Appendix H - Technical Memorandum – Groundwater Model

Piedmont Lithium Carolinas, Inc. I North Carolina Mining Permit Application
Appendices
PIEDMONT
LITHIUM
Appendix H: Technical
Memorandum — Groundwater
Model

JI2NVA[!
Technical
Memorandum
Groundwater Model
Piedmont Lithium Carolinas Inc.
Gaston County, North Carolina
August 30, 2021

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Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model ���
Contents
Contents
1
Introduction.........................................................................................................................
1
2
Conceptual Site Model/Groundwater Model Framework
..................................................... 1
2.1.1 Mine Pits...............................................................................................................
1
2.1.2 Temporal Constraints............................................................................................
2
2.1.3 Dewatering and Water Handling...........................................................................
2
3
Transient Model Set-up.......................................................................................................
3
3.1
Modeling Software..............................................................................................................
3
3.2
Discretization......................................................................................................................
3
4
Dewatering Simulations......................................................................................................
3
4.1
Dewatering Effect on Water Supply Wells...........................................................................
4
4.2
Dewatering Effect on Wetlands...........................................................................................
5
4.3
Dewatering Effect on Streams............................................................................................
9
5
Model Limitations...............................................................................................................10
6
Summary and Conclusions................................................................................................10
7
References........................................................................................................................11
Figures
Figure 1 — Groundwater Model Domain
Figure 2 — Site and Receptor Well Location Map
Figure 3 — Revised Model Grid
Figures 4A — 4J — Model Predicted Drawdown from Dewatering
Figure 5 — HDR Delineated Wetlands
Figure 6 — Location of Stream Reaches
Tables
Table 1 - Transient model sequence of mine pits....................................................................... 2
Table 2 - Model predicted dewatering withdrawal rates.............................................................. 4
Table 3 - Model Predicted Drawdown in Local Wells.................................................................. 5
Table 4 - Model predicted changes in groundwater flow to wetlands(gmp)................................ 7
Table 5 - Changes in base flow to streams that cross the site .................................................... 9

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model ���
Contents
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Piedmont Lithium Carolinas, Inc. i Technical Memorandum — Groundwater Model ���
Introduction
1 Introduction
Piedmont Lithium Carolinas, Inc. (PLCI) is proposing to construct an open pit mine in the
Carolina Tin-Spodumene Belt (TSB) of North Carolina where lithium -bearing pegmatites have
been identified. The Concentrate Operations and the Lithium Hydroxide Conversion Plant (the
Site) is in the TSB of the Piedmont physiographic province in south-central North Carolina. The
approximately 1,548-acre Site is in an unincorporated area of Gaston County, on private land
surrounding portions of Hephzibah Church Road, Whitesides Road, and St. Mark's Church
Road, approximately 1 mile east of Cherryville, North Carolina.
The overall Concentrate Operations are composed of three components: the Piedmont Lithium
Carolinas Mine #1, a Concentrate Plant, and an Industrial Minerals Plant. The Piedmont Lithium
Carolinas Mine #1 (Figure 1) will consist of four open pits of varying sizes, a waste rock
disposal area, topsoil stockpiles areas, haul roads, and other mine support areas. Mining will
occur through open pit excavations which will require dewatering. On behalf of PLCI, HDR
Engineering, Inc. of the Carolinas (HDR) performed groundwater modeling to estimate the rate
of water withdrawal during pit dewatering and evaluate possible effects pit dewatering may have
on local water resources and water users. The base groundwater model was developed by HDR
for PLCI and documented in a Technical Memorandum Groundwater Model dated July 2, 2019
(HDR, 2019). The groundwater model updates include a refined model grid, revised pit shell
geometries, and transient simulations of pit dewatering.
2 Conceptual Site Model/Groundwater Model
Framework
The groundwater flow model domain includes the southern portion of Indian Creek watershed,
Beaverdam Creek watershed, and a reach of the South Fork Catawba River. The 32.5 square
mile (mil) model domain and Site boundary are shown in Figure 1. Model input parameters
were, in part, derived from hydrogeologic data obtained during an aquifer test conducted in
2018; however, those data have been manipulated during calibration of the groundwater flow
model. The conceptual model, model framework, and model calibration for natural state
conditions are described in the 2019 Technical Memorandum (HDR, 2019).
2.1.1 Mine Pits
PLCI plans to remove resource from four mine pits (North, South, East, and West pits) within
the permitted mine boundary. The current mining operations plan calls for no more than two pits
to be actively mine at the same time, as shown in Table 3. PLCI intends to dewater mine pits to
facilitate removal of the resource. Groundwater removed from the pits during dewatering will be
pumped to settling ponds throughout the permitted area prior to discharge through outfalls
monitored via National Pollutant Discharge Elimination System (NPDES) permitting and
compliance.
PLCI's most recent estimate of resource extent was used to establish the potential extents of pit
excavation used in the transient model (see Figure 2). The mine pit geometries over time were

