mainstem
EpUirmlon 00 (mgll.)
Seg 22
Sag 23
Seg 24
Seg 25
8eg 28
Sog 27
Seg 28
Seg 29
Seg 30
Seg 31
Seg 32
Seg 33
Seg 34
Seg 35
Seg 38
Sag 37
Seg 38
Seg 39
Seg 40
Seg 41
Seg 42
Seg 43
Seg 44
Seg 45
Baseline
7.16
7.13
7.09
7.06
7.06
6.92
6.97
7.02
7.14
7.18
7.25
7.21
7.15
7.22
7.18
7.15
7.12
7.06
6.98
6.87
6.72
6.57
6.26
8.48
All A
7.15
7.11
7.07
7.05
7.06
8.94
8.97
7.02
7.14
7.17
7.27
7.23
7.15
7.25
7.19
7.15
7.12
7.04
6.95
8.83
6.86
8.47
8.11
6.38
AR B
7.15
7.11
7.07
7.05
7.05
8.93
8.97
7.01
7.12
7.17
7.25
7.20
7.13
7.22
7.17
7.13
7.10
7.04
6.96
8.85
6.70
6.54
6.22
8.45
ARC
7.15
7.12
7.07
7.05
7.05
8.93
8.97
7.01
7.13
7.17
7.25
7.21
7.14
7.23
7.17
7.14
7.11
7.04
6.96
6.85
6.70
8.54
6.21
8.45
Hypotmnion 00 (mg&L)
Baseline
3.70
3.88
3.41
3.21
3.15
2.89
2.87
2.97
3.05
2.94
3.00
2.85
2.83
2.88
2.73
2.69
2.58
2,47
2.46
2,45
2.38
2.33
2.26
2.30
MA
3.59
3.58
3.28
3.07
3.01
2.77
2.73
2.81
2.89
2.77
2.81
2.85
2.62
2.84
2.51
2.47
2.37
2.25
2.22
2.20
2.11
2.04
1.97
1.98
All B
3.62
3.62
329
3.10
3.04
2.80
2.77
2.88
2.95
2.84
2.89
2.73
2.71
273
2.81
2.57
2.47
2.38
2.33
2.34
2.27
2.19
2.18
2.15
ARC
3.59
3.56
3.27
3.07
3.01
2.77
2.73
2.81
2.90
2.78
2.83
2.688
2.63
2.68
2.53
2.50
2.40
2.30
2.28
2.27
2.20
2.14
2.07
2.09
Photic zone cM a (uglL)
Base8me
5.73
5.83
5.57
5.54
5.80
5.51
5.59
5.66
5.77
5.70
5.91
5.79
5.63
5.87
5.75 ,
5.83
5.50
5.36
521
4.99
4.87
4.39
3.92
4.17
AR A
8.29
628
629
6.38
8.51
6.53
6.88
8.80
7.01
8.97
7.42
7.33
7.15
7.58
7.46
7.37
724
7.14
8.77
8.33
5.80
5.39
4.76
5.08
AR B
5.95
5.85
5.78
5.77
5.84
5.76
5.81
5.87
5.97
5.91
8.14
8.01
5.83
6.08
5.94
5.82
5.68
5.52
5.36
5.13
4.79
4.49
4.02
427
ARC
5.95
5.86
5.81
5.80
5.88
5.83
5.90
5.97
6.09
8.03
629
8.17
5.98
825
8.10
5.97
5.83
5.68
5.51
5.25
4.90
4.59
4.09
4.38
Fal
Epilimnion 00 (mglL)
Seg 22
Seg 23
Seg 24
Sag 25
Seg 28
Seg 27
Seg_28
Seg 29
Seg 30
Seg 31
Seg 32
Seg 33
Seg 34 ,
Seg 35
Seg 38
Seg 37
Seg 38
Seg 39
Sog 40
Seg 41
Sog 42
Seg 43
Seg 44
Seg 45
Baseline
8.40
8.34
829
8.14
8.13
7.97
8.19
8.36
8.46
8.52
8.50
8.48
8.45
8.39
8.37
8.35
8.34
8.33
828
8.21
8.15
8.09
8.04
8.08
AR A
8.37
8.32
8.27
8.11
8.09
7.96
8.17
8.34
8.44
8.50
8.47
8.45
8.41
8.34
8.32
8.31
829
8.30
823
8.16
8.10
8.03
7.97
8.02
AR B
8.39
8.34
829
8.13
8.12
7.98
8.19
8.35
8.45
8.52
8.49
8.47
8.44
8.38
8.35
8.33
8.32
8.33
8.26
8.t9
8.13
8.07
8.01
8.05
ARC
8.40
8.35
8.30
8.12
8.12
7.98
820
8.37
8.47
8.53
8.51
8.48
8.45
8.39
8.36
8.34
8.33
8.33
827
820
8.14
8.07
8.01
8.08
Hypolimnion 00 (mglL)
,
Baseline
8.18
8.18
8.08
8.01
7.98
7.79
7.90
7.87
8.01
8.15
8.09
7,93
7.92
7.85
7.75
7.58
7.42
7.26
7.13
6.94
6.74
8.58
6.47
-
8.30
All A
8.14
8.12
8.04
7.98
7.93
7.70
7.84
7.81
7.95
8.09
8.02
7.84
7.83
7.75
7.86
7.49
7.32
7.17
7.03
6.83
8.63
6.46
8.34
8.18
AR B
8.18
8.13
8.05
7.97
7.94
7.72
7.84
7.81
7.98
8.10
8.02
7.83
7.84
7.78
7.88
7.51
7.35
720
7.06
6.86
8.68
6.50
6.39
823
ARC
8.16
8.14
8.07
7.99
7.95
7.73
7.88
7.83
7.98
8.13
8.06
7.88
7.87
7.80
7.71
7.53
7.37
7.21
7.06
6.88
8.87
8.50
6.38
8.19
Photic zone chi a (uglt)
Baseline
329
321
3.18
2.87
2.91
2.84
2.95
2.92
2.97
2.92
2.88
2.58
252
2.37
2.34
2.31
2.33
2.41
2.39
2.40
2.38
2.34
2.32
2.34
AR A
3.87
3.80
3.82
3.46
3.49
3.37
3.55
3.60
3.71
3.70
3.48
3.39
3.33
3.13
3.09
3.10
3.15
3.35
3.26
3.24
3.19
3.10
100
3.07
AR B
3.55
3.44
3.40
3.05
3.08
2.98
3.10
3.09
,
3.15
3.12
2.88
2.78
2.69
2.53
2.48
2.45
2.47
2.55
2.50
2.50
2.49
2.43
2.40
2.43
ARC
3.80
3.73
3.75
3.35
3.40
3.30
3.47
3.52
3.63
3.62
3.40
329
322
3.03
2.98
2.95
2.99
3.13
3.05
3.06
3.03
2.94
2.88
2.92

Table 2. Simulated Seasonal Dissolved Oxygen Concentrations for Lake Norman Tributaries
Branch 4
Branch 5
Winter
Seg_62
Sep 63
Sep 64
Sop 65
Sop 68
Seg_67
Sep_70
Sep 71
Seg 72
Epilimnlon DO (mgll.)
Baseline
11.58
11.44
11.36
11.30
11.19
11.10
10.82
10.80
10.72
AMA
11.55
11.43
11.35
11.29
11.19
11.10
10.82
10.80
10.72
Alt 8
11.58
11.44
11.35
11.30
11.19
11.10
10.82
10.80
10.72
AMC
11.57
11.43
11.34
1129
11.19
11.09
10.82
10.80
10.72
Hypolimnlon DO (mg/L)
Baseline
11.53
11.37
11.21
11.17
11.05
10.96
10.46
10.62
10.67
AR A
11.51
11.37
11.23
11.17
11.05
10.96
10.47
10.62
10.67
AM B
11.53
11.38
11.21
11.17
11.05
10.96
10.47
10.62
10.67
AP C
11.53
11.36
1124
11.16
11.04
10.96
10.47
10.62
10.67
Photic zone chl a (ug/L)
Baseline
2.17
2.17
2.16
2.15
2.13
2.13
2.15
2.18
2.10
AMA
•
2.17
2.17
2.15
2.14
2.13
2.13
2.15
2.18
2.10
P8 B
2.17
2.17
2.16
2.14
2.13
2.13
2.15
2.18
2.10
AMC
2.18
2.17
2.16
2.15
2.13
2.13
2.15
2.18
2.10
Spring
Epiliimnion DO (mg 1.)
Seg_62
Sep 83
Sea 84
Sep 65
Seg_66
Sep 67
600_70
Sep 71
Seo 72
Baseline
8.29
8.37
8.47
8.50
8.52
8.54
8.31
8.33
7.97
AMA
8.42
8.44
8.52
8.54
8.55
8.58
8.30
8.31
7.88
All B
828
8.38
8.47
8.51
8.53
8.54
8.30
8.31
7.92
AM C
8.28
8.38
8.48
8.52
8.53
8.54
8.31
8.32
7.90
Hypolimnion DO OW.)_
Baseline
8.82
8.48
6.47
8.53
8.63
6.68
8.78
6.78
8.82
AR A
823
5.97
6.08
623
6.37
6.45
6.48
6.52
6.57
AM B
8.68
6.34
6.33
8.40
6.51
6.57
6.64
8.67
8.71
All C
8.58
822
6.23
6.32
8.42
6.47
6.55
6.57
6.61
Photic zone chl a (ug/L)
Baseline
5.08
5.21
5.58
5.71
5.78
5.85
6.34
5.99
4.04
AMA
12.04
9.84
8.86
8.16
7.88
7.62
725
6.78
4.40
AM B
5.47
5.60
5.99
8.12
6.18
824
8.62
6.24
4.14
AMC
8.02
8.11
6.48
8.54
8.56
6.57
6.89
6.44
4.23

