20190752 Ver 6_TR0795 GW Model Simulated Water Table Assessment-Rev_20220720

Geosyntect>
consultants
Geosyntec Consultants of NC, P.C.
Memorandum
Date: 11 January 2022
To: Chemours
Copies to: GeoServices
From: Geosyntec Consultants
Subject: Groundwater Model Simulated Water Table Assessment
SAW-2019-0026 Chemours
2501 Blue Ridge Road, Suite 430
Raleigh, NC 27607
PH 919.870.0576
www.geosyntec.com
INTRODUCTION
This memorandum was prepared by Geosyntec Consultants of NC, P.C. (Geosyntec) for The
Chemours Company FC, LLC, to support the evaluation of wetland impacts from the remedial
system implementation at the Chemours Fayetteville Works property located at 22828 NC
Highway 87, Fayetteville NC 28306 (the Site). A numerical groundwater model was developed to
simulate groundwater flow conditions at the Site. The primary objectives for developing the model
included: 1) gaining a better understanding of the groundwater flow system and associated
parameters; and 2) using the model as a tool for projecting groundwater flow conditions into the
future based on proposed remedial design.
The groundwater flow model was developed and calibrated to simulate groundwater flow
conditions at the Site during the pre -remedial development stage (baseline) and to form the basis
of design for the remedial system implementation. By extension, the simulated model results can
be used to assess the potential groundwater area of remedy influence (lowering of groundwater in
response to the remedy) downgradient of the barrier wall associated with the remedial system
implementation.
GROUNDWATER FLOW MODEL
A three-dimensional (3D) transient -state finite element numerical groundwater flow model was
developed to simulate groundwater flow at the site and allow for testing the effectiveness of
different remedial scenarios. The model was constructed in FEFLOW® version 7.2 (DHI-WASY),
TR0795/GW Model Simulated Water Table Assessment-Rev.docx
engineers I scientists I innovators

Post Remedy Assessment
11 January 2022
Page 2
and incorporates field -observed parameters, which were interpolated to approximate aquifer
conditions across the model domain and assumed to be representative in between measured
locations.
The 3D flow model was calibrated to 139 Site Wells: 60 wells in the perched zone, 32 wells in the
Surficial Aquifer and 47 wells in the Black Creek Aquifer. The calibration results and statistics
show the flow model is well calibrated, based on a reasonable agreement between the observed
and calculated heads and flows. A model is considered to be well calibrated when the normalized
root mean square (NRMS) is below 10%. The RMS for the Surficial aquifer was 5.65 ft; the NRMS
was 6.4% and the RMS for the Black Creek Aquifer was 4.58 ft; the NRMS was 5.2%. Detailed
information regarding the model construction, and calibration is presented in the 3-Dimensional
Groundwater Flow Model report which was prepared for the Chemours Fayetteville Works 60%
Design Report and is provided as Attachment A to this memorandum.
POST REMEDIAL IMPLEMENTATION DESIGN AND RESULT
The pre -remedial development model (baseline) was used to provide the initial condition for the
post remedial system implementation simulated over a 5-year time period. The stresses applied
(recharge) for the projected simulation were the same stresses applied during the last calibration
stress period (2018-2020) of the baseline model.
The simulated water table post remedy indicates cones of depression develop outwards from each
of the extraction wells and overall water elevation slightly increased upgradient of the barrier. The
area downgradient of the barrier wall simulated water table elevations decreased for up to 500 feet
from the barrier wall toward the Cape Fear River.
MODEL REMEDY INFLUENCE CALCULATION
The post remedy implementation projected water table elevations were compared to the pre -
remedy water table elevations in the area downgradient of the remedy. The post remedy model
simulated water table surface was subtracted from the pre -remedy water table surface to assess the
magnitude and location of projected changes in the water table after remedy implementation; see
Figure 1. The area immediately downgradient of the barrier wall shows a water table elevation
decrease of up to a maximum of 4.5 ft and then this decreases downgradient of the wall to reach
pre -remedy water levels.
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Post Remedy Assessment
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Figure 1: Simulated Water Table Elevation Changes Post Remedial System Implementation
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TR0795/GW Model Simulated Water Table Assessment-Rev.docxTR0795 USACE Model Drawdown-Rev.docx

Post Remedy Assessment
11 January 2022
Page 4
Attachment A: 60% Design 3-Dimensional Groundwater Flow Model Chemours Fayetteville
Works
TR0795/GW Model Simulated Water Table Assessment-Rev.docxTR0795 USACE Model Drawdown-Rev.docx