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model ���
Conceptual Site Model/Groundwater Model Framework
estimated by the mining engineer, Marshall Miller & Associates (MMA), in 2021 and provided as
3-dimensional shapefiles of topography for each year. MMA used MiningMath SimSched
software to optimize pit geometries and Maptek's Vulcan Evolution software to establish the
mine operations schedule (MMA, 2021)1. The differences in yearly topography were used in the
model to represent transient change in mine pit geometry (newly mined volume for each year).
Mine pits were simulated in the transient models as water -filled, high conductivity cells. Mine pit
extents for model layers were based on contours from the pit excavation geometries that
coincide with model layers. Seepage into cells was accounted for with drain return package
boundary conditions set to the bottom of lowest layers of the mine pits. Water collected by the
drains was returned to model cells at the discharge locations provided by MMA where pumped
water may discharge to a stream or wetland or infiltrate to groundwater.
2.1.2 Temporal Constraints
The calibrated steady state model of natural state conditions provided the initial conditions for
the transient modeling. Pit dewatering operations were simulated with a series of transient
models to account for temporal variation. The transient models represent mine pit extents at
various points in time with portions of different pits open at the same time. Drawdown due to
dewatering is greatest when the mine pits have been excavated to the designed terminal depth.
After completion of mining, pits may be allowed to fill with water or be filled by native waste rock
material, native mine tailings, and the non -hazardous residue created by the Lithium Hydroxide
Conversion Plant. The mine pit dewatering sequence for predictive simulations is shown in
Table 1.
Table 1 - Transient model sequence of mine pits
Pits with Dewatering
Model Year
South Pit
East Pit West Pit North Pit
1
Mining
2
Mining
Mining
3
Mining
Mining
4
Filling
Mining
5
Filling
Mining
6-10
Filling
Mining
11
Filling
Mining
12
Filling
Mining Mining
13
Filling
Filling Mining Mining
14-20
Fillina
Fillina Minina Minina
2.1.3 Dewatering and Water Handling
Water is assumed to be pumped from the lowest levels of the mine pit into settling basins prior
to discharge to adjacent streams or wetlands. Dewatering is simulated with a MODFLOW drain
cell (water level controlled by a conductance value at a specified elevation) to estimate the
amount of water removal necessary to achieve dewatering of the mine pits. The water removed
by drain cells is returned to the model at discharge locations identified by MMA (Figure 2).
Water from mine pit dewatering returned to the model infiltrates to groundwater or flows out of
The mine pit geometries are resource -based and in some locations extend beyond the mine permit boundaries. For this reason,
the effects of dewatering are conservative and at some places reflect greater dewatering than is currently envisioned.

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model ���
Transient Model Set-up
the model domain through streams and wetlands. Returning water from dewatering operations
to the model provides a better representation of aquifer recovery after dewatering ceases.
3 Transient Model Set-up
The set-up and calibration of the steady state model, which provides the initial conditions for the
transient groundwater flow models, is described in the Technical Memorandum Groundwater
Model dated July 2, 2019 (Tech Memo) (HDR, 2019). The model layers and boundary
conditions were not modified (including how wetlands and surface water bodies were
simulated). This section describes the revisions and updates required for the transient models.
3.1 Modeling Software
Transient groundwater modeling was performed using the United States Geological Survey
(USGS) groundwater model software MODFLOW-2005 (Harbaugh, 2005). MODFLOW-2005 is
an enhanced version of the USGS modular groundwater flow model, MODFLOW. MODFLOW-
2005 allows for enhanced management of internal data. Aquaveo's 2021 Groundwater Modeling
System, GMS, (Aquaveo, 2021) was used to manage data to develop the groundwater flow
models and to evaluate model simulations. GMS's graphic interface and data handling functions
were used develop and update the base conceptual model and the hydrogeologic framework
described in the previous Tech Memo. GMS was used to display and evaluate transient model
results.
3.2 Discretization
The model grid was refined to focus on the area near the Site, allowing for increased resolution
in the vicinity of the mine pits. The refined portion of the model grid was expanded to the south
and west from the original steady state model to include the pit extents used for this transient
model. Cells in the model for the previous and current modeling efforts range in size from 50
feet on a side in refined areas in the vicinity of the Site to 500 feet on a side in remote areas.
The revised model grid is shown in Figure 3.
4 Dewatering Simulations
Mine pit dewatering was simulated by changing model cells within the horizontal and vertical
extent of the pit to a high conductivity material. Drains cells were placed at the base of the
lowest layers and the elevations of the drains adjusted to the bottom elevation of the pit
coincident with the timeframe being simulated. Water seeping out of the cells surrounding the pit
was removed by the drains. The water removed by all drains used to simulate dewatering was
summed to estimate dewatering volumes and rates needed to dewater the pits. The water
removed from the pits by the drains was returned to the model at locations identified as
discharge from settling ponds by MMA. Stream cells connected to the stream network were
placed in the same cell and given large conductance values so the water would be simulated to
be returned to the streams. Drawdown of the water table resulting from dewatering was
calculated based on the total change in water level between the initial steady state non -pumping
model and the mine -year simulated (model year). The estimated withdrawal rates are presented
in Table 2.

