NC0004979_5. Allen CAP Part 2 Appx B_FINAL_20160219

Appendix B

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CI�21ELECTRIC POWER
I RESEARCH INSTITUTE Memorandum
February 18, 2016
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 caveat
associated with this opinion is:
• 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 transport model for constituents identified as COIs; and 3) predictive transport simulations
based on two corrective action options — existing conditions and cap -in -place.
b) Is the site description adequate?
Yes. The site description provided in Section 1.1 is sufficient for the 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
February 18, 2016
Page 2
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 model discretization in the lateral direction is consistent at 20 ft by 20 ft and with the
noted longitudinal and transverse lateral dispersivity values result in Grid Peclet numbers of
approximately 0.25 and 2.5, which is adequate. The model discretization in the vertical
direction is variable ranges from 20 to 40 ft and thus with the noted transverse dispersivity
values, the Grid Peclet numbers range from 0.625 to 5, with the maximum value higher than
preferable but still within the acceptable range.
ii) Hydrologic framework — hydraulic properties
The hydrostratigraphy appears to be implemented reasonably 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 included aerially distributed recharge,
drains, no -flow and constant -heads.
Aerially distributed recharge was the primary source of water inflow to the model and
represents 99.99% of the simulated inflow. The remaining inflow, less than 0.01% of the
total inflow, occurs in constant -head boundaries. The recharge rate was applied based on
type of land cover. The recharge value assigned to non -impacted land was within the defined
applicable range. The method for calculating the recharge in the ash basins and ash ponds
based on depth of water or thickness of saturated ash is appropriate.
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

Allen Model Review
February 18, 2016
Page 3
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. These CHBs constitute 96% of the simulated outflow in the model. 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.
As noted in the report, 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. Residential wells in the model domain were included and account for 4% of the
simulated outflow in the model.
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 background concentration for each COI prior to the
start of the ash basin usage with the ash basins acting as a constant concentration sources in
model layer 4 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 negligible flow mass balance errors.
The cumulative concentration mass balance discrepancy from MT3DMS is consistently less
than 1 percent for the transport simulations. All of the cumulative mass balance errors are
adequate in ensuring minimal constituent mass balance errors by the end of the historical
simulation.
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 Root Mean Absoluter Error over the range in observed
heads of 6.2 percent which is within the industry standard of 10 percent. Therefore the flow
model adequately matches the observed values of July 2015.
The report Section 5.1 states that this single time frame of July 2015 was selected to be
representative of a "long-term average condition." For selection of a long-term average
water -level surface, it would be more appropriate to do a quantitative analysis on the
variation in the water levels over a period of time. However, based on communication with
the model author there was an insufficient amount of water -level data, both spatially and
temporally, to conduct a quantitative analysis. As noted in Section 5.1, this should be
evaluated in the future as more site wide data is collected.

Allen Model Review
February 18, 2016
Page 4
Comparison of simulated and observed concentrations for each of the COIs is discussed by
constituent. In general, the transport calibration is judged by the model simulating high
concentrations where measured concentrations are significantly above background. Because
for many of the constituents, simulated background concentrations are higher than a
significant number of the measured values, matching values in the low range is not possible.
The higher simulated background concentrations should be considered conservative.
Antimony: Of the 13 measured values above background, eight had simulated concentrations
above background.
Arsenic: Of the 18 values that are above the background level, 16 were simulated with a
concentration higher than background but seven values are under estimated by more than 50
percent.
Barium: Of the 26 measured values above background, all but five were simulated with
concentrations above background.
Boron: Of the 29 measured values above background, all but one were simulated with
concentrations above background. Of these, only seven simulated concentrations were
underestimated by greater than 50 percent.
Chromium: Only four measured values were above background. Of these four, only one was
simulated with elevated concentrations.
Cobalt: Of the 24 measured values above background, 18 have simulated concentrations
above background. Of these, 11 had simulated concentrations that were underestimated by 50
percent or more.
Hexavalent Chromium: There were 25 measured values above background with all simulated
values also above background. A total of nine values had simulated concentrations that were
underestimated by 50 percent or more.
Selenium: Of the 14 measured values above background, 10 were simulated to have
concentrations above background. Of these, four were simulated with concentrations that
were underestimated by 50 percent or more.
Sulfate: Of the 25 measured values above background, 20 were simulated to have
concentrations above background. Of these, nine had simulated concentrations that were
underestimated by 50 percent or more.
Vanadium: Of the seven measured values above background, three were simulated at
concentrations above background while the remaining four were simulated at background
values.
In summary, the transport calibration varies among the thirteen constituents. Barium, boron
and sulfate can be considered to have a good fit between measured and simulated, as
low/high concentration trends are generally similar between the measured and simulated
values. Arsenic, hexavalent chrome, selenium and vanadium can also be considered adequate
but with slight underestimation at wells with higher measured concentrations. Antimony,

Allen Model Review
February 18, 2016
Page 5
chromium and cobalt have high measured values that consistently have lower simulated
values than the higher measured values.
Overall, it is difficult to achieve strong concentration match for large numbers of modeled
constituents, particularly if some are affected by geochemical reactions that are not simulated
by MT3DMS. However, the constituents with good concentration match will enable use of
the model for its stated objective.
i) Property/boundary condition correlation —parameter bounds
For the flow model calibration, the recharge was held constant at the assigned values based
on land cover type 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. This is a reasonable and typical approach.
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.
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% and the results indicate the selected parameters for which the calibration
results were most sensitive.
For the transport models, the report noted that a formal sensitivity was not conducted as part
of CAP Part 2 as the parameter sensitivity did not change as a result of updated modeled
parameters. The previous model review conducted indicated that no qualitative comparison
was provided for the transport sensitivity results but an overall discussion was provided.
That review and this subsequent review recommends the inclusion of the constant
concentration source magnitude and location to be included in the sensitivity analysis, along
with the previously included Kd and porosity. In addition, a quantitative description of the
sensitivity results would be beneficial.

Allen Model Review
February 18, 2016
Page 6
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 over 99.99% of the inflows to the model is from
recharge with the remaining from the CHBs and is appropriate given the conceptual model.
A check of the water balances for the outflows shows approximately 96% is attributed to the
CHBs and the remaining 4% is attributed to the domestic production wells.
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
Contributors:
F)2
HDR Engineering, Inc.
440 S. Church St, Suite 1000
Charlotte, NC 28202
Investigators:
11,�
UNC, c
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 February 18, 2016

Groundwater Flow and Transpot Model
Allen Steam Station
TABLE OF CONTENTS
1 Introduction............................................................................................................................1
1.1 General Setting and Background...................................................................................1
1.2 Third Party Review.........................................................................................................2
2 Conceptual Model..................................................................................................................2
2.1 Geology and Hydrogeology............................................................................................2
2.2 Hydrostratigraphic Layer Development..........................................................................3
2.3 Ash Basins and Ash Storage Areas...............................................................................4
2.3.1 Ash Basin................................................................................................................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.........................................................................................................10
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.........................................................................16
4.10 Transport Model Sources and Sinks............................................................................16

Groundwater Flow and Transpot Model
Allen Steam Station
4.11 Transport Model Calibration Targets............................................................................16
5 Model Calibration to Current Conditions..............................................................................16
5.1 Flow Model Residual Analysis......................................................................................16
5.2 Flow Model Sensitivity Analysis....................................................................................17
5.3 Transport Model Calibration and Sensitivity.................................................................18
5.4 Advective Travel Times................................................................................................18
5.5 One Year's Advective Travel Time from Residential Pumping Wells ...........................18
6 Simulations of Closure Scenarios........................................................................................18
6.1 Existing Conditions Scenario........................................................................................19
6.2 Cap -In -Place Scenario.................................................................................................19
7 Closure Scenario Results....................................................................................................19
7.1 Antimony.......................................................................................................................20
7.2 Arsenic..........................................................................................................................20
7.3 Barium..........................................................................................................................20
7.4 Boron............................................................................................................................21
7.5 Chromium.....................................................................................................................21
7.6 Hexavalent Chromium..................................................................................................21
7.7 Cobalt...........................................................................................................................21
7.8 Selenium.......................................................................................................................21
7.9 Sulfate..........................................................................................................................22
7.10 Vanadium.....................................................................................................................22
8 Summary .............................................................................................................................22
8.1 Model Assumptions and Limitations.............................................................................22
8.2 Model Predictions.........................................................................................................23
9 References..........................................................................................................................24
TABLES
Table 1 MODFLOW and MT31DMS Input Packages Utilized
Table 2 Model Hydraulic Conductivity
Table 3 Observed vs. Predicted Hydraulic Head
Table 4 Model Effective Porosity
Table 5 Flow Parameter Sensitivity Analysis
Table 6 Transport Model Calibration Results
Table 7 Predicted Advective Travel Time

Groundwater Flow and Transpot Model
Allen Steam Station
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 Transition Zone Model Layer (Model Layer 8)
Figure 12 Hydraulic Conductivity Zonation in Bedrock Model Layers (Model Layers 9 and10)
Figure 13 Modeled Hydraulic Head vs. Observed Hydraulic Head
Figure 14 Hydraulic Head in Shallow Groundwater Zone (Model Layer 6)
Figure 15 Particle Tracking Results (see Table 6 for Advective Travel Times)
Figure 16 1 Year Reverse Particle Tracking from Residential Wells
Figure 17 Predicted Antimony in Monitoring Well AB-22S
Figure 18 Predicted Antimony in Monitoring Well AB-26S
Figure 19 Predicted Antimony in Monitoring Well AB-32S
Figure 20 Initial (2015) Antimony Concentrations in Shallow Groundwater Zone
Figure 21 Initial (2015) Antimony Concentrations in Deep Groundwater Zone
Figure 22 Initial (2015) Antimony Concentrations in Bedrock Groundwater Zone
Figure 23 Existing Conditions Scenario 1 - 2115 Predicted Antimony in Shallow Groundwater
Zone
Figure 24 Existing Conditions Scenario 1 - 2115 Predicted Antimony in Deep Groundwater Zone
Figure 25 Existing Conditions Scenario 1 - 2115 Predicted Antimony in Bedrock Groundwater
Zone
Figure 26 Cap -in -Place Scenario 2 - 2115 Predicted Antimony in Shallow Groundwater Zone
Figure 27 Cap -in -Place Scenario 2 - 2115 Predicted Antimony in Deep Groundwater Zone
Figure 28 Cap -in -Place Scenario 2 - 2115 Predicted Antimony in Bedrock Groundwater Zone
Figure 29 Predicted Arsenic in Monitoring Well AB-22S
Figure 30 Predicted Arsenic in Monitoring Well AB-26S
Figure 31 Predicted Arsenic in Monitoring Well AB-32S
Figure 32 Initial (2015) Arsenic Concentrations in Shallow Groundwater Zone
Figure 33 Initial (2015) Arsenic Concentrations in Deep Groundwater Zone
Figure 34 Initial (2015) Arsenic Concentrations in Bedrock Groundwater Zone
Figure 35 Existing Conditions Scenario 1 - 2115 Predicted Arsenic in Shallow Groundwater
Zone
Figure 36 Existing Conditions Scenario 1 - 2115 Predicted Arsenic in Deep Groundwater Zone
Figure 37 Existing Conditions Scenario 1 - 2115 Predicted Arsenic in Bedrock Groundwater
Zone
Figure 38 Cap -in -Place Scenario 2 - 2115 Predicted Arsenic in Shallow Groundwater Zone

Groundwater Flow and Transpot Model
Allen Steam Station
Figure 39 Cap -in -Place Scenario 2 - 2115 Predicted Arsenic in Deep Groundwater Zone
Figure 40 Cap -in -Place Scenario 2 - 2115 Predicted Arsenic in Bedrock Groundwater Zone
Figure 41 Predicted Barium in Monitoring Well AB-22S
Figure 42 Predicted Barium in Monitoring Well AB-26S
Figure 43 Predicted Barium in Monitoring Well AB-32S
Figure 44 Initial (2015) Barium Concentrations in Shallow Groundwater Zone
Figure 45 Initial (2015) Barium Concentrations in Deep Groundwater Zone
Figure 46 Initial (2015) Barium Concentrations in Bedrock Groundwater Zone
Figure 47 Existing Conditions Scenario 1 - 2115 Predicted Barium in Shallow Groundwater
Zone
Figure 48 Existing Conditions Scenario 1 - 2115 Predicted Barium in Deep Groundwater Zone
Figure 49 Existing Conditions Scenario 1 - 2115 Predicted Barium in Bedrock Groundwater
Zone
Figure 50 Cap -in -Place Scenario 2 - 2115 Predicted Barium in Shallow Groundwater Zone
Figure 51 Cap -in -Place Scenario 2 - 2115 Predicted Barium in Deep Groundwater Zone
Figure 52 Cap -in -Place Scenario 2 - 2115 Predicted Barium in Bedrock Groundwater Zone
Figure 53 Predicted Boron in Monitoring Well AB-22S
Figure 54 Predicted Boron in Monitoring Well AB-26S
Figure 55 Predicted Boron in Monitoring Well AB-32S
Figure 56 Initial (2015) Boron Concentrations in Shallow Groundwater Zone
Figure 57 Initial (2015) Boron Concentrations in Deep Groundwater Zone
Figure 58 Initial (2015) Boron Concentrations in Bedrock Groundwater Zone
Figure 59 Existing Conditions Scenario 1 - 2115 Predicted Boron in Shallow Groundwater Zone
Figure 60 Existing Conditions Scenario 1 - 2115 Predicted Boron in Deep Groundwater Zone
Figure 61 Existing Conditions Scenario 1 - 2115 Predicted Boron in Bedrock Groundwater Zone
Figure 62 Cap -in -Place Scenario 2 - 2115 Predicted Boron in Shallow Groundwater Zone
Figure 63 Cap -in -Place Scenario 2 - 2115 Predicted Boron in Deep Groundwater Zone
Figure 64 Cap -in -Place Scenario 2 - 2115 Predicted Boron in Bedrock Groundwater Zone
Figure 65 Predicted Chromium in Monitoring Well AB-22S
Figure 66 Predicted Chromium in Monitoring Well AB-26S
Figure 67 Predicted Chromium in Monitoring Well AB-32S
Figure 68 Initial (2015) Chromium Concentrations in Shallow Groundwater Zone
Figure 69 Initial (2015) Chromium Concentrations in Deep Groundwater Zone
Figure 70 Initial (2015) Chromium Concentrations in Bedrock Groundwater Zone
Figure 71 Existing Conditions Scenario 1 - 2115 Predicted Chromium in Shallow Groundwater
Zone
Figure 72 Existing Conditions Scenario 1 - 2115 Predicted Chromium in Deep Groundwater
Zone
Figure 73 Existing Conditions Scenario 1 - 2115 Predicted Chromium in Bedrock Groundwater
Zone
Figure 74 Cap -in -Place Scenario 2 - 2115 Predicted Chromium in Shallow Groundwater Zone
Figure 75 Cap -in -Place Scenario 2 - 2115 Predicted Chromium in Deep Groundwater Zone
Figure 76 Cap -in -Place Scenario 2 - 2115 Predicted Chromium in Bedrock Groundwater Zone
Figure 77 Predicted Hexavalent Chromium in Monitoring Well AB-22S
iv

Groundwater Flow and Transpot Model
Allen Steam Station
Figure 78 Predicted Hexavalent Chromium in Monitoring Well AB-32S
Figure 79 Initial (2015) Hexavalent Chromium Concentrations in Shallow Groundwater Zone
Figure 80 Initial (2015) Hexavalent Chromium Concentrations in Deep Groundwater Zone
Figure 81 Initial (2015) Hexavalent Chromium Concentrations in Bedrock Groundwater Zone
Figure 82 Existing Conditions Scenario 1 - 2115 Predicted Hexavalent Chromium in Shallow
Groundwater Zone
Figure 83 Existing Conditions Scenario 1 - 2115 Predicted Hexavalent Chromium in Deep
Groundwater Zone
Figure 84 Existing Conditions Scenario 1 - 2115 Predicted Hexavalent Chromium in Bedrock
Groundwater Zone
Figure 85 Cap -in -Place Scenario 2 - 2115 Predicted Hexavalent Chromium in Shallow
Groundwater Zone
Figure 86 Cap -in -Place Scenario 2 - 2115 Predicted Hexavalent Chromium in Deep
Groundwater Zone
Figure 87 Cap -in -Place Scenario 2 - 2115 Predicted Hexavalent Chromium in Bedrock
Groundwater Zone
Figure 88 Predicted Cobalt in Monitoring Well AB-22S
Figure 89 Predicted Cobalt in Monitoring Well AB-26S
Figure 90 Predicted Cobalt in Monitoring Well AB-32S
Figure 91 Initial (2015) Cobalt Concentrations in Shallow Groundwater Zone
Figure 92 Initial (2015) Cobalt Concentrations in Deep Groundwater Zone
Figure 93 Initial (2015) Cobalt Concentrations in Bedrock Groundwater Zone
Figure 94 Existing Conditions Scenario 1 - 2115 Predicted Cobalt in Shallow Groundwater Zone
Figure 95 Existing Conditions Scenario 1 - 2115 Predicted Cobalt in Deep Groundwater Zone
Figure 96 Existing Conditions Scenario 1 - 2115 Predicted Cobalt in Bedrock Groundwater Zone
Figure 97 Cap -in -Place Scenario 2 - 2115 Predicted Cobalt in Shallow Groundwater Zone
Figure 98 Cap -in -Place Scenario 2 - 2115 Predicted Cobalt in Deep Groundwater Zone
Figure 99 Cap -in -Place Scenario 2 - 2115 Predicted Cobalt in Bedrock Groundwater Zone
Figure 100 Predicted Selenium in Monitoring Well AB-22S
Figure 101 Predicted Selenium in Monitoring Well AB-26S
Figure 102 Predicted Selenium in Monitoring Well AB-32S
Figure 103 Initial (2015) Selenium Concentrations in The Shallow Groundwater Zone
Figure 104 Initial (2015) Selenium Concentrations in Deep Groundwater Zone
Figure 105 Initial (2015) Selenium Concentrations in Bedrock Groundwater Zone
Figure 106 Existing Conditions Scenario 1 - 2115 Predicted Selenium in Shallow Groundwater
Zone
Figure 107 Existing Conditions Scenario 1 - 2115 Predicted Selenium in Deep Groundwater
Zone
Figure 108 Existing Conditions Scenario 1 - 2115 Predicted Selenium in Bedrock Groundwater
Zone
Figure 109 Cap -in -Place Scenario 2 - 2115 Predicted Selenium in Shallow Groundwater Zone
Figure 110 Cap -in -Place Scenario 2 - 2115 Predicted Selenium in Deep Groundwater Zone
Figure 111 Cap -in -Place Scenario 2 - 2115 Predicted Selenium in Bedrock Groundwater Zone
Figure 112 Predicted Sulfate In Monitoring Well AB-22S
v

Groundwater Flow and Transpot Model
Allen Steam Station
Figure 113 Predicted Sulfate In Monitoring Well AB-26S
Figure 114 Predicted Sulfate In Monitoring Well AB-32S
Figure 115 Initial (2015) Sulfate Concentrations in Shallow Groundwater Zone
Figure 116 Initial (2015) Sulfate Concentrations in Deep Groundwater Zone
Figure 117 Initial (2015) Sulfate Concentrations in Bedrock Groundwater Zone
Figure 118 Existing Conditions Scenario 1 - 2115 Predicted Sulfate in Shallow Groundwater
Zone
Figure 119 Existing Conditions Scenario 1 - 2115 Predicted Sulfate in Deep Groundwater Zone
Figure 120 Existing Conditions Scenario 1 - 2115 Predicted Sulfate in Bedrock Groundwater
Zone
Figure 121 Cap -in -Place Scenario 2 - 2115 Predicted Sulfate in Shallow Groundwater Zone
Figure 122 Cap -in -Place Scenario 2 - 2115 Predicted Sulfate in Deep Groundwater Zone
Figure 123 Cap -in -Place Scenario 2 - 2115 Predicted Sulfate in Bedrock Groundwater Zone
Figure 124 Predicted Vanadium In Monitoring Well AB-22S
Figure 125 Predicted Vanadium In Monitoring Well AB-26S
Figure 126 Predicted Vanadium In Monitoring Well AB-32S
Figure 127 Initial (2015) Vanadium Concentrations in Shallow Groundwater Zone
Figure 128 Initial (2015) Vanadium Concentrations in Deep Groundwater Zone
Figure 129 Initial (2015) Vanadium Concentrations in Bedrock Groundwater Zone
Figure 130 Existing Conditions Scenario 1 - 2115 Predicted Vanadium in Shallow Groundwater
Zone
Figure 131 Existing Conditions Scenario 1 - 2115 Predicted Vanadium in Deep Groundwater
Zone
Figure 132 Existing Conditions Scenario 1 - 2115 Predicted Vanadium in Bedrock Groundwater
Zone
Figure 133 Cap -in -Place Scenario 2 - 2115 Predicted Vanadium in Shallow Groundwater Zone
Figure 134 Cap -in -Place Scenario 2 - 2115 Predicted Vanadium in Deep Groundwater Zone
Figure 135 Cap -in -Place Scenario 2 - 2115 Predicted Vanadium in Bedrock Groundwater Zone
vi