Geosyntec
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Geosyntec Consultants of NC, P.C.
NC License No.: C-3500 and C-295
GE#S
GEGSMCC, EEC, GMtecnneal ine Matendk Eng, neerc
Appendix B
Groundwater Flow Model Report
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3-Dimensional Groundwater Flow Model
Chemours Fayetteville Works
Prepared for
The Chemours Company FC, LLC
22828 NC Highway 87
Fayetteville, NC 28306
Prepared by
Geosyntec Consultants of NC, P.C.
2501 Blue Ridge Road, Suite 430
Raleigh, NC 27607
Geosyntec Project Number TR0795
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Table of Contents
1 Introduction and Objectives 1
1.1 Scope of Work 1
1.2 Report Organization 2
2. Groundwater Model Software Selection 2
2.1 Model Limitations 2
3. Groundwater Model Setup 3
3.1 Model Domain and Grid 3
3.2 Flow Boundary Conditions 4
3.3 Hydraulic Parameters 5
4. Groundwater Model Calibration 6
5. Remedial Design Simulations 7
5.1 Scenario 1: Baseline Conditions 7
5.2 Scenario 2: Vertical Barrier Alone 8
5.3 Scenario 3: Hydraulic Barrier Alone 8
5.4 Scenario 4: Optimized Scenario 9
6. Summary 10
7 References 12
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List of Tables
Table B.01 Model Hydraulic Conductivity Zones
Table B.02 Calibration Results: Observed vs. Model Predicted Hydraulic Head Data
List of Figures
Figure B.01 Model Domain and Grid
Figure B.02 Boundary Conditions and Recharge Zones
Figure B.03 Monitoring Well Locations
Figure B.04 Calibration Statistics
Figure B.05 Equipotential Head Contours — Base Model
Figure B.06 Scenario 1 — Particle Tracking from Plant Area Baseline Conditions
Figure B.07 Scenario 2 — Vertical Barrier Remedial Design
Figure B.08 Scenario 2 — Particle Tracking from Plant Area - Vertical Barrier
Figure B.09 Scenario 3 — Hydraulic Barrier Remedial Design
Figure B.10 Scenario 3 — Particle Tracking from Plant Area — Hydraulic Barrier
Figure B.11 Scenario 4 — Vertical and Hydraulic Remedial Design
Figure B.12 Scenario 4 — Particle Tracking from Plant Area — Vertical and Hydraulic Barrier
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Acronyms and Abbreviations
a alpha
8 delta
lambda
6 unsaturated -flow porosity
3D three-dimensional
CAP Corrective Action Plan
cm/s centimeter per second
CO Consent Order
COA Addendum to Consent Order Paragraph 12
CPT piezoCone Penetration Tests
ft feet
ft/d feet per day
ft2 feet square
gpm gallons per minute
HPT hydraulic profiling tool
K hydraulic conductivity
LiDAR Light Detection and Ranging
NRMS normalized root mean square
P� capillary pressure
PDI Predesign Investigation
PFAS per- and polyfluoroalkyl substances
ROI radii of influence
RMS root mean square
Sr residual wetting phase saturation
SS specific storage
SW wetting phase saturation
USGS United States Geological Survey
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1. Introduction and Objectives
This groundwater modeling report was prepared by Geosyntec Consultants of NC, P.C.
(Geosyntec) for The Chemours Company FC, LLC (Chemours) to describe the numerical
groundwater model used to develop the basis of design for the groundwater remedy to be
implemented pursuant to paragraph 3 of the Addendum to Consent Order Paragraph 12 (COA)
among Chemours, the North Carolina Department of Environmental Quality and Cape Fear River
Watch. Geosyntec initially developed a three-dimensional (3D) numerical groundwater transient
flow model in the Corrective Action Plan (Geosyntec, 2019). The model has been further refined
to incorporate results of the Pre -Design Investigation (PDI) efforts (Geosyntec, 2021). The updated
model incorporates refinements of the hydrostratigraphic units and aquifer properties that were
completed in 2020. The model was used as the basis of design for the groundwater remedy
including preparing estimates the amount of collected water that would require treatment.
Modeling objectives included:
• Simulate the capacity of a vertical physical barrier parallel to the Cape Fear River to
control discharge of groundwater to the River.
• Simulate capacity of a groundwater extraction system, upgradient of the vertical barrier
to control discharge of groundwater to the River.
• Utilize the model to evaluate possible optimal combinations of groundwater extraction
and physical barrier scenarios that would sufficiently control discharge of groundwater
to Cape Fear River, which would inform the basis of design for the overall remedy.
1.1 Scope of Work
The scope of work to achieve the above objectives included modifications to the model and the
incorporation of data acquired during the PDI. The majority of the changes to the model focused
on the area surrounding the proposed vertical barrier and extraction well network. The scope of
work included:
• Refining the grid cell spacing near the vertical barrier.
• Modifying the recharge zonation to better simulate site conditions.
• Modifying the hydraulic conductivity zonation based on data collected during the PDI.
• Examining and modifying the river stages in the various simulated surface water bodies
in the model.
• Re -calibrating the modified model to October 2019 and November 2020 measured
groundwater elevations.
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The current conditions base model was calibrated using statistical analysis and used as the basis
for several predictive scenarios. Each scenario was sequentially constructed to be able to assess
the performance of the hydraulic containment required in accordance with the objectives set forth
in COA Paragraph 3 (NCDEQ, 2020).
1.2 Report Organization
The remainder of this report includes the following subsections:
• Section 2 — Groundwater model software selection
• Section 3 — Groundwater model setup
• Section 4 — Groundwater model calibration
• Section 5 — Remedial design simulations
• Section 6 — Summary
• Section 7 — References
2. Groundwater Model Software Selection
The 3D model was constructed using FEFLOW, version 7.2 (DHI-WASY), which incorporates
the Richards' equation, the conservation of mass, and nonlinear relationships between capillary
pressure (Pc) and wetting phase saturation (SW) and between SW and hydraulic conductivity (K) to
solve for hydraulic heads. The model was constructed using field -observed parameters, which
were interpolated to approximate aquifer conditions across the model domain and assumed to be
representative in between measured locations.
2.1 Model Limitations
Simulation of groundwater flow involves using specific measured data (e.g., groundwater
elevation, hydraulic conductivity) and regional data (e.g., recharge) that are used to develop site -
wide fields of hydraulic heads. By nature, the groundwater model is an approximation based on
a limited number of data points, and thus in a complex environment, there are unavoidable
uncertainties. The groundwater model was constructed based on field -observed parameters, which
were then interpolated to approximate aquifer conditions across the model domain and assumed to
be representative in between the measured points. Numerical groundwater flow models, therefore,
are approximations of real -world hydrogeological systems. Nevertheless, models are commonly
used as a means of representing the available data on a specific groundwater system and evaluating
groundwater remedial design alternatives.
The model calibration was conducted for the purpose of the simulating potential groundwater
remedies pursuant to COA paragraph 3. Therefore, the primary importance of calibration results
was placed on the flow features salient to the simulation of groundwater flow within the vicinity
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between the bluff and the Cape Fear River where the vertical barrier and extraction well network
are proposed.
The validity and applicability of the model for purposes other than the stated objectives must be
independently evaluated based on the professional judgment of the model user.
3. Groundwater Model Setup
The original groundwater flow model developed in 2019 as part of the Corrective Action Plan
(CAP) was designed to represent the major physical and hydraulic features of the flow system in
the Site Aquifers (Perched, Surficial, and Black Creek) in and around the Chemours Fayetteville
Site. Construction and calibration of the original CAP groundwater model are described in
Appendix H of the CAP report (Geosyntec, 2019).
Portions of the PDI focused on collecting data for further refining the groundwater model. The
scope items included aquifer testing at five locations, a high -resolution cross section, and
assessment of per- and polyfluoroalkyl substances (PFAS) chemistry in groundwater along the
remedy alignment. This section describes the current version of the model developed for vertical
barrier depth design and extraction well network evaluation, and where appropriate, how the model
has been modified since inception.
3.1 Model Domain and Grid
The model domain covers an area of 72,690,473 feet square (ft2) (2.61 square miles). The revised
grid consists of 2,099,240 nodes and 4,154,656 elements and 7 model hydrostatigraphic units. The
number of nodes and elements were increased to refine the model domain from the edge of the
bluff to Cape Fear River. The model domain and grid location are presented in Figure B.01.
The model uses 7 hydrostratigraphic units to represent, from surface downward, the Floodplain
deposits, Perched Zone, Perched Clay, Surficial aquifer, Black Creek Confining unit, Black Creek
aquifer, and Cape Fear Confining unit. The model varies in thickness from about 170 feet (ft) near
the plant to 55 ft at the base of the bluff adjacent to the Cape Fear River.
The Light Detection and Ranging (LiDAR) elevation model prepared by the North Carolina
Department of Public Safety was imported to represent ground surface topography (NC DPS,
2015), which was corrected with ground survey data, where available, in areas that could impact
performance of the model. The topography of the underlying model layers were based on
lithostratigraphic data obtained from Site monitoring wells, soil borings, hydraulic profiling tool
(HPT), and piezoCone Penetration Tests (CPT) contained in the three-dimensional visualization
model, EVSTM.
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3.2 Flow Boundary Conditions
Boundary conditions are used to simulate flow of water into and out of a model domain.
Upgradient regional conditions, river and recharge boundaries are used in the updated model to
simulate Site conditions. Figure B.02 presents the locations of the boundary conditions within the
model domain. The numerical model extent was closely tied to the boundary conditions chosen
for the model:
Top Boundary: Established as the ground surface, taken from a combination of LiDAR data and
topographic surveys performed along Willis Creek and the Outfall. Boundary conditions on the
top boundary were either constant flux (to simulate rainfall recharge) or constant head equal to
elevation (with a no inward flow constraint) to simulate seepage faces on the bluffs. Initial rainfall
recharge values were selected with reference to the annual precipitation and evapotranspiration
estimates for the Mid -Atlantic Coastal Plain (United States Geological Survey [USGS], 2005).
Bottom Boundary: Chosen as flat at an elevation of -20 ft above MSL which is located within the
Upper Cape Fear confining unit. A no -flow hydraulic condition was applied to the entire bottom
boundary of the model.
Northern Boundary: Willis Creek forms a hydraulic boundary north of the model domain. The
creek is treated as a spatially -varying constant hydraulic head boundary from the northwest model
corner to the outflow to the Cape Fear River located at the northeast model corner. The uppermost
active nodes in the mesh along the Willis Creek boundary were linearly interpolated, from west to
east along the creek, from a hydraulic head equal to the ground surface elevation at the western
most part of Willis Creek to a hydraulic head equal to the constant hydraulic head boundary value
of the Cape Fear River. Application of this constant head condition to only the upper nodes in the
mesh forces all groundwater flowing towards the boundary to discharge into the creek (as all nodes
below the upper nodes were assigned a no -flow condition).
Eastern Boundary: The Cape Fear River forms a hydraulic boundary east of the model domain.
The river is treated as a constant hydraulic head boundary in the uppermost active nodes with an
elevation representative of a daily median water elevation in the river, as measured at the W.O.
Huske Dam (USGS, 2105500). The river wraps partially around the northeast and southeast
corners of the model. Application of this constant head condition to only the uppermost nodes in
the mesh forces all groundwater flowing towards the boundary to discharge into the river.
Southern Boundary: The model domain southern extent was chosen to represent a flow line from
the western boundary to the eastern boundary. This selection was based on the available measured
hydraulic head data and professional judgment (Geosyntec, 2019). A no -flow condition was
applied to the southern boundary.
Western Boundary: The western model boundary is not bounded by any clearly defined hydraulic
features and maybe a flow divide beneath a topographic high. This boundary was chosen as parallel
to the Cape Fear River as limited hydraulic information was available to make a more refined
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choice. This boundary is located more than a quarter mile from the manufacturing area of the Site.
Spatially -varying constant hydraulic head boundary conditions were applied linearly ranging from
125 ft (in the shallower portion of the domain) or 122 ft (in the deeper portion of the domain) at
the southern end of the boundary to the elevation of Willis Creek at the northern end of the
boundary.
3.3 Hydraulic Parameters
The model parameters were chosen based on the available field data, such as CPT, HPT, and
aquifer test data collected from 2018 to 2020. Where ranges in data existed, mid -points of the
ranges were chosen as the initial set of parameters.
Hydraulic conductivity, specific storage (Ss), unsaturated -flow porosity (0), residual wetting phase
saturation (Sr), and Brooks-Corey-Burdine Pc-SW-K constitutive parameters (alpha (a), lambda (X,),
delta (8)) are the main hydraulic parameters in the model. The distribution and assignment of these
parameters are based on the conceptual model hydrostratigraphy. Hydraulic parameter distribution
in the model was uniform across individual hydrostratigraphic units. The parameter values for each
hydrostratigraphic unit were determined during the flow model calibration process (Section 3) and
presented in Table 1.
Table 1: Calibrated Model Hydraulic Parameters For Each Hvdrostratigraphic Unit
Hydrostratigraphic Unit
K (ft/day)
Ss (m-1)
0
Sr (-)
a (m-1)
A (-)
S (-)
Floodplain Deposits
1.4
1.0 x 10-8
0.32
0.2
0.5
0.15
25
Perched Zone
2.6
1.0 x 10-3
0.3
0.1
11.5
0.56
7.3
Perched Clay
0.0014
1.0 x 10-8
0.5
0.2
0.5
0.15
25
Surficial Aquifer
25 to 72
1.0 x 10-3
0.33
0.1
11.5
0.56
7.3
Black Creek Confining Unit
0.43
1.0 x 10-8
0.55
0.2
0.5
0.15
25
Black Creek Aquifer
3.8 to 102
5.1 x 10-5
0.34
0.1
11.5
0.56
7.3
Cape Fear Confining Unit
1.1
1.0 x 10-8
0.28
0.2
0.5
0.15
25
Sr and the Brooks-Corey-Burdine (a, X, 8) constitutive parameters for each hydrostratigraphic unit
were selected based on the soil textural class and the estimated model parameters reviewed from
Madi et al. (2018), Matlan et al. (2014), and Shao and Irannejad (1999). These parameter
assignments were simplified for the model by separating the hydrostratigraphic units as either
aquifers or aquitards after performing the first set of flow model calibration runs where each
hydrostratigraphic unit was assigned distinct parameter sets. Aquifer units were assigned Sr and
Brooks-Corey-Burdine constitutive parameters representative of sands; aquitard units were
assigned Sr and Brooks-Corey-Burdine constitutive parameters representative of sandy clay, silty
clay, and clay soil types.
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4. Groundwater Model Calibration
Model calibration is an iterative process where the initial parameters values (e.g., hydraulic
conductivities, boundary conditions, recharge) are adjusted incrementally to produce a better
match between simulated and observed water level elevations.
Site -wide synoptic water level rounds (July 2020 and December 2020) were collected that
incorporated newly installed wells during the PDI.
A total of 96 monitoring well points were used to calibrate the model. Table 2 provides the wells,
coordinates, hydrostratigraphic unit, observed and predicted hydraulic heads, and the residual
heads. The residual head for each monitoring point is the calculated hydraulic head minus the
observed hydraulic head (Xcal— Xobs). Figure B.03 presents the locations of the monitoring wells
used to calibrate the base model.
Figure B.04 presents the calibration statistics and a graph of the calculated heads versus observed
heads. Calibration statistics presented include the range of residuals, residual mean, absolute
residual mean, the standard error of the estimate, the root mean squared error, the normalized root
mean squared error, and the flow mass balance.
The maximum residual (difference between observed and calculated head) occurs in the Perched
zone at MW-27 (8.52 ft), Surficial aquifer at SMW-09 (13.5 ft), and in the Black Creek at PW-
10R (10.27 ft). The residual mean is a measure of the average residual head because it is possible
that over -calculated and under -calculated values will negate each other thus producing a residual
mean value closer to zero (which is ideal), it is preferable to use the absolute residual mean as an
indicator of model calibration. The residual mean was -0.66 ft; the absolute residual mean was
2.94 ft.
The root mean square (RMS) is a statistical measure of the magnitude of the residual and is useful
as an indicator of error where values are both positive and negative. The normalized root mean
square (NRMS) is the RMS divided by the maximum difference in observed head values,
expressed in percent (%). A model is considered to be well calibrated when the NRMS is below
10%. The RMS for the Perched zone was 4.34 ft; the NRMS was 23.9%, the RMS for the Surficial
aquifer was 5.65 ft; the NRMS was 6.4% and the RMS for the Black Creek Aquifer was 4.58 ft;
the NRMS was 5.2%. The Perched zone NRMS value exceeds 10%, but is unconfined and thin,
and the perched zone can be significantly influenced by small scale local recharge patterns making
calibration more difficult. The primary targets of the remedy are the Surficial and Black Creek
aquifers, not the perched, so calibration does not need to be as refined.
The flow mass balance is a measure of the volume and rates of water entering and leaving the
system through the flow boundary conditions, and from aquifer storage at the end of each stress
period (in the case of transient simulations). Ideally, the flow balance should be as close as
practicable to a discrepancy of 0%. The flow mass balance in this model has a discrepancy of
0.78%.
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Figure B.05 presents the simulated equipotential head contours for the Surficial aquifer and Black
Creek aquifer layers in the calibrated base model. Field -measured groundwater elevation contours
are also included for comparison. Although the focus during model calibration was the area where
the vertical barrier and extraction wells will be installed, the model is adequately simulating the
groundwater within the plant area.
5. Remedial Design Simulations
The remedial design for Site groundwater includes the installation of a vertical barrier and a
groundwater extraction and treatment system to control discharge of PFAS containing
groundwater to the Cape Fear River.
The following describes a summary of the conclusions from the PDI and the model results for
consideration into the vertical barrier design and groundwater extraction system remedy. The Site
geology is highly variable along the groundwater remedy alignment. Consistent with the
interpretation of a deltaic depositional environment, the Black Creek aquifer along the alignment
is a mixture of high-energy channel sands and lower -energy mud flats. Geosyntec prepared a high -
resolution cross section along the groundwater remedy alignment using a combination of data
collected during the PDI and previous investigations (Figure is located in PDI document in
Appendix A) (Geosyntec, 2021). Three distinct sections of the groundwater remedy alignment are
described as follows. Black Creek aquifer soils in the northern portion of the groundwater remedy
alignment are dominated by more fine-grained materials indicative of a transition to a low -energy
deposition environment. The central portion of the alignment is characterized by higher -energy
channel sands and correlates to the locations of a majority of the seeps. The southern portion is
similar to the central portion of the alignment but is hydraulically influenced by the Old Outfall.
Particle tracking was incorporated to display flow direction and magnitude between the Site and
Cape Fear River under baseline conditions and after the addition of the vertical barrier and the
groundwater extraction network. Particle tracking starting locations were released from the Plant
Area upgradient of the proposed remedy area.
Particle track and water budget analyses have been completed for various scenarios to quantify
groundwater discharge between the Site and the Cape Fear River. This was accomplished using
particle tracking and the rate budget analyzer within FEFLOW to assess the groundwater discharge
to the Cape Fear River. Groundwater discharge was first estimated under baseline conditions (i.e.,
Scenario 1, the base case model). As the subsequent scenarios were developed, the particles
discharged to Cape Fear River were compared to baseline conditions to evaluate the scenario's
control of groundwater flow.
5.1 Scenario 1: Baseline Conditions
The base case model is equivalent to the model calibration conducted during the PDI where the
model was adjusted to simulate current conditions prior to remedy implementation.
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Figure B.06 presents particle -tracking results for Scenario 1 which uses a 5-year model run time
and releases particles from the Plant Area. Under these conditions, particles released from the
perimeter of the plant migrate horizontally, then eventually discharge to Cape Fear River.
5.2 Scenario 2: Vertical Barrier Alone
In this scenario, a five-year model simulation, the vertical barrier parallel to the Cape Fear River
(shown by the green line in Figure B.07) is simulated to the top of the Upper Cape Fear Confining
unit by creating a zone to represent the vertical boundary. The length of the barrier is
approximately 9,000 ft, and the depth embeds five feet into the Upper Cape Fear Confining unit.
Approximate depth of the barrier ranges from approximately 60 to 80 ft. The barrier is assigned a
thickness of 1.6 ft (0.5-meter) and a hydraulic conductivity of 2.8 x 10-3 feet per day (ft/d) (1.0 x
10-6 centimeter per second [cm/s]). Figure B.08 presents the particle -tracking results for Scenario
2. In this five-year simulation, many of the particles released from the Site pass over, around, and
through the vertical barrier, and eventually discharge to the Cape Fear River. Specifically, in the
area near Seep A and B where there is high transmissivity, particles migrate over, around and
through the barrier and discharge to Cape Fear River at a relatively high rate.
Results from the particle tracking and flow analysis indicated that the physical barrier wrap -around
flow occurred at the barrier edges after 7 days, breakthrough occurs in multiple locations along the
barrier, and groundwater discharges to surface. Specifically, in the areas near Seeps A and B,
particles migrate over, around, and through the barrier and discharge to Cape Fear River.
5.3 Scenario 3: Hydraulic Barrier Alone
In Scenario 3, a hydraulic barrier alone was simulated using a groundwater extraction network
between the bluff and the Cape Fear River (shown by the wells in Figure B.09). This simulation
used 64 extraction wells (10 wells located in the surficial aquifer and 54 wells located in the Black
Creek aquifer) to mitigate groundwater discharge to the Cape Fear River.
The simulated extraction well flow rates ranged from 5 to 35 gallons per minute (gpm) depending
on location and the total cumulative flow rate for the extraction well network simulated was 980
gpm. Well spacing is generally 200 ft apart; well spacings are closer where there is higher
groundwater flux, particularly in the vicinity of Seeps A and B, and along the southern end near
the Old Outfall 002. Figure B.10 presents the particle -tracking results for Scenario 3. In this
simulation, the particles are released from the Site in the plant area and many are contained by the
extraction system. However, some particles are ultimately discharged to the Cape Fear River.
Specifically, in the areas near Seeps A and B, particles migrate between some of the extraction
wells and discharge to Cape Fear River. An evaluation of the extraction well network indicated
insufficient overlap of the radii of influence (ROI) for the extraction wells in many areas of the
hydraulic barrier remedy. This results in incomplete capture in the areas where there is increased
groundwater flow due to the presence of highly transmissive material.
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Additional extraction wells and increased pumping would allow for sufficient overlapping ROI,
however, the resulting cone of depression is of sufficient size to begin drawing in Cape Fear River
water with limited additional capture of groundwater, reducing overall efficiency. Sensitivity
analysis was performed to optimize the well placement and well density along the proposed
remedy route. In addition to the spacing specified in the above figures, simulations with a well
spacing of 100 ft apart with tighter spacing of 25 feet apart (total of 135 wells) near Seep A, Seep
B and near Outfall 003 (higher transmissible areas) were assessed. In the highly transmissive areas,
particles from the plant area were still not fully captured by the groundwater extraction well
network. Site conditions are such that groundwater from under the plant facility cannot be fully
captured without also capturing some portion of Cape Fear River water. It was determined
pumping alone could not match the performance of a combination pumping with a physical barrier,
Scenario 4 below, with respect to capture.
Notably, in the northern area of the site, where the overall hydraulic conductivity is lower, the ROI
of the extraction wells in this area sufficiently overlap and allows for capture of groundwater over
the area. Evaluation of the two stand-alone approaches demonstrate that the barrier wall only or
pumping only is not sufficient to meet overall Consent Order (CO) objectives. However, the
simulation also demonstrated that pumping alone near Willis Creek controls the discharge to
surface water in the northern portion.
5.4 Scenario 4: Optimized Scenario
In scenario 4, the vertical barrier and a hydraulic barrier containing 64 extraction wells (10 wells
located in the surficial aquifer and 54 wells located in the Black Creek aquifer) were combined
and simulated to assess performance of remedy (shown by the wells in Figure B.11).
Attachment 5 to the COA identified that the barrier wall could extend along Willis Creek in the
northern alignment. Based on the favorable simulated performance of pumping only (see section
5.3 above) along the northern section and the identified constructability considerations along the
northern section (section 3.2.4 of the 60% Design Report), the length of the barrier wall was set to
approximately 6,000 ft from near the intake road to near the Old Outfall. The depth of the barrier
extends into the upper five ft of the Upper Cape Fear Confining unit, for a total depth of
approximately 60 to 80 ft. The barrier is assigned a 1.6-ft (0.5-meter) thickness and hydraulic
conductivity of 2.8 x 10-3 ft/d (1.0 x 10-6 cm/s).
The simulated extraction well flow rates range from 5 to 35 gpm depending on location, and the
total cumulative flow rate for the extraction well network simulated was 980 gpm. The presence
of the vertical barrier effectively reduces overall hydraulic conductivity over the alignment where
the barrier wall is present. As a result, the effective ROI of the wells is generally extended to allow
sufficient overlap to capture groundwater flow. In those areas where a 200-ft spacing is not
sufficient to capture released particles, spacing was tightened to provide adequate overlap of the
ROI. Spacing is tighter at the northern and southern ends of the barrier wall and in the vicinity of
the Seeps A and B where overall transmissivity is higher and to reduce potential for wrap around.
TR0795
9 Aug-2021

