NC0004979_Allen CAP Part 1_Appx C_Final_20151120

This page intentionally left blank

ELECTRIC
CI"�21 I RESEARCH INSTITUTE Memorandum
October 20, 2015
TO: Ed Sullivan and Tyler Hardin, Duke Energy
FROM: Bruce Hensel, EPRI
SUBJECT: ALLEN MODEL REVIEW
Summary
EPRI has reviewed the Allen model report and files provided by Duke Energy, HDR
Engineering, Inc., and the University of North Carolina Charlotte. The review was performed
by Tim Dale and John Ewing (Intera), with input by Chunmiao Zheng and myself. Based on
this review, it is our opinion that, subject to the caveats below, this model is set-up and meets
its flow and transport calibration objectives sufficiently to meet its final objective of
predicting effects of corrective action alternatives on groundwater quality. The caveats
associated with this opinion are:
• Constant heads used to represent the Catawba River may provide an unmitigated
source of water for simulation of any corrective action alternatives that potentially
involve pumping near those boundaries. If corrective actions involve pumping, drain
boundaries may be a more appropriate boundary condition selection than constant
heads for this boundary.
Specific Comments
Model Report, Setup, and Calibration
a) Is the objective/purpose of modeling clearly defined?
Yes. The purpose of the study is clearly defined in Section 1 as three activities: 1)
development of a calibrated steady-state flow model of current conditions; 2) development of
a historical transient model of constituent transport that is calibrated to current conditions;
and 3) predictive simulations of the different corrective action options.
b) Is the site description adequate?
Yes. The site description provided in Section 1.1 is sufficient for purposes of evaluating the
model.
c) Is the conceptual model well described with appropriate assumptions?
Yes. The conceptual model section contains subsections discussing the regional and local
geology and hydrogeology, the evolution of the ash basin system, the local groundwater flow
system, local hydrologic and hydraulic boundaries, groundwater sources and sinks, water
budget, modeled constituents of interest, and constituent transport. The CSA report is
referenced as the source of the conceptual model and assumptions. The method used to
estimate recharge is briefly discussed along with references. The rationale behind the choice
of constituents to be modeled is discussed.

Allen Model Review
October 20, 2015
Page 2
The impact of the public and private water supply wells outside and inside the model domain
along the assumed no -flow boundary to the west was not incorporated into the model. The
cumulative impact of these wells on the potential for gradient reversal (to the west) in this
area may or may not result in transport of constituents off site to the west. Personal
communication with the model author indicated that these wells were not considered
significant in the CSA and thus they were not included. A sensitivity analysis of the impact
of these wells might be considered to document that they are not significant.
d) Is the numerical model properly set up (steady state or transient; initial condition;
boundary conditions; parameterization; etc)?
i) Appropriateness of the simulator
The use of MODFLOW-NWT and MT3DMS to simulate groundwater flow and contaminant
transport, respectively, are both appropriate for the modeling objectives and represent an
industry standard in choice of simulators.
ii) Discretization: temporal and spatial (x y notably z)
The spatial discretization for this model appears more than adequate to delineate differences
in simulated heads and concentrations for all reasonable calibration and predictive purposes.
For transport simulations, the Courant Number and the Grid Peclet Number can be used to
determine whether discretization is numerically appropriate for a given model. In this model,
transport time steps are automatically calculated by the simulator based on a specified
Courant Number constraint of 1. This ensures that temporal discretization is appropriate for
the spatial discretization of the model.
The Grid Peclet Number (Pe_grid = Al/a) can be used to evaluate whether numerical
dispersion dominates constituent transport based on spatial discretization and physical
dispersion. Grid Peclet numbers preferably less than 2 and no more than 10 are generally
recommended to minimize numerical dispersion.
The lateral discretization (Ax = 20 feet, Ay = 20 feet) of the area comprising the ash pond and
constituent sources, coupled with the longitudinal dispersivity of 80 feet in the
Allen_Arsenic*.dsp and Allen_Boron*.dsp files results in Grid Peclet number of
approximately 0.25 which is adequate. The transverse lateral dispersivity of 8 feet results in
Grid Peclet numbers of approximately 2.5 which is within the acceptable range.
The vertical discretization is more variable than the horizontal discretization with M1/M2
and fracture bedrock layers at approximately 30 to 40 feet, and the transition zone on the
order of 10 feet or less. The vertical dispersivity of 0.8 feet results in Grid Peclet numbers of
approximately 12.5 to 50, which is relatively high but given the predominately horizontal
flow in the groundwater system, the amount of numerical dispersion in the vertical direction
should have a small impact and is unlikely to influence model predictions in a meaningful
way.

Allen Model Review
October 20, 2015
Page 3
iii) Hydrologic framework — hydraulic properties
The hydrostratigraphy appears to be implemented correctly within the model domain. The
hydraulic property values implemented in the model fall within their respective ranges as
presented in the CSA report.
iv) Boundary conditions
The boundary conditions implemented in the model include aerially distributed recharge,
drains, no -flow, and constant -heads.
Aerially distributed recharge was noted as being a calibration parameter with a range based
on a referenced mean annual range for the Piedmont range. Two zones of non -zero recharge
were implemented in the model with both being at the low end of the referenced range.
No -flow boundaries were assigned along the northern, western, and southern edges of the
model domain. These were assigned at locations that were noted as a natural topographic
divide and thus a presumed natural groundwater divide. This justification appears
reasonable.
The eastern boundary of the model is the Catawba River. The effects of the river on the flow
field is incorporated through the use of constant -head boundary (CHB) conditions in model
layers 5 through 8. The CHBs are used to assign a constant hydraulic head to a model cell
and allows an unrestricted amount of water to move both into and out of the model
depending on the hydraulic gradient. The use of the CHB should be carefully considered
during the predictive simulations if any corrective actions are to include pumping near the
assigned CHBs.
v) Initial conditions in transient simulations
The flow models are run in steady state, where initial conditions are not relevant apart from
numerical convergence, which was achieved. The transient transport model assumes a zero
concentration prior to the start of the ash pond usage with the ash pond acting as a constant
concentration source thereafter. These initial conditions are reasonable.
vi) Convergence criteria and mass balance errors
The head tolerance in the NWT packages of 1 e-4 is more than adequate in ensuring head
precision for the purposes of the model. The flow mass balance discrepancy in the
MODFLOW Listing file of 0.00 percent is indicative of essentially no flow mass balance
errors.
The concentration mass balance discrepancy from MT3DMS is approximately 0.1 and 0.007
percent for the arsenic inactive and active basin simulations, respectively, and 0.02 and 0.008
percent for the boron inactive and active basin simulations, respectively. The maximum
discrepancy value of 0.1 percent is adequate in ensuring minimal constituent mass balance
errors and thus minimal impact on the contaminant transport model solutions.

Allen Model Review
October 20, 2015
Page 4
e) Is the calibration done properly and adequately?
The flow model calibration head targets were based on the observed hydraulic heads
from a single point in time of July 2015. The calibration results indicate a Mean
Absoluter Error over the range in observed heads of 6.9 percent which is within the
industry standard of 10 percent. Therefore the flow model adequately matches the
observed values of July 2015.
Concentration calibration was evaluated based on the model's ability to simulate high
concentrations where high concentrations were observed and low concentrations where
low concentrations were observed.
• Calibrated arsenic concentrations were greater than 100 ug/L at eight of the 10
monitoring points with observed concentrations greater than 100 ug/L. Calibrated
arsenic concentrations were less than 100 ug/L at four of the eight monitoring points
with observed concentrations less than 100 ug/L. The simulated arsenic
concentrations generally correlated to the observed magnitude of the arsenic
concentrations over all of the observed depth intervals.
• Calibrated boron concentrations were greater than 700 ug/L at 13 of 17 monitoring
points with observed concentrations greater than 700 ug/L. Calibrated boron
concentrations were less than 700 ug/L at 10 of 12 monitoring points with observed
concentrations less than 700 ug/L. The simulated boron concentrations generally
correlated to the observed magnitude of the boron concentrations over all of the
observed depth intervals.
i) Property/boundary condition correlation —parameter bounds
The report denotes that the recharge to the ash basin systems and the hydraulic conductivity
were both used as calibration targets in the early phases of the flow model calibration. For
the final flow model calibration, the recharge was held constant at the low end of the
recharge range and the hydraulic conductivity was varied. As the overall magnitude of the
recharge is less uncertain than the hydraulic conductivity distribution across the site, setting
the recharge to a constant value during the calibration process is a reasonable assumption.
ii) Discretization of calibration parameters
Hydraulic properties vary primarily by model layer which is used to differentiate between
hydrologic units. Within a given layer, calibrated hydraulic properties are either uniform or
based on zones of piece -wise constancy.
iii) Appropriateness of target as a metric of simulation objectives (e.g., calibrating
primarily to heads when transport is the primary purpose)
The use of hydraulic heads and observed concentration values for calibration of the flow and
transport models, respectively, are appropriate targets for the stated objectives.

Allen Model Review
October 20, 2015
Page 5
Is the sensitivity analysis conducted and if so, correctly?
i) Sensitivity Analysis approach (look for parameters which maybe insensitive to flow
but not to transport)
A flow model sensitivity analysis was conducted whereby the horizontal and vertical
hydraulic conductivity of the shallow and transition zone, and the recharge outside and inside
the ash basin system were varied. The parameter values were varied about the calibrated
values by ±20%. The results indicate which of the selected parameters the calibration results
are most sensitive.
For the transport models, a sensitivity analysis was conducted by increasing the Kd by a
factor of 10 and increasing the porosity by 50%. No qualitative comparison was provided for
the change in results but an overall discussion was provided.
Model Files:
a) Can the model be run with the input files provided by the developer?
Yes.
b) Do the model results match those presented in the report?
i) Independent check of input data vs. conceptual model/report
An independent check of the input data files shows that the conceptual model was
implemented as noted in the report and the parameter values as noted in the report were input
into the model.
ii) Check of water balance vs. conceptual model
A check of the water balance shows that approximately 87% of the inflows to the model is
from recharge with 13% from the CHBs and is appropriate given the conceptual model. A
check of the water balances for the outflows shows approximately 83% is attributed to the
CHBs and the remaining 17% is attributed to the drains. While the expected amount of the
outflow to the drains is not discussed, the magnitude of 17% seems high given the small areal
outflow to the drains as compared to the river. However, this is not expected to appreciably
affect the model's ability to meet its stated objective.
iii) Independent check of model results vs. those reported
The model results were independently checked and agree with those reported.

Groundwater Flow and Transport Model
Allen Steam Station
Gaston County, NC
Prepared for:
HDR Engineering, Inc.
Hydropower Services
440 S. Church St, Suite 1000
Charlotte, NC 28202
Investigators:
William G. Langley, Ph.D., P.E.
Dongwook Kim, Ph.D.
UNC Charlotte / Lee College of Engineering
Department of Civil and Environmental Engineering
EPIC Building 3252
9201 University City Blvd.
Charlotte, NC 28223
Revised November 17, 2015

TABLE OF CONTENTS
1 Introduction......................................................................................................................... 1
1.1 General Setting and Background.................................................................................
1
1.2 Study Objectives..........................................................................................................
2
2 Conceptual Model...............................................................................................................
2
2.1 Geology and Hydrogeolo9y (HDR 2015)......................................................................
3
2.2 Hydrostratigraphic Layer Development (HDR 2015)....................................................
3
2.3 Ash Basins and Ash Storage Areas.............................................................................
4
2.3.1 Ash Basin (HDR 2015)..........................................................................................
5
2.3.2 Ash Landfill...........................................................................................................
5
2.3.3 Structural Fills.......................................................................................................
6
2.3.4 Ash Storage..........................................................................................................
6
2.4 Groundwater Flow System...........................................................................................
7
2.5 Hydrologic Boundaries.................................................................................................
7
2.6 Hydraulic Boundaries...................................................................................................
7
2.7 Sources and Sinks.......................................................................................................
8
2.8 Water Balance.............................................................................................................
8
2.9 Modeled Constituents of Interest (COI)........................................................................
8
2.10 COI Transport..............................................................................................................
9
3 Computer Model.................................................................................................................
9
3.1 Model Selection...........................................................................................................
9
3.2 Model Description........................................................................................................
9
4 Groundwater Flow and Transport Model Construction.......................................................10
4.1 Model Hydrostratigraphy.............................................................................................10
4.2 GMS MODFLOW Version 10......................................................................................11
4.3 Model Domain and Grid..............................................................................................12
4.4 Hydraulic Parameters.................................................................................................13
4.5 Flow Model Boundary Conditions................................................................................13
4.6 Flow Model Sources and Sinks...................................................................................14
4.7 Flow Model Calibration Targets...................................................................................14
4.8 Transport Model Parameters......................................................................................14
4.9 Transport Model Boundary Conditions........................................................................15
4.10 Transport Model Sources and Sinks...........................................................................15

4.11 Transport Model Calibration Targets...........................................................................16
5 Model Calibration to Current Conditions.............................................................................16
5.1 Flow Model Residual Analysis.....................................................................................16
5.2 Transport Model Calibration........................................................................................17
5.3 Advective Travel Times...............................................................................................17
5.4 Flow and Transport Model Sensitivity Analysis...........................................................17
6 Simulation of Closure Scenarios........................................................................................18
6.1 Existing Conditions.....................................................................................................19
6.2 Cap-in-Place...............................................................................................................21
6.3 Excavation..................................................................................................................23
7 Summary and Conclusions................................................................................................25
7.1 Model Assumptions and Limitations............................................................................25
7.2 Model Predictions.......................................................................................................26
8 References........................................................................................................................27
111r_r34:110
Table 1. MODFLOW and MT3DMS Input Packages Utilized
Table 2. Model Hydraulic Conductivity
Table 3. Observed vs. Predicted Hydraulic Head (ft MSL)
Table 4. Model Effective Porosity
Table 5. Transport Model Calibration Results
Table 6. Predicted Advective Travel Time
Table 7. Flow and Transport Parameter Sensitivity Analysis
FIGURES
Figure 1. Conceptual Groundwater Flow Model/Model Domain
Figure 2. Model Domain North -South Cross Section (A -A') through Inactive and Active Ash
Basins
Figure 3. Model Domain East-West Cross Section (B-B') through the Active Ash Basin
Figure 4. Flow Model Boundary Conditions
Figure 5. Model Recharge Areas and Contaminant Source Zones (Constant Concentration
Cells)
Figure 6. Observation Wells in Shallow Groundwater Zone
Figure 7. Observation Wells in Deep Groundwater Zone
Figure 8. Observation Wells in Bedrock Groundwater Zone
Figure 9. Hydraulic Conductivity Zonation in S/M1 Model Layers (Model Layers 5-6)
Figure 10. Hydraulic Conductivity Zonation in M2 Model Layer (Model Layer 7)
Figure 11. Hydraulic Conductivity Zonation in TZ Model Layer (Model Layer 8)
Figure 12. Hydraulic Conductivity Zonation in BR Model Layers (Model Layers 9 and10)
Figure 13. Modeled Hydraulic Head (feet) vs. Observed Hydraulic Head (feet)
Figure 14. Hydraulic Head (feet) in Shallow Groundwater Zone (Model Layer 6)

Figure 15. Particle Tracking Results (see Table 6 for Advective Travel Times)
Figure 16. Predicted Antimony (pg/L) in Monitoring Well AB-26D for Model Scenarios 1-3
Figure 17. Predicted Antimony (pg/L) in Monitoring Well AB-31D for Model Scenarios 1-3
Figure 18. Initial (2015) Antimony Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 19. Initial (2015) Antimony Concentrations (pg/L) in the Deep Groundwater Zone
Figure 20. Initial (2015) Antimony Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 21. "Existing Conditions" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Shallow
Groundwater Zone
Figure 22. "Existing Conditions" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Deep
Groundwater Zone
Figure 23. "Existing Conditions" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Bedrock
Groundwater Zone
Figure 24. "Cap -in -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Shallow
Groundwater Zone
Figure 25. "Cap -in -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Deep
Groundwater Zone
Figure 26. "Cap -in -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Bedrock
Groundwater Zone
Figure 27. "Excavation" Scenario 3 - 2115 Predicted Antimony (pg/L) in the Shallow
Groundwater Zone
Figure 28. "Excavation" Scenario 3 - 2115 Predicted Antimony (pg/L) in the Deep Groundwater
Zone
Figure 29. "Excavation" Scenario 3 - 2115 Predicted Antimony (pg/L) in the Bedrock
Groundwater Zone
Figure 30. Predicted Arsenic (pg/L) in Monitoring Well AB-22S For Model Scenarios 1-3
Figure 31. Predicted Arsenic (pg/L) in Monitoring Well GWA-6S For Model Scenarios 1-3
Figure 32. Initial (2015) Arsenic Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 33. Initial (2015) Arsenic Concentrations (pg/L) in the Deep Groundwater Zone
Figure 34. Initial (2015) Arsenic Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 35. "Existing Conditions" Scenario 1 - 2115 Predicted Arsenic (pg/L) in the Shallow
Groundwater Zone
Figure 36. "Existing Conditions" Scenario 1 - 2115 Predicted Arsenic (pg/L) in the Deep
Groundwater Zone
Figure 37. "Existing Conditions" Scenario 1 - 2115 Predicted Arsenic (pg/L) in the Bedrock
Groundwater Zone
Figure 38. "Cap -in -Place" Scenario 2 - 2115 Predicted Arsenic (pg/L) in the Shallow
Groundwater Zone
Figure 39. "Cap -in -Place" Scenario 2 - 2115 Predicted Arsenic (pg/L) in the Deep Groundwater
Zone
Figure 40. "Cap -in -Place" Scenario 2 - 2115 Predicted Arsenic (pg/L) in the Bedrock
Groundwater Zone
Figure 41. "Excavation" Scenario 3 - 2115 Predicted Arsenic (pg/L) in the Shallow Groundwater
Zone
Figure 42. "Excavation" Scenario 3 - 2115 Predicted Arsenic (pg/L) in the Deep Groundwater
Zone
Figure 43. "Excavation" Scenario 3 - 2115 Predicted Arsenic (pg/L) in the Bedrock Groundwater
Zone
Figure 44. Predicted Barium (pg/L) in Monitoring Well AB-22S For Model Scenarios 1-3
Figure 45. Predicted Barium (pg/L) in Monitoring Well AB-26S For Model Scenarios 1-3
Figure 46. Initial (2015) Barium Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 47. Initial (2015) Barium Concentrations (pg/L) in the Deep Groundwater Zone
IV

Figure 48. Initial (2015) Barium Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 49. "Existing Conditions" Scenario 1 - 2115 Predicted Barium (pg/L) in the Shallow
Groundwater Zone
Figure 50. "Existing Conditions" Scenario 1 - 2115 Predicted Barium (pg/L) in the Deep
Groundwater Zone
Figure 51. "Existing Conditions" Scenario 1 - 2115 Predicted Barium (pg/L) in the Bedrock
Groundwater Zone
Figure 52. "Cap -in -Place" Scenario 2 - 2115 Predicted Barium (pg/L) in the Shallow
Groundwater Zone
Figure 53. "Cap -in -Place" Scenario 2 - 2115 Predicted Barium (pg/L) in the Deep Groundwater
Zone
Figure 54. "Cap -in -Place" Scenario 2 - 2115 Predicted Barium (pg/L) in the Bedrock
Groundwater Zone
Figure 55. "Excavation" Scenario 3 - 2115 Predicted Barium (pg/L) in the Shallow Groundwater
Zone
Figure 56. "Excavation" Scenario 3 - 2115 Predicted Barium (pg/L) in the Deep Groundwater
Zone
Figure 57. "Excavation" Scenario 3 - 2115 Predicted Barium (pg/L) in the Bedrock Groundwater
Zone
Figure 58. Predicted Boron (pg/L) in Monitoring Well AB-22D For Model Scenarios 1-3
Figure 59. Predicted Boron (pg/L) in Monitoring Well AB-26S For Model Scenarios 1-3
Figure 60. Predicted Boron (pg/L) in Monitoring Well GWA-4S For Model Scenarios 1-3
Figure 61. Predicted Boron (pg/L) in Monitoring Well GWA-5BR For Model Scenarios 1-3
Figure 62. Initial (2015) Boron Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 63. Initial (2015) Boron Concentrations (pg/L) in the Deep Groundwater Zone
Figure 64. Initial (2015) Boron Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 65. "Existing Conditions" Scenario 1 - 2115 Predicted Boron (pg/L) in the Shallow
Groundwater Zone
Figure 66. "Existing Conditions" Scenario 1 - 2115 Predicted Boron (pg/L) in the Deep
Groundwater Zone
Figure 67. "Existing Conditions" Scenario 1 - 2115 Predicted Boron (pg/L) in the Bedrock
Groundwater Zone
Figure 68. "Cap -in -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater
Zone
Figure 69. "Cap -in -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Deep Groundwater
Zone
Figure 70. "Cap -in -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater
Zone
Figure 71. "Excavation" Scenario 3 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater
Zone
Figure 72. "Excavation" Scenario 3 - 2115 Predicted Boron (pg/L) in the Deep Groundwater
Zone
Figure 73. "Excavation" Scenario 3 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater
Zone
Figure 74. Predicted Chromium (pg/L) in Monitoring Well AB-6R For Model Scenarios 1-3
Figure 75. Predicted Chromium (pg/L) in Monitoring Well AB-26D For Model Scenarios 1-3
Figure 76. Initial (2015) Chromium Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 77. Initial (2015) Chromium Concentrations (pg/L) in the Deep Groundwater Zone
Figure 78. Initial (2015) Chromium Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 79. "Existing Conditions" Scenario 1 - 2115 Predicted Chromium (pg/L) in the Shallow
Groundwater Zone
v