Groundwater Flow and Transpot Model
Allen Steam Station
ACRONYMS
2L Standard North Carolina groundwater standards as specified
3D three-dimensional
BR bedrock wells
CAP Corrective Action Plan
CCR coal combustion residuals
COI constituent of interest
CSA comprehensive site assessment
D deep wells
NCDHHS North Carolina Department of Health and Human Services
DORS distribution of residuals solids
EPRI Electric Power Research Institute
FGD flue gas desulfurization
GIS geographic information systems
HSL health screening level
IMAC interim maximum allowable concentration
MW megawatt
NRMSE normalized root mean square error
RAB retired ash basin
REC recovery
RMS root mean squared
RQD rock quality designation
S shallow wells
in T15A NCAC 02L
vii

Groundwater Flow and Transpot Model
Allen Steam Station
INTRODUCTION
The purpose of this study is to predict the groundwater flow and constituent transport that may
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 site conditions observed
in June 2015, development of a historical transient model for constituent transport calibrated to
current conditions, and predictive simulations of the closure scenarios.
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 is a coal-fired
electricity generating facility with a capacity of 1,155 megawatts (MW) along the Lake Wylie
portion of the Catawba River. 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 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 Lake Wylie (CSA Report
Figures 2-1 through 2-4)1. The ash basin system at Allen consists of an active ash basin and an
inactive ash basin. For convenience, the two ash basins are sometimes jointly referred to as the
ash basin in this report. 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.
In general, the ash basin is located south of the power complex in historical drainage features
formed from tributaries that flowed toward Lake Wylie. There are two earthen dikes impounding
the active ash basin: the East Dike, located along the west bank of Lake Wylie; 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 Dike where
tributaries flowed toward Lake Wylie. As the original ash basin capacity diminished over time,
the active ash basin was formed by constructing the southern portion of the East Dike and
raising the North Dike. Ash has been sluiced to the active ash basin since 1973.
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) (CSA
Report Figure 2-2). Natural topography at the site generally slopes downward and eastward
from that divide toward Lake Wylie, from 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).
1 Please refer to the Comprehensive Site Assessment (CSA) Report, Allen Steam Station Ash Basin, August 2015
(HDR 2015a) for more information and referenced CSA Report figures and tables.
1

Groundwater Flow and Transpot Model
Allen Steam Station
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 Figure 2-4 in the CSA Report.
Based on the CSA, 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 groundwater flow layers (CSA Report 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 Lake Wylie and to the north
toward Duke Energy property and the Station Discharge Canal.
1.2 Third Party Review
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) Report (HDR 2015a), 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 initial Allen groundwater model, the model was refined to
incorporate post-CSA data. These changes did not affect the model structure or boundaries and
did not deviate from EPRI guidelines.An independent review of the refined Allen model was
reviewed by EPRI and found that the model was sufficient to meet the objective of predicting
effects of corrective action alternatives on groundwater quality.
2 CONCEPTUAL MODEL
The site conceptual model for Allen is primarily based on the CSA Report. The CSA Report
contains extensive detail and data related to most aspects of the site conceptual model that are
used in this report.
2.1 Geology and Hydrogeology
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 (CSA Report 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 on CSA Report Figure 5-2.
2

Groundwater Flow and Transpot Model
Allen Steam Station
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. 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 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 2015a).
2.2 Hydrostratigraphic Layer Development
Soil conditions encountered in the borings showed minimal variation across the site. Residual
soil consists of clayey sand, silty sand, silty sand with gravel, micaceous silty sand, and gravel
with silt and sand. The following materials were encountered during the CSA and are consistent
with material descriptions from previous site exploration studies:
Ash — Ash was encountered in borings advanced within the ash basins, 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 reworked silts, clays, and sands that were borrowed
from one area of the site and redistributed 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 areas.
Alluvium —Alluvium encountered in borings during the project was classified as clay and sand
with clay. In some cases alluvium was logged beneath ash.
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

Groundwater Flow and Transpot Model
Allen Steam Station
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 material designations shown below (M1, M2, TZ, and BR) are used on the geologic cross -
sections with transect locations in the CSA (CSA Report Figure 11-1). The ash, fill and alluvial
layers are represented by A, F, and S, respectively, on cross sections and in tables in the CSA.
The ranges of hydrostratigraphic layer properties measured at Allen are provided in CSA Report
Tables 11-8 through 11-12. To further define the hydrostratigraphic units, the following
classification system was used based on standard penetration testing values, recovery (REC),
and rock quality designation (RQD) collected during 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 transition zone just in case it extended into the next core run,
which when reviewed alone might have met the bedrock criterion, because of potential core loss
or fractured/jointed rock with indications of water movement (iron/manganese staining).
2.3 Ash Basins and Ash Storage Areas
Historical and current information about the Allen ash basin system assembled during the CSA
is relevant to developing the conceptual and numerical groundwater flow models. Refer to CSA
Report 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
CSA Report 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. In general, the ash basin is
located in historical depressions formed from tributaries that flowed toward Lake Wylie. The ash
basin is operated as an integral part of the station's wastewater treatment system, which
4

Groundwater Flow and Transpot Model
Allen Steam Station
receives flows from the ash removal system, coal pile runoff, landfill leachate, FGD wastewater,
the station yard drain sump, and site stormwater.
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
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 Lake Wylie.
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, station yard drain sump, and stormwater flows. Due to variability in station
operations and weather, 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 (North Carolina
Department of Environmental Quality (NCDEQ2) 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 dike comprises the eastern boundary of the landfill. Lake Wylie is located
2 Prior to September 18, 2015, the NCDEQ was referred to as the North Carolina Department of Environment and
Natural Resources (NCDENR). Both naming conventions are used in this report, as appropriate
5

Groundwater Flow and Transpot Model
Allen Steam Station
immediately to the east of 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 11), 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 II 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 CSA Report Figure 2-2.
The permit to construct for 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 is situated
over the inactive ash basin and was constructed with a leachate collection and removal system;
a three -component liner system consisting of a primary and secondary geomembrane with a
leak detection system between them; and a 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 pumped to the discharge location in the
northeastern portion of the active ash basin. NCDEQ Division of Water Quality determined that
use of the leachate collection system and leak detection system, coupled with and leachate
sampling, is an acceptable alternative to groundwater monitoring for the landfill which would be
difficult conduct due to 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
portion of the active ash basin in order to provide capacity for sluiced ash in the active ash basin
0

Groundwater Flow and Transpot Model
Allen Steam Station
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 to 24 inches of
soil cover was placed on the top slopes and side slopes, respectively, and vegetation was
established. The ash storage areas encompass an area of approximately 15 to 20 acres and
contain approximately 300,000 cubic yards of ash.
2.4 Groundwater Flow System
Groundwater recharge 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, then
laterally through unconsolidated material (residual soil/saprolite) into the transition zone and,
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
and bedrock zones to distinguish the flow layers within the connected aquifer system. In
general, groundwater within each layer at the site flows from west and southwest to the east
toward Lake Wylie and to the northeast and north toward Duke Energy property and the station
discharge canal (CSA Report 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 (LeGrand 2004), fractured density in
bedrock decreases with depth, limiting deep groundwater flow (CSA Report Figure 5-5).
2.5 Hydrologic Boundaries
The major discharge locations for the groundwater system at Allen, Lake Wylie to the east and
the Station Discharge Canal to the north, act as hydrologic boundaries for the site (CSA Report
Figure 2-4). A no -flow boundary is located between the Discharge Canal and the ash basin
system at a presumptive, natural groundwater divide corresponding to a topographic divide.
Thus, the Discharge Canal is not a component of the ash basin model to the south.
2.6 Hydraulic Boundaries
The RAS Ash Landfill acts as a hydraulic boundary due to its leachate collection system and
three -component liner. Otherwise, the 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.

Groundwater Flow and Transpot Model
Allen Steam Station
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 Lake Wylie. 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. Fifty-eight private water supply wells are included within
the model domain.
The CSA does not consider any effect these wells may have on groundwater flow at the site,
nor does it identify other sources or sinks. The CSA does not suggest the Allen ash basin is
within the capture zone or zone of influence of any extraction well or supply 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.
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 Lake Wylie.
2.9 Modeled Constituents of Interest (COI)
As defined in the CSA, COls are those chemicals or compounds identified in the approved
groundwater assessment plans for sampling and analysis. The following criteria were used to
determine if a COI required modeling: if the constituent exceeded regulatory groundwater
standards (15A NCAC 02L.0202 groundwater 2L Standard or IMAC), and was traceable back
to the source (i.e., existed in porewater), the constituent was 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 may warrant more complex modeling than what is
currently being performed. Thallium has only one estimated value above the exceedence
threshold detected in groundwater which does not yield a discerned plume for calibration
purposes. The simulated COls all occur at elevated levels in groundwater near the ash basins
(CSA Report 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 (Kd) analysis performed.
3 2L Standard North Carolina groundwater standards as specified in T15A NCAC 02L.
8

Groundwater Flow and Transpot Model
Allen Steam Station
2.10 COI Transport
COls enter 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 Kd). 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 of constituents in solution occurs downward
through the stored ash and underlying, unsaturated soils and finally into groundwater at the
water table. Dissolved phase constituents may incur phase changes 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.
The following approach was used for transport modeling:
• A physical -type modeling approach was used, as site -specific geochemical conditions
are not understood or characterized at the scale and extent required for inclusion in the
model.
• The flux of contaminant mass from the ash sources is not quantified, so it is not included
in the conceptual site model or represented in the numerical model. As such, a simplified
approach was used and the entry of constituents was represented in the model using a
constant concentration in the saturated zone of the basin (which is continually flushed by
water moving through the porous media). The constant concentration cells cover the ash
basin Primary Cells and ash storage area sources and the concentrations for each of
these sources were determined during transport model calibration.
The retardation effects of the COls (e.g., by adsorption onto solid surfaces) were
collectively taken into account by specifying a linear soil -water partitioning coefficient
(Kd)-
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. MODFLOW can simulate steady-state and transient flow, as
0

Groundwater Flow and Transpot Model
Allen Steam Station
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 three-dimensional (3-D)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 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 revising flow parameters to best match the observed 2015 concentrations and
water levels 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 (3D) surfaces representing contacts between
hydrostratigraphic units with properties provided in CSA Tables 11-8 through 11-12.
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.
10

Groundwater Flow and Transpot Model
Allen Steam Station
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
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 3D 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 foot x 20 foot grid across the area
to be modeled, a hybrid algorithm was used with inverse distance weighted two and
triangulation weighted one 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
11

Groundwater Flow and Transpot Model
Allen Steam Station
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.
Step 1.
Creating raster files for the model layer
-
Three surface layers (pre -construction, pre -construction with dike, and existing surface
including dike and ash) using GIS and AutoCAD
-
Ttwo subsurface layers transition and bedrock 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., triangulated irregular network (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 and 2) Cap in -place
4.3 Model Domain and Grid
The model domain encompasses the Allen site, including a section of Lake Wylie 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 345,996 active cells in eleven layers. In plan view,
the Allen model domain is bounded by the following hydrologic features of the site.
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Allen Steam Station
• the western shore of 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
• 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 two -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
800 feet below the base of the transition zone across the site upper limit based on a review of
boring logs contained in the CSA Report.
There are a total of 11 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 1 through 3
• Model layers 2 through 4
• Model layer 5 and 6
• Model layer 7
• Model layer 8
• Model layers 9 through 11
Ash Material
Dike and ash storage material
M1 Saprolite and alluvium where present
M2 Saprolite
Transition Zone
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 on 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 Report Tables 11-8 through 11-12 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 Lake Wylie, constant head boundaries representing the
river stage elevation were applied to those layers above fractured bedrock (model layers 9
through 11) with bottom elevations below the water surface interpolated from photogrammetric
surveys.
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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.
4.6 Flow Model Sources and Sinks
Recharge is the main source considered in the model. (Drainage boundaries are described
above as flow boundary conditions.) Mean annual recharge in the Piedmont ranges from 4.0 to
9.7 inches per year (Daniel 2001). Recharge applied to the area of the model outside the ash
basins was assigned a value of 7 inches per year. Recharge within the ash basins was
calculated using Darcy's Law based on the area of the ash basin, the approximate depth of
water or saturated ash, and the range of measured hydraulic conductivity values within the ash
and fill. The calculation provided a narrow range of recharge values, with a value of 14.5 inches
per year applied to the ash basins and a value of 21.9 inches per year over the ash pond.
Recharge in the model is shown on Figure 5.
Pumping wells were identified in the CSA. 44 residential pumping wells are within the current
model domain and have been included as active pumping wells completed within the bedrock
layer during calibration and predictive scenarios. Actual pumping rates are unknown, so a
constant pumping rate of 400 gallons per day, which is the average EPA household usage, has
been used.
4.7 Flow Model Calibration Targets
The steady-state flow model calibration targets are the 56 static water level measurements
taken in observations made in July 2015. The observation wells included 22 wells screened in
the shallow saprolite flow layers (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,
and bedrock groundwater zones are shown on 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 (CSA Report 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 were the constant concentration at
the source zone, the linear sorption coefficient (Kd) for sorptive constituents (including all COls,
except for sulfate), the effective porosity, and the dispersivity tensor.
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.
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The conceptual transport model specifies that Cols enter the model from the shallow saturated
source zones in the ash basins. The range of Kd values applied was derived from UNCC
laboratory measured values and adjusted to achieve calibration in the model. The most
appropriate method to calibrate the transport model was to use the lower limit of measured Kd
values to produce an acceptable agreement between measured and modeled concentrations.
Thus, an effective Kd value results which 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:
• Antimony: 2 ml/g
• Arsenic: 30 ml/g
• Barium: 2.5 ml/g
• Boron: 1 ml/g
• Chromium: 4 ml/g
• Cobalt: 2 ml/g
• Hexavalent Chromium: 0.8 ml/g
• Selenium: 5 ml/g
• Sulfate: conservative (sorption not modeled)
• Vanadium: 10 ml/g
The bulk density used in the model is 2.65 grams/cubic centimeter for saprolite, deep, 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
(CSA Report Tables 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 2002). The dispersivity
quantifies the degree to which mechanical dispersion of COls occurs. Dispersivity values of 80
feet, 8 feet, and 8 feet (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 and transverse
dispersivity, and the ratio of layer thickness to vertical dispersivity, should be less than two and
no more than 10 to minimize numerical dispersion (Zheng and Bennett 2002). The longitudinal
and transverse dispersivity results in grid Peclet numbers of 0.25 and 2.5, which is within the
acceptable range. The vertical discretization is more variable than the horizontal discretization
with model layers 5 and 6 and fracture bedrock layers at approximately 20 to 40 feet, and the
transition zone on the order of 10 feet or less. The variable vertical discretization results in grid
Peclet numbers of 0.625 to 5, which is within the acceptable range.
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Groundwater Flow and Transpot Model
Allen Steam Station
4.9 Transport Model Boundary Conditions
The transport model boundary conditions have an initial concentration of zero where water
leaves the model. The background concentration used as initial concentrations for each COI is
specified as the proposed provisional background concentration (PPBC) identified in the Allen
Corrective Action Plan (CAP) Part 1 (HDR 2015b).
The background concentrations for the COls applied as initial concentrations are as follows:
• Antimony: 0.5 pg/L/g
• Arsenic: 2.3 pg/L
• Barium: 99 pg/L
• Boron: 50 pg/L
• Chromium: 16 pg/L/g
• Cobalt: 0.74 pg/L
• Hexavalent Chromium: 0.05 pg/L
• Selenium: 0.5 pg/L
• Sulfate: 30,300 pg/L
• Thallium: 0.1 pg/L
• Vanadium: 22.5 pg/L
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
5). Their magnitudes are based on COI measurements in the shallow groundwater zone from
the June/July 2015 sampling event.
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 Report Tables 7-6 and 10-8. 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
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Groundwater Flow and Transpot Model
Allen Steam Station
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 on 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 on 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.
The calibrated flow model parameters are provided in Table 2. Modeled and observed water
levels (post -calibration) are compared in Table 3 and on 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 6.2%.
Contours of hydraulic heads in the calibrated flow model are shown for the shallow groundwater
zone (model layer 6) on 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 groundwater zone. Groundwater within the shallow, deep, and
bedrock layers flows from the west and southwest to the east and discharges to Lake Wylie.
Locally the water table gradient is reduced beneath Primary Ponds 1, 2, and 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 Landfill dikes.
5.2 Flow Model Sensitivity Analysis
It is important to understand the sensitivity of the flow model parameters on the predicted
hydraulic head field, so that the affects of changing the parameters are known. The sensitivity of
flow model parameters was tested by varying a subset of parameters by 20% above and below
the values used in the calibrated flow model. The sensitivity was evaluated by re -running the
model and comparing the NRMSE for each simulation (Table 5). A smaller NRMSE indicates
that the model is better calibrated (i.e., model -predicted hydraulic head values better match the
actual or observed values). Using this approach, it was determined that NRMSE is maximized
and the flow model is most sensitive to positive or negative changes in horizontal hydraulic
conductivity in the shallow aquifer, followed by changes in recharge outside of the ash basins.
The least sensitive flow model parameter tested (minimized NRMSE) was changes in the
vertical hydraulic conductivity in the shallow groundwater zone and transition zone.
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Groundwater Flow and Transpot Model
Allen Steam Station
5.3 Transport Model Calibration and Sensitivity
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 based on the measured
pore water concentrations 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 COIs. Table 6 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 on 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 zones of each COI for each
closure simulation.
Detailed sensitivity analyses for porosity, dispersivity, and sorption were not completed as part
of CAP Part 2 as informal sensitivity analysis indicated that sensitive parameters did not change
due to revisions to the model parameters. A decrease in the Kd resulted in an increase in the
spatial extent in the modeled concentrations from the source areas. An increase in porosity and
dispersivity also resulted in an increase in the spatial extent in the modeled concentrations from
the source areas.
5.4 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 Lake Wylie and also near the
western model boundary. The particle tracks are shown on Figure 15 and predicted advective
travel times are provided in Table 7.
5.5 One Year's Advective Travel Time from Residential Pumping Wells
As previously discussed, 44 residential pumping wells are included in the model domain,
pumping at a rate of 400 gallons per day each. The advective travel time one year from each
each well was performed using MODPATH and is shown on Figure 16. The one year advective
travel time pathlines do not intersect the Compliance Boundary at Allen.
6 SIMULATIONS OF CLOSURE SCENARIOS
The groundwater model, calibrated for flow and constituent fate and transport under existing
conditions, was applied to evaluate two ash basin closure scenarios at Allen: 1) Existing
Conditions and 2) Cap -in -Place. Being predictive, these simulations produce flow and transport
results for conditions that are beyond the range of those considered during the calibration. Thus,
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Groundwater Flow and Transpot Model
Allen Steam Station
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 scenario. For the Cap -in -Place scenario, recharge was set to zero over the
ash basin and ash storage areas to simulate an engineered cap. Source concentrations
remained active in the model, as long as, they remained saturated. Water levels were reduced
due to zero recharge over the ash basin and ash storage areas and flow parameters for this
model were identical to the Existing Conditions scenario.
6.1 Existing Conditions Scenario
The Existing Conditions scenario consists of modeling each COI using the calibrated model for
steady-state flow and transient transport under the existing conditions across the site to
estimate when steady-state concentrations would be reached across the site and at the
Compliance Boundary. COI concentrations can only remain the same or increase initially for this
scenario with source concentrations being held at their constant value over all time. Thereafter,
their concentrations and discharge rates remain constant. This scenario represents the most
conservative case in terms of groundwater concentrations on and off site, and COls discharging
to surface water at steady-state.
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 reach steady-state sooner. The time to reach 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 both sorptive and non-sorptive COIs. Lower total porosity will
result in longer times for sorptive COIs.
6.2 Cap -In -Place Scenario
The Cap -in -Place scenario simulates the effects of covering the ash basins at the beginning of
the predictive simulation with an engineered cap. In the model, recharge at the ash basins is 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 24 feet relative to the level
simulated under the Existing Conditions scenario. In the active ash basins, the difference in
water level is approximately 32 feet. 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 migration in groundwater is retarded relative to the pore velocity of
groundwater due to sorption. The model uses the predicted concentration from the 2015
calibration as the initial concentration at the start of the model scenario.
7 CLOSURE SCENARIO RESULTS
Closure scenario results are presented as predicted concentration vs. time plots in
downgradient monitor wells and as predicted groundwater concentration maps for each
modeled COI on Figures 17 through 135, as discussed in the following sub -sections.
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Groundwater Flow and Transpot Model
Allen Steam Station
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. Concentration contours and concentration breakthrough
curves are referenced to 1957, since that is the year that the ash basin became effective.
Constituent concentrations were analyzed at three downgradient monitoring wells: AB-22S, AB-
26S and AB-36S (Figure 6) for all COls. Each of these wells is directly downgradient from the
ash basins or ash storage area and upgradient of the ash basin Compliance Boundary at Lake
Wylie.
7.1 Antimony
Figures 17 through 28 show predicted antimony concentrations for the modeled downgradient
monitoring wells. The concentration versus time curves (Figures 17 to 19) show that, under the
Existing Conditions scenario, antimony exceeds the IMAC of 1 pg/L in 2015 at AB-26S. The
Cap -in -Place scenario results in the reduction of concentrations over time. However, the
observed antimony value in AB-26S is 0.5 pg/L and the model is overpredicting (based on
calibrated input values ) the concentration. Figures 20 to 22 show initial (2015) antimony
concentrations in the shallow, deep and bedrock groundwater zones. In 2115, antimony is
predicted to exceed the IMAC along the Compliance Boundary along Lake Wylie in all layers
under both the Existing Conditions scenario (Figures 23 to 25) and the Cap -in -Place scenario
(Figures 26 to 28).
7.2 Arsenic
Figures 29 through 40 show predicted arsenic concentrations for the modeled downgradient
monitoring wells. The concentration versus time curves (Figures 29 to 31) show that, under the
Existing Conditions scenario, arsenic exceeds the 2L Standard (10 pg/L) at AB-22S and AB-32S
within the next 85 years and is below the 2L Standard at AB-26S. The Cap -in -Place scenario
shows an increase in concentration at two wells over time, exceeding the standard at AB-22S
by the end of the modeling period. Although, the observed arsenic value in AB-22S and AB-32S
is below 0.5 ug/L and the model is overpredicting the concentration partially due to the initial
concentration in the model of 2.3 ug/L. Figures 32 to 34 show initial (2015) arsenic
concentrations in the shallow, deep and bedrock groundwater zones. Arsenic is predicted to
exceed the groundwater standard at the Compliance Boundary under both the Existing
Conditions scenario (Figures 35 to 37) and Cap -in -Place scenario (Figures 38 to 40) in shallow
and deep groundwater layers.
7.3 Barium
Figures 41 through 52 show predicted barium concentrations for the modeled downgradient
monitoring wells. The concentration versus time curves (Figures 41-43) show thatwhile barium
is predicted to show a slight increase in concentration, it remains far below the 2L Standard
(700 pg/L) through the modeled period. Figures 44 to 46 show initial (2015) barium
concentrations in the shallow, deep and bedrock groundwater zones. After 100 years, barium is
not predicted to exceed the 2L Standard at the Compliance Boundary under the Existing
Conditions scenario (Figures 47 to 49) or the Cap -in -Place scenario (Figures 50 to 52) in all
groundwater layers.
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Groundwater Flow and Transpot Model
Allen Steam Station
7.4 Boron
Figures 53 through 64 show predicted boron concentrations for the modeled downgradient
monitoring wells. The concentration versus time curves (Figures 53 to 55) show that, under the
Existing Conditions scenario, boron is predicted to exceed the 2L Standard of 700 lag/L at AB-
22S and AB-26S, but remain under the 2L Standard in all three wells under the Cap -in -Place
scenario. Figures 56 to 58 show initial (2015) boron concentrations in the shallow, deep and
bedrock groundwater zones. After 100 years, boron is predicted to exceed the 2L Standard at
Lake Wylie Compliance Boundary under both the Existing Conditions scenario (Figures 59 to
61) and Cap -in -Place scenario (Figures 62 to 64) in the shallow and deep groundwater zones.
7.5 Chromium
Figures 65 through 76 show predicted chromium concentrations for the modeled downgradient
monitoring wells. The concentration versus time curves (Figures 65 to 67) show that chromium
decreases to below the 2L Standard of 10 lag/L in the all three downgradient monitor wells
under both scenarios. Figures 68 to 70 show initial (2015) chromium concentrations in the
shallow, deep and bedrock groundwater zones. After 100 years, chromium is predicted to
remain above the 2L Standard at the Compliance Boundary under both the Existing Conditions
and Cap -in -Place scenario (Figures 71 to 73 and 74 to 76, respectively).
7.6 Hexavalent Chromium
Figure 77 through 87 shows predicted hexavalent chromium concentrations at AB-22S and AB-
32S downgradient of the ash storage area for both scenarios. The concentration versus time
curves (Figures 77 to 78) show hexavalent chromium is predicted to remain above the
NCDHHS HSL of 0.07 lag/L. However, the model overpredicts concentrations in these monitor
wells, which both show measured concentrations below the NCDHHS HSL. Figures 79 to 81
show initial (2015) hexavalent chromium concentrations in the shallow, deep and bedrock
groundwater zones. After 100 years, hexavalent chromium is predicted to exceed the NCDHHS
HSL at the southern Compliance Boundary in all groundwater zones under the Existing
Conditions scenario (Figures 82-84) and in the shallow zone only under the Cap -in -Place
scenario (Figures 85 to 87.
7.7 Cobalt
Figures 88 through 99 show predicted cobalt concentrations for the modeled downgradient
monitoring wells. The concentration versus time curves (Figures 88 to 90) for the three
downgradient monitor wells show that cobalt is predicted to remain above the IMAC of 1 lag/L for
both scenarios, although the Cap -in -Place scenario shows a slower rate of increase in two wells
and decreases the third. Figures 91 to 93 show initial (2015) cobalt concentrations in the
shallow, deep and bedrock groundwater zozones. After 100 years, cobalt is predicted to exceed
the IMAC at Compliance Boundary under both the Existing Conditions scenario (Figures 94 to
96) and the Cap -in -Place scenario (Figures 97 to 99) in all groundwater zones.
7.8 Selenium
Figures 100 through 111 show predicted selenium concentrations for the modeled downgradient
monitoring wells. The concentration versus time curves (Figures 100 to 102) show that selenium
21