COMPARISON OF SIMULATED LAKE NORLIIIN DISSOLVED OXYGEN CONCENTRATIONS
Table 2. Simulated Seasonal Dissolved Oxygen Concentrations for Lake Norman Tributaries (continued)
Summer
Branch 4
Branch 5
Epitmnion DO (mg/1.)
Seg_62
Seg_63
Seg64
Sea_65
Seri 66
Seg_67
Sea_70
Seg_71
Sea 72
Baseline
7.24
7.28
7.31
7.30
7.28
7.22
7.08
6.99
6.00
All A
7.56
7.44
7A0
7.38
7.33
7.24
7.07
6.98
5.80
All B
724
7.28
7.30
7.29
7.28
7.21
7.06
6.98
5.93
At C
7.25
7.29
7.31
7.30
7.29
7.22
7.07
6.99
5.93
Hypolimnion 00 (mg/L)
Baseline
5.34
3.80
3.11
2.89
2.87
2.71
3.18
2.62
2.45
AN A
4.93
3.43
2.78
2.61
2.60
2.43
2.74
2.23
2.08
AB B
5.18
3.67
2.99
2.78
2.75
2.59
3.01
2.47
2.29
Alt C
5.14
3.62
2.98
2.74
2.70
2.53
2.98
2.40
2.24
Photo zone chl a (ug/L)
Baseline
525
5.39
5.65
5.78
5.81
5.71
6.43
5.87
3.60
ABA
13.55
10.89
9.47
8.71
8.38
7.96
7.91
7.19
4.34
All B
5.49
5.65
5.88
5.99
8.04
5.93
6.63
6.05
3.65
Alt C
5.87
5.96
8.14
8.22
6.27
6.14
6.88
6.25
3.73
Fat
Epilimnion DO (mg41.)
Sea 82
Seg_63
Sea 84
Sog_65
Sea_668
Seg_67
Seg_70
Sog_71
Sea 72
Baseline
8.75
8.66
8.58
8.50
8.45
8.41
8.35
8.29
8.03
Alt A
8.81
0.68
8.57
8.48
8.42
8.38
8.35
8.28
7.96
AB B
8.75
8.65
8.57
8.48
8.43
8.40
8.34
8.28
8.00
All C
8.81
8.71
0.61
8.51
8.48
8.42
8.38
8.31
8.00
HYpottmnion DO (mgf.)
Baseline
8.70
8.57
8.03
7.81
7.76
7.82
7.38
6.94
6.82
ABA
8.72
8.58
7.98
7.75
7.68
7.53
7.28
8.76
6.66
AB B
8.70
8.58
7.99
7.76
7.70
7.55
7.32
8.84
8.72
AB C
8.75
8.59
8.01
7.78
7.72
7.57
7.28
6.82
8.70
Photo zone chl a (ug/1.)
Baseline
3.43
3.09
2.86
2.89
2.60
2.51
3.13
2.90
229
ABA
5.60
4.54
4.05
3.81
3.68
3.58
4.11
3.78
2.95
All B
3.70
3.31
3.04
2.86
2.75
2.87
3.32
3.08
2.38
ABC
5.01
4.29
3.87
3.58
3.44
3.33
4.14
3.78
2.82

COMPARISON OF 6WTED LAKE NORMAN DISSOLVED OXYGEN CONCENTRATIONS
Table 3. Range of Epilimnion Dissolved Oxygen Concentrations on Critical Days
Day 160
Seg_23
Sea_24
Se8_25
Sea 39
Seg_40
Seg44
Sea 45
Seg_61
Sep 62
8eg 63
Sea_64
Sea_65
Seg 66
Seg 67
Baseline
Min (mglL)
8.05
8.05
8.03
8.21
8.20
7.86
7.93
7.35
7.53
7.71
7.89
8.00
8.06
8.19
Ave (mglL)
8.09
8.10
8.10
8.28
8.28
7.90
7.99
7.49
7.64
7.79
7.96
8.06
8.14
8.27
Max (mg/L)
8.13
8.14
8.19
8.32
8.34
7.99
8.03
7.75
7.83
7.91
8.02
8.13
8.22
8.35
Location A
Min (mglL)
8.04
8.04
8.03
8.32
6.30
7.79
7.90
7.34
7.81
7.81
8.04
8.14
8.20
8.31
Ave (mg/L)
8.08
8.09
8.10
8.40
8.38
7.85
7.97
7.78
7.91
7.99
8.14
8.24
8.31
8.42
Max (mg/1.)
8.12
8.15
8.18
8.43
8.43
7.96
8.01
8.59
8.43
8.25
8.23
8.35
8.42
8.54
Location B
Min (mglL)
8.05
8.05
8.02
8.23
8.21
7.81
7.90
7.28
7.48
7.68
7.89
8.00
8.07
8.20
Ave (mg/L)
8.09
8.11
8.11
8.29
8.29
7.86
7.98
7.44
7.60
7.77
7.95
8.07
8.15
8.29
Max (mg/L)
8.14
8.16
8.20
8.33
8.38
7.96
8.00
7.73
7.82
7.91
8.02
8.14
8.24
8.38
Location C
Min (mg/L)
8.04
8.05
8.02
8.25
8.24
7.60
7.91
7.21
7.43
7.65
7.87
8.01
8.09
8.22
Ave (mg/L)
8.08
8.10
8.10
8.32
8.32
7.86
7.97
7.39
7.57
7.75
7.95
8.09
8.17
8.32
Max (mglL)
8.13
8.15
8.19
8.36
8.38
7.97
8.01
7.73
7.83
7.91
8.02
8.17
8.27
8.41
Day 175
Sea 23
Seg 24
Sea 26
Sea 39
Seg_40
Seg_44
Seg_45
8e0_61
Sea 62
Sea 63
Seg_64
Seg_65
Seg_66
Seg_67
Baseline
Min (mg/L)
7.27
7.27
7.24
7.32
7.30
8.78
7.00
6.40
6.71
7.08
7.28
7.29
7.30
7.30
Ave (mglL)
7.31
7.34
7.28
7.39
7.36
6.84
7.04
6.63
6.92
7.13
7.28
7.31
7.33
7.37
Max (m0A.)
7.34
7.38
7.33
7.44
7.44
8.91
7.10
6.84
7.04
7.18
729
7.33
7.34
7,42
Location A
Min (mglL)
7.25
7.24
7.20
7.29
7.25
6.66
6.95
6.18
8.58
7.06
7.23
7.25
7.25
7.25
Ave (mg/I.)
7.29
7.32
7.25
7.39
7.35
8.75
8.99
6.35
6.80
7.11
7.29
7.31
7.32
7.38
Max (mg/1.)
7.32
7.38
7.31
7.48
7.47
6.85
7.07
6.57
6.98
7.13
7.35
7.35
7.38
7.45
Location B
Min (mall.)
7.24
7.24
7.20
7.31
7.29
6.74
7.00
628
6.61
7.03
7.25
7.28
7.28
7.29
Ave (m9/L)
7.28
7.32
7.24
7.38
7.35
8.82
7.03
6.52
8.85
7.09
7.27
7.30
7.32
7.35
Max (mg/L)
7.32
7.35
7.30
7.44
7.43
6.91
7.10
8.72
6.99
7.15
7.27
7.32
7.34
7.41
Location C
Min (mgA.)
725
724
720
7.30
7.28
6.72
8.98
6.22
6.56
7.02
724
7.27
7.28
7.27
Ave (mg/L)
7.29
7.32
7.25
7.37
7.35
8.80
7.02
6.46
8.81
7.07
728
7.29
7.31
7.35
Max (m(1A.)
7.33
7.38
7.31
7.44
7.43
8.90
7.10
6.87
6.96
7.13
728
7.31
7.33
7.41
Day207
Sag 23
Seg 24
Sea 26
Seg 39
Seg 40
Seg 44
Se9_45
8e0_61
8eg_62
Sea 63
Sea64
Sea 66
Seg_66
Sea-67
Baseline
Min (mall)
8.13
8.02
628
5.40
5.74
4.86
4.30
728
7.27
7.30
7.17
7.03
6.84
8.53
Ave (mglL)
829
8.19
6.44
5.81
5.97
5.15
4.75
7.32
7.31
7.32
7.20
7.05
8.89
8.63
Max (mg/L)
8.48
8.43
6.68
8.18
6.09
5.32
5.25
7.37
7.35
7.33
7.22
7.09
6.92
8.70
Location A
Min (mg/L)
8.10
5.98
625
4.90
5.40
4.59
3.77
7.56
7.43
7.40
7.15
6.94
6.87
6.27
Ave (mg/L)
825
6.13
6.41
5.44
5.67
4.86
4.33
7.79
7.52
7.44
721
8.99
6.77
8.43
Max (mg/L)
6.44
8.38
8.67
5.90
5.82
5.05
4.95
8.02
7.58
7.46
7.28
7.04
6.82
8.55
Location B
Min (m0IL)
6.10
5.98
6.24
527
5.68
4.87
4.11
7.28
7.27
7.31
7.17
7.01
8.80
6.48
Ave (mg/L)
824
8.13
8.40
5.72
5.89
5.09
4.84
7.32
7.31
7.32
720
7.03
8.88
8.59
Max (mglL)
6.43
6.37
6.64
6.13
6.03
520
5.17
7.37
7.35
7.33
722
7.07
6.90
8.66
Location C
Min (mglL)
6.11
5.97
823
521
5.84
4.78
4.12
727
7.27
7.30
7,16
7.00
6.79
6.48
Ave (mal1.)
6.25
8.14
6.40
5.68
5.87
5.04
4.61
7.31
7.30
7.32
7.20
7.03
6.85
8.57
Max (mglL)
6.44
8.38
6.65
8.11
6.00
523
5.18
7.37
7.35
7.33
7.22
7.07
8.89
6.85
MULE HOANCEOUAL-W2Tit3v2,D0C
COPYRIGHT 2007 BY CHDA HILL NC • 001PANY CONF1DFN111L

