1812_DukeMarshall_ModelingSupport_FID1616244_20211005

(' DUKE
ENERGY-.
October 5, 2021
North Carolina Department of Environmental Quality
Division of Waste Management
Solid Waste Section
1646 Mail Service Center
Raleigh, North Carolina 28778
Attn: Ms. Sarah Moutos (submitted electronically)
Re: Groundwater Model Tech Memo Submittal
Permit to Construct Modification —
Industrial Landfill No. 1 Phase 2 Expansion
Permit No.: 1812-INDUS-2008
Marshall Steam Station
Terrell, North Carolina 28682
Dear Ms. Moutos:
526 South Church St.
Charlotte, NC 28202
Mailing Address
P.O. Box 1006
Mail Code EC 13K.
Charlotte, NC 28201-1006
717-982-0986
This submittal includes the groundwater modeling tech memo, prepared by SynTerra Corporation (SynTerra) on
behalf of Duke Energy Carolinas, LLC (Duke Energy), with the subject: Modeling Support for the ILF Phase 2
Permit to Construct Modifications. Groundwater modeling was completed by SynTerra to support design
modifications included in the Permit to Construct (PTC) Modification Request for the Marshall Steam Station
Industrial Landfill No.1 (1812-INDUS-2008) Phase 2 expansion.
Upon completion of the modeling evaluation in early September 2021, an overview of the groundwater model setup
and results were presented by SynTerra during a meeting between the Solid Waste Section (Section), Duke
Energy, and SynTerra on September 9, 2021. The modeling presentation and AQUAVEO GMS MODFLOW
modeling files were submitted to the Section as part of the overall PTC Modification Request submittal package for
review on September 9, 2021 and September 14, 2021, respectively.
Although approval for the Permit to Construct design modifications has been issued by the Section in a letter titled
Phase 2 Permit to Construct Modification, Approval and dated September 17, 2021, Duke Energy is submitting the
this tech memo to complete the PTC Modification Request submittal package. Additionally, this tech memo
provides further detail on the groundwater modeling set up, methods and depiction of results.
If you have any questions or need any clarification regarding this submittal, please contact me at [phone] or
by email at Ashley.Albert(a�duke-energy.com.
Respectfully submitted,
4f
Ashley Albert, P.G.
Environmental Services
Attachments: ILF Phase 2 PTC Mod. Modeling Support (SynTerra, 2021)
cc (via e-mail): Ben Jackson, NCDEQ
Larry Frost, NCDEQ
Ed Mussler, NCDEQ
Sherri Stanley, NCDEQ
www.duke-energy.com Page 1 of 2

Kyle Baucom, Duke Energy
Johnathan Ebenhack, SynTerra
Chris Varner, Duke Energy
Ryan Czop, Duke Energy
Bryson Allison, Duke Energy
Ed Sullivan, Duke Energy
www.duke-energy.com Page 2 of 2

