Radius of Influence Evaluation 6-24-21 - DWW

W asiela
sulrung rLLc
Fngmeenng, Pemuthng & Compliance
317 B=12am PI
Foit:YM, SC 29708
(980) 355--4535
June 24, 2021
Tim Morton Trucking, LLC.
121 Garnet Lane,
Jacksonville, N.C. 28546
Attention: Mr. Tim Morton
Reference: Potential Radius of Influence from Open Pit Dewatering
Proposed Scott Farm Road Mine - Tim Morton Trucking, LLC
Jones County, North Carolina
Mr. Morton:
Wasiela Consulting PLLC (WC) is submitting this letter and attachments based on your
request to evaluate potential groundwater radius of influence for proposed dewatering at the
referenced project. It is our understanding that this evaluation has been requested by NCDEQ
during the mine permitting process. In particular, NCDEQ along with Jones County, have
identified two (2) groundwater wells located in excess of 2,000 feet from the proposed mine
dewatering boundary.
WC has evaluated the potential radius of influence to develop a range based on varying
surficial aquifer soil permeability values and producing a range from worst case (largest
radius of influence; highest permeability) to best case (smallest radius of influence; lowest
permeability). Based on our information, the soils within and surrounding the proposed mine
are sandy and vary from fine to medium in grain size. The soils also contain varying levels of
silts and clays that may produce even lower permeability values not considered in this
evaluation. For the purpose of this evaluation, we have assumed soil properties are
continuous throughout the radius of influence. The attached calculations provide details for
each case considered in the evaluation with summary presented below:
• Worst Case; 125 m; 410 feet
• Likely Case; 57 m; 187 feet
• Likely Case; 39 m; 127 feet
• Best Case; 29 m; 95 feet
For the purpose of this evaluation, the "Worst Case" reflects a clean medium to fine sand with
minimal amounts of impurities (silts and/or clays) that is unlikely for this area of Jones
County. Based on soils information in the area of the proposed mine dewatering, the potential
radius of influence should range from 95 to 187 feet.

Mr. Tim Morton
June 24, 2021
Page 2
If you should have any questions or require additional information concerning this evaluation,
please contact me at dwasiela0wasielallc.com or [phone] at your convenience.
Sincerely,
Wasiela Consulting PLLC
NC Certificate No. P-1974
David W. Wasiela, P.E.
Senior Engineer
NC Registration #20770
Attch: Calculations for Potential Radius of Influence of Open Pit Dewatering

Calculations for Potential Radius of
Influence of Open Pit Dewatering

Estimation of Radius of Influence from Open Pit Dewatering
In order to evaluate the radius of influence to groundwater table from proposed Scott Farm
Mine dewatering operations, the following is assumed to establish estimated "worst case
conditions".
• The entire proposed mine footprint would be dewatered.
• Dewatering elevations would be maintained with no periodic recovery intervals.
• Rainfall recharge is not considered when estimating radius of influence.
• Recharge from onsite infiltration pond is not considered when estimating radius of
influence.
Site Conditions taken from Application for Mining Permit and Plans prepared by Wasiela
Consulting PLLC.
• Length of Dewatered Excavation = 1,300 feet; 396 meters
• Width of Dewatered Excavation = 500 feet; 152 meters
• Required Groundwater Table Drawdown = 14 feet; 4.27 meters
• Saturated Thickness of Unconfined Aquifer Assumed = 25 feet; 7.5 meters
Methodology used for estimating potential radius of influence is taken from Government of
Western Australia Department of Water and Environmental Regulation. The empirical
methods for dewatering calculations and subsequent radius of influence are attached for
reference.
As physical soil properties within the dewatering radius of influence may vary based on
various soil types present, several iterations of calculations have been performed to
develop a range of potential "radius of influence". This range is established by varying
permeability (k values) of the surficial unconfined aquifer. The following presents
calculations for "Radius of Influence of Dewatering, R." for varying permeabilities.
Results of the calculations yield a range for potential Radius of Influence of Dewatering of:
• Worst Case; 125 m; 410 feet
• Likely Case; 57 m; 187 feet
• Likely Case; 39 m; 127 feet
• Best Case; 29 m; 95 feet