Geosyntee °
consultants
Geasyntec Consultants of NC, P.C.
NC License No.: C-35917 and C•295
Figure B.12 presents the particle -tracking results for Scenario 4. In this simulation, the particles
released from the Site in the plant area are controlled by the combination vertical and hydraulic
barrier. Effectiveness of the simulated remedy was largely equal for both the surficial aquifer
above the barrier wall and the Black Creek Aquifer. Groundwater that is present downgradient of
the remedy after startup becomes largely stagnant; over time, continuing rainwater recharge and
fluctuation of the Cape Fear river slowly drives remaining water present downgradient of the wall
toward the Cape Fear River.
Additional sensitivity analyses were performed during the PDI to determine the impacts of key
variables on the remedial design; see Appendix A. In addition, precipitation and Cape Fear River
model inputs were simulated at the upper range of the observed data to develop upper range of the
cumulative flow rates for the extraction well network.
6. Summary
The original groundwater model developed during the CAP and the PDI from 2019 through 2021
was updated to include water level, hydraulic conductivity, and hydrostratigraphic unit elevation
data collected during the PDI in 2020/2021. The model was also further discretized vertically and
horizontally to allow a more complex simulation of site conditions, simulate potential remedies
and help provide a basis for remedy design.
The model was calibrated to synoptic groundwater data collected from 2018 to 2020 by adjusting
the hydraulic conductivity distribution, boundary conditions, and recharge. Model calibration
statistics indicate a root mean square result of 5.65 ft and a normalized root mean square of 6.4%
for the surficial Aquifer and a root mean square result of 4.58 ft and a normalized root mean square
of 5.2% for the Black Creek Aquifer and, indicating a well calibrated model. The calibrated model
was validated by effectively simulating the pump tests for EW-1, EW-2, EW-3, and EW-4
conducted during the PDI in 2020.
Several model scenarios were completed to assess basis of design for the remedy:
• Scenario 1 simulates the current conditions base model updated with PDI data.
• Scenario 2 simulates a vertical barrier only.
• Scenario 3 simulates a hydraulic barrier via an extraction system only.
• Scenario 4 simulates an optimized remedy that takes advantages of the strengths of
both the vertical barrier and hydraulic barrier via an extraction system.
The modeling results indicate that the groundwater in the northern alignment portion can be
intercepted using extraction wells alone and that a barrier wall is not required. Particle tracking of
the scenario simulations indicate that surficial aquifer to the seeps east of the barrier wall and the
Black Creek Aquifer to the Cape Fear River controls groundwater and meets CO objectives under
Scenario 4, the optimized solution.
TR0795
10 Aug-2021