L�
synTerra
Date: October 5, 2021
Science & Engineering Consultants
148 River St., Suite 220, Greenville, SC 29601 1864.421.9999
TECHNICAL MEMORANDUM
File: 0083.46.02
To: Ashley Albert, P.G.
NSF
Cc: Kathy Webb, P.G. (SynTerra)
SEA.
n i 272� '� a
From: Johnathan Ebenhack, P.G., Senior Project Scientist
FQL0r,7`�_ �aZ'
Thomas Colton, Project Manager -
Craig Eady, Senior Peer Review
A4811 -
Subject: Modeling Support for the ILF Phase 2 Permit to Con truct Modifications
This technical memorandum presents results from modeling to support the Industrial
Landfill (ILF) Phase 2 Cell 5 Permit to Construct (PTC) modifications for the Marshall
Steam Station (Marshall or Site) (Figure 1). At the request of Duke Energy Carolinas,
LLC (Duke Energy), SynTerra Corporation (SynTerra) conducted groundwater flow
modeling to evaluate the performance and operational life of a proposed blanket
underdrain beneath Cell 5 of the ILF Phase 2. The proposed blanket underdrain would
be constructed to control groundwater elevations below Cell 5 of the ILF Phase 2. Model
results indicate the estimated steady-state flowrate to the blanket underdrain is
approximately 18 gallons per minutes (gpm). Transient simulations indicate that the
initial flowrate to the Cell 5 blanket underdrain can potentially exceed 100 gpm but that
flowrates to the underdrain will significantly decrease within a short period of time
(days to months) and will continue to decrease over time (within the first year).
Simulation results indicate that the Cell 5 blanket underdrain will stop receiving flow
after approximately 1.5 years after operation begins. Furthermore, this evaluation
indicates that the proposed underdrains beneath the Phase 3 through 5 ILF expansions
are capable of maintaining groundwater elevations low enough in the Phase 2 Cell 5
footprint to prevent reactivation of the Cell 5 blanket underdrain.
METHODS
The groundwater flow models used to evaluate the performance and operational life of
the proposed blanket underdrain beneath Cell 5 include a current conditions steady-
state flow model, a steady-state current conditions model with the proposed Cell 5
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Modeling Support for the ILF Phase 2 Permit to Construct Modifications October 5, 2021
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Page 2 of 12
blanket underdrain operating, and near -term and long-term predictive transient flow
models.
MODEL CONSTRUCTION AND CONDITIONS
The steady-state decanting flow model presented in Appendix G of the Updated 2019
Corrective Action Plan (CAP) for the Marshall Steam Station (SynTerra, 2019) was
modified to conduct the evaluation of the proposed Cell 5 blanket underdrain.
Modifications included recent changes at the Site, as of July 2021, to represent current
conditions (i.e., material excavation, new drainage features, new recharge distributions,
etc.). Current Site conditions were verified by SynTerra during a site walk on August 6,
2021, and from aerial survey data collected by Trans -Ash, Inc. (Trans -Ash) on July 20,
2021. This modified steady-state current conditions model is referred to as the current
conditions model hereafter. The current conditions model was further modified to
develop the steady-state current conditions model with the proposed Cell 5 blanket
underdrain operating (referred to as the steady-state blanket underdrain model), and
the predictive transient simulations.
The numerical grid used in the models was refined from the steady-state decanting
CAP flow model in the horizontal and vertical directions to improve model resolution
near the area of interest. The horizontal grid spacing in the area of interest was refined
from approximately 50 feet or less in the CAP model to approximately 30 feet or less.
The upper layers of the vertical grid, in which the proposed blanket underdrain would
be located, were refined to a grid thickness of approximately 5 feet or less. The vertical
refinement increased the number of model layers from 21 to 26.
Steady -State Current Conditions Mode/
The primary modifications to the CAP model to represent current conditions included
edits to the hydraulic features, edits to the recharge distribution, and the inclusion of
excavated areas around the Site.
Hydraulic features were updated in the simulation to represent conditions in July 2021
(Figure 2). The primary hydraulic features added to the model included:
• A drainage feature west of the Cell 5 footprint that directs flow into the MAR-145
stormwater basin (simulated as a drain)
• A French drain feature located along the east side of the Cell 6 footprint
(simulated as a drain)
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• Ponded water which formed at the end of the French drain along the east side of
Cell 6 (maintained at an elevation of approximately 810 feet; simulated as a
general head)
• Dewatering ditches installed within the Phase 3 through 5 ILF expansions to
facilitate ash dewatering during excavation (simulated as drains)
• Ponded water features in the northeastern area of the Site associated with ash
excavation and site construction in the eastern most fingers of the ash basin
(simulated as general heads)
• A drainage feature that extends north to south located east of the 1804 Phase 2
Landfill that ties into the future MAR-152 stormwater basin (simulated as a
drain)
• Additional drainage features and ponded water features that have formed in the
main ash basin after ash basin decanting (simulated as drains and general heads)
Drainage features in the simulations are modeled using the DRAIN package in
MODFLOW. Bottom elevations for drain features are set to survey data provided by
Trans -Ash and Duke Energy. Drain conductance terms are assumed to be 10 feet
squared per day per foot (feetz /day)/(foot). Ponded water features are simulated as
general head boundaries with head -stages set to elevations from survey data and
provided by Duke Energy.
The recharge distribution was modified to current conditions by removing recharge
from newly formed ponded water and the lined MAR-145 stormwater basin (Figure 3).
To adjust for ongoing Site construction and excavation, the hydraulic conductivity field
in the upper layers of the model were modified to represent excavation. Excavated
areas were given a high hydraulic conductivity of 100 feet per day (feet/day) to
represent excavation. The original model ground surface was compared to the current
ground surface obtained from the July 2021 aerial survey data. Material was "removed"
from areas where large differences in the two surfaces were identified by adjusting the
hydraulic conductivity. This method is similar to that used in the 2019 CAP models to
represent ash excavation during closure.
Steady -State Current Conditions Model Calibration
The current conditions model was calibrated to water -level data from observation wells,
newly installed piezometers, and hydraulic test pits in the Cell 5 footprint. Site -wide
hydraulic head data was collected from those observation points on July 20 and July 21,
2021. The current conditions model was calibrated by adjusting the hydraulic
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conductivity field to improve the fit between groundwater -level measurements at
observation locations and the computed heads at observation locations. A Normalized
Root Mean Square Error (NRMSE) of 2.75 percent was achieved for the fit to the
observed water -level data and in general a NRMSE of 10 percent or less demonstrates a
good fit to the data. Figure 4 shows the computed hydraulic heads compared to the
observed hydraulic heads, with those data and the residuals provided in Table 1. The
calibrated current conditions model flow field was used as the starting hydraulic heads
for the steady-state blanket drain model and the near -term transient models.
Steady -State Blanket Underdrain Model
The steady-state blanket underdrain model uses the same model setup as the current
conditions model but includes the proposed blanket underdrain within the Cell 5
footprint and assumes material has been backfilled within the Cell 5 and Cell 6 ILF
expansions (Figure 5). The purpose of the steady-state blanket underdrain model is to
estimate the flowrate to the proposed underdrain under current conditions. The Cell 5
blanket underdrain design is based on AECOM's proposed designs provided to
SynTerra by Duke Energy on August 20, 2021 (AECOM, 2021). Figure 6 shows the
proposed Cell 5 blanket underdrain design. The model only incorporates the blanket
stone portion of the underdrain and does not include the underlying connector pipes.
This approach was taken since it is a more conservative approach when evaluating
reductions in groundwater elevations caused by the proposed blanket underdrain
because the underlying connector pipes have a lower elevation than the bottom
elevation of the overlying blanket stone.
The blanket underdrain is simulated in the model with the DRAIN package in
MODFLOW. The simulated drain assumes the drain elevation is the bottom elevation of
the blanket underdrain stone bed. The bottom elevation of the proposed blanket
underdrain ranges from approximately 828 feet in the northeastern corner to
approximately 810 feet within the sump of the drain in the southwestern corner. To
simulate the change in elevation along the drain feature, the blanket underdrain is
simulated using a series of polygon drain boundaries with bottom elevations
corresponding to 1 foot elevation interval changes along the blanket drain (Figure 5).
The blanket underdrain feature in the model assumes a conductance of 2 feet squared
per day per feet squared (ft2/day)/(ft2). A hydraulic conductivity of 0.5 feet/day was
applied to previously excavated regions in Cell 5 and Cell 6 to represent backfill in
those areas. To be conservative, this hydraulic conductivity is the lowest value in the
range of potential backfill hydraulic conductivity values provided to SynTerra by Duke
Energy and AECOM.
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PREDICTIVE SHORT-TERM TRANSIENT SIMULATION
The predictive near -term transient model covers a period of time from current
conditions until expected completion of the excavation of the Phase 3 through 5 ILF
expansions. The model accounts for anticipated Site changes and construction activities
during this period. The dates for anticipated Site events are conservative estimates of
currently planned construction dates. Table 2 shows the anticipated construction
activities and estimated dates for the near -term transient model. The near -term transient
model described below is referred to as the "near -term base model".
Table 2. Anticipated Site Activities/Construction During the
Near -Term Transient Model
Site Event
Approximate Date of
Completion
Near -Term Transient Model Start
10/1/2021
Blanket Drain Installation
1/1/2022
Cell 5 Liner Installation
6/1/2022
Cell 6 Liner Installation
12/1/2022
Phase 3 through 5 Excavation
12/31/2022
PVSF Cap Installation
4/1/2023
Near -Term Transient Model End
9/30/2023
The near -term base model assumes that excavation and dewatering within the Phase 3
through 5 ILF expansions occur concurrently in all three phases and that excavation and
dewatering occur at a constant rate. Transient drain features were used to simulate
dewatering during excavation. The model assumes that the current dewatering ditches
for the Phase 3 through 5 excavations are lowered as excavation progresses until they
reach the estimated bottom of ash, or the original ground surface elevations. The model
assumes the current configuration of the dewatering ditches stays the same throughout
their operational life. The configuration of the dewatering ditches is based on
observations during the site visit on August 6, 2021 and aerial survey data from Trans -
Ash. The initial bottom elevations of the ditches are set to survey data from July 2021,
and the elevations are lowered at a linear rate until the Phase 3 through 5 ILF expansion
excavations are expected to be complete on December 31, 2022. Excavation for the
proposed underdrain network for the Phase 3 through 5 ILF expansions is expected to
be completed during the excavation process. The design for the proposed Phase 3
through 5 underdrain is based on AutoCAD files provided to SynTerra by Duke Energy
on 8/12/2021. The proposed Phase 3 through 5 underdrains are initially set to the
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ground surface elevation in the model, and the underdrains are lowered as excavation
progresses until the bottom drain elevations are approximately 1 foot below the former
stream valley grades. At the beginning of the simulation, the dewatering ditches control
most of the groundwater discharge in the Phase 3 through 5 ILF expansion area. As the
simulation progresses and the proposed Phase 3 through 5 underdrains approach the
final bottom elevations located in the historical stream valleys, groundwater discharge
transitions primarily to the proposed Phase 3 through 5 underdrain network.
Time -dependent hydraulic conductivity fields to represent excavation and material
removal are difficult to implement in the Groundwater Modeling System (GMS)
software. Therefore, the model assumes that the material/ash in the Phase 3 through 5
ILF expansions is fully excavated at the start of the simulation. This excavated
material/ash is given a high hydraulic conductivity (100 feet/day) to simulate
excavation. Additional transient comparison models were developed to evaluate the
effect of assuming excavation at the start of the model on the performance and
operational life of the Cell 5 blanket underdrain and are discussed below. Additionally,
the backfill material in Cell 5 and Cell 6 are assumed to be in place at the start of the
model, and this backfill material is given a hydraulic conductivity of 0.5 feet/day.
The Cell 5 blanket underdrain is assumed to be completed by January 1, 2022, and is
inactive in the model until this date. To simulate placement of the Cell 5 and Cell 6 liner
systems, a time -dependent recharge rate was used in the model within the footprint of
those two cells. At the start of the model, the recharge rate in the footprints of those two
cells is set to the background recharge rate of 0.0018 feet/day. The recharge rate in the
footprint of those two cells is then reduced to near zero (1E-7 feet/day) at the dates
given in Table 1. The model assumes that the French drain along the east side of Cell 6
and the ponded water that formed at the toe of this French drain are abandoned and no
longer active. Figure 7 shows the important hydraulic features and Site changes
associated with the near -term base model. Figure 8 shows the recharge distribution for
the near -term base model.
To be conservative, the model assumes a relatively high specific yield of 0.2 for the
saprolite and ash material. In general, the specific yield in saprolite and ash will have
the largest effect on the performance and operational life of the Cell 5 blanket
underdrain compared to other storage coefficients (i.e., bedrock specific yield, specific
storage coefficients). The higher the specific yield the longer it will take the system to
equilibrate to dewatering in the Phase 3 through 5 ILF expansions, and the longer the
estimated operational life. The specific yield in the bedrock is assumed to be 0.001. The
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specific storage coefficients are assumed to range from 0.0001 to 0.00001 with the lowest
values in bedrock.
The simulated hydraulic heads from the steady-state current conditions model are
assumed to be the starting heads for the near -term base model.
PREDICTIVE LONG-TERM TRANSIENT SIMULATION
The predictive long-term transient model (long-term base model) covers an
approximately 16 year period after the Phase 3 through 5 ILF expansions are fully
backfilled with compacted material, and the proposed Phase 3 through 5 ILF
underdrain network is permanently installed. The model accounts for anticipated Site
changes during this time period. The dates for Site events are conservative estimates of
currently planned construction dates. Table 3 shows the anticipated construction
activities and estimated dates for the long-term base model. The near -term base model
was modified to develop the long-term base model.
Table 3. Anticipated Site Activities/Construction During the
Long -Term Transient Model
Site Event
Approximate Date of Completion
Long -Term Transient Model Start
10/1/2023
Phase 3 through 5 backfill
complete and proposed
underdrains installed
10/1/2023
1804 Phase 2 Cap Installation
12/1/2023
Phase 3 Liner Installation
12/1/2024
Phase 4 Liner Installation
5/1/2026
Phase 5 Liner Installation
6/1/2027
Long -Term Transient Model End
1/1/2040
The long-term base model assumes that the Phase 3 through 5 ILF expansions have
been backfilled to accommodate construction of the expansions. The long-term base
model also assumes that the proposed Phase 3 through 5 ILF underdrains are operating
but that the dewatering ditches from the near -term base model are no longer present.
The backfill material was given a hydraulic conductivity of 0.5 feet/day. The remainder
of the hydraulic features in the long-term base model are the same as those in the near -
term base model (Figure 9).
The placement of caps and liner systems are handled in the long-term base model using
the same method as the near -term base model. Initial recharge rates in areas where caps
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or liners are placed during the modeled period are set to the background recharge rate
of 0.0018 feet/day and then reduced to near zero (1E-7 feet/day) when the cap or liner is
estimated to be completed, as given in Table 3. Figure 10 gives the recharge distribution
for the long-term base model.
The storage coefficients for the long-term base model are the same as those used in the
near -term base model.
The simulated hydraulic heads from the end of the near -term base model are assumed
to be the starting heads for the long-term base model.
TRANSIENT COMPARISON MODELS
Additional transient models were run to evaluate the effects of material/ash removal
from the Phase 3 through 5 excavation and the long-term seasonal high (LTSH)
recharge rate on the performance and operational life of the blanket underdrain. The
comparison models evaluating the effects of material/ash removal are referred to as the
near -term and long-term non -excavation models. The LTSH recharge comparison
models are referred to as the near -term and long-term LTSH models.
The near -term non -excavation model is run without any material/ash removed from
within the Phase 3 through 5 ILF expansion area. All other model conditions and
hydraulic features are the same as the near -term base model. The hydraulic heads from
the end of the near -term non -excavation model are used as the starting heads in the
long-term non -excavation model. No additional changes were made to the long-term
base model to develop the long-term non -excavation model except the starting heads
for the simulation run.
The LTSH comparison models are run using the same model conditions and boundaries
as the near -term and long-term base models but with the estimated LTSH recharge rate
of 0.0022 feet per day, which is 20 percent greater than the base recharge rate of 0.0018
feet per day. The method for determining an appropriate LTSH recharge rate is
documented in the "Long -Term Seasonal High Groundwater Elevation Estimation, Marshall
Steam Station" (SynTerra, 2020).
RESULTS
Results from the steady-state and transient models are presented below.
Steady -State Model Results
A hydraulic head map with residual error bars showing the approximate groundwater
table elevations near the ILF expansions is shown in Figure 11. The calibrated steady-
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state current conditions model gave a good fit to observed data with a NRMSE of
approximately 2.75 percent. Residuals between the computed and observed heads
within the area of interest generally were within two feet or less, and heads were
generally overestimated by the model.
Hydraulic heads from the steady-state blanket underdrain model are presented in
Figure 12. The estimated steady-state flowrate to the Cell 5 blanket underdrain is
approximately 18 gallons per minutes (gpm).
Near -Term and Long -Term Base Model Results
Hydraulic head maps showing hydraulic heads 1 month, 1 year, 1.5 years, and 5 years
after operation of the proposed Cell 5 blanket underdrain begins are shown in
Figure 13. The estimated flowrate to the Cell 5 blanket underdrain is shown in
Figure 14.
The transient models estimate an initial flowrate to the blanket underdrain of
approximately 530 gpm when the underdrain becomes active. The initial estimated
flowrate from the simulation is expected to be an overestimate since dewatering in the
area will be necessary to install the blanket underdrain, which is not accounted for in
the simulation. After approximately 3 days, this estimated flowrate decreases to
approximately 100 gpm. After 1 month of drain operation, the flowrate is reduced to
approximately 31 gpm. The simulated flowrate to the blanket underdrain continues to
decrease over time, and only receives approximately 3 gpm after 1 year of operation.
The transient models estimate that the blanket underdrain will stop receiving water
after approximately 1.5 years (Figure 14).
The long-term base model indicates that groundwater levels are maintained below the
bottom elevation of the Cell 5 blanket underdrain after the Phase 3 through 5 ILF
expansions are backfilled for construction and the proposed Phase 3 through 5 ILF
underdrains are installed (Figure 13 and Figure 14). These findings indicate that the
proposed Phase 3 through 5 underdrains are capable of maintaining groundwater
elevations low enough in the area to prevent reactivation of the Cell 5 blanket
underdrain.
Transient Comparison Model Results
Results from the non -excavation transient models indicate that removal of material/ash
has limited effects on the flowrates and operational lifetime of the Cell 5 blanket
underdrain (Figure 15). Not removing material/ash from the Phase 3 through 5 ILF
expansion area results in slightly higher initial flowrates compared to the base transient
models. Flowrates after one month of operating the Cell 5 blanket underdrain are
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approximately 35 gpm and are reduced to approximately 5 gpm after one year of
operation. The non -excavation models predict that the blanket underdrain will stop
receiving flow after approximately 1.6 years of operation. Those results indicate that the
primary reduction in flowrates to the Cell 5 blanket underdrain is the result of
dewatering in the Phase 3 through 5 ILF expansion area and not the removal of material
from the area.
The LTSH models show that increased recharge rates have an even more limited effect
on the Cell 5 blanket underdrain performance and operational life compared to the
effects of not removing material from the Phase 3 through 5 ILF expansion area (Figure
16). After approximately 1 month of operation, flowrates to the blanket underdrain
have reduced to 32 gpm. After approximately 1 year, the flowrate to the blanket
underdrain is reduced to 3 gpm, and the blanket underdrain stops receiving flow after
approximately 1.6 years (Figure 16). The effect of the LTSH recharge rate is limited in
the area of the ILF expansions due to the installation of liner systems, which reduce the
overall recharge in those regions.
Phase 3 through 5 Dewatering Ditches/Underdrain Flowrates
Figure 17 shows the estimated flowrates to the Phase 3 through 5 ILF expansion
dewatering ditches and proposed underdrains. Model results indicate that flowrates to
the dewatering ditches and proposed underdrains increase with excavation depth as
expected and reach a peak after excavation is completed. As water levels around the
excavated area equilibrate, those flowrates decrease with time. The combined simulated
flowrate for both the dewatering ditches and proposed Phase 3 through 5 underdrains
is initially around 50 gpm. As excavation progresses and the drains are lowered to the
original ground surface, the combined flowrate increases to as much as 460 gpm at the
end of excavation. Toward the end of the near -term base model, the combined flowrates
decrease to approximately 300 gpm. The long-term base model only simulates the
permanently installed underdrains, and the estimates for the total flowrate is
approximately 250 gpm initially. As Site conditions stabilize, the flowrates in the
proposed underdrains approach a steady-state value likely between approximately 125-
150 gpm.
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ATTACHMENTS:
Page 11 of 12
FIGURES:
Figure 1- Site Location Map
Figure 2 - Current Conditions Model Hydraulic Features
Figure 3 - Current Conditions Model Recharge Distribution
Figure 4 - Computed versus Observed Hydraulic Heads for Current Conditions
Figure 5 - Steady -State Cell 5 Blanket Underdrain Model Hydraulic Features
Figure 6 - Proposed Cell 5 Blanket Underdrain Design (AECOM, 2021)
Figure 7 - Near -Term Transient Model Hydraulic Features and Model Setup
Figure 8 - Near -Term Transient Model Recharge Distribution
Figure 9 - Long -Term Transient Model Hydraulic Features and Model setup
Figure 10 - Long -Term Transient Model Recharge Distribution
Figure 11- Estimated Groundwater Elevations for the Current Conditions Model
Figure 12 - Estimated Groundwater Elevations for the Steady -State Cell 5 Blanket
Underdrain Model
Figure 13 - Estimated Groundwater Elevations During Operation of the Cell 5 Blanket
Underdrain
Figure 14 - Simulated Flowrate to the Cell 5 Blanket Underdrain (Base Model)
Figure 15 - Effect of Phase 3 through 5 Material/Ash Excavation on the Simulated
Flowrate to the Cell 5 Blanket Underdrain
Figure 16 - Effect of Long -Term Seasonal High Recharge on the Simulated Flowrate to
the Cell 5 Blanket Underdrain
Figure 17 - Estimated Flowrates to the Phase 3 through 5 Dewatering Ditches and
Proposed Underdrains
TABLES:
Table 1- Observed and Simulated Current Conditions Hydraulic Heads and
Calibration Residuals
Table 2 - Anticipated Site Activities/Construction During the Near -Term Transient
Model (embedded)
Table 3 - Anticipated Site Activities/Construction During the Long -Term Transient
Model (embedded)
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REFERENCES:
AECOM, 2021, Industrial Landfill No.1 (1812-INDUS) Phase 2 (Cells 5 and 6) Expansion,
Marshall Steam Station, Catawba County, North Carolina (Draft), 2021.
SynTerra, 2019, Updated Groundwater Flow and Transport Modeling Report, Marshall
Steam Station, Terrell, NC. December, 2019
SynTerra, 2020, Long -Term Seasonal High Groundwater Elevation Estimation, Marshall
Steam Station, Terrell, NC. June 2020.
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FIGURES
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DUKE
NOTES:
INDUSTRIAL � ♦r. • r-•
LANDFILL #1
/ PHASE
ENERGY CAROLINAS CELL 5
PROPERTY LINE",,," PHASE II CELL 6
�.00e PHASE 3-5
ASH BASIN
WASTE BOUNDARY
•
ASH BASIN
s
`--
1 _
ASH BASIN
cam
1 /0
I
Lake Norman
of Catawba
1. ALL BOUNDARIES ARE APPROXIMATE.
2. TOPOGRAPHIC MAP SOURCE: 2019 USGS TOPOGRAPHIC MAP,
TROUTMAN & LAKE NORMAN NORTH QUADRANGLE, OBTAINED
FROM THE USGS NATIONAL MAP AT https://www.usgs.gov
DUKE I ATCOUNTY t
ENERGY
CAROLINAS
0
synTerra
MARSHALL
;TEAM STATION\
FIGURE 1
SITE LOCATION MAP
MODELING SUPPORT FOR THE ILF PHASE 2 CELL 5 PERMIT TO
CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
CATAWBA COUNTY, NORTH CAROLINA
DRAWN BY: A. ROBINSON DATE: OS/1212019
REVISED BY: W. PRATER DATE: 09/17/2021 GRAPHIC SCALE i,000 0 LE 2.000
CHECKED BY. J. EBENHACK DATE: 09/17/2021
APPROVED BY: C. EADV DATE: 09/17/2021
PROJECT MANAGER: T. COLTON (IN FEET)