Figure 80. "Existing Conditions" Scenario 1 - 2115 Predicted Chromium (pg/L) in the Deep
Groundwater Zone
Figure 81. "Existing Conditions" Scenario 1 - 2115 Predicted Chromium (pg/L) in the Bedrock
Groundwater Zone
Figure 82. "Cap -in -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Shallow
Groundwater Zone
Figure 83. "Cap -in -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Deep
Groundwater Zone
Figure 84. "Cap -in -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Bedrock
Groundwater Zone
Figure 85. "Excavation" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Shallow
Groundwater Zone
Figure 86. "Excavation" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Deep Groundwater
Zone
Figure 87. "Excavation" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Bedrock
Groundwater Zone
Figure 88. Predicted Hexavalent Chromium (pg/L) in Monitoring Well AB-9D For Model
Scenarios 1-3
Figure 89. Predicted Hexavalent Chromium (pg/L) in Monitoring Well AB-31 S For Model
Scenarios 1-3
Figure 90. Predicted Hexavalent Chromium (pg/L) in Monitoring Well GWA-3D For Model
Scenarios 1-3
Figure 91. Predicted Hexavalent Chromium (pg/L) in Monitoring Well AB-10D Model Scenarios
1-3
Figure 92. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Shallow
Groundwater Zone
Figure 93. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Deep Groundwater
Zone
Figure 94. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Bedrock
Groundwater Zone
Figure 95. "Existing Conditions" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Shallow Groundwater Zone
Figure 96. "Existing Conditions" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Deep Groundwater Zone
Figure 97. "Existing Conditions" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Bedrock Groundwater Zone
Figure 98. "Cap -in -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Shallow Groundwater Zone
Figure 99. "Cap -in -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep
Groundwater Zone
Figure 100. "Cap -in -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Bedrock Groundwater Zone
Figure 101. "Excavation" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Shallow Groundwater Zone
Figure 102. "Excavation" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep
Groundwater Zone
Figure 103. "Excavation" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Bedrock Groundwater Zone
Figure 104. Predicted Cobalt (pg/L) in Monitoring Well AB-10S For Model Scenarios 1-3
Figure 105. Predicted Cobalt (pg/L) in Monitoring Well AB-26S For Model Scenarios 1-3
Figure 106. Predicted Cobalt (pg/L) in Monitoring Well AB-32D For Model Scenarios 1-3
vi

Figure 107. Predicted Cobalt (pg/L) in Monitoring Well GWA-5S For Model Scenarios 1-3
Figure 108. Initial (2015) Cobalt Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 109. Initial (2015) Cobalt Concentrations (pg/L) in the Deep Groundwater Zone
Figure 110. Initial (2015) Cobalt Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 111. "Existing Conditions" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Shallow
Groundwater Zone
Figure 112. "Existing Conditions" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Deep
Groundwater Zone
Figure 113. "Existing Conditions" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Bedrock
Groundwater Zone
Figure 114. "Cap -in -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Shallow
Groundwater Zone
Figure 115. "Cap -in -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater
Zone
Figure 116. "Cap -in -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Bedrock
Groundwater Zone
Figure 117. "Excavation" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Shallow Groundwater
Zone
Figure 118. "Excavation" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater
Zone
Figure 119. "Excavation" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Bedrock Groundwater
Zone
Figure 120. Predicted Selenium (pg/L) in Monitoring Well GWA-6S For Model Scenarios 1-3
Figure 121. Predicted Selenium (pg/L) in Monitoring Well AB-22S For Model Scenarios 1-3
Figure 122. Initial (2015) Selenium Concentrations (pg/L) in The Shallow Groundwater Zone
Figure 123. Initial (2015) Selenium Concentrations (pg/L) in the Deep Groundwater Zone
Figure 124. Initial (2015) Selenium Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 125. "Existing Conditions" Scenario 1 - 2115 Predicted Selenium (pg/L) in the Shallow
Groundwater Zone
Figure 126. "Existing Conditions" Scenario 1 - 2115 Predicted Selenium (pg/L) in the Deep
Groundwater Zone
Figure 127. "Existing Conditions" Scenario 1 - 2115 Predicted Selenium (pg/L) in the Bedrock
Groundwater Zone
Figure 128. "Cap -in -Place" Scenario 2 - 2115 Predicted Selenium (pg/L) in the Shallow
Groundwater Zone
Figure 129. "Cap -in -Place" Scenario 2 - 2115 Predicted Selenium (pg/L) in the Deep
Groundwater Zone
Figure 130. "Cap -in -Place" Scenario 2 - 2115 Predicted Selenium (pg/L) in the Bedrock
Groundwater Zone
Figure 131. "Excavation" Scenario 3 - 2115 Predicted Selenium (pg/L) in the Shallow
Groundwater Zone
Figure 132. "Excavation" Scenario 3 - 2115 Predicted Selenium (pg/L) in the Deep Groundwater
Zone
Figure 133. "Excavation" Scenario 3 - 2115 Predicted Selenium (pg/L) in the Bedrock
Groundwater Zone
Figure 134. Predicted Sulfate (pg/L) In Monitoring Well AB-33S For Model Scenarios 1-3
Figure 135. Predicted Sulfate (pg/L) In Monitoring Well GWA-6S For Model Scenarios 1-3
Figure 136. Initial (2015) Sulfate Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 137. Initial (2015) Sulfate Concentrations (pg/L) in the Deep Groundwater Zone
Figure 138. Initial (2015) Sulfate Concentrations (pg/L) in the Bedrock Groundwater Zone
vii

Figure 139. "Existing Conditions" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Shallow
Groundwater Zone
Figure 140. "Existing Conditions" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Deep
Groundwater Zone
Figure 141. "Existing Conditions" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Bedrock
Groundwater Zone
Figure 142. "Cap -in -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Shallow
Groundwater Zone
Figure 143. "Cap -in -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater
Zone
Figure 144. "Cap -in -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Bedrock
Groundwater Zone
Figure 145. "Excavation" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Shallow Groundwater
Zone
Figure 146. "Excavation" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater
Zone
Figure 147. "Excavation" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Bedrock
Groundwater Zone
Figure 148. Predicted Vanadium (pg/L) In Monitoring Well AB-6R For Model Scenarios 1-3
Figure 149. Predicted Vanadium (pg/L) In Monitoring Well AB-10D For Model Scenarios 1-3
Figure 150. Predicted Vanadium (pg/L) In Monitoring Well GWA-4S For Model Scenarios 1-3
Figure 151. Predicted Vanadium (pg/L) In Monitoring Well GWA-5BR For Model Scenarios 1-3
Figure 152. Initial (2015) Vanadium Concentrations (pg/L) in the Shallow Groundwater Zone
Figure 153. Initial (2015) Vanadium Concentrations (pg/L) in the Deep Groundwater Zone
Figure 154. Initial (2015) Vanadium Concentrations (pg/L) in the Bedrock Groundwater Zone
Figure 155. "Existing Conditions" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Shallow
Groundwater Zone
Figure 156. "Existing Conditions" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Deep
Groundwater Zone
Figure 157. "Existing Conditions" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Bedrock
Groundwater Zone
Figure 158. "Cap -in -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Shallow
Groundwater Zone
Figure 159. "Cap -in -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Deep
Groundwater Zone
Figure 160. "Cap -in -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Bedrock
Groundwater Zone
Figure 161. "Excavation" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Shallow
Groundwater Zone
Figure 162. "Excavation" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Deep
Groundwater Zone
Figure 163. "Excavation" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Bedrock
Groundwater Zone
viii

INTRODUCTION
The calibrated flow and transport model third -party peer review team was coordinated by the
Electric Power Research Institute (EPRI) and included Dr. Chunmiao Zheng from the University
of Alabama, James Rumbaugh from Environmental Simulations, Inc, and experienced modelers
from Intera, Inc. The reviewers were provided with the conceptual site model, the
Comprehensive Site Assessment (CSA), a draft model report, and digital model input and
output files, allowing them to reconstruct the model for independent review. During the course of
the review, the reviewers communicated with the modelers in order to better understand how
the model was developed and calibrated. As a result of these communications, the model was
modified and recalibrated, which allowed the reviewers to conclude that the model was
constructed and calibrated sufficiently to achieve its primary objective of comparing the effects
of closure alternatives on nearby groundwater quality. In addition, the reviewers identified
limitations with the model, which are included in the discussion of model limitations later in this
documentation.
After EPRI acceptance of the Allen Groundwater model, the model was improved using
measured aquifer test and water level results from monitor wells at the Allen site. In addition, a
drainage feature was removed from the model near the northwest model boundary after further
review of the CSA data. These changes did not change the model structure or boundaries and
did not deviate from EPRI guidelines.
1.1 General Setting and Background
Duke Energy owns and operates the Allen Steam Station (Allen), which is located on a 1,009
acre tract near the town of Belmont, in Gaston County, North Carolina. Allen began operation in
1957 as a coal-fired generating station and currently operates five coal-fired units. The coal ash
residue from Allen's coal combustion process has historically been disposed in the ash basin
system located to the south of the station and adjacent to the Catawba River (HDR Figures 2-1
through 2-41)(HDR 2015).
The ash basin system at Allen consists of an active ash basin and an inactive ash basin. In
general, the ash basin is located south of the power complex in historical drainage features
formed from tributaries that flowed toward the Catawba River. There is one earthen
embankment dam and one earthen dike impounding the active ash basin: the East Dam,
located along the west bank of the Catawba River, and the North Dike, separating the active
and inactive ash basins. The original ash basin at the Allen site (the inactive ash basin) began
operation in 1957 and was formed by constructing an underlying portion of the earthen North
Dike and the northern portion of the main East Dam where tributaries flowed toward the
Catawba River. As the original ash basin capacity diminished over time, the active ash basin
was formed in 1973 by constructing the southern portion of the East Dam and raising the North
Dike. Ash has been sluiced to the active ash basin since 1973 (HDR 2015).
1 Please refer to the Comprehensive Site Assessment Report, ALSS Steam Station Ash Basin, August 2015 (HDR)
for more information and referenced figures and tables (referred to herein as HDR tables and HDR figures).
1

Two unlined dry ash storage areas, two unlined structural fill units, and a double -lined dry ash
landfill are located within the footprint of the inactive ash basin. The ash landfill was constructed
in 2009. Construction of the structural fill units began in 2003 and was completed in 2009. The
dry ash storage areas were constructed in 1996 (HDR 2015). Allen is a coal-fired electricity
generating facility with a capacity of 1,155 megawatts (MW) along the Catawba River
(specifically Lake Wylie). The five -unit station began commercial operation in 1957 with
operation of coal-fired Units 1 and 2 (330 MW total). Unit 3 (275 MW) was placed into
commercial operation in 1959, followed by Unit 4 (275 MW) in 1960, and Unit 5 (275 MW) in
1961.
The Allen ash basin is situated between the Allen powerhouse to the north and topographic
divides to the west (along South Point Road) and south (along Reese Wilson Road) (HDR
Figure 2-2). Natural topography at the site generally slopes downward and eastward from that
divide toward Lake Wylie. The topography at the site generally slopes from west to east,
approximately 650 feet to 680 feet elevation near the west and southwest boundaries of the site
to an approximate low elevation of 570 feet at the shoreline of Lake Wylie (an approximate
distance of 0.8 miles).
The air pollution control system for the coal-fired units at Allen includes a flue gas
desulfurization (FGD) system that was placed into operation in 2009. Coal is delivered to the
station by a railroad line. Other areas of the site are occupied by facilities supporting the
production and transmission of power (two switchyards and associated transmission lines), the
FGD wastewater treatment system, and the gypsum handling station (associated with the FGD
system). A site features map is included as HDR Figure 2-4.
Based on the CSA site investigation (HDR 2015), the groundwater system in the natural
materials (alluvium, soil, soil/saprolite, and bedrock) at Allen is consistent with the Piedmont
regolith-fractured rock system and is an unconfined, connected system of flow layers (HDR
Figure 5-5). In general, groundwater within the shallow and deep layers (S and D wells) and
bedrock layer (BR wells) flows from west and southwest to the east toward the Catawba River
(Lake Wylie) and to the north toward Duke Energy property and the station discharge canal.
1.2 Study Objectives
The purpose of this study is to predict the groundwater flow and constituent transport that will
occur as a result of different possible closure actions at the site. The study consists of three
main activities: development of a calibrated steady-state flow model of current conditions,
development of a transport model for constituents identified as COls, and simulating transport
for the following scenarios: Scenario 1) "Existing Conditions" scenario of existing site conditions,
Scenario 2) "Cap in -Place" where impermeable cap(s) are placed over existing active/inactive
ash basins and ash storage area, and Scenario 3) "Excavation" where ash is removed from the
Allen ash basins and ash storage area.
2 CONCEPTUAL MODEL
The site conceptual model for Allen is primarily based on the CSA Report (HDR 2015) for the
Allen Steam Station. The CSA report contains extensive detail and data related to most aspects
of the site conceptual model that are used in this report.
P

2.1 Geology and Hydrogeology (HDR 2015)
The Allen site is located within the Charlotte terrane, one of a number of tectonostratigraphic
terranes that have been defined in the southern and central Appalachians and is in the western
portion of the larger Carolina superterrane (HDR Figure 5-1). The Charlotte terrane is
dominated by a complex sequence of plutonic rocks that intrude a suite of metaigneous rocks.
A geologic map of the area around Allen is shown in CSA Figure 5-2 (HDR 2015).
The fractured bedrock is overlain by a mantle of unconsolidated material known as regolith. The
regolith includes residual soil and saprolite zones and, where present, alluvial deposits.
Saprolite, the product of chemical weathering of the underlying bedrock, is typically composed
of clay and coarser granular material and reflects the texture and structure of the rock from
which it was formed. The weathering products of granitic rocks are quartz -rich and sandy
textured. Rocks poor in quartz and rich in feldspar and ferro-magnesium minerals form a more
clayey saprolite.
The groundwater system in the Piedmont Province, in most cases, is comprised of two
interconnected layers, or mediums: 1) residual soil/saprolite and weathered fractured rock
(regolith) overlying 2) fractured crystalline bedrock (HDR 2015). The regolith layer is a
thoroughly weathered and structureless residual soil that occurs near the ground surface with
the degree of weathering decreasing with depth. The residual soil grades into saprolite, a
coarser grained material that retains the structure of the parent bedrock. Beneath the saprolite,
partially weathered/fractured bedrock occurs with depth until sound bedrock is encountered.
This layer serves as the principal storage reservoir and provides an intergranular medium
through which the recharge and discharge of water from the underlying fractured rock occurs.
Within the fractured crystalline bedrock layer, the fractures control both the hydraulic
conductivity and storage capacity of the rock mass. A transition zone (TZ) at the base of the
regolith has been interpreted to be present in many areas of the Piedmont. It is described as
consisting of partially weathered/fractured bedrock and lesser amounts of saprolite that grades
into bedrock and is considered to be the most permeable part of the system (HDR 2015).
2.2 Hydrostratigraphic Layer Development (HDR 2015)
Soil conditions encountered in the borings showed minimal variation across the site. Residual
soil consists of clayey sand (SC), silty sand (SM), silty sand with gravel (SM), micaceous silty
sand (SM), and gravel with silt and sand (GP). The following materials were encountered during
the site exploration and are consistent with material descriptions from previous site exploration
studies:
Ash — Ash was encountered in borings advanced within the ash basin and ash storage areas,
as well as through dikes. Ash was generally described as gray to dark gray, non -plastic, loose to
medium dense, dry to wet, fine to coarse -grained.
Fill — Fill material generally consisted of re -worked silts, clays, and sands that were borrowed
from one area of the site and re -distributed to other areas. Fill was generally classified as silty
sand, clay with sand, clay, and sandy clay on the boring logs. Fill was used in the construction
of dikes, and as cover for ash storage area.
Alluvium —Alluvium encountered in borings during the project was classified as clay and sand
with clay. In some cases alluvium was logged beneath ash.
3

Residuum (Residual soils) — Residuum is the in -place weathered soil that consists primarily of
silt with sand, clayey sand, sandy clay, clay with gravel, and clayey silts. Residuum varied in
thickness and was relatively thin compared to the thickness of saprolite.
Saprolite/Weathered Rock — Saprolite is soil developed by in -place weathering of rock that
retains remnant bedrock structure. Saprolite consists primarily of medium dense to very dense
silty sand, sandy silt, sand, sand with gravel, sand with clay, clay with sand, and clay. Sand
particle size ranges from fine to coarse grained. Much of the saprolite is micaceous.
Partially Weathered/Fractured Rock — Partially weathered (slight to moderate) and/or highly
fractured rock encountered below auger refusal.
Bedrock — Sound rock in boreholes, was generally slightly weathered to fresh and relatively
unfractured.
Based on the CSA, the groundwater system is consistent with the regolith-fractured bedrock
system. To define the hydrostratigraphic units the following classification system was used and
is based on Standard Penetration Testing (N) values, Recovery (REC), and Rock Quality
Designation (RQD) collected during the drilling and logging of boreholes.
The ash, fill, and alluvial layers are as encountered at the site. The natural system (except
alluvium) includes the following layers:
M1 — Soil/Saprolite:
M2 — Saprolite/Weathered Rock:
TZ — Transition Zone:
BR — Bedrock:
N <50
N>50 or REC<50%
REC>50% and RQD<50%
REC>85% and RQD>50%.
Rock core runs that fell between the values for TZ and BR (REC<85% and RQD>50% or
REC>85% and RQD<50%) were assigned a hydrostratigraphic layer based on a review of the
borehole logs, rock core photographs, and geologic judgment. The same review was performed
to determine the thickness of the TZ just in case it extended into the next core run, which when
reviewed alone might have met the BR criterion, because of potential core loss or
fractured/jointed rock with indications of water movement (iron/manganese staining).
The above layers designations (M1, M2, TZ, and BR) are used on the geologic cross sections
with transect locations shown on HDR Figure 8-2. The ash, fill and alluvial layers are
represented by A, F, and S, respectively, on cross sections and in tables in the CSA.
Ranges of hydrostratigraphic layer properties measured at Allen are provided in CSA Tables 11-
8 through 11-12 (HDR 2015).
2.3 Ash Basins and Ash Storage Areas
Historical and current information about the Allen ash basin system assembled by HDR (2015)
is relevant to developing the conceptual and numerical groundwater flow models. Refer to HDR
Figures 2-2 and 2-4 for locations of ash basin system components described below.
Coal ash residue from the coal combustion process has historically been disposed in the Allen
ash basin. The area contained within the entire ash basin waste boundary, which is shown on
HDR Figures 2-2 and 2-7, encompasses approximately 322 acres. The ash basin system is
comprised of an inactive ash basin and an active ash basin. For convenience, the two ash
2