Geosyntee °
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Geasyntec Consultants of NC, P.C.
NC License No.: C-35917 and C•295
Based on these model results, Scenario 4 was selected as a suitable option for limiting the
groundwater discharge to the Cape Fear River and forms the basis of design for the groundwater
remedy. Scenario 4 demonstrates that to provide adequate hydraulic containment, 64 extraction
wells (10 wells located in the surficial aquifer, and 54 wells located in the Black Creek aquifer)
and a vertical barrier wall installed through the central and southern sections of the alignment
successfully reduce the groundwater discharging to the Cape Fear River. The estimated
cumulative flow rates for the extraction well network is about 980 gpm.
TR0795
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Geosyntec °
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Geosyntec Consultants of NC, P.C.
NC License No.: C-35917 and C•295
7. References
Diersch, H.J.G. 2014. FEFLOW: Finite Element Modeling of Flow, Mass and Heat Transport in
Porous and Fractured Media. Springer-Verlag Berlin Heidelberg. 2014.
Geosyntec, 2019. On and Offsite Assessment Report, Chemours Fayetteville Works. Geosyntec
Consultants of NC, PC. September 30, 2019.
Geosyntec, 2021. Pre -Design Investigation Summary. Chemours Fayetteville Works. June 29,
2021
Madi, R., de Rooij, G.H., Mielenz, H., & Mai, J. 2018. Parametric soil water retention models:
critical evaluation of expressions for the full moisture range. Hydrology and Earth System
Sciences, 22. 2018.
Matlan, S.J., Mukhlisin, M., & Taha, MR. 2014. Performance Evaluation of Four -Parameter
Models of the Soil -Water Characteristic Curve. The Scientific World Journal,
2014(569851). 2014.
NCDEQ, 2007. Groundwater Modeling Policy, North Carolina Department of Environmental
Quality. May 31, 2007.
NCDEQ, 2019. Addendum to Consent Order Paragraph 12. General Court of Justice Superior
Court Division. State of North Carolina. County of Bladen. February 25, 2019.
Parsons, 2018. Additional Site Investigation Report, Chemours Fayetteville Works Site, RCRA
Permit No. NCD047368641-R1. March 30, 2018.
Shao, Y., & Irannejad, P. 1999. On The Choice of Soil Hydraulic Models in Land -Surface
Schemes. Boundary -Layer Meteorology, 90(1). 1999.
USGS. A Surficial Hydrogeologic Framework for the Mid -Atlantic Coastal Plain, Professional
Paper 1680. 2005.
TR0795
12 Aug-2021