4 EA
,
r a `
LEGEND •�
ie WATER SUPPLY WELLS WITH SEPTIC RETURN
ie SEPTIC RETURN -1
DRAIN FEATURES AND DEWATERING DITCHES
® MAR-145 STORMWATER BASIN GRAPHIC SCALE
FUTURE MAR-152 STORMWATER BASIN % DUKE 390 0 390 so
ENERGY (IN FEET)
PONDED WATER CAROLINAS
DRAWN BY: W. PRATER DATE: 09/15/2021
pWETLANDS REVISED BY: J. EBENHACK DATE: 09/30/2021
CHECKED BY:J. EBENHACK DATE: 09/30/2021
1804 PHASE 2 LANDFILL APPROVED BY: C. EADY DATE: 09/30/2021
fff PROJECT MANAGER: T. COLTON
AREAS OF EXCAVATED ASH/MATERIAL Terra
www.synterracorp.com
APPROXIMATE EXTENT OF THE PHASE 1 ILF AND
PROPOSED PHASE 2-5 ILF EXPANSIONS FIGURE 2
NOTES: CURRENT CONDITIONS MODEL
1. ALL BOUNDARIES ARE APPROXIMATE. HYDRAULIC FEATURES
2. MODELASSUMES JULY 2021 CONDITIONS AT SITE. MODELING SUPPORT FOR THE ILF PHASE 2 PERMIT
3. FEATURES DATA, AND SITE HOWN ARE BASED ON RECENT D DATA FROM PREVIOUS MODELING EFFORTS. OBSERVATIONS IN THE FIELD, RECENT SURVEY TO CONSTRUCT MODIFICATIONS
4. AERIAL PHOTOGRAPHY PROVIDED BY TRANS ASH WAS COLLECTED ON JULY 20, 2021. MARS HALL TEAM STATION
5. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE TERRELL, NORTH CAROLINA
COORDINATE SYSTEM FIPS 3200 (NAD83 AND NAVD88).