COMPARISON OF SIMULATED LAKE NORMAN DISSOLVED OXYGEN CONCENTRATIONS
Table 3. Range of Epilimnion Dissolved Oxygen Concentrations on Critical Days (continued)
Day 250
Sog_23
Seg 24
Seg_25
8.9_39
Seg_40
Seg_44
Seg_45
Seg_61
Sag 62
Seg 63
Seg 64
Seg_65
7.14
Seg_66
7.18
Seg_67
7.15
BaseD9e
Min (mg/L)
7.08
8.94
6.80
6.79
8.64
8.01
8.30
7.24
7.13
7.12
7.14
Ave (mg/L)
7.12
7.00
6.89
6.81
6.68
6.05
8.33
7.28
7.20
7.19
7.21
7.22
7.24
7.19
Max (mgA.)
7.24
7.12
6.97
6.84
6.70
8.07
8.39
7.32
7.27
7.28
7.28
7.28
7.27
7.23
Location A
Min (mgA.)
7.05
8.88
8.74
8.74
8.58
5.81
6.14
7.90
7.39
7.20
7.23
7.16
7.24
7.19
Ave (mglL)
7.11
8.94
6.84
8.77
8.63
5.87
620
0.16
7.61
7.36
7.32
7.28
7.32
7.26
Max (mg/t.)
7.21
7.06
6.93
8.81
6.66
5.90
8.28
8.53
7.81
7.49
7.39
7.37
7.37
7.32
Location B
Min (mg/L)
7.08
8.91
6.77
6.77
8.62
5.95
6.25
7.24
7.13
7.11
7.13
7.15
7.19
7.14
Ave (mgA.)
7.13
8.97
6.87
6.79
6.65
6.00
628
7.28
7.20
7.18
7.20
7.22
7.24
7.18
Max (mgl1.)
7.22
7.09
6.94
8.83
6.68
6.02
8.34
7.32
7.27
7.26
7.28
7.28
7.27
7.23
Location C
Min (mg/L)
7.07
6.91
8.77
8.78
6.60
5.91
8.22
7.25
7.13
7.11
7.13
7.13
7.19
7.14
Avo (mail.)
7.12
6.97
6.87
8.79
8.64
5.97
6.26
7.29
7.20
7.19
720
7.22
7.24
7.18
Max (mg/l.)
7.22
7.09
8.94
8.83
8.66
6.00
8.32
7.33
7.27
7.28
7.26
7.28
7.28
7.23
Day 276
Seg 23
Seg 24
Seg_25
Beg 39
Seg 40
Bag 44
Seg 45
Seg_61
Seg_62
Sea 63
Seg_64
Seg_65
Seg 66
Sap 67
Baselno
Min (mglL)
6.80
6.40
8.02
7.11
_
7.03
6.45
6.71
8.08
7.87
7.76
7.68
7.55
7.48
7.42
Ave (mg/L)
6.99
6.55
8.20
7.16
7.06
6.47
8.79
8.11
7.93
7.83
7.74
7.60
7.51
7.46
Max (mgA.)
721
6.77
8.42
7.28
7.11
6.49
6.86
8.16
8.00
7.92
7.79
7.63
7.55
7.49
Location A
Min (mg/L)
6.78
8.38
6.00
7.07
8.97
8.33
8.71
8.49
8.08
7.80
7.69
7.55
7.44
7.40
Ave (mg/L)
6.98
6.52
6.17
7.12
7.01
6.37
8.75
8.71
8.22
7.92
7.78
7.82
7.52
7.48
Max (mg/I.)
7.20
8.74
6.40
7.22
7.06
6.40
6.80
8.99
8.37
8.06
7.87
7.67
7.58
7.50
Location B
Min (mg/)
6.80
8.41
6.01
7.11
7.03
8.42
6.77
8.04
7.65
7.73
7.87
7.55
7.46
7.42
Ave (mg/L)
8.99
6.55
8.19
7.18
7.05
6.44
8.80
8.09
7.91
7.80
7.73
7.60
7.51
7.48
Max (mgA.)
7.21
6.76
8.42
7.25
7.10
6.47
8.85
8.14
7.98
7.90
7.79
7.84
7.55
7.49
Location C
Min (mall)
6.80
8.40
6.01
7.13
7.05
6.42
6.70
8.12
7.94
7.81
7,74
7.60
7.50
7.48
Ave (mg/L)
8.99
0.55
6.20
7.19
7.08
6.44
8.80
8.20
8.03
7.91
7.82
7.68
7.56
7.51
Max (mg/L)
7.20
6.76
6.42
7.29
7.14
6.48
6.88
8.30
8.18
8.04
7.89
7.71
7.61
7.54
MAKE NORMAN CE CUALYY2 T1M 3VZ000 6
COPYRIGHT VC 6Y CN2U TILL INC. • CWPANY CO EMIAL

TECHNICAL MEMORANDUM CH2MHILL
Comparison of Time -Depth Dissolved Oxygen Plots
PREPARED FOR: Pam Behm/DWQ
PREPARED BY: Klaus Albertin/CH2M HILL
COPIES: Ruth Swanek/CH2M HILL
DATE: May 29, 2007
Evaluation of changes in water quality due to an addition of a point source discharge can be
difficult due to the spatial and temporal complexity of the system. The CE-QUAL-W2
model only provides snapshots into the behavior of the system over time and is limited as to
the number of dates and times that can be output. Seasonal averages, as shown in Table 1
and Table 2, can provide a fair understanding of average water quality conditions but do
not show the full range of values. The seasonal averages were reviewed to identify the most
impacted segments under the discharge scenarios. This information was then used to
generate dissolved oxygen timeseries for the baseline and potential discharge scenarios at
the critical locations.
It can be seen that segments 44 and 45 of the mainstem show the greatest difference in DO
concentrations, most notably in the summer. Figure 1 and Figure 2 show the time -depth
profile for segments 44 and 45, respectively. Segments 39 and 40 (See Figures 3 and 4) were
also exported at the request of DWQ. Segments 65 and 67 of Branch 4 of the model show the
greatest difference in DO and chlorophyll a concentrations, also in the summer. Figure 5 and
Figure 6 show the time -depth profile for segments 65 and 67, respectively. Segments 61, 62,
63, 64, and 66 (See Figures 7 through 11) were also exported at the request of DWQ.
Segments 23, 24, and 25 are likely to show the greatest difference in DO and chlorophyll a
concentrations due to the proposed discharge at Highway 150. Figure 12 through Figure 14
show the time -depth profile for segments 23, 24, and 25, respectively. Initial review of these
results do not show significant difference between the baseline and the discharge
alternatives. Individual dates can be selected and output if specific dissolved oxygen values
are required.
RDUIDO COMPARISON TECHNICAL MEMO.DOC 1
COPYRIGHT 2007 BY CH2M HILL, INC. • COMPANY CONFIDENTIAL