basins are sometimes jointly referred to as the "ash basin" in this report. In general, the ash
basin is located in historical depressions formed from tributaries that flowed toward the Catawba
River. The ash basin is operated as an integral part of the station's wastewater treatment
system, which receives flows from the ash removal system, coal pile runoff, landfill leachate,
FGD wastewater, the station yard drain sump, and site stormwater.
There are two earthen dikes impounding the active ash basin: the East Dike, located along the
west bank of the Catawba River; and the North Dike, separating the active and inactive ash
basins. The original ash basin at the Allen site (the inactive ash basin) began operation in 1957
and was formed by constructing the earthen North Dike and the north portion of the East Dike
where tributaries flowed toward Lake Wylie. As the original ash basin capacity diminished over
time, the active ash basin was formed in 1973 by constructing the southern portion of the East
Dike. Ash has been sluiced to the active ash basin since 1973. In addition to the ash basin, two
unlined dry ash storage areas, two unlined structural fill units, and a lined dry ash landfill are
located on top of the inactive ash basin. The ash landfill was constructed in 2009. Construction
of the structural fill units began in 2003 and was completed in 2009. The dry ash storage areas
were constructed in 1996. Additional information pertaining to each ash management unit is
provided below.
2.3.1 Ash Basin (HDR 2015)
The active ash basin, located on the southern portion of the property, is approximately 169
acres in area and contains an estimated 7,660,000 tons of ash. The inactive ash basin, located
between the generating units and the active ash basin, is approximately 132 acres in area and
contains approximately 3,920,000 tons of ash.
The inactive ash basin was commissioned in 1957 and is located adjacent to and north of the
active ash basin. Coal ash was sluiced to the inactive ash basin until the active ash basin was
constructed in 1973. Fly ash precipitated from flue gas and bottom ash collected in the bottom
of the boilers were sluiced to the ash basin using conveyance water withdrawn from the
Catawba River. Since 2009, fly ash has been dry -handled and disposed in the on -site ash
landfill, and bottom ash has continued to be sluiced to the active ash basin. During operations,
the sluice lines discharge the water/ash slurry (and other permitted flows) into the Primary
Ponds of the northern portion of the active ash basin. Primary Ponds 1, 2, and 3 were
constructed in approximately 2004. Currently, Primary Ponds 2 and 3 are utilized for settling
purposes.
Other inflows to the ash basin include flows from coal pile runoff, landfill leachate, FGD
wastewater, the station yard drain sump, and stormwater flows. Due to variability in station
operations and weather, the inflows to the ash basin are highly variable. Effluent from the ash
basin is discharged from the discharge tower to Lake Wylie via a 42-inch-diameter reinforced
concrete pipe located in the southeastern portion of the ash basin (Outfall 002). The water
surface elevation in the ash basin is controlled by the use of stop logs in the discharge tower.
2.3.2 Ash Landfill
The ash landfill unit, referred to as the Retired Ash Basin (RAB) Ash Landfill (NCDENR Division
of Waste Management (DWM) Solid Waste Section Permit No. 3612-INDUS), is located on the
eastern portion of the Allen site, on top of the inactive ash basin. The landfill is bound to the
north, east, and south by earthen dikes. The RAB Ash Landfill dam comprises the northern and
5

eastern boundaries of the landfill. The Catawba River is located immediately to the east and
below the landfill. To the south of and adjacent to the RAB Ash Landfill is the existing active ash
basin, and to the west is a structural fill area. The lined landfill is permitted to receive coal
combustion residuals (CCR) including fly ash, bottom ash, boiler slag, mill rejects, and FGD
waste generated by Duke Energy. In addition to these CCR materials, the landfill is permitted to
receive nonhazardous sandblast material, limestone, coal, carbon, sulfur pellets, cation and
anion resins, sediment from sumps, and cooling tower sludge.
The RAB Ash Landfill is planned to contain two phases (Phase I and Phase II), and when fully
constructed will cover a total of 47 acres. Phase I has been constructed and encompasses 25
acres on the southern half of the landfill footprint. The estimated gross capacity of Phase I is
2,082,500 cubic yards. Phase 11 has not yet been constructed and is planned to encompass 22
acres immediately north of the Phase I footprint. The estimated gross capacity of Phase 11 is
3,958,200 cubic yards. The entire landfill facility, including the waste footprint, associated
perimeter berms, ditches, stormwater management systems and roads, is projected to
encompass an area of approximately 62 acres, when complete. The approximate boundary of
the RAB Ash Landfill is shown on HDR Figure 2-2.
The Permit to Construct Phase I of the landfill was issued by NCDENR DWM in September
2008. Its initial Permit to Operate was issued by NCDENR DWM in December 2009, and the
most recent Permit to Operate renewal was issued in December 2014. The landfill was
constructed with a leachate collection and removal system and a three -component liner system
consisting of a primary geomembrane, secondary geomembrane (with a leak detection system
between them), and clay soil liner. Placement of waste material in the RAB Ash Landfill began
in December 2009. Phase I contact stormwater and leachate are collected in the leachate
collection pipe system and then pumped to the discharge location in the northeastern portion of
the active ash basin. Since the landfill is situated over the inactive ash basin, the landfill was
constructed with a double liner, leachate collection system (LCS) and leak detection system
(LDS). NCDENR DWR determined that inclusion of the LCS, LDS, and leachate sampling is an
acceptable alternative to groundwater monitoring for the landfill, which would be difficult to
assess with the underlying inactive ash basin.
2.3.3 Structural Fills
Two unlined Distribution of Residuals Solids (DORS) structural ash fills are located on top of the
western portion of the inactive ash basin, adjacent to and west of the RAB Ash Landfill. These
fills were constructed of ponded ash removed from the active ash basin per Duke Energy's
DORS Permit issued by NCDENR DWQ. Placement of dry ash in the structural fills began in
2003 and was completed in 2009. During and following the completion of filling, the structural fill
areas were graded to drain, and soil cover was placed on the top slopes and side slopes, and
vegetation was established. The eastern structural fill covers approximately 17 acres and
contains approximately 500,000 tons of ash. The western structural fill covers approximately 17
acres and contains approximately 328,000 tons of ash.
2.3.4 Ash Storage
Two unlined ash storage areas are located on top of the western portion of the inactive ash
basin, adjacent to and west of the two DORS structural fills. Similar to the two DORS structural
fills, the ash storage areas were constructed in 1996 by excavating ash from the northern
M.

portion of the active ash basin in order to provide capacity for sluiced ash in the active ash basin
and the future construction of Primary Ponds 1, 2, and 3. Following the completion of
stockpiling, the ash storage areas were graded to drain, and a minimum of 18 and 24 inches of
soil cover were placed on the top slopes and side slopes, respectively, and vegetation was
established. Approximately 300,000 cubic yards of ash is stored in the ash storage areas, which
encompass an area of approximately 15 to 20 acres of the western portion of the inactive ash
basin.
2.4 Groundwater Flow System
Groundwater recharged occurs from precipitation infiltration into the subsurface where the
ground surface is permeable, including the dikes and ash of the ash basin system where
exposed at the ground surface. After infiltrating the ground surface, water in the unsaturated
zone percolates downward to the unconfined water table, except where ponded water
conditions exist on portions of the Active Ash Basin. From the water table, groundwater moves
downward and then laterally through unconsolidated material (residual soil/saprolite) into the
TZ, then fractured bedrock. Mean annual recharge to shallow unconfined aquifers in the
Piedmont ranges from 4.0 to 9.7 inches per year (Daniel 2001).
Based on the site investigation, the groundwater system in the natural materials (alluvium, soil,
soil/saprolite, and fractured bedrock) at Allen is consistent with the regolith-fractured rock
system and is an unconfined, connected aquifer system without confining layers. The Allen
groundwater system is divided into three layers referred to in this report as the shallow, deep
(TZ), and bedrock flow layers to distinguish the flow layers within the connected aquifer system.
In general, groundwater within the shallow flow layer, deep flow layer, and bedrock flow layer at
the site flows from west and southwest to the east toward the Catawba River and to the
northeast and north toward Duke Energy property and the station discharge canal (HDR Figures
6-5 through 6-7).
Locally, groundwater is mounded beneath Primary Ponds 1 through 3 and depressed beneath
the ash landfill and the southeastern Active Ash Basin. Steep hydraulic gradients are
associated with the North and East Dikes.
In accordance with the Piedmont Slope Aquifer System of LeGrand (2004), fractured density in
bedrock decreases with depth, limiting deep groundwater flow (HDR Figure 5-5).
2.5 Hydrologic Boundaries
The major discharge locations for the groundwater system at Allen, the Catawba River to the
east and the Station Discharge Canal to the north (HDR Figure 2-4), act as a hydrologic
boundaries for the site. A no -flow boundary is located between the Station Discharge Canal and
the ash basin system at a presumptive, natural groundwater divide corresponding to a
topographic divide. Thus, the Station Discharge Canal is not a component of the ash basin
model to the south.
2.6 Hydraulic Boundaries
The ash landfill situated over the RAB was constructed with a double liner, leachate collection
system (LCS) and leak detection system (LDS) that act as a hydraulic boundary. Otherwise, the
7

groundwater flow system at Allen does not contain impermeable barriers or boundaries with the
exception of bedrock at depth where fracture density, and fracture flow, is minimal. Natural
groundwater divides exist along topographic divides, but are a result of local flow conditions as
opposed to barriers.
2.7 Sources and Sinks
Recharge, including to the ash basins, is the major source of water for the groundwater system.
Most of this water discharges to the hydrologic boundary at the Catawba River. Recharge that
infiltrates the Ash Landfill is intercepted by the liner system at depth and is diverted to the Active
Ash Basin.
Four public water supply wells and 219 private water supply wells have been identified within a
0.5-mile radius of the ash basin compliance boundary at Allen. Two existing water supply wells
at the Allen site (CIF Well and pH Well) were sampled to supplement groundwater quality data
in the vicinity of the Active Ash Basin. However, the CSA does not consider any effect that
these wells may have on groundwater flow at the site, nor does it identify other sources or sinks.
The CSA does not suggest that the Allen ash basin is within the capture zone or zone of
influence of any extraction well or wells. Furthermore, it states that the groundwater flow
direction across the site is away from the direction of the nearest public or private water supply
wells (HDR 2015).
2.8 Water Balance
Over an extended period of time, the rate of water inflow to the modeled area is equal to its rate
of water outflow. That is, there is no net change in groundwater storage. Water enters the
groundwater system through recharge and ultimately discharges to the Catawba River.
2.9 Modeled Constituents of Interest (COI)
As defined in the CSA, constituents are those chemicals or compounds that were identified in
the approved groundwater assessment plans for sampling and analysis (HDR 2015). The
following criteria were used to determine if a COI required modeling: if the constituent exceeded
regulatory groundwater standards (15A NCAC 02L.0202 groundwater standard or IMAC), and is
traceable back to the source (i.e., existed in porewater) - the constituent was then deemed a
COI for transport modeling. Per the CSA, the metals and trace metals detected in ash basin
porewater are: antimony, arsenic, barium, boron, chromium, hexavalent chromium, cobalt,
selenium, iron, manganese, sulfate, thallium, and vanadium. Exclusive of iron, manganese, and
thallium, all of these COls were considered in the transport simulations. Iron and manganese
are naturally occurring in the groundwater system and require more complex modeling than
which is currently being performed. Thallium has only one estimated value above the
exceedence threshold detected in groundwater, which does not yield a discerned plume to
calibrate to. The simulated COls all occur at elevated levels in groundwater near the ash basins
(HDR Figures 10-80 to 10-89, 10-93 to 10-95, 10-99 to 10-104, 10-114 to 10-119, and 10-126 to
10-128). Boron and sulfate are considered very mobile in groundwater as they do not readily
precipitate or adsorb to soils. The other COls adsorb to commonly occurring soil types based
upon the linear sorption coefficient ([KdD analysis performed by UNCC.
P]

2.10 COI Transport
COls entered the ash basin system in the dissolved phase and solid phase of the station's
wastewater discharge. Some constituents are also present in native soils and groundwater
beneath the basin. The accumulation and subsequent release of chemical constituents in the
ash basin over time is complex. In the active and inactive ash basin, constituents may incur
phase changes via dissolution, precipitation, chemical reactions and adsorption/desorption.
Dissolved phase constituents may incur these phase changes as they are transported by
advection and dispersion in groundwater flowing downgradient from the ash basins. In the fate
and transport model, chemical constituents enter the basin in the dissolved phase by specifying
a steady state concentration in the ash porewater. Phases changes (dissolution, precipitation,
adsorption, and desorption) are collectively taken into account by specifying a linear sorption
coefficient (distribution coefficient [KdD. The accumulation and subsequent release of chemical
constituents in the ash basin over time is a complex process. In the conceptual fate and
transport model, it was assumed that the entry of constituents into the ash basin is represented
by a constant concentration in the saturated zone of the basin, which is continually flushed by
recharge water infiltrating from above.
At the ash storage area, leachable constituents enter the dissolved phase during transient
infiltration events through the stored ash. Infiltration with constituents in solution moves
downward through the stored ash and underlying, unsaturated soils and finally into groundwater
at the water table. Dissolved phase constituents may incur phase changes also as they migrate
through the stored ash and native soils to the water table. In the conceptual fate and transport
model, it was assumed that the entry of constituents into groundwater beneath the ash storage
area is represented by a constant concentration at the water table beneath the ash storage
area, which is continually flushed by infiltrating recharge from above.
3 COMPUTER MODEL
3.1 Model Selection
The computer code MODFLOW solves the system of equations that quantify the flow of
groundwater in three dimensions (3D). MODFLOW can simulate steady-state and transient
flow, as well as confined and water table conditions. Additional components of groundwater can
be considered, including: pumping wells, recharge, evapotranspiration, rivers, streams, springs,
and lakes. The information assembled in the conceptual site model is translated into its
numerical equivalent from which a solution is generated by MODFLOW.
3.2 Model Description
The specific MODFLOW package chosen for the study is NWT —a Newton formulation of
MODFLOW-2005 that is specifically designed for improving the stability of solutions involving
drying and re -wetting under water table conditions (Niswonger, et al. 2011). The numerical
code selected for the transport model is MT3DMS (Zheng and Wang 1999). MT3DMS is multi -
species 3-dimensional mass transport model that can simulate advection, dispersion/diffusion,
and chemical reaction of COls in groundwater flow systems, and has a package that provides a
link to the MODFLOW codes. The MODFLOW-NWT and MT3DMS input packages used to
M

create the groundwater flow and transport models, and a brief description of their use, are
provided in Table 1.
4 GROUNDWATER FLOW AND TRANSPORT MODEL CONSTRUCTION
The flow and transport model for the study was developed through a multi -step process. First, a
3D model of the site hydrostratigraphy was constructed based on historical site construction
drawings and field data. Once the model domain was determined, a 3D steady-state
groundwater model based on the hydrostratigraphy and the site conceptual model was
produced. Flow parameters, assigned to the numerical grid, were adjusted during the steady-
state flow model calibration process. Once the flow model was calibrated, a transient transport
simulation for the selected COls was developed, and then calibrated by adjusting transport
parameters and source zone concentrations to best match the observed (2015) concentrations
in selected monitoring wells.
Three terrain surface models for Allen were created using geographic information systems (GIS)
software: 1) current existing surface, 2) pre -construction surface without ash and ash basin
dikes, and 3) pre -construction surface with dikes but without ash. An interpolation tool in
ArcGIS 10.3 software was used to generate the terrain surfaces as raster datasets with 20-foot
cells. Each surface was created to cover the extent of the groundwater model domain.
4.1 Model Hydrostratigraphy
The model hydrostratigraphy was developed using historical site construction drawings and
borehole data to construct three-dimensional surfaces representing contacts between
hydrostratigraphic units with properties provided in CSA Tables 11-8 through 11-12 (HDR
2015).
1) Existing Ground Surface
Topographic and bathymetric elevation contours and spot elevations were produced from
surveys conducted in 2014. Since these surveys did not cover the entire model extent,
elevation data extracted as spot elevations from the North Carolina Floodplain Mapping
Program's 2010 LiDAR elevation data were used for the areas surrounding the surveys. At
Allen, simplified elevation contours were digitized along the river channels to depress the
surface a small amount below water level.
2) Pre -construction Surface
Elevation contours of the original ground surface were digitized in CAD from engineering
drawings supplied by Duke Energy. These data were imported into GIS, and georeferenced.
These contours were trimmed to the areas underlying ash basins, dams, dikes and ash storage
areas. The source data used in the existing surface were then replaced by the original surface
data where there was overlap. Elevation data from coal storage areas were removed. The pre -
construction surface was then created using the combination of original surface elevations,
2014 survey elevations, and 2010 LiDAR elevations.
3) Pre -construction Surface with Dikes
Surface models of the ash basin dams and dikes were constructed from crest elevations as
determined from the 2014 survey and slopes given on the engineering drawings. Only the
10

sections of the dams and dikes facing the ash basins were modeled in this way. The 2014
survey data were used for dike/dam crests and outwardly facing surfaces. These surfaces were
merged with the pre -construction surface. These GIS data sets were exported into formats
readable by RockWorks and GMS MODFLOW.
4) 3-D Hydrostratigraphic Grids
The natural materials in the CSA boreholes and existing boreholes were assigned a
hydrostratigraphic layer using the above classification scheme and judgment and the borehole
data entered into RockWorks 16TM for 3-D modeling. In the portions of the area to be modeled
for which borehole data is not available, dummy boreholes were used to extend the model to the
model boundaries. These boreholes were based on the hydrostratigraphic thickness of the
existing boreholes and the elevation of the existing boreholes based on the assumption that the
hydrostratigraphic layers are a subdued replica of the original topography of the site and
geologic judgment.
The grid of the pre -construction ground surface (described above) was used to constrain the
modeling of the natural layers. For gridding the data on a 20 ft x 20 ft grid across the area to be
modeled, a hybrid algorithm was used with inverse distance weighted two (2) and triangulation
weighted one (1) and declustering, smoothing, and densifying subroutines. The declustering
option is used to remove duplicate points and de -cluster clustered points. The option creates a
temporary grid with a z-value assigned based on the closet data point to the midpoint of a voxel.
The smoothing option averages the z-values in a grid based on a filter size. For this modeling,
the z-value is assigned the average of itself and that of the eight nodes immediately surrounding
it. One smoothing pass is made. The densify option adds additional points to the xyz input by
fitting a Delaunay triangulation network to the data and adding the midpoint of each triangle to
the xyz input points. The net result is that the subsequent gridding process uses more control
points and tends to constrain algorithms that may become creative in areas of little control.
Only one densification pass is made. The completed model grids were exported in spreadsheet
format for use in the groundwater flow and transport model.
4.2 GMS MODFLOW Version 10
The conceptual model approach to construct a MODFLOW simulation in GMS MODFLOW
consists of employing GIS tools in a Map module to develop a conceptual model of the site
being modeled. The location of sources/sinks, layer parameters (such as hydraulic
conductivity), and all other data necessary for the simulation can be defined at the conceptual
model level. Once this model is complete, the grid is generated and the conceptual model is
converted to the grid model and all of the cell -by -cell assignments are performed automatically.
The following table presents the sequence of the steps used for the groundwater modeling.
Steps 1 through 6 describe the creation of 3D MODFLOW model.
11

Step 1. Creating raster files for the model layer
3 surface layers (pre -construction, pre -construction with dike, and existing surface including dike and
ash) using GIS and AutoCAD
2 subsurface layers transition TZ and bedrock BR by converting 3D scatter data
Step 2. Creating the Raster Catalog to group the raster layers
Assigning Horizons and materials for each layer
Step 3. Creating horizon surfaces (i.e. TIN) from raster data
Used exiting surface and bedrock rasters
Step 4. Building Solids from the Raster Catalog and TINs
Used raster data for the top and bottom elevations of the solids
Step 5. Creating the conceptual model
Building model boundary, specified head boundary
Defining zones and assigning hydraulic conductivity and recharge rate
Importing observation wells and surface flow data
Step 6. Creating the MODFLOW 3D grid model
Converting the solids to 3D grid model using boundary matching
Mapping the conceptual model to 3D MODFLOW grid
Step 7. Flow model calibration/Sensitivity Analysis
Initializing the MODFLOW model
Steady-state calibration with the trial -and error method
Parameters: hydraulic conductivity and recharge rate
Used observation well and surface flow data
Step 8. Setting the transport model (MT3DMS)
Species
Stress periods
Porosity and dispersion coefficient
Distribution coefficient (Kd) from the lab experiments
Recharge concentrations
Step 9. Performing model simulations
Model scenarios — 1) Existing Conditions, 2) Cap in -place, and 3) Excavation/removal of ash
4.3 Model Domain and Grid
The model domain encompasses the Allen site, including a section of the Catawba River and all
site features relevant to the assessment of groundwater associated with the ash basins. Figure
1 shows the conceptual groundwater flow model and model domain. The model domain
extends beyond the ash management areas to hydrologic boundaries so groundwater flow and
COI transport through the area is accurately simulated without introducing artificial boundary
effects.
The bounding rectangle around the model domain extends 9,000 feet north to south and 6,000
feet east to west and has a grid consisting of 306,802 active cells in ten layers. In plan view, the
Allen model domain is bounded by the following hydrologic features of the site.
• the western shore of the Catawba River (Lake Wylie) to the east;
• the groundwater divide corresponding to the topographic divide to the north along Plant
Allen Road;
• the groundwater divide corresponding to the topographic divide to the east along NC
273/South Pointe Road; and
12