i - Ponded Water
Recharge = 0 feet/day
Industrial Landfill �..,.
t' Recharge = 1 E-7 feet/day ,.
Drainage Valley
?K ` Recharge = 0.0002 feet/day
Industrial Area
Recharge = 0 feet/day - -
* -
MAR-145 Stormwater Basin
.. Recharge = 0 feet/day h
f Ponded Water
s ti Recharge = 0 feet/day
Ponded Water
n 9- j zm�
L: e
e
Ponded Water
Recharge = 0 feet/day
b`
rBackground
Recharae = 0.0018
alday -
Y
Constructed Wetlands o "
Recharge = 0 feet/day
Industrial Area 1 .: Ponded Water
Recharge = 0.00022 feet/day Recharge = 0 feet/day
LEGEND
C-3 RECHARGE ZONES
NOTES:
1. ALL BOUNDARIES ARE APPROXIMATE.
2. MODELASSUMES JULY 2021 CONDITIONS AT SITE.
3. RECHARGE DISTRIBUTION IS BASED ON RECENT OBSERVATIONS IN THE FIELD AND SITE
DATA FROM PREVIOUS MODELING EFFORTS.
4. AERIAL PHOTOGRAPHY PROVIDED BY TRANS ASH WAS COLLECTED ON JULY 20, 2021.
5. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE
COORDINATE SYSTEM RIPS 3200 (NAD83 AND NAVD88).
G
DUKE 390 OGRAPHICSLE
780
ENERGY. (IN FEET)
CAROLINAS
DRAWN BY: W. PRATER DATE: 09/15/2021
REVISED BY: J. EBENHACK DATE: 09/17/2021
CHECKED BY: J. EBENHACK DATE: 09/17/2021
APPROVED BY: C. EADY DATE: 09/17/2021
Terra PROJECT MANAGER: T C1111
s�mwww.synterracorp.com
FIGURE 3
CURRENT CONDITIONS MODEL
RECHARGE DISTRIBUTION
MODELING SUPPORT FOR THE ILF PHASE 2
PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
TERRELL, NORTH CAROLINA

880
870
860
850
840
-0 830
N
820
v
Q 810
E
U 800
790
780
770
760
750
4' DUKE
ENERGY
10
synTerm
DRAWN BY: W. PRATER
REVISED BY: J. EBENHACK
CHECKED BY: J.EBENHACK
APPROVED BY: C. EADY
PROJECT MANAGER: T. COLTON
DATE: 09/15/2021
DATE: 09/17/2021
DATE: 09/17/2021
DATE: 09/17/2021
www.synterracorp.com
u
Observed Head
FIGURE 4
COMPUTED VS OBSERVED HYDRAULIC HEADS FOR CURRENT CONDITIONS
MODELING SUPPORT FOR THE ILF PHASE 2
PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
TERRELL, NORTH CAROLINA

Phase 1
��� • Phase 2
Phase 2
Cell 5
/ Phase 4
0
P16
r
r
1* Aihmor..
r ; y
L.-I
.� .
LEGEND I• � •
PROPOSED CELL 5 BLANKET UNDERDRAIN * `i
WATER SUPPLY WELLS WITH SEPTIC RETURN:
SEPTIC RETURN
DRAIN FEATURES AND DEWATERING DITCHES �> DUKE GRAPHIC SCALE
390 0 390 780
®MAR 145 STORMWATER BASIN ENERGY, (IN FEET)
CAROLINAS
=PONDED WATER DRAWN BY: W. PRATER DATE: 09/15/2021
REVISED BY: J. EBENHACK DATE: 09/28/2021
p WETLANDS CHECKED BY: J. EBENHACK DATE: 09/28/2021
APPROVED BY: C. EADY DATE: 09/28/2021
AREAS OF EXCAVATED ASH/MATERIAL Terra PROJECT MANAGER: T. coLroN
APPROXIMATE EXTENT OF THE PHASE 1 AND www.synterracorp.com
PROPOSED PHASE 2-5 ILF EXPANSIONS FIGURE 5
NOTES: STEADY-STATE CELL 5 BLANKET UNDERDRAIN
1. ALL BOUNDARIES ARE APPROXIMATE. MODEL HYDRAULIC FEATURES
2. MODELASSUMES JULY 2021 CONDITIONS AT SITE. MODELING SUPPORT FOR THE ILF PHASE 2
3. FEATURES DATA, AND SITE HOWN ARE BASED ON RECENT D DATA FROM PREVIOUS MODELING EFFORTS. OBSERVATIONS IN THE FIELD, RECENT SURVEY PERMIT TO�+SCONSTRUCT MODIFICATIONS
4. AERIAL PHOTOGRAPHY PROVIDED BY TRANS ASH WAS COLLECTED ON JULY 20, 2021. MARS HALL TEAM STATION
5. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE TERRELL, NORTH CAROLINA
COORDINATE SYSTEM FIPS 3200 (NAD83 AND NAVD88).