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model ���
Dewatering Simulations
Table 2 - Model predicted dewatering withdrawal rates
Pumping Rate (gpm)
Model Year
South Pit
East Pit
West Pit North Pit
Total
1
525
50
575
2
975
1,225
2,300
3
725
775
1,500
4
25'
1,025
1,050
5
75'
950
1,025
6-10
N/A2
1,250
1,250
11
N/A2
1,575
1,575
12
N/A2
1,050
950
2,000
13
N/A2
0
500 850
1,350
14-16
N/A2
N/A2
10753
1,075
Pumping to maintain drawdown while filling pit with excavated material
2 No dewatering modeled.
3 West and North Pits are merged.
4.1 Dewatering Effect on Water Supply Wells
Predicted drawdown in wells within the Site boundary, which will be decommissioned by PLCI
during mine development, ranged from 0 feet to 17.8 feet and averaged approximately 1.9 feet.
Predicted drawdown in wells outside the Site boundary ranged from 0 feet to 21.5 feet and
averaged approximately 4.0 feet. Within the Site boundary, four wells are expected to
experience significant loss of water column (available drawdown) during dewatering of East,
West, and North Pits. Outside the site, two wells are expected to experience significant loss of
water column during dewatering of West and North Pits. Estimated drawdown in wells in the
vicinity of the Site are shown in Table 3 and on Figures 4A, though 4J. Note that the
excavation extents used in the models are based on the extent of the resources and not
necessarily the extent of planned mining activities, specifically along the southern permit
boundary where the resource is estimated to extend beyond the permit boundary (MMA, 2021).
The greatest extent of drawdown is simulated to occur in years 14 through 20 when the West Pit
is being dewatered and the East Pit is filling. The drawdown shown in Figure 4 represents
dewatering to the extent of the resource boundaries rather than the permit boundaries of the
pits, providing a worst -case estimate of drawdown that may occur.

Piedmont Lithium Carolinas, Inc. I Technical Memorandum - Groundwater Model ���
Dewatering Simulations
Table 3 - Model Predicted Drawdown in Local Wells
South Pit Pumping
East Pit Pumping
West Pit Pumping
North Pit Pumping
Receptor Well Drawdown (ft)
Well
Year
1
Year 2
Year
3
Year
4
Year
5
Year6-
10
Year 11
Year 12
Year 13
Year14-
20
Wells Within Site Boundary
1523 R W McLamb Dr.
DRY
DRY
DRY
DRY
DRY
DRY
12.1
13.1
13.4
12.5
819 Whitesides Rd.
0.0
0.0
0.2
0.4
0.4
0.4
0.4
0.5
1.0
1.4
1121 He hzibah Church Rd.
3.1
1.8
1.2
1.0
0.8
0.7
0.7
10.6
16.9
17.8
901 Whitesides Rd.
0.0
0.0
0.0
0.1
0.1
0.1
0.3
0.1
0.2
1.1
921 Whitesides Rd.
0.0
0.1
0.1
0.2
0.2
0.3
0.3
0.3
0.8
2.4
1266 He hzibah Church Rd.
0.5
0.7
1.1
2.9
3.4
5.2
5.2
7.6
13.3
17.5
1021 He hzibah Church Rd.
1.3
1.1
0.0
0.7
0.6
0.6
0.5
0.5
0.6
1.3
633 Aderholdt Rd. 2
0.0
0.0
0.0
0.1
0.3
0.5
0.5
0.5
0.6
8.5
1029 He hzibah Church Rd.
2.3
1.3
0.7
0.4
0.3
0.2
0.1
0.4
1.1
2.4
Wells Outside of Site Domain
732 Whitesides Rd.
8.5
13.7
21.5
18.9
15.0
15.6
12.4
11.1
11.4
11.2
129 George Pa seur Rd.
0.3
0.5
0.9
2.0
2.2
3.3
3.4
3.4
3.5
4.2
663 Aderholdt Rd. 1
0.0
0.0
0.0
0.0
0.0
0.1
0.1
0.1
1.2
20.4
534 Whitesides Rd.
0.0
0.0
0.0
0.1
0.2
0.3
0.3
0.3
0.5
0.8