Worst Case - Radius of Influence of Dewatering, Ro, Permeability for Fine to Medium Sand
k = 0.00949 cm/sec; .0000949 m/s
Input
Length of excavation
(metres).,
Width of excavation
(metres) :
Required groundwater
dradon (metres):
Saturated thickness of
the unconfined
aquifer"') (metres):
Hydraulic conductivity
of the aquifer (K)
(metros per second);
Results
Effective radius of
pumping well , Re
(metres):
Radius of influence of
dewatering, Rc,
(metres) :
(i.e. radius of the cone
of depression)
Total pumping rate
(litres per second):
Time taken to establish
the cone of depression
(hours):
396
152
4.27
7.5
0.0000949
Calculate
m/sec
138m
125m
-1311/sec
627hrs

Likely Case - Radius of Influence of Dewatering, Ro, Permeability for Fine to Very Fine Sand
k = 0.00197 cm/sec; .0000197 m/s
Input
Length of excavation
396
(metres);
IT,
Width of excavation
15
(metres);
m
Required groundwater
4 7
drawrdown (metres):
m
Saturated thickness of
the unconfined
7-5 m
aquifer(') (metres):
Hydraulic conductivity
F —,
of the aquifer (K) O.CQ00197 m/sec
(metres per second);
Calculate
Results
Effective radius of
pumping well , Re 138m
(metres);
Radius of influence of
dewatering, R.
(metres): 57m
(i.e. radius of the cone
of depression)
Total pumping rate-31/sec
(litres per second):
Time taken to establish
the cone of depression 627hrs
(hours):

Likely Case - Radius of Influence of Dewatering, Ro, Permeability for Very Fine Sand
k = 0.000926 cm/sec; .00000926 m/s
Input
Length of excavation
396
(metres);
m
Width of excavation
15
(metres);
m
Required groundwater
4-27
drawdown (metres):
m
Saturated thickness of
the unconfined
7-5 r-rr
aquifer�4) (metres):
Hydraulic conductivity
0-000009 6
of the aquifer (K)
rn/sec
(metres per second):
Calculate
Results
Effective radius of
pumping well , R, 138m
(metres):
Radius of influence of
dewatering, R,
(metres); 39m
(i.e. radius of the cane
of depression)
Total pumping rate-1I/sec
(litres per second):
Time taken to establish
the cone of depression 627hrs
(hours):

Best Case - Radius of Influence of Dewatering, Ro, Permeability for Silty Fine to Very Fine
Sand; k = 0.0005 cm/sec; .000005 m/s
Input
Length of excavation
396 m
(metres);
Width of excavation
15 m
(metres);
Required groundwater
4.27 m
dradon (metres):
Saturated thickness of
the unconfined
7-5 m
aquiferN (metres):
Hydraulic conductivity
0.000005
of the aquifer (K)
m/sec
(metres per second);
Calculate
Results
Effective radius of
pumping well , Re 138m
(metres):
Radius of influence of
dewatering, R.
(metres): 29m
(i.e. radius of the cone
of depression)
Total pumping rate DI/sec
(litres per second):
Time taken to establish
the cone of depression 627hrs
(hours):

REFERENCES FOR CALCULATIONS
Government of Western Australia Department of Water and
Environmental Regulation

Department of Environment Regulation
Appendix E Empirical methods for dewatering calculations
Empirical methods for calculating the radial extent of the groundwater cone of
depression as well as the estimated pumping rates and times necessary to achieve
the required groundwater drawdown for dewatered excavations.
A web -based tool for conducting these calculations, based on the methods described
below, can be found www.der.wa.gov.au/ass.
Calculation methods
Dewatering of a rectangular excavation with dimensions a metres wide and b metres
long can be approximated as pumping from a large -diameter bore with an equivalent
radius of re metres, where:
Figure E1 Equation No 1
The radius of influence of this large -diameter bore (i.e radius of the cone of depression
of the watertable) can be approximated using Sichardt's equation:
O= 3 — h Ro=3000xsx
Figure E2 Equation No 2
Where: Ro = radius of influence of an equivalent pumping bore (m)
s = maximum groundwater draw down (m)
K = hydraulic conductivity of aquifer matrix (units of m/s)
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Treatment and management of soil and water in acid sulfate soil landscapes (June 2015)