LEGEND
ILE PHASE I
VE OPERA
yAC I I 1'.'S,
q
T
t
I -
CELL 1 I U
J
— —
CELL 3
j
I
Ij
T
Exi s I I W; MAR-145
1,10POHARYSTORMWATERVV; If
% OND FORCE MAIN ft-, 61
1
1�,r-
CELL
CELL 2
v
)t
8-IN CIA - - - - - -
PERMITrED ILF
LIMIT-OF-WABTE BOUNDARY
'UNDERDRAIN - - - - -
/ FIRE R�IEDHDPE (D DIVIDER GERM
PIPE, TYP
NOTES
/rSUBCELL
"L66ATE MAR-145
VORMWATER POND
ORCE MAIN
DOUBLE 1-4�ACE8,9
PERI ETFRBER�
1, d %
T
REFERENCES
A
UNDERDFRMAPJN
FUSER PAD
UNDERDRAIN PUMP L
RI F P OF 1,
LIND R 1, SUMP
ELEVATION oog 5 FT
RELOCA
PHASE
CLLL 5 N
____-(13.7 ACRES)
PHASE 2
CELL 6
STO Rm WATER POND CELL 5 S U11F
F N L�.',!TOM OF UNDERDRAIN
LAYER ELkVATION = 811,5 FT
`Rc 7
�17 9 ACRESI DOUBLE LANE
ACCESS
t P IMETERBERM
EXISTING MAR-11 TEMPORARY��
STORMWATERPOND
NOT FOR U��nRJC710N�
COMPACTED SOIL LINER SUBGRADIE &
BOTTOM LINDERDRAIN GRADING PLAN
SING LANE ACCESS PROPOSED
PE VIETEREEFT A.1;1. FIC.r
�R117, -U
ALL SfEAMBTATOx
LANDFILI.1101VNA 2EXPAmMum
CA7A�WUNW WMCAROLINA
N
6"DIA HOP OR DERbRAIN
DISCHARGE TO
(0 ISCHARGE TD`AC9EAM=IN)
INTOCELL5&BA C
(SEE NOTE 5) OVI\L ASBESTOS LANDFILL
E 31 PERMIT NO 18[A
nir
me 2'
IS71NGc,os
�j
ENEIM.
'=71- i�l
M AIR C907;9..1107 06E
4 DUKE
n ENERGY.
DRAWN BY: W. PRATER
REVISED BY: J. EBENHACK
DATE: 09/13/2021
DATE: 09/17/2021
C! 'JAS
CHECKED BY: J. EBENHACK
DATE: 09/17/2021
APPROVED BY: C. EADY
PROJECT MANAGER: T. COLTON
DATE: 09/17/2021
www.synterracorp.com
WnTerm
FIGURE 6
PROPOSED CELL 5 BLANKET UNDERDRAIN DESIGN (AECOM, 2021)
MODELING SUPPORT FOR THE ILF PHASE 2
PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
TERRELL, NORTH CAROLINA

} ` - Blanket Underdrain
Approximate Date of -
Completion: 1/1/2022
jPhase 3-5 Excavation
Approximate Date of
Completion: 12/31/2022
4-1
• RI
.F
Y'
- {
e a
- + 4k -
LEGEND i �w''Sod
C PROPOSED CELL 5 BLANKET UNDERDRAIN
PHASE 3-5 DEWATERING DITCHES AND PROPOSED •I
UNDERDRAINS
.01
WATER SUPPLY WELLS WITH SEPTIC RETURN
ie SEPTIC RETURN
DRAIN FEATURES (> DUKE 390 GRAPHICSCALE
0 390 780
® MAR-145 STORMWATER BASIN ENERGY (IN FEET)
CAROLINAS
PONDED WATER DRAWN BY: W. PRATER DATE: 09/15/2021
REVISED BY: J. EBENHACK DATE: 09/28/2021
p WETLANDS �� CHECKED BY: J. EBENHACK DATE: 09/28/2021
APPROVED BY: C. EADY DATE: 09/28/2021
PHASE 3-5 EXCAVATION synTerra PROJECT MANAGER: T. COLTON
NOTES: www.synterracorp.com
1. ALL BOUNDARIES ARE APPROXIMATE. FIGURE 7
2. THE MODEL ACCOUNTS FOR DURING THE MODELED PERIOD, ANID CIPATED THE DATES OR ANTICIPATED SITE EVENTSSITE CHANGES AND A ETIVITIES NEAR -TERM TRANSIENT MODEL
CONSERVATIVE ESTIMATES OF CURRENTLY PLANNED CONSTRUCTION DATES. HYDRAULIC FEATURES AND MODEL .SETUP
3. FEATURES SHOWN ARE BASED ON RECENT OBSERVATIONS IN THE FIELD, RECENT SURVEY
DATA, SITE DATA FROM PREVIOUS MODELING EFFORTS, AND ANTICIPATED FUTURE SITE MODELING SUPPORT FOR THE ILF PHASE 2
CONDITIONS BASED ON DUKE ENERGY'S PLANNED ACTIVITIES.
4. NEAR TERM TRANSIENT MODEL STARTS 10/1/2021 AND ENDS 9/30/2023. PERMIT TO CONSTRUCT MODIFICATIONS
5. AERIAL PHOTOGRAPHY PROVIDED BY TRANS ASH WAS COLLECTED ON JULY 20,2021. MARSHALL STEAM STATION
6. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE TERRELL, NORTH CAROLINA
COORDINATE SYSTEM RIPS 3200 (NAD83 AND NAVD88).

Industrial Landfill
Recharqe = 1 E-7 feet/day
Cell 5 Transient Recharge
10/1/2021 - 5/31/2022: 0.0018 feet/da
6/1 /2022 - 9/30/2023: 1 E-7 feet/day
Industrial Area
Recharge = 0 feet/day
1
MAR-145 Stormwater
Recharge = fir i0feet/day
. J6
4,
PVSF Recharge
10/1/2023 - 3/31/2023: 0.0018 feet/day
4/1/2023 - model end: 1E-7 feet/day
Industrial Area
�Ponded Water
Recharqe = 01
I
Drainage Valley
Recharge = 0.0002 feet/day
Ponded Water
Recharge = 0 feet/d
•
Cell 6 Transient Recharge
10/1/2021-11/30/2022: 0.0018 feet/day
12/1/2022 - 9/30/2023: 1 E-7 feet/day
AL
Background
Recharge = 0.0018 feet/day
Leachate Basin
Recharge = 1 E-7 feet/day
Background
Recharge = 0.0018 feet/day
Recharge = 0.00022 feet/day
LEGEND
L___p RECHARGE ZONES
Constructed Wetlands
Recharge = 0 feet/day
� s
MAR-152 Liner
Recharge = 1 E-7 feet/day
Y
�. Ponded Water
Recharge = 0 feet/day /d
DUKE 390 GRAPHIC SCALE390 780
ENERGY (IN FEET)
CAROLINAS
DRAWN BY: W. PRATER DATE: 09/15/2021
REVISED BY: J. EBENHACK DATE: 10/05/2021
CHECKED BY: J. EBENHACK DATE: 10/05/2021
APPROVED BY: C. EADY DATE: 10/05/2021
PROJECT MANAGER: T. COLTON
NOTES:
FIGURE 8
1. ALL BOUNDARIES ARE APPROXIMATE.
NEAR -TERM TRANSIENT MODEL
2. THE MODEL ACCOUNTS FOR ANTICIPATED SITE CHANGES AND CONSTRUCTION ACTIVITIES
DURING THE MODELED PERIOD, AND THE DATES FOR ANTICIPATED SITE EVENTS ARE
RECHARGE DISTRIBUTION
CONSERVATIVE ESTIMATES OF CURRENTLY PLANNED CONSTRUCTION DATES.
3. RECHARGE DISTRIBUTION IS BASED ON RECENT OBSERVATIONS IN THE FIELD, SITE DATA
MODELING SUPPORT FOR THE ILF PHASE 2
ON DUKE ENOM EOUSRGY'S PLANNED PLAN ED ACDELING TRTSIVITIES. ITIES.D ANTICIPATED FUTURE SITE CONDITIONS BASED
PERMIT TO CONSTRUCT MODIFICATIONS
3. AERIAL PHOTOGRAPHY PROVIDED BY TRANS ASH WAS COLLECTED ON JULY 20, 2021.
MARSH ALL .STEAM STATION
4. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE
TERRELL, NORTH CAROLINA
COORDINATE SYSTEM FIPS 3200 (NAD83 AND NAVD88).