• the groundwater divide corresponding to the topographic divide to the south along
Reese Wilson Road and Bell Post Road.
The domain boundary was developed by manually digitizing the topographic divides using a
base map containing 2-foot Lidar contours. The lower limit of the model domain coincides with
an assumed maximum depth of water yielding fractures in bedrock. This was estimated to be 80
feet below the base of the transition zone across the site upper limit based on a review of boring
logs contained in the CSA (HDR 2015).
There are a total of 10 model layers divided among the identified hydrostratigraphic units to
simulate flow with a vertical flow component. The units are represented by the model layers
listed below:
• Model layers 13 Ash Material
• Model layers 2— - 4 Dike and Ash Storage Material
• Model layer 5 and 6 M1 Saprolite and Alluvium where present
• Model layer 7 M2 Saprolite
• Model layer 8 TZ Transition Zone
• Model layers 9 and 10 Fractured Bedrock
In the groundwater flow model, fractured bedrock was simulated as an equivalent porous
medium. The materials comprising each layer and typical layer thicknesses are shown in the
north -south and east -west cross -sections through the ash basins in Figure 2 and Figure 3.
4.4 Hydraulic Parameters
Horizontal and vertical hydraulic conductivities, which are specific for each hydrostratigraphic
unit, are the primary determinants of groundwater flow for a given configuration of boundary
conditions and sources and sinks, including recharge. Field measurements of these parameters
from CSA Tables 11-8 through 11-12 (HDR 2015) provided guidance for their selection during
the flow model calibration. Values assigned to the model are shown in Table 2.
4.5 Flow Model Boundary Conditions
Boundary conditions for the Allen flow model are constant head. The outer boundary of the
model domain was selected to coincide with physical hydrologic boundaries at rivers and
drainage features, and no flow boundaries at groundwater divides corresponding to topographic
divides (Section 2.5 and Figure 4). At the Catawba River, constant head boundaries
representing the river stage elevation were applied to those layers above fractured bedrock
(Layers 9 and 10) with bottom elevations below the water surface interpolated from
photogrammetric surveys.
It is noted that constant head boundary conditions may not be valid for groundwater extraction
as a corrective action alternative. In this case, the constant head boundary assumption should
be validated by a pump test or other means.
13

4.6 Flow Model Sources and Sinks
Recharge is the only water source considered in the model. . The mean annual recharge in the
Piedmont ranges from 4.0 to 9.7 inches per year (Daniel 2001). Recharge applied in the model
is 5.0 inches per year outside the ash basin and 8.5 inches per year inside the ash basin,
except where the RAB Ash Landfill is located where a rate of zero (0) inches per year was
applied, as shown in Figure 5.
The CSA does not consider any effect that extraction wells may have on groundwater flow at
the site, nor does it identify other sources or sinks (see Section 2.7).
4.7 Flow Model Calibration Targets
The steady-state flow model calibration targets are the 66 static water level measurements
taken in observations made in July 2015. The observation wells included 32 wells screened in
the ash, dikes, and shallow saprolite zones (S/M1/M2), 27 wells screened in the deep transition
zone; and eight (7) wells screened in fractured bedrock. The observation wells in shallow
(M1/M2), deep (TZ), and bedrock (BR) groundwater zones are shown in Figures 6, 7, and 8.
Observations were assigned by layer as shown in Table 3.
4.8 Transport Model Parameters
The calibrated, steady-state flow model was used to apply flow conditions for the transport
model at the active ash basin and the inactive ash basin (HDR Figures 2-2 and 2-4) where the
elevated concentrations of COls were detected during the June/July 2015 sampling event.
Although their approximate dates of operation are known, the sluiced ash loading histories for
these locations are not available. In order to calibrate the transport model to existing conditions,
constant concentration source zones were applied at the ash (model layer 4) in the active and
inactive ash basins starting from the date when the first ash basin was placed in service (i.e.,
1957). The relevant input parameters are the constant boundary concentrations and the linear
sorption coefficient (Kd) for sorptive constituents (including all Cols, except for boron and
sulfate).
Because a portion of the inactive ash basin was covered by the lined RAB Ash Landfill, the
constant concentration in the inactive ash basin at that location was simulated as being covered
and receives no recharge. This is discussed further in Section 4.10.
The conceptual transport model specifies that Cols enter the model from the shallow saturated
source zones in the ash basins. When the measured Kd values are applied in the numerical
model to COls migrating from the source zones, some COls do not reach the downgradient
observation wells where they were observed in June/July 2015 at the end of the simulation
period. The most appropriate method to calibrate the transport model in this case is to lower the
Kd values until an acceptable agreement between measured and modeled concentrations is
achieved. Thus, an effective Kd value results that likely represents the combined result of
intermittent activities over the service life of the ash basin. These may include pond dredging,
dewatering for dike construction, and ash grading and placement. This approach is expected to
produce conservative results, as sorbed constituent mass is released and transported
downgradient.
The Kd values for the Cols were applied as follows:
14

• Antimony: 0.1 ml/g
• Barium: 0.7 ml/g
• Boron: conservative (sorption not modeled)
• Cobalt: 0.1 ml/g
• Sulfate: conservative (sorption not modeled)
• Vanadium: 0.5 ml/g
• Chromium: 0.4 ml/g
• Hexavalent Chromium: 0.5 ml/g
• Selenium: 0.1 ml/g
• Arsenic: 0.8 ml/g
Preliminary results for sorption studies on soil samples obtained during the CSA at Allen
indicate that the approximate minimum Kd for arsenic of native soils in or near the ash basins is
10 ml/gram in the transition zone and 200 ml/gram in the shallow zone (Langley and Oz 2015).
Sorption was considered to be a calibration parameter as discussed above, and in Section 5.3.
The bulk density used in the model is 2.65 grams/cubic centimeter for saprolite, TZ, and
bedrock materials, and 2.12 grams/cubic centimeter for ash and dike materials.
The velocity of COls in groundwater is directly related to the effective porosity of the porous
medium. Effective porosity applied was estimated based on the values reported in the CSA
(Table 11-9 and 11-12). All values applied to the model are shown in Table 4. Dispersivity is a
physical property of the aquifer medium and is normally a fraction of the field scale problem (i.e.,
plume length), commonly 10% (Zheng and Bennett [20021). The dispersivity quantifies the
degree to which mechanical dispersion of COls occurs. Dispersivity values of 80 ft, 8 ft, and 0.8
ft (longitudinal, transverse horizontal, transverse vertical) were applied in this model.
In order to avoid artificial oscillation in the numerical solution to the advection dispersion
equation, the grid Peclet number, or the ratio of grid spacing to longitudinal dispersivity, should
be less than two (Zheng and Bennett [20021). Directly beneath the ash basin system, shallow
groundwater flow is vertical downward. In this case, the grid Peclet number criteria will not be
met due to the relatively small value for vertical dispersivity and the relatively large grid spacing,
or thickness of the model layers at depth. The effect of numerical oscillation on modeled
concentration and mass transport is indeterminate. However, any effect is considered to be
limited as vertical groundwater flow transitions to horizontal over a short distance beneath the
ash basin system.
4.9 Transport Model Boundary Conditions
The transport model boundary conditions have zero concentration where water leaves the
model. Initial concentrations, and concentrations in infiltrating recharge water, are zero. No
background concentration is specified. The inactive and active ash basins are represented by
constant concentration boundary conditions.
4.10 Transport Model Sources and Sinks
The active and inactive ash basins are the sources for COls in the model. During the transport
model calibration and the existing conditions scenario, the sources were modeled as constant
concentration cells in the saturated portions of the ash (model layer 4) of the ash basin (Figure
15

5). Their magnitudes are based on COI measurements in the shallow zone from the June/July
2015 sampling event and are further refined during model calibration, as described in Section
5.3.
The source zone for the inactive ash basin is covered in part by the lined RAB Ash Landfill.
Recharge to this area beneath the landfill was set to zero to represent the effects of the
overlying landfill liner system.
The transport model sinks correspond to the constant head boundaries of the flow model.
Water and COI mass are removed as they enter cells comprising these boundaries.
4.11 Transport Model Calibration Targets
The calibration targets are the measured COI concentrations for the June/July 2015 sampling
event as shown in CSA Tables 7-6 and 10-8 (HDR 2015). Specific calibration targets for the
transport model calibration are discussed in Section 5.3.
5 MODEL CALIBRATION TO CURRENT CONDITIONS
5.1 Flow Model Residual Analysis
The flow model was calibrated to the water level observations obtained during June 2015 in the
shallow, deep, and bedrock wells (Table 3). The water table elevation in the ash basin cells and
selected depressions across the site were also considered as calibration targets. The
observation data from this single point in time were used as a flow model calibration data set.
The locations of the observation wells are provided in Figures 6, 7, and 8. The initial trial -and -
error calibration assumed homogeneous conditions in each model layer. Recharge was also
fixed at reasonable values early in the calibration process, and then refinements were made by
adjusting hydraulic conductivity zones, as shown in Figures 9, 10,11, and 12. The basis for
delineating the zones in this way was to obtain the best local calibration using conductivity
values within the range of measurements from monitor well testing as documented during the
CSA (HDR 2015).
The calibrated flow model parameters are provided in Table 2. Modeled and observed water
levels (post -calibration) are compared in Table 3 and Figure 13. The calibrated flow model is
assumed to represent long term, steady-state flow conditions for the site and the ash basin
system under long-term, average conditions. This assumption should be verified as additional
data are collected from the existing and any additional monitoring wells.
The square root of the average square error (also referred to as the root mean squared error, or
RMS error) of the modeled versus observed water levels for wells gauged in June 2015 is also
provided in Table 3. The model calibration goal is an RMS error less than 10% of the change in
head across the model domain. The ratio of the average RMS error to total measured head
change is the normalized root mean square error (NRMSE). The NRMSE of the calibrated
model is 9.5%.
Contours of hydraulic heads in the calibrated flow model are shown for the shallow groundwater
zone (model layer 6) in Figure 14. Groundwater flow transitions from vertical to primarily
horizontal flow directly beneath the ash basins due to the absence of a dike or fill layer beneath
the ash and above the shallow zone. Groundwater within the shallow, deep, and bedrock zones
16

flows from the west and southwest to the east and discharges to the Catawba River. Locally the
water table gradient is reduced beneath Primary Ponds 1 through 3, and increased beneath the
RAB Ash Landfill and the southeastern portion of the active ash basin. Steep hydraulic
gradients are associated with the North, East and RAB Dikes.
5.2 Transport Model Calibration
For the transport model calibration, the calibration parameters consisted of the constant source
concentrations, porosity and the linear sorption coefficient (Kd) for each COI. These parameters
were adjusted to minimize residual concentrations in target wells. The model assumed an initial
concentration of 0 within the groundwater system for all Cols at the beginning of operations
approximately 58 years ago. A source term matching the pore water concentrations for each
COI was applied within the inactive ash basin, active ash basin and the ash storage areas at the
start of the calibration period. The source concentrations were adjusted to match measured
values in the downgradient monitoring wells that had exceedances of the 2L Standard for each
COI in June 2015. Calibration results comparing measured versus predicted model
concentrations are provided in Table 5 for the modeled COls. Table 5 also shows the calibration
source concentrations in the inactive ash basin, active ash basin and the ash storage areas.
The locations of the monitoring wells are provided in Figures 6, 7, and 8.
These calibration parameters were used in the transport model to simulate the initial (2015)
concentrations in the shallow, deep and bedrock groundwater flow zones of each COI for each
closure simulation. COI
5.3 Advective Travel Times
Particle tracking was performed during model calibration to determine if advective travel times
are reasonable. Particles were placed at wells located near the Catawba River and also near
the western model boundary. The particle tracks are shown in Figure 15 and predicted
advective travel times are provided in Table 6.
5.4 Flow and Transport Model Sensitivity Analysis
Sensitivity model runs were performed to evaluate the parameters with the greatest influence on
the modeled hydraulic heads and COI concentrations when key transport parameters are
varied. Sensitivity of the flow model was considered by varying selected parameters by 20%
above and below their respective calibration values and calculating the NRMSE for comparison
with the calibration value as shown in Table 7. In addition to the flow model sensitivity analysis,
the calibrated transport model parameters, including effective porosity and sorption coefficient
(Kd), were varied by 20% above and below their respective calibration values to determine the
affect on COI transport. The average modeled concentration change relative to the calibrated
concentration of arsenic and boron at monitoring wells, used during transport model calibration,
were calculated to show the transport model sensitivity.
Based on this approach, the flow model was most sensitive to increased and decreased
horizontal hydraulic conductivity of the shallow aquifer, followed by decreased recharge outside
the ash basins, and then decreased recharge within the ash basins. The model was less
sensitive to changing vertical hydraulic conductivity in the shallow and transition zones
(S/M 1 /M2/TZ), as groundwater flow is dominantly horizontal in these hydrostratigraphic layers.
17

Arsenic concentrations were most sensitive to increased recharge in areas outside the ash
basins, followed by Kd and then horizontal hydraulic conductivity of the shallow
hydrostratigraphic layers (S/M1/M2). The concentrations of arsenic were the least sensitive to
changing vertical hydraulic conductivity in the transition zone (TZ) (Table 7).
The Kd relates the adsorbed COI concentration to the concentration of the COI dissolved in
water. Non -reactive, or conservative COIs, which at this site include boron and sulfate, are
assumed to have a Kd of zero and therefore move at advective flow rates (average linear
groundwater velocity). The movement of reactive COIs, such as arsenic and chromium is
retarded by sorption. A decrease of Kd increases the rate of COI transport resulting in increased
concentrations at downgradient monitoring wells by the end of the calibration period (58 years).
An increase of Kd decreases the rate of COI transport resulting in decreased concentrations in
downgradient monitoring wells by the end of the calibration period (58 years) (Table 7).
Boron concentrations were most sensitive to both increased and decreased horizontal hydraulic
conductivity of the shallow hydrostratigraphic layers (S/M1/M2) and increased and decreased
recharge inside the ash basins. The concentrations of boron were the least sensitive to
changing vertical hydraulic conductivity in the transition zone (TZ) (Table 7).
Effective porosity of a porous medium is the porosity that is available for continuous fluid flow
through the material. The effective porosity primarily affects the velocity at which fluid can move
through a material where a smaller value increases fluid velocity and a greater value decreases
fluid velocity. Boron and arsenic concentrations are relatively unaffected by increasing or
decreasing the effective porosity in the transport model sensitivity runs.
Longitudinal dispersivity is an empirical factor quantifying how much contaminants stray away
from a path parallel to the primary direction of groundwater flow, or how much of the
contaminant moves faster than or slower than the average groundwater velocity. Increasing
dispersivity results in increased COI concentrations at the leading edge of the plume as
dissolved COI mass is spread more easily throughout the aquifer when a relatively high
dispersivity value is applied.
6 SIMULATION OF CLOSURE SCENARIOS
The groundwater model, calibrated for flow and constituent fate and transport under existing
conditions, was applied to evaluate four ash basin closure scenarios at Allen: 1) the Existing
Conditions scenario; the 2) ash basin Cap -in -Place scenario; and the 3) Excavation scenario
(ash removal), which comprises a combination of excavation, partial excavation, and capping
over some of the ash basin. Being predictive, these simulations produce flow and transport
results for conditions that are beyond the range of those considered during the calibration.
Thus, the model should be recalibrated and verified over time as new data becomes available in
order to improve its accuracy and reduce its uncertainty.
The model domain developed for existing conditions was applied without modification for the
Existing Conditions and Cap -in -Place scenarios. For the Excavation scenario, the basins were
removed. The flow parameters for this model were identical to the Existing Conditions scenario,
except for the removal of ash related layers, and the same recharge being applied to the ash
basin as the remainder of the site. Similarly for the Hybrid Cap, excavated areas have ash
related layers removed and recharge adjusted.
in

6.1 Existing Conditions
The Existing Conditions scenario consists of modeling each constituent using the calibrated
models for flow and transport under the existing conditions across the site for 250 years into the
future. This length of time is sufficient in allowing near -steady-state concentrations to be
reached across the site and at the compliance boundary. Concentrations can only increase
initially for this scenario with source concentrations being held at their constant value the entire
simulated time period. Thereafter, the concentrations and mass flux of dissolved constituents at
the compliance boundary remain constant. This scenario represents the worst case in terms of
groundwater concentrations on and offsite, and COls discharging to the Catawba River.
The time to achieve a steady-state concentration plume depends on the source zone location
relative to the compliance boundary and its loading history. Source zones close to the
compliance boundary will cause steady-state conditions to be reached relatively faster. The
time to steady-state concentration is also dependent on the sorptive characteristics of each COI.
Sorptive COls will be transient for a longer time period as their peak breakthrough concentration
travels at a rate that is less than the groundwater pore velocity. Lower effective porosity will
result in shorter times to achieve steady-state for sorptive and non-sorptive COls.
Concentration contours and concentration breakthrough curves are all referenced to a time zero
that represents the time the closure action was implemented, which for the purposes of
modeling is assumed to be 2016. The scenario models COI concentrations forward from the
end of the 58 year simulation and represents 2015 as the initial concentrations.
Figures 16 and 17 show predicted antimony concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Existing Conditions scenario, antimony concentrations increase at downgradient
wells over the modeled time period of 250 years after 2015. Antimony concentrations remain
elevated above the Interim Maximum Allowable Concentration (IMAC) for antimony, which is 1
pg/l, at all wells under the Existing Conditions scenario at the compliance boundary. Figures 18
through 20 show the shallow, deep and fractured bedrock zones in 2015 and Figures 21
through 23 show them in 2115, or in 100 years. Antimony exits the model with groundwater
discharging at the Catawba River to the east of the site in all zones in 2015 and 2115. In 2115,
the shallow groundwater zone has the highest concentrations.
Figures 30 and 31 show predicted arsenic concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curves
show that under the Existing Conditions scenario, arsenic concentrations in monitoring well AB-
22S increase over time, but remain below the 2L Standard of 10 pg/I and nearly reach steady-
state conditions near the end of the modeling period. Monitoring well GWA-6S arsenic levels
continue increasing through the model period with concentrations above the 2L Standard.
Figures 32 though 34 and Figures 35 through 37 show the shallow, deep and fractured bedrock
zones in 2015 and 2115, respectively. Under existing conditions, arsenic is above the 2L
Standard at the compliance boundary downgradient of the inactive ash landfill in all model
layers and below the 2L Standard downgradient of the active ash basin.
Figures 44 and 45 shows predicted barium concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curves
show that under the Existing Conditions scenario, barium concentrations remain below the 2L
19