Table 1. Simulated Seasonal Dissolved Oxygen Concentrations for Lake Norman Mainstem
Wnter
Mainstem
EpBAmnion DO (mglL)
Sag 22
Seg 23
Seg 24
Seg 25
Seg 28
Seg 27
Sog 28
Sog_29
Sog 30
Seg 31
Sog 32
Sog 33
Sog 34
Seg 35
Seg 38
Seg 37
Seg 38
Seg 39
Sog 40
Seg 41
Sog 42
Seg 43
Seg 44
Sog 45
Baselno
10.95
10.86
10.74
10.65
10.45
10.49
10.60
10.66
10.68
10.87
10.88
10.05
11.03
11.02
11.07
11.07
11.02
10.95
10.81
10.71
10.69
10.69
10.69
10.68
AR A
10.95
10.86
10.74
10.65
10.45
10.49
10.60
10,66
10,68
10.87
10.88
10.95
11.03
11.01
11.06
11.06
11.02
10.96
10.82
10.72
10.69
10.89
10.70
10.68
AIYB
10.93
10.86
10.74
10.65
10.44
10.49
10.60
10.86
10.67
10.87
10.88
10.94
11.02
11.01
11.07
11.07
11.02
10.96
10.81
10.71
10.69
10.69
10.69
10.68
Alt C
10.95
10.86
10.74
10.85
10.44
10.49
10.60
10.66
10.68
10.87
10.88
10.95
11.03
11.01
11.07
11.06
11.02
10.96
10.81
10.72
10.69
10.69
10.69
10.68
Hypolmnion DO (mgA.)
Baseline
11.02
11.00
10.88
10.77
10.74
10.77
10.81
10.81
10.83
10.84
10.93
10.95
11.00
10.88
10.90
10.88
10.84
10.89
10.82
10.78
10.75
10.74
10.71
10.65
AR A
11.02
11.00
10.88
10.77
10.74
10.77
10.81
10.81
10.83
10.84
10.92_
10.95
11.00
10.87
10.90
10.88
10.84
10.89
10.82
10.78
10.75
10.74
10.72
10.66
Alt B
11.02
10.93
10.84
10.74
10.71
10.74
10.79
10.82
10.83
10.84
10.92
10.94
10.99
10.86
10.89
10.85
10.84
10.90
10.82
10.78
10.75
10.74
10.72
10.66
Alt C
11.02
11.00
10.88
10.77
10.74
,
10.77
10.81
10.81
10.83
10.84
10.93
10.95
11.00
10.88
10.91
10.85
10.83
10.89
10.82
10.77
10.75
10.74
10.72
10.65
Photic zone ell a (ugA.)
Baseline
2.20
2.18
2.16
2.17
2.20
2.14
2.12
2.11
2.11
2.13
2.12
2.13
2.13
2.11
2.12
2.11
2.11
2.11
2.09
2.07
2.06
2.06
2.09
2.10
Alt A
2.20
2.18
2.17
2.17
220
2.14
2.12
2.11
2.11
2.13
2.12
2.13
2.13
2.11
2.12
2.11
2.11
2.11
2.09
2.07
2.06
2.06
2.09
2.10
Alt B
2.21
2.18
2.17
2.17
2.20
2.14
2.11
2.11
2.11
2.13
2.12
2.13
2.13
2.11
2,12_
2.11
2.11
2.11 ,
2.09
2.07
2.08
2.08
2.09
2.10
ARC
220
2.16
2.17
2.17
220
2.14
2.12
2.11
2.11
2.13
2.12
2.13
2.13
2.11
2.12
2.11
2.11
2.11
2.09
2.07
2.08
2.06
2.09
2.10
Spring
Epilmnion DO (mglL)
Seg 22
Seg 23
Seg 24
Sag 25
Seg 26
Sog 27
Seg 28
Seg 29
Seg 30
Sag 31
Seg 32
Seg 33
Seg 34
Seg 35
Seg 36
Seg 37
Seg 38
Seg 39
Seg 40
Scg 41
Sog 42
Seg 43
Sog 44
Sog 45
Baseline
8.36
8.41
8.39
8.32
821
8.13
623
8.35
8.39
8.38
8.42
8.43
8.47
8.43
8.42
8.45
8.53,
8.53
8.52
8.51
8.45
8.34
8.12
8.27
MA
8.34
8.40
8.39
8.31
820
8.12
8.22
8.33
8.37
8.37
8.41
8.41
8.46
8.42
8.42
8.46
8.55
8.55
8.54
8.52
8.44
8.32
8.06
8.25
All B
8.35
8.40
8.39
8.32
820
8.12
8.22
8.33
8.38
8.37
8.41
8.42
8A6
8.42
8.41
8.45
8.53
8.53
8.53
8.51
8.44
8.34
8.11
827
AR C
8.34
8.40
8.39
8.32
820
8.13
8.22
8.33
8.38
8.37
8.41
8.42
8.46
6.42
8.41
8.45
8.53
8.53
8.53
8.51
8.44
8.33
8.09
8.26
Hypolmnion DO (rngA.)
Bastin
6.12
6.26
6.26
8.18
8.14
6.14
623
6.24
6.34
6.38
6.44
6.46
6.58
6.59
6.59
6.64
6.67
6.63
6.89
8,76
6,77
6.75
6.77
6.85
AR A
5.99
6.13
8.12
6.05
6.02
6.02
6.08
6.09
6.18
6.19
627
628
6.39
6.39
6.39
6.44
6.47
6.40
6.48
6.53
8.55
6.52
6.55
6.64
AR B
6.03
6.16
6.15
6.07
8.04
6.04
6.11
6.11
621
622
6.32
8.34
6.48
8.47
8.47
6,53
6,58
8,52
6,58
8.85
6.67
6.64
6.67
8.75
ARC
5.98
6.12
6.10
8.03
6.00
6.00
6.07
6.08
6.17
8.17
625
625
8.37
6.38
6.37
6.42
6A5
8A1
8.47
6.54
8.56
6S4
6.57
8.66 ,
Photic zone chi a (ug)1.)
Baseline
6.13
6.30
622
6.10
5.82
5.65
5.78
5.83
5.77
5.68
5.73
5.75
5.79
5.75
5.78
5.68
6.01
5.85
5,76
5.62
S.37
5.05
4.42
4.78
Alt A
6.44
6.66
6.61
6.52
626
6.13
8.35
6.48
6.47
6.38
6.50
6.63
6.76
8.75
6.87
7.01
7.34
7.37
7.09
8.64
6.35
5.78
4.90
5.37
AR B
6.67
6.85
8.74
6.59
6.28
6.08
622
6.29
6.25
6.13
8.18
6.18
8.22
8.16
8.19
627
6.41
622
8,09
5.93
5.64
528
4.59
4.99
Alt C
6.43
6.63
6.57
6.45
6.18
6.02
620
6.29
6.28
6.17
6.25
6.30
6.36
8.32
6.37
8.47
8.66
8.50
6.33
6.14
5.82
5.42
4.70
5.11
RDUA0 COLIPARISON TECM0CAL 10.IA0DOC
3
COPYRIGHT 2007 BY CH21A HILL. INC. • COLPANY CONFIDENTIAL

COLPARooN of n1WE.oEFrH DISSOLVED OXYGEN PLOTS
Summer
Malnatem
Epiimnlon DO (mgfL)
Seg 22
Seg 23
Seg 24
Sog 25
Seg 26
Sep 27
Seg 28
Seg 29
Seg 30
Sep 31
Sep 32
Seg 33
Sep 34
Son 35
Sep 38
Sea 37
Seg 38
Seg 39
Seg 40
Seg 41
Sep 42
Seg 43
Sep 44
Seg 45
Baseline
7.16
7.13
7.09
7.06
7.06
6.92
8.97
7.02
7.14
7.18
7.25
7.21
7.15
7.22
7.18
7.15
7.12
7.06
8.98
6.87
6.72
6.57
6.26
6.48
AS A
7.15
7.11
7.07
7.05
7.06
6.94
6.97
7.02
7.14
7.17
7.27
7.23
7.15
7.25
7.19
7.15
7.12
7.04
6.95
8.83
6.66
6.47
6.11
6.38
Aft B
7.15
7.11
7.07
7.05
7.05
6.93
6.97
7.01
7.12
7.17
7.25
7.20
7.13
7.22
7.17
7.13
7.10
7.04
6.96
6.85
6.70
6.54
6.22
6.45
Aft C
7.15
7.12
7.07
7.05
7.05
6.93
6.97
7.01
7.13
7.17
7.25
7.21
7.14
7.23
7.17
7.14
7.11
7.04
6.96
8.85
6.70
6.54
6.21
6.45
FypoOmolon DO (mg/1.)
Sasebo
3.70
3.68
3.41
321
3.15
2.89
2.87
2.97
3.05
2.94
3.00
2.65
2.63
2.86
2.73
2.69
2.58
2.47
2.48
2.45
2.38
2.33
2.26
2.30
Aft A
3.59
3.56
3.28
3.07
3.01
2.77
2.73
2.81
2.89
2.77
2.81
2.65
2.62
2.64
2.51
2.47
2.37
2.25
2.22
2.20
2.11
2.04
1.97
1.98
Aft B
3.62
3.62
3.29
3.10
3.04
2.80
2.77
2.86
2.95
2.84
2.89
2.73
2.71
2.73
2.61
2.57
2.47
2.36
2.33
2.34
2.27
2.19
2.18
2.15
Aft C
3.59
3.56
3.27
3.07
3.01
2.77
2.73
2.81
2.90
2.78
2.83
2.66
2.63
2.68
2.53
2.50
2.40
2.30
2.28
227
2.20
2.14
2.07
2.09
Photic zone chl a (ug4.)
Sasebo
5.73
5.63
5.57
5.54
5.60
5.51
5.59
5.66
5.77
5.70
5.91
5.79
5.63
5.87
5.75
5.83
5.50
5.36
5.21
4.99
4.67
4.39
3.92
4.17
Att A
6.29
6.26
629
8.36
6.51
6.53
6.68
6.80
7.01
6.97
7.42
7.33
7.15
7.56
7.46
7.37
724
7.14
6.77
6.33
5.80
5.39
4.76
5.08
Aft B
5.95
5.85
5.78
5.77
5.84
5.78
5.81
5.87
5.97
5.91
8.14
6.01
5.83
8.08
5.94
5.82
5.66
5.52
5.36
5.13
4.79
4.49
4.02
427
Alt C
5.95
5.86
5.81
5.80
5.88
5.83
5.90
5.97
6.09
6.03
6.29
6.17
5.98
625
8.10
5.97
5.83
5.68
5.51
525
4.90
4.59
4.09
4.38
Fall
Epi0mnlon DO (mg/1.)
Seg 22
Seg 23
Seg 24
Seg 25
Sag 28
Sag 27
Sog 28
Sag 29
Sog 30
Sog 31
Sag 32
Seg 33
Sap 34
Seg 35
Seg 36
Sag 37
Sag 38
Sog 39
Sog 40
Seg 41
Sep 42
Seg 43
Seg 44
Sog 45
Baseine
8.40
8.34
829
8.14
8.13
7.97
8.19
8.38
8.46
8.52
8.50
8.48
8.45
8.39
8.37
8.35
8.34
8.33
828
8.21
8.15
8.09
8.04
8.08
Aft A
8.37
8.32
8.27
8.11
8.09
7.96
8.17
8.34
8.44
8.50
8.47
8.45
8.41
8.34
8.32
8.31
8.29
8.30
8.23
8.16
8.10
8.03
7.97
8.02
Aft B
8.39
8.34
829
8.13
8.12
7.96
8.19
8.35
8.45
8.52
8.49
8.47
8.44
8.38
8.35
8.33
8.32
8.33
8.26
8.19
8.13
8.07
8.01
8.05
MC
8.40
8.35
8.30
8.12
8.12
7.98
8.20
8.37
8.47
8.53
8.51
8.48
8.45
8.39
8.36
8.34
8.33
8.33
827
820
8.14
8.07
8.01
8.06
Hypotlmnlon DO (mg/L)
Sasebo
8.18
8.16
8.08
8.01
7.98
7.79
7.90
7.87
8.01
8.15
8.09
7.93
7.92
7.85
7.75
7.58
7.42
7.28
7.13
6.94
6.74
6.58
6.47
6.30
MA
8.14
8.12
8.04
7.96
7.93
7.70
7.84
7.81
7.95
8.09
8.02
7.84
7.83
7.75
7.66
7.49
7.32
7.17
7.03
6.83
6.83
6.46
6.34
6.18
Aft B
8.16
8.13
8.05
7.97
7.94
7.72
7.84
7.81
7.96
8.10
8.02
7.83
7.84
7.76
7.68
7.51
7.35
7.20
7.06
6.86
6.66
6.50
6.39
623
Aft C
8.18
8.14
8.07
7.99
7.95
7.73
7.88
7.83
7.98
8.13
8.06
7.88
7.87
7.80
7.71
7.53
7.37
7.21
7.06
6.66
6.87
6.50
6.38
6.19
Photic zone dale (ug/.)
Baseifne
3.29
321
3.18
2.87
2.91
2.84
2.95
2.92
2.97
2.92
2.68
2.58
2.52
2.37
2.34
2.31
2.33
2.41
2.39
2.40
2.38
2.34
2.32
2.34
Aft A
3.87
3.80
3.82
3.46
3.49
3.37
3.55
3.60
3.71
3.70
3.48
3.39
3.33
3.13
3.09
3.10
3.15
3.35
3.28
3.24
3.19
3.10
3.00
3.07
Alt B
3.55
3.44
3.40
3.05
3.08
2.98
3.10
3.09
3.15
3.12
2.86
2.78
2.69
2.53
2.48
2.45
2.47
2.55
2.50
2.50
2.49
2.43
2.40
2.43
Aft C
3.80
3.73
3.75
3.35
3.40
3.30
3.47
3.52
3.63
3.62
3.40
3.29
3.22
3.03
2.98
2.95
2.99
3.13
3.05
3.06
3.03
2.94
2.86
2.92
RDUSO COLIPAWSON TECHNICAL 1.E110.DOC
1
COPYRIGHT 2637 BYCH211 HILL, INC. • COMPANY CONFIDENTIAL