Department of Environment Regulation
In the absence of site -specific hydraulic data, Table 5A below lists default hydraulic
conductivity values (K) for a variety of Western Australian soil types.
Table 5A. Default hydraulic conductivity values (K) for a variety of Western
Australian soil types
. so
2_1
Sand
Very coarse to gravel
0.002847
Very coarse
0.002361
Coarse
0.000845
Medium to coarse (moderately sorted)
0.000579
Fine to gravel (poorly sorted)
0.000116
Medium
0.000191
Fine to medium
9.49 x10-5
Fine
4.75 x10-5
Fine to very fine
1.97 x10-5
Very fine
9.26 x10-6
Silty
4.63 x10-5
Clayey
1.16 x10-5
Clay
4.63 x10-6
Sand and limestone: Ascot Formation
9.26 x10-5
Limestone and calcarenite: Tamala Limestone
0.001157 to 0.011574
Adapted from Davidson, 1995.
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Treatment and management of soil and water in acid sulfate soil landscapes (June 2015)

Department of Environment Regulation
As a first approximation, changes in watertable elevation caused by dewatering are
related to the pumping rate, hydraulic conductivity of the aquifer matrix and radius of
influence of pumping by the equation:
iiq
h"' 17k (In R.
Figure E3 Equation No 3
Where: H = saturated thickness of the aquifer undisturbed by pumping (m)
h = saturated thickness of the aquifer at maximum drawdown (m)
k = hydraulic conductivity of aquifer matrix (units of m/s)
Ro = radius of influence of an equivalent pumping bore (m)
re = effective radius of an equivalent pumping bore (m)
q = pumping rate of individual dewatering well points (m3/s)
n = number of well points used to dewater the excavation
In the absence of site -specific information, the saturated thickness of superficial
aquifers may be obtained from:
• the `Groundwater Atlas' (for sites in the Perth metropolitan region); or
• information held by the Department of Water (for sites elsewhere in the state).
The pumping time needed for the cone of depression of the watertable to extend out
to Ro is given by the Cooper -Jacob empirical relationship.
Ro = Q2.25 k h t)/S)0.5
Figure E4 Equation No 4
Where: t = pumping time (seconds)
S = specific yield of aquifer sediments
Other parameters as previously defined
In the absence of site -specific hydraulic information, assume a specific yield of 0.1.
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Treatment and management of soil and water in acid sulfate soil landscapes (June 2015)

Department of Environment Regulation
The following example demonstrates how these equations can be used to estimate
the radius of influence of a dewatering program and the pumping rate and time
needed to lower the watertable by a specified amount in the area of excavation:
Example 1
A dewatering program is planned at a site underlain by sandy sediments where the
saturated thickness of the superficial aquifer is 45 metres. It is planned to lower the
watertable by 5 metres in a rectangular area of dimensions 30 metres by 15 metres. It
is proposed to use 26 well points around the rectangular area to lower the watertable
to the base of the excavation.
Solution:
Firstly, use Sichardt's equation (Equation No 2) to determine the radius of influence
(i.e. radius of ultimate cone of depression) if one large pumping bore is used to
dewater the excavation:
Ro = 3000 x 5 x (3.5 x 10-4)0.5
= 281 metres
The equivalent radius of this pumping bore is determined using Equation No 1.
re = (30 x 15/7u)0.5
= 12 metres
The pumping rate to dewater the excavation can be determined using Equation No 3:
(45)2 — (40)2 =
nq
7r x (3.5 x 10-4)
i.e. nq = 0.15 m3/s
x ((In(281) — In(12))
Given that there are 26 well points in use to dewater the excavation, the pumping rate
of each well point must be 0.15/26 m3/s, or about 5.8 Us.
The pumping time needed is given by the Cooper -Jacob equation (Equation No 4)
281 = ((2.25 x 3.5 x 10-4 x 40)/0.1)0.5 x (t)o.5
i.e. 281/0.56 = (t)0.5
i.e. t = 251789 seconds or about 70 hours or 3 days
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Treatment and management of soil and water in acid sulfate soil landscapes (June 2015) M