Standard, which is 700 pg/I, in monitoring well AB-22S and AB-26S and approach steady-state
conditions near the end of the modeling period. Figures 46 through 48 and Figures 49 through
51 show the shallow, deep and fractured bedrock zones in 2015 and 2115, respectively.
Barium is not above the 2L Standard at the compliance boundary in 2015, but is predicted to
approach the 2L Standard in 2115 within the shallow zone at the compliance boundary
downgradient of the retired ash landfill.
Figures 58 through 61 show predicted boron concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curves
show that under the Existing Conditions scenario, boron concentrations remain elevated above
the 2L Standard, which is 700 pg/l, and concentrations reach steady state for the entire
modeling period in wells AB-22D, AB-26S, GWA-4S and GWA-5BR. Figures 62 through 64 and
Figures 65 through 67 show the shallow, deep and fractured bedrock zones in 2015 and 2115,
respectively. Barium is above the 2L Standard at the compliance boundary in 2015, and is
predicted to remain above 2L Standard in 2115 downgradient of the retired ash landfill and the
active ash basin.
Figures 74 and 75 show predicted chromium concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curves
show that under the Existing Conditions scenario, chromium concentrations remain elevated
above the 2L Standard, which is 10 pg/l, for the entire modeling period in monitoring well AB-6R
and exceeds the 2L Standard at monitoring well AB-26D by 2125. Figures 76 through 78 and
Figures 79 through 81 show the shallow, deep and fractured bedrock zones in 2015 and 2115,
respectively. Chromium is above the 2L Standard at the compliance boundary in 2015, and is
predicted to remain above 2L Standard in 2115 downgradient of the retired ash landfill and the
active ash basin.
Figures 88 through 91 show predicted hexavalent chromium concentrations versus time at
downgradient monitoring wells under all three model scenarios. The concentration versus time
curves show that under the Existing Conditions scenario, hexavalent chromium concentrations
remain elevated above the North Carolina Department of Health and Human Services (DHHS)
health screening level (HSL), which is 0.07 pg/l, and increase over time. Figures 92 through 94
and Figures 95 through 97 show the predicted hexavalent chromium concentrations in the
shallow, deep and fractured bedrock zones in 2015 and 2115, respectively. Hexavalent
chromium is above the DHHS HSL at the compliance boundary in 2015, and is predicted to
remain above DHHS HSL in 2115 downgradient of the retired ash landfill and the active ash
basin.
Figures 104 through 107 show predicted cobalt concentrations versus time at downgradient
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Existing Conditions scenario, cobalt concentrations remain elevated above the
IMAC, which is 1 pg/I, and increase over time. Figures 108 through 110 and Figures 111
through 113 show the predicted cobalt concentrations in the shallow, deep and fractured
bedrock zones in 2015 and 2115, respectively. Cobalt is above the IMAC at the compliance
boundary in 2015, and is predicted to remain above the IMAC in 2115 downgradient of the
retired ash landfill and the active ash basin.
Figures 120 and 121 shows predicted selenium concentrations versus time at monitoring wells
GWA-6S and AB-22S, respectively, under all three model scenarios. Monitor Well GWA-6S is
20

downgradient of the inactive ash basin and shows elevated selenium above the 21 Standard of
20 ug/L. AB-22S is downgradient of the active ash basin and is not above the 2L Standard.
Figures 122 through 124 and Figures 125 through 127 show the predicted selenium
concentrations in the shallow, deep and fractured bedrock zones in 2015 and 2115,
respectively. Selenium is above the 2L Standard at the compliance boundary in 2015
downgradient of the retired ash landfill in the shallow and deep groundwater zones, and is
predicted to remain above the 2L Standard in 2115 downgradient of the retired ash landfill.
Figures 134 and 135 show predicted sulfate concentrations versus time at downgradient
monitoring wells under all three model scenarios. In well AB-33S sulfate concentrations exceed
the 2L Standard of 250,000 pg/I about 10 years after initial use of the inactive ash basin.
Concentration of sulfate in well GWA-6S does not exceed the 2L Standard. Figures 136 through
138 and Figures 139 through 141 show the predicted sulfate concentrations in the shallow,
deep and fractured bedrock zones in 2015 and 2115, respectively. Sulfate is above the 2L
Standard at the compliance boundary in 2015 downgradient of the retired ash landfill in the
shallow and deep groundwater zones, and is predicted to remain above the 2L Standard in
2115 downgradient of the retired ash landfill.
Figures 148 through 151 show predicted vanadium concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Existing Conditions scenario, vanadium concentrations increase over the course
of the model time period. Concentrations generally continue to increase over time without
reaching a steady-state. Vanadium concentrations at all monitoring wells exceed the IMAC,
which is 0.3 pg/I. Figures 152 through 154 and Figures 155 through 157 show the predicted
vanadium concentrations in the shallow, deep and fractured bedrock zones in 2015 and 2115,
respectively. Vanadium is above the IMAC at the compliance boundary in 2015 downgradient
of the retired ash landfill and the active ash basin in all groundwater zones, and is predicted to
remain above the IMAC in 2115 downgradient at the compliance boundary.
6.2 Cap -in -Place
The Cap -in -Place scenario simulates the effects of covering the ash basins at the beginning of
the predictive simulation with an impermeable cap. In the model, recharge and source zone
concentrations at the ash basins are set to zero. Groundwater flow is affected by this scenario
as the water table is lowered and groundwater velocities may be reduced beneath the capped
areas. Near the center of the inactive ash basin, the water table is lowered by approximately 26
ft relative to the level simulated under the Existing Conditions scenario. In the active ash
basins, the difference in water level is approximately 36 ft. In the model, non-sorptive COls will
move downgradient at the pore velocity of groundwater and will be displaced by the passage of
a single pore water volume, while sorptive COI's migration in groundwater is retarded because
of sorption with soils/rocks. The model uses the predicted concentration from the 2015
calibration as the initial concentration at the start of the model scenario.
Figures 16 and 17 show predicted antimony concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Cap -in -Place scenario, antimony concentrations decrease and remain above the
IMAC throughout the modeling period. Figures 24 through 26 show the predicted antimony
concentrations under this scenario in the shallow, deep and fractured bedrock zones,
21

respectively, at 100 years post closure implementation. Antimony remains above the IMAC at
the compliance boundary at the Catawba River downgradient of the active and inactive ash
basins.
Figures 30 and 31 show predicted arsenic concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curves
show that under the Cap -in -Place scenario, arsenic concentrations begin to decrease upon
implementation, but remain above the 2L Standard through the modeling period at monitoring
well AB-22S. For monitoring well GWA-6S, this area of the model goes dry due to lack of
recharge. Figures 38 through 40 show the shallow, deep and fractured bedrock zones in 2115,
or 100 years post closure implementation. Arsenic remains above the 2L Standard at the
compliance boundary at the Catawba River downgradient of the inactive ash basin.
Figures 44 and 45 shows predicted barium concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curve
shows that under the Cap -in -Place scenario, barium concentrations decrease upon
implementation and decrease slowly throughout the modeling period and remain below the 2L
Standard in the downgradient monitoring wells throughout the 250 year modeling period.
Figures 52 through 54 show the shallow, deep and fractured bedrock zones in 2115, or 100
years post closure implementation. Barium remains below the 2L Standard at the compliance
boundary at the Catawba River downgradient of the inactive ash basin and active ash basin.
Figures 58 through 61 show predicted boron concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curves
show that under the Cap -in -Place scenario, boron concentrations in all wells decrease sharply
immediately after implementation. Figures 68 through 70 show the shallow, deep and fractured
bedrock zones in 2115, or 100 years post closure implementation. Boron is below the 2L
Standard at the compliance boundary at the Catawba River downgradient of the inactive ash
basin and active ash basin.
Figures 74 and 75 show predicted chromium concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curve
at AB-26D shows that under the Cap -in -Place scenario, chromium concentrations increase
upon implementation, but remain below the 2L Standard throughout the modeling period. At
well AB-6R, chromium concentrations decrease, but remain above the 2L Standard until 2225,
or 210 years after closure implementation. Figures 82 through 84 show the shallow, deep and
fractured bedrock zones in 2115, 100 years after closure implementation. Chromium is above
the 2L Standard at the compliance boundary at the Catawba River downgradient of the inactive
ash basin and active ash basin in the shallow, deep, and bedrock zones.
Figures 88 through 91 show predicted hexavalent chromium concentrations versus time at
downgradient monitoring wells under all three model scenarios. The concentration versus time
curves show that under the Cap -in -Place scenario, hexavalent chromium concentrations
increase after implementation and continue to increase (AB-91D) or remain steady (AB-31S &
GWA-31D) during the model period. Figures 98 through 100 show the shallow, deep and
fractured bedrock zones under this scenario in 2115, 100 years after closure implementation.
Hexavalent chromium remains above the DHHS HSL at the compliance boundary at the
Catawba River.
18JOIJ

Figures 104 through 107 show predicted cobalt concentrations versus time at downgradient
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Cap -in -Place scenario, cobalt concentrations show an overall decrease over
time, but remain above the IMAC. Figures 114 through 116 show the shallow, deep and
fractured bedrock zones under this scenario in 2115, 100 years after closure implementation.
Under the Cap -in -Place scenario, cobalt remains above the IMAC at the compliance boundary
at the Catawba River.
Figures 120 and 121 shows predicted selenium concentrations versus time at monitoring wells
GWA-6S and AB-22S, respectively, under all three model scenarios. The concentration versus
time curves show that under the Cap -in -Place scenario, selenium concentrations decrease
below the 2L Standard following closure implementation. Figures 128 through 130 show the
shallow, deep and fractured bedrock zones under this scenario in 2115. Selenium is associated
with the inactive ash storage basin and is highest in the shallow layer. Under the Cap -in -Place
scenario, selenium remains above the 2L Standard at the compliance boundary at the Catawba
River in the deep and bedrock zones, but is above the 2L Standard within the shallow zone.
Figures 134 and 135 show predicted sulfate concentrations versus time at downgradient
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Cap -in -Place scenario, the monitor wells downgradient of the active ash basin go
dry due to reduced recharge to the groundwater system. Figures 142 through 144 show the
shallow, deep and fractured bedrock zones under this scenario in 2115, 100 years after closure
implementation. Sulfate concentrations under the Cap -in -Place scenario fall below the 2L
Standard at the compliance boundary at the Catawba River downgradient of the inactive ash
basin and active ash basin.
Figures 148 through 151 show predicted vanadium concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Cap -in -Place scenario, vanadium concentrations increase over time and then
remain fairly constant. Figures 158 through 160 show the shallow, deep and fractured bedrock
zones under this scenario in 2115, 100 years after closure implementation. Vanadium
concentrations under the Cap -in -Place scenario remain above the IMAC at the compliance
boundary at the Catawba River downgradient of the inactive ash basin and active ash basin.
6.3 Excavation
In the Excavation scenario, all ash from the ash basins and ash storage areas is removed and
transported offsite. In the model, the constant concentration sources and all ash above and
below the water table are removed. Unlike the Cap -in -Place scenario, this scenario assumes
recharge rates become equal to rates surrounding the ash basins, except for the RAB Ash
Landfill where the recharge rate remains zero (0) inches per year in all scenarios (see Figure 5).
Starting from the time that excavation is complete, COls already present in the groundwater
continue to migrate downgradient as clean water infiltrates from ground surface and recharges
the aquifer at the water table. The COls are flushed from the saturated zone beneath the
source areas. COI migration is retarded relative to the pore water velocity as sorptive COls
adsorb to the soil/rock surfaces. The model uses the predicted concentration from the 2015
calibration as the initial concentration.
23

Figures 16 and 17 show predicted antimony concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Excavation scenario, antimony concentrations decrease and fall below the IMAC
toward the end of the modeling period. Figures 27 through 29 show the predicted antimony
concentrations under this scenario in the shallow, deep and fractured bedrock zones,
respectively, at 100 years post closure implementation. Antimony remains above the IMAC at
the compliance boundary at the Catawba River.
Figures 30 and 31 show predicted arsenic concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curves
show that under the Excavation scenario, arsenic concentrations decrease upon implementation
and fall below the 2L Standard at monitoring well GWA-6S near the end of the simulation.
Figures 41 through 43 show the shallow, deep and fractured bedrock zones in 2115 or 100
years post closure implementation. Arsenic remains above the 2L Standard at the compliance
boundary at the Catawba River.
Figures 44 and 45 shows predicted barium concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curve
shows that under the Excavation scenario, barium concentrations decrease upon
implementation and decrease slowly throughout the modeling period and remain below the 2L
Standard in the downgradient monitoring wells throughout the modeling period. Figures 55
through 57 show the shallow, deep and fractured bedrock zones in 2115, or 100 years post
closure implementation. Barium remains below the 2L Standard at the compliance boundary at
the Catawba River downgradient of the inactive ash basin and active ash basin.
Figures 58 through 61 show predicted boron concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curves
show that under the Excavation scenario, boron concentrations in all wells decrease sharply
immediately after implementation. Figures 71 through 73 show the shallow, deep and fractured
bedrock zones in 2115, or 100 years post closure implementation. Boron is below the 2L
Standard at the compliance boundary at the Catawba River downgradient of the inactive ash
basin and active ash basin.
Figures 74 and 75 show predicted chromium concentrations versus time at representative
downgradient monitoring wells under all three scenarios. The concentration versus time curve
at AB-26D shows that under the Excavation scenario, chromium concentrations increase upon
implementation, but remain below the 2L Standard throughout the modeling period. At well AB-
6R, chromium concentrations decrease, but remain above the 2L Standard until 2075, or 60
years post implementation. Figures 85 through 87 show the shallow, deep and fractured
bedrock zones in 2115, 100 years after closure implementation. Chromium is below the 2L
Standard at the compliance boundary at the Catawba River downgradient of the inactive ash
basin and active ash basin in the deep and bedrock groundwater zones and above the 2L
Standard in the shallow groundwater zone.
Figures 88 through 91 show predicted hexavalent chromium concentrations versus time at
downgradient monitoring wells under all three model scenarios. The concentration versus time
curves show that under the Excavation scenario hexavalent chromium concentrations increases
after implementation and slowly decreases during the model period. Figures 101 through 103
show the shallow, deep and fractured bedrock zones under this scenario in 2115, 100 years
24

after closure implementation. Hexavalent chromium remains above the DHHS HSL at the
compliance boundary at the Catawba River.
Figures 104 through 107 show predicted cobalt concentrations versus time at downgradient
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Excavation scenario, cobalt concentrations show an overall decrease over time
and fall below the IMAC in three out of four monitoring wells. Figures 117 through 119 show the
shallow, deep and fractured bedrock zones under this scenario in 2115, 100 years after closure
implementation. Cobalt remains above the IMAC at the compliance boundary at the Catawba
River.
Figures 120 and 121 shows predicted selenium concentrations versus time at monitoring wells
GWA-6S and AB-22S, respectively, under all three model scenarios. The concentration versus
time curves show that under the Excavation scenario, selenium concentrations decrease below
the 2L Standard following closure implementation. Figures 131 through 133 show the shallow,
deep and fractured bedrock zones under this scenario in 2115. Under the Excavation scenario,
selenium is below the 2L Standard at the compliance boundary at the Catawba River in all
groundwater zones.
Figures 134 and 135 show predicted sulfate concentrations versus time at downgradient
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Excavation scenario, sulfate concentrations decrease to zero shortly after
implementation. Figures 145 through 147 show the shallow, deep and fractured bedrock zones
under this scenario in 2115, 100 years after closure implementation. Sulfate concentrations
under the Excavation scenario fall below the 2L Standard at the compliance boundary at the
Catawba River downgradient of the inactive ash basin and active ash basin.
Figures 148 through 151 show predicted vanadium concentrations versus time at representative
monitoring wells under all three model scenarios. The concentration versus time curves show
that under the Excavation scenario, vanadium concentrations increase over time and begin to
decrease towards the end of the model scenario. Figures 161 through 163 show the shallow,
deep and fractured bedrock zones under this scenario in 2115, 100 years after closure
implementation. Vanadium concentrations under the Excavation scenario remain above the
IMAC at the compliance boundary at the Catawba River downgradient of the inactive ash basin
and active ash basin.
7 SUMMARY AND CONCLUSIONS
7.1 Model Assumptions and Limitations
The model assumptions include the following:
• The steady-state flow model was calibrated to hydraulic heads measured at observation
wells in June 2015 and considered the ash basin water level. The model is not calibrated
to transient water levels over time, recharge, or river flow. A steady-state calibration
does not consider groundwater storage and does not calibrate the groundwater flux into
adjacent surface water bodies.
• MODFLOW simulates flow through porous media and groundwater flow in the bedrock
groundwater zone is via fractures in the bedrock. A single domain MODFLOW modeling
25

approach for simulating flow in the primary porous groundwater zones and bedrock was
used for contaminant transport at the Allen site.
• The model was calibrated by adjusting the constant source concentrations at the ash
basins and ash storage area to reasonably match 2015 COI concentrations in
groundwater.
• For the purposes of numerical modeling and comparing closure scenarios, it is assumed
that the selected closure scenario will be completed in 2016.
• Predictive simulations were performed and steady-state flow conditions were assumed
from the time that the ash basins and ash storage area were placed in service through
the current time until the end of the predictive simulations (2265).
• COI source zone concentrations at the inactive and active ash basins and ash storage
area were applied uniformly within each source area and assumed to be constant with
respect to time for transport model calibration.
• The uncertainty in model parameters and predictions has not been quantified; therefore,
the error in the model predictions is not known. It is assumed the model results are
suitable for a relative comparison of closure scenario options.
• Model results along certain boundaries are impacted by the cell saturation level resulting
in some numerical spikes in the calculations that do not represent concentrations in
surrounding cells. These numerical spikes are localized calculations and do not impact
the overall model results.
• Since the Catawba River is modeled as a constant head boundary in the numerical
model, it will not be possible to assess the effects of pumping wells or other groundwater
sinks that are near the river.
• The model does not account for varying geochemical conditions such as pH and redox
potential that could affect COI mobility and change modeling results. As identified by
HDR, site -specific geochemistry and geochemical modeling will be considered in CAP 2.
7.2 Model Predictions
The model predictions are summarized as follows:
• The model predicts that all of the closure scenarios will reduce concentrations of
antimony. The model predicted the Excavation scenario to be the most effective at
reducing antimony concentrations. Under all scenarios, the model predicts
concentrations of antimony will exceed the IMAC at the compliance boundary.
Concentrations of antimony are greater in shallow portions of the groundwater system
than the deep and bedrock groundwater system.
• The model predicts that all of the closure scenarios will reduce concentrations of arsenic.
The model predicted the Cap -In -Place scenario to be the most effective at reducing
arsenic concentrations. Under all scenarios, the model predicts concentrations of
arsenic will exceed the 2L Standard at the compliance boundary. Concentrations of
arsenic are greater in shallow portions of the groundwater system than the deep and
bedrock groundwater system.
W

• The model predicts that barium is below the 2L Standard at the compliance boundary
and that the closure scenarios will further reduce concentrations of barium in all
groundwater zones.
• The model predicts rapid reduction of boron under the ash basin closure scenarios. The
Excavation scenario reduces boron concentrations quicker than the Cap -in -Place option
with reduction of boron concentrations below the 2L Standard across the entire model
domain by 2115.
• The model predicts that all of the closure scenarios will reduce concentrations of
chromium. The model predicted the Excavation scenario to be the most effective at
reducing chromium concentrations. Under all scenarios, the model predicts
concentrations of chromium will exceed the 2L Standard at the compliance boundary in
all groundwater zone. Concentrations of chromium are greater in shallow portions of the
groundwater system than the deep and bedrock groundwater system.
• The model predicts that all of the closure scenarios will reduce concentrations of
hexavalent chromium. The model predicted the Excavation scenario to be the most
effective at reducing hexavalent chromium concentrations. Under all scenarios, the
model predicts concentrations of hexavalent chromium will exceed the DHHS HSL at the
compliance boundary in all groundwater zones. Concentrations of hexavalent chromium
are greater in shallow portions of the groundwater system than the deep and bedrock
groundwater system.
• The model predicts that both closure scenarios reduce selenium concentrations below
the 2L Standard at the compliance boundary in a short period of time. The Excavation
scenario was predicted by the model to be most effective at reducing selenium
concentrations.
• The model predicts that all of the closure scenarios will reduce concentrations of cobalt.
The model predicted the Excavation scenario to be the most effective at reducing cobalt
concentrations. Under all scenarios, the model predicts concentrations of cobalt will
exceed the IMAC at the compliance boundary in all groundwater zones. Concentrations
of cobalt are greater in deeper portions of the groundwater system than the shallow
system over time as the plume moves downward.
• The model predicts that the closure scenarios will slightly reduce concentrations of
vanadium and that the IMAC will be exceeded at the compliance boundary in all
groundwater zones. The Excavation scenario is predicted by the model to be most
effective at reducing vanadium concentrations. Vanadium concentrations are greater in
shallow portions of the groundwater system than in the deep or bedrock zones.
• Among the COls, sulfate, and boron are similar in that both are considered conservative;
that is, neither has a strong affinity to attenuate nor adsorb to soil/rock surfaces. As a
result, the model predicts similar behavior for both of these COls, and other COls with
low sorption coefficients (Kd)—rapid and nearly complete reduction predicted under all
closure scenarios, with the Excavation scenario proving the most effective.
MA

8 REFERENCES
Daniel, C.C., III, 2001, Estimating ground -water recharge in the North Carolina Piedmont for
land use planning [abs.], in 2001 Abstracts with Programs, 50th Annual Meeting,
Southeastern Section, April 5-6, 2001: Raleigh, N.C., The Geological Society of
America, v. 33, no. 2, p. A-80.
Haven, W.T. Introduction to the North Carolina Groundwater Recharge Map -Groundwater
Circular Number 19, North Carolina Department of Environment and Natural Resources
Division of Water Quality, Groundwater Section.
HDR. Comprehensive Site Assessment Report, ALSS Steam Station Ash Basin, August 2015.
Langley, W.G. and Oz, S. Soil Sorption Evaluation for ALSS Steam Station, UNC-Charlotte, in
preparation.
LeGrand, H. E. 2004. A Master Conceptual Model for Hydrogeological Site Characterization in
the Piedmont and Mountain Region of North Carolina, A Guidance Manual, North
Carolina Department of Environment and Natural Resources Division of Water Quality,
Groundwater Section.
Niswonger, R.G., Panday, S., and Ibaraki, M. 2011. MODFLOW-NWT, A Newton formulation for
MODFLOW-2005: U.S. Geological Survey Techniques and Methods 6-A37, 44 p.
Zheng, C. and Bennett, G. 2002. Applied Contaminant Transport Modeling, Second Edition,
Wiley Interscience.
Zheng, C. and Wang, P. 1999. MT3DMS, A modular three-dimensional multi -species transport
model for simulation of advection, dispersion and chemical reactions of contaminants in
groundwater systems, Documentation and Users Guide, U.S. Army Engineer Research
and Development Center Contract Report SERDP-99-1, Vicksburg, MS, 202 p.
W