Groundwater Flow and Transpot Model
Allen Steam Station
remains at background concentrations well under the 2L Standard of 20 pg/L under both
scenarios. Figures 103 to 105 show initial (2015) selenium concentrations in the shallow, deep
and bedrock groundwater zones. After 100 years, selenium is not predicted to exceed the 2L
Standard of 20 pg/L at the Compliance Boundary under either the Existing Conditions scenario
(Figures 206 to 108) or Cap -in -Place scenario (Figures 109 to 111) within all groundwater
zones.
7.9 Sulfate
Figures 112 through 123 show predicted sulfate concentrations for the modeled downgradient
monitoring wells for both scenarios. The concentration versus time curves (Figures 112 to 114)
for all three monitoring wells show that sulfate remains below the 2L Standard of 250,000 pg/L
for both scenarios. Figures 115 to 117 show initial (2015) sulfate concentrations exceeding the
2L Standard in the shallow, deep and bedrock groundwater zones. After 100 years, sulfate is
predicted to exceed the 2L Standard at the northern Compliance Boundary under the Existing
Conditions scenarios within all groundwater zones (Figures 118 to 121). Under the Cap -in -Place
scenario (Figures 121 to 123), sulfate is predicted to fall below the standard at the Compliance
Boundary in all groundwater zones.
7.10 Vanadium
Figures 124 through 135 show predicted vanadium concentrations for the modeled
downgradient monitoring wells. The concentration versus time curves (Figures 124 to 126) show
that vanadium remains elevated above the IMAC of 0.3 pg/L for both scenarios due to the initial
background concentrations of 22.5 pg/L. Figures 127 to 129 show initial (2015) vanadium
concentrations in the shallow, deep and bedrock groundwater zones. After 100 years, vanadium
is predicted to exceed the proposed rpovisional background concentration at Lake Wylie
Compliance Boundary under the Existing Conditions scenario (Figures 130 to 132), and the
Cap -in -Place scenario (Figures 133 to 135) within all groundwater zones.
8 SUMMARY
8.1 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 included considereation of ash basin water levels. 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
approach for simulating flow in the primary porous groundwater zones and bedrock was
used for contaminant transport at Lake Wylie.
The model was calibrated by adjusting the constant source concentrations at the ash
basins and ash storage area to genearally match 2015 COI concentrations in
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Groundwater Flow and Transpot Model
Allen Steam Station
groundwater. The ash basin and ash storage area source concentrations are held
constant throughout the simulation period which results in greater contaminant mass
entering the groundwater system than would occur in the system.
• 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 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. As previously mentioned,
model predictions ultimately overpredict to remain conservative.
• Since Lake Wylie 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.
• Presented travel times are advective and do not account for sorption of COls to host
rock, which would cause the travel times to be reduced.
• Residential wells have an assumed constant pumping rate of 400 gallons per day and
are completed within bedrock.
• The model does not account for varying geochemical conditions such as pH and redox
potential that could affect COI mobility and change modeling results.
8.2 Model Predictions
The model predictions are summarized as follows:
• Antimony and cobalt are predicted to exceed the IMAC at Compliance Boundary along
Lake Wylie in all groundwater zones under both the Existing Conditions and Cap -in -
Place scenarios.
• Barium, selenium are not predicted to exceed the 2L Standard at the Compliance
Boundary under either scenario.
• Chromium and arsenic are predicted to exceed the 2L Standard at the Compliance
Boundary under the Existing Conditions and Cap -in -Place scenarios for all groundwater
zones.
• Boron is predicted to exceed the 2L Standard at the Compliance Boundary along Lake
Wylie under the Existing Conditions and Cap -in -Place scenarios in both the shallow and
deep groundwater zones, but not the bedrock layer.
23

Groundwater Flow and Transpot Model
Allen Steam Station
• Hexavalent chromium is predicted to exceed the NCDHHS HSL at the southern
Compliance Boundary under the Existing Conditions scenario in all groundwater zones
and in the shallow layer only under the Cap -in -Place scenario.
• Sulfate Is predicted to exceed the 2L Standard at the northern Compliance Boundary
under the Existing Conditions scenario but not under the Cap -in -Place scenario. Among
the COls, sulfate is considered conservative; that is, this constituent does not have a
strong affinity to attenuate nor adsorb to soil/rock surfaces.
• Vanadium is predicted to exceed the IMAC at Compliance Boundary along Lake Wylie
under the Existing Conditions scenario and under the Cap -in -Place scenario.
• COls are not predicted to exceed standards at the western Compliance Boundary.
9 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. 2015a. Comprehensive Site Assessment Report, Allen Steam Station Ash Basin, August
23, 2015.
HDR, 2015b. Corrective Action Plan Part 1. Allen Steam Station Ash Basin, November 20,
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.
24

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Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Tables
Table 1 MODFLOW and MT3DMS Input Packages Utilized
Table 2 Model Hydraulic Conductivity
Table 3 Observed vs. Predicted Hydraulic Head
Table 4 Model Effective Porosity
Table 5 Flow Parameter Sensitivity Analysis
Table 6 Transport Model Calibration Results
Table 7 Predicted Advective Travel Time

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
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

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 2 Model Hydraulic Conductivity
Model
Layer
Hydrostrati-
graphic Unit
Measured
Value Range
Calibrated Model Value
Horizontal
Hydraulic
Conductivity
(ft/day)
Horizontal Hydraulic
Conductivity (ft/day)
Vertical Hydraulic
Conductivity (ft/day)
1-4
Ash
9.12-0.05
Z-1
5
1
Z-2
2
0.8
4
Dike
7.86-0.01
Z-3
0.004
0.004
5-6
7
M1/Alluvium
M2
14.29-0.0033
11.67-0.0042
Z-4
0.1480
0.0500
Z-5
0.2700
0.1000
Z-6
0.5000
0.5000
Z-7
1.0000
0.2000
Z-8
1.3000
0.1000
Z-9
1.4000
0.1000
Z-10
2.0000
0.8000
Z-11
3.1260
0.3126
Z-12
6.0000
2.0000
Z-13
14.0000
1.0000
Z-25
2.3300
0.5000
Z-26
2.6990
0.2699
8
Transition
Zone
60.06-0.09
Z-5
0.2700
0.1000
Z-6
0.5000
0.5000
Z-7
1.0000
0.2000
Z-17
5.0000
2.0000
Z-18
9.0000
2.0000
9-11
Bedrock
5.52-0.0004
Z-19
0.0001
0.00001
Z-20
0.0010
0.0001
Z-21
0.0050
0.0005
Z-22
0.0070
0.0007
Z-23
0.0100
0.0010
Z-24
1.4000
0.1000
'Range = geometric mean +/- one standard deviation (see CSA Report Tables 11-10)

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 3 Observed vs. Predicted Hydraulic Head
Well Name
Model
Layer
Meas. WL
ft MSL
Model WL
ft MSL
Residual
ft
AB-20S
6
636.88
636.98
-0.10
AB-21 BR
9
635.69
632.13
3.56
AB-22D
8
599.04
596.27
2.77
AB-23S
6
636.29
630.93
5.36
AB-24D
8
634.68
625.59
9.09
AB-26D
8
583.61
584.09
-0.48
AB-27D
8
617.22
607.19
10.03
AB-28D
8
629.26
616.99
12.27
AB-29D
8
612.71
606.22
6.49
AB-30D
8
619.54
615.34
4.20
AB-31 D
8
578.91
581.30
-2.39
AB-31 S
8
577.90
581.30
-3.40
AB-32D
8
577.00
581.71
-4.71
AB-32S
6
582.74
582.52
0.22
AB-33D
8
593.95
599.20
-5.25
AB-33S
6
600.39
599.41
0.98
AB-34D
8
611.73
612.47
-0.74
AB-34S
6
612.65
612.17
0.48
AB-35BR
9
620.57
619.61
0.96
AB-35D
8
620.47
618.48
1.99
AB-35S
6
619.80
618.49
1.31
AB-36D
8
620.93
623.26
-2.33
AB-36S
6
620.23
623.42
-3.19
AB-37D
8
622.69
625.49
-2.80
AB-37S
6
621.13
625.35
-4.22
AB-38D
8
624.26
622.78
1.48
AB-38S
6
624.70
622.78
1.92
AB-39D
8
619.72
613.59
6.13
GWA-14D
8
626.04
631.12
-5.08
GWA-14S
6
627.66
631.42
-3.76
GWA-15D
8
625.87
627.06
-1.19
GWA-15S
6
625.80
627.36
-1.56
GWA-1 BR
9
614.27
613.25
1.02
GWA-1 D
8
614.73
614.82
-0.09
GWA-1S
6
615.24
614.82
0.42
GWA-21D
8
573.27
576.72
-3.45
GWA-2S
6
570.53
576.88
-6.35
GWA-313R
9
573.69
578.06
-4.37
Continued on next page

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 3 Observed vs. Predicted Hydraulic Head (continued)
Well Name
Model
Layer
Meas. WL
ft MSL
Model WL
ft MSL
Residual
ft
GWA-3D
8
573.82
574.41
-0.59
GWA-3S
6
571.48
574.65
-3.17
GWA-4D
8
570.83
570.57
0.26
GWA-4S
6
571.72
571.13
0.59
GWA-5BR
9
562.37
574.61
-12.24
GWA-51D
8
571.24
570.81
0.43
GWA-5S
6
567.19
572.00
-4.81
GWA-6BR
9
588.56
595.80
-7.24
GWA-6D
8
586.68
599.52
-12.84
GWA-6S
6
597.31
598.72
-1.41
GWA-9D
8
636.70
637.26
-0.56
GWA-9S
6
635.68
637.30
-1.62
AB-21 D
8
635.70
632.53
3.17
AB-20D
8
636.41
636.97
-0.56
AB-22S
6
595.01
596.76
-1.75
AB-26S
6
582.05
584.23
-2.18
SSE 1143.62
Max 636.88 OBS 54
Min 562.37 MSE 4.60
Max -Min 74.51 NRMSE 0.062

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
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

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 5 Flow Parameter Sensitivity Analysis
Calibrated
Calibrated +20%
Calibrated -20%
Parameter
NRMSR (Head)
NRMSR (Head)
%
NRMSR (Head)
%
Shallow
0.0900
45.16
0.1070
72.58
Zone Kh
Shallow
0.0620
0.00
0.0610
-1.61
Zone Kv
Transition
0.0640
3.23
0.0640
3.23
Zone Kh
0.0620
Transition Zone
0.0640
3.23
0.0620
0.00
Kv
Recharge
0.0860
38.71
0.0840
35.48
ex. ash basin
Recharge
0.0680
9.68
0.0730
17.74
ash basin

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results
COI
Monitoring
Well
Measured
Concentration
(pg/L)/L
Predicted
Concentration
Antimony
Ash Basin Constant
Concentration Range
= 0.5 - 20 pg/I
Ash Storage
Area Concentration Range
= 0.5 - 20 pg/I
Sorption
Coefficient [Kd] =
2 mI/g
AB-1 OD
0.28
0.49
AB-1 OS
0.50
0.48
AB-11 D
0.50
0.44
AB-12D
0.50
0.50
AB-12S
0.50
0.47
AB-13D
0.50
0.50
AB-13S
0.43
0.48
AB-14D
0.50
0.50
AB-1 R
0.50
0.50
AB-2
0.50
0.50
AB-20D
0.50
0.50
AB-21 BR
0.50
0.50
AB-21 D
0.18
0.50
AB-22D
0.21
0.50
AB-22S
0.50
0.50
AB-23BRU
1.10
0.50
AB-24 D
1.30
0.60
AB-25BR
0.63
0.52
AB-25BRU
0.50
0.52
AB-26D
2.70
0.77
AB-26S
0.50
2.15
AB-27D
0.19
0.54
AB-28D
0.50
0.50
AB-29D
0.50
2.00
AB-21D
0.20
0.50
AB-30D
0.50
0.50
AB-31 D
6.00
2.49
AB-31 S
0.50
7.01
AB-32D
0.50
0.49
AB-32S
0.36
0.48
AB-33D
0.50
0.49
AB-33S
0.50
0.48
AB-34D
0.23
0.50
AB-34S
0.50
0.48

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Antimony
(cont.)
AB-35BR
0.50
0.50
AB-35D
0.33
0.50
AB-36D
0.50
0.50
AB-36S
0.50
0.50
AB-37D
1.00
0.49
AB-38D
0.24
0.49
AB-39D
0.21
0.58
AB-4S
0.50
0.47
AB-5
0.50
0.49
AB-6R
0.50
0.50
AB-91D
0.19
0.79
AB-9S
0.50
1.78
AB-20S
0.50
0.50
AB-21 S
1.30
0.50
AB-21SL
8.00
0.50
AB-23S
0.28
0.42
AB-24S
1.00
1.00
AB-24SL
0.27
1.00
AB-25S
9.90
10.00
AB-25SL
0.63
10.00
AB-27S
0.50
0.60
AB-28S
0.30
0.44
AB-29S
0.38
10.00
AB-29SL
10.30
10.00
AB-30S
0.23
0.50
AB-35S
0.50
0.50
AB-37S
0.50
0.50
AB-38S
1.20
0.43
Arsenic
Ash Basin Constant Concentration Range = 42 - 1600 pg/I
Ash Storage Area Concentration Range = 42 - 1600 pg/I
Sorption Coefficient [Kd] = 30 ml/g
AB-10D
0.13
2.30
AB-10S
0.50
2.29
AB-11 D
0.50
2.25
AB-12D
0.15
2.30
AB-12S
0.50
2.30
AB-13D
0.18
2.30

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Arsenic
(cont.)
AB-13S
0.50
2.30
AB-14D
0.50
2.30
AB-1 R
1.70
2.30
AB-2
0.50
2.30
AB-20D
1.70
2.30
AB-21 BR
1.50
2.30
AB-21 D
1.20
2.30
AB-22D
0.30
2.35
AB-22S
0.19
4.57
AB-23BRU
2.40
2.30
AB-24D
1.00
2.31
AB-25BR
1.40
2.30
AB-25BRU
1.80
2.30
AB-26D
6.90
2.30
AB-26S
0.16
2.39
AB-27D
0.39
2.31
AB-28D
0.68
2.30
AB-29D
0.91
2.36
AB-21D
0.15
2.30
AB-30D
0.32
2.31
AB-31 D
0.68
2.30
AB-31 S
0.13
2.30
AB-32D
0.43
2.33
AB-32S
0.21
2.94
AB-33D
0.47
2.30
AB-33S
0.18
2.41
AB-34D
0.52
2.30
AB-34S
0.33
2.30
AB-35BR
0.84
2.30
AB-35D
1.20
2.30
AB-36D
1.10
2.32
AB-36S
369.00
204.15
AB-37D
0.37
2.31
AB-38D
0.41
2.30
AB-39D
2.40
2.38
AB-4S
0.12
2.30
AB-5
0.50
2.30