Phase 3-5 Backfill
Approximate Date of
144
Completion: 10/1 /2023
d
k.
rr
LEGEND '
PROPOSED CELL 5 BLANKET UNDERDRAIN+
PHASE 3-5 PROPOSED UNDERDRAINS i. a
WATER SUPPLY WELLS WITH SEPTIC
RETURN
Q� SEPTIC RETURN
RAPHICSC LE
DUKE
390 O390 780
DRAIN FEATURES
ENERGY.
ImKzzmmlzzzzz��
CAROLINAS
N FEET)
IM PO N D E D WATER
DRAWN BY: W. PRATER DATE: 09/15/2021
REVISED BY: J. EBENHACK DATE: 09/17/2021
WETLANDS
CHECKED BY: J. EBENHACK DATE: 09/17/2021
APPROVED BY: C. EADY DATE: 09/17/2021
PHASE 3-5 BACKFILLED AREA
Terra
synwww.synterracorp.com
PROJECT MANAGER: T. COLTON
NOTES:
1. ALL BOUNDARIES ARE APPROXIMATE.
FIGURE 9
2. THE MODEL ACCOUNTS FOR ANTICIPATED SITE CHANGES AND CONSTRUCTION ACTIVITIES
LONG-TERM TRANSIENT MODEL
DURING THE MODELED PERIOD, AND THE DATES FOR ANTICIPATED SITE EVENTS ARE
CONSERVATIVE ESTIMATES OF CURRENTLY PLANNED CONSTRUCTION DATES.
HYDRAULIC FEATURES AND MODEL SETUP
3. FTURES SHOWN ARE BASED ON RECENT OSERVTIONS IN THE FIELD, SURVEY
MODELING SUPPORT FOR THE ILF PHASE 2
DATFAA,, SITE DATA FROM PREVIOUS MODELING EFFOR SA AND ANTICIPATED FUTURENSITE
CONDITIONS BASED ON DUKE ENERGY'S PLANNED ACTIVITIES.
PERMIT TO CONSTRUCT MODIFICATIONS,
4. LONG TERM TRANSIENT MODEL STARTS 10/1/2023 AND ENDS 1/1/2040.
MARSHALL STEAM STATION
5. AERIAL PHOTOGRAPHY PROVIDED BY TRANS ASH WAS COLLECTED ON JULY 20, 2021.
TERRELL, NORTH CAROLINA
6. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE
COORDINATE SYSTEM FIPS 3200 (NAD83 AND NAVD88).

Ponded Water
arty` " Recharge = 0 feet/day
Industrial Landfill
Industrial Area Recharge =1 E-7 feet/day Drainage Valley
-1 Recharge=y0 feet/day Recharge = 0.0002 feet/day
IL 'T
- Ponded Water
Recharge = 0 feet/day
Cell 5 and 6
Recharge = 1 E-7 feet/day
MAR-145 Stormwater Basin -" 5
Recharge = 1 E-7 feet/day
1804 Phase 2 Recharge
10/1/2023-11/30/2023: 0.0018 feet/day
+ 12/1/2023 - model end: 1 E-7 feet/day
hase 5 Recharge
0/1/2023 - 5/31/2027: 0.0018 feet/da ,,
11/2027 - model end: 1.E-7 feet/day
Leachate Basin
Recharge = 1 E-7 feet/day
PVSF Recharge = 1 E-7 feet/day
l
W
e 3 Recharge 4
2023 -11/30/2024: 0.0018 feet/day I
12/1/2024 -model end: 1 E-7 feet/day
Phase 4 Recharge MAR 152 Liner
10/1/2023 - 4/30/2026: 0.0018 feet/dayRecharge = 1 E-7 feet/day
5/1/2026 -model end: 1E-7 feet/day.
Background
Recharge = 0.0018 feet/day
Constructed Wetlands
Recharge = 0 feet/day
w -
_ Industrial Area
Recharge = 0.00022 feet/(
rZ
C.
LEGEND
r- .RECHARGE ZONES
NOTES:
1. ALL BOUNDARIES ARE APPROXIMATE.
2. THE MODEL ACCOUNTS FOR ANTICIPATED SITE CHANGES AND CONSTRUCTION ACTIVITIES
DURING THE MODELED PERIOD, AND THE DATES FOR ANTICIPATED SITE EVENTS ARE
CONSERVATIVE ESTIMATES OF CURRENTLY PLANNED CONSTRUCTION DATES.
3. RECHARGE DISTRIBUTION IS BASED ON RECENT OBSERVATIONS IN THE FIELD, SITE DATA
FROM PREVIOUS MODELING EFFORTS, AND ANTICIPATED FUTURE SITE CONDITIONS BASED
ON DUKE ENERGY'S PLANNED ACTIVITIES.
3. AERIAL PHOTOGRAPHY PROVIDED BY TRANS ASH WAS COLLECTED ON JULY 20, 2021.
4. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE
COORDINATE SYSTEM FIPS 3200 (NAD83 AND NAVD88).
l
1
Ponded Water
Recharge = 0 feet/day
DUKE 390 GRAPHIC SCALE390 780
ENERGY (IN FEET)
CAROLINAS
DRAWN BY: W. PRATER DATE: 09/15/2021
REVISED BY: J. EBENHACK DATE: 10/05/2021
CHECKED BY: J. EBENHACK DATE: 10/05/2021
101 APPROVED BY: C. EADY DATE: 10/05/2021
PROJECT MANAGER: T. COLTON
FIGURE 10
LONG-TERM TRANSIENT MODEL
RECHARGE DISTRIBUTION
MODELING SUPPORT FOR THE ILF PHASE 2
PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
TERRELL, NORTH CAROLINA

I
5i
' LJ
LE
'
LEGEND 250 ORAPHICSC2
DUKE 50 500
ENERGY (IN FED
ago ESTIMATED GROUNDWATER CAROLINAS
ELEVATION . DRAWN BY: W. PRATER DATE: 09/15/2021
REVISED BY: J. EBENHACK DATE: 09/17/2021
CHECKED BY: J. EBENHACK DATE: 09/17/2021
APPROXIMATE EXTENT OF THE I APPROVED BY: C.EADY DATE: 09/17/2021
PHASE 1 ILF AND PROPOSED PROJECT MANAGER: T. COLTON
PHASE 2-5 ILF EXPANSIONS synTena www.synterracorp.com
NOTES: FIGURE 11
1. ALL BOUNDARIES ARE APPROXIMATE. ESTIMATED GROUNDWATER ELEVATIONS
2. MODEL ASSUMES JULY 2021 CURRENT CONDITIONS AT THE SITE. FOR THE CURRENT CONDITIONS MODEL
3. GROUNDWATER ELEVATION CONTOUR INTERVAL IS 5 FEET MODELING SUPPORT FOR THE ILF PHASE 2 PERMIT
4. APPROXIMATE FOOTPRINT OF THE PHASE 2-5 ILF EXPANSIONS BASED ON AECOM CLOSURE TO CONSTRUCT MODIFICATIONS
DESIGNS (AECOM, 2021) AND CAD FILES PROVIDED TO SYNTERRA BY DUKE ENERGY ON
8/1212021. MARSHALL STEAM STATION
5. AERIAL PHOTOGRAPHY PROVIDED BY TRANS ASH WAS COLLECTED ON JULY 20, 2021. TERRELL, NORTH CAROLINA
6. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE
COORDINATE SYSTEM FIPS 3200 (NAD83 AND NAVD88).

LEGEND
�' DUKE
GRAPHIC SCALE
250 0 250 500
ENERGY
j PROPOSED CELL 5 BLANKET UNDERDRAIN
(IN FED
CAROLINAS
8zo ESTIMATED GROUNDWATER ELEVATION
DRAWN BY: W. PRATER DATE: 09/15/2021
REVISED BY: J. EBENHACK DATE: 09/17/2021
APPROXIMATE EXTENT OF THE PHASE 1ILF AND
CHECKED BY:J.EBENHACK DATE: 09/17/2021
—
PROPOSED PHASE 2-5 ILF EXPANSIONS
APPROVED BY: C. EADY DATE: 09/17/2021
T2
synwww.synterracorp.com
PROJECT MANAGER: T, COLTON
NOTES:
FIGURE 12
1. ALL BOUNDARIES ARE APPROXIMATE.
ESTIMATED GROUNDWATER ELEVATIONS FOR THE
2021 OPERATRRENT CONDITIONS AT THE SITE WITH THE PROPOSED CELL
2. 5BLANKET UNDERDRAIN OPERATING.
5 BLANKET UNDERDRAIN OPERATING.
STEADY-STATE CELL 5 BLANKET UNDERDRAIN MODEL
3. GROUNDWATER ELEVATION CONTOUR INTERVAL IS 5 FEET
MODELING SUPPORT FOR THE ILF PHASE 2
FF THE PHASE 2-5 ILFIERRAONS
4. BASED ON AECOM
PERMIT TO CONSTRUCT MODIFICATIONS
DESIGNS AECOM,20 1)AINDCADFILESPROVIDEDTOSYNTPROXIMATE
BYDUKEENERGYONSURE
8/1212021.
MARSHALL STEAM STATION
5. AERIAL PHOTOGRAPHY PROVIDED BY TRANS ASH WAS COLLECTED ON JULY 20, 2021.
TERRELL, NORTH CAROLINA
6. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE
COORDINATE SYSTEM FIPS 3200 (NAD83 AND NAVD88).