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model ���
Dewatering Simulations
4.2 Dewatering Effect on Wetlands
Potential changes to groundwater flow into wetlands during dewatering operations were
evaluated by comparing flow into wetlands in the steady state model with the dewatering
predictive simulations. Dewatering of the South Pit caused Wetland 2 to go dry and it remains
dry during the remainder of the 20-year mining operation. Dewatering of the South Pit also
results in drying of Wetlands 11 and 12, although they are restored when dewatering operations
shift to the East Pit and dry up again when dewatering commences in the West Pit. Dewatering
of the East Pit results in drying of Wetlands 4 through 8; these wetlands remained dry for the
remainder of the 20-year mining operation. Simulated West Pit dewatering resulted in drying of
Wetland 16 prior to its elimination by mining operations when the West Pit and North Pit merge.
Note that pit dewatering water discharged near wetlands helps maintain flow in some of those
wetlands; routing of additional flow into wetlands may help mitigate the drying predicted by the
model. Wetlands 6, 7, and 8 maintain some flow from groundwater while discharge from the
South Pit is occurring nearby. Changes to predicted groundwater discharge to wetlands are
presented in Table 4. The location of wetlands in the vicinity of the Site are shown in Figure 5.
Note that although the model returns water removed from the pits to the simulated streams, this
return only marginally influences the impacts on the wetlands.

Piedmont Lithium Carolinas, Inc. I Technical Memorandum - Groundwater Model ���
Dewatering Simulations
Table 4 - Model predicted changes in groundwater flow to wetlands (gmp)
Model Year 1
Model Year 2
Model Year 3
Model Year 4
Model Year 5
Model Year 6 - 10
Model Year 11
Model Year 12
Model Year 13
Model Year 14 - 20
Pits D watering
S
S, E
S, E
E
E
E
E
E, W
W, N
W, N
Wetland
Wetland
Size
Acres
Steady
State Flow
m
Flow
Ft3/d
Percent
Change'
Flow
Ft3/d
Percent
Change'
Flow
Ft3/d
Percent
Change'
Flow
Ft3/d
Percent
Change'
Flow
Ft3/d
Percent
Change'
Flow
Ft3/d
Percent
Change'
Flow
Ft3/d
Percent
Change'
Flow
Ft3/d
Percent
Change'
Flow
Ft3/d
Percent
Change
'
Flow
Ft3/d
Percent
Change'
Wetland 1
0.28
1,327
1328
-0.03
1330
-0.20
1323
0.36
1262
4.92
1204
9.33
1104
16.79
1103
16.88
486
63.41
0
Dry
0
Dry
Wetland 2
0.15
6,330
4634
26.79
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
Wetland 3
3.19
11,519
11517
0.02
11730
-1.83
7261
36.97
5282
54.15
4485
61.06
4424
61.59
6204
46.14
5737
50.19
4597
60.09
0
Dr
Wetland 4
0.66
1,703
1671
1.88
1670
1.94
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dr
Wetland 5
2.21
5,483
5270
3.89
5269
3.92
1706
68.88
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
Wetland 6
0.09
2,061
2197
-6.62
2014
2.26
1190
42.25
130
93.71
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dr
Wetland 7
0.38
3,752
3233
13.83
2968
20.90
2698
28.08
35
99.06
0
Dry
0
Dry
351
90.64
0
Dry
0
Dry
0
Dry
Wetland 8
0.23
2,559
535
79.07
432
83.10
481
81.21
320
87.50
0
Dry
0
Dry
0
Dry
0
Dry
0
Dry
0
Dr
Wetland 9
0.18
660
1028
-55.67
1002
-51.79
1000
-51.50
1001
-51.63
1005
-52.29
1010
-52.99
1019
-54.42
1021
-54.74
1011
-53.22
0
Dr
Wetland 10
0.12
1,796
1785
0.62
1783
0.72
1781
0.85
1780
0.87
1780
0.87
1781
0.85
1782
0.78
1783
0.73
1782
0.79
0
Dr
Wetland 11
0.04
1,930
693
64.09
427
77.87
0
Dr
0
Dry
0
Dry
147
92.40
351
81.82
0
Dry
0
Dry
0
Dr
Wetland 12
0.06
1,930
0
Dry
0
Dry
380
80.31
395
79.53
442
77.10
653
66.15
830
57.01
0
Dry
0
Dry
0
Dr
Wetland 13
0.09
2,007
1939
3.38
1824
9.10
1741
13.26
1707
14.95
1703
15.16
1720
14.31
1768
11.90
1555
22.54
1269
36.79
0
Dr
Wetland 14
5.45
5,310
5296
0.27
5279
0.58
5252
1.09
5223
1.65
5204
2.00
5194
2.19
5194
2.18
5165
2.73
4964
6.52
0
Dry
Wetland 15
0.04
2,147
2086
2.86
2085
2.89
2085
2.88
2088
2.77
2090
2.68
2094
2.47
2100
2.22
2099
2.23
2086
2.86
0
Dr
Wetland 16
0.08
76
70
8.52
69
9.74
69
10.25
55
27.66
61
20.60
68
11.62
73
4.68
0
Dry
0
Dry
0
Dry
' Negative indicates an increase in flow to the wetland from groundwater. Positive indicates a decrease in flow to the wetland from groundwater.