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
p /L
Predicted
Concentration
N /L
Arsenic
(cont.)
AB-6R
0.14
2.30
AB-91D
0.50
2.30
AB-9S
0.15
2.30
AB-20S
1230.00
1200.00
AB-21 S
351.00
350.00
AB-21 SL
759.00
350.00
AB-23S
1060.00
8.35
AB-24S
41.80
50.00
AB-24SL
867.00
50.00
AB-25S
74.70
865.00
AB-25SL
865.00
293.12
AB-27S
56.40
17.66
AB-28S
27.60
15.47
AB-29S
671.00
280.00
AB-29SL
69.80
280.00
AB-30S
284.00
280.00
AB-35S
83.10
83.00
AB-37S
0.40
45.41
AB-38S
0.50
2.28
Barium
Ash Basin Constant
Concentration Range
= 160 - 1000 pg/I
Ash Storage Area
Concentration Range
= 160 - 1000 pg/I
Sorption
Coefficient [Kd] =
2.5 ml/g
AB-10D
34.00
166.86
AB-10S
51.00
183.21
AB-11 D
40.00
78.84
AB-12D
42.00
88.81
AB-12S
31.00
69.22
AB-13D
41.00
95.03
AB-13S
37.00
72.20
AB-14D
61.00
94.56
AB-1 R
16.00
99.00
AB-2
26.00
91.48
AB-20D
14.00
109.32
AB-20S
240.00
250.00
AB-21 BR
10.00
99.00
AB-21 D
41.00
174.75
AB-21 S
380.00
250.00

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Barium
(cont.)
AB-21 SL
250.00
250.00
AB-22D
82.00
202.46
AB-22S
64.00
223.30
AB-23BRU
17.00
99.00
AB-23S
60.00
127.78
AB-24D
130.00
144.64
AB-24S
170.00
200.00
AB-24SL
100.00
200.00
AB-25BR
150.00
99.05
AB-25BRU
12.00
99.05
AB-25S
170.00
200.00
AB-25SL
190.00
200.00
AB-26D
140.00
202.36
AB-26S
100.00
326.10
AB-27D
51.00
163.75
AB-27S
110.00
182.09
AB-28D
38.00
136.84
AB-28S
110.00
169.25
AB-29D
35.00
140.93
AB-29S
300.00
160.00
AB-29SL
150.00
160.00
AB-21D
26.00
87.42
AB-30D
40.00
119.11
AB-30S
280.00
160.00
AB-31 D
25.00
127.98
AB-31 S
20.00
128.32
AB-32D
46.00
134.95
AB-32S
27.00
143.03
AB-33D
46.00
127.31
AB-33S
27.00
139.62
AB-34D
16.00
108.22
AB-34S
39.00
112.07
AB-35BR
19.00
99.00
AB-35D
21.00
122.92
AB-35S
160.00
160.00
AB-36D
18.00
342.90
AB-36S
990.00
794.52

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Barium
(cont.)
AB-37D
27.00
68.25
AB-37S
21.00
21.00
AB-38D
140.00
141.68
AB-38S
31.00
-
AB-39D
180.00
352.68
AB-4S
27.00
71.93
AB-5
30.00
85.75
AB-6R
28.00
98.99
AB-91D
28.00
115.66
AB-9S
150.00
125.92
GWA-14D
210.00
95.60
GWA-14S
110.00
66.33
GWA-15D
32.00
82.15
GWA-15S
39.00
63.36
GWA-1 BR
72.00
102.79
GWA-1 D
30.00
115.87
GWA-1 S
60.00
118.53
GWA-21D
20.00
89.27
GWA-2S
49.00
77.58
GWA-3BR
9.40
123.32
GWA-31D
4.60
181.26
GWA-3S
37.00
284.90
GWA-41D
20.00
119.78
GWA-4S
55.00
126.77
GWA-5BR
15.00
111.85
GWA-51D
26.00
125.76
GWA-5S
140.00
131.59
GWA-6BR
110.00
98.16
GWA-6S
250.00
93.13
GWA-91D
36.00
92.87
GWA-9S
35.00
72.45
Boron
Ash Basin Constant Concentration Range = 50 - 3800 pg/I
Ash Storage Area Concentration Range = 50 - 3800 pg/I
Sorption Coefficient [Kd] = 1 ml/g
AB-10D
50.00
254.72
AB-10S
50.00
347.27
AB-11 D
50.00
42.95

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Boron'
(cont.)
AB-12D
50.00
48.63
AB-12S
50.00
42.72
AB-13D
50.00
49.77
AB-13S
50.00
44.67
AB-14D
37.00
49.65
AB-1 R
50.00
49.99
AB-2
50.00
51.40
AB-20D
50.00
121.92
AB-21 BR
50.00
53.47
AB-21 D
29.00
531.02
AB-22D
1500.00
451.28
AB-22S
50.00
596.26
AB-23BRU
30.00
71.77
AB-24D
50.00
102.13
AB-25BR
50.00
84.09
AB-25BRU
50.00
87.03
AB-26D
93.00
169.89
AB-26S
730.00
479.14
AB-27D
1500.00
1362.05
AB-28D
37.00
80.38
AB-29D
210.00
527.02
AB-21D
50.00
48.80
AB-30D
50.00
149.02
AB-31 D
310.00
864.76
AB-31 S
1800.00
1739.38
AB-32D
490.00
49.55
AB-32S
50.00
48.70
AB-33D
180.00
341.23
AB-33S
690.00
627.41
AB-34D
50.00
83.97
AB-34S
230.00
141.61
AB-35BR
50.00
63.70
AB-35D
50.00
187.71
AB-36D
50.00
107.01
AB-36S
260.00
274.53
AB-37D
50.00
49.08
AB-38D
50.00
46.58

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
p /L
Predicted
Concentration
N /L
Boron
(Cont.)
AB-39D
80.00
353.00
AB-4S
50.00
44.10
AB-5
50.00
47.46
AB-6R
50.00
95.04
AB-91D
520.00
62.37
AB-9S
620.00
92.91
AB-20S
6800.00
3800.00
AB-21 S
3800.00
3800.00
AB-21 SL
7400.00
3800.00
AB-23S
560.00
520.73
AB-24S
190.00
200.00
AB-24SL
650.00
200.00
AB-25S
2800.00
3000.00
AB-25SL
1400.00
3000.00
AB-27S
470.00
2256.51
AB-28S
960.00
168.99
AB-29S
1100.00
1100.00
AB-29SL
2400.00
1100.00
AB-30S
830.00
830.00
AB-35S
860.00
860.00
AB-37S
50.00
27.18
AB-38S
50.00
-
Chromium
Ash Basin Constant
Concentration Range
= 2 - 35 pg/I
Ash Storage
Area Concentration Range
= 2 - 35 pg/I
Sorption
Coefficient [Kd] =
4 ml/g
AB-10D
4.30
15.74
AB-10S
0.26
15.16
AB-11 D
3.10
14.64
AB-12D
0.73
15.98
AB-12S
0.88
15.61
AB-13D
1.70
16.00
AB-13S
0.74
15.79
AB-14D
1.40
16.00
AB-1 R
4.20
16.00
AB-2
0.60
15.98
AB-20D
3.60
16.00
AB-21 BR
18.90
16.00

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Chromium
(cont.)
AB-21 D
13.90
15.87
AB-22D
1.20
13.57
AB-22S
0.61
10.15
AB-23BRU
65.60
15.99
AB-24D
13.30
15.04
AB-25BR
9.10
15.99
AB-25BRU
2.30
15.99
AB-26D
29.80
15.86
AB-26S
1.90
14.31
AB-27D
1.70
15.10
AB-28D
4.00
15.86
AB-29D
1.50
14.96
AB-21D
2.70
15.98
AB-30D
0.82
15.75
AB-31 D
4.40
15.56
AB-31 S
0.79
12.92
AB-32D
5.00
13.54
AB-32S
0.94
9.65
AB-33D
2.20
15.65
AB-33S
0.50
12.33
AB-34D
3.80
15.98
AB-34S
0.33
15.62
AB-35BR
3.40
16.00
AB-35D
24.70
16.07
AB-36D
1.60
15.85
AB-36S
0.38
7.67
AB-37D
1.00
15.37
AB-38D
0.61
15.72
AB-39D
2.20
14.34
AB-4S
1.80
15.72
AB-5
12.50
15.95
AB-6R
15.90
15.99
AB-91D
0.85
15.91
AB-9S
0.61
15.24
AB-20S
0.20
2.00
AB-21 S
0.56
2.00
AB-21 SL
0.55
2.00

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Chromium
(cont.)
AB-23S
0.19
12.04
AB-24S
0.25
2.00
AB-24SL
0.30
2.00
AB-25S
0.38
2.00
AB-25SL
1.60
2.00
AB-27S
0.78
10.42
AB-28S
0.70
8.65
AB-29S
0.24
2.00
AB-29SL
0.63
2.00
AB-30S
0.42
2.00
AB-35S
0.43
2.00
AB-37S
1.00
2.00
AB-38S
0.87
12.97
Cobalt
Ash Basin Constant
Concentration Range
= 0.5 - 45 pg/I
Ash Storage
Area Concentration Range
= 0.5 - 45 pg/I
Sorption
Coefficient [Kd] =
2 ml/g
AB-10D
0.29
1.96
AB-10S
1.60
2.94
AB-11 D
0.50
0.65
AB-12D
0.50
0.73
AB-12S
0.72
0.69
AB-13D
0.50
0.74
AB-13S
1.10
0.71
AB-14D
10.10
0.74
AB-1 R
0.50
0.74
AB-2
2.00
0.73
AB-20D
0.22
0.74
AB-21 BR
0.50
0.74
AB-21 D
0.22
0.81
AB-22D
0.62
4.81
AB-22S
8.60
8.27
AB-23BRU
0.19
0.74
AB-24D
0.50
0.69
AB-25BR
0.50
0.74
AB-25BRU
0.50
0.74
AB-26D
9.90
1.86
AB-26S
5.90
7.05

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Cobalt
(Cont.)
AB-27D
0.50
6.02
AB-28D
0.15
1.44
AB-29D
0.13
1.49
AB-21D
0.18
0.73
AB-30D
1.40
0.78
AB-31 D
0.79
0.78
AB-31 S
0.18
0.78
AB-32D
2.00
8.55
AB-32S
14.30
14.98
AB-33D
0.53
3.61
AB-33S
12.30
10.12
AB-34D
0.32
0.74
AB-34S
40.00
0.72
AB-35BR
0.50
0.74
AB-35D
1.70
0.72
AB-36D
0.15
0.72
AB-36S
0.32
0.57
AB-37D
0.20
0.71
AB-38D
5.00
1.14
AB-39D
0.90
3.11
AB-4S
0.40
0.70
AB-5
0.40
0.73
AB-6R
0.17
0.74
AB-91D
0.50
0.78
AB-9S
6.80
0.95
AB-20S
2.10
2.00
AB-21 S
5.20
2.00
AB-21 SL
0.26
2.00
AB-23S
0.29
0.93
AB-24S
0.66
0.50
AB-24SL
0.50
0.50
AB-25S
2.90
0.50
AB-25SL
0.29
0.50
AB-27S
14.20
14.00
AB-28S
42.30
17.37
AB-29S
0.50
1.10
AB-29SL
0.22
1.10

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Cobalt
(cont.)
AB-30S
1.10
1.10
AB-35S
0.50
0.50
AB-37S
0.23
-
AB-38S
11.80
2.69
Hexavalent
Chromium
Ash Basin Constant
Concentration Range
= 0.02 - 45 pg/I
Ash Storage
Area Concentration Range
= 0.02 - 45 pg/I
Sorption
Coefficient [Kd] =
0.8 ml/g
AB-10D
3.00
0.32
AB-10S
0.02
0.24
AB-11 D
2.60
0.95
AB-12D
0.47
0.48
AB-12S
0.10
0.41
AB-13D
1.20
0.50
AB-13S
0.43
0.43
AB-14D
0.87
0.49
AB-1 R
4.00
0.50
AB-20D
1.70
0.65
AB-21 BR
20.00
0.50
AB-21 D
20.00
12.61
AB-22D
0.02
0.26
AB-22S
0.02
0.15
AB-24D
19.00
17.46
AB-25BR
4.70
0.50
AB-25BRU
0.83
0.50
AB-29D
0.82
2.23
AB-31 D
1.40
1.02
AB-31 S
0.16
1.03
AB-32D
0.02
1.26
AB-32S
0.02
1.60
AB-33D
0.07
1.05
AB-33S
0.02
1.47
AB-35BR
2.90
0.50
AB-35D
6.10
5.53
AB-36D
0.73
0.87
AB-36S
0.02
1.66
AB-37D
0.34
0.79
AB-38D
0.02
0.43

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
p /L
Predicted
Concentration
N /L
Hexavalent
Chromium
(cont.)
AB-39D
0.02
0.89
AB-4S
0.36
0.43
AB-91D
0.08
0.79
AB-9S
0.02
1.14
GWA-31D
0.92
0.44
GWA-3S
0.02
0.31
GWA-91D
0.64
0.50
GWA-9S
0.02
0.43
Selenium
Ash Basin Constant
Concentration Range
= 1 - 20 pg/I
Ash Storage
Area Concentration Range
= 1 - 20 pg/I
Sorption
Coefficient [Kd] =
5 ml/g
AB-10D
0.50
0.50
AB-10S
0.50
0.50
AB-11 D
0.50
0.46
AB-12D
0.71
0.50
AB-12S
0.50
0.49
AB-13D
0.50
0.50
AB-13S
0.50
0.50
AB-14D
0.50
0.50
AB-1 R
0.32
0.50
AB-2
0.50
0.50
AB-20D
0.30
0.50
AB-21 BR
1.10
0.50
AB-21 D
0.84
0.60
AB-22D
0.50
0.56
AB-22S
0.50
0.68
AB-23BRU
6.70
0.50
AB-24D
0.91
0.93
AB-25BR
0.82
0.50
AB-25BRU
0.34
0.50
AB-26D
0.88
0.52
AB-26S
0.50
0.73
AB-27D
0.50
0.70
AB-28D
0.27
0.50
AB-29D
0.44
1.40
AB-21D
0.50
0.50
AB-30D
0.50
0.51

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Selenium
(cont.)
AB-31 D
2.10
0.85
AB-31 S
0.50
0.88
AB-32D
0.50
0.56
AB-32S
0.50
0.67
AB-33D
0.50
0.50
AB-33S
0.50
0.58
AB-34D
0.50
0.50
AB-34S
0.50
0.50
AB-35BR
0.50
0.50
AB-35D
0.31
0.50
AB-36D
0.24
0.50
AB-36S
0.50
0.74
AB-37D
0.50
0.51
AB-38D
0.50
0.53
AB-39D
1.70
1.67
AB-4S
0.50
0.49
AB-5
0.50
0.50
AB-6R
0.41
0.50
AB-91D
2.70
0.51
AB-9S
0.50
0.68
AB-20S
0.48
1.00
AB-21 S
0.50
20.00
AB-21 SL
1.20
20.00
AB-23S
0.24
2.76
AB-24S
0.50
10.00
AB-24SL
0.22
10.00
AB-25S
1.90
5.00
AB-25SL
0.44
5.00
AB-27S
0.50
2.78
AB-28S
0.57
0.70
AB-29S
0.50
20.00
AB-29SL
18.70
20.00
AB-30S
0.50
1.00
AB-35S
0.50
1.00
AB-37S
0.24
0.11
AB-38S
0.50
-

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Sulfate
Ash Basin Constant
Concentration Range
p /I
= 25,000 - 350,000
Ash Storage Area
Concentration Range =
25,000 - 350,000 pg/I
Sorption
Coefficient [Kd] =
0 ml/g
AB-10D
20700
45874
AB-10S
16700
45250
AB-11 D
1000
6990
AB-12D
4100
6744
AB-12S
1000
5731
AB-13D
490
6423
AB-13S
760
4030
AB-14D
11100
5611
AB-1 R
37800
9728
AB-2
1000
8039
AB-20D
11700
46030
AB-21 BR
46800
36449
AB-21 D
23600
90428
AB-22D
42800
49297
AB-22S
55300
49192
AB-23BRU
171000
66065
AB-24D
13200
40512
AB-25BR
22200
40280
AB-25BRU
15800
40225
AB-26D
57100
59608
AB-26S
68400
56592
AB-27D
109000
60853
AB-28D
23400
25916
AB-29D
41600
119951
AB-21D
1000
5567
AB-30D
18900
36242
AB-31 D
35800
80146
AB-31 S
108000
79754
AB-32D
23300
58049
AB-32S
2100
54164
AB-33D
12500
298187
AB-33S
337000
297471
AB-34D
3900
110093

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Sulfate
(cont.)
AB-34S
119000
110241
AB-35BR
3900
48077
AB-35D
15700
32652
AB-36D
18900
31060
AB-36S
1400
36497
AB-37D
6100
18758
AB-38D
35100
11237
AB-39D
26400
214389
AB-4S
10100
4471
AB-5
950
3562
AB-6R
26400
31163
AB-91D
42500
65117
AB-9S
30100
63497
AB-20S
390000
125000
AB-21 S
80400
80000
AB-21 SL
122000
80000
AB-23S
9900
55477
AB-24S
12800
25000
AB-24SL
23300
25000
AB-25S
127000
25000
AB-25SL
79800
25000
AB-27S
30000
72404
AB-28S
158000
23529
AB-29S
93700
200000
AB-29SL
220000
200000
AB-30S
46500
48000
AB-35S
313000
40000
AB-37S
4200
22100
AB-38S
1100
-
Vanadium
Ash Basin Constant Concentration Range = 10 - 50 pg/I
Ash Storage Area Concentration Range = 10 - 50 pg/I
Sorption Coefficient [Kd] = 10 ml/g
AB-10D
5.30
22.47
AB-10S
0.37
22.25
AB-11 D
1.80
21.41
AB-12D
3.90
22.50
AB-12S
0.37
22.39

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Vanadium
(cont.)
AB-13D
7.10
22.50
AB-13S
1.10
22.45
AB-14D
0.96
22.50
AB-1 R
21.50
22.50
AB-2
0.54
22.50
AB-20D
36.90
22.50
AB-21 BR
17.70
22.50
AB-21 D
14.00
22.50
AB-22D
3.30
22.50
AB-22S
1.20
22.45
AB-23BRU
29.90
22.50
AB-24D
16.80
22.50
AB-25BR
27.20
22.50
AB-25BRU
18.10
22.50
AB-26D
93.20
22.53
AB-26S
2.10
23.36
AB-27D
6.30
22.50
AB-28D
13.20
22.50
AB-29D
16.30
22.52
AB-21D
6.10
22.50
AB-30D
13.60
22.50
AB-31 D
13.90
22.50
AB-31 S
1.10
22.50
AB-32D
9.50
22.54
AB-32S
0.81
22.66
AB-33D
7.60
22.50
AB-33S
1.00
22.30
AB-34D
16.30
22.50
AB-34S
1.00
22.41
AB-35BR
16.10
22.50
AB-35D
21.10
22.50
AB-36D
16.80
22.50
AB-36S
0.39
23.26
AB-37D
8.60
22.51
AB-38D
3.00
22.46
AB-39D
6.30
22.53
AB-4S
0.60
22.42

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 6 Transport Model Calibration Results (continued)
COI
Monitoring
Well
Measured
Concentration
N /L
Predicted
Concentration
N /L
Vanadium
(cont.)
AB-5
2.30
22.49
AB-6R
4.40
22.50
AB-91D
7.20
22.49
AB-9S
1.00
22.36
AB-20S
0.99
22.50
AB-21 S
3.00
22.50
AB-21 SL
28.60
22.50
AB-23S
5.10
21.02
AB-24S
3.10
22.50
AB-24SL
2.20
22.50
AB-25S
47.40
50.00
AB-25SL
18.00
50.00
AB-27S
2.10
21.63
AB-28S
1.00
20.70
AB-29S
13.50
25.00
AB-29SL
70.80
25.00
AB-30S
2.20
25.00
AB-35S
1.90
25.00
AB-37S
7.90
13.37
AB-38S
1.10
-

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Table 7 Predicted Advective Travel Time
Groundwater
Zone
Monitoring Well
Advective Travel Time
to Model Boundary
(days)
Shallow
AB-35S
6,659
AB-36S
8,093
AB-24S
16,212
AB-20S
126,138
GWA-1 S
2,508
AB-32S
276
GWA-3S
406
GWA-2S
669
Deep
AB-35D
9,559
AB-36D
4,393
AB-24D
12,209
GWA-1 D
87
AB-32D
8
GWA-3D
28
GWA-2D
24
Bedrock
AB-35BR
182,978
GWA-1 BR
2,021
GWA-5BR
1,035
GWA-3BR
20,413
AB-21 BR
6,784,247
'Computed travel time over 3-D flow path using flow and transport terms
from the groundwater flow and transport model.

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
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 Transition Zone Model Layer (Model Layer 8)
Figure 12 Hydraulic Conductivity Zonation in Bedrock Model Layers (Model Layers 9 and10)
Figure 13 Modeled Hydraulic Head vs. Observed Hydraulic Head
Figure 14 Hydraulic Head in Shallow Groundwater Zone (Model Layer 6)
Figure 15 Particle Tracking Results (see Table 6 for Advective Travel Times)
Figure 16 1 Year Reverse Particle Tracking from Residential Wells
Figure 17 Predicted Antimony in Monitoring Well AB-22S
Figure 18 Predicted Antimony in Monitoring Well AB-26S
Figure 19 Predicted Antimony in Monitoring Well AB-32S
Figure 20 Initial (2015) Antimony Concentrations in Shallow Groundwater Zone
Figure 21 Initial (2015) Antimony Concentrations in Deep Groundwater Zone
Figure 22 Initial (2015) Antimony Concentrations in Bedrock Groundwater Zone
Figure 23 Existing Conditions Scenario 1 - 2115 Predicted Antimony in Shallow Groundwater
Zone
Figure 24 Existing Conditions Scenario 1 - 2115 Predicted Antimony in Deep Groundwater Zone
Figure 25 Existing Conditions Scenario 1 - 2115 Predicted Antimony in Bedrock Groundwater
Zone
Figure 26 Cap -in -Place Scenario 2 - 2115 Predicted Antimony in Shallow Groundwater Zone
Figure 27 Cap -in -Place Scenario 2 - 2115 Predicted Antimony in Deep Groundwater Zone
Figure 28 Cap -in -Place Scenario 2 - 2115 Predicted Antimony in Bedrock Groundwater Zone
Figure 29 Predicted Arsenic in Monitoring Well AB-22S
Figure 30 Predicted Arsenic in Monitoring Well AB-26S
Figure 31 Predicted Arsenic in Monitoring Well AB-32S
Figure 32 Initial (2015) Arsenic Concentrations in Shallow Groundwater Zone
Figure 33 Initial (2015) Arsenic Concentrations in Deep Groundwater Zone
Figure 34 Initial (2015) Arsenic Concentrations in Bedrock Groundwater Zone
Figure 35 Existing Conditions Scenario 1 - 2115 Predicted Arsenic in Shallow Groundwater
Zone
Figure 36 Existing Conditions Scenario 1 - 2115 Predicted Arsenic in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 37 Existing Conditions Scenario 1 - 2115 Predicted Arsenic in Bedrock Groundwater
Zone
Figure 38 Cap -in -Place Scenario 2 - 2115 Predicted Arsenic in Shallow Groundwater Zone
Figure 39 Cap -in -Place Scenario 2 - 2115 Predicted Arsenic in Deep Groundwater Zone
Figure 40 Cap -in -Place Scenario 2 - 2115 Predicted Arsenic in Bedrock Groundwater Zone
Figure 41 Predicted Barium in Monitoring Well AB-22S
Figure 42 Predicted Barium in Monitoring Well AB-26S
Figure 43 Predicted Barium in Monitoring Well AB-32S
Figure 44 Initial (2015) Barium Concentrations in Shallow Groundwater Zone
Figure 45 Initial (2015) Barium Concentrations in Deep Groundwater Zone
Figure 46 Initial (2015) Barium Concentrations in Bedrock Groundwater Zone
Figure 47 Existing Conditions Scenario 1 - 2115 Predicted Barium in Shallow Groundwater
Zone
Figure 48 Existing Conditions Scenario 1 - 2115 Predicted Barium in Deep Groundwater Zone
Figure 49 Existing Conditions Scenario 1 - 2115 Predicted Barium in Bedrock Groundwater
Zone
Figure 50 Cap -in -Place Scenario 2 - 2115 Predicted Barium in Shallow Groundwater Zone
Figure 51 Cap -in -Place Scenario 2 - 2115 Predicted Barium in Deep Groundwater Zone
Figure 52 Cap -in -Place Scenario 2 - 2115 Predicted Barium in Bedrock Groundwater Zone
Figure 53 Predicted Boron in Monitoring Well AB-22S
Figure 54 Predicted Boron in Monitoring Well AB-26S
Figure 55 Predicted Boron in Monitoring Well AB-32S
Figure 56 Initial (2015) Boron Concentrations in Shallow Groundwater Zone
Figure 57 Initial (2015) Boron Concentrations in Deep Groundwater Zone
Figure 58 Initial (2015) Boron Concentrations in Bedrock Groundwater Zone
Figure 59 Existing Conditions Scenario 1 - 2115 Predicted Boron in Shallow Groundwater Zone
Figure 60 Existing Conditions Scenario 1 - 2115 Predicted Boron in Deep Groundwater Zone
Figure 61 Existing Conditions Scenario 1 - 2115 Predicted Boron in Bedrock Groundwater Zone
Figure 62 Cap -in -Place Scenario 2 - 2115 Predicted Boron in Shallow Groundwater Zone
Figure 63 Cap -in -Place Scenario 2 - 2115 Predicted Boron in Deep Groundwater Zone
Figure 64 Cap -in -Place Scenario 2 - 2115 Predicted Boron in Bedrock Groundwater Zone
Figure 65 Predicted Chromium in Monitoring Well AB-22S
Figure 66 Predicted Chromium in Monitoring Well AB-26S
Figure 67 Predicted Chromium in Monitoring Well AB-32S
Figure 68 Initial (2015) Chromium Concentrations in Shallow Groundwater Zone
Figure 69 Initial (2015) Chromium Concentrations in Deep Groundwater Zone
Figure 70 Initial (2015) Chromium Concentrations in Bedrock Groundwater Zone
Figure 71 Existing Conditions Scenario 1 - 2115 Predicted Chromium in Shallow Groundwater
Zone
Figure 72 Existing Conditions Scenario 1 - 2115 Predicted Chromium in Deep Groundwater
Zone
Figure 73 Existing Conditions Scenario 1 - 2115 Predicted Chromium in Bedrock Groundwater
Zone
Figure 74 Cap -in -Place Scenario 2 - 2115 Predicted Chromium in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 75 Cap -in -Place Scenario 2 - 2115 Predicted Chromium in Deep Groundwater Zone
Figure 76 Cap -in -Place Scenario 2 - 2115 Predicted Chromium in Bedrock Groundwater Zone
Figure 77 Predicted Hexavalent Chromium in Monitoring Well AB-22S
Figure 78 Predicted Hexavalent Chromium in Monitoring Well AB-32S
Figure 79 Initial (2015) Hexavalent Chromium Concentrations in Shallow Groundwater Zone
Figure 80 Initial (2015) Hexavalent Chromium Concentrations in Deep Groundwater Zone
Figure 81 Initial (2015) Hexavalent Chromium Concentrations in Bedrock Groundwater Zone
Figure 82 Existing Conditions Scenario 1 - 2115 Predicted Hexavalent Chromium in Shallow
Groundwater Zone
Figure 83 Existing Conditions Scenario 1 - 2115 Predicted Hexavalent Chromium in Deep
Groundwater Zone
Figure 84 Existing Conditions Scenario 1 - 2115 Predicted Hexavalent Chromium in Bedrock
Groundwater Zone
Figure 85 Cap -in -Place Scenario 2 - 2115 Predicted Hexavalent Chromium in Shallow
Groundwater Zone
Figure 86 Cap -in -Place Scenario 2 - 2115 Predicted Hexavalent Chromium in Deep
Groundwater Zone
Figure 87 Cap -in -Place Scenario 2 - 2115 Predicted Hexavalent Chromium in Bedrock
Groundwater Zone
Figure 88 Predicted Cobalt in Monitoring Well AB-22S
Figure 89 Predicted Cobalt in Monitoring Well AB-26S
Figure 90 Predicted Cobalt in Monitoring Well AB-32S
Figure 91 Initial (2015) Cobalt Concentrations in Shallow Groundwater Zone
Figure 92 Initial (2015) Cobalt Concentrations in Deep Groundwater Zone
Figure 93 Initial (2015) Cobalt Concentrations in Bedrock Groundwater Zone
Figure 94 Existing Conditions Scenario 1 - 2115 Predicted Cobalt in Shallow Groundwater Zone
Figure 95 Existing Conditions Scenario 1 - 2115 Predicted Cobalt in Deep Groundwater Zone
Figure 96 Existing Conditions Scenario 1 - 2115 Predicted Cobalt in Bedrock Groundwater Zone
Figure 97 Cap -in -Place Scenario 2 - 2115 Predicted Cobalt in Shallow Groundwater Zone
Figure 98 Cap -in -Place Scenario 2 - 2115 Predicted Cobalt in Deep Groundwater Zone
Figure 99 Cap -in -Place Scenario 2 - 2115 Predicted Cobalt in Bedrock Groundwater Zone
Figure 100 Predicted Selenium in Monitoring Well AB-22S
Figure 101 Predicted Selenium in Monitoring Well AB-26S
Figure 102 Predicted Selenium in Monitoring Well AB-32S
Figure 103 Initial (2015) Selenium Concentrations in The Shallow Groundwater Zone
Figure 104 Initial (2015) Selenium Concentrations in Deep Groundwater Zone
Figure 105 Initial (2015) Selenium Concentrations in Bedrock Groundwater Zone
Figure 106 Existing Conditions Scenario 1 - 2115 Predicted Selenium in Shallow Groundwater
Zone
Figure 107 Existing Conditions Scenario 1 - 2115 Predicted Selenium in Deep Groundwater
Zone
Figure 108 Existing Conditions Scenario 1 - 2115 Predicted Selenium in Bedrock Groundwater
Zone
Figure 109 Cap -in -Place Scenario 2 - 2115 Predicted Selenium in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 110 Cap -in -Place Scenario 2 - 2115 Predicted Selenium in Deep Groundwater Zone
Figure 111 Cap -in -Place Scenario 2 - 2115 Predicted Selenium in Bedrock Groundwater Zone
Figure 112 Predicted Sulfate In Monitoring Well AB-22S
Figure 113 Predicted Sulfate In Monitoring Well AB-26S
Figure 114 Predicted Sulfate In Monitoring Well AB-32S
Figure 115 Initial (2015) Sulfate Concentrations in Shallow Groundwater Zone
Figure 116 Initial (2015) Sulfate Concentrations in Deep Groundwater Zone
Figure 117 Initial (2015) Sulfate Concentrations in Bedrock Groundwater Zone
Figure 118 Existing Conditions Scenario 1 - 2115 Predicted Sulfate in Shallow Groundwater
Zone
Figure 119 Existing Conditions Scenario 1 - 2115 Predicted Sulfate in Deep Groundwater Zone
Figure 120 Existing Conditions Scenario 1 - 2115 Predicted Sulfate in Bedrock Groundwater
Zone
Figure 121 Cap -in -Place Scenario 2 - 2115 Predicted Sulfate in Shallow Groundwater Zone
Figure 122 Cap -in -Place Scenario 2 - 2115 Predicted Sulfate in Deep Groundwater Zone
Figure 123 Cap -in -Place Scenario 2 - 2115 Predicted Sulfate in Bedrock Groundwater Zone
Figure 124 Predicted Vanadium In Monitoring Well AB-22S
Figure 125 Predicted Vanadium In Monitoring Well AB-26S
Figure 126 Predicted Vanadium In Monitoring Well AB-32S
Figure 127 Initial (2015) Vanadium Concentrations in Shallow Groundwater Zone
Figure 128 Initial (2015) Vanadium Concentrations in Deep Groundwater Zone
Figure 129 Initial (2015) Vanadium Concentrations in Bedrock Groundwater Zone
Figure 130 Existing Conditions Scenario 1 - 2115 Predicted Vanadium in Shallow Groundwater
Zone
Figure 131 Existing Conditions Scenario 1 - 2115 Predicted Vanadium in Deep Groundwater
Zone
Figure 132 Existing Conditions Scenario 1 - 2115 Predicted Vanadium in Bedrock Groundwater
Zone
Figure 133 Cap -in -Place Scenario 2 - 2115 Predicted Vanadium in Shallow Groundwater Zone
Figure 134 Cap -in -Place Scenario 2 - 2115 Predicted Vanadium in Deep Groundwater Zone
Figure 135 Cap -in -Place Scenario 2 - 2115 Predicted Vanadium in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Groundwater
Discharge
Figure 1 Conceptual Groundwater Flow Model/Model Domain

0
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
W
7
Figure 2 Model Domain North -South Cross Section (A -A') through Inactive and Active Ash Basins

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
B B'
Figure 3 Model Domain East-West Cross Section (B-B') through the Active Ash Basin

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 4 Flow Model Boundary Conditions

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 5 Model Recharge Areas and Contaminant Source Zones (Constant Concentration
Cells)

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 6 Observation Wells in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 7 Observation Wells in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 8 Observation Wells in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
.. Z-6
LEGEND
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
MODELDOMAIN
Z-10 I Z-11
I
Z-12 I
Z!7
I
/
Z-8:� -
Z-12
�i
Z-6
f
a` Zi.
5
.r
N
0 500 1,000
Feet
Figure 9 Hydraulic Conductivity Zonation in S/M1 Model Layers (Model Layers 5-6)

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Z-4
LEGEND
DUKE ENERGY
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 S00 1,000
Feet
Figure 10 Hydraulic Conductivity Zonation in M2 Model Layer (Model Layer 7)

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
I `\
!!M
I Z-7
LEGEND
DUKE ENERGY
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
} ;I
")Z-6
7Af
N
A
0 S00 1,000
Feet
Figure 11 Hydraulic Conductivity Zonation in Transition Zone Model Layer (Model Layer 8)

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 12 Hydraulic Conductivity Zonation in Bedrock Model Layers (Model Layers 9
and10)

Me
630
620
aD
610
m
600
-o 590
0
580
570
560
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Observed vs. Computed Target Values
o�
0110
0
00 4
0
0
0
0
0
o
oao
00
0
I
0
0 0
�
560 570 580 590 600 610 620 630 640
Observed Value (feet)
Figure 13 Modeled Hydraulic Head vs. Observed Hydraulic Head
Layer 6
0 Layer 8
Layer 9

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 14 Hydraulic Head in Shallow Groundwater Zone (Model Layer 6)

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 15 Particle Tracking Results (see Table 6 for Advective Travel Times)

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 16 1 Year Reverse Particle Tracking from Residential Wells

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Predicted Antimony Concentration at AB-22S
1.2
1.0
0.8
J
1
a� 0.6
•..r
0
+� 0.4 —
l'R
}, Existing Conditions
c
0 2 _ Cap -in -Place _
0
V Antimony IMAC
0.0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ln rti a7 r-I m Ln r- a7 r-� m Ln r- a) r-I m Ln rti
a� a) a7 0 0 0 0 0 r-� r-I r-� r-I r-� rU rU rU rU
rti rIIj rU rIIj r i rU rIIj rU rIIj rU rU rIIj rU rti
Notes:
1. µg/L = micrograms per liter Time (Years)
2.Antimony IMAC value = 1 µg/L
3. Antimony PPBC = 0.5 µg/L
Figure 17 Predicted Antimony in Monitoring Well AB-22S

Predicted Antimony Concentration at AB-26S
12.0
MIXI]
:1
J
1
6.0
0
4.0
L
a 2.0
U
0.0
0 0 O
Ln rl- 61
61 61 61
Notes: ri ri r-I
1. µg/L = micrograms per liter
2.Antimony IMAC value = 1 µg/L
3. Antimony PPBC = 0.5 µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
O 0 0 O 0 0 O O O 0 O O 0
rq M Ln 61 r- M Ln f 61 r-I ro Ln
O p r- r-I r-I r-I r- rti rV rU
rV rJ rV rV rV rV rV rV rV rV rV rV rV
Time (Years)
Figure 18 Predicted Antimony in Monitoring Well AB-26S

Predicted Antimony Concentration at AB-32S
1.2
1.0
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
- Existing Conditions
0.8
-
Cap -in -Place
J
0.6
Antimony IMAC
0
4-1
0.4
L
Q
0.2
U
0.0 -!—-
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ln � C) � ro Ln � C m Ln � al � CO Ln �
a, a) c, 0 0 0 0 o r r ri � rti rti rU rU
r rl r rU rV rU rV ri rU rU rU rV rU rU rV rU rU
Notes:
1. µg/L = micrograms per liter
2.Antimony IMAC value = 1 µg/L
3. Antimony PPBC = 0.5 µg/L
Figure 19 Predicted Antimony in Monitoring Well AB-32S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 0.5 (Background
Concentration)
0.5 - 1.0 (Standard)
1.0 - 2.5
2.5 - 5.0
5.0 - 7.5
i 7.5 - 10.0
w
10.0 - 12.26
9
DUKE ENERGY
'a PROPERTY BOUNDARY
f
ASH BASIN WASTE
m BOUNDARY
w
S LANDFILL/ASH STORAGE
AREA BOUNDARY
w ASH BASIN COMPLIANCE
BOUNDARY
Q
ASH BASIN COMPLIANCE
w BOUNDARY COINCIDENT
'o WITH DUKE ENERGY
a PROPERTY BOUNDARY
a MODEL DOMAIN
1. Ng/L = micrograms per liter
2. Antimony IMAC value = 1 Ng/L
3. Antimony PPBC = 0.5 Ng/L
N
A
0 500 1,000
Feet
Figure 20 Initial (2015) Antimony Concentrations in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
N
Z
O
�7
Z
w
N
O
g
LEGEND
b <= 0.5 (Background
g Concentration)
0.5 - 1.0 (Standard)
N'
1.0 - 2.5
2.5 - 5.0
rc
8
5.0 - 7.5
6 7.5 - 10.0
10.0 - 12.26
DUKEENERGY
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
Notes:
1. Ng/L = micrograms per liter
2. Antimony [MAC value = 1 Ng/L
3. Antimony PPBC = 0.5 pg/L
L J
N
A
0 500 1,000
Feet
Figure 21 Initial (2015) Antimony Concentrations in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
r-
LEGEND
— 0.5 (Background
Concentration)
0.5 - 1.0 (Standard)
1.0 - 2.5
2.5 - 5.0 J
5.0 - 7.5
6 7.5 -10.0
= 10.0 - 12.26
DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
pMODEL DOMAIN
1. Ng/L = micrograms per liter
2. Antimony IMAC value = 1 Ng/L
3. Antimony PPBC = 0.5 Ng/L
LAKE
7A
L
N
A
0 500 1,000
Feel
Figure 22 Initial (2015) Antimony Concentrations in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0
a
a
a
0
Q
}
1
AffiI
F
H�
1
Or
low
I
LEGEND
— 0.5 (Background
Concentration)
0.5 - 1.0 (Standard) j
1.0 - 2.5 I /
2.5 - 5.0
5.0 - 7.5
7.5 - 10.0
- 10.0 - 12.26
DUKE ENERGY •/
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE AN
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT NOteS:
WITH DUKE ENERGY 1. Ng/L = micrograms per liter 0 500 1,000
PROPERTY BOUNDARY 2. Antimony ]MAC value = 1 Ng/L
MODEL DOMAIN 3. Antimony PPBC = 0.5 ug/L Feet
Figure 23 Existing Conditions Scenario 1 - 2115 Predicted Antimony in Shallow
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0-
o _ ,
a.
N
a
0
VEASH BASIN
LEGEND
- 0.5 (Background
Concentration)
0.5 - 1.0 (Standard)
j
1.0 - 2.5
+ `�
2.5 - 5.0
5.0 - 7.5
7.5 - 10.0
- 10.0 - 12.26
I DUKE ENERGY
_ _
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
Notes:
WITH DUKE ENERGY
1. Ng/L = micrograms per liter
PROPERTY BOUNDARY
2. Antimony ]MAC value = 1 pg/L
3. Antimony PPBC = 0.5 Ng/L
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 24 Existing Conditions Scenario 1 - 2115 Predicted Antimony in Deep
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
}
1
�1
11
r�
f
I
rf
e
u
i
LEGEND a
�= 0.5 (Background
Concentration)
0.5 - 1.0 (Standard) j
1.0 - 2.5
25-5-0
5.0 - 7.5
7.5 - 10.0
- 10.0 - 12.26
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLJASH STORAGE
AREA BOUNDARY -
ASH BASIN COMPLIANCE AN
BOUNDARY J1
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT Notes: WITH DUKE ENERGY 1. pg/L = micrograms per liter
PROPERTY BOUNDARY 2. Antimony IMAC value = 1 pg/L 0 500 1,000
3. Antimony PPBC = 0.5 pg/L �
MODEL DOMAIN Feet
Figure 25 Existing Conditions Scenario 1 - 2115 Predicted Antimony in Bedrock
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
i�
LEGEND
�= 0.5 (Background
Concentration)
0.5 - 1.0 (Standard)
j
1.0 - 2.5
I
/
2.5 - 5.0
5.0 - 7.5
7.5 - 10.0
- 10.0 - 12.26
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
AN
ASH BASIN COMPLIANCE
J
JN4
BOUNDARY COINCIDENT
Notes: -
WITH DUKE ENERGY
1. ug/L = micrograms per liter
0 500 1,000
PROPERTY BOUNDARY
2. Antimony [MAC value = 1 pg/L
3. Antimony PPBC = 0.5 pg/L
Feet
MODEL DOMAIN
Figure 26 Cap -in -Place Scenario 2 - 2115 Predicted Antimony in Shallow Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
c
N
Z
O
�7
Z
w
N
O
g
LEGEND
b <= 0.5 (Background
g Concentration)
0.5 - 1.0 (Standard)
N'
1.0 - 2.5
2.5 - 5.0
rc
8
5.0 - 7.5
6 7.5 - 10.0
10.0 - 12.26
DUKEENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
pMODEL DOMAIN
Notes:
1. Ng/L = micrograms per liter
2. Antimony IMAC value = 1 pg/L
3. Antimony PPBC = 0.5 Ng/L
N
A
0 500 1,000
Feet
Figure 27 Cap -in -Place Scenario 2 - 2115 Predicted Antimony in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
�= 0.5 (Background
s Concentration)
0.5 - 1.0 (Standard)
1.0 - 2.5 j
25-5.0
IL
8
5.0 - 7.5
10.0 - 12.26
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
Notes:
1. pg/L = micrograms per liter
2. Antimony ]MAC value = 1 pg/L
3. Antimony PPBC = 0.5 pg/L
PC
N
A
0 500 1,000
Feet
Figure 28 Cap -in -Place Scenario 2 - 2115 Predicted Antimony in Bedrock Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Predicted Arsenic Concentration at AB-22S
20.0
Existing Conditions
15.0 -
Cap -in -Place
16.0
Arsenic 2L
14.0
12.0
10.0
8.0
6.0
LAKIR
PAIL
0.0
C CD CD CD CD
M CD CD
Notes: �q �q rU rU
1. µg/L = micrograms per liter
2. Arsenic 2L Standard = 10 µg/L
3. Arsenic PPBC = 2.3 µg/L
C CD CD C CD CD 0
d1 rl m Ln r� a) �
o �q �q �q �q rU
N rl rl N rl rl N
Time (Years)
Figure 29 Predicted Arsenic in Monitoring Well AB-22S

20.0
18.0
16.0
14.0
12.0
10.0
8.0
6.0
I Kf
Predicted Arsenic Concentration at AB-26S
Existing Conditions _
Cap -in -Place
Arsenic 2L
2.0
0.0
0 0 0 0
Ln r� a) r-I
0) al 0) 0
" N
Notes:
1. µg/L = micrograms per liter
2. Arsenic 2L Standard =10 µg/L
3. Arsenic PPBC = 2.3 µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0 0 0 0 0 0 0 0 0 0 0 0 0
m Ln rti a) IH m Ln r- rn r-I m Ln r-
0 0 0 0 N N N N
N N N N N N N N N N N N N
Time (Years)
Figure 30 Predicted Arsenic in Monitoring Well AB-26S

Predicted Arsenic Concentration at AB-32S
20.0
18.0
16.0
14.0
12.0
J
10.0
o 8.0
6.0
4.0
V 2.0
0.0
0 0 0
Ln r
rn rn a�
r-I r-�
Notes:
1. µg/L = micrograms per liter
2. Arsenic 2L Standard = 10 µg/L
3. Arsenic PPBC = 2.3 µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0 0 0 0 0 0 0 0 0 0 0 0 0 0
"i m Ln C) �4 m Ln rI_ C) r-I m Ln rI_
0 0 0 0 0 r-i T--� r-i T rU rU rU rU
rU rti rU rU rti rU rti rU rti rti rU rU rU rU
Time (Years)
Figure 31 Predicted Arsenic in Monitoring Well AB-32S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
a = 2.3 (Background
Concentration)
2.3 - 10 (Standard)
10-25
25 - 50
50 -100
100- 150
150 - 205
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
Notes:
1. pg/L = micrograms per liter
2. Arsenic 2L Standard = 10 pg/L
3. Arsenic PPBC = 2.3 pg/L
N
A
0 500 1,000
monsoons
Feet
Figure 32 Initial (2015) Arsenic Concentrations in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
I,
I
LEGEND
G
(Background
Concentration)
2.3 - 10 (Standard)
10 - 25'�
25 - 50
50 -100
100- 150
150 - 205 =
DUKE ENERGY -
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. pg/L = micrograms per liter .'
0 500 1,000
PROPERTY BOUNDARY
2. Arsenic 2L Standard = 10 Ng/L �
MODEL DOMAIN 3. Arsenic PPBC = 2.3 pg/L Feet
Figure 33 Initial (2015) Arsenic Concentrations in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
u
I
I
= 1
1
LEGEND
G
(Background
Concentration)
2.3 - 10 (Standard)
10-25
25 - 50
50 -100
loo- 150
150 - 205 =
DUKE ENERGY -
PROPERTY BOUNDARY P
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE +
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCEr2.
es:
BOUNDARY COINCIDENT _
WITH DUKE ENERGY g/L = microgram110pg/L
PROPERTY BOUNDARYrsenic 2L Standa1 0 500 1,000
rsenic PPBC = 24.
MODEL DOMAIN - Feet
Figure 34 Initial (2015) Arsenic Concentrations in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
<= 2.3 (Background
g 'Concentration)
2.3 - 10 (Standard)
10-25 j
25 - 50
L
8
50 -100
100- 150
150 - 205
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"P.
Notes:
1. Ng/L = micrograms per liter
2. Arsenic 2L Standard = 10 pg/L
3. Arsenic PPBC = 2 3 Ng/L
Figure 35 Existing Conditions Scenario 1 - 2115 Predicted Arsenic in Shallow
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
[
�= 0.5 (Background
nConcentration)
0.5 - 1.0 (Standard)
1.0-2.5
2-5 - 5-0
2
s.o 7.s
° 7.5 - 10.0
w
10.0 - 12.26
u
0
DUKE ENERGY
a PROPERTY BOUNDARY
a
ASH BASIN WASTE
m
BOUNDARY
ti
5
LANDFILLIASH STORAGE
u
w
AREA BOUNDARY
w
ASH BASIN COMPLIANCE
'a
BOUNDARY
ASH BASIN COMPLIANCE
w
BOUNDARY COINCIDENT
3
WITH DUKE ENERGY
a
PROPERTY BOUNDARY
ODEL DOMAIN
Notes:
1. Ng/L = micrograms per liter
2. Arsenic 2L Standard = 10 pg/L
3. Arsenic PPBC = 2.3 Ng/L
N
A
0 500 1,000
Feet
Figure 36 Existing Conditions Scenario 1 - 2115 Predicted Arsenic in Deep Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
f
LEGEND
<= 2.3 (Background
g 'Concentration)
2.3 - 10 (Standard)
10-25
25 - 50
rc
8
50 -100
100- 150
150 - 205
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
Notes:
1. pg/L = micrograms per liter
2. Arsenic 2L Standard = 10 pg/L
3. Arsenic PPBC = 2.3 pg/L
I
I
I
I
I
I
I
P
e
N
A
0 500 1,000
Feet
Figure 37 Existing Conditions Scenario 1 - 2115 Predicted Arsenic in Bedrock
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 38 Cap -in -Place Scenario 2 - 2115 Predicted Arsenic in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
a = 2.3 (Background
Concentration)
2.3 - 10 (Standard)
10-25
25 - 50
50 -100
100- 150
150 - 205
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Notes:
1. pg/L = micrograms per liter
2. Arsenic 2L Standard = 10 pg/L
3. Arsenic PPBC = 2.3 pg/L
Nor
A
0 500 1,000
monsoons
Feet
Figure 39 Cap -in -Place Scenario 2 - 2115 Predicted Arsenic in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
eli
LEGEND
<= 2.3 (Background
g 'Concentration)
2.3 - 10 (Standard)
10-25 j
25 - 50
L
8
50 -100
100- 150
150 - 205
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
Notes: / V
1. Ng/L = micrograms per liter 0 500 1,000
2. Arsenic 2L Standard = 10 pg/L
3. Arsenic PPBC = 2.3 pg/L Feet
Figure 40 Cap -in -Place Scenario 2 - 2115 Predicted Arsenic in Bedrock Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Predicted Barium Concentration at AB-22S
1 r,
Existing Conditions
600.0
-
Cap -in -Place
500.0
-
Barium 2L
J
•..r
400.0
p
300.0
fC
L
200.0
G
100.0
"'•
U
0.0
C C C CDLn CD CD Ln 4 C
Ln CDLn
M O O rq rq N iV
N N fV N N N
Notes:
1. µg/L = micrograms per liter Time (Years)
2. Barium 2L Standard = 700 µg/L
3. Barium PPBC = 99 µg/L
Figure 41 Predicted Barium in Monitoring Well AB-22S

Predicted Barium Concentration at AB-26S
:rr r
700.0
600.0 -Existing Conditions
500.0 Cap -in -Place
Barium 2L
400.0
HIIIXr]
200.0
100.0
0.0
0 0 0 0 0 0 0
ai a) CD 0 0 0
Notes: r_� rti r i r i r i
1. µg#L = micrograms per liter
2. Barium 2L Standard = 700 µg/L
3. Barium PPBC = 99 µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0 0 0 0 0 0 0 0 0 0
o � � r ram., r�.i r�.i rNi
ri ry ri ri ri ri ri ry ri ri
Time (Years)
Figure 42 Predicted Barium in Monitoring Well AB-26S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Predicted Barium Concentration at AB-32S
800.0
Existing Conditions
700.0
Cap -in -Place
600.0 — — Barium 2L
I.71I1Xr]
J
400.0
300.0
t0
L
200.0
Q 100.0
U
Jxon=
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ln rl- rn r-I m Ln r� a) r m Ln r- 01 r m Ln �
M M a) 0 0 0 0 0 r rI r r r-I rU rU rI4 rU
r rl r-I rU rV rV rU rV rV rU rU rU rU rU rU rU rU
Notes:
1. µg/L = micrograms per liter Time (Years)
2. Barium 2L Standard = 700 µg/L
3. Barium PPBC= 99 µg/L
Figure 43 Predicted Barium in Monitoring Well AB-32S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
ey
I
I
u
P
P
4
_I
LEGEND
�= 99 (Background
Concentration)
99 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700 (Standard)
DUKE ENERGY -
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE Notes:
BOUNDARY COINCIDENT
WITH DUKE ENERGY 1. pg/L = micrograms per liter
PROPERTY BOUNDARY 2. Barium 2L Standard = 700 pg/L 0 500 1,000
3. Barium PPBC = 99 pg/L �
MODEL DOMAIN Feet
Figure 44 Initial (2015) Barium Concentrations in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
11
11
1
I
u
I
LEGEND
— 99(Background
Concentration)
99 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700 (Standard)
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE Notes:
BOUNDARY COINCIENERGY
1. /L = micrograms per liter
WITH DUKE ENERGY ug 9
PROPERTY BOUNDARY 2. Barium 2L Standard = 700 Ng/L - - 0 500 1,000
3. Barium PPBC = 99 Ng/L
MODEL DOMAIN _ y y Feet
Figure 45 Initial (2015) Barium Concentrations in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 99 (Background
Concentration)
99 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700 (Standard)
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
1`
l
1. Ng/L = micrograms per liter�,{j
2. Barium 2L Standard = 700 pg/L
3. Barium PPBC = 99 pg/L
N
A
0 500 1,000
monsoons
Feet
Figure 46 Initial (2015) Barium Concentrations in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
l
LEGEND
— 99(Background
Concentration)
99 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700 (Standard)
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
_ ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
E BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
N
A
0 500 1,000
Feet
Figure 47 Existing Conditions Scenario 1 - 2115 Predicted Barium in Shallow
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 99(Background
Concentration)
99 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700 (Standard)
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
3. Barium PPBC = 99 Ng/L
Feet
Figure 48 Existing Conditions Scenario 1 - 2115 Predicted Barium in Deep Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
f
LEGEND
�= 99 (Background
g Concentration)
99 - 200
200 - 300 f
300 - 400
IL
8
400 500
500 - 600
600 - 700 (Standard)
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
Notes:
1. pg/L = micrograms per liter
2. Barium 2L Standard = 700 pg/L
3. Barium PPBC = 99 pg/L 0
r'
Feet
Figure 49 Existing Conditions Scenario 1 - 2115 Predicted Barium in Bedrock
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
ey
I
I
u
P
P
4
_I
LEGEND
�= 99 (Background
Concentration)
99 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700 (Standard)
DUKE ENERGY -
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE Notes:
BOUNDARY COINCIDENT
WITH DUKE ENERGY 1. Ng/L = micrograms per liter
PROPERTY BOUNDARY 2. Barium 2L Standard = 700 pg/L 0 So0 1,000
3. Barium PPBC = 99 pg/L
MODEL DOMAIN _ Feet
Figure 50 Cap -in -Place Scenario 2 - 2115 Predicted Barium in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 99(Background
Concentration)
99 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700 (Standard)
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Notes:
1. pg/L = micrograms per liter
2. Barium 2L Standard = 700 Ng/L
3. Barium PPBC = 99 pg/L
N
A
0 S00 1,000
monsoons
Feet
Figure 51 Cap -in -Place Scenario 2 - 2115 Predicted Barium in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 99(Background
Concentration)
99 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700 (Standard)
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Figure 52 Cap -in -Place Scenario 2 - 2115 Predicted Barium in Bedrock Groundwater Zone

Predicted Boron Concentration at AB-22S
►11IIXII
600.0
500.0
J
1
400.0
300.0
L
200.0
u 100.0
0.0
rl-C,
C, C, C, CD
Notes: � � � rU
1. µg/L = micrograms per liter
2. Boron 2L Standard = 700 µg/L
3. Boron PPBC = 50 µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Existing Conditions
- Cap -in -Place
Boron 2L
T
0 0 0 0 0 0 0 0
CD CD CD CD
Time (Years)
Figure 53 Predicted Boron in Monitoring Well AB-22S

1,000.0
900.0
500.0
700.0
600.0
J
500.0
LI00.0
0
-1
300.0
L
+j
200.0
c�
c
u
100.0
Predicted Boron Concentration at AB-26S
0 0 0 0 0 0 0 0 0 0
C) C) C) CD CO 0 CD C
Notes:
1. µg/L = micrograms per liter Time (Years)
2. Boron 2L Standard = 700 µg/L
3. Boron PPBC = 50 µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Existing Conditions
Cap -in -Place
Boron 2L
0 0 0 0 0 0 0
� CO Ln
nl PV N eV PV PV eV
Figure 54 Predicted Boron in Monitoring Well AB-26S

Predicted Boron Concentration at AB-32S
700.0
600.0
500.0
J
400.0
300.0
L
C 200.0
0 100.0
0.0
0 0 0 0
Ln r- a) r-I
rn rn a) 0
� ri
Notes:
1. µg/L = micrograms per liter
2. Boron 2L Standard = 700 µg/L
3. Boron PPBC = 50 µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Existing Conditions -
Cap -in -Place
Boron 2L
0 0 0 0 0 0 0 0 0 0 0 0 0
m Ln rl- M �_I m Ln � a) r-I m Ln r-
0 0 0 0 rU rU rU rU
rN rU ri ri ri rU ri ri rU ri rU ri rU
Time (Years)
Figure 55 Predicted Boron in Monitoring Well AB-32S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 50(Background
Concentration)
50 - 200
200 - 400
400 - 700 (Standard)
700- 1,500
1,500 - 2,500
2,500 - 3,044
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
e-
Notes:
1. Ng/L = micrograms per liter
2. Boron 21- Standard = 700 pg/L
3. Boron PPBC = 50 Ng/L
N
A
fl Sfl0 1,000
Feet
Figure 56 Initial (2015) Boron Concentrations in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 50(Background
Concentration)
50 - 200
200 - 400
400 - 700 (Standard)
700- 1,500
1,500 - 2,500
2,500 - 3,044
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
1`
t
Notes:
1. pg/L = micrograms per liter
2. Boron 2L Standard = 700 pg/L
3. Boron PPBC = 50 pg/L
N
A
0 S00 1,000
monsoons
Feet
Figure 57 Initial (2015) Boron Concentrations in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 50 (Background
Concentration)
50 - 200
200 - 400
400 - 700 (Standard)
700- 1,500
1,500-2,500
2,500 - 3,044
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
WTH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAdN
r
Notes:
1. Ng/L = micrograms per liter
2. Boron 2L Standard = 700 Ng/L
3. Boron PPBC = 50 pg/L
1
N
A
0 500 1,000
monsoons
Feel
Figure 58 Initial (2015) Boron Concentrations in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 50(Background
Concentration)
50 - 200
200 - 400
400 - 700 (Standard)
700- 1,500
1,500 - 2,500
2,500 - 3,044
_ 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
Notes:
1. pg/L = micrograms per liter
2. Boron 2L Standard = 700 pg/L
3. Boron PPBC = 50 ug/L
r
SLAKE'
N
A
0 500 1,000
Feet
Figure 59 Existing Conditions Scenario 1 - 2115 Predicted Boron in Shallow Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0
z
0
LEGEND /
— 50(Background
Concentration)
50 - 200
200 - 400
400 - 700 (Standard)
700- 1,500
1,500 - 2,500
2,500 - 3,044
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
Notes:
1. pg/L = micrograms per liter
2. Boron 2L Standard = 700 pg/L
3. Boron PPBC = 50 ug/L
r 7
. 1
N
A
0 500 1,000
Feet
Figure 60 Existing Conditions Scenario 1 - 2115 Predicted Boron in Deep Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
r
LEGEND
— 50(Background
Concentration)
50 - 200
200 - 400
400 - 700 (Standard)
700- 1,500
1,500 - 2,500
2,500 - 3,044
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
ANotes:
1. Ng/L = micrograms per liter 0 500 1,000
2. Boron 2L Standard = 700 pg/L
3. Boron PPBC = 50 Ng/L Feet
Figure 61 Existing Conditions Scenario 1 - 2115 Predicted Boron in Bedrock
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 50(Background
Concentration)
50 - 200
200 - 400
400 - 700 (Standard)
700- 1,500
1,500 - 2,500
2,500 - 3,044
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
e-
Notes:
1. pg/L = micrograms per liter
2. Boron 2L Standard = 700 pg/L
3. Boron PPBC = 50 Ng/L
N
A
0 S00 1,000
monsoons
Feet
Figure 62 Cap -in -Place Scenario 2 - 2115 Predicted Boron in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
M
i
LEGEND
— 50 (Background
hL Concentration)
50 - 200
200 - 400
400 - 700 (Standard)
700 - 1,500
1,500 - 2,500
2,500 - 3,044
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
MODELDOMAIN
Notes:
1. Ng/L = micrograms per liter
2. Boron 2L Standard = 700 Ng/L
3. Boron PPBC = 50 Ng/L
I
1
1
1
r
1
N
A
0 500 1,000
Feet
Figure 63 Cap -in -Place Scenario 2 - 2115 Predicted Boron in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 99(Background
Concentration)
99 - 200
200 - 300
300 - 400
400 - 500
500 - 600
600 - 700 (Standard)
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Figure 64 Cap -in -Place Scenario 2 - 2115 Predicted Boron in Bedrock Groundwater Zone

Predicted Chromium Concentration at AB-22S
14.0
a�
3
8.4
0
+�
6.4
c
Existing Conditions
r-
4.4
Cap -in -Place
V
2.4
Chromium 2L
4.4
0
0 0 0 0 0
Ln
a,
rl- a7 r-� m Ln
a, a7 0 0 0
rl
r-I rl N N N
Notes:
1. µg/L
= micrograms per liter
2. Chromium
2L Standard
= 10 µg/L
3. Chromium
PPBC
= 16 µg/L
0 0 0 0 0 0 0 0 0
0 0 � � � � � rri �
N N N N N N N N N
Time (Years)
Figure 65 Predicted Chromium in Monitoring Well AB-22S
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0 0
rU N
N N

Predicted Chromium Concentration at AB-26S
16.4
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
14.4
12.4
14.4
8.4
0
L6.4
- Existing Conditions
4-1
4.4 Cap -in -Place
U
u
2.4 Chromium 2L
4.0 -
0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
Ln r- a) r-� m Ln r-
a7 a7 a) 0 0 0 0
07 r-I m Ln r- a7 r-� m Ln rti
0 r-I r-� r-� r-� r-I rU rU rU rU
Notes:
�q ry ry rIIj ry
ry r�j ry r�j ry r�j r�j ry r�j r�j
1. µg/L
= micrograms per liter
2. Chromium 2L Standard = 10 µg/L
Time (Years)
3. Chromium PPBC = 16 µg/L
Figure 66 Predicted Chromium in Monitoring Well AB-26S

Predicted Chromium Concentration at AB-32S
4-0
W 4.4
U Cap -in -Place
r-
U 2.4 Chromium 2L
4.4
a o o a o
Ln
0) ai rn o 0
� ry rU
Notes:
1. µg/L = micrograms per liter
2. Chromium 2L Standard = 10 µg/L
3. Chromium PPBC = 16 µg/L
o a o o a o o a o
0 0 0 rM n - CrrIj
rti ry rti rU rU rti rU rU rti
Time (Years)
Figure 67 Predicted Chromium in Monitoring Well AB-32S
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
o a o
m Ln
rU rU rti
rti rti rU

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
R
K
a
K
N
o
o
a
x
LEGEND
— 10 (Standard)
10- 12
12 - 14
14 - 16 (Background
Concentration)
16 - 18
0
O _ _ DUKE ENERGY
a PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
5 LANDFILL/ASH STORAGE
AREA BOUNDARY
u�
w ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
w — BOUNDARY COINCIDENT
o WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
r-
Notes:
1. pg/L = micrograms per liter
2. Chromium 2L Standard = 10 pg/L
3. Chromium PPBC = 16 pg/L
r
I
I
1
r�
I
1
tt
— — — — — — — — — — 1 \y
N
A
0 500 1,000
Feet
Figure 68 Initial (2015) Chromium Concentrations in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 10 (Standard)
10 - 12
12 - 14
14 - 16 (Background
Concentration)
16 - 18
18 - 19
- 19 - 19.6fi
_ — DUKE ENERGY
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
Notes:
1. pg/L = micrograms per liter
2. Chromium 2L Standard = 10 pg/L
3. Chromium PPBC = 16 Ng/L
l
I
I
I
I
I
I
I
I
I
I
\
\
r\
I
i
tt /�
♦y
--———— — — — —
ll
N
A
0 500 1,000
Feet
Figure 69 Initial (2015) Chromium Concentrations in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
ow-
R
a
a
N
2
c
LEGEND
— 10 (Standard)
10 - 12
12 - 14
14 - 16 (Background
Concentration)
16 - 18
21 - 118-19
9 - 19.66
C
DUKE ENERGY
a PROPERTY BOUNDARY
g
a ASH BASIN WASTE
m BOUNDARY
x
N
S LANDFILL/ASH STORAGE
AREA BOUNDARY
u�
w ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
w — — BOUNDARY COINCIDENT
o W9TH DUKE ENERGY
a PROPERTY BOUNDARY
MODEL DOMAIN
V
\1
/—
Notes:
1. pg/L = micrograms per liter
2. Chromium 2L Standard = 10 pg/L
3. Chromium PPBC = 16 pg/L
N
A
0 500 1,000
Feet
Figure 70 Initial (2015) Chromium Concentrations in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
,1
i I 4
r
7
r
I
J
I
I
I
t
r
I
= J
I
LEGEND
— 10 (Standard)
10 - 12
12-14 ` (-
�' 14 - 16 (Background
Concentration) 6
8
a
16 - 18
i 18 - 19
y ISO 19 - 19.66
LAKE WYLE
O
DUKE ENERGY
`< PROPERTY BOUNDARY
ASH BASIN WASTE
m BOUNDARY '
z
s LANDFILLIASH STORAGE
AREA BOUNDARY
w
w ASH BASIN COMPLIANCE
! BOUNDARY n
1 ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes:
WTH DUKE ENERGY 1. pg/L = micrograms per liter 0 500 1,000
Q PROPERTY BOUNDARY 2 Chromium 2L Standard
T MODEL DOMAIN 3. Chromium PPBC = 16 pg/L Feet
I
Figure 71 Existing Conditions Scenario 1 - 2115 Predicted Chromium in Shallow
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
�1
! �1
1
1
�r
� r
I
I I
I I
I
I
I
I
I
= r
1
= r�
- r
LEGEND
<- 10 (Standard)
10 - 12
12 - 14
14 - 16 (Background
Concentration) r
8 — f
a
16 - 18
i 18 - 19
y ISO 19 - 19.66
LAKE WYLE
O
DUKE ENERGY
`< PROPERTY BOUNDARY
ASH BASIN WASTE
m BOUNDARY
z
s LANDFILLIASH STORAGE
AREA BOUNDARY
w
w ASH BASIN COMPLIANCE
! BOUNDARY n
1 ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT NOteS:
WITH DUKE ENERGY 1. pg/L = micrograms per liter 0 500 1,000
g PROPERTY BOUNDARY 2 Chromium 2L Standard
T MODEL DOMAIN 3. Chromium PPBC = 16 pg/L Feet
I
Figure 72 Existing Conditions Scenario 1 - 2115 Predicted Chromium in Deep
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
�1
! �1
1
1
zj-
�i
I
I I
I I
I
I
I
1
1
I
= r
= r�
- r
LEGEND 1
- <- 10 (Standard)
10 - 12
w 12 - 14 l
14 - 16 (Background '
Concentration) r
g _ 1
16 - 16
Q
w � 18-19
y 19. 19.66
U
OLAKE WYLE
DUKE ENERGY -
`< PROPERTY BOUNDARY
ASH BASIN WASTE
m BOUNDARY
N
5 LANDFILLIASH STORAGE
AREABOUNDARY
w
w ASH BASIN COMPLIANCE
BOUNDARY n
r ASH BASIN COMPLIANCE
w BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. pg/L = micrograms per liter 0 500 1,000
e PROPERTY BOUNDARY 2. Chromium 2L Standard = 10 pg/L
MODEL DOMAIN 3. Chromium PPBC = 16 pg/L Feet
a
Figure 73 Existing Conditions Scenario 1 - 2115 Predicted Chromium in Bedrock
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 10 (Standard)
s
10- 12
12 - 14
14 - 16 (Background
Concentration)
0
a
a
16 - 18
i 18 - 19
y ISO 19 - 19.66
U
O
DUKE ENERGY
`< PROPERTY BOUNDARY
ASH BASIN WASTE
m BOUNDARY
z
s UANDFILLIASH STORAGE
a
AREA BOUNDARY
w ASH BASIN COMPLIANCE
! BOUNDARY
0
1 ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
o WITH DUKE ENERGY
g PROPERTY BOUNDARY
T MODEL DOMAIN
I
ffW
Notes:
1. pg/L = micrograms per liter
2. Chromium 2L Standard = 10 pg/L
3. Chromium PPBC = 16 pg/L
N
k
0 500 1,000
Feet
Figure 74 Cap -in -Place Scenario 2 - 2115 Predicted Chromium in Shallow Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 10 (Standard)
10- 12
12 - 14
14 - 16 (Background
Concentration)
16 - 18
18 - 19
_ 19 - 19.66
_ — 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
!—
Notes:
1. pg/L = micrograms per liter
2. Chromium 2L Standard = 10 pg/L
3. Chromium PPBC = 16 pg/L
�I
I
I
I
I
I
I
I
I
1
r
I
I
1
1
I
i
1
tt /
♦y
--———— — — — —
ll
N
A
0 500 1,000
Feet
Figure 75 Cap -in -Place Scenario 2 - 2115 Predicted Chromium in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
�1
! �1
1
1
zj-
�l
I
I I
I
I
I
I
1
I
= r
= r�
- r
LEGEND 1
- <- 10 (Standard)
10 - 12
w 12 - 14
14 - 16 (Background '
Concentration) r
g _ 1
16 - 16
LAKE WYLE
w � 18-19
y 19. 19.66
U
O
DUKEENERGY
`< PROPERTY BOUNDARY
ASH BASIN WASTE
m BOUNDARY
N
5 LANDFILLIASH STORAGE
AREABOUNDARY
w
w ASH BASIN COMPLIANCE
BOUNDARY n
r ASH BASIN COMPLIANCE
w BOUNDARY COINCIDENT
a WITH DUKE ENERGY Notes:
a PROPERTY BOUNDARY 1. pg/L = micrograms per liter 0 500 1,000
2. Chromium 2L Standard = 10 pg/L
MODEL DOMAIN 3. Chromium PPBC = 16 pg/L Feet
a
Figure 76 Cap -in -Place Scenario 2 - 2115 Predicted Chromium in Bedrock Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Predicted Hexavalent Chromium Concentration at AB-22S
2.0
1.8 — Existing Conditions
1.6 Cap -in -Place
— Chromium VI DHHS HSL
1.4
1.2
J
1.0
0.8
O
[C 0.6
L
0.4
V
V 0.2
0.0
0 a a
0 0
o a o
0 o a o 0 0 a o 0
Ln rl-
a7 07 07
r-� rn
0 0
Ln rl- C)
0 0 0
�4 m Ln rl- C) �4 m Ln rl-
�q � � rU r l N N
ri ri
ri ri ri
ri ri ri ri ri ri ri ri ri
Notes:
1. µg/L = micrograms per liter
2. Hexavalent chromium DHHS
HSL value =
0.07 µg/L
Time (Years)
3. Hexavalent chromium PPBC=
0.05 µg/L
Figure 77 Predicted Hexavalent Chromium in Monitoring Well AB-22S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Predicted Hexavalent Chromium Concentration at AB-32S
2.0
1.8
1.6
1.4
1.2
J
1.0
0.8
0
0.6
0.4
0
V
0.2
00
— — — :
— : :
: — —
rl r-I c-I
N N
N N N
Notes:
1. µg/L =
micrograms per liter
2. Hexavalent chromium DHHS
HSL value =
0.07 µg/L
3. Hexavalent chromium PPBC=
0.05 µg/L
Existing Conditions
Cap -in -Place
Chromium VI DHHS HSL
I
0 O 0 0 O 0 O 0
rl r4 rl N N N N
N N N N N N N N
Time (Years)
Figure 78 Predicted Hexavalent Chromium in Monitoring Well AB-32S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
N � <=0.07 (Standard)
0.07 - 5
N
5-10
LL
10-15
8
15-25
i 25 - 35
35 - 43.02
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
1
r
V
N
Notes: A
1. Ng/L = micrograms per liter 0 500 1,000
2. Hexavalent chromium DHHS HSL value = 0.07 pg/L
3. Hexavalent chromium PPBC = 0.05 pg/L Feel
Figure 79 Initial (2015) Hexavalent Chromium Concentrations in Shallow Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
1
u
�a
�r
P
LEGEND
_ c=0.07 (Standard)
0.07 - 5 1
5-10
10 - 15 +
�I
15-25
25 - 35
35 - 43,02
_ DUKE ENERGY �-
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. pg/L = micrograms per liter 0 500 1,000
PROPERTY BOUNDARY 2. Hexavalent chromium DHHS HSL value = 0.07 pg/L
MODEL DOMAIN 3. Hexavalent chromium PPBC = 0.05 pg/L Feet
Figure 80 Initial (2015) Hexavalent Chromium Concentrations in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
°1
1
1
1
ram!!
rJ
� f
LEGEND
— 0.07 (Standard)
0.07-5
5-10
10-15
15-25
25 - 35
35 - 43.02
— — 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
V
N
Notes: A
1. Ng/L = micrograms per liter 0 500 1,000
2. Hexavalent chromium DHHS HSL value = 0.07 pg/L
3. Hexavalent chromium PPBC = 0.05 Ng/L Feel
Figure 81 Initial (2015) Hexavalent Chromium Concentrations in Bedrock Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
°1
1
1
1
ram!!
rJ
F
LEGEND
— 0.07 (Standard)
0.07-5
5-10
10-15
15-25
25 - 35
35 - 43.02
— — 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
V
■nN1
Notes:
1. pg/L = micrograms per liter 0 500 1,000
2. Hexavalent chromium DHHS HSL value = 0.07 pg/L NOMENEME::=
3. Hexavalent chromium PPBC = 0.05 pg/L Feel
Figure 82 Existing Conditions Scenario 1 - 2115 Predicted Hexavalent Chromium in
Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
°1
1
!
1
r
LEGEND
W
S — 0.07 (standard)
0.07-5
N
5-10
U
10-15
rc
8
15-25
i 25 - 35
35 - 43.02
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
I
I
I
I
I
I
I
J
r
N
Notes: A
1. Ng/L = micrograms per liter 0 500 1,000
2. Hexavalent chromium DHHS HSL value = 0.07 Ng/L MONEENNE::=
3. Hexavalent chromium PPBC = 0.05 pg/L Feel
Figure 83 Existing Conditions Scenario 1 - 2115 Predicted Hexavalent Chromium in Deep
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
°1
1
1
1
ram!!
rJ
� f
LEGEND
— 0.07 (Standard)
0.07-5
5-10
10-15
15-25
25 - 35
35 - 43.02
— — 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
V
JjN�1
Notes:
1. pg/L = micrograms per liter 0 500 1,000
2. Hexavalent chromium DHHS HSL value = 0.07 Ng/L NOMENEME::=
3. Hexavalent chromium PPBC = 0.05 pg/L Feel
Figure 84 Existing Conditions Scenario 1 - 2115 Predicted Hexavalent Chromium in
Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
°1
1
1
1
ram!!
rJ
F
LEGEND
S � <=0.07 (Standard)
0.07 - 5
N
5-10
U
10-15
rc
8
15-25
i 25 - 35
35 - 43.02
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
V
• � N
Notes: A
1. pg/L = micrograms per liter fl 500 1,000
2. Hexavalent chromium DHHS HSL value = 0.07 pg/L
3. Hexavalent chromium PPBC = 0.05 Ng/L io Feet
Figure 85 Cap -in -Place Scenario 2 - 2115 Predicted Hexavalent Chromium in Shallow
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 86 Cap -in -Place Scenario 2 - 2115 Predicted Hexavalent Chromium in Deep
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
11 4
r
a
I
I
I
I
r
i
0
a I
_ 1
LEGEND
— 0.07 (Standard)
0.07-5 ' yf
I IJ
5-10 o r e
10-15
15-25
25 - 35
35 - 43.02 1t�
— — DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY -
LANDFILLIASH STORAGE
AREA BOUNDARY
_ ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE "_ N
_ BOUNDARY COINCIDENT Notes:
E WITH DUKE ENERGY 1. pg/L = micrograms per liter fl 500 1,000
PROPERTY BOUNDARY 2. Hexavalent chromium DHHS HSL value = 0.07 pg/L �
MODEL DOMAIN 3. Hexavalent chromium PPBC = 0.05 pg/L Feel
Figure 87 Cap -in -Place Scenario 2 - 2115 Predicted Hexavalent Chromium in Bedrock
Groundwater Zone

Predicted Cobalt Concentration at AB-22S
12.0
10.0
:1
J
1
6.0
0
4.0
L
2.0
0
U
0.0
O O O
Ln rl- 61
ff1 ff1 ff1
Notes:
1. µg/L = micrograms per liter
2. Cobalt IMAC value = 1 µg/L
3. Cobalt PPBC = 0.74 µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
O O O O O O O Q O O O O O
O O 0 O O r-I r-I r-I r-I r-I nl N N
N N N N N N N N N N N N N
Time (Years)
Figure 88 Predicted Cobalt in Monitoring Well AB-22S
ons
C
r-
N
N

Predicted Cobalt Concentration at AB-26S
12.0
10.0
W
J
1
6.0
0
4-1 4.0
L
4-1
2.0
0
U
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
ions
0.0 -h
Ln (l- al r-I rn Ln r- 61 ri rn Ln rI% a) r-I rn Ln (I%
a) a) 61 O O 0 O 0 ri ri r-I r-I ri N N N N
r-I r-I r-I N N N N N N N N N N N N N N
Notes:
1. µg/L = micrograms per liter
2. Cobalt IMAC value = 1 µg/L Time (Years)
3. Cobalt PPBC = 0.74 µg/L
Figure 89 Predicted Cobalt in Monitoring Well AB-26S

Predicted Cobalt Concentration at AB-32S
25.0
20.0
15.0
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Existing Conditions
Cap -in -Place
Cobalt IMAC
0.4
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ln rl- ¢, r-q m Ln rl- C) r- m Ln rl- al ri rn Ln rl-
61 61 a) O O 0 O 0 r-I r- r-I r-I r-I N N N N
r-I r-I r- N N N N N N N N N N N N N N
Notes:
1. µg/L = micrograms per liter Time (Years)
2. Cobalt IMAC value = 1 µg/L
3. Cobalt PPBC = 0.74 µg/L
Figure 90 Predicted Cobalt in Monitoring Well AB-32S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
M
i
i
u I
I
I
I
I
f
1
1
1
I
LEGEND
{background
Concentration)
0.74 - 1 (Standard)
1-5 ^'
5-10
to- 15
15-20
20 - 22,84
DUKE ENERGY -
PROPERTY BOUNDARY P
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. Ng/L = micrograms per liter I fl Sfl0 1,000
PROPERTY BOUNDARY
2. Cobalt IMAC value = 1 pg/L
MODEL DOMAIN 3. Cobalt PPBC = 0.74 Ng/L Feet
Figure 91 Initial (2015) Cobalt Concentrations in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Figure 92 Initial (2015) Cobalt Concentrations in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 0.74 (Background
Concentration)
0.74 - 1 (Standard)
1-5
5-10
10 - 15
15-20
20 - 22,84
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
-------A
4
N
Notes: A
1. Ng/L =micrograms per liter
2. Cobalt IMAC value = 1 pg/L fl 500 1,000
3. Cobalt PPBC = 0.74 Ng/IL
Feet
Figure 93 Initial (2015) Cobalt Concentrations in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 0.74 (Background
Concentration)
0.74 - 1 (Standard)
1-5
5-10
10 - 15
15-20
20 - 22.84
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
IF-'P'W�
Notes: M-
1. pg/L = micrograms per liter
2. Cobalt [MAC value = 1 pg/L
3. Cobalt PPBC = 0.74 pg/L
N
A
0 500 1,000
Feet
Figure 94 Existing Conditions Scenario 1 - 2115 Predicted Cobalt in Shallow Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0
K
LEGEND
�= 0.74 (Background
g Concentration)
- 1 (Standard)
1-5
5-10
8
10-15
i 15-20
20 - 22.84
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
Notes:
1. pg/L = micrograms per liter 0 500 1,000
2. Cobra value = 1 pg/L
3. Cobalt PPBC = 0.74 pg/L N, Feel
Figure 95 Existing Conditions Scenario 1 - 2115 Predicted Cobalt in Deep Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
eli
LEGEND
�= 0.74 (Background
g 'Concentration)
0.74 - 1 (Standard)
1-51 5 j
5-10
IL
8
10-15
15-20
20 - 22.84
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
Notes:
1. pg/L = micrograms per liter
2. Cobalt IMAC value = 1 Ng/L
3. Cobalt PPBC = 0.74 pg/L
I
I
I
I
I
I
I
Feet
Figure 96 Existing Conditions Scenario 1 - 2115 Predicted Cobalt in Bedrock
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 0.74 (Background
Concentration)
0.74 - 1 (Standard)
1-5
5-10
10 - 15
15-20
20 - 22,84
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
4
Notes:
1. Ng/L = micrograms per liter
2. Cobalt IMAC value = 1 Ng/L
3. Cobalt PPBC = 0.74 Ng/L
N
A
0 500 1,000
monsoons
Feet
Figure 97 Cap -in -Place Scenario 2 - 2115 Predicted Cobalt in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 0.74 (Background
Concentration)
0.74 - 1 (Standard)
1-5
5-10
10 - 15
15-20
20 - 22,84
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
1`
t
4
Notes:
1. Ng/L = micrograms per liter
2. Cobalt IMAC value = 1 pg/L
3. Cobalt PPBC = 0.74 Ng/L
N
A
0 S0o 1,000
Feet
Figure 98 Cap -in -Place Scenario 2 - 2115 Predicted Cobalt in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
1`
1
II
u
p
u I
I
I
I
I
LEGEND
— 0.74 (Background
Concentration)
0.74 - 1 (Standard)
1-5 ^'
5-10
d
10 - 15
15-20
20 - 22,84
DUKE ENERGY -
PROPERTY BOUNDARY P
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes: 3 _.
w17H DUKE ENERGY 1. Ng/L = micrograms per liter I fl Sfl0 1,000
PROPERTY BOUNDARY 2, Cobalt IMAC value = 1 pg/L
MODEL DOMAIN 3. Cobalt PPBC = 0.74 Ng/L Feet
Figure 99 Cap -in -Place Scenario 2 - 2115 Predicted Cobalt in Bedrock Groundwater Zone

Predicted Selenium Concentration at AB-22S
25.0
20.0
.... 15.0
J
1
0 10.0
4-1
c
5.0
0
U
0.0
0 0 0 0
Ln rl- C,
a, c, C) 0
Notes: r- r-� r-I rU
1. µg/L = micrograms per liter
2. Selenium 2L Standard = 20 µg/L
3. Selenium PPBC = 0.5. µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
- Existing Conditions
Cap -in -Place
Selenium 2L
0 0
0
0
0
0
0
0
0
0
0
0
0
ro Ln
�
C,
ro
Ln
�
C,
�
ro
Ln
�
0 0
0
0
�
�
ry
rti
rU
rti
rU rU
rV
rV
rU
rV
ri
rV
rU
rnl
rV
rU
rV
Time (Years)
Figure 100 Predicted Selenium in Monitoring Well AB-22S

25.0
Predicted Selenium Concentration at AB-26S
Existing Conditions
20.0 -- Cap -in -Place
Selenium 2L
15.0
J
1
10.0
L
4-J
5.0
0
U
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0.0 -r-
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ln rti a7 r-I m Ln r- a7 ri rm Ln r- a) r1 m Ln r%
a) a) a7 O O 0 O O ri r-I r-I r-I ri nl N N N
r-I r-I rl N N N N N N N N N N N N N N
Notes:
1. µg/L = micrograms per liter Time (Years)
2. Selenium 2L Standard = 20 µg/L
3. Selenium PPBC = 0.5. µg/L
Figure 101 Predicted Selenium in Monitoring Well AB-26S

PA61f
20.0
15.0
c 10.0
0
L
5.0
ca
c
0
V
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Predicted Selenium Concentration at AB-32S
Existing Conditions
Cap -in -Place
Selenium 2L
0.0
0 o a o a a o a a o a a o a a a a
Ln r- 07 r-I rn Ln r- rn r1 rn Ln � a) r1 rn Ln �
a7 al 01 O 0 Q O O r-I r r-I r-I r fV N ftil N
r-I ri r-I fV fV fV fV fV fV fV fV fV fV fV fV fV fV
Notes:
1. µg/L = micrograms per liter
2. Selenium 2L Standard = 20 µg/L Time (Years)
3. Selenium PPBC = 0.5. µg/L
Figure 102 Predicted Selenium in Monitoring Well AB-32S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
1`
1
u
I
I
I
LEGEND I ,
{background
Concentration)
0.70 - 2
2-4
4-6
6-8
8-12
12 - 20 (Standard)
DUKE ENERGY - -
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLMSH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. pg/L = micrograms per liter0 500 1,000
PROPERTY BOUNDARY 2. Selenium 2L Standard = 20 pg/L
3. Selenium PPBC = 0.5. pg/L
MODEL DOMAIN Feet
Figure 103 Initial (2015) Selenium Concentrations in The Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
I �1
I�
u
_ I
1
LEGEND I ,
{background
Concentration)
0.70 - 2
2-4
4-6
-- — — —
�
6-8
8-12
12 - 20 (Standard)
DUKE ENERGY - -
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes: _
WITH DUKE ENERGY
PROPERTY BOUNDARY 1. =micrograms per liter 0 500 1,000
Selenium
2. Selenium 2L Standard = 20 Ng/L �
MODEL DOMAIN 3. Selenium PPBC = 0.5. ug/L Feet
Figure 104 Initial (2015) Selenium Concentrations in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
uJAL
_ I
I
1
LEGEND I ,
�= 0.70 {background
Concentration)
0.70 - 2
2-4
4-6
-- — — —
�
6-8
8-12
12 - 20 (Standard)
DUKE ENERGY - -
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. pg/L = micrograms per liter 0 500 1,000
PROPERTY BOUNDARY 2. Selenium 2L Standard = 20 Ng/L
MODEL DOMAIN 3. Selenium PPBC = 0.5. pg/L Feet
Figure 105 Initial (2015) Selenium Concentrations in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
a.
N
2
O
N
2
W
N
E
LEGEND
<= 0.70 (Background
s
Concentration)
0.70 - 2
N
W
W
2-4
LL'
4-6
6-8
8-12
12 - 20 (Standard)
_ DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
_ ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ E BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Notes:'
1. pg/L = micrograms per liter
2. Selenium 21 Standard = 20 pg/L
3. Selenium PPBC = 0.5. Ng/L
N
A
0 500 1,000
Feet
Figure 106 Existing Conditions Scenario 1 - 2115 Predicted Selenium in Shallow
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
�= 0.70 (Background
g Concentration)
0.70 - 2
F 2-4
rc
4-6
8
6-8
8-12
12 - 20 (Standard)
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
r
es:'g/L= micrograms per liter 0 500 1,000
elenium 2L Standard = 20 Ng/Lelenium PPBC = 0.5. Ng/L Feet
Figure 107 Existing Conditions Scenario 1 - 2115 Predicted Selenium in Deep
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
�= 0.70 (Background
g Concentration)
0.70 - 2
2 a j
4-fi
IL
8
8-12
12 - 20 (Standard)
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
Notes:
1. pg/L = micrograms per liter
2. Selenium 2L Standard = 20 pg/L
3. Selenium PPBC = 0.5. pg/L
N
A
0 500 1,000
Feet
Figure 108 Existing Conditions Scenario 1 - 2115 Predicted Selenium in Bedrock
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
�= 0.70 (Background
g Concentration)
0.70 - 2
2 a j
� 4-fi
IL
6-8
8-12
12 - 20 (Standard)
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
sIgo
Notes:
1. pg/L = micrograms per liter
2. Selenium 2L Standard = 20 pg/L
3. Selenium PPBC = 0.5. pg/L no
N
A
0 500 1,000
Feet
Figure 109 Cap -in -Place Scenario 2 - 2115 Predicted Selenium in Shallow Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
11
11
4
u
I
I
I
1
LEGEND I ,
{background
Concentration)
0.70 - 2
2-4
4-6
-- — — —
�
6-8
8-12
12 - 20 (Standard)
DUKE ENERGY -
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. pg/L = micrograms per liter I 0 500 1,000
PROPERTY BOUNDARY 2. Selenium 2L Standard = 20 Ng/L-
MODEL DOMAIN 3. Selenium PPBC = 0.5. Ng/L Feet
Figure 110 Cap -in -Place Scenario 2 - 2115 Predicted Selenium in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
eli
LEGEND
�= 0.70 (Background
g Concentration)
0.70 - 2
2 a j
� 4-fi
IL
6-8
8-12
12 - 20 (Standard)
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
sIgo
• `�' N
T
crograms per liter 0 500 1,000
2L Standard = 20 pg/L
PPBC = 0.5. ug/L Feet
Figure 111 Cap -in -Place Scenario 2 - 2115 Predicted Selenium in Bedrock Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Predicted Sulfate Concentration at A13-22S
300,000
250,000
200,000 i Existing Conditions
J Cap -in -Place
150,000 Sulfate 2L
r-
0
-J 100,000
L
4-J
i..i
50,000
U
0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ln rti rn r1 rm Ln r- a) ri rn Ln r- rn r m Ln r�
a) M 61 0 0 0 0 0 ri r-1 ri ri r-1 N N N N
Notes: r- ci r1 N N N N N N N N N N N N N N
1. µg/L = micrograms per liter
2. Sulfate 2L Standard = 2500000 µg/L Time (Years)
3. Sulfate PPBC = 30,300 µg/L
Figure 112 Predicted Sulfate In Monitoring Well AB-22S

Predicted Sulfate Concentration at A13-26S
300,000
250,000
200,000
J
1
150,000
C
0
4- 100,000
L
4-J
i..i
C 50,000
U
0
0 0 0 0
Ln r- a) r-1
a) rn a) 0
r r-1 r rV
Notes:
1. µg/L = micrograms per liter
2. Sulfate 2L Standard = 250,000 µg/L
3. Sulfate PPBC = 30,300 µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0 0 0 0 0 0 0 0 0 0 0 0 0
m Ln rl- rn T.-I m Ln r- a) r1 m Ln rti
0 0 0 a r1 r rl rl r rV rU rV rU
ri rV rV rV rV rV rV rV rV rV rV rV rV
Time (Years)
Figure 113 Predicted Sulfate In Monitoring Well AB-26S

300,000.0
250,000.0
200,000.0
J
150,000.0
c
0
100,000.0
L
G50,000.0
U
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Predicted Sulfate Concentration at A13-32S
Existing Conditions
Cap -in -Place
�Sulfate 2L
O O O O O O O O O O O O O O O O O
Ln r- 0) r-� m Ln � 0) r-� m Ln r� rn r-1 m Ln r-
61 61 61 O O O O O rl c- rl c- c- N N N N
Notes:
1. µg/L = micrograms per liter Time (Years)
2. Sulfate 2L Standard = 250,000 µg/L
3. Sulfate PPBC = 30,300 µg/L
Figure 114 Predicted Sulfate In Monitoring Well AB-32S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
11
1,
I
l
I
u I
I
I
I
I
— � s
6
r
�I
LEGEND
�= 30,300 (Background
Concentration)
30,300 - 50,000
50,000 - 100,000
100,000 - 200,000
200,000 - 250,000
250,000 - 300,000
300,000 - 336,186
_ DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. pg/L = micrograms per liter I fl Sfl0 1,000
PROPERTY BOUNDARY 2. Sulfate 2L Standard = 250,000 pg/L
MODEL DOMAIN 3. Sulfate PPBC = 30,300 pg/L Feet
Figure 115 Initial (2015) Sulfate Concentrations in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
1�
I�
' _ I
u
I
I
I
I
I
I
I
LEGEND
�= 30,300 (Background
Concentration)
30,300 - 50,000
50,000 - 100,000
100,000 - 200,000
200,000 - 250,000
250,000 - 300,000
300,000 - 336,186
_ DUKE ENERGY -
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY AI
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY OOINCIDENT Notes:
WITH DUKE ENERGY 1. Ng/L = micrograms per liter .'1 0 500 1,000
PROPERTY BOUNDARY 2. Sulfate 2L Standard = 250,000 pg/L
MODEL DOMAIN 3_ Sulfate PPBC = 30,300 Ng/L Feet
Figure 116 Initial (2015) Sulfate Concentrations in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
�1
I
_ I
u
I
I
I
I
a
l
r,.
I
LEGEND
�= 30,300 (Background
Concentration)
30,300 - 50,000
50,000 - 100,000
100,000 - 200,000
200,000 - 250,000
250,000 - 300,000
300,000 - 336,186
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
_ ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT Notes:
WTH DUKE ENERGY 1. pg/L = micrograms per liter I fl Sfl0 1,000
PROPERTY BOUNDARY 2. Sulfate 2L Standard = 250,000 pg/L
MODEL DOMAIN 3. Sulfate PPBC = 30,300 pg/L Feet
Figure 117 Initial (2015) Sulfate Concentrations in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
J' I
u I
� I
I
I
I
I
1
� � I
r
I
LEGEND \
— 30,300(Background
Concentration) '
30,300 - 50,D00 +�--
50,000 - 100,000
100,000 - 200,000
200,000 - 250,000 �I -
250,000 - 300,000
s
300,000 - 336,186
DUKE ENERGY p . •�,
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE _
AREA BOUNDARY
ASH BASIN COMPLIANCES AN
BOUNDARY J,
ASH BASIN COMPLIANCEN1
_ BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. pg/L =micrograms per liter 0 500 1,000
PROPERTY BOUNDARY 2. Sulfate 2L Standard = 250,000 pg/L
3. Sulfate PPBC = 30,300 pg/L �
MODEL DOMAIN Feel
Figure 118 Existing Conditions Scenario 1 - 2115 Predicted Sulfate in Shallow
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
I
I I
I
I
I
I
r
I
LEGEND
�= 30,300 (Background
Concentration)
30,300 - 50,D00 '
50,000 - 100,000
100,000 - 200,000
200,000 - 250,000
250,000 - 300,000
s
300,000 - 336,186 - f
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY -
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE AN
BOUNDARY J,
ASH BASIN COMPLIANCEN1
_ BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. pg/L = micrograms per liter 0 500 1,000
PROPERTY BOUNDARY 2. Sulfate 2L Standard = 250,000 pg/L
MODEL DOMAIN 3. Sulfate PPBC = 30,300 Ng/L Feel
Figure 119 Existing Conditions Scenario 1 - 2115 Predicted Sulfate in Deep Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 30,300 (Background
Concentration)
30,300 - 50,D00
50,000 - 100,000
100,000 - 200,000
200,000 - 250,000
250,000 - 300,000
300,000 - 336,186
y 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
,W
Notes:
1. pg/L = micrograms per liter
2. Sulfate 2L Standard = 250,000 Ng/L
3. Sulfate PPBC = 30,300 pg/L
I
I
I
I
I
I
I
I
4
f
I
r
lLAKE'
A
N
A
0 500 1,000
Feet
Figure 120 Existing Conditions Scenario 1 - 2115 Predicted Sulfate in Bedrock
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 30,300 (Background
Concentration)
30,300 - 50,D00
50,000 - 100,000
100,000 - 200,000
200,000 - 250,000
250,000 - 300,000
300,000 - 336,186
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
v
N
Notes:' A
1. Ng/L = micrograms per liter 0 500 1,000
2. Sulfate 2L Standard = 250,000 Ng/L
3. Sulfate PPBC = 30,300 pg/L Feet
Figure 121 Cap -in -Place Scenario 2 - 2115 Predicted Sulfate in Shallow Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 30,300 (Background
Concentration)
30,300 - 50,000
50,000 - 100,000
100,000 - 200,000
200,000 - 250,000
250,000 - 300,000
300,000 - 336,186
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
Notes:
1. ug/L = micrograms per liter
2. Sulfate 2L Standard = 250,000 pg/L
3. Sulfate PPBC = 30,300 pg/L
N
A
0 500 1,000
monsoons
Feet
Figure 122 Cap -in -Place Scenario 2 - 2115 Predicted Sulfate in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
— 30,300 (Background
Concentration)
30,300 - 50,D00
50,000 - 100,000
100,000 - 200,000
200,000 - 250,000
250,000 - 300,000
300,000 - 336,186
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
Notes:
1. pg/L = micrograms per liter
2. Sulfate 2L Standard = 250,000 pg/L
3. Sulfate PPBC = 30,300 pg/L
Feet
Figure 123 Cap -in -Place Scenario 2 - 2115 Predicted Sulfate in Bedrock Groundwater
Zone

Predicted Vanadium Concentration at AB-22S
J
c
0
L
U
r-
0
U
25.0
20.0
15.0
10.0
5.0
0.0
0 0 0
Ln r- a)
61 61 61
Notes: r-� r-1 r-�
1. µg/L = micrograms per liter
2. Vanadium IMAC value = 0.3 µg/L
3. Vanadium PPBC = 22.5 µg/L
0 0 0 0 0
0 0 0 0 0
ni ni r i ni ni
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Existing Conditions
Cap -in -Place
Vanadium IMAC
0 0 0 0 0 0 0 0 0
r-I � - r-1 r-1 ' r-rJ rV rV rV
ri ri ri ri ri ri ri ri ri
Time (Years)
Figure 124 Predicted Vanadium In Monitoring Well AB-22S

30.0
25.0
20.0
J
1
15.0
s`
0
4-1
10.0
L
a
5.0
U
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Predicted Vanadium Concentration at AB-26S
Existing Conditions
Cap -in -Place
Vanadium IMAC
0.0 -
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Ln r� a) r-q m Ln rl- a) r-q m Ln r� M rn Ln r�
a, a) a, o 0 0 0 0 r-q r-q r-q r rU r., rti r.,
rl rl rl rU N rV rV nl rU rV nl rU rV rV rV rU rV
Notes:
1. µg/L = micrograms per liter Time (Years)
2. Vanadium IMAC value = 0.3 µg/L
'I lfanarlii im PPRf = ?? S i iQfl
Figure 125 Predicted Vanadium In Monitoring Well AB-26S

25.0
PDXII
15.0
J
10.0
L
5.0
c
U
Predicted Vanadium Concentration at AB-325
0 0 0 0
Ln r- a) r-1
r-I r-I r-I N
Notes:
1. µg/L = micrograms per liter
2. Vanadium IMAC value = 0.3 µg/L
3. Vanadium PPBC = 22.5 µg/L
Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
Existing Conditions
Cap -in -Place
Vanadium IMAC
—
— —
r-W
0
0
0
0
0
0
0
0
0
0
0
0
0
m
Ln
r-
rn
r-�
m
Ln
r-
a)
r1
m
Ln
rti
0
0
0
0
r
r
rl
rl
r
rU
rU
r.l
r.l
ry
rU
ry
rN
rU
rU
rU
ry
rU
rti
ry
rU
rU
Time (Years)
Figure 126 Predicted Vanadium In Monitoring Well AB-32S

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
7-1 c 0.3 (Standard)
030-5.0
5-10
10-15
15 - 22.5 (Background
Concentration)
22.5 - 28
28 - 35.5
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Notes:
1. pg/L = micrograms per liter
2. Vanadium IMAC value = 0.3 Ng/L
3. Vanadium PPBC = 22.5 Ng/L
N
A
0 S00 1,000
monsoons
Feet
Figure 127 Initial (2015) Vanadium Concentrations in Shallow Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
fJ
LEGEND
— 0.3 (standard)
03-5
5-10
10 - 15
15 - 22.5 (Backgroun
Concentration)
22.5 - 28
28 - 35.5
DUKE ENERGY
PROPERTY BOUNDAF
ASH BASIN WASTE
BOUNDARY
LANDFILLlASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
c BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Notes:
1. Ng/L = micrograms per liter
2. Vanadium IMAC value = 0.3 Ng/L
3. Vanadium PPBC = 22.5 pg/L
N
A
0 500 1,000
Feet
Figure 128 Initial (2015) Vanadium Concentrations in Deep Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
I
/
1
r�l V
p
I I
I
I
I
9
i
I
a� I
r
I
LEGEND
=0.3 (Standard)
0.3 - 5 +
d
5-10 ` l"
10 - 15
15 - 22.5 (Background -
Concentration)
22.5 - 28
- 28 - 35.5
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILUASH STORAGE
AREABOUNDARY
ASH BASIN COMPLIANCE N
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT Notes:
WITH DUKE ENERGY 1. Ng/L = micrograms per liter - �'' I 0 500 1,D00
PROPERTY BOUNDARY 2. Vanadium IMAC value = 0.3 Ng/L
MODEL DOMAIN 3. Vanadium PPBC = 22.5 Ng/L Feet
Figure 129 Initial (2015) Vanadium Concentrations in Bedrock Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
I
LEGEND
—0.3 (Standard)
0.30 - 5.0
5-10
10 - 15
15 - 22.5 (Background
Concentration)
— 22.5 - 28
28 - 35.5
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
V14TH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Notes:
1. pg/L = micrograms per liter
2. Vanadium IMAC value = 0.3 pg/L
3. Vanadium PPBC = 22.5 Ng/L
W
N
A
0 500 1,000
Feet
Figure 130 Existing Conditions Scenario 1 - 2115 Predicted Vanadium in Shallow
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
I
LEGEND
—0.3 (Standard)
0.30 - 5.0
5-10
10 - 15
15 - 22.5 (Background
Concentration)
— 22.5 - 28
28 - 35.5
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
V14TH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Notes:
1. Ng/L = micrograms per liter
2. Vanadium IMAC value = 0.3 Ng/L
3. Vanadium PPBC = 22.5 Ng/L
W
N
A
0 500 1,000
Feet
Figure 131 Existing Conditions Scenario 1 - 2115 Predicted Vanadium in Deep
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
0
LEGEND
—0.3 (Standard)
0.30 - 5.0
5-10
10 - 15
15 - 22.5 (Background
Concentration)
— 22.5 - 28
28 - 35.5
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
V14TH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Notes:
1. pg/L = micrograms per liter
2. Vanadium IMAC value = 0.3 Ng/L
3. Vanadium PPBC = 22.5 pg/L
W
N
A
0 500 1,000
Feet
Figure 132 Existing Conditions Scenario 1 - 2115 Predicted Vanadium in Bedrock
Groundwater Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
—0.3 (Standard)
0.30 - 5.0
5-10
10 - 15
15 - 22.5 (Background
Concentration)
22.5 - 28
- 28 - 35.5
_ DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
_ BOUNDARY COINCIDENT
V14TH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
C
I
I I
I
I
I
I
I
_ I
Notes:
1. pg/L = micrograms per liter
2. Vanadium IMAC value = 0.3 Ng/L
3. Vanadium PPBC = 22.5 pg/L
l
1
1
ra,
I
4
N
A
0 500 1,000
Feet
Figure 133 Cap -in -Place Scenario 2 - 2115 Predicted Vanadium in Shallow Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
LEGEND
—0.3 (Standard)
030-5.0
5-10
10 - 15
15 - 22.5 (Background
Concentration)
22.5 - 28
28 - 35.5
DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
_ ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
E BOUNDARY COINCIDENT
WITH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
Notes:
1. Ng/L = micrograms per liter
2. Vanadium IMAC value = 0.3 pg/L
3. Vanadium PPBC = 22.5 pg/L
N
A
0 500 1,000
Feet
Figure 134 Cap -in -Place Scenario 2 - 2115 Predicted Vanadium in Deep Groundwater
Zone

Groundwater Flow and Transport Model
Allen Steam Station Ash Basin
I
LEGEND
—0.3 (Standard)
0.30 - 5.0
5-10
10 - 15
15 - 22.5 (Background
Concentration)
— 22.5 - 28
28 - 35.5
_ DUKE ENERGY
PROPERTY BOUNDARY
ASH BASIN WASTE
BOUNDARY
LANDFILLIASH STORAGE
AREA BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY
ASH BASIN COMPLIANCE
BOUNDARY COINCIDENT
V14TH DUKE ENERGY
PROPERTY BOUNDARY
MODEL DOMAIN
°1
1
I
1
1
Notes:
1. Ng/L = micrograms per liter
2. Vanadium IMAC value = 0.3 Ng/L
3. Vanadium PPBC = 22.5 Ng/L
M
N
A
0 500 1,000
Feet
Figure 135 Cap -in -Place Scenario 2 - 2115 Predicted Vanadium in Bedrock Groundwater
Zone