0
AVLxAls,
LEGEND
PROPOSED CELL 5 BLANKET UNDERDRAIN
PHASE 3-5 PROPOSED UNDERDRAINS
azo ESTIMATED GROUNDWATER ELEVATION
NOTES:
1. ALL BOUNDARIES ARE APPROXIMATE.
2. GROUNDWATER ELEVATION CONTOUR INTERVAL IS 5 FEET.
3. GROUNDWATER ELEVATIONS FOR 1 MONTH, 1 YEAR, AND 1.5 YEARS ARE FROM THE NEAR -TERM BASE MODEL.
4. GROUNDWATER ELEVATIONS FOR 5 YEARS ARE FROM THE LONG-TERM BASE MODEL.
5. THE MODEL ACCOUNTS FORANTICIPATED SITE CHANGES AND CONSTRUCTION ACTIVITIES DURING THIS PERIOD, AND THE
DATES FOR ANTICIPATED SITE EVENTS ARE CONSERVATIVE ESTIMATES OF CURRENTLY PLANNED CONSTRUCTION DATES.
8. PROPOSED PHASE 3-5 UNDERDRAINS BASED ON AUTOCAD FILES PROVIDED TO SYNTERRA BY DUKE ENERGY ON 8112 2021.
3. AERIAL PHOTOGRAPHY PROVIDED BY TRANS ASH WAS COLLECTED ON JULY 20, 2021.
4. DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINA STATE PLANE COORDINATE SYSTEM RIPS 3200(NAD83 AND
NAVD88).
�80
GRAPHIC SCALE
330 0 330 660
s m errs DRAWN
FEET)
DRAWN BY: W. PRAYER DATE: 09/15/2021
REVISED BY: J. EBENHACK DATE: 10/04/2021
DUKE CHECKED BY:J. EBENHACK DATE: 10/04/2021
APPROVED BY: C. EA
4♦ ENERGY- PROJECT MANAGER:DT. OLTON DATE: 10/04/2021
c
www.synterracorp.com
FIGURE 13
ESTIMATED GROUNDWATER ELEVATIONS DURING
OPERATION OF THE CELL 5 BLANKET UNDERDRAIN
MODELING SUPPORT FOR THE ILF PHASE 2
PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
TERRELL, NORTH CAROLINA

1 Month
-31 gpm
n
Fa
CL
an
c
ru 80
v
c
4-j
v
60
m
ca
Q]
J3
.(.0 40
m
LL
v
ru 20
�o
Notes:
1. gpm = gallons per minute.
1 year 1.5 years
-3 gpm <0.01 gpm
I.I Start of the Long Term Transient Simulation
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
Steady -State Flow to Blanket Underdrain (-18 GPM)
I
I
I
I■
oQ h? 4� "Q a°
Years of Blanket Drain Operation
4DUKE DRAWN BY: W. PRATER DATE: 09/13/2021 FIGURE 14
' ENERGY REVISED BY: J. EBENHACK DATE: 09/17/2021 SIMULATED FLOWRATE TO THE CELL 5
c' CHECKED BY: J. EBENHACK DATE: 09/17/2021 BLANKET UNDERDRAIN (BASE MODEL)
APPROVED BY: C. EADY DATE: 09/17/2021 MODELING SUPPORT FOR THE ILF PHASE 2
�� PROJECT MANAGER: T. COLTON PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
synTena www.synterracorp.com TERRELL, NORTH CAROLINA

I
X I ■ Base Mode
E 100
CL
do
L
L Qj 80
i�
Ca 60
Qj
i�
i-j
Qj
i-j
40
LL
v
ry
=; 20
E
(A
1 -
�O 00 y0 00 41 00 1? 00
O' ti ti ti' ti'
Years of Blanket Drain Operation
Notes:
1. gpm = gallons per minute.
4 n
DUKE DRAWN BY: W. PRATER DATE: 09/13/2021 FIGURE 15
ENERGY REVISED BY: J. EBENHACK DATE: 09/17/2021 EFFECT OF PHASE 3 THROUGH 5 MATERIAL/ASH EXCAVATION ON THE
c' CHECKED BY: J. EBENHACK DATE: 09/17/2021 SIMULATED FLOWRATE TO THE CELL 5 BLANKET UNDERDRAIN
APPROVED BY: C. EADY DATE: 09/17/2021 MODELING SUPPORT FOR THE ILF PHASE 2
�� PROJECT MANAGER: T. COLTON PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
VnTerM www.synterracorp.com TERRELL, NORTH CAROLINA

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❑ Model with LTSH
Recharge
M0M••MM0
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ti ry ry rrj' rrj tic
Years of Blanket Drain Operation
Notes:
1. gpm = gallons per minute.
2. Long term seasonal high recharge rate = 0.0022 feet per day.
�O Op
O' ti
4 S
DUKE DRAWN BY: W. PRATER DATE: 09/13/2021 FIGURE 16
ENERGY REVISED BY: J. EBENHACK DATE: 09/17/2021 EFFECT OF LONG-TERM SEASONAL HIGH RECHARGE ON THE
C' CHECKED BY: J. EBENHACK DATE: 09/17/2021 SIMULATED FLOWRATE TO THE CELL 5 BLANKET UNDERDRAIN
APPROVED BY: C. EADY DATE: 09/17/2021 MODELING SUPPORT FOR THE ILF PHASE 2
PROJECT MANAGER: T. COLTON PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
WnTerM www.synterracorp.com TERRELL, NORTH CAROLINA

500
450
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Years of Dewatering and Underdrain Operation
Notes:
1. Only the proposed underdrains are present after the start of the Long Term transient model.
LI' DUKE DRAWN BY: W. PRATER DATE: 09/13/2021 FIGURE 17
Z ENERGY REVISED BY: J. EBENHACK DATE: 09/17/2021 ESTIMATED FLOWRATES TO THE PHASE 3 THROUGH 5
c' CHECKED BY: J. EBENHACK DATE: 09/17/2021 DEWATERING DITCHES AND PROPOSED UNDERDRAINS
APPROVED BY: C. EADY DATE: 09/17/2021 MODELING SUPPORT FOR THE ILF PHASE 2
It
� PROJECT MANAGER: T. COLTON PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
synTena www.synterracorp.com TERRELL, NORTH CAROLINA

Modeling Support for the ILF Phase 2 Permit to Construct Modifications October 5, 2021
Duke Energy Carolinas, LLC, Marshall Steam Station
TABLES
synterracorp.com

TABLE 1
OBSERVED AND SIMULATED CURRENT CONDITIONS
HYDRAULIC HEADS AND CALIBRATION RESIDUALS
MODELING SUPPORT FOR THE ILF PHASE 2 PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
DUKE ENERGY PROGRESS, LLC, TERRELL, NC
Well
Identification
Observed
Head (ft)
Computed
Head (ft)
Residual
AB-01BR
769.41
765.99
3.4
AB-01BRL
767.19
765.69
1.5
AB-01BRLL
767.24
765.69
1.6
AB-01BRLLL
768.51
765.79
2.7
AB-01 D
767.90
767.26
0.6
AB-01S
766.51
767.64
-1.1
AB-02BR
781.06
770.17
10.9
AB-02D
764.97
764.83
0.1
AB-02S
760.70
761.88
-1.2
AB-03D
787.55
788.65
-1.1
AB-04D
784.64
791.85
-7.2
AB-04S
790.29
792.08
-1.8
AB-04SL
788.87
791.84
-3.0
AB-05BR
795.86
796.98
-1.1
AB-05D
796.50
796.99
-0.5
AB-05DU
796.63
797.12
-0.5
AB-05S
796.26
797.67
-1.4
AB-06BRA
826.09
818.31
7.8
AB-06BRL
824.29
818.19
6.1
AB-06D
826.66
818.12
8.5
AB-06S
828.35
818.84
9.5
AB-07D
821.91
817.36
4.5
AB-07DU
821.78
819.20
2.6
AB-07S
823.84
818.93
4.9
AB-08D
790.48
793.77
-3.3
AB-08DU
790.40
793.76
-3.4
AB-08S
790.01
793.28
-3.3
AB-09BR
785.84
785.79
0.0
AB-09D
784.57
785.80
-1.2
AB-09S
785.58
785.89
-0.3
AB-10BR
784.37
786.15
-1.8
AB-10BRL
792.94
786.23
6.7
AB-10D
783.75
786.18
-2.4
AB-10S
785.43
786.85
-1.4
AB-10SL
784.16
786.31
-2.2
AB-13 D
799.77
804.67
-4.9
AB-13S
801.28
804.02
-2.7
AB-15BR
807.49
805.07
2.4
AB-15D
803.74
805.06
-1.3
AB-15SL
801.73
805.01
-3.3
AB-21 D
788.06
790.39
-2.3
AB-21S
786.24
790.46
-4.2
AL-01 BR
774.28
771.32
3.0
AL-01 BRL
775.28
772.54
2.7
AL-01 D
775.04
771.41
3.6
AL-01S
775.89
771.57
4.3
AL-02BR
805.62
799.29
6.3
AL-02BRL
800.07
799.42
0.7
Page 1 of 4