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model ���
Dewatering Simulations
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Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model ���
Dewatering Simulations
4.3 Dewatering Effect on Streams
Mine pit dewatering alters stream base flow by reducing the contribution of groundwater to
streamflow. Change in stream baseflow was assessed by comparing stream baseflow estimated
by the steady state model with stream baseflow in the dewatering predictive simulations.
Baseflow was evaluated for three streams crossing the Site (Figure 6). Decreases in simulated
baseflow to Beaverdam Creek up stream of Little Beaverdam Creek ranged from 2.2 percent in
model year 11 (when dewatering in East Pit occurs) to 5.9 percent in model year 12 (when
dewatering occurs in East Pit and West Pit). Simulated baseflow in Beaverdam Creek
downstream of the confluence with Little Beaverdam Creek ranges from 3.1 percent in model
year 1 (when dewatering occurs in South Pit) to 9.0 percent at the end of plan year 20 (when
West Pit is dewatered). Decreases in simulated baseflow to Little Beaverdam Creek ranged
from 0.1 percent in model year 1 (when South Pit is dewatered) to 6.9 percent in model year 13
(when East Pit is being filled and West Pit is dewatered). An unnamed tributary to Beaverdam
Creek (Stream 3) exhibited baseflow decreases ranging from 0.4 percent during model year 2
(when South Pit is dewatered) to 3.1 percent (when West Pit is dewatered). Model -predicted
changes in stream baseflow are presented in Table 5.
Table 5 - Changes in base flow to streams that cross the site
Beaverdam Creek
Above Confluence'
Little Beaverdam
Creek
Beaverdam Creek
Below Confluence'
Unnamed Tributary
Model
Flow2
Percent
Flow'
Percent
Flow'
Percent
Flow'
Percent
Year
(Ft3/d)
Change
(Ft3/d)
Change
(Ft3/d)
Change
(Ft3/d)
Change
Steady
-569,356
-435,255
-1,681,833
-163,653
State
1
-545,113
4.3
-434,660
0.1
-1,631,117
3.0
-162,320
0.8
2
-541,563
4.9
-433,446
0.4
-1,622,721
3.5
-162,917
0.4
3
-538,616
5.4
-431,440
0.9
-1,609,935
4.3
-162,797
0.5
4
-538,716
5.4
-428,394
1.6
-1,608,281
4.4
-160,529
1.9
5
-541,270
4.9
-418,435
3.9
-1,600,251
4.9
-162,576
0.7
6-10
-548,891
3.6
-418,899
3.8
-1,615,812
3.9
-161,519
1.3
11
-556,696
2.2
-419,820
3.5
-1,629,960
3.1
-160,985
1.6
12
-535,792
5.9
-414,010
4.9
-1,580,594
6.0
-161,027
1.6
13
-536,719
5.7
-405,337
6.9
-1,553,419
7.6
-159,911
2.3
14-20
-539,972
5.2
-406,888
6.5
-1,530,283
9.0
-158,582
3.1
Confluence is with Little Beaverdam
Creek.
2 Negative
sign indicates stream baseflow from groundwater.
Groundwater removed from the pits during dewatering will be pumped to settling ponds
throughout the permitted area prior to discharge through outfalls monitored via NPDES
permitting and compliance. In the transient model simulations, water lost from stream baseflow
due to pit dewatering was recycled back to the streams through the settling basins and
discharge points shown in Figure 6.
Note that there is a stream that flows into the West Pit starting in about Year 14 once the West
Pit and the North Pit merge. The model estimated that this stream will still receive about 13,000
9