Table 1. MODFLOW and MT3DMS Input Packages Utilized
MODFLOW Input Package
Description
Name (NAM)
Contains the names of the input and output files used in the
model simulation and controls the active model program
Basic (BAS)
Specifies input packages used, model discretization, number of
model stress periods, initial heads and active cells
Contains finite -difference grid information, including the number
Discretization (DIS)
and spacing of rows and columns, number of layers in the grid,
top and bottom model layer elevations and number of stress
periods
Specified Head and
Specifies a head and/or a concentration that remains constant
Concentration (CHD)
throughout the simulation
Drain (DRN)
Acts as a "drain" to remove water from the groundwater system.
Simulates drainage areas within the model
Recharge (RCH)
Simulates areal distribution of recharge to the
groundwater system
Newton Solver (NWT)
Contains input values and the Newton and matrix
solver options
Upstream Weighting (UPW)
Replaces the LPF and/or BCF packages and contains the input
required for internal flow calculations
Flow Transfer Link File (LMT)
Used by MTDMS to obtain the location, type, and flow rates of
all sources and sinks simulated in the flow model
MT3DMS Input Package
Description
Flow Transfer Link File (FTL)
Reads the LMT file produced by MODFLOW
Basic Transport Package (BTN)
Reads the MODFLOW data used for transport simulations and
contains transport options and parameters
Advection (ADV)
Reads and solves the selected advection term
Dispersion (DSP)
Reads and solves the dispersion using the explicit finite -
difference formulation
Source and Sink Mixing (SSM)
Reads and solves the concentration change due to sink/source
mixing using the explicit finite -difference formulation
Chemical Reaction (RCT)
Reads and solves the concentration change due to chemical
reactions using the explicit finite -difference formulation
Generalized Conjugate Gradient
Solves the matrix equations resulting from the implicit solution of
(GCG) Solver
the transport equation

Table 2. Model Hydraulic Conductivity
Model
Layer
Hydrogeologic
Unit
Measured ,
Value Range
Calibrated Model Value
Horizontal
Hydraulic
Conductivity
(feet/day)
Horizontal Hydraulic
Conductivity (feet/day)
Vertical Hydraulic
Conductivity (feet/day)
1 - 4
Ash
0.652-19.843
2
0.37
2-4
Dike
0.0074 —0.179
0.004 — 0.008
0.004 — 0.007
5-6
M1-Saprolite
0.210-12.760
S-1
0.70
0.020
S-7
3.98
0.398
S-13
2.33
0.233
S-14
2.07
0.100
S-16
2.70
0.270
S-22
1.00
0.020
S-25
1.50
0.020
7
M2-Saprolite
0.082-3.40
S-5
3.13
0.313
S-7
3.98
0.398
S-10
0.27
0.027
S-12
0.15
0.015
S-13
2.33
0.233
S-14
2.07
0.100
S-16
2.70
0.270
8
TZ
0.156-9.921
S-14
2.07
0.100
S-19
2.80
0.100
S-21
5.00
0.100
9 - 10
BR
0.0145-0.116
S-20
0.01
0.001
S-23
0.1
0.001
S-24
0.001
0.001
'Range = geometric mean +/- one standard deviation (see HDR Tables 11-10)

Table 3. Observed vs. Predicted Hydraulic Head (ft MSL)
Well Name
Model Layer
Observed
Hydraulic
Head (feet)
Modeled
Hydraulic Head
(feet)
Sq. Error
AB-21 S
2
635.6
634.2
2.0
AB-21 SL
2
635.9
634.2
2.9
AB-24S
2
636.8
627.4
88.4
AB-24SL
2
637.1
627.5
93.7
AB-25S
2
639.9
619.8
403.7
AB-25SL
2
637.0
619.9
294.3
AB-27S
2
638.8
616.7
488.7
AB-28S
2
641.0
625.3
247.3
AB-29S
2
611.1
607.0
16.4
AB-29SL
2
611.4
607.1
18.3
AB-30S
3
617.9
617.1
0.5
AB-39S
3
619.7
617.1
6.6
AB-20S
6
636.9
636.7
0.1
AB-22S
6
595.0
595.7
0.5
AB-23S
6
636.3
629.3
49.0
AB-26S
6
582.1
591.8
96.0
AB-32S
6
582.7
577.2
30.6
AB-33S
6
600.4
598.8
2.7
AB-34S
6
612.7
615.2
6.5
AB-35S
6
619.8
622.5
7.3
AB-36S
6
620.2
628.6
70.7
AB-37S
6
621.1
630.7
91.4
AB-38S
6
624.7
625.0
0.1
GWA-14S
6
627.7
631.6
15.8
GWA-15S
6
625.8
631.6
33.3
GWA-1 S
6
615.2
607.5
60.2
GWA-2S
6
570.5
579.1
73.9
GWA-3S
6
571.5
582.5
121.1
GWA-4S
6
571.7
573.6
3.7
GWA-5S
6
567.2
570.4
10.3
GWA-6S
6
597.3
601.9
21.5
GWA-9S
6
635.7
636.9
1.4
AB-20D
8
636.4
636.6
0.0
AB-21 D
8
635.7
631.8
15.5
AB-22D
8
599.0
593.7
28.7
AB-24D
8
634.7
625.4
85.3
AB-26D
8
583.6
589.7
36.6

Table 3. Observed vs. Predicted Hydraulic Head (ft MSL) (cont.)
Well Name
Model Layer
Observed
Hydraulic
Head (feet)
Modeled
Hydraulic Head
(feet)
Sq. Error
AB-27D
8
617.2
606.4
116.6
AB-28D
8
629.3
618.1
125.0
AB-29D
8
612.7
605.9
46.4
AB-30D
8
619.5
617.3
4.8
AB-31 D
8
578.9
578.6
0.1
AB-31 S
8
577.9
578.6
0.5
AB-32D
8
577.0
576.1
0.7
AB-33D
8
594.0
598.2
18.3
AB-34D
8
611.7
615.5
13.9
AB-35D
8
620.5
622.6
4.4
AB-36D
8
620.9
628.6
58.5
AB-37D
8
622.7
630.7
64.0
AB-38D
8
624.3
625.0
0.5
AB-39D
8
619.7
615.7
16.4
GWA-14D
8
626.0
631.5
30.0
GWA-15D
8
625.9
631.5
32.0
GWA-1 D
8
614.7
605.4
87.1
GWA-21D
8
573.3
578.4
26.0
GWA-31D
8
573.8
579.8
35.4
GWA-41D
8
570.8
572.0
1.3
GWA-51D
8
571.2
568.7
6.5
GWA-61D
8
586.7
602.1
236.5
GWA-91D
8
636.7
636.7
0.0
AB-21 BR
10
635.7
631.8
15.3
AB-35BR
10
620.6
622.6
3.9
GWA-1 BR
10
614.3
608.4
34.0
GWA-3BR
10
573.7
579.8
36.8
GWA-5BR
10
562.4
571.1
75.9
GWA-6BR
10
588.6
595.3
45.8
Max 641.0 Sum s.e 3661.7
Min 562.4 No. of wells 66
Max -Min 78.6 Sgrt(Avg s.e.) 7.45
NRMSE 0.095

Table 4. Model Effective Porosity
Model
Layer
Hydrogeologic
Unit
Effective Porosity
1-3
Ash and Dike Materials
0.14
4
Dike Materials
0.10
5-6
M1 — Saprolite and
Alluvium
0.12
7
M2 — Saprolite
0.20
8
Transition Zone
0.01
9 — 10
Bedrock
0.005

Table 5. Transport Model Calibration Results
COI
Monitoring
Well
Measured Concentration
(pg/L)
Predicted Concentration
(pg/L)
Inactive Ash Basin Constant Concentration = 15 pg/L
Ash Storage / Landfill Constant Concentration = 25 pg/L
Ash Ponds Constant Concentration = 10 pg/L
Active Ash Basin Constant Concentration = 15 pg/L
Sorption coefficient [Kd] = 0.1 mL/g
Antimony
AB-24D
1.30
0.80
AB-26D
2.70
3.29
AB-31 D
6.00
5.95
GWA-14D
1.60
0.00
AB-23BRU
1.10
0.53
Inactive Ash Basin Constant Concentration = 700 pg/L
Ash Storage / Landfill Constant Concentration = 700 pg/L
Ash Ponds Constant Concentration = 10 pg/L
Active Ash Basin Constant Concentration = 10 pg/L
Sorption coefficient [Kd] = 0.8 mL/g
Arsenic
AB-36S
369.00
359.22
GWA-6S
193.00
54.10
AB-22S
0.19
4.37
AB-26S
0.16
1.39
AB-20D
1.70
0.02
AB-21 D
1.20
0.01
Inactive Ash Basin Constant Concentration = 1000 pg/L
Ash Storage / Landfill Constant Concentration = 1800 pg/L
Ash Ponds Constant Concentration = 600 pg/L
Active Ash Basin Constant Concentration = 200 pg/L
Barium
Sorption coefficient [Kd] = 0.7 mUg
AB-22S
64.00
93.92
AB-26S
100.00
104.26
AB-36S
990.00
977.62
Inactive Ash Basin Constant Concentration = 2600 pg/L
Ash Storage / Landfill Constant Concentration = 1800 pg/L
Ash Ponds Constant Concentration = 600 pg/L
Active Ash Basin Constant Concentration = 1800 pg/L
Boron
Sorption coefficient [Kd] = No Sorption
AB-31 S
1,800
1,564
GWA-4S
1,700
1,332
AB-26S
900
1,346
GWA-6S
1,400
448

Table 5. Transport Model Calibration Results (cont.)
COI
Monitoring
Well
Measured Concentration
(Ng/L)
Predicted Concentration
(Ng/L)
AB-22D
1,400
1,411
Boron (cont.)
AB-27D
1,500
1,076
GWA-5BR
750
910
Inactive Ash Basin Constant Concentration = 30 pg/L
Ash Storage / Landfill Constant Concentration = 20 pg/L
Ash Ponds Constant Concentration = 32 pg/L
Active Ash Basin Constant Concentration = 32 pg/L
Sorption coefficient [Kd] = 0.4 mL/g
AB-6R
15.9
16.8
Chromium
AB-5
12.5
0.0
AB-21 D
13.9
0.7
AB-24D
13.3
0.8
AB-26D
29.8
1.7
AB-35D
24.7
0.8
GWA-14D
24.5
0.0
AB-21 BR
18.9
0.0
AB-23BRU
65.6
0.1
Inactive Ash Basin Constant Concentration = 33 pg/L
Ash Storage / Landfill Constant Concentration = 45 pg/L
Ash Ponds Constant Concentration = 36 pg/L
Active Ash Basin Constant Concentration = 36 pg/L
Sorption coefficient [Kd] = 0.5 mL/g
AB-12S
0.47
0.00
AB-13S
0.43
0.00
AB-31 S
0.16
1.01
AB-4S
0.36
0.05
Hexavalent
AB-1 OD
3.00
2.97
Chromium
AB-11 D
2.60
0.03
AB-12D
0.10
0.00
AB-14D
0.87
0.00
AB-20D
1.70
0.45
AB-21 D
20.00
0.38
AB-24D
19.00
0.69
AB-29D
0.82
0.91
AB-31 D
1.40
0.80
AB-33D
0.07
1.00
AB-35D
6.10
0.79

Table 5. Transport Model Calibration Results (cont.)
COI
Monitoring
Well
Measured Concentration
(pg/L)
Predicted Concentration
(pg/L)
AB-36D
0.73
0.56
AB-37D
0.34
0.36
AB-91D
0.64
0.38
GWA-31D
0.92
0.76
Hexavalent
GWA-91D
0.64
0.12
Chromium
(cont.)
AB-1 R
4.00
0.00
AB-21 BR
20.00
0.01
AB-25BRU
0.83
0.31
AB-35BR
2.90
0.06
AB-25BR
4.70
0.00
Inactive Ash Basin Constant Concentration = 38 pg/L
Ash Storage / Landfill Constant Concentration = 45 pg/L
Ash Ponds Constant Concentration = 38 pg/L
Active Ash Basin Constant Concentration = 38 pg/L
Sorption coefficient [Kd] = 0.1 mL/g
AB-10S
1.60
24.11
AB-13S
1.10
1.68
AB-22S
8.60
30.42
AB-32S
14.30
29.58
AB-34S
40.00
14.36
AB-9S
6.80
19.31
GWA-1 S
11.40
8.46
GWA-2S
2.40
5.90
GWA-4S
5.50
19.48
Cobalt
GWA-5S
29.70
29.34
GWA-9S
8.50
6.64
AB-26S
5.90
14.27
AB-33S
12.30
12.62
GWA-14S
8.30
0.00
GWA-3S
16.20
13.16
GWA-6S
4160.00
5.75
AB-14D
10.10
0.03
AB-26D
9.90
13.26
AB-30D
1.40
1.49
AB-32D
2.00
18.50
AB-35D
1.70
3.50
AB-38D
5.00
0.57
GWA-91D
1.90
3.87

Table 5. Transport Model Calibration Results (cont.)
COI
Monitoring
Well
Measured Concentration
(Ng/L)
Predicted Concentration
(Ng/L)
Inactive Ash Basin Constant Concentration = 100 pg/L
Ash Storage / Landfill Constant Concentration = 10 pg/L
Ash Ponds Constant Concentration = 10 pg/L
Selenium
Active Ash Basin Constant Concentration = 10 pg/L
Sorption coefficient [Kd] = 0.1 mL/g
AB-22S
0.50
8.11
GWA-6S
73.50
22.07
AB-21 BR
1.10
0.63
Inactive Ash Basin Constant Concentration = 530,000 pg/L
Ash Storage / Landfill Constant Concentration = 10 pg/L
Ash Ponds Constant Concentration = 10 pg/L
Active Ash Basin Constant Concentration = 200,000 pg/L
Western Fingers Constant Concentration = 200,000 pg/L
Sulfate
Sorption coefficient [Kd] = No Sorption
AB-33S
337,000
340,763
GWA-6S
1,830,000
82,503
AB-22S
55,300
61,285
AB-26S
68,400
67,455
GWA-9S
12,300
13,844
Inactive Ash Basin Constant Concentration = 90 pg/L
Ash Storage / Landfill Constant Concentration = 120 pg/L
Ash Ponds Constant Concentration = 90 pg/L
Active Ash Basin Constant Concentration = 90 pg/L
Sorption coefficient [Kd] = 0.5 mL/g
AB-10S
0.37
25.40
AB-12S
0.37
0.00
AB-13S
1.10
0.00
AB-22S
1.20
47.89
Vanadium
AB-26S
2.10
26.01
AB-32S
0.81
54.45
AB-36S
0.39
18.47
AB-5
2.30
0.00
GWA-1 S
0.39
6.65
GWA-2S
1.30
0.02
GWA-4S
1.20
15.03
GWA-9S
0.97
4.26
AB-31 S
1.10
3.71

Table 5. Transport Model Calibration Results (cont.)
COI
Monitoring
Well
Measured Concentration
(Ng/L)
Predicted Concentration
(Ng/L)
AB-4S
0.60
0.13
AB-6R
4.40
15.64
GWA-15S
3.10
0.01
AB-1 OD
5.30
7.45
AB-11 D
1.80
0.09
AB-12D
3.90
0.00
AB-14D
0.96
0.00
AB-20D
36.90
1.14
AB-21 D
14.00
0.97
AB-22 D
3.30
12.04
AB-24D
16.80
1.73
AB-26D
93.20
3.20
AB-27D
6.30
5.91
AB-28D
13.20
0.60
AB-29D
16.30
2.86
AB-21D
6.10
0.22
AB-30D
13.60
0.29
AB-31 D
13.90
2.92
Vanadium
(cont.)
AB-32D
9.50
13.34
AB-33D
7.60
3.66
AB-34D
16.30
0.60
AB-35D
21.10
1.62
AB-36D
16.80
1.12
AB-37D
8.60
0.72
AB-38D
3.00
0.85
AB-39D
6.30
3.84
AB-91D
7.20
1.37
GWA-14D
7.60
0.00
GWA-15D
17.80
0.00
GWA-1 D
14.30
3.28
GWA-21D
11.80
0.27
GWA-31D
18.70
1.93
GWA-41D
4.10
2.34
GWA-51D
22.50
14.71
GWA-5S
0.99
14.71
GWA-91D
13.00
0.30
AB-1 R
21.50
0.00

Table 5. Transport Model Calibration Results (cont.)
COI
Monitoring
Well
Measured Concentration
(lag/L)
Predicted Concentration
(lag/L)
AB-21 BR
17.70
0.02
AB-23BRU
29.90
0.09
AB-25BRU
18.10
0.78
AB-35BR
16.10
0.12
Vanadium
(cont.)
GWA-1 BR
2.60
0.78
GWA-3BR
17.90
0.61
GWA-5BR
10.10
3.61
GWA-6BR
4.60
1.04
AB-25BR
27.20
0.00

Table 6. Predicted Advective Travel Time
Groundwater
Zone
Monitoring Well
Advective Travel Time
to Model Boundary
(years)
Shallow
AB-22S
5.2
AB-26S
3.0
AB-31 S
2.1
AB-32S
2.4
AB-6R
12.9
AB-9S
1.6
GWA-2S
4.7
GWA-6S
6.2
GWA-9S
232
GWA-15S
66.5
Deep
AB-9D
(21)
AB-11 D
2.0
AB-22D
(41)
AB-26D
(38)
AB-31 D
(37)
AB-32D
(43)
GWA-2D
(38)
GWA-9D
5.0
GWA-15D
3.4
Bedrock
GWA-1 BR
1.3
GWA-5BR
(29)
GWA-6BR
13.1
'Computed travel time over 3-D flow path using flow and transport
terms from the groundwater flow and transport model.
2Travel time is displayed in days in parentheses if travel times are
less than one year.

Table 7. Flow and Transport Parameter Sensitivity Analysis
Calibrated
Calibrated +20%
Calibrated -20%
Average
Average
Concentration
Concentration
Hydraulic
Hydraulic
Change in
Hydraulic
Change in
Parameter
Head
Head
%
Calibration
Head
%
Calibration
NRMSE
NRMSE
Change
Monitor Wells
NRMSE
Change
Monitor Wells
N
N
(ug/L)
N
(ug/L)
Arsenic
Boron
Arsenic
Boron
Horizontal K
9.4
12.5
3.1
2.9
-160.3
11.5
2.1
2.6
105.6
in S/M1/M2
Horizontal K
9.4
9.9
0.5
0.4
-34.1
9.3
-0.1
-0.8
20.9
in TZ
Vertical K in
9.4
9.5
0.1
-0.4
-1.7
9.4
0.0
0.4
7.1
S/M 1 /M2
Vertical K in
9.4
9.4
0.0
0.0
-0.8
9.4
0.0
0.0
0.1
TZ
Recharge in
the Ash
9.4
9.5
0.1
1.2
111.8
11.0
1.6
-0.4
-136.5
Basin
Recharge in
9.4
10.7
1.3
12.8
37.1
11.1
1.7
-7.3
-62.0
Other Areas
Kd
-7.6
-
7.4
-
Effective
Porosity in
-0.5
-20.3
0.4
17.5
S/M1/M2

�Y
Groundwater i
Discharge
Figure 1. Conceptual Groundwater Flow Model/Model Domain

a
n
Figure 2. Model Domain North -South Cross Section (A -A') through Inactive and Active Ash Basins

i
B
_t
Bt
B By
Figure 3. Model Domain East-West Cross Section (B-B') through the Active Ash Basin

Figure 4. Flow Model Boundary Conditions

Figure 5. Model Recharge Areas and Contaminant Source Zones (Constant Concentration Cells)

Figure 6. Observation Wells in Shallow Groundwater Zone

Figure 7. Observation Wells in Deep Groundwater Zone

Figure 8. Observation Wells in Bedrock Groundwater Zone

Figure 9. Hydraulic Conductivity Zonation in S/M1 Model Layers (Model Layers 5-6)

Figure 10. Hydraulic Conductivity Zonation in M2 Model Layer (Model Layer 7)

Figure 11. Hydraulic Conductivity Zonation in TZ Model Layer (Model Layer 8)

Figure 12. Hydraulic Conductivity Zonation in BR Model Layers (Model Layers 9 and10)

b4U.(
632.(
624.
616.(
0)
608.(
> 600.(
a�
0 592.(
584.(
576.(
568.(
...................
...................
...................
...................
......
..............
...................
...................
....
................
560.
560.0 568.0 576.0 584.0 592.0 600.0 608.0 616.0 624.0 632.0 640.0
Observed Value
Figure 13. Modeled Hydraulic Head (feet) vs. Observed Hydraulic Head (feet)
° ° Layer L
Layer 3
Layer 6
Layer 8
Layer 10

6 �►
II
f�
/
/ ^ ! 1t 1
LEGEND
DUKE ENERGY
i PROPERTY BOUNDARY
ASH BASIN WASTE
` BOUNDARY
i
n
3 LANDfILIJASFi STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Ad
v v
Active Ash Basin;
r
_ I
� 1
- --f— f- f -,( — W- _jf
N
A
0 500 1,000
Feet
Figure 14. Hydraulic Head (feet) in Shallow Groundwater Zone (Model Layer 6)