Table 2 Simulated Seasonal Dissolved Oxygen Concentrations for Lake Norman Tributaries
Branch 4
Branch 6
Winter
Sog 62
Sep 83
8ee_84
Seg 65
Sag 66
Sag 67
Sog_70
Seg 71
Seg 72
Epi mnlon DO (mall.)
Baseline
11.58
11.44
11.36
11.30
11.19
11.10
10.82
10.80
10.72
Alt A
11.55
11.43
11.35
11.29 ,
11.19
11.10
10.82
10.80
10.72
Alt B
11.58
11.44
11.35
11.30
11.19
11.10
10.82
10.80
10.72
ARC
11.57
11.43
11.34
11.29
11.19
11.09
10.82
10.80
10.72
Fypotmnlon DO (melt.)
Baseline
11.53
11.37
11.21
11.17
11.05
10.98
10.46
10.82
10.67
All A
11.51
11.37
1123
11.17
11.05
10.96
10.47
10.62
10.67
All B
11.53
11.38
11.21
11.17
11.05
10.96
10.47
10.62
10.67
Alt C
11.53
11.38
11.24
11.16
11.04
10.96
10.47
10.62
10.87
Phalle zone cht a (ua/l.)
Base8no
2.17
2.17
2.16
2.15
2.13
2.13
2.15
2.18
2.10
Att A
2.17
2.17
2.15
2.14
2.13
2.13
2.15
2.18
2.10
Alt B
2.17
2.17
2.16
2.14
2.13
2.13
2.15
2.18
2.10
AR C
2.18
2.17
2.16
2.15
2.13
2.13
2.15
2.18
2.10
Spring
Ep6tmnfon DO (mglL)
Sep 82
Sag 83
Seg 84
Sog 85
Sog 88
Sog 87
Sog_70
Sag 71
Sag 72
Baseine
8.29
8.37
8.47
8.50
8.52
8.54
8.31
8.33
7.97
Alt A
8.42
8.44
8.52
8.54
8.55
8.56
8.30
8.31
7.88
Alt B
8.28
8.38
8.47
8.51
8.53
8.54
8.30
8.31
7.92
AS C
8.28
8.36
8.48
8.52
8.53
8.54
8.31
8.32
7.90
Fypo8mnton DO (mall.)
Baseline
8.82
8.48
6.47
6.53
8.83
8.88
6.76
6.78
8.82
MA
6.23
5.97
8.08
823
8.37 I
8.45
6.48
8.52
6.57
AR B
6.88
8.34
6.33
8.40
6.51
8.57
6.84
6.67
,
6.71
Alt C
8.58
8.22
8.23
6.32
8.42
6.47
6.55
8.57
6.81
Photle zone chi a (ua&L)
Baseline
5.08
5.21
5.58
5.71
5.78
5.85
6.34
5.99
4.04
Alt A
12.04
9.84
8.66
8.16
7.88
7.62
7.25
6.78
4.40
Alt B
5.47
6.60
5.99
6.12
6.18
6.24
GM824
4.14
_
Alt C
6.02
8.11
8.48
8.54
8.58
6.57
8.89
8.44
423
MOO COIPARISOH TECHNICAL I0/3.000
5
COPYRIGHT 2007 OY C112U HILL.INC. • COLPANY CONFIDENTIAL

COMPARISON OF TORE.OEPTH DISSOLVED OXYGEN PLOTS
Summer
Branch 4
Branch 5
Ep1imnlon DO (mg/L)
Sea 62
Sop 63
Sea 64
Sep 65
Sag 66
Sep 67
Sop 70
Sep_71
Sop 72
Baseline
7.24
7.28
7.31
7.30
7.28
7.22
7.08
6.99
6.00
Ali A
7.56
7.44
7.40
7.38
7.33
7.24
7.07
6.98
5.80
Alt 8
7.24
7.28
7.30
7.29
7.28
7.21
7.06
6.98
5.93
Ak C
725
7.29
7.31
7.30
7.29
7.22
7.07
6.99
5.93
Hypolmnion DO (mgA.)
Baseline
5.34
3.80
3.11
2.89
2.87
2.71
3.18
2.62
2.45
Ak A
4.93
3.43
2.78
2.61
2.60
2.43
2.74
2.23
2.08
Aft B
5.18
3.67
2.99
2.78
2.75
2.59
3.01
2.47
229
ARC
5.14
3.62
2.98
2.74
2.70
2.53
2.96
2.40
2.24
Phollc zone chl a (ugLL)
Baseline
525
5.39
5.65
5.76
5.81
5.71
6.43
5.87
3.60
Ak A
13.55
10.89
9.47
8.71
8.38
7.96
7.91
7.19
4.34
Ak B
5.49
5.65
5.88
5.99
6.04
5.93
6.63
6.05
3.65
MC
5.87
5.96
6.14
6.22
627
6.14
6.88
625
3.73
Fall
Eplimnlon DO (mgli.)
Sap 62
Sep 63
Sep_64
Sep 65
Sag 66
Sep 67
,
Sep 70
Sep 71
Sea 72
Baseline
8.75
8.66
8.58
8.50
8.45
8.41
8.35
8.29
8.03
Ak A
8.81
8.68
8.57
8.48
8.42
8.38
8.35
8.28
7.96
Al2B
8.75
8.65
8.57
8.48
8.43
8.40
8.34
8.28
8,00
AR C
8.81
8.71
8.61
8.51
8.48
8.42
8.38
8.31
8.00
Hypoimnion DO (mgA.)
Baseline
8.70
8.57
8.03
7.81
7.78
7.62
7.38
6.94
6.82
All A
8.72
8.56
7.98
7.75
7.66
7.53
7.26
6.76
6.66
Aft 8
8.70
8.56
7.99
7.76
7.70
7.55
7.32
6.84
6.72
ARC
8.75
8.59
8.01
7.78
7.72
7.57
728
6.82
6.70
Pholc zone chl a (ugR.)
Baseline
3.43
3.09
2.86
2.69
2.60
2.51
3.13
2.90
2.29
AR A
5.60
4.54
4.05
3.81
3.68
3.56
4.11
3.78
2.95
All B
3.70
3.31
3.04
2.86
2.75
2.67
3.32
3.06
2.38
ARC
5.01
429
3.87
3.58
3.44
3.33
4.14
3.76
2.82
RDU00 COMPARISON TECHNICAL LEYD.DOC
0
COPYRIGHT 2007 BY CH2M HILL. INC. • COMPANY CONFIDENTLIL

COAPAHISON OF TIME -DEPTH DISSOLVED OXYGEN PLOTS
Figure 1. Time -depth Profile of Dissolved Oxygen at Segment 44
250
245 -
240 -
235 -
d 230
F. 225
.3 220
215
W 210
205
200
250
245
240
7 235
230
? 225
.. 220
215
w 210
205
200
195
baseline-1
50 100 150 200 250
Day
AItB-1
LOC:1.10
LOC:1.18
0 58 100 150 200
Day
250 300 350
400
Dissolved
Oxygen
fmg/LI
15
12
9-
6-
3
0
Dissolved
Oxygen
Img/LI
15
12
9-
6-
all
250
245
240
w 235
2 230
F 225
220
m 215
210
205
200
195
250
245
240
7 235
t 230
a 225
c
,0 220
215-.
210
205 -
200 -:
195 U
AltA-1
LOC-1.18
0 50 100 150 200 250 300 350 400
Day
AIIC-1
LOC-1.113
50 100 150 200 250 300
Day
350
400
Dissolved
Oxygen
fmg/LI
15
1211
9-
6-
3 -I
0J
Dissolved
Oxygen
(mg/LI
15
12
9-
6-
3 -.
0�
HDueO COMPARISON TECHMCAL LEMODOC
7
COPYHIGFIT 1007 BY CHILI MIL, INC. • COLPANY CONFIDENTIAL