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model
Model Limitations
cubic feet per day of base flow, which then flows towards the pit and is not accounted for in the
dewatering estimates. The water from this stream will either be re-routed to Beaverdam Creek
or will be included in water pumped from the West Pit to Beaverdam Creek. Either way, this
water, which is not accounted for in Table 5, will be included in the flow of Beaverdam Creek.
When it is included, the greatest percent reduction in flow, which occurs in Year 20, is reduced
from 9.0 percent to 8.2 percent.
5 Model Limitations
Groundwater flow models are generalizations of complex groundwater flow systems that cannot
be reasonably simulated without extensive data, detailed inputs, and large computational
requirements. The complexity is contained in the generalization, but local effects may influence
real world outcomes. Other limitations of the groundwater model of the Site are described in the
Tech Memo.
6 Summary and Conclusions
Transient groundwater flow modeling was used to estimate the rate of groundwater withdrawal
required to dewater four planned mine pits and evaluate potential impacts on adjacent water
resources due to dewatering. The transient groundwater model was developed from the
calibrated, steady state model for natural conditions described in the Tech Memo and refined to
capture currently planned resource extents and sequencing, as provided by PLCI and MMA.
• Model -predicted dewatering rates ranged from 525 gpm for the South Pit to 1,575 gpm
for East Pit. The total dewatering rate in any given year ranged from 575 to 2,300 gpm,
with the greatest amount of pumping occurring in year 2.
Predicted drawdowns for wells located within the Site, which will be decommissioned by
PLIC during mine development, ranged from 0 to 17.8 feet and averaged about 1.9 feet.
Predicted drawdowns for wells outside the Site ranged from 0 to 21.5 feet with an
average of approximately 4.0 feet. Four wells within the site are predicted to have
significant loss of available drawdown (water column) during dewatering of the East,
West, and North Pits. Beyond the permit boundary, two wells are predicted to
experience significant reduction of available drawdown during dewatering. One well was
predicted to experience significant water column loss throughout most of the 20-year
mine operation, while another is predicted to experience significant water column loss
during dewatering of the combined West and North Pits in years 14 to 20.
• Predicted impact to wetlands were most significant during the East and West/North Pit
dewatering simulations, indicating drying of 7 and 10 wetlands, respectively. Three
wetlands are predicted to dry up during dewatering of South Pit. Note that routing of
additional flow into wetlands may help mitigate the drying predicted by the model.
The contribution of groundwater to stream flow (baseflow) to the three streams crossing
the Site decreases between 0.1 to 9.0 percent based on the location of the stream
relative to the pit which is being dewatered. The largest predicted decrease in baseflow
occurred in Beaverdam Creek at the very end of the last year simulated after the West
Pit merged with the North Pit. Adding flow from a stream that is disconnected from the
stream network would decrease this impact to 8.2 percent.
10

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model
References
• PLCI will return water withdrawn during dewatering to streams at NPDES permitted
discharge points to reduce potential pumping effects due to mine operation. Some water
withdrawn due to dewatering may be diverted to wetlands to offset potential impacts to
wetlands.
7 References
Aquaveo, 2021, Groundwater Modeling System (GMS)
Harbaugh, A.W., 2005, MODFLOW-2005, The U.S. Geological Survey modular ground -water
model —the Ground -Water Flow Process: U.S. Geological Survey Techniques and Methods 6-
A16, variously p.
HDR, 2019, Technical Memorandum Groundwater Model. Prepared for Piedmont Lithium.
Marshall Miller & Associates (MMA), 2021, Estimated Mine Pit Extent with optimization using
MiningMath's SimSched program and scheduling using Maptek's Vulcan Evolution program.
11

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model
References
This page intentionally left blank.
12

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model ���
Figures
Figures
F
1

Piedmont Lithium Carolinas, Inc. I Technical Memorandum — Groundwater Model ���
Figures
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