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consultants
Geasyntec Consultants of NC, P.C.
NC License No.: C-3500. and C• 295
Tables
TR0795
Aug-2021

Geosyntec Consultants of NC, P.C.
Table B.02: Calibration Results: Observed vs
Model Predicted Hydraulic Head Data
Chemours Fayetteville Works, North Carolina
Location Name
Aquifer
Observation Date
Observed
Head
(ft)
Calculated
Head
(ft)
Residual
(Obs. - Calc.)
(ft)
BCA-01
Black Creek Aquifer
Oct-19
87.38
83.58
-3.80
BCA-02
Black Creek Aquifer
Oct-19
74.55
81.52
6.97
BCA-04
Black Creek Aquifer
Oct-19
121.55
114.41
-7.14
BCA-03R
Black Creek Aquifer
Oct-19
101.27
101.05
-0.22
PW-10R
Black Creek Aquifer
Oct-19
48.15
54.43
6.28
PW-12
Black Creek Aquifer
Oct-19
92.65
100.70
8.05
LTW-02
Black Creek Aquifer
Oct-19
42.19
39.36
-2.83
LTW-05
Black Creek Aquifer
Oct-19
42.35
42.42
0.07
PIW-2D
Black Creek Aquifer
Oct-19
64.55
64.30
-0.25
PIW-3D
Black Creek Aquifer
Oct-19
35.8
39.02
3.22
PIW-4D
Black Creek Aquifer
Oct-19
41.68
50.02
8.34
PIW-7D
Black Creek Aquifer
Oct-19
42.69
45.68
2.99
PIW-8D
Black Creek Aquifer
Oct-19
41.11
43.33
2.22
PIW-9D
Black Creek Aquifer
Oct-19
42.08
49.40
7.32
PW-09
Black Creek Aquifer
Oct-19
52.24
47.48
-4.76
PW-11
Black Creek Aquifer
Oct-19
39.6
40.57
0.97
PW-13
Black Creek Aquifer
Oct-19
119.79
117.30
-2.49
PW-14
Black Creek Aquifer
Oct-19
86.86
84.49
-2.37
PW-15R
Black Creek Aquifer
Oct-19
76.96
77.63
0.67
PZ-22
Black Creek Aquifer
Oct-19
44.06
43.02
-1.04
SMW-12
Black Creek Aquifer
Oct-19
33.44
38.88
5.44
LTW-01
Floodplain Deposits
Oct-19
37.3
40.33
3.03
LTW-03
Floodplain Deposits
Oct-19
39.71
39.06
-0.65
LTW-04
Floodplain Deposits
Oct-19
42.55
43.63
1.08
PIW-1S
Floodplain Deposits
Oct-19
32.59
35.56
2.97
PIW-6S
Floodplain Deposits
Oct-19
38.6
41.90
3.30
PIW-7S
Floodplain Deposits
Oct-19
42.51
50.33
7.82
PIW-7S
Floodplain Deposits
Oct-19
42.51
43.21
0.70
MW-13D
Surficial Aquifer
Oct-19
104.33
99.89
-4.44
MW-14D
Surficial Aquifer
Oct-19
109.67
107.09
-2.58
MW-16D
Surficial Aquifer
Oct-19
113.02
106.38
-6.64
MW-17D
Surficial Aquifer
Oct-19
117.09
114.11
-2.98
MW-18D
Surficial Aquifer
Oct-19
87.28
87.89
0.61
MW-19D
Surficial Aquifer
Oct-19
88.24
86.19
-2.05
MW-20D
Surficial Aquifer
Oct-19
89.51
85.37
-4.14
MW-21D
Surficial Aquifer
Oct-19
105.71
102.86
-2.85
MW-22D
Surficial Aquifer
Oct-19
113.82
110.93
-2.89
PIW-1D
Surficial Aquifer
Oct-19
32.81
32.17
-0.64
PIW-5S
Surficial Aquifer
Oct-19
60.46
48.36
-12.10
PW-02
Surficial Aquifer
Oct-19
90.05
82.82
-7.23
PW-05
Surficial Aquifer
Oct-19
121.25
121.37
0.12
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Page 1 of 6
August 2021

Geosyntec Consultants of NC, P.C.
Table B.02: Calibration Results: Observed vs
Model Predicted Hydraulic Head Data
Chemours Fayetteville Works, North Carolina
Location Name
Aquifer
Observation Date
Observed
Head
(ft)
Calculated
Head
(ft)
Residual
(Obs. - Calc.)
(ft)
MW-15DRR
Surficial Aquifer
Oct-19
103.37
101.34
-2.03
PW-03
Surficial Aquifer
Oct-19
105.57
95.39
-10.18
SMW-03B
Surficial Aquifer
Oct-19
93.4
100.72
7.32
SMW-05P
Surficial Aquifer
Oct-19
105.31
106.23
0.92
SMW-06B
Surficial Aquifer
Oct-19
103.15
102.07
-1.08
SMW-08B
Surficial Aquifer
Oct-19
108.29
106.71
-1.58
SMW-09
Surficial Aquifer
Oct-19
85.2
71.65
-13.55
SMW-10
Surficial Aquifer
Oct-19
46.69
53.70
7.01
SMW-11
Surficial Aquifer
Oct-19
57.87
54.34
-3.53
SMW-04B
Surficial Aquifer
Oct-19
102.94
100.42
-2.52
FTA-02
Perched Zone
Oct-19
133.61
131.69
-1.92
MW-1S
Perched Zone
Oct-19
132.9
130.81
-2.09
MW-2S
Perched Zone
Oct-19
130.69
129.30
-1.39
MW-9S
Perched Zone
Oct-19
130.36
124.57
-5.79
MW-11
Perched Zone
Oct-19
132.81
132.54
-0.27
MW-23
Perched Zone
Oct-19
131.61
128.04
-3.57
MW-24
Perched Zone
Oct-19
133.93
140.50
6.57
MW-26
Perched Zone
Oct-19
133.29
133.17
-0.12
MW-28
Perched Zone
Oct-19
131.99
123.47
-8.52
MW-31
Perched Zone
Oct-19
130.2
124.77
-5.43
MW-33
Perched Zone
Oct-19
132.36
128.58
-3.78
NAF-03
Perched Zone
Oct-19
139.43
139.36
-0.07
NAF-06
Perched Zone
Oct-19
139.99
139.05
-0.94
NAF-08A
Perched Zone
Oct-19
138.92
136.52
-2.40
NAF-09
Perched Zone
Oct-19
138.54
142.64
4.10
NAF-10
Perched Zone
Oct-19
136.38
141.43
5.05
NAF-11A
Perched Zone
Oct-19
135.76
132.42
-3.34
PZ-11
Perched Zone
Oct-19
133.55
126.63
-6.92
PZ-12
Perched Zone
Oct-19
137.02
130.84
-6.18
PZ-13
Perched Zone
Oct-19
130.74
131.00
0.26
PZ-20R
Perched Zone
Oct-19
135.54
131.57
-3.97
PZ-21R
Perched Zone
Oct-19
135.47
131.66
-3.81
PZ-24
Perched Zone
Oct-19
136.22
132.30
-3.92
PZ-25
Perched Zone
Oct-19
133.36
130.49
-2.87
PZ-27
Perched Zone
Oct-19
134.8
132.63
-2.17
PZ-28
Perched Zone
Oct-19
133.97
130.07
-3.90
PZ-29
Perched Zone
Oct-19
135.14
127.78
-7.36
PZ-32
Perched Zone
Oct-19
130.7
130.14
-0.56
PZ-34
Perched Zone
Oct-19
132.72
126.76
-5.96
SMW-03
Perched Zone
Oct-19
136.32
132.76
-3.56
NAF-13
Perched Zone
Oct-19
133.01
139.18
6.17
TR0795
Page 2 of 6
August 2021

Geosyntec Consultants of NC, P.C.
Table B.02: Calibration Results: Observed vs
Model Predicted Hydraulic Head Data
Chemours Fayetteville Works, North Carolina
Location Name
Aquifer
Observation Date
Observed
Head
(ft)
Calculated
Head
(ft)
Residual
(Obs. - Calc.)
(ft)
PZ-17
Perched Zone
Oct-19
135.12
141.51
6.39
SMW-02
Perched Zone
Oct-19
121.81
119.60
-2.21
PZ-12
Perched Zone
Dec-20
132
131.00
1.00
PZ-15
Perched Zone
Dec-20
135.85
141.51
-5.66
PZ-17
Perched Zone
Dec-20
121.85
119.60
2.25
PZ-19R
Perched Zone
Dec-20
137.14
131.57
5.57
PZ-20R
Perched Zone
Dec-20
137.07
131.66
5.41
PZ-21R
Perched Zone
Dec-20
138.62
132.30
6.32
PZ-35
Perched Zone
Dec-20
138.07
132.76
5.31
BCA-01
Black Creek Aquifer
Dec-20
84.43
83.58
0.85
BCA-02
Black Creek Aquifer
Dec-20
75.07
81.52
-6.45
BCA-03R
Black Creek Aquifer
Dec-20
101.29
101.05
0.24
BCA-04
Black Creek Aquifer
Dec-20
122.38
114.41
7.97
EW-1
Perched Zone
Dec-20
60.15
65.66
-5.51
EW-2
Perched Zone
Dec-20
43.35
44.10
-0.75
EW-3
Perched Zone
Dec-20
61.55
57.17
4.38
EW-4
Perched Zone
Dec-20
50.57
48.39
2.18
EW-5
Perched Zone
Dec-20
45.38
43.41
1.97
FTA-01
Perched Zone
Dec-20
134.14
131.69
2.45
FTA-02
Perched Zone
Dec-20
132.88
136.39
-3.51
FTA-03
Perched Zone
Dec-20
133.68
130.81
2.87
LTW-01
Floodplain Deposits
Dec-20
38.88
40.33
-1.45
LTW-02
Black Creek Aquifer
Dec-20
43.2
39.36
3.84
LTW-03
Floodplain Deposits
Dec-20
41.24
39.06
2.18
LTW-04
Floodplain Deposits
Dec-20
44.19
43.63
0.56
LTW-05
Black Creek Aquifer
Dec-20
42.78
42.42
0.36
MW-11
Perched Zone
Dec-20
125.15
125.90
-0.75
MW-12S
Perched Zone
Dec-20
132.56
128.04
4.52
MW-13D
Surficial Aquifer
Dec-20
104.75
99.89
4.86
MW-14D
Surficial Aquifer
Dec-20
110.29
107.09
3.20
MW-15DRR
Surficial Aquifer
Dec-20
103.21
101.34
1.87
MW-16D
Surficial Aquifer
Dec-20
112.89
106.38
6.51
MW-17D
Surficial Aquifer
Dec-20
117.74
114.11
3.63
MW-18D
Surficial Aquifer
Dec-20
88.79
87.89
0.90
MW-19D
Surficial Aquifer
Dec-20
90.03
86.19
3.84
MW-1S
Perched Zone
Dec-20
131.34
129.30
2.04
MW-20D
Surficial Aquifer
Dec-20
90.88
85.37
5.51
MW-21D
Surficial Aquifer
Dec-20
106.77
102.86
3.91
MW-22D
Surficial Aquifer
Dec-20
113.64
110.93
2.71
MW-23
Perched Zone
Dec-20
134.33
140.50
-6.17
MW-24
Perched Zone
Dec-20
128.92
134.53
-5.61
TR0795
Page 3 of 6
August 2021

Geosyntec Consultants of NC, P.C.
Table B.02: Calibration Results: Observed vs
Model Predicted Hydraulic Head Data
Chemours Fayetteville Works, North Carolina
Location Name
Aquifer
Observation Date
Observed
Head
(ft)
Calculated
Head
(ft)
Residual
(Obs. - Calc.)
(ft)
MW-25
Perched Zone
Dec-20
134.11
133.17
0.94
MW-26
Perched Zone
Dec-20
136.5
137.05
-0.55
MW-27
Perched Zone
Dec-20
132.44
123.47
8.97
MW-28
Perched Zone
Dec-20
131.29
124.77
6.52
MW-30
Perched Zone
Dec-20
135.1
139.18
-4.08
MW-31
Perched Zone
Dec-20
131.82
135.53
-3.71
MW-32
Perched Zone
Dec-20
132.24
128.58
3.66
MW-33
Perched Zone
Dec-20
132.47
129.72
2.75
MW-34
Perched Zone
Dec-20
132.13
136.43
-4.30
MW-35
Perched Zone
Dec-20
132.21
129.61
2.60
MW-36
Perched Zone
Dec-20
132.29
135.91
-3.62
MW-7S
Perched Zone
Dec-20
137.49
135.52
1.97
MW-8S
Perched Zone
Dec-20
141.94
147.54
-5.60
MW-9S
Perched Zone
Dec-20
133.39
132.54
0.85
NAF-01
Perched Zone
Dec-20
140.95
140.28
0.67
NAF-02
Perched Zone
Dec-20
141.05
139.36
1.69
NAF-03
Perched Zone
Dec-20
140.92
144.15
-3.23
NAF-06
Perched Zone
Dec-20
134.87
131.08
3.79
NAF-07
Perched Zone
Dec-20
140.6
136.52
4.08
NAF-08A
Perched Zone
Dec-20
140.73
142.64
-1.91
NAF-08B
Perched Zone
Dec-20
95.44
100.44
-5.00
NAF-09
Perched Zone
Dec-20
137.93
141.43
-3.50
NAF-10
Perched Zone
Dec-20
138.54
132.42
6.12
NAF-11A
Perched Zone
Dec-20
136.82
139.97
-3.15
NAF-11B
Perched Zone
Dec-20
94.13
99.26
-5.13
NAF-12
Perched Zone
Dec-20
140.15
136.79
3.36
OW-1
Perched Zone
Dec-20
59.78
62.67
-2.89
OW-1
Perched Zone
Dec-20
59.78
65.69
-5.91
OW-10
Perched Zone
Dec-20
59.82
60.49
-0.67
OW-2
Perched Zone
Dec-20
50.34
53.62
-3.28
OW-3
Perched Zone
Dec-20
50.14
48.81
1.33
OW-4
Perched Zone
Dec-20
61.57
62.16
-0.59
OW-5
Perched Zone
Dec-20
61.78
65.79
-4.01
OW-6
Perched Zone
Dec-20
42.8
42.55
0.25
OW-7
Perched Zone
Dec-20
45.35
44.40
0.95
OW-8
Perched Zone
Dec-20
44.6
45.95
-1.35
OW-9
Perched Zone
Dec-20
61.71
57.79
3.92
PIW-10DR
Perched Zone
Dec-20
61.16
60.94
0.22
PIW-10S
Perched Zone
Dec-20
57.93
53.29
4.64
PIW-11
Perched Zone
Dec-20
45.11
40.55
4.56
PIW-12
Perched Zone
Dec-20
35.53
34.75
0.78
TR0795
Page 4 of 6
August 2021

Geosyntec Consultants of NC, P.C.
Table B.02: Calibration Results: Observed vs
Model Predicted Hydraulic Head Data
Chemours Fayetteville Works, North Carolina
Location Name
Aquifer
Observation Date
Observed
Head
(ft)
Calculated
Head
(ft)
Residual
(Obs. - Calc.)
(ft)
PIW-13
Perched Zone
Dec-20
36.2
31.75
4.45
PIW-14
Perched Zone
Dec-20
37.01
38.24
-1.23
PIW-15
Perched Zone
Dec-20
35.58
33.96
1.62
PIW-16D
Perched Zone
Dec-20
131.11
135.13
-4.02
PIW-16S
Perched Zone
Dec-20
134.79
136.41
-1.62
PIW-1D
Surficial Aquifer
Dec-20
36.37
32.17
4.20
PIW-1S
Floodplain Deposits
Dec-20
35.35
35.56
-0.21
PIW-2D
Black Creek Aquifer
Dec-20
64.4
64.30
0.10
PIW-3D
Black Creek Aquifer
Dec-20
37.56
39.48
-1.92
PIW-4D
Black Creek Aquifer
Dec-20
42.67
47.23
-4.56
PIW-5S
Surficial Aquifer
Dec-20
61.17
48.36
12.81
PIW-6S
Floodplain Deposits
Dec-20
40.19
41.90
-1.71
PIW-7D
Black Creek Aquifer
Dec-20
43.35
45.96
-2.61
PIW-7S
Floodplain Deposits
Dec-20
43.42
50.33
-6.91
PIW-8D
Black Creek Aquifer
Dec-20
41.55
43.33
-1.78
PIW-9D
Black Creek Aquifer
Dec-20
42.49
49.40
-6.91
PIW-9S
Perched Zone
Dec-20
50.81
47.88
2.93
PW-01
Perched Zone
Dec-20
135.72
126.63
9.09
PW-02
Surficial Aquifer
Dec-20
89.99
82.82
7.17
PW-03
Surficial Aquifer
Dec-20
106.2
95.39
10.81
PW-04
Perched Zone
Dec-20
74.81
78.81
-4.00
PW-05
Surficial Aquifer
Dec-20
123.57
121.37
2.20
PW-06
Perched Zone
Dec-20
128.17
131.47
-3.30
PW-07
Perched Zone
Dec-20
118.6
123.45
-4.85
PW-09
Black Creek Aquifer
Dec-20
53.04
47.48
5.56
PW-10R
Black Creek Aquifer
Dec-20
47.18
54.43
-7.25
PW-11
Black Creek Aquifer
Dec-20
38.66
40.57
-1.91
PW-12
Black Creek Aquifer
Dec-20
93.77
100.70
-6.93
PW-13
Black Creek Aquifer
Dec-20
117.22
117.30
-0.08
PW-14
Black Creek Aquifer
Dec-20
86.49
84.49
2.00
PW-15R
Black Creek Aquifer
Dec-20
67.05
77.63
-10.58
PZ-11
Perched Zone
Dec-20
141.57
130.84
10.73
PZ-13
Perched Zone
Dec-20
138.5
134.75
3.75
PZ-14
Perched Zone
Dec-20
136.36
138.10
-1.74
PZ-22
Black Creek Aquifer
Dec-20
44.7
43.02
1.68
PZ-24
Perched Zone
Dec-20
134.15
130.49
3.66
PZ-26
Perched Zone
Dec-20
136.97
132.63
4.34
PZ-27
Perched Zone
Dec-20
133.16
130.07
3.09
PZ-28
Perched Zone
Dec-20
135.47
127.78
7.69
PZ-29
Perched Zone
Dec-20
133.18
133.94
-0.76
PZ-31
Perched Zone
Dec-20
130.16
130.14
0.02
TR0795
Page 5 of 6
August 2021

Geosyntec Consultants of NC, P.C.
Table B.02: Calibration Results: Observed vs
Model Predicted Hydraulic Head Data
Chemours Fayetteville Works, North Carolina
Location Name
Aquifer
Observation Date
Observed
Head
(ft)
Calculated
Head
(ft)
Residual
(Obs. - Calc.)
(ft)
PZ-32
Perched Zone
Dec-20
132.92
138.25
-5.33
PZ-33
Perched Zone
Dec-20
132.67
126.76
5.91
PZ-34
Perched Zone
Dec-20
131.89
127.62
4.27
PZ-36
Perched Zone
Dec-20
132.64
130.52
2.12
PZ-37
Perched Zone
Dec-20
132.8
136.02
-3.22
PZ-38
Perched Zone
Dec-20
131.01
130.93
0.08
PZ-39
Perched Zone
Dec-20
134.26
135.43
-1.17
PZ-40
Perched Zone
Dec-20
134.5
137.68
-3.18
PZ-41
Perched Zone
Dec-20
134.86
132.79
2.07
PZ-42
Perched Zone
Dec-20
134.77
140.74
-5.97
PZ-43
Perched Zone
Dec-20
132.73
134.40
-1.67
PZ-44
Perched Zone
Dec-20
133.27
129.63
3.64
PZ-45
Perched Zone
Dec-20
133.19
135.67
-2.48
PZ-L
Perched Zone
Dec-20
117.82
115.81
2.01
SMW-01
Perched Zone
Dec-20
124.9
127.26
-2.36
SMW-02
Perched Zone
Dec-20
136.55
140.08
-3.53
SMW-02B
Perched Zone
Dec-20
89.2
89.69
-0.49
SMW-03B
Surficial Aquifer
Dec-20
93.84
100.72
-6.88
SMW-04B
Surficial Aquifer
Dec-20
103.26
100.42
2.84
SMW-05
Perched Zone
Dec-20
125.2
121.64
3.56
SMW-05P
Surficial Aquifer
Dec-20
105.5
106.23
-0.73
SMW-06
Perched Zone
Dec-20
125.92
126.41
-0.49
SMW-06B
Surficial Aquifer
Dec-20
103.22
102.07
1.15
SMW-07
Perched Zone
Dec-20
128.15
127.29
0.86
SMW-08
Perched Zone
Dec-20
116.82
119.40
-2.58
SMW-08B
Surficial Aquifer
Dec-20
108.26
106.71
1.55
SMW-09
Surficial Aquifer
Dec-20
85.91
71.65
14.26
SMW-10
Surficial Aquifer
Dec-20
47.37
53.70
-6.33
SMW-11
Surficial Aquifer
Dec-20
59.58
54.34
5.24
SMW-12
Black Creek Aquifer
Dec-20
36.01
38.88
-2.87
Notes:
ft - feet
Obs. - Observed
Calc. - Calculated
TR0795 Page 6 of 6 August 2021