CO LPAWSON OF TpE-EPTH DISSOLVED OXYGEN PLOTS
Figure 2. Time -depth Profile of Dissolved Oxygen at Segment 45
250
245
240
@ 235
u 230
? 225
220
d 215
L 210
205 -
200 -
195
0
base0ne-1
LOCO.
250
245
240
235
u 230 J
? 225 -
0 220
v 215
210
205
200
195 0
50 100 150 200 250
Day
AItD-1
300
350
400
LOCO.
50 100 150 200 250
Day
300
350
400
Dissolved
Oxygen
[mg/L)
15
12
9-
6-
0
Dissolved
Oxygen
(mg/L)
15
12 -
9-
6-
250
245
240
« 235
▪ 230
Z 225
.3 220
m 215
210-
205 -
200
195
250
245
240
7 235
t 230
? 225
0 220
▪ 215
210
205
200
AItA-1 I.00:0
0
195
0
50 100
150
200
Day
AItC-1
250
300
350
400
LOCO.
50 100
150
200 250
Day
300
350
400
Dissolved
Oxygen
[mg/LI
15
12 11
9-
6-
3
0 III
Dissolved
Oxygen
[mg/L)
15
12
9-
6-
HOIAVO CO WAPoSOH TECINCAL IEtq.DOC
COPYRIGHT 2001 BY CHILI MLL INC. • COMPANY CONFIDENTIAL

COIPA RISON OF TILE.DEPTH DISSOLVED OXYGEN PLOTS
Figure 3. Time -depth Profile of Dissolved Oxygen at Segment 39
250
245
240
— 235
m 230
225
.1 22o
O 215
W 210
205
200
195
250
245
240
-- 235
▪ 230
a, 225
.E 22o
215
W 210
205
200
195
0
50
100
150
200
Day
A11B-1
0 50 100 150 200
Day
250
300
350
400
LOC:5.932
250 300 350
400
Dissolved
Oxygen
(mg/L)
15
12
9-
6-
3-
Dissolved
Oxygen
(mg/L]
15
12
9-
6-
3 i 0
250
245
240
— 235
d • 230
225
220
.11
215 -
W 210-
205 -
200
195 OI
250
245
240
w 235
6' 230
a 225
S 220
u 215
W 210
205
200
195
AItA-1
LOC:5.932
50 100 150 200 250 300 350
Day
AltC-1
0 50 100 150 200 250
Day
300
400
LOC:5.932
350
400
Dissolved
Oxygen
(mg/L)
15
12
9-
6-
Dissolved
Oxygen
(mg/L]
15
12
9-
6-
0
RDUIDO CONPMISON IECWUCAL LEMO.DOC
Y
COPYRIGHT 200T BY CH2M HILL INC. • COMPANY CONFIDENTIAL

COMPARISON OF TIME.OEPTH DISSOLVED OXYGEN PLOTS
Figure 4. Time -depth Profile of Dissolved Oxygen at Segment 40
250
245
240
235
6 230
Z 225
0 220
E 215
w 210
205
200
195
0
250
245
240
w 235
m 230
? 225
E 220
215
" 210
205
200
195
0
baseline-1
LOC:4.909
50 100 150 200 250 300 350
Day
50
100
150
A1tB-1
200
Day
250
300
400
LOC:4.909
350
400
Dissolved
Oxygen
[mg/L)
15
12
9-
6-
3
0
Dissolved
Oxygen
[mg/L)
15
12 1111
9-
6-
3
0
250
245
240
• 235
d 230
• 225
220
i • 215
IL 210
205
200
195
250
AItA-1
50 100 150 200
Day
AItC-1
LOC:4.909
400
LOC:4.909
245
240
235
t1 230 -r
a 225
0 220
E 215
L 210
205
200 -I
1951
0
50
100
150
200 250
Day
300
350
400
Dissolved
Oxygen
(mg/L)
15
12
9-
6-
3
0
Dissolved
Oxygen
[mg/L)
15
12
9-
6-
3
0�
ROUAO COMPARISON TECHNICAL LEMIO.DOC
m
COPYRIGHT 2002 BY CHID Ial, INC. • COMPANY CONFIDENTIAL

COMPARISON OF TILE.EPTH DISSOLVED 0%YCEN PLOTS
Figure 5. Time -depth Profile of Dissolved Oxygen at Segment 65
250
245
240
N 235
u 230
? 225
`= 220
215
LLI 210
205
200
195
250
245
240
w 235
230
225
220
215
uI 210
205
200
195
0
0
50
50
100
100
150
150
baseline-4
200
Day
AITB-4
200
Day
250
250
300
300
LOC:3.795
350
400
LOC:3_795
350
400
Dissolved
Oxygen
(mg/L)
15
12
9-
6-
3
0
Dissolved
Oxygen
(mg/L)
15
12
9-
6-
0
250
245
240
— 235
230
225
1 220
215
"' 210
205
200
195
250
245
240
235
230
? 225
.1 220
E 215
`y 210
2D5
200 195 0
AIIA-4
LOC:3.795
0 50 100 150 200 250 300 350 400
Day
50 100 150 200 250 300
Day
LOC:3.795
350
400
Dissolved
Oxygen
Img/Ll
15
12
9-
6-
Dissolved
Oxygen
(mg/L)
15
12 IR
9-
6-
3
0 -1111
RDILOO COMPARISON TECHNICAL LEMO.DOC
1
COPYRIGHT 2007 BYCH2M HILL INC. • COMPANY CONFIDENTIAL

COMPARISON OF nI..E-DEPTH DISSOLVED OXYGEN PLOTS
Figure 6. Time -depth Profile of Dissolved Oxygen at Segment 67
250
245
240 -
235 -
230
= 225 220 -
215 -
W 215-
205 • 1-
200
195
250
245
240
-. 235
230
225
.0 220
9 215
baseline-4
LOCO.
0 50 100 150 200
Day
w 210
205
200 1 195
0
50
100
150
AI1B-4
200
Day
250 300 350 400
250
LOC:0
400
Dissolved
Oxygen
(mg/L)
15
12
9-
6-
3
0 III
Dissolved
Oxygen
(mg/L)
15
12
9-
6-
0
250
245
240 -
235 -
u 230
2 225
220
215
W 210
205
200
195 0
250
245
240
72 235
230
a. 225
,0 220
215
w 210
205
200 1 195
0
AItA-4
LOCO.
50 100 150 200 250 300 350
Day
50 100
150
AItC-4
200 250
Day
300
400
LOCO.
350
400
Dissolved
Oxygen
(mg/L)
15
12 11
9-
6-
3-
0
ill
Dissolved
Oxygen
(mg/L)
15
12
9-
6-
RDUgD COMPARISON TECHNICAL MEM0.000
COPYRIGHT 2007 BY C711M HILL, INC. • COMPANY CONFIDENTIAL

CO/PARSON OF TY,E.OEPTH DISSOLVED OXYGEN PLOTS
Figure 7. Time -depth Profile of Dissolved Oxygen at Segment 61
250
245
^, 240
235
230
w 225
220
215 0
baseline-4
LOC:12.096
250
245
7 240
235
c
°- 230
225
220
215
0
50 100 150 200 250 300 350
Day
AItB-4
400
LOC:12.096
50 100 150 200 250 300
Day
350
400
Dissolved
Oxygen
(mg/LI
15
12
9-
6-
0 1
250
AItA-4
LOC:12.096
245 •
^„ 240 -
235
° 230 113
11.
id 225 I
220 1 215 JI
250
Dissolved
Oxygen 245
(mg/t•I
15 w 240 -
12 a, 235 -
0 50
c
9 - q 230
6- w 225-
3 220 1
0 215
0
100 150 200 250 300 350 400
Day
AI(C-4
ILL, I
LOC:12.096
50 100 150 200 250 300
Day
350
400
Dissolved
Oxygen
(mg/L)
15
12
9-
6-
Dissolved
Oxygen
[m9/LI
15
12
9-
6-
3
ill
RO1100 COMPARISON TECHNICAL IAEMOOOC
COPYRIGHT 207 BY CH11.I HILL INC. • COWAN( COtiDENTML

COLPARISON OF TIME-OEPTH DISSOLVED OXYGEN PLOTS
Figure 8. Time -depth Profile of Dissolved Oxygen at Segment 62
250
245
» 240
235
230
ww • 225
220
215
baseline-4
O 50 100 150 200 250
Day
AItB-4
250
245
» 240
• 235 -
c
230
w 225
220 -
215
O 50 100 150 200
Day
300
LOC:9.250
400
LOC:9.250
350 400
250
Dissolved
Oxygen 245
(mg/L)
15 » 240
12 J Z 235
e
9 - A 230
d
6- w 225
0
Dissolved
Oxygen
(mg/L)
15
12
9-
220
215
0 50
250
245
» 240 -
235 -
•900 230
6 - w 225
3 - - 220
0 215 I
AItA-4
LOC:9.250
150 200 250 300
ARC-4
0 50 100 150 200
Day
350 400
LOC_9.258
300 350
400
Dissolved
Oxygen
(mg/L)
15
12
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TECHNICAL MEMORANDUM No. 1 01-H2MHILL
Lake Norman Modeling Approach for Mooresville
WWTP Expansion Environmental Assessment
PREPARED FOR:
PREPARED BY:
COPIES:
DATE:
Introduction
NC Division of Water Quality
CH2M HILL
Tonia Wimberly/Town of Mooresville
Duke Energy
October 13, 2006
The Town of Mooresville, NC is evaluating alternatives for increasing the capacity of its
wastewater treatment plant to meet future demands. Several discharge alternatives are
being evaluated that include discharges to Lake Norman. The North Carolina Division of
Water Quality requires that mathematical modeling be performed to identify water quality
responses to the discharge alternatives. Therefore, a modeling work plan is required to
describe the actions to be taken for applying a water quality model to Lake Norman and
calculating potential water quality responses to alternatives.
This technical memorandum first provides background information for the Mooresville
WWTP expansion, regulatory requirements relevant to modeling, and a description of the
existing water quality model of Lake Norman. This is followed by modeling work plan
elements including modeling goals, approach, quality control, and deliverables.
Background
The Town of Mooresville currently operates a WWTP with a permitted treatment capacity
of 5.2 million gallons per day (MGD) and average day flows of approximately 3.0 MGD.
The expected high growth rate and increased availability of potable water from the Town's
current water treatment plant (WTP) expansion will considerably increase the demand for
municipal sewer service in southern Iredell County and possibly other jurisdictions (Black &
Veatch, 2006).
The Town currently operates a completely mixed activated sludge -based facility. The
treated wastewater (effluent) is discharged to Dye Branch, a tributary to the Rocky River in
the Yadkin River Basin. The proposed project would expand the WWTP capacity from 5.2
MGD to 19 MGD (in two Phases) by supplementing existing treatment mechanisms with
new equipment and structures (CH2M HILL, 2006). The Town is examining several
discharge alternatives. Under one alternative, the newly expanded WWTP would discharge
to Lake Norman, Dye Branch and, the Municipal Mooresville Golf Course (MMGC) may
utilize a portion of the discharge as reuse irrigation. Other reuse opportunities are also
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LAKE NORMAN MODELING APPROACH FOR MOORESVILLE WWTP EXPANSION ENVIRONMENTAL ASSESSMENT
being investigated. Under this discharge alternative, the combined discharge to Lake
Norman, Dye Branch, and reuse at MMGC will avoid the need to request an Interbasin
Transfer (IBT) from the Catawba River Basin to the Rocky River subbasin in the near future.
Consumptive transfers to both the South Yadkin and Rocky River subbasins may eventually
require a certificate but this is not projected until about 2016 according to master planning
information (Black & Veatch, 2006).
Several locations are being evaluated for potential surface water discharges of the expanded
WWTP to Lake Norman. These locations are the NC 150 Bridge, Reedy Creek Cove, or
Langtree Road. The North Carolina Division of Water Quality (DWQ 2006) requested the
Town to evaluate the impacts of the proposed discharge on Lake Norman water quality.
DWQ provided speculative limits for the expansion of the WWTP of 5 mg/L for BOD and 1
mg/L for NH3-N for an expanded discharge to Dye Branch. Since some discharge will
remain into Dye Branch, these limits also represent the minimum quality for the effluent
that would be returned to Lake Norman. The effluent would also meet reuse requirements
which would include Fecal Coliform of 14 MFFCC/100 mL, maximum turbidity of 10 NTU,
and monthly average total suspended solids of 5 mg/L plus reliability requirements
necessary for reuse systems. The modeling will determine whether additional effluent
requirements are necessary to maintain lake water quality.
Regulatory Requirements
The DWQ has responded to a request for information regarding additional data, modeling
analyses, and other information that would be required for the issuance of speculative limits
for a new discharge to Lake Norman (S. Wilson letter to W. Martin, June 28, 2006). The
response established the DWQ's position that to evaluate a speculative limits request to
discharge into Lake Norman, the DWQ would require a detailed, calibrated nutrient
response model for the lake to demonstrate assimilative capacity. The model would need to
be able to show any associated localized impacts and behavior of the lake during critical
conditions.
In its response, the DWQ also described how Duke Energy has developed a modified CE-
QUAL-W2 model for Lake Norman. DWQ recommended that CH2M HILL request to use
the input files and code from this model and specified a number of requirements, as follows:
• The model will need to be calibrated for nutrients.
• The model will also need to incorporate existing NPDES discharges in the Lake Norman
watershed to fully evaluate assimilative capacity.
• The model should predict dissolved oxygen impacts as well as the nutrient response of
the Lake.
• Temperature effects of the Duke Energy Marshall Steam Station need to be included in
the nutrient response model.
CH2M HILL has obtained input files and water quality data for the CE-QUAL-W2 model of
Lake Norman developed by Reservoir Environmental Management Inc. (REMI) and
Loginetics, Inc. for Duke Energy.
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LAKE NORMAN MODELING APPROACH FOR MOORESVILLE WWTP EXPANSION ENVIRONMENTAL ASSESSMENT
Existing Lake Norman Model
The objectives of the Duke Energy modeling effort were to provide a calibrated reservoir
model for planning purposes to explore water quality effects (primarily temperature and
dissolved oxygen) on Lake Norman and its releases that arise from altered operating
policies and varying hydrology. In particular, Duke Energy's primary Lake Norman
modeling objectives were to predict:
• Temperature and dissolved oxygen in the forebay and releases;
• The effects of hydropower operations on reservoir and release temperature and
dissolved oxygen; and
• The effects of phosphorus reductions in selected watersheds on algal levels and
dissolved oxygen in the reservoir and its releases.
The model was constructed to assess primary factors influencing temperature and dissolved
oxygen. Although not the focus, the model was reasonably calibrated for nutrients and
organics to enable a dissolved oxygen calibration. Model development and calibration
followed a detailed QA/QC process that included internal and external review by modeling
experts, open model review meetings, and other elements. Model segmentation of Lake
Norman is illustrated in Figure 1.
The Duke Energy modeling approach used a modified version of the July 2004 release of
CE-QUAL-W2 v3.11 (Cole and Wells, 2002) to model Lake Norman. CE-QUAL-W2 is a two-
dimensional, longitudinal/vertical, hydrodynamic and water quality model. Because the
model assumes lateral homogeneity, it is best suited for relatively long and narrow
waterbodies exhibiting longitudinal and vertical water quality gradients. The model has
been applied to rivers, lakes, reservoirs, estuaries, and combinations thereof (Cole and
Wells, 2002). The model computes water levels, horizontal and vertical velocities,
temperature, and 21 other water quality parameters such as dissolved oxygen, nutrients,
organic matter, algae, pH, the carbonate cycle, bacteria, and dissolved and suspended
solids.
The DWQ stated in their June 28 letter that Duke Energy applied a modified CE-QUAL-W2
model to Lake Norman. REMI and Loginetics have confirmed that model code was
modified. The modified model code was employed as a proprietary "research" version of
CE-QUAL-W2. The modifications were made to simulate thermal characteristics of power
station withdrawals and returns, and to better simulate nutrient kinetics. CH2M HILL has
discussed the modifications and alternative modeling techniques to facilitate consistent
calculations using the public domain version of CE-QUAL-W2; further details are provided
in the Modeling Approach section below.
Bathymetry for the Lake Norman model was developed from existing survey information.
Water quality data collected by Duke Energy and the DWQ were used to develop model
inputs. At the onset, it was desired to calibrate the models using two years of data: 1) a
normal year, and 2) a dry year. The years 1998 and 2001 were chosen as the normal and dry
calibration years, respectively. These years were selected because of their total annual flows
with respect to other years, and because each year contained an extensive set of tailrace
data.
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LAKE NORMAN MODEUNG APPROACH FOR MOORESVILLE WWTP EXPANSION ENVIRONMENTAL ASSESSMENT
Duke Energy prepared a water quality database using available data from three primary
sources: monitoring stations in Norman; continuous monitors in the Lookout Shoals and
Cowans Ford tailraces; and grab samples from the Lookout Shoals and Cowans Ford
tailraces. These data provided calibration information and boundary conditions for the
model. In addition, hourly data from the Hickory National Climatic Data Center
meteorological station were used to represent ambient conditions.
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. LAKE NORMAN MODELING APPROACH FOR MOORESVILLE WWTP EXPANSION ENVIRONMENTAL ASSESSMENT
FIGURE 1
Lake Norman Model Segmentation (Source: REMI and Loginetics, 2006)
Model segments captured the essential geometric features while limiting the size of the model to ensure that computation
times would not be excessive. Duke Energy determined that computing the detailed water quality characteristics of each of
the embayments was not a primary objective its modeling effort. Therefore, some of the segments in the embayments were
combined to reduce the model size and keep computational times within reasonable limits.
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LAKE NORMAN MODELING APPROACH FOR MOORESVILLE WWTP EXPANSION ENVIRONMENTAL ASSESSMENT
Modeling Goals
The DWQ requires that at highly detailed, calibrated nutrient response model of Lake
Norman be employed to demonstrate assimilative capacity. The model would need to be
able to show any associated localized impacts and behavior of the lake during critical
conditions. To fulfill these requirements, the primary modeling goals are to:
1. Provide a modeling tool that will accurately simulate existing temperature, nutrients,
and dissolved oxygen conditions in Lake Norman; and,
2. Provide a tool that will reasonably predict water quality responses in Lake Norman to
new WWTP discharges at several alternative locations.
Duke Energy calibrated its research version of the CE-QUAL-W2 model to observations in
what they concluded to be a normal and a dry hydrologic calendar year, 1998 and 2001
respectively. It is recognized that the Duke Energy model was constructed and calibrated to
satisfy different modeling goals than what is required by the DWQ for this modeling effort.
However, the modeling goals will be achieved by applying the public -domain version of the
CE-QUAL-W2 model to these two calendar years for validating the model, and for