TABLE 1
OBSERVED AND SIMULATED CURRENT CONDITIONS
HYDRAULIC HEADS AND CALIBRATION RESIDUALS
MODELING SUPPORT FOR THE ILF PHASE 2 PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
DUKE ENERGY PROGRESS, LLC, TERRELL, NC
Well
Identification
Observed
Head (ft)
Computed
Head (ft)
Residual
AL-02BRLL
798.19
799.57
-1.4
AL-02BRLLL
798.20
799.56
-1.4
AL-02D
804.24
799.14
5.1
AL-02S
802.94
799.59
3.3
AL-03BR
805.15
804.74
0.4
AL-03D
806.62
806.12
0.5
AL-03S
808.19
807.15
1.0
AL-04BR
813.47
809.97
3.5
AL-04BRL
798.32
802.30
-4.0
AL-04D
817.65
810.06
7.6
BG-01 BRA
799.13
804.06
-4.9
BG-01 D
808.59
806.84
1.8
BG-01S
807.85
810.62
-2.8
BG-02BR
809.45
809.92
-0.5
BG-02S
809.07
811.19
-2.1
BG-03BR
834.93
828.10
6.8
BG-03D
829.04
829.39
-0.3
BG-03S
828.71
829.74
-1.0
C5-TP-01*
825.40
828.12
-2.7
C5-TP-02*
824.45
823.63
0.8
C5-TP-03*
821.30
822.50
-1.2
C5-TP-04*
818.45
821.04
-2.6
C5-TP-07*
819.70
820.94
-1.2
CCR-01 D
792.23
790.76
1.5
CCR-01S
795.86
790.89
5.0
CCR-02D
786.73
787.05
-0.3
CCR-02S
786.57
787.53
-1.0
CCR-03D
758.34
759.56
-1.2
CCR-03S
757.69
759.33
-1.6
CCR-04D
760.32
761.89
-1.6
CCR-04S
759.37
762.86
-3.5
CCR-05D
760.22
762.47
-2.2
CCR-05S
760.24
759.30
0.9
CCR-09DA
764.37
765.37
-1.0
CCR-09S
762.47
766.44
-4.0
CCR-15D
788.92
788.30
0.6
CCR-16D
794.08
797.18
-3.1
CLF-21-02R*
822.55
821.81
0.7
CLF-21-05R*
819.76
819.69
0.1
CLF-21-10
841.06
841.39
-0.3
CLF-21-11*
828.73
829.12
-0.4
CLF-21-12*
822.99
822.31
0.7
CLF-21-13*
820.09
820.04
0.0
CLF-21-14
821.43
821.69
-0.3
CLF-21-15
826.12
823.32
2.8
CLF-301
817.36
816.49
0.9
CLF-302
812.96
810.39
2.6
CLF-303
800.68
804.14
-3.5
Page 2 of 4

TABLE 1
OBSERVED AND SIMULATED CURRENT CONDITIONS
HYDRAULIC HEADS AND CALIBRATION RESIDUALS
MODELING SUPPORT FOR THE ILF PHASE 2 PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
DUKE ENERGY PROGRESS, LLC, TERRELL, NC
Well
Identification
Observed
Head (ft)
Computed
Head (ft)
Residual
CLF-304
798.68
804.64
-6.0
CLF-401
815.71
817.92
-2.2
CLF-402
812.02
812.66
-0.6
CLF-403
812.19
815.43
-3.2
CLF-404
811.39
811.97
-0.6
CP-01 D
785.92
783.97
1.9
CP-02D
797.28
794.43
2.8
CP-02S
797.38
795.40
2.0
CP-03D
795.64
791.65
4.0
CP-03S
794.89
795.88
-1.0
GP-01D
801.83
800.66
1.2
GP-01S
801.79
801.31
0.5
GP-02D
806.18
800.06
6.1
GP-02S
806.65
801.48
5.2
GP-03D
806.22
798.73
7.5
GP-03S
806.37
802.93
3.4
GWA-01 BR
764.29
763.89
0.4
GWA-01D
761.89
763.97
-2.1
GWA-01S
760.96
764.09
-3.1
GWA-02DA
804.97
798.77
6.2
GWA-02S
805.75
801.30
4.5
GWA-03D
837.72
835.97
1.7
GWA-03S
837.47
835.90
1.6
GWA-04D
851.91
850.31
1.6
GWA-04S
851.18
853.28
-2.1
GWA-05D
814.64
813.22
1.4
GWA-06D
810.58
803.61
7.0
GWA-06S
811.05
804.33
6.7
GWA-07D
803.92
797.77
6.2
GWA-07S
800.37
799.65
0.7
GWA-08D
825.52
821.91
3.6
GWA-08S
827.06
827.75
-0.7
GWA-09BR
847.55
846.39
1.2
GWA-10D
766.22
765.31
0.9
GWA-10S
764.14
764.31
-0.2
GWA-11BR
760.23
762.24
-2.0
GWA-11 D
760.46
762.08
-1.6
GWA-11S
762.64
762.23
0.4
GWA-12BR
863.23
861.07
2.2
GWA-12D
864.20
861.16
3.0
GWA-12S
877.53
870.22
7.3
GWA-13DA
868.42
866.53
1.9
GWA-13S
874.56
868.80
5.8
GWA-14D
874.22
873.50
0.7
GWA-14S
874.67
877.35
-2.7
GWA-15D
757.20
757.75
-0.6
GWA-15S
757.04
757.55
-0.5
ILF-02D
845.02
839.84
5.2
Page 3 of 4

TABLE 1
OBSERVED AND SIMULATED CURRENT CONDITIONS
HYDRAULIC HEADS AND CALIBRATION RESIDUALS
MODELING SUPPORT FOR THE ILF PHASE 2 PERMIT TO CONSTRUCT MODIFICATIONS
MARSHALL STEAM STATION
DUKE ENERGY PROGRESS, LLC, TERRELL, NC
Well
Identification
Observed
Head (ft)
Computed
Head (ft)
Residual
ILF-02S
841.79
842.97
-1.2
MAR-145-midPt
820.00
821.22
-1.2
MS-08
832.94
827.91
5.0
MS-10
834.09
833.84
0.2
MS-11
826.83
826.45
0.4
MS-13
812.46
812.13
0.3
MW-01
772.43
770.53
1.9
MW-02
785.76
787.39
-1.6
MW-03
803.69
807.30
-3.6
MW-04
831.82
833.59
-1.8
MW-04D
831.97
831.47
0.5
MW-06 (OB-02)
815.19
814.54
0.6
MW-06D
764.61
762.86
1.8
MW-06S
765.73
762.88
2.8
MW-07 (OB-03)
818.11
817.16
0.9
MW-07D
765.46
765.54
-0.1
MW-07S
760.39
766.35
-6.0
MW-08D
759.58
762.50
-2.9
MW-08S
757.83
759.95
-2.1
MW-09D
758.77
761.82
-3.0
MW-09S
760.66
759.25
1.4
MW-10D
756.29
758.51
-2.2
MW-10S
755.91
757.93
-2.0
MW-11D
845.25
844.31
0.9
MW-11S
845.34
845.38
0.0
MW-12D
856.93
859.45
-2.5
MW-12S
857.35
860.82
-3.5
MW-13D
847.05
845.32
1.7
MW-13S
846.24
844.91
1.3
MW-14BR
772.41
772.35
0.1
MW-14BRL
776.97
775.02
1.9
MW-14D
773.39
772.13
1.3
MW-14S
772.27
772.22
0.0
Pond-EofSF
823.00
823.46
-0.5
PVSF-01BR
830.29
828.48
1.8
PVSF-01D
833.76
828.76
5.0
PVSF-01S
834.63
829.36
5.3
PVSF-04BR
838.95
840.70
-1.7
PVSF-04D
851.28
842.96
8.3
PVSF-04S
851.75
844.21
7.5
Test Pit 1 Sump*
818.20
821.76
-3.6
Test Pit 2*
819.45
821.14
-1.7
RMSE
3.350
NRMSE
0.028
J
Notes:
Ft - feet
NAVD 88 - North American Vertical Datum 1988
RMSE - Root mean squared error
NRMSE - Normalized root mean square error (normalized to the range of observed hydraulic heads)
*Observation point near proposed blanket underdrain in Cell 5
Prepared by: WTP Checked by: JFE
Page 4 of 4

Modeling Support for the ILF Phase 2 Permit to Construct Modifications October 5, 2021
Duke Energy Carolinas, LLC, Marshall Steam Station
TABLE 2
ANTICIPATED SITE ACTIVITIES/CONSTRUCTION
DURING THE NEAR -TERM TRANSIENT MODEL
PROVIDED ON PAGE 5
synterracorp.com

Modeling Support for the ILF Phase 2 Permit to Construct Modifications October 5, 2021
Duke Energy Carolinas, LLC, Marshall Steam Station
TABLE 3
ANTICIPATED SITE ACTIVITIES/CONSTRUCTION
DURING THE LONG-TERM TRANSIENT MODEL
PROVIDED ON PAGE 7
synterracorp.com