GWA-6
AB-32
GWA-5
AB-31
GWA-15
u
AB-5 w—
EGENDLAKE WYLE
\
_ DUKE ENERGY (CATAWBA RIVER
PROPERTY BOUNDARY
- ASH BASIN WASTE
BOUNDARY --
LANDFILLIASH STORAGE _
41— F'.
AREABOUNDARY
ASH BASIN COMPLIANCE hN
_ BOUNDARY „
ASH BASIN COMPLIANCE I/•�jiV
BOUNDARY COINCIDENT
WITH DUKE ENERGY 0 500 1,i100
PROPERTY BOUNDARY
MODEL DOMAIN4d
Feet
9
Figure 15. Particle Tracking Results (see Table 6 for Advective Travel Times)

8
7
6
5
a,
O 4
E
4—
C—
< 3
2
1
0
Predicted Antimony at AB-26D
Existing Condition
Cap -in -Place
Excavation
IMAC/2L Standard
LO LO LO LO tin LD ua in (n LO ur (n LO ua V) ua
(D 03 O N It (D 03 0 N Kt (D 00 0 Oil �t (D
(3) 0 a 0 C� rD ry C%I N cu
r r C%I CV N CV R! K K K N N N CAI CAI N
Figure 16. Predicted Antimony (Ng/L) in Monitoring Well AB-26D for Model Scenarios 1-3

10
s
4
N
Predicted Antimony at AB-31 D
:.0 00 O CV CO cc O N -3 CO CO 0 N It w
fJ7 CA © Q C, 0 CD CV N CV N
r +— N N N N CJ N N N N N CJ N CA N
Figure 17. Predicted Antimony (Ng/L) in Monitoring Well AB-31D for Model Scenarios 1-3

LEGEND
z
5
7
10
15
18
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
MATH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
0 5�00
Feet
Figure 18. Initial (2015) Antimony Concentrations (Ng/L) in the Shallow Groundwater Zone

4
I�
LANDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WTH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 19. Initial (2015) Antimony Concentrations (pg/L) in the Deep Groundwater Zone

is
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
L4NDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
NTH DUKE ENERGY
PROPERTY BOUNDARY
MODELDOMAIN
�nrin
t:;_
N
A
0 500 1,000
Feet
Figure 20. Initial (2015) Antimony Concentrations (pg/L) in the Bedrock Groundwater Zone

r-
r
1
4
ACTIVE ASH BASIN
rl
1
LEGEND
�"
1
'
m 10
IN
15
5 18
0
DUKE ENERGY
_
_
a PROPERTY BOUNDARY
E
N ASH BASIN WASTE
m BOUNDARY
e LANDFILLIASH STORAGE
u AREABOUNDARY
N
_ ASH BASIN COMPLIANCE
x - SCUNDARY
0
ASH BASIN COMPLIANCE
w BOUNDARY COINCIDENT
_ _
N4TH DUKE ENERGY
0
500 1,000
f PROPERTY BOUNDARY
MODEL DOMAIN
Feet
Figure 21. "Existing Conditions" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Shallow
Groundwater Zone

�1
FI
I
I
1
I
I
1
1
1
I
1
1
J
A
500 1,000
0
�eet
Figure 22. "Existing Conditions" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Deep
Groundwater Zone

Figure 23. "Existing Conditions" Scenario 1 - 2115 Predicted Antimony (pg/L) in the Bedrock
Groundwater Zone

LEGEND
1
'r
6
10
15
18
_ DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREABOUNDARY
_ ASH BASIN COMPLIANCE
80UNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
VATH DUKE ENERGY
PROPERTYBOUNDARY
MODEL DOMAIN
w� -
N
A
0 500 1,000
Feet
Figure 24. "Cap -in -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Shallow
Groundwater Zone

Figure 25. "Cap -in -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Deep
Groundwater Zone

ti
i00 1,000
0
eet
Figure 26. "Cap -in -Place" Scenario 2 - 2115 Predicted Antimony (pg/L) in the Bedrock
Groundwater Zone

LEGEND
2
5
6
40
15
18
` DUKE ENERGY 4
PROPERTY BOUNDARY I
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
NTH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
—1 -
I
1
I
I
1
N
A
0 500 1,000
Feet
Figure 27. "Excavation" Scenario 3 - 2115 Predicted Antimony (Ng/L) in the Shallow
Groundwater Zone

�e1
�1
rr
r TP
a I
I I
I �
I
h
r
I
x
r�
LEGEND �
t '
1
7
tU
tj
a _ l
DUKE ENERGY I _
a PROPERTY BOUNDARY
E
N ASH BASIN WASTE
m BOUNDARY
LANDFILL/ASH STORAGE
a AREA BOUNDARY
ASH BASIN COMPLIANCE
N
x BOUNDARY
0
ASH BASIN COMPLIANCE
BOUWITH DARYUKE ECOINCIDENT yy „�•
PRO DUKE ENERGY 0 500 1,600
PROPERTY BOUNDARY
?� MODEL DOMAIN Feet
i
Figure 28. "Excavation" Scenario 3 - 2115 Predicted Antimony (Ng/L) in the Deep Groundwater
Zone

Figure 29. "Excavation" Scenario 3 - 2115 Predicted Antimony (Ng/L) in the Bedrock
Groundwater Zone

Predicted Arsenic at AB-22S
Existing Condition
10 cap -in -Place - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - —
Excavation
m
11
(D m C7 N ]' (0 CC) 0 N Et (D co 0 N I:t (0
Cf3 CF7 n C7 0 0 C] N N N N
r r N N CV N N N N N N N CV N N N
Figure 30. Predicted Arsenic (pg/L) in Monitoring Well AB-22S For Model Scenarios 1-3

140
120
100
80
60
L
40
NA
0
Predicted Arsenic at GWA-6S
Existing Condition
Cap -in -Place
Excavation -
IMAC/2L Standard
ED m La N � L.O CO a N it (O CO O N 'Kt Liz
Cfl Cfl C] C] C7 O C7 N N N N
r N N N N N N N N N N C'J CW N N
Figure 31. Predicted Arsenic (Ng/L) in Monitoring Well GWA-6S For Model Scenarios 1-3

LEGEND
10
SQ
100
200
ass
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 32. Initial (2015) Arsenic Concentrations (fag/L) in the Shallow Groundwater Zone

Figure 33. Initial (2015) Arsenic Concentrations (Ng/L) in the Deep Groundwater Zone

1,
�V
a
�f f11 iZ� n
LEGEND
� 1
5
10
50
100
200
- 399
❑UKE ENERGY
a
PROPERTY BOUNDARY
ASH BASIN WASTE
m
x
BOUNDARY
y
S
LANDF3LLlASH STORAGE
'u
AREABOUNDARY
g
ASH BASIN COMPLIANCE
i
0
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
d
WITH DUKE ENERGY
a
PROPERTY BOUNDARY
MODEL DOMAIN
g
N
A
0 500 1,000
Feet
Figure 34. Initial (2015) Arsenic Concentrations (fag/L) in the Bedrock Groundwater Zone

Figure 35. "Existing Conditions" Scenario 1 - 2115 Predicted Arsenic (pg/L) in the Shallow
Groundwater Zone

LEGEND
1
5
10
50
100
200
= 399
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFfiLL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 36. "Existing Conditions" Scenario 1 - 2115 Predicted Arsenic (pg/L) in the Deep
Groundwater Zone

Figure 37. "Existing Conditions" Scenario 1 - 2115 Predicted Arsenic (pg/L) in the Bedrock
Groundwater Zone

Figure 38. "Cap -in -Place" Scenario 2 - 2115 Predicted Arsenic (pg/L) in the Shallow
Groundwater Zone

LEGEND
1
5
10
50
100
200
399
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
I L J MODEL DOMAIN
a
I
I
I
I
I
I
I
I
1
1
r'
1
N
A
0 500 1,000
Feet
Figure 39. "Cap -in -Place" Scenario 2 - 2115 Predicted Arsenic (pg/L) in the Deep Groundwater
Zone

Figure 40. "Cap -in -Place" Scenario 2 - 2115 Predicted Arsenic (pg/L) in the Bedrock
Groundwater Zone

F—
LEGEND
1
5
10
50
100
200
399
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFfiLL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1.000
Feet
Figure 41. "Excavation" Scenario 3 - 2115 Predicted Arsenic (Ng/L) in the Shallow Groundwater
Zone

I
LEGEND
1
5
10
50
100
200
399
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILIJASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
I L J MODEL DOMAIN
a
N
A
0 500 1,000
Feet
Figure 42. "Excavation" Scenario 3 - 2115 Predicted Arsenic (pg/L) in the Deep Groundwater
Zone

LEGEND
5
10
50
100
200
- 399
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
monsoons
Feet
Figure 43. "Excavation" Scenario 3 - 2115 Predicted Arsenic (pg/L) in the Bedrock Groundwater
Zone

F11
.M
500
Z33
E 400
i
Cz 300
m
200
100
0
Predicted Barium at AB-22S
Existing Condition
Cap -in -Place - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Excavation
IMAC/21- Standard - -
un u> u3 to LO L u7 ua LO LO LO LO in V) LO u7
(D CO Q CQ d` Cp 00 O N S.fl m 0 N �t CD
rn rn ca o C� o o Cv N N C\j
r r C!! CV CV CV CU CU CL CU N CV CU N CV C41
Figure 44. Predicted Barium (pg/L) in Monitoring Well AB-22S For Model Scenarios 1-3

F11
o
500
E 400
CO
300
200
100
C
Predicted Barium at AB-26S
in uD u7 to LO LO LO LO w M w V) V) M in
[D CC} Q CU d' (0 CO O Cm [D CO C) N [D
C3) Ci7 n C7 C] C7 n N N N N
r r N N N N N N N N CV N N N N N
Figure 45. Predicted Barium (pg/L) in Monitoring Well AB-26S For Model Scenarios 1-3

�-7—
LEGEND
1
10
50
100
350
700
9I = 903
0
❑UKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
m BOUNDARY
S LANdF3LLlASH STORAGE
u AREA BOUNDARY
g
w ASH BASIN COMPLIANCE
i BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
d WITH DUKE ENERGY
a PROPERTY BOUNDARY
MODEL DOMAIN
g
N
A
0 500 1,000
Feet
Figure 46. Initial (2015) Barium Concentrations (fag/L) in the Shallow Groundwater Zone

Figure 47. Initial (2015) Barium Concentrations (pg/L) in the Deep Groundwater Zone

0
LEGEND
� 1
10
50
100
350
700
- 903
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
i
4.
N
A
0 500 1,000
Feet
Figure 48. Initial (2015) Barium Concentrations (pg/L) in the Bedrock Groundwater Zone

LEGEND
� 1
10
50
100
350
700
903
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
.� BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
= MODEL DOMAIN
I
u
I
I
1
N
A
0 500 1.000
Feet
Figure 49. "Existing Conditions" Scenario 1 - 2115 Predicted Barium (fag/L) in the Shallow
Groundwater Zone

LEGEND
�t
10
50
100
350
700
903
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
I
f
I
I
I
1
I
f
1
Il
N
A
0 500 1.000
Feet
Figure 50. "Existing Conditions" Scenario 1 - 2115 Predicted Barium (pg/L) in the Deep
Groundwater Zone

LEGEND
10
50
100
350
700
903
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
I
I
I
I
I
r
N
A
0 500 1.000
Feet
Figure 51. "Existing Conditions" Scenario 1 - 2115 Predicted Barium (pg/L) in the Bedrock
Groundwater Zone

Figure 52. "Cap -in -Place" Scenario 2 - 2115 Predicted Barium (pg/L) in the Shallow
Groundwater Zone

1 �\
1\
ICI
LEGEND
10
50
100
350
700
903
— — DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1.000
Feet
Figure 53. "Cap -in -Place" Scenario 2 - 2115 Predicted Barium (fag/L) in the Deep Groundwater
Zone

LEGEND
r"M 1
10
50
100
350
700
903
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE ,
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY _
MODEL DOMAIN
I
I
I
I
I
I
I
I
I
1
1
1
r�
I
1
N
A
0 500 1,000
Feet
Figure 54. "Cap -in -Place" Scenario 2 - 2115 Predicted Barium (pg/L) in the Bedrock
Groundwater Zone

LEGEND
�t
10
50
100
350
700
903
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
1
4
J
A
I
I
I
I
I
J
N
A
0 500 1.000
Feet
Figure 55. "Excavation" Scenario 3 - 2115 Predicted Barium (fag/L) in the Shallow Groundwater
Zone

LEGEND
10
50
100
350
700
903
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
.000
Feet
Figure 56. "Excavation" Scenario 3 - 2115 Predicted Barium (pg/L) in the Deep Groundwater
Zone

LEGEND
1
10
50
100
350
700
_ 903
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 57. "Excavation" Scenario 3 - 2115 Predicted Barium (pg/L) in the Bedrock Groundwater
Zone

1600
1400
1200
•—• 1000
800
Q
i
N • 1 !,
400
I!m
0
Predicted Boron at AB-22D
Existing Condition
Cap -in -Place
Excavation
— — — — — — — — — — — — — — — — — — — — — — — — — — — — — IMAC/2L Standard
CD CO C7 N � CD 09 0 Cm St tD m C7 N It (D
CA CA C� O C7 C7 C7 CQ N N N
r N N N N N CU N N CV N N CU N N
Figure 58. Predicted Boron (Ng/L) in Monitoring Well AB-22D For Model Scenarios 1-3

IIEDIV,
1200
1000
C— 800
O
�Me,
400
WE
u
Predicted Baran at AB-26S
to LO LO LO LI7 Liz LO LO Ln LO LO CS} w Lit Ln LC3
w CO C7 Cq � CD CO 0 N Ct CD m 0 N tt CD
t77 [3] C3 C3 C3 C3 C3 CV N N N
r N N N N CV C%I N N N N N N CU N
Figure 59. Predicted Boron (Ng/L) in Monitoring Well AB-26S For Model Scenarios 1-3

1400
1200
1000
800
O
O
m 600
400
200
0
Predicted Baron at C WA-45
Existing condition
Cap -in -Place
Excavation
— — — — — — — — — — — — — — — — — — — — — — — — — — — — IMACI2L Standard — -�
u) ur Ln LO in U') uO ua U') uO uO to err w m u)
QD m C] N � (R m O N �t tD m CD N et to
0) 0) n C] C] O O N N N N
r r N N N iV CV N N N N N N CV N N
Figure 60. Predicted Boron (Ng/L) in Monitoring Well GWA-4S For Model Scenarios 1-3

1000
m
C 600
D
L
/©
W
f II
200
0
Predicted Boron at GWA-5BR
u7 Un sn 1.0 to LO u') �n Un LO en LO u7 u7 Un u�
to 00 0 N -f t9 00 C4 N CD CO 0 N It (D
to G) O O O O O (V N Cat (V
r r N N N N CJ N N N N C I N N [\t N
Figure 61. Predicted Boron (Ng/L) in Monitoring Well GWA-5BR For Model Scenarios 1-3

LEGEND
50
100
300
500
700
1,200
- 1,921
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
+MTH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
,000
Figure 62. Initial (2015) Boron Concentrations (pg/L) in the Shallow Groundwater Zone

Figure 63. Initial (2015) Boron Concentrations (pg/L) in the Deep Groundwater Zone

R
01
z
a
a
0
LEGEND
s 50
100
300
u
500
P
s 700
�z 1,200
9I = 1,921
0
DUKEENERGY
a PROPERTY BOUNDARY
ASH BASIN WASTE
m BOUNDARY
x
w
S LANDFILVASH STORAGE
'u AREA BOUNDARY
g
ASH BASIN COMPLIANCE
i BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
d ` WITH DUKE ENERGY
a PROPERTY BOUNDARY
.x. MODEL DOMAIN
r
N
A
0 500 1,000
Feet
Figure 64. Initial (2015) Boron Concentrations (Ng/L) in the Bedrock Groundwater Zone

LEGEND
50
100
300
500
700
1,200
1,921
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
*1
fi
N
A
0 500 1,000
Feet
Figure 65. "Existing Conditions" Scenario 1 - 2115 Predicted Boron (pg/L) in the Shallow
Groundwater Zone

LEGEND
50
100
300
500
700
1,200
1,921
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
© MODEL DOMAIN
l
_t
N
A
0 500 1,000
Feet
Figure 66. "Existing Conditions" Scenario 1 - 2115 Predicted Boron (pg/L) in the Deep
Groundwater Zone

LEGEND
50
100
300
500
700
1,200
1,921
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
© MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 67. "Existing Conditions" Scenario 1 - 2115 Predicted Boron (fag/L) in the Bedrock
Groundwater Zone

r�
rr
rr
fr
LEGEND
50
100
300
500
700
1,200
1,921
❑UKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
.� WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 68. "Cap -in -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Shallow Groundwater
Zone

r`
rr
rr
fr
LEGEND
50
100
300
500
700
1,200
1,921
❑UKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
.� WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 69. "Cap -in -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Deep Groundwater
Zone

r`
rr
rr
fr
LEGEND
50
100
300
500
700
1,200
1,921
❑UKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
.� WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 70. "Cap -in -Place" Scenario 2 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater
Zone

LEGEND
50
100
000
500
700
1,200
1,921
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFiLLlASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE ,
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY _
I L J MODEL DOMAIN
iL
1
N
A
0 500 1,000
Feet
Figure 71. "Excavation" Scenario 3 - 2115 Predicted Boron (Ng/L) in the Shallow Groundwater
Zone

r�
rr
rr
fr
LEGEND
50
100
300
500
700
1,200
1,921
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
I L J MODEL DOMAIN
iL
N
A
0 500 1,000
Feet
Figure 72. "Excavation" Scenario 3 - 2115 Predicted Boron (pg/L) in the Deep Groundwater
Zone

LEGEND
50
100
300
500
700
1,200
1,921
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL%SH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
1MTH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1.000
monsoons
Feet
Figure 73. "Excavation" Scenario 3 - 2115 Predicted Boron (pg/L) in the Bedrock Groundwater
Zone

20
0] 15
ZI
E
E
O 10
L7
5
U
Predicted Chromium at AB-f R
u-) M Un uO cn in uO M u7 to w u7 M Ln ua uO
CD 00 (D N 'IT 0 CO O N 'd' cD CO C) N d' (D
(7S Cfl O 0 0 Q 0 N N N N
r r N N N N N N N N N N N N N N
Figure 74. Predicted Chromium (Ng/L) in Monitoring Well AB-6R For Model Scenarios 1-3

16
14
12
4
:a
81
Predicted Chromium at AB-26D
(O M C] N d' (D CO C7 N (D CO C) N tt w
65 C] C7 C7 0 C7 N N N N
r r CV N N N CV N N N N N N N N N
Figure 75. Predicted Chromium (pg/L) in Monitoring Well AB-26D For Model Scenarios 1-3

w
i
r
I
ILI
1
n I
- I
4'
LEGEND
1
2
5
10
15
11L 20
® 27
DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 76. Initial (2015) Chromium Concentrations (pg/L) in the Shallow Groundwater Zone

f
' I
I
I
I
I
1
1
,
LEGEND
1
2
5
10
15
20
27
DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE I `�
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY 0 500 1,000
MODEL DOMAIN Feet
Figure 77. Initial (2015) Chromium Concentrations (pg/L) in the Deep Groundwater Zone

LEGEND
1
2
5
10
15
20
27
DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
�k
1
a
I
I
I
I
N
A
0 500 1,000
Feet
Figure 78. Initial (2015) Chromium Concentrations (pg/L) in the Bedrock Groundwater Zone

Figure 79. "Existing Conditions" Scenario 1 - 2115 Predicted Chromium (Ng/L) in the Shallow
Groundwater Zone

i
i
LEGEND
2
5
10
15
20
27
_ DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILUASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
ti
f
t
r �
i
,
V6
N
k
0 500 1,000
Feet
Figure 80. "Existing Conditions" Scenario 1 - 2115 Predicted Chromium (Ng/L) in the Deep
Groundwater Zone

LEGEND
2
S
10
15
20
27
DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 81. "Existing Conditions" Scenario 1 - 2115 Predicted Chromium (Ng/L) in the Bedrock
Groundwater Zone

Pp-MEWIL-9
—i
LEGEND
2
S
10
15
20
Mb 27
DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
ri
N
A
0 500 1,000
Feet
Figure 82. "Cap -in -Place" Scenario 2 - 2115 Predicted Chromium (fag/L) in the Shallow
Groundwater Zone

7LEGEN'
D
2
S
10
15
20
Mb 27
DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
r
I
I
I
I
I
I
1
N
A
0 500 1,000
Feet
Figure 83. "Cap -in -Place" Scenario 2 - 2115 Predicted Chromium (pg/L) in the Deep
Groundwater Zone

i
/
LEGEND
2
S
10
15
20
27
_ DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 84. "Cap -in -Place" Scenario 2 - 2115 Predicted Chromium (Ng/L) in the Bedrock
Groundwater Zone