Geosyntee °
consultants
Geasyntec Consultants of NC, P.C.
NC License No.: C-35911 and C• 295
Figures
TR0795
Aug-2021

Legend
QModel Boundary
Model Grid
Notes
1. Basemap source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Community.
1,000 500 0
1,000 Feet
Model Domain and Grid
Chemours Fayetteville Works, North Carolina
Geosyntec'%
consultants
Raleigh
Gcosyntcc Consultants of NC, P.C.
NC License No.: C-3500 and C-295
August 2021
Figure
B.01

Legend
40 Constant Head Boundary
River Boundary (Willis Creek)
40 River Boundary (Cape Fear)
Recharge Area
Notes
1. Basemap source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Community.
Model Boundary Conditions
Chemours Fayetteville Works, North Carolina
Geosyntec'%
consultants
Gcosyntcc Consultants of NC, P.C.
NC License No.: C-3500 and C-295
Raleigh
August 2021
Figure
B.02

Legend
Perched Zone
Surficial Aquifer
Black Creek Aquifer
Model Boundary
Notes
1. Basemap source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Community.
Model Calibration Targets
Chemours Fayetteville Works, North Carolina
Geosyntec'%
consultants
Gcosyntcc Consultants of NC, P.C.
NC License No.: C-3500 and C-295
Raleigh
August 2021
Figure
B.03

150
125
50
25
0
•
•
• •
• . •
•
OD��
•
• •
•
••
•M.
• 4!.
•
•
0 25 50 75 100 125 150
Measured Head
Calibration Results
Correlation Coefficient
0.98
Flow Mass Balance
-0.78%
Normalized RMS
23.9% (Perched zone)
7.1% (Surficial Aquifer)
5.8% (Black Creek)
Maximum Residual
6.57 ft(Perched zone)
7.32 ft (Surficial Aquifer)
10.27 ft (Black Creek)
Minimum Residual
-8.52 ft(Perched zone)
-13.54 ft (Surficial Aquifer)
-0.007ft (Black Creek)
Residual Mean
-0.66 (ft)
Absolute Residual Mean
2.94 (ft)
Root Mean Square
4.34 ft(Perched zone)
6.24 ft (Surficial Aquifer)
5.08 ft (Black Creek)
Legend
• Black Creek Aquifer
Surficial Aquifer Perched Zone
Flow Model Calibration Results
Chemours Fayetteville Works, North Carolina
Geosyntec°
consultants
Geosyntec Consultants of NC, P.C.
NC License No.: C-3500 and C-295
Raleigh
August 2021
Figure
B.04

Legend
Simulated Equipotentials (feet NAVD 88)
- Constant Head Boundary
Constant Head River Boundary (Willis Creek)
- Transient Head River Boundary (Cape Fear)
Recharge Area
Model Boundary
Notes
1. Basemap source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Community.
2,000
1,000
0
2,000 Feet
Flow Model Simulated Equipotentials - Base Model
Chemours Fayetteville Works, North Carolina
Geosyntec c
consultants
Gearyntec Consultants of NC, P.C.
NC License No.: C-3500 and C-295
Raleigh
August 2021
Figure
B.05

Legend
5 year Particle Tracks - No Remedy
River Boundary (Willis Creek)
River Boundary (Cape Fear)
Model Boundary
Notes
1.3asemap source Esri, Maxar, GeoEye, EarthstarGeographics, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Community.
Scenario 1 - Particle Tracking from
Plant Area Ambient Conditions
Chemours Fayetteville Works, North Carolina
Geosyntec
consultants
Geosynrec Consulianrs of NC. P. (
NC License Net C 3500and C 295
Raleigh
August 2021
Figure
B.06

rs w
Legend
Barrier Wall
River Boundary (Willis Creek)
40 River Boundary (Cape Fear)
Model Boundary
Notes
1. Basemap source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Community.
N
Scenario 2 — Vertical Barrier Remedial Design
Chemours Fayetteville Works, North Carolina
Geosyntec'%
consultants
Gcosyntcc Consultants of NC, P.C.
NC License No.: C-3500 and C-295
Raleigh
August 2021
Figure
B.07

Legend
5 year Particle Tracks
Barrier Wall
River Boundary (Willis Creek)
400 River Boundary (Cape Fear)
Model Boundary
Notes
1. Basemap source: Esri, Maxar, GeoEye, EarthstarGeographics, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Community.
Scenario 2 - Particle Tracking from
Plant Area - Vertical Barrier
Chemours Fayetteville Works, North Carolina
Geosyntec
consultants
Geosynlec Consuliaurs of NC. P.C.
NC License No.:C 3500and C 295
Raleigh
August 2021
Figure
B.08

Legend
9- Extraction Well Location
River Boundary (Willis Creek)
River Boundary (Cape Fear)
Model Boundary
Notes
1. Basemap source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Community.
Scenario 3 — Hydraulic Barrier Remedial Design
Chemours Fayetteville Works, North Carolina
Geosyntec'%
consultants
Gcosyntcc Consultants of NC, P.C.
NC License No.: C-3500 and C-295
Raleigh
August 2021
Figure
B.09

Legend
River Boundary (Willis Creek)
400 River Boundary (Cape Fear)
Model Boundary
Notes
1. Basemap source: Esri, Maxar, GeoEye, EarthstarGeographics, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Community.
Scenario 3 - Particle Tracking from
Plant Area — Hydraulic Barrier
Chemours Fayetteville Works, North Carolina
Geosyntec
consultants
Geosynrec Consulianrs oaNC. P.C.
NC License No.: C 3500 and C 295
Raleigh
August 2021
Figure
B.1 O

Legend
9- Extraction Well Location
Barrier Wall
River Boundary (Willis Creek)
River Boundary (Cape Fear)
Model Boundary
Notes
1. Basemap source: Esri, Maxar, GeoEye, Earthstar Geographics, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Community.
Scenario 4 — Vertical and Hydraulic Remedial Design
Chemours Fayetteville Works, North Carolina
Geosyntec'%
consultants
Gcosyntcc Consultants of NC, P.C.
NC License No.: C-3500 and C-295
Raleigh
August 2021
Figure
B.11

Legend
Extraction Well Location
Barrier Wall
5 year Particle Tracks
River Boundary (Willis Creek)
River Boundary (Cape Fear)
Model Boundary
Notes
1. Basemap source: Esri, Maxar, GeoEye, Earthstar Geographies, CNES/Airbus DS,
USDA, USGS, AeroGRID, IGN, and the GIS User Communi .
Scenario 4 - Particle Tracking from
Plant Area — Vertical and Hydraulic Barrier
Chemours Fayetteville Works, North Carolina
Geosyntec Geosyntec Consntlanrs of NC. N,[
NC License No.: C 3500and C 295
consultants
Figure
B.12
Raleigh
August 2021