predicting water quality responses to discharge alternatives.
Modeling Approach
The modeling approach has several main steps as follows:
1. Reconstruct Duke Energy's Lake Norman model
2. Verify model calibration
3. Perform sensitivity analysis
4. Evaluate water quality responses to discharge alternatives
The following describes each step of the modeling approach.
Reconstruct Duke Energy's Lake Norman Model
CH2M HILL will reconstruct Duke Energy's model of Lake Norman using their input files
and making modifications to closely simulate the model that was previously constructed.
Modifications will be made to input files acquired from the Duke Energy modeling team to
assure that they work with the public domain version of CE-QUAL-W2. The model will be
reconstructed for the two simulation periods with changes described below and then
verified by a calibration check.
The Duke Energy modeling team modified the CE-QUAL-W2 model code and applied it to
Lake Norman as a proprietary "research" version of CE-QUAL-W2. The modifications were
made to simulate thermal characteristics of power station withdrawals and returns, and to
better simulate nutrient kinetics. The modifications and alternative modeling techniques
employed by the Duke Energy modeling team are documented and the team is available for
consultation. Model inputs can and will be modified to facilitate consistent calculations
using the public domain version of CE-QUAL-W2.
The modifications applied in the proprietary model to simulate the thermal characteristics
of power station withdrawals and returns can be reproduced by adding thermal input files
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to the model. The modifications calculated the changes in water temperatures due to power
station processes in real time as the model performed time -step calculations. This was
performed to closely simulate thermal changes as the lake temperature changed throughout
the seasons without having to manually calculate them in a circular procedure. The
application of this modification was validated via model calibration. The Duke Energy
modeling team saved the thermal changes for the calibration periods and has provided
them to CH2M HILL. The thermal changes will be applied to the model as inputs for the
two calibration periods to simulate the thermal changes as a forcing function.
Other modifications were made to the CE-QUAL-W2 model code to better simulate nutrient
kinetics. For instance, the Duke Modeling team identified that organic matter and its
phosphorus and nitrogen content are important components in ecosystem models like CE-
QUAL-W2. The public domain version of CE-QUAL-W2 assumes that all organic matter
has the same nutrient content, i.e., ORGP and ORGN are the same for both labile and
refractory matter. A number of investigators cited by the modeling team reported that
phosphorus and nitrogen content is much lower in refractory organic matter and that
luxury uptake of phosphorus by algae affects the stoichiometric ratios between phosphorus
and organic matter. The Duke Energy modeling team developed a procedure to determine
the labile and refractory components using the available data and modified the model code
so that nutrient content of the labile and refractory organic matter were calculated
differently within the model (Ruane and Hauser, 2006). The modeling team has
advisedCH2M HILL that model inputs specifying refractory dissolved organic matter
concentrations and kinetic rates can be adjusted to closely simulate the model code change
using the public domain version of CE-QUAL-W2.
The remaining features of the Duke Energy model do not need to be modified in any way.
For instance, the bathymetry in the Lake Norman model was developed from existing
survey information. This input hasn't been changed and wasn't altered by the modeling
team for their purposes. Meteorology conditions will remain unchanged. Inflows at the
headwaters of Lake Norman and from its watershed are valid and will not change. Major
and minor NPDES discharges in the Lake Norman watershed are simulated in the existing
model and will not require modification.
Verify Model Calibration
The reconstructed model of Lake Norman will require a verification to assure that the model
has been applied to Lake Norman correctly and the changes made to use the public domain
version of CE-QUAL-W2 are effective and correct. Therefore, a model calibration effort will
be executed to verify the calibration for Duke Energy's two calibration years using data and
calibration report figures.
The Duke Energy calibration goal for Lake Norman model was to calibrate it to a normal
and a dry meteorological year. The years 1998 and 2001 were chosen by the Duke Energy
modeling team as the normal and dry calibration years, respectively. These years were
selected because of their total annual flows with respect to other years, and because each
year contained an extensive set of tailrace data.
The proprietary model was calibrated to a water quality database prepared by Duke Energy
using available data described above. These data provided calibration information and
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boundary conditions for the model that remain valid for use with the public domain version
of CE-QUAL-W2. CH2M HILL will verify model calibration using the public domain
version of CE-QUAL-W2 for the two calibration years using the Duke Energy database.
Model calculations will be compared to those documented in the Duke Energy calibration
report to verify that the public domain model application is successful.
The Duke Energy modeling team modified the CE-QUAL-W2 model code for both physical
and kinetic components of their modeling framework. Adjustments to model parameters
will be required using sound engineering judgment to verify the calibration. Therefore, the
calibration will first be verified to the physical parameter of temperature to confirm that the
manual thermal inputs are correctly simulating the calculated changes performed by the
proprietary model. Once the temperature calibration is verified, the nutrient calibration and
subsequently the dissolved oxygen calibration will be verified.
Perform Sensitivity Analysis
Lake Norman is the largest reservoir within the Catawba-Wateree Hydroelectric Project.
Lake Norman has 520 miles of shoreline, a surface area of more than 32,745 acres and a
maximum forebay depth of approximately 112 feet at a full pond elevation of 760 feet (REMI
and Loginetics, 2006). The volumetric residence time for the lake is well over 100 days. The
total facility expansion being evaluated by the Town of Mooresville is to increase the
treatment capacity from 5.2 mgd to 19 mgd. The potential discharge alternative flows to
Lake Norman will not exceed 20 mgd and may be a portion of that. Three Lake Norman
discharge location alternatives are being considered. Considering the size of the lake,
existing inflows and residence time, it is prudent to first perform a sensitivity analysis to
determine if lake water quality will be sensitive to the discharge alternatives.
A sensitivity analysis will be performed for maximum loading conditions at the three
proposed discharge points using Duke Energy's two calibration years. CH2M HILL will
construct model input files using the calibration inputs to simulate maximum thermal and
pollutant loading conditions at the NC 150 Bridge, Reedy Creek Cove, and Langtree Road.
The loading condition will be characterized as the peak anticipated flow at each location
with worse -case temperature and pollutant concentrations. Sensitivity will be measured
using existing calibration locations throughout the lake. In addition, water quality
responses will also be assessed in the model segments at and in the proximity of the three
discharge alternatives. Water quality responses will be assessed for temperature, nutrients
and dissolved oxygen.
The results of the sensitivity analysis will be assessed and documented. If it is determined
that Lake Norman water quality is not sensitive to the proposed alternatives at maximum
loading conditions, no further modeling may be necessary.
Evaluate Water Quality Responses to Discharge Alternatives
If the sensitivity analysis indicates that Lake Norman water quality is sensitive to any of the
maximum -loading discharge alternatives, a more detailed water quality response evaluation
will be conducted. CH2M HILL will construct model input files using the calibration inputs
to simulate anticipated discharge conditions for each of the three alternatives. CH2M HILL
will identify and assess any calculated changes in temperature, nutrients, and dissolved
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oxygen for the alternatives. The calculated responses will be assessed as a projected change
in water quality conditions. Water quality responses will also be compared to water quality
standards.
Quality Control
Quality assurance/quality control will be provided by conducting a technical modeling
review at the onset of the modeling effort and after each step of the modeling approach is
executed. CH2M HILL will assign several modeling technologists to review the details of
model reconstruction prior to starting the effort.
After the model is reconstructed, the calibration will be reviewed to verify the application of
the public domain CE-QUAL-W2 model. If the calibration is deemed acceptable within
reasonable limits, the model will be recommended for further application to alternative
evaluations. If the calibration cannot be verified, then the review team will recommend that
the modeling framework be reevaluated and adjusted if necessary to assure that the model
simulates existing conditions and can reasonable calculate water quality responses to
discharge alternatives.
Water quality response evaluations will be overseen to assure that proper application of
anticipated conditions are applied to the model. The sensitivity analysis and alternative
analysis will be reviewed and validated.
Deliverables
The deliverable for the modeling effort will be documentation of the modeling effort that
shall describe the following:
• A public domain version of CE-QUAL-W2 for Lake Norman reconstructed from input
files from the proprietary version of the model,
• Modifications made to input files to compensate for Duke Energy proprietary model
code modifications,
• Calibration results for the two Duke Energy calibration years comparing calculated
water quality parameters including temperature, nutrients and dissolved oxygen to the
Duke Energy calibrations and water quality data,
• Water quality responses to the maximum loading conditions for the three discharge
alternatives in the sensitivity analysis,
• Water quality responses to anticipated discharge alternatives (if deemed necessary
following the sensitivity analysis.
References
Black and Veatch, 2006 "Water and Wastewater Planning Study." Charlotte, North Carolina.
CH2M HILL, 2006. "Rocky River WWTP Expansion - Preliminary Engineering Report."
Charlotte, North Carolina.
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LAKE NORMAN MODELING APPROACH FOR MOORESVILLE WWTP EXPANSION ENVIRONMENTAL ASSESSMENT
Cole, T.M., and S. A. Wells, 2003. "CE-QUAL-W2: A two-dimensional, laterally averaged,
Hydrodynamic and Water Quality Model, Version 3.1," Instruction Report EL-03-1, US
Army Engineering and Research Development Center, Vicksburg, MS.
REMI and Loginetics, 2006. "Calibration of the CE-QUAL-W2 Model for Lake Norman,"
prepared by Reservoir Environmental Management, Inc. (REMI) and Loginetics Inc. for
Duke Energy, Chattanooga, TN, July 2006.
Ruane and Hauser, 2006. `Background Document for Catawba-Wateree Water Quality
Models," prepared by Reservoir Environmental Management, Inc. (REMI) and Loginetics
Inc. for Duke Energy, Chattanooga, TN, 2006.
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