I
I
I
I
1
LEGEND
S 1 t�
10
J
15
20
27
_ DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE AN
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY 0 500 1,000
MODEL DOMAIN Feet
Figure 85. "Excavation" Scenario 3 - 2115 Predicted Chromium (Ng/L) in the Shallow
Groundwater Zone

I 'rr
r►
1-71
�_11
rI 1 �r
I
I
I
I
I
I
- F
tt.
9
w -
0
a
r
LEGEND r
w
2 tv�
S
10 A+
a
15
a'
a
20
I
27
0
DUKEENERGY
PROPERTY BOUNDARY
ten' ASH BASIN WASTE
m BOUNDARY
x
s LANDFILL/ASH STORAGE
AREA BOUNDARY
w ASH BASIN COMPLIANCE AN
BOUNDARY
a
ASH BASIN COMPLIANCE
w BOUNDARY COINCIDENT
p WITH DUKE ENERGY
0 500 1,000
PROPERTY BOUNDARY
a
MODEL DOMAIN Feet
Figure 86. "Excavation" Scenario 3 - 2115 Predicted Chromium (pg/L) in the Deep Groundwater
Zone

LEGEND
2
S
10
15
20
Mb 27
DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
1
I
I
I
I
I
I
1
N
A
0 500 1,000
Feet
Figure 87. "Excavation" Scenario 3 - 2115 Predicted Chromium (Ng/L) in the Bedrock
Groundwater Zone

Wa
a
Predicted Hexawalent Chromium at AB-9D
Existing Condition
Cap-ln-Place
Excavation
DHHS HSL
M N V. � CO a N Itace C) N ED
CF1 CA C7 C7 C] C] C7 N N N N
r r N N N N N N N N N N N N N N
Figure 88. Predicted Hexavalent Chromium (Ng/L) in Monitoring Well AB-91D For Model Scenarios 1-3

12
0) 10
E
P
0
C) g
4-
4]
7 4
(z
X
CU
rJ
Predicted Hexa►ralent Chromium at AB-31'S
Existing Condition
Cap-ln-Place
Excavation
QHHS HSL
La W) LO In to Usa u> u} Ley to ua Vr ua
Cfl M C] N d- (D CO O N d' CP CO Ci N (D
CA Cn C7 C] C] CQ C7 N N N N
w-- r N N N N N N N N N N N CV N N
Figure 89. Predicted Hexavalent Chromium (pg/L) in Monitoring Well AB-31S For Model Scenarios 1-3

16
14
12
E
10
0
Z g
U
6
[[S
0] X 4
_.
81
Predicted Hexavalent Chromium at GWA-3D
LO LO (n ua w LO LO (n on (n era u) u) V) u>
(0 M ® i11 I:t (0 CO O N It (D CO O N (D
CT� Ol C7 C] C7 O C] N N N N
r r Cq N N N N N N N N N N N N N
Figure 90. Predicted Hexavalent Chromium (Ng/L) in Monitoring Well GWA-31D For Model Scenarios 1-3

20
0)
F
15
F
0
C)
10
a�
x
9
Predicted Hexa►ralent Chromium at AB-10D
fD M C7 N CD CO O N KD CO C3 N �t (D
CS7 0) C7 C7 0 C? C3 N N N N
r r CV N N N N N N N N N N N N N
Figure 91. Predicted Hexavalent Chromium (Ng/L) in Monitoring Well AB-10D Model Scenarios 1-3

LEGEND
- 0.07
5
10
15
® 20
30
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILIJASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 92. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Shallow
Groundwater Zone

I
I
R
I
I
I
e
I
I
1
LEGEND �
�I 0.07 a
t"
s �
10
15
20
30
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFfiLL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY - 0 500 1.000
PROPERTY BOUNDARY
MODEL DOMAIN Feet
Figure 93. Initial (2015) Hexavalent Chromium Concentrations (fag/L) in the Deep Groundwater
Zone

Figure 94. Initial (2015) Hexavalent Chromium Concentrations (pg/L) in the Bedrock
Groundwater Zone

Figure 95. "Existing Conditions" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Shallow Groundwater Zone

LEGEND
�I 0.07
5
10
15
20
30
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFfiLL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
I L� MODEL DOMAIN
a
'M
N
A
0 500 1,000
Feet
Figure 96. "Existing Conditions" Scenario 1 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Deep Groundwater Zone

LEGEND
0.07
s
10
15
20
30
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFfiLL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
pq
. .y
N
A
0 500 1.000
Feet
Figure 97. "Existing Conditions" Scenario 1 - 2115 Predicted Hexavalent Chromium (fag/L) in the
Bedrock Groundwater Zone

Figure 98. "Cap -in -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Shallow Groundwater Zone

LEGEND
0.07
s
10
15
20
30
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFfiLL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
I
I
I
f
I
I
I
N
A
0 500 1.000
Feet
Figure 99. "Cap -in -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep
Groundwater Zone

i \1
�i
!t
rI �—tl
F i
LEGEND
0.07
s
10
15
20
30
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFfiLL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1.000
Feet
Figure 100. "Cap -in -Place" Scenario 2 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Bedrock Groundwater Zone

Figure 101. "Excavation" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Shallow Groundwater Zone

LEGEND
�I 0.07
s
10
15
20
30
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFfiLL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
L
1
I
!
I
Q
I
I
I
1
N
A
0 500 1.000
Feet
Figure 102. "Excavation" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the Deep
Groundwater Zone

LEGENI
- 0.07
N1� 1
5
u
10
8 15
i 20
_ 30
DUKE ENERC
PROPERTYE
ASH BASIN V
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
= MODEL DOMAIN
1'r �
r r --
u
r►
A 1Zn r--,-�
N
A
0 500 1,000
Feet
Figure 103. "Excavation" Scenario 3 - 2115 Predicted Hexavalent Chromium (pg/L) in the
Bedrock Groundwater Zone

30
25
p� 20
03
-0 15
O
U
10
5
0
Predicted Cobalt at AB-1 OS
u7 un u) U-) +.ra an Ln u-) U") (n 4n m Asa s.e) u7 u)
(D CO CD N co CO O N d CO I70 G) N EI' (D
m G7 O O O O O N N N N
r +-- N N N N N N CV N N N CJ N N N
Figure 104. Predicted Cobalt (pg/L) in Monitoring Well AB-1 OS For Model Scenarios 1-3

30
25
z
0)
15
10
5
0
Predicted Cobalt at AB-26D
w CO C) N �t cD CO O CV -t CO CO G) N IS CD
QS 9) i7 O O a O N N CV CV
r .-- N N N N N N N N N N N N N N
Figure 105. Predicted Cobalt (pg/L) in Monitoring Well AB-26S For Model Scenarios 1-3

25
20
5
0
Predicted Cobalt at AB-32D
u7 to LO Un Un s n Ln Sri u-) Un u r Urn sn Vi ua w
(D CO CD CV It CD CO O) CL It CO 00 C) N V (D
QS G) (D O CD 0 C7 C+J N Cm N
r +-- N N N N N N CA R1 N N C i NN N
Figure 106. Predicted Cobalt (pg/L) in Monitoring Well AB-32D For Model Scenarios 1-3

35
30
0)
=L 20
_-I.—
Cz
© 15
WA
10
5
Lei
Predicted Cobalt at GWA-5S
LO U"� U-) U-) U') in m ua u7 m u7 Ln to Un �n uO
CD C6 f7 N �t cD CO O N d' cD CO C N � CD
m G) O O O O O N N N C\!
r - N N RI N N N N N N N CJ N N Ctd
Figure 107. Predicted Cobalt (Ng/L) in Monitoring Well GWA-5S For Model Scenarios 1-3

R
LEGEND
1
2
5
10
15
25
_ 36
_ DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
r
N
A
0 500 1,000
Feet
Figure 108. Initial (2015) Cobalt Concentrations (fag/L) in the Shallow Groundwater Zone

9
Figure 109. Initial (2015) Cobalt Concentrations (pg/L) in the Deep Groundwater Zone

,1
1,
�I
a
l�
LEGEND
15
25
- 36
_ DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
= MODEL DOMAIN
�1
I
I
I
I
I
I
I
I
7
1
I
I
r�
l\
i
E"
l�
N
/ a
0 500 1,000
Feet
Figure 110. Initial (2015) Cobalt Concentrations (pg/L) in the Bedrock Groundwater Zone

LEGEND
2
5
10
15
25
36
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
= MODEL DOMAIN
1,000
Feet
Figure 111. "Existing Conditions" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Shallow
Groundwater Zone

Figure 112. "Existing Conditions" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Deep
Groundwater Zone

Figure 113. "Existing Conditions" Scenario 1 - 2115 Predicted Cobalt (pg/L) in the Bedrock
Groundwater Zone

Figure 114. "Cap -in -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Shallow
Groundwater Zone

Figure 115. "Cap -in -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater
Zone

Figure 116. "Cap -in -Place" Scenario 2 - 2115 Predicted Cobalt (pg/L) in the Bedrock
Groundwater Zone

Figure 117. "Excavation" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Shallow Groundwater
Zone

Figure 118. "Excavation" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Deep Groundwater
Zone

LEGEND
1
2
5
10
15
25
L 36
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL%SH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
1MTH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1.000
monsoons
Feet
Figure 119. "Excavation" Scenario 3 - 2115 Predicted Cobalt (pg/L) in the Bedrock Groundwater
Zone

QI
20
15
10
5
Predicted Selenium at G'WA-6S
Existing Condition
Cap -in -Place
Excavation
IMRC/2L standard —
u> oO U') to in Ln w uO LO 07 w U) V) u) Ln ua
to M o Cu t sD CO _o N � (D co a I* w N
CS? 0) C] C7 0 C7 C] CV N N N
r r CV N N N N N N N N N C'J CV N N
Figure 120. Predicted Selenium (pg/L) in Monitoring Well GWA-6S For Model Scenarios 1-3

20
A
9
Predicted Selenium at AS-22S
U� uD U) LO in LO Ut'r LO LO Un U') V) LO in LO u)
to M C7 N d to CO C7 N 'cl- tD CO C) N t (D
Cf3 v) C] C] C] C� C] N N N N
r r N N N N N N N CV N N N CU N N
Figure 121. Predicted Selenium (Ng/L) in Monitoring Well AB-22S For Model Scenarios 1-3

1,
k`
�I
1% n
N' 0-0
LEGEND
1
5
10
20
30
40
60
g _ _ DUKEENERGY
'a PROPERTY BOUNDARY
ASH BASIN WASTE
m BOUNDARY
x
w
S LANdFILLlASH STORAGE
'u AREABOUNDARY
g
ASH BASIN COMPLIANCE
i BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
d WITH DUKE ENERGY
a PROPERTY BOUNDARY
MODEL DOMAIN
g
N
A
0 500 1,000
Feet
Figure 122. Initial (2015) Selenium Concentrations (Ng/L) in The Shallow Groundwater Zone

Figure 123. Initial (2015) Selenium Concentrations (Ng/L) in the Deep Groundwater Zone

,1
1,
a
l�
1--zn
p �I
E
R
QI
LEGEND
s
5
w 10
u
a�
20
P
g 30
w
40
_ 60
g _ _ ❑UKE ENERGY
'a PROPERTY BOUNDARY
ASH BASIN WASTE
m BOUNDARY
x
w
S LANdFILLlASH STORAGE
'u AREABOUNDARY
g
ASH BASIN COMPLIANCE
i BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
d WITH DUKE ENERGY
a PROPERTY BOUNDARY
i MODEL DOMAIN
i
,000
7
Figure 124. Initial (2015) Selenium Concentrations (pg/L) in the Bedrock Groundwater Zone

Figure 125. "Existing Conditions" Scenario 1 - 2115 Predicted Selenium (pg/L) in the Shallow
Groundwater Zone

LEGEND
1
5
10
20
30
40
® 60
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY C04NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
1
i
I
I
h
I
I
1
t"
N
A
0 500 1.000
Feet
Figure 126. "Existing Conditions" Scenario 1 - 2115 Predicted Selenium (pg/L) in the Deep
Groundwater Zone

LEGEND
1
5
10
20
30
40
® 60
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY C04NCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
0
N
A
0 500 1.000
Feet
Figure 127. "Existing Conditions" Scenario 1 - 2115 Predicted Selenium (pg/L) in the Bedrock
Groundwater Zone

LEGEND
1
5
10
20
30
40
60
❑UKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
.� WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
r�r
!r 1
N
A
0 500 1,000
Feet
Figure 128. "Cap -in -Place" Scenario 2 - 2115 Predicted Selenium (pg/L) in the Shallow
Groundwater Zone

LEGEND
5
10
20
30
® 40
60
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WSATH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
l
I
I
I
I
I
I
I
I
I
I
1
1
1
I
1
N
A
0 500 1,000
Feet
Figure 129. "Cap -in -Place" Scenario 2 - 2115 Predicted Selenium (pg/L) in the Deep
Groundwater Zone

I �1\
�I
u�
ff
7y`
^! J
LEGEND
n
5
10
20
S
30
40
60
0
DUKE ENERGY
a PROPERTY BOUNDARY
ASH BASIN WASTE
m BOUNDARY
s
m
s LANDFiLLlASH STORAGE
'u AREABOUNDARY
�i
w ASH BASIN COMPLIANCE
x BOUNDARY
0
h ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
d _ WITH DUKE ENERGY
a. PROPERTY BOUNDARY
MODEL DOMAIN
I
I
I
I
r
N
k
0 500 1,000
Feel
Figure 130. "Cap -in -Place" Scenario 2 - 2115 Predicted Selenium (pg/L) in the Bedrock
Groundwater Zone

11
it
11
1 r�
LEGEND
1
5
10
20
30
40
60
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
I= MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 131. "Excavation" Scenario 3 - 2115 Predicted Selenium (pg/L) in the Shallow
Groundwater Zone

LEGEND
1
5
10
20
30
40
60
❑UKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
.� WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 132. "Excavation" Scenario 3 - 2115 Predicted Selenium (pg/L) in the Deep Groundwater
Zone

�I
!d
h d
r � J
LEGEND
5
10
20
30
40
_ 60
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1.000
monsoons
Feet
Figure 133. "Excavation" Scenario 3 - 2115 Predicted Selenium (pg/L) in the Bedrock
Groundwater Zone

350000
300000
250000
200000
Cz
150000
U)
i111111111111h111113
0
Predicted Sulfate at AB-33S
Existing Condition
Cap -in -Place
Excavation
IMAC/2L Standard — —
CO CD C? N It (D CO C? N CA CO O N d• (D
C s33 0 CD C3 CC] N N N N
r N N N N N CV N cl3 N N N. CV CQ N
Figure 134. Predicted Sulfate (Ng/L) In Monitoring Well AB-33S For Model Scenarios 1-3

250000
200000
- 150000
U) i00000
50000
C
Predicted Sulfate at GWA-6S
LO to LO LO Ura era LO LO LO LO w 4.0 (n Un LO LO
w w 0 N t (D CO O CU t (D CO 4 N (D
0) CA 0 0 C3 C3 C3 r N N N N
r r N N N N N N N N N N N N CAl N
Figure 135. Predicted Sulfate (pg/L) In Monitoring Well GWA-6S For Model Scenarios 1-3

I�
dd
r�l!
a �d
m
LEGEND
1,000
5,000
20,000
75,000
150,000
250,000
- 390,590
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feel
Figure 136. Initial (2015) Sulfate Concentrations (pg/L) in the Shallow Groundwater Zone

Figure 137. Initial (2015) Sulfate Concentrations (pg/L) in the Deep Groundwater Zone

LEGEND
1,000
5,000
20,000
75,000
150,000
250,000
_ 390,590
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
+MTH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
k
0 500 1,000
monsoons
Feet
Figure 138. Initial (2015) Sulfate Concentrations (Ng/L) in the Bedrock Groundwater Zone

LEGEND
1,000
5,000
20,000
75,000
150,000
250,000
390,590
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
= MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 139. "Existing Conditions" Scenario 1 - 2115 Predicted Sulfate (fag/L) in the Shallow
Groundwater Zone

LEGEND
1,000
5,000
20,000
75,000
150,000
250,000
390,590
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
= MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 140. "Existing Conditions" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Deep
Groundwater Zone

LEGEND
1,000
5,000
20,000
75,000
150,000
250,000
390,590
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
= MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 141. "Existing Conditions" Scenario 1 - 2115 Predicted Sulfate (pg/L) in the Bedrock
Groundwater Zone

Figure 142. "Cap -in -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Shallow
Groundwater Zone

Figure 143. "Cap -in -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater
Zone

Figure 144. "Cap -in -Place" Scenario 2 - 2115 Predicted Sulfate (pg/L) in the Bedrock
Groundwater Zone

Figure 145. "Excavation" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Shallow Groundwater
Zone

Figure 146. "Excavation" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Deep Groundwater
Zone

Figure 147. "Excavation" Scenario 3 - 2115 Predicted Sulfate (pg/L) in the Bedrock
Groundwater Zone

Ac
40
E
30
CO
(Z
20
IN
Predicted Vanadium at AB-6R
cn Ln LO en ua Ln Ln Ln LD Ln ua V) u) Vn u)
M O N � (D CD 4 t J � CO CD C7 N �t cn
CAS CD C7 C7 C7 0 0 N N CU CV
r r- N N N N N N Ctl CR1 Rt 713 N N CV CV
Figure 148. Predicted Vanadium (pg/L) In Monitoring Well AB-6R For Model Scenarios 1-3

50
40
0)
1
E30
C
ciS
2©
10
0
Predicted Vanadium at AB-10D
Existing Condition
Cap -in -Place
Excavation
IMAC12L Standard — —
CD M Q N d' (D CO Ca N d- (D CO C) N (D
Cf} i37 C] C7 C7 C] C3 04 N N N
r r N N N N N N N N N N N N N N
Figure 149. Predicted Vanadium (pg/L) In Monitoring Well AB-1 OD For Model Scenarios 1-3

A
40
E
_D 30
([S
c[S
> 20
10
A
Predicted Vanadium at GWA-45
LO LO LO LO cn to sn LO U') in rn ua u) u) LO u)
CD M C7 N I:t (D CO O N CD ao C? CL �t (D
i7'i O] C7 C] C] C] C7 N N N N
r r C\j N N N N N N N N N N Cm N N
Figure 150. Predicted Vanadium (fag/L) In Monitoring Well GWA-4S For Model Scenarios 1-3

50
40
i~33
30
E
D_
0
M
(Z 20
10
01
Predicted Vanadium at GWA-5BR
Existing Condition
LO LO LO LO LO sn LO U) LO Ln ;n LO LO u) u) LO
(4 M C7 N <! to CO C3 N Q- M CO C7 N �t (D
Cf; 07 C] C] C7 C] C] CV N N N
r r C�1 N N N N CV CV N N N N N N N
Figure 151. Predicted Vanadium (pg/L) In Monitoring Well GWA-5BR For Model Scenarios 1-3

LEGEND
0.30
2
5
15
30
50
77
_ DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
ra ,
N
0 500 1,000
Feet
Figure 152. Initial (2015) Vanadium Concentrations (Ng/L) in the Shallow Groundwater Zone

LEGEND
0.30
2
5
15
30
50
77
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
,000
Figure 153. Initial (2015) Vanadium Concentrations (pg/L) in the Deep Groundwater Zone

Figure 154. Initial (2015) Vanadium Concentrations (Ng/L) in the Bedrock Groundwater Zone

Figure 155. "Existing Conditions" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Shallow
Groundwater Zone

f
I
I
I
I
1
I
I
I
LEGEND
0.30
2
5
15 �
30
50
77
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
WITH DUKE ENERGY - 0 500 1.000
PROPERTY BOUNDARY
MODEL DOMAIN Feet
Figure 156. "Existing Conditions" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Deep
Groundwater Zone

Figure 157. "Existing Conditions" Scenario 1 - 2115 Predicted Vanadium (pg/L) in the Bedrock
Groundwater Zone

Figure 158. "Cap -in -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Shallow
Groundwater Zone

Figure 159. "Cap -in -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Deep
Groundwater Zone

/ Mf7
LEGEND
0,30
15
30
50
77
— — DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY CO4NCIDENT
.� WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 160. "Cap -in -Place" Scenario 2 - 2115 Predicted Vanadium (pg/L) in the Bedrock
Groundwater Zone

LEGEND
0,30
2
5
15
30
50
77
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILL/ASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
1
!
I
I
I
I
1
N
A
0 500 1.000
Feet
Figure 161. "Excavation" Scenario 3 - 2115 Predicted Vanadium (fag/L) in the Shallow
Groundwater Zone

Figure 162. "Excavation" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Deep
Groundwater Zone

Figure 163. "Excavation" Scenario 3 - 2115 Predicted Vanadium (pg/L) in the Bedrock
Groundwater Zone