Supplement 1

SUPPLEMENT 1
MATERIALS PROVIDED IN RESPONSE TO AUGUST 2018
SCIENCE PANEL MEETING DISCUSSION ON
HISTORY OF FLOW MONITORING,
FLOW OBSERVATIONS, AND
CHARACTER OF STUDY CREEKS

DETERMINING FLOWS IN SMALL WATERSHEDS AND BAYS ON SOUTH CREEK,
BEAUFORT COUNTY, NORTH CAROLINA
(Skaggs et a12009)
July 2020 S-2 Supplement 1 2019 Data Year PCS Creeks Report

Determining Flows in Small Watersheds and Bays on South Creek
Beaufort County North Carolina
Wayne Skaggs, G.M. Chescheir and Chad Poole
PCS Phosphate Company, Inc. has recently been granted a permit to mine phosphate
ore on lands adjacent to South Creek. The new permit expands mining in the NCPC Tract
close to the PCS plant in Beaufort County, near Aurora, NC. During the mining process,
surface water from the site is redirected (pumped) and released at a location different than the
natural outlet. The effect of mining is to reduce the watershed area contributing to flow to
the small streams that feed into the creek (stream segments impacted by mining are mostly
intermittent). Our objective in the new project is to determine the impact of mining on flows
from the small watersheds immediately adjacent to South Creek and other similar systems
within the permit area.
We have collected data and intensively studied the hydrology of 8 subwatersheds
within 3 creeks on the NCPC Tract over the past 10 years. See reports by Skaggs and Group
(2000 to 2009). The subwatersheds varied in size from 19 to 129 acres. All had upstream
segments where flow was concentrated and of sufficient elevation such that triangular weirs
and flow meters could be installed to measure instantaneous flow rates and cumulative flows.
In addition to analyzing continuous data on watershed outflow, water table depths, and
rainfall for each watershed, we tested and applied the simulation model DRAE% MOD to
characterize the hydrology of the watersheds and predict effects of mining on daily and
cumulative outflows. The new permit allows mining closer to South Creek, such that the
watershed remaining after mining and prior to reclamation will be smaller, and as now, the
remaining creek segments or outlets may be subject to tides, both wind and lunar. The
outlets of interest are most often small bays where flow is not concentrated and flow rates are
difficult to measure. Furthermore, hydrology and water quality in the bays, and the impact of
mining thereon, is of great environmental interest. Methods described herein are proposed to
estimate the effect of flows from small coastal watersheds on hydrology (water balance) in
the bays, and the impact of mining on flow conditions.
METHODS
A schematic of a small watershed draining directly into South Creek is shown in Figure 1.
The objective is to continuously measure flow rate at the mouth of the watershed, both before
and after mining. By comparing flows before and after mining, the effect of mining on the
hydrology can be determined. The problem in this case is that the outlet of the watershed
may be affected by wind and lunar tides. Furthermore, the outlet may be wide with velocities
that change in both magnitude and direction over the course of the day. Thus it does not
appear feasible to use either weirs or velocity meters, as we have used before, to measure
flow rates at the outlet. Rather we propose to use water level measurements in the bay, along
with detailed information on the topography of the bay, to determine flows into and out of
the bay by mass balance. One of the inputs to the mass balance is flow from the watershed
upslope of the bay. We propose to determine this flow by measurement at a position
unaffected by tide, such as point A in Figure 1.
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-1
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-3 Supplement 1 2019 Data Year PCS Creeks Report

fkjver
Figure 1. Schematic of small coastal watershed adjacent to river or creek affected by wind
and/or lunar tides.
Alternatively, it may be possible to predict the upstream flows using a calibrated model
(DRAINMOD).
A mass balance may be written as follows for the area denoted as Bay in Figure 1:
p4S = pQI - pQo
(1)
Where 4S is change in storage of water in the bay (fe) over a given time increment, p is
density (lbm/fe), and QI and Qo are flows into and out of the bay, respectively, during the
time increment. Assuming the density is the same for inflows, outflows and water in the bay
allows simplification of Eq. 1 to the following,
4S=QI-Qo
(2)
The inflow is the sum of flow from the watershed, QIw, and flow from the river or sound,
QIs,
QI = QIw + QIs (3)
July 2020 S-4 Supplement 1 2019 Data Year PCS Creeks Report

The outflow, Qo, is simply flow from the bay to the sound or river. Then
AS = Qjw + Qis - Qo (4)
If the stage (water level elevation in the bay) is measured and recorded on a continuous basis,
AS can be determined for any time increment. If flow from the watershed, QjW, is also
measured, flow into or out of the bay for the same time increment can be determined as
follows.
1. For rising stage. If the stage is rising due to wind or lunar tide, the flow direction
will be from the sound or river to the bay, Qo = 0, AS > 0, and, from
Eq. 4, AS = Qjw + Qis. Then Qis = AS - Qjw.
2. For falling stage. Flow direction will be from bay to sound, AS < 0, Qis =0, and,
AS = Qjw - Qo. Or Qo = Qjw — AS.
3. Stage is steady. No change with time. AS = 0, and Qo - Qis = Qjw. That is, the net
flow out of the bay (Qo - Qis) during the time increment will be equal to flow in from
the watershed.
L�
Vj= Area(1)*Depth(1 )
V2=Vl + A2*(D2-Dl )
V3=Vl +V2+A3*(D3- D2)
Vd=Vj +V2+V3+A4*(D4-D3)
Figure 2. The relationship between storage in the bay and stage (or depth of water) at the
outlet of the bay can be determined from topographic data as shown schematically here. This
information will be developed from a detailed topographic survey; it is shown here for
demonstration purposes.
July 2020 S-5 Supplement 1 2019 Data Year PCS Creeks Report

In order to calculate flows using the above equations, we need to know the relationship
between storage, S, and elevation (stage) of the water surface in the bay, or depth of water at
bay outlet. A topo map of the bay near the outlet of Jacks Creek is shown in Figure 2, along
with calculations for storage given stages (or depth of water at the outlet) ranging from 1 to 4
feet. Results are tabulated in Table 1 and volume stored is plotted as a function of stage or
depth of water at the bay outlet in Figure 3. Once this relationship is defined, it is possible to
determine the change in storage in the bay due to a change in stage, or water surface
elevation. An exponential relationship was fitted to the data as shown in Figure 3 so that
storage volume, S can be calculated in terms of stage, or depth at the outlet, X, as,
S = 105899 X2.9772 (5)
This relationship will clearly vary from site to site, and must be independently determined for
each bay.
Tide Depth Area (ac) Volume (ft^3)
Or Stage (ft) i
1 2.1 93,000
2 23.3 1,110,000
3 35.3 2,647,000
4 75.4 5,933,000
Table 1. Relationship between depth of water at outlet of bay, water surface area and storage
in the bay at outlet of Jacks Creek.
Example Calculations
Assuming No Flow From Watershed
The methods for determining flows in and out of tidal bays along South Creek will be
demonstrated for Jacks Creek. Water surface elevations (stage) in the Jacks Creek bay have
been recorded for some years. We used the methods described above to estimate flows due
to tidal fluctuations for year 2003. Stage was recorded at 1.5 hr (90 min) intervals. Stage is
plotted as a function of time for day 1 of 2003 in Figure 4. For purposes of this example we
will assume that flow from the watershed is zero. We will rerun the example later to include
effects of flows from the watershed. Assuming Qjw = 0, Eq. 4 may be written, Qis = 4S
for a rising stage and Qo = - 4S for a falling stage.
July 2020 S-6 Supplement 1 2019 Data Year PCS Creeks Report

7000000
.11111I,
M
5000000
d
a�
4000000
0
co
c 3000000
d
= 2000000
0
1000000
Volume vs. Tide Depth
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
Tide Depth at Outlet (ft)
Figure 3. Relationship between volume of water in the bay and stage or depth of water at bay
outlet for the bay at the point where Jacks Creek enters South Creek
Starting at time, T=O, on day 1, the stage, X, was 1.55 ft. Applying Eq. 5 gives a storage
volume in the bay of S = 390,434 ft3. At T=1:30, X=1.378 and S = 275,084 ft3. The stage is
falling and the change in storage has decreased by 115,350 ft3. That
is, 4S =-115,350 ft3 and the outflow during the 1.5 hour period was Qo = - 4S=115,350 ft3.
At T = 3:00, X=1.267 and S= 214229 ft3. Thus 4S = 214229-275084 = -60854 ft3, the stage
is still falling, and Qo = - 4S = 60854 ft3 for the period from 1:30 to 3:00 AM. At T=4:30,
X=1.329 (stage now rising) and S = 246974 ft3. For this time increment 4S = 246974 —
214229 = 32744 ft3, and QIs = 4S = 32744 ft3. Since the stage is rising, Qo = 0. These
simple mass balance calculations were repeated for the remainder of the day; the results are
summarized in Table 2. Total daily flow from South Creek to the bay (due to tide) was
calculated as 755,529 ft3 and flow from the bay to South Creek as 786,190 ft3. Total flow in
both directions (which would ordinarily have to be measured using conventional methods)
was 1,541,720 ft3.
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-5
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-7 Supplement 1 2019 Data Year PCS Creeks Report

Stage vs Time
2.5
2
847
R 1.668
w 1.5
0.5
0
0:00 3:00 6:00 9:00 12:00 15:00 18:00 21:00
Time
Figure 4. Recorded stage at outlet of Jacks Creek Bay for 1/l/2003.
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-6
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-8 Supplement 1 2019 Data Year PCS Creeks Report

Table 2. Summary of water balance calculations for Jacks Creek Bay for day 1 (Jan. 1)
2003. Calculations to demonstrate the method; inflow from the watershed assumed zero.
Time
Stage
Volume
Change in
Inflow, Sound
Inflow, Water-
Outflow, Bay
Volume
to Bay
shed to Bay
to Sound
hrs
ft
Cu ft
Cu ft
Cu ft
Cu ft
Cu ft
0
1.55
390434
1:30
1.378
275084
-115350
0
0
115350
3:00
1.267
214229
-60854
0
0
60854
4:30
1.329
246974
32744
32744
0
0
6:00
1.332
248637
1664
1664
0
0
7:30
1.464
329413
80776
80776
0
0
9:00
1.493
349223
19810
19810
0
0
10:30
1.651
471160
121937
121937
0
0
12:00
1.715
527646
56486
56486
0
0
13:30
1.867
679427
151780
151780
0
0
15:00
2.001
835150
155724
155724
0
0
16:30
2.094
956101
120950
120950
0
0
18:00
2.104
969759
13658
13658
0
0
19:30
1.988
819100
-150658
0
0
150658
21:00
1.847
657987
-161114
0
0
161114
22:30
1.668
485751
-172235
0
0
172235
0:00
1.508
359773
-125978
0
0
125978
Sum 755529 786190
Total Flow 1541720
Figure 5 shows the recorded stage for a 9-day period starting January 1, 2003. A smoothing
routine was used to take out effects of erratic data that usually are erroneous. The stage data
were smoothed for the entire year 2003 and the methods demonstrated above were applied to
determine inflows and outflows to the bay. Results are summarized in Tables 3 and 4. These
calculations show that total flow to and from the bay, mostly resulting from tidal influence,
was over 10,700 ac-ft. The area of the entire Jacks Creek watershed is about 228 acres.
Based on our measurements over a 10 year period and the application of simulation models
over a longer period, mean annual outflow from the watershed is expected to be about 1.17
ft, or 266 ac-ft from the 228 acres, or about 2.4% of the outflow resulting from tidal
fluctuations. Note that 266 ac-ft is about 2.4% of the total water flowing from the bay to
South Creek. But almost the same amount of water flows in from South Creek to the bay due
to wind tides. So the 266 ac-ft is about 1.2% of the total flow to and from the bay to South
Creek. The total flow to and from the bay to South Creek is relevant in that conventional
methods of determining the effect of mining on outflow would require measurement of flows
both to and from the bay.
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-7
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-9 Supplement 1 2019 Data Year PCS Creeks Report

Table 3. Calculated annual flows for the Jacks Creek Bay for 2003. Runoff from the 228 ac.
watershed is ignored in these calculations.
Annual Flow
W MdL
ac-ft
Outflow 468,622,069
10,758
Inflow-468,904,276
-10,765
Net Flow-282,207
-7
Total Flow 937,526,345
21,523
Table 4. Summary of calculated annual flows for the Jacks Creek Bay for 2003 assuming
total flow from the 228 ac watershed is equal to the long term average of 1.17 ft (14 in).
Watershed Area 228 ac
Mean Watershed Outflow 1.17 ft
Mean Watershed Outflow 266 ac-ft
Total Flow in Bay 21,523 ac-ft
Watershed Input to Bay as % of Total Flow 1.2 %
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-8
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-10 Supplement 1 2019 Data Year PCS Creeks Report

3.0
2.5
W 1.0
0.5
0.0
Measured and Smoothed Water Elevations
/V�011 AAk
�I
111103 112103 113103 114103 115103 116103 117103 118103 119103
Date
i Stage tSmooth
Figure 5. Recorded water surface elevation or stage at outlet of Jacks Creek bay for first 9
days of 2003. Data were smoothed to remove effects of erratic spikes in records
Considering Flow (Runoff) From Watershed.
The calculations in the above example did not include the effect of daily runoff from the watershed
on the water balance in the bay. The purpose of that example was to demonstrate methods
for determining inflows and outflows to or from the bay, and to evaluate the magnitude of
those flows in comparison to flows (runoff) from the watershed. The following example
includes the effects of runoff from the watershed on day-to-day and annual flows to and from
the bay.
Our group measured outflow from an upstream sub -watershed on Jacks Creek for 2003.
These measurements (inches per hour) were multiplied by the area of the whole Jacks Creek
watershed (228 ac) to determine outflow (fe) for each 1.5 hour interval for the entire year.
These values were then combined with the change in volume stored in the bay for each time
interval, as described in the above example, to determine inflow (from South Creek to the
bay) and outflow (from the bay to South Creek) for each 1.5 hr time interval. Results are
given in Table 5 for one day, June 10, 2003. Rainfall of 1.5 inches occurred on June 10 and
resulted in 1.33 in of runoff (1,104,000 ft) from the 228 ac watershed to the bay. Wind tide
caused over 693,000 fe to flow into the bay from South Creek, and a total of 1,556,000 fe
(including over 1.1 million cu ft of runoff) flowed from the bay to South creek. For this day
runoff from the watershed exceeded that flowing into the bay due to wind tide, but this is not
usually the case.
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-9
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-11 Supplement 1 2019 Data Year PCS Creeks Report

Table 5. Summary of water balance calculations for Jacks Creek Bay for June 10, 2003.
Calculations to demonstrate the method; inflow from the watershed is included.
Change in
Inflow, Sound
Inflow, Water-
Outflow, Bay
Time
Stage
Volume
Volume
to Bay
shed to Bay
to Sound
ft
Cu ft
Cu ft
Cu ft
Cu ft
Cu ft
0:00
1.744
2138731
1:30
1.629
1880929
-257802
0
15566
273368
3:00
1.594
1807373
-73556
0
143211
216767
4:30
1.633
1891429
84056
0
194757
110701
6:00
1.753
2157811
266381
91637
174745
0
7:30
1.887
2485644
327833
188924
138909
0
9:00
1.954
2662015
176371
70582
105789
0
10:30
1.999
2784095
122080
43365
78715
0
12:00
1.977
2724090
-60005
0
57458
117463
13:30
1.900
2519429
-204661
0
45616
250278
15:00
1.824
2327928
-191501
0
36767
228268
16:30
1.762
2180856
-147072
0
29740
176812
18:00
1.774
2209243
28387
4751
23636
0
19:30
1.842
2373843
164600
145851
18750
0
21:00
1.875
2456330
82487
66985
15501
0
22:30
1.912
2550665
94335
81145
13190
0
0:00
1.844
2379284
-171381
0
11193
182574
Sum
240554
693241
1103543
1556231
Total Flow
2249471
Figure 6 shows the measured water surface elevation in the bay, measured flow from the
watershed to the bay, and calculated flow rates into and out of the bay for the 7-day period,
June 6-13, 2003. The flow rates in fe/hr (cu ft/hr) were determined by dividing the
calculated flows for a 1.5 hour period (Table 5) by 1.5, so they represent the average flow
rate over the 1.5 hour period. While the water surface elevation in the bay was highest during
the heavy rainfall period, it was nearly as high June 6-7 when flow from the watershed was
very small. Flows are summarized on a daily basis in Table 6. Flows in and out of the bay
during June 6-7 were primarily driven by wind tides, but were of about the same magnitude
as during the period of heavy runoff from the watershed. Note that "Net Flow" in Table 6 is
the total flow into the bay (flow into the bay from South Creek caused by wind tide plus
inflow as runoff from the watershed) minus the flow from the bay to South Creek. A
negative Net Flow means there was more flow out during the day than in. Total Net Flow for
the 7 day period was -17.6 ac ft. This negative Net Flow results from the fact that the stage
(water surface elevation) at the end of the 7-day period (1.16 ft) was lower than at the
beginning (1.55 ft.), so storage in the bay was 17.6 ac ft. less at the end of the 7-day period
than at the beginning. Total flow in and out of the bay during the week was calculated to be
304 ac-ft, compared to 33 ac-ft of runoff from the watershed.
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-10
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-12 Supplement 1 2019 Data Year PCS Creeks Report

500000
400000
300000
s
M
w
3
O
LL 200000
100000
2
1.6
r_
1.2 ,
O
R
N
W
0.8 >,
R
CO
0.4
0 0
6/6/03 6/7/03 6/8/03 619103 6/10/03 6/11/03 6/12/03 6/13/03
Date
Inflow from Watershed -Inflow from South Creek -Outflow to South Creek -Bay Elevation
Figure 6. Inflow to (Blue curve) and outflow from (Red curve) the Jacks Creek bay at the bay
outlet for 7 days from June 6, 2003 to June 13, 2003. Also shown are the inflow to the Jacks Creek
bay from the watershed (Black curve) and the measured elevation of the bay (Green curve).
Table 6. Calculated daily flows for the Jacks Creek Bay from June 6, 2003 to June 13, 2003.
Daily Flow
ac-ft
6/6
6/7
6/8
6/9
6/10
6/11
6/12
Total
Outflow to
37.7
39.7
13.9
8.3
35.7
31.3
10.8
177.3
South Creek
Inflow from
42.0
9.9
13.8
36.3
15.9
4.1
5.1
127.0
South Creek
Inflow from
0.1
0.7
2.7
1.9
25.3
1.6
4.1
32.7
Watershed
Net Flow
4.5
-29.2
2.6
29.9
5.5
-25.7
-5.3
-17.6
Total Flow
79.7
49.6
27.6
44.5
51.6
35.4
15.9
304.3
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-11
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-13 Supplement 1 2019 Data Year PCS Creeks Report

Table 7. Calculated annual flows for the Jacks Creek Bay for 2003.
Annual Flow
W
ac-ft
Outflow to South Creek
485,044,086
11,135
Inflow from South Creek
457,011,082
10,492
Inflow from Watershed
27,759,797
637
Net Flow
-282,207
-7
Total Flow
942,055,168
21,627
Annual results for the Jacks Creek Bay in 2003 are summarized in Figure 7 and in Tables 7
and 8. Annual flows from the bay to South Creek were 11,135 ac-ft, compared to 637 ac-ft
of runoff. That is, runoff from the watershed was only 5.7% of the total flow from the bay to
South Creek. The annual inflow to the bay from South Creek was 10,492 ac-ft which is
about 16 times the annual inflow to the bay from the watershed. The total flow to and from
the bay resulting from tidal fluctuations is over 30 times greater than the runoff to the bay
from the watershed.
Table 8. Summary of the calculated annual flows for the Jacks Creek Bay for 2003.
Annual Flow
Watershed Area
228 ac
Watershed Outflow (depth)
2.79 ft
Watershed Outflow (volume)
637 ac-ft
Total Outflow from Bay to South Creek
11,135 ac-ft
Watershed Outflow as % of Total
5.7%
Outflow to South Creek
Total Flow from Bay to/from South
21,627 ac-ft
Creek
Watershed Outflow as % of Total Flow
2.9%
to/from South Creek
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-12
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-14 Supplement 1 2019 Data Year PCS Creeks Report

ILUUU
11000 -
10000 --------------------------------------
9000 -----------------------------------
8000
--------------------------------------- - - - - --
3 7000 -----------------------------
-------------------
O
u_ 6000
is5000 ---------------- --------------------------------
E4000-------- ---------------------------------------
0
U
3000 - - - - -- ----------------------------
2000 --- -----------------
1000 �r ----
0
1/1/03 1/31/03 3/3/03 4/2/03 5/3/03 6/2/03 7/3/03 8/2/03 9/2/03 10/2/03 11/2/03 12/2/03 1/2/04
Date
Inflow from Watershed —Inflow from South Creek —Outflow to South Creek
Figure 7. Cumulative inflow to (Blue curve) and outflow from (Red curve) the Jacks Creek
bay at the bay outlet for the year 2003. Also shown is the inflow to the Jacks Creek bay from the
watershed (Black curve).
35
30
25
3
w
20
O
15
Q 10
5
0
2003
Jacks Creek 1 & 2, PCS Phosphate, 1951-2003 Simulation
2000
2001
2002
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 8. Frequency distribution of predicted annual outflow (runoff + shallow subsurface
flow) for a 53 year (1951-2003) simulation at Jacks Creek. Measured annual flows for four
years of observations are shown on the graph.
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-13
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-15 Supplement 1 2019 Data Year PCS Creeks Report

Results for a long term simulation for the Jacks Creek watershed are shown in Figure 8.
These results indicate that the measured outflow (runoff + subsurface flow) from the
Jacks Creek watershed in 2003 was the largest in 53 years. Predicted outflow for 2003 was
31 inches, which was 2 inches less than measured for that year. The main point, however, is
that, even when the annual watershed outflow was the greatest of the last 53 years, flow from
the watershed was only 5.7% of the total outflow from the bay to South Creek. If we were
measuring flows using conventional metering methods, we would have to measure both
inflow to the bay from South Creek, as well as, outflow from the bay to South Creek. The
flow from the watershed would be the difference between these measured outflows and the
inflows. On that basis, flow from the watershed would be only 2.9% of the total flow that
would need to be measured.
Summary
The data and analysis presented herein support the following conclusions:
• Flows in and out of the stream/bay systems, due primarily to wind and lunar tides, are
large compared to flows from the small watersheds. This means that conventional
methods of measuring flow rates at the watershed outlet (where, in this case, the
outlet is affected by tides) to determine effect of mining on the hydrology, is not
practical. Determining the outflow from the watershed would require measuring total
outflow and inflow from the bay (two large values), and taking the difference to get
watershed outflow. Errors in measurements of inflow and outflow from the bay
would likely be of equal or larger magnitude than outflow from the watershed.
Methods presented and demonstrated herein appear to be a better alternative.
• Flow from small coastal watersheds to and through the stream/bay systems such as
Jacks Creek is a small percentage of the total flow to and from the bay and South
Creek.
• This implies that significant reductions in the watershed area due to mining would not
have a great impact on the flow and associated conditions in the bay.
• Flow between bays and South Creek depends on wind and lunar tides, orientation of
the bay with respect to South Creek and prevailing winds, as well as the shape of the
bay and its topography. Thus additional measurements and analyses are needed for a
range of watershed -bay systems before final conclusions can be drawn.
• The analysis presented herein did not consider flow dynamics within the bay and the
effect of runoff from the watershed and the effect of watershed reduction on factors
such as salinity distributions therein.
Draft Plan of Study for Potential Effects of Headwater Wetland Reduction on Downstream Aquatic Functions C-14
Appendix C - Determining Flows in Small Watersheds and Bays on South Creek
PCS Phosphate Company, Inc.
December 2009
July 2020 S-16 Supplement 1 2019 Data Year PCS Creeks Report

MONITORING LOCATIONS IN
HUDDLES CUT, TOOLEY CREEK, AND JACKS CREEK ON
AERIAL PHOTOS THROUGH TIME (19997 20027 2020)
July 2020 S-17 Supplement 1 2019 Data Year PCS Creeks Report

July 2020 S-18 Supplement 1 2019 Data Year PCS Creeks Report

1
1
S
r
SOURCE:
GOGGLE EARTH PRO HISTORICAL AERIAL
DATED: JANUARY 24, 1999
`r
3
1 4
6
GOGGLE EARTH PRO HISTORICAL AERIAL
DATED: DECEMBER 31, 2002
I
SOURCE:
AERIAL PROVIDED BY: PCS PHOSPHATE COMPANY, INC.
1530 NC HIGHWAY 306 SOUTH, AURORA, NORTH
CAROLINA 27806, 252-322-5121, FLIGHT DATE:
JANUARY 7, 2020
J2CW MW� \
C�--�cJ •y� '` f
JACKS
CREEK
. N
LEGEND
MODIFIED ALT L PERMIT BOUNDARY
j
COASTLINE AND EXISTING FEATURES
SKAGGS SUB-BASINS(1999)
BOTTOMLAND HARDWOOD COMMUNITY
PUBLIC TRUST CREEK
PERENNIAL STREAM
INTERMITTENT STREAM
ELECTRONIC HYDROLOGY WELL
0
MANUAL HYDROLOGY WELL
FLOW MONITOR STATION
WATER QUALITY SAMPLE LOCATION
Mill
SALINITY MONITOR
D
SKAGGS MONITORING LOCATIONS
NOTE:
STREAM DETERMINATIONS AS PER THE 2008 FEIS.
"
0 1,500 3,000
4/
SCALE IN FEET
INSTRUMENT LOCATIONS AND
SUB -BASINS IN JACKS CREEK
J
PAST AND CURRENT
CREEKS MONITORING STUDY
PCS PHOSPHATE COMPANY, INC.
SCALE: AS SHOWN APPROVED BY: DRAWN BY: TLJ
DATE: 04/13/20 FILE: 174547 JACKS —CREEK.
R--i 4709 COLLEGE ACRES DRIVE CP# 1745.47
F--`/1\
jZ
SUITE 2
ENVIRONMENTAL CONSULTANTS
WILMINGTON, NORTH CAROLINA 3�22-T403 FI G U R E
�1✓� FAX 91%392-9139 SUPPLEMENT 1 —C
July 2020 S-19 Supplement 1 2019 Data Year PCS Creeks Report

AS,
OURCE:
OOGLE EARTH PRO HISTORICAL AERIAL
ATED: JANUARY 24, 1999
OOGLE EARTH PRO HISTORICAL AERIAL
ATED: DECEMBER 31, 2002
OURCE: "-
ERIAL PROVIDED BY: PCS PHOSPHATE COMPANY, INC. -
1530 NC HIGHWAY 306 SOUTH, AURORA, NORTH
AROLINA 27806, 252-322-5121, FLIGHT DATE:
ANUARY 7, 2020
TOOLEY
CREEK
GIN
S�
-
LEGEND
MODIFIED ALT L PERMIT BOUNDARY
COASTLINE AND EXISTING FEATURES
SKAGGS SUB-BASINS(1999)
BOTTOMLAND HARDWOOD COMMUNITY
PUBLIC TRUST CREEK
PERENNIAL STREAM
INTERMITTENT STREAM
ELECTRONIC HYDROLOGY WELL
•
MANUAL HYDROLOGY WELL
FLOW MONITOR STATION
WATER QUALITY SAMPLE LOCATION
Mill
SALINITY MONITOR
D
SKAGGS MONITORING LOCATIONS
NOTE:
STREAM DETERMINATIONS AS PER THE 2008 FEIS.
w.
0 1,500 3,000
SCALE IN FEET
INSTRUMENT LOCATIONS AND
SUB -BASINS IN TOOLEY CREEK
PAST AND CURRENT
CREEKS MONITORING STUDY
PCS PHOSPHATE COMPANY, INC.
SCALE: AS SHOWN APPROVED BY: DRAWN BY: TLJ
DATE: 04 13 20 FILE:174547 TOOLEY-CRK
F-CZR--i CP# 1745.47
4709 COLLEGE ACRES DRIVE
ENRONENTSU CONSULTANTS SUITE 2 IVI�A
WILMINGTON, NORTH CAROLINA 29253 FIGURE
TEL FAX [phone] SUPPLEMENT 1 —B
July 2020 S-20
Supplement 1 2019 Data Year PCS Creeks Report

PHOTOGRAPHS OF HUDDLES CUT 2001 STREAM DETERMINATIONS:
UPSTREAM AND DOWNSTREAM VIEWS FROM
UPPER LIMIT INTERMITTENT (ULI) AND LOWER LIMIT INTERMITTENT (LLI)
(refer to Figure Supp. I -A and field copy of USGS topographic map for locations)
July 2020 S-21 Supplement 1 2019 Data Year PCS Creeks Report

VA
Huddles West Prong ULI- view upstream at HF2, southern most weir on Walton Road (USGS topo
HWP4 ULI); 2001 jurisdictional stream upper limit at Walton Road.
•
Huddles West Prong ULI-view downstream from HF2 on Walton Road (USGS topo HWP4 ULI);
2001 jurisdictional stream determination.
July 2020 S-22 Supplement 1 2019 Data Year PCS Creeks Report

Huddles Cut West Prong LLI- view upstream (USGS topo HWP3 LLI); 2001 jurisdictional stream
limit at flagging to right.
t
[,
Huddles Cut West Prong LLI- view downstream (USGS topo HWP3 LLI; lizard tail is upper edge of
"BREAK" in jurisdiction); 2001 jurisdictional stream limit at flagging.
July 2020 S-23 Supplement 1 2019 Data Year PCS Creeks Report

Huddles Cut West Prong ULI- view upstream towards "BREAK" (USGS topo HWP2 ULI); 2001
jurisdictional stream limit at flagging.
' 1
�
I�
Huddles Cut West Prong ULI- view downstream (USGS topo HWP2 ULI); 2001 jurisdictional stream
limit at flagging.
July 2020 S-24 Supplement 1 2019 Data Year PCS Creeks Report

e,F i � � d F it ,.' .� '•" � �r .,¢,� � � �'� ! � • ,
Lam• .t _ `�.,." ,' .... V �� `. .. (.r �1'� EKE•, - •�Rf,,' •I � .r, ;.,,:. -'�� ,�
�s_- � P1; - r T,'et'�tf{•. 1 �F r's• �..`r�•. 'r 1� r'A� :,�'�� .
��� -. +. -� Ate,,(/-/ fR �• . � - ' � '-
•dr
-ti�� to"
4 � WL�
I -A Ir
ir
ti, ` 'jam •C -y �� K
r�^ v 1 � � � !`•#mod �' r. f?: ��/+ •'•i '�U ���
{• F
l y i '.,•L t� ..

Huddles West Prong ULI- view upstream at HF1, northern weir on Walton Road (USGS topo HWP6
ULI); 2001 jurisdictional stream upper limit at Walton Road.
IM M
Huddles West Prong ULI- view downstream at HF1, northern weir on Walton Road (USGS topo
HWP6 ULI); 2001 jurisdictional stream upper limit at Walton Road.
July 2020 S-26 Supplement 1 2019 Data Year PCS Creeks Report

Huddles Cut West Prong LLI-view upstream near HWW1 (USGS topo HWP5 LLI); 2001 jurisdictional
stream determination.
Huddles Cut West Prong LLI-view downstream into swamp from LLI (USGS topo HWP5 LLI); 2001
jurisdictional stream determination.
July 2020 S-27 Supplement 1 2019 Data Year PCS Creeks Report

2000 PHOTOGRAPHS OF TOOLEY CREEK EAST PRONG VEGETATION
(2001 CZR STREAM PHOTOS UNAVAILABLE)
(refer to Figure Supp. I-B for locations)
July 2020 S-28 Supplement 1 2019 Data Year PCS Creeks Report

r� r
I"
A- z
Tooley Creek east prong view upstream from TW1 towards TF2 (left photo) and downstream
towards TW2 (right photo). 2001 ULI determination at TF2 (Fig. Supp. 1-B).
T, e
Tooley Creek east prong view upstream from TW3 towards TW2 (left photo) and downstream
(right photo). 2001 LLI/ULP determination at TW3 (Fig. Supp. 1-B).
July 2020 S-29 Supplement 1 2019 Data Year PCS Creeks Report

PHOTOGRAPHS OF JACKS CREEK MAIN PRONG 2001 STREAM DETERMINATIONS:
UPSTREAM AND DOWNSTREAM VIEWS FROM
UPPER LIMIT INTERMITTENT (ULI), LOWER LIMIT INTERMITTENT (LLI),
UPPER LIMIT PERENNIAL (ULP), AND LOWER LIMIT PERENNIAL (LLP)
(refer to Figure Supp. I-C and field copy of USGS topographic map for locations)
July 2020 S-30 Supplement 1 2019 Data Year PCS Creeks Report

l
Jacks Creek main prong view upstream at ULI (USGS topo JC4 ULI); 2001 stream determinations.
Jacks Creek main prong view downstream at ULI (USGS topo JC4 ULI); 2001 stream
determinations.
July 2020 S-31 Supplement 1 2019 Data Year PCS Creeks Report

�• 1
� MAII- I
.t
Jacks Creek main prong view upstream at CZR LLI (USGS topo JC3 LLI); 2001stream determinations.
NOTE: final segment had no breaks above Sandy Landing Road (Fig. Supp. 1-C).
Jacks Creek main prong view downstream at CZR LLI (USGS topo JC3 LLI); 2001 stream
determinations. NOTE: final segment had no breaks above Sandy Landing Road (Fig. Supp. 1-C).
July 2020 S-32 Supplement 1 2019 Data Year PCS Creeks Report

Jacks Creek main prong view upstream at CZR ULI (USGS topo JC2 ULI/Break); 2001 stream
determinations. NOTE: final segment had no breaks above Sandy Landing Road (Fig. Supp. 1-C).
Jacks Creek main prong view downstream at CZR's ULI (USGS topo JC2 ULI/Break); 2001 stream
determinations. Sandy Landing Road crossing in background, JF1 located on other side of road.
July 2020 S-33 Supplement 1 2019 Data Year PCS Creeks Report

ic
41,
iM =
T..-»�
4
16
Jacks Creek main prong view upstream at ULP/LLI (USGS topo JC1 ULP/1-1-I); 2001 stream
determinations. NOTE: main prong final ULP was marked at Sandy Landing Road (Fig. Supp. 1-C)
Jacks Creek main prong view upstream at CZR's ULP/LLI (USGS JC1 ULP/1-1-I); 2001 stream
determinations. NOTE: main prong final ULP was marked at Sandy Landing Road (Fig. Supp. 1-C).
July 2020 S-34 Supplement 1 2019 Data Year PCS Creeks Report

:'AYES AURORA QUADRANGLE
COMMERCE ,��,+`''� y
IETIC SURVEY NORTH CAROLINA-BEAUFORT CO. .06p���v+
^'E 7.5 MINUTE SERIES (TOPOGRAPHIC)
' 3M 33J 4T30"
J t --- -7--._ _ I �38 -- 3� �rrr ri JRv !mac ln.�r 3 s n.;/. 34a 2-670 ODO FEET,7E� 4 ' �1
` t . 3 '22`30' 0,
i
t
{
4' -15
L
/I
n
b { rb°
Al
ilz
c
,
,
3%14
(
" = _
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-4
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o
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rg t0 4't;4 r�v �` . ,
a C�
1 1. `.�7 - i' � !C 1 0/ VM /t i Td f��t/A `��• � -.r\ V- ,4�'�'� � .l�Y'SP
`�` --- ..., ,,. rr ice'•- �S4Jq �U� t �*_ ,—,_��'",�� 4 ;��` ;�
Li
77
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4 /,(I V ' coo j -' ^✓f '[� v ..��1t
,� ���y `� t1Vot0_ �� C i:� �1,-Ihi' {�. j�r�'^t.M i/- � Fh •:.
w/I F
M% r < x �♦,: r`"Fk1',1/�.d'".^i r fYJti , i;
7.
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Creek }S4 , r !
w
. 0Z%
1
July 2020 S-35 Supplement 1 2019 Data Year PCS Creeks Report

EFFECTS OF ALTERNATIVE MINING SCENARIOS ON HYDROLOGY
OF HUDDLES CUT AND CYPRESS RUN WATERSHEDS
(SKAGGS 2006)
July 2020 S-36 Supplement 1 2019 Data Year PCS Creeks Report

EFFECTS OF ALTERNATIVE NHNING SCENARIOS ON HYDROLOGY
OF HUDDLES CUT AND CYPRESS RUN WATERSHEDS
Introduction
PCS is developing plans for mining phosphorus from deposits in Beaufort County
near Aurora, NC. These plans would continue and expand mining activities that have
been conducted in the area since the 1960s. Permits by federal and state agencies (US
Army Corps of Engineers (USACOE) and North Carolina (DENR) require
Environmental Impact Statements (EIS) documenting the effects of proposed mining and
related activities on the environment. Mining involves extraction of phosphate ore from
deposits extending many feet below sea level. The process involves hydraulically and
hydrologically isolating the pit area from its natural watershed. Water from rainfall and
seepage are pumped from the pit and treated before eventual return to surface waters at a
location remote from the natural watershed outlet. This effectively reduces the area of
the watershed feeding its natural outlet, with a consequent reduction of outflow
(subsurface drainage and surface runoff) rates and volumes. The purpose of this report is
to document the results of hydrologic analyses of the impact of various mining scenarios
on the hydrology of two watersheds near Aurora, N.C.
The first watershed is the Huddles Cut watershed on the NCPC tract adjacent to the
existing PCS mining site. The hydrology of the Huddles Cut watershed, which drains
directly to the Pamlico River, was studied in detail by Skaggs and Group
(2001,2002,2003,2004,2005). The study included continuous monitoring of four sub -
watersheds over a 5-year period and the calibration and application of simulation
modeling to describe the hydrology. The study also included two other watersheds on the
NCPC tract, Jacks Creek and Tooley Creek. Inputs to the simulation model
DRAINMOD from this study were used herein to analyze the effects of various mining
alternatives on the hydrology of the Huddles Cut watershed. Results from the Huddles
watersheds were similar to results from the Jacks and Tooley watersheds and are
representative of the relatively small naturally drained basins that comprise the NCPC
tract and most of the Bonnerton tract. Long-term (54 year) simulations were conducted
for each mining scenario considered for the Huddles watershed, and average annual and
monthly outflows were predicted. Results for each year were used to construct
probability distributions for daily, monthly and annual outflows.
The second watershed is Cypress Run located South of Route 33 near Aurora. Cypress
Run is located among, and is representative of, Broomfield Swamp, Bailey Creek and
South Creek watersheds, which are also potential mining sites. Cypress Run is a 3046 ac
watershed with 713 acres located on the slope of the Suffolk Scarp and 2333 acres on the
nearly flat lower coastal plain. The flat land is primarily used for agricultural cropland
(75%) with 25% in managed forest. It is drained with a network of drainage ditches and
outlet canals at various depths and spacings. DRAIN -MOD was developed to simulate the
hydrology of lands with parallel drains such as exist on the flat lands of this watershed.
Inputs were determined for the two major soil types making up this part of the watershed
and DRAIN -MOD was used to simulate the hydrology of the different combinations of
July 2020 S-37 Supplement 1 2019 Data Year PCS Creeks Report

soil, crop (including forest) and drainage treatment. Inputs for the scarp area were
obtained from soil property measurements and from water table measurements conducted
over a 6-month period in 2005. As with the Huddles watershed long-term simulations
were conducted for the many combinations of soils, crop or cover, and drainage
treatments to analyze the hydrologic effects of the various mining alternatives considered
for the Cypress Run watershed.
Methods.
Huddles Cut.
DRAINMOD was used to analyze the hydrologic effects of the various mining
scenarios for the Huddles Cut watershed. Model inputs were determined and the model
validated in a hydrologic study conducted during the period 1999-2005. Results of the
study were reported in detail in annual reports of the "NCPC Stream Monitoring Program
for PCS Phosphate Company, Inc." for years 2000-2006. The reports were prepared by
CZR, Inc., R. Wayne Skaggs and Group, and Donald W. Stanley. The parts of the report
concerning the hydrologic study were prepared by the Skaggs Group. To be consistent
with previous reports, we refer herein to the hydrologic results for the various years as
Skaggs and Group (xxxx), where xxxx is the year of the report. Usually the report dated
for a given year contains results for the previous year, although in the case of hydrology,
cumulative results from several years may be presented in some cases.
Background Data and Model Inputs. The hydrologic study involved 8 sub
watersheds (Figure 1). Four of the sub watersheds were on Huddles Cut, which drains
directly to the Pamlico River, two on Tooley Creek, and two on Jacks Creek. The Jacks
Creek sub watersheds were hydraulically connected and were ultimately analyzed as a
single watershed. Each sub watershed was instrumented to continuously measure flow
rates at the outlet and water table depth at two locations in the catchment (see Figure 2
and Skaggs and Group, 2001). Additional water table wells were installed and monitored
manually. Rainfall was continuously measured and recorded on each site. Soils on the
watersheds were primarily Roanoke, Augusta, Tomotly and associated series. Soil
samples were taken at three depths from pits at multiple locations in each sub watershed
and soil water characteristics were measured in the lab. Saturated hydraulic conductivity
was measured in the field by the auger hole method. These data are reported in detail by
Skaggs and Group (2002) and were used to determine soil property inputs for
DRAE% MOD.
DRAINMOD was originally developed (Skaggs, 1978) to simulate the
performance of parallel drainage systems and their effect on the soil water balance. Its
use for natural watersheds such as those on the NCPC tract required calibration to
determine effective drain depths and spacings that would emulate the natural drainage
processes. This was done on the Huddles sub watersheds by using rainfall data measured
on -site to predict outflows and water table depths for a 32 month (May 1999-December
2001) calibration period. Predicted results were compared to measured values, and the
inputs adjusted, within physically acceptable ranges, to minimize differences. Calibrated
July 2020 S-38 Supplement 1 2019 Data Year PCS Creeks Report

model inputs for soil properties and drainage system parameters for the Huddles 4 sub
watershed are given in Appendix A.
After calibration, the model was tested by comparing predicted with measured
results for a validation period of at least two years for all sub watersheds (Skaggs and
Group, 2005). The model did a good to excellent job of describing the hydrology of all
four Huddles sub watersheds, the Tooley Creek 2 sub watershed and the combined Jacks
Creek 1 and 2 sub watershed (Skaggs and Group, 2005). Performance for the Tooley
Creek 1 sub watershed was only fair, due primarily to loss of record and uncertainty in
flow measurements for that catchment. Examples of the agreement between measured
and predicted cumulative outflow volumes for the entire 5 year observation period are
given in Figure 3 for Huddles 2. Out of the total rainfall of 249 inches for the period,
Figure 1. Schematic of sub watersheds monitored in the NCPC Tract near Aurora, NC
July 2020 S-39 Supplement 1 2019 Data Year PCS Creeks Report

PAMLICO RIVER
HUDDLES CUT
a Huddles 1 .
a05
O - HUDDV GUT
a�a
U a
U
a • Manual Water Table Well
uddles 3
Huddles 2 0 Automatic Water Table Well
•0 Automatic Flow Station
Huddle_
0 �
Tooley 1 Tooley 2
rcb.Fr 90'1 � E
Mk,,
Figure 2. Distribution of outflow stations and water table wells on the Huddles and
Tooley sub watersheds.
measured outflow from Huddles 2 was 63 inches compared to 64 inches predicted. It is
obvious from Figure 3 that predicted outflows were in good agreement with measured
over the entire period. Predicted outflow for the 5-year period was only 1 inch greater
than measured, which amounts to an error of less than 2% on average. Outflows
amounted to 25 percent of rainfall for the period, which is well within published data for
similar forested watersheds in coastal North Carolina (Chescheir et al., 2003). Predicted
monthly outflows are compared to measured values for the 5-year observation period in
Figure 4. Predicted values were in good agreement with measured with an R2 of 0.88 and
a slope of the regression line of nearly 1 (0.96).
Predicted water table depths were generally good agreement with measured
values. An example is shown in Figure 5 for 2003, which was the wettest (highest annual
rainfall) of the years monitored. There was variation among measured water table
depths, which were generally deeper for the higher elevations in the watershed and
shallower (closer to the surface) in the lower elevations. Predicted water table depths
generally fell within the values measured across the watershed.
July 2020 S-40 Supplement 1 2019 Data Year PCS Creeks Report

300
250
t
c 200
c
150
0
a
0 100
U
50
0
Cumulative Measured/Predicted Water Balance for Huddles 2
1999-------2000------------2001--------2002------20032004 ------
----------------------------------------- --PET --------------
Rain
-------------------------------- - - - - --00 ------- ---'------------
�♦ Periods with soil water deficits
Predicted Flow
'\ Measured Flow
5 10 15 20 25 30 35 40 45 50 55 60 65
Months beginning in May 1999
Rain PET Meas Flow - Pred Flow - - - - - Pred ET
Figure 3. Predicted and measured cumulative outflows for Huddles Cut 2 for the 5-year
observation period. Other water balance components are also shown.
7.0
6.0
c
3 5.0
0
>1 4.0
1.0
0.0
DRAINMOD predictions, Huddles Cut 2, 1999-2004
--------------------------------- I
O
y = 0.9568x + 0.0625
RZ = 0.8763
o
O--------------------- e
O
O
............................................................................................................
O o
O O
-o--o° o Qo ----------------------------------------------------------------------------------
O O O
I
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0
Measured monthly outflow, in
♦ Meas-DRAINMOD ----- 1:1 Line Linear (Meas-DRAINMOD)
Figure 4. Predicted versus measured monthly outflows for Huddles 2 over the 5 year
observation period.
July 2020
S-41 Supplement 1 2019 Data Year PCS Creeks Report

Examination of the measured outflow and water table depths over the course of
the monitoring period reveals important information regarding the drainage
characteristics of the watersheds. Figure 6 shows the relationship between flow rate and
average water table depth (water table below the surface indicated by negative values,
depth of surface ponding by positive numbers) for Huddles 2 for 2004. Results indicate
that outflow is primarily a surface runoff phenomenon. Even though there are differences
in surface elevations on these relatively flat watersheds with the natural streams often 1 to
3 feet below the surface elevation, subsurface drainage is relatively small. Flow rates are
close to zero for average water table depths greater than 10 inches. These flow
characteristics are well described by the calibrated DRAINMOD as indicated by Figures
3-5. Results are described in more detail by Skaggs and Group (2005).
its]
0
E- -10
s -20
CL
p -30
-40
-50
L
-60
OMI
M
.E
Huddles 4, PCS Phosphate, 2003
Day of the Year
H4CW1 ........ H4CW2 ■ HOW
♦ H4MW2 ♦ H4MW3 Predicted
Figure 5. Predicted and measured water table depths on Huddles 4 during 2003. Note
that the predicted water table is generally between that measured on the relative high
ground (H4CW2) and that measured at a relatively lower surface elevation (H4CW 1).
July 2020 S-42 Supplement 1 2019 Data Year PCS Creeks Report

AVERAGE WTD (H2CW1 & H2CW2) vs FLOW RATE,
Huddles 2, 2004
Flow = 0.8 (1.487AWTD)(1.023AWTD^10)
°
0
o Measured Approx Fit
o °
0
5
4 T
ai
3 L
3
0
0
12 -9 -6 -3 0 3 6
Average Water Table Depth, in
Figure 6. Relationship between outflow rates and average water table depth for Huddles
2. Note water table below ground surface is indicated by negative numbers while ponded
water depth is denoted by positive numbers.
Long-term simulations were conducted for Huddles Cut 2, Tooley Creek 2 and
Jacks Creek 1&2 by using the calibrated DRAIN -MOD inputs with local weather data for
years 1951-2003. Annual outflows for each year of the 53 year simulations were ranked
and plotted as shown in Figure 7 for Jacks Creek 1&2. Predicted annual outflows varied
from 1 to 31 inches for Jacks Creek with a median of 12.5 inches. Measured outflows are
also plotted in Figure 7. Note that the observed annual outflows over the six year
observation period for Jacks Creek are well distributed over the predicted range from
nearly the lowest flow in 2002 to the highest in 53 years in 2003. This means that the
model was tested for a complete range of weather conditions expected at this location.
July 2020 S-43 Supplement 1 2019 Data Year PCS Creeks Report

35
30
25
3
,° 20
O
15
Q 10
5
0
Jacks Creek 1 & 2, PCS Phosphate, 1951-2004 Simulation
2003
---------------------- --------------------------------------------------------------------------
2005
1------------------------------------------ 2000----------... ................................
2002
0 20 40 60 80
Percent of Years Flow Equaled or Exceeded
Figure 7. Frequency distribution of predicted annual outflows for a 55 year (1951-1955)
simulation for Jacks Creek 1&2. Measured annual flows for six years of observations, as
plotted on the graph, span the range of predicted outflows for the 55 year period.
Predicted frequency distributions for Huddles Cut 2, Tooley Creek 2 and Jacks
Creek 1&2 are plotted for comparison in Figure 8. Results are very similar with very
little difference between predicted outflows from the watersheds at any probability level.
This indicates that the hydrologic effects of mining, so far as annual outflows are
concerned, will be similar for these watersheds, and, by extrapolation, for many of the
small coastal watersheds in the NCPC and similar tracts.
100
July 2020 S-44 Supplement 1 2019 Data Year PCS Creeks Report

32
24
0
w
0 16
0
ZI
O Tooley Creek 2
❑ Jacks Creek 1 & 2
♦ Huddles Cut 2
10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 8. Frequency distributions of predicted annual outflows for Huddles Cut 2,
Tooley Creek 2 and Jacks Creek 1&2 for the 53-year period 1951-2003.
Methods for Modeling the Hydrology of the Huddles Cut Watershed. The
hydrology of the Huddles Cut watershed was modeled using DRAINMOD. Our
objective was to consider the whole watershed rather than the sub watersheds
individually, as was done in our previous study. The current watershed was considered to
be the "pre -developed" condition. It is not the same as the watershed we originally
studied as indicated in Figure 9. Based on an examination of Air Photos, most of the
original sub watersheds Huddles I and Huddles 2, and about half of Huddles 3, have
already been developed (prepared for mining) and thereby removed from the watershed.
The existing, "pre -developed" or pre -mined watershed is shown in Figure 10. We
analyzed the hydrology of this watershed by considering it to be made up of a high
ground section, a low ground section and the marsh based on an examination of Lidar
elevation data. DRAINMOD inputs (Appendix A) developed for the Huddles 4 sub
watershed, which makes up a good part of the existing watershed, were used for the high
ground section. These are the same soil property inputs as were used in the previous
study for Huddles 2 with somewhat deeper more closely spaced drains as determined by
calibration. The same inputs with shallower drains (to reflect the lower landscape
position), were used for the low ground section of the watershed. The high ground
section had one agricultural area (29 acres, Figure 10). This section was modeled as an
agricultural field using the same inputs as were used for the Roanoke soil in agricultural
fields south of Route 33 (Appendix A). Runoff and shallow subsurface flow from the
high ground section was assumed to flow through the low ground section to the marsh.
The marsh was treated as part of the outlet.
July 2020 S-45 Supplement 1 2019 Data Year PCS Creeks Report

Simulations were conducted for a 54 year period (1951-2004) for each proposed
mining alternative. The proposed mining alternatives are shown schematically in Figures
10 through 14. The mining alternatives are given in Table 1. The areas shown are the
areas remaining in the watershed and draining to the marsh after mining.
Table 1. Mining alternatives and corresponding areas draining to the outlet.
Mining Treatment
Area, Acres
Reference
Pre -Development or current
677
Figure 10
Dra line Plan
580
Figure 11
SCRA Plan
230
Figure 12
SRA Plan
160
Figure 13
Preferred Plan
4.7
Figure 14
The primary objective of the simulations was to determine how the various
mining alternatives would affect outflows from the watershed. Outflows (the sum of
surface runoff and subsurface drainage) for each section were predicted and stored on a
day-by-day, monthly and annual basis for the 54-year simulation period for each mining
alternative. The model outputs for flow were in units of depth (cm). These values were
converted to inches, multiplied by the relevant watershed area and summed to get flow in
acre -inches per day, month, and year for every year of the simulation period. Results
were then plotted, summarized, and analyzed to determine effects of various mining
alternatives on outflows from the watersheds.
Old Huddles Cut Watersheds
In -'ative to Current
relopment Condition
Figure 10. Current Huddles Cut watershed (shaded area) and estimated relative positions
of the old Huddles Cut sub watersheds.
July 2020 S-46 Supplement 1 2019 Data Year PCS Creeks Report

uddles Cut Watershed
Pre -Development
High Ground Forest (523 ac)
High Ground Agriculture (29 ac)
Low Ground Forest (125 ac)
Tidal Marsh (30 ac)
Figure 11. Huddles Cut Watershed under existing conditions (before proposed mining).
addles Cut Watershed
Dragline Plan
High Ground Forest (431 ac)
] High Ground Agriculture (29 ac)
Low Ground Forest (120 ac)
Tidal Marsh (30 ac)
Figure 12. Huddles Cut Watershed showing the undisturbed area (shaded) after
development using the Dragline Plan
July 2020 S-47 Supplement 1 2019 Data Year PCS Creeks Report

uddles Cut Watershed
SCRA Plan
High Ground Forest (129 ac)
Low Ground Forest (101 ac)
Tidal Marsh (30 ac)
Figure 13. Huddles Cut Watershed showing the undisturbed area (shaded) after
development using the SCRA Plan
addles Cut Watershed
SRA Plan
High Ground Forest(92 ac)
Low Ground Forest (68 ac)
Tidal Marsh (28 ac)
Figure 14. Huddles Cut Watershed showing the undisturbed area (shaded) after
development using the SRA Plan
July 2020 S-48 Supplement 1 2019 Data Year PCS Creeks Report

uddles Cut Watershed
Preferred Plan
High Ground Forest (1.0 ac)
Low Ground Forest (0.9 ac)
Tidal Marsh (2.8 ac)
Figure 15. Huddles Cut Watershed showing the undisturbed area (shaded) after
development using the SRA Plan
Cypress Run.
Long-term flow rates from the Cypress Run watershed were determined from
DRAINMOD simulations of the different soil, land cover, drainage designs, and
topographic conditions on the watershed. The total flow from the watershed was
calculated as the area weighted sum of the flows from different conditions on the
watershed. Input data for the DRAINMOD simulations were determined from field
measurements of soil properties and drainage parameters, and from calibrating the model
to agree with field measured water tables and flow rates.
Background Data and Model Inputs. The Cypress Run watershed is 3046 ac
and includes two distinct topographies (Figure 16). The western section (713 ac) of the
watershed is located on the Suffollk Scarp, the sloping Pleistocene shoreline that
separates the inner coastal plain from the outer coastal plain. Land on the scarp section
of the watershed slopes down from west to east at a rate of 50 ft per mile. The
topography of eastern section (2333 ac) of the watershed is typical of the outer Coastal
Plain with land slopes about 1 ft per mile.
July 2020 S-49 Supplement 1 2019 Data Year PCS Creeks Report

Figure 16. Diagram of the Cypress Run watershed overlaying a USGS topographic map.
The diagram shows the Scarp section and the Flatland section of the watershed and the
locations of wells and weirs for monitoring the hydrology of representative conditions.
Over 95% of the land in the scarp section is covered with forest vegetation, with the
remaining land is in roads and residential land use. Predominant soil types in this section
are Leon sand and Torhunta sandy loam. Surface drainage from the scarp section is by
overland flow to 5 to 20 ft wide natural drainage ways about 0.5 to 1 foot deep.
About 75% of the land in the flatland section is in agricultural row crops with the
remaining land in managed forest. All of the crop land is drained by 1 to 3 ft deep field
ditches at spacings ranging from 90 to 230 ft. Most of the cropland is planted in a two
year rotation of corn, wheat, and soybeans. About 10% of the managed forest in the
flatland section had ditch drainage. Predominant soil types in the flatland section are
Roanoke fine sandy loam and Tomotley fine sandy loam. Drainage from the fields and
field ditches flows to main canals about 6 ft deep and 30 ft wide. Stream channels near
the outlet of the watershed reach depths of 10 ft.
Field Measurments. Undisturbed soil cores were taken at two depths from pits at
multiple locations on the watershed. The pits located on the flatland section were on the
Roanoke and Tomotley soils for both agriculture and forest landuses. Pits were also
located on the scarp section in both the Leon soils and the Torhunta soils. Soil water
characteristic curves for the soil samples were measured in the lab using standard
methods. The soil water characteristic data are plotted in Appendix 2.
July 2020 S-50 Supplement 1 2019 Data Year PCS Creeks Report

Saturated hydraulic conductivity was measured in the field using the auger hole
method. At least ten measurements were collected for each combination of Roanoke and
Tomotley soil with agriculture and forest land uses on the flatland section and for the
Leon and Tornhunta soils on the scarp section. The calculated saturated hydraulic
conductivity values for each test are given in Appendix 3.
In -field measurements of drainage rates and water table depths were recorded for
a two month period (March and April, 2003) on agricultural fields in the flatland section.
Measurements were made on both Tomotley and Roanoke soils. Three adjacent field
ditches were selected on each soil type. Two water table wells were installed at each site:
one at the mid point between the first and second field ditches, and the other at the mid
point between the second and third field ditches. The wells were equipped with
continuous water level recorders. V-notch weirs were located in each ditch and the water
levels were continuously measured behind the weirs to calculate flow rates. The data
collected from these sites were used to calibrate DRAINMOD for the flatland soils
(Appendix 4).
Water table depths were measured in wells at ten locations on the scarp section of
the watershed (Figure 16). The wells were located such that the water table depths could
be recorded for different topographic conditions on each soil type (Leon and Torhunta).
Since the scarp was dissected by natural drainage ways, the wells were located on high
ground between the drainage ways and on low ground near the drainage ways (see
Appendix 4 for details). The wells were equipped with continuous water level recorders
and measurements were recorded from January through June, 2005. The data collected
from these sites were used to calibrate DRAINMOD for the soil and topographic
conditions on the scarp section.
Methods for Modeling the Hydrology of the Cypress Run Watershed. The
hydrology of Cypress Run watershed was modeled using multiple DRAINMOD
simulations. The basic procedure for simulating outflow from the entire watershed was
to: 1) divide the watershed into fields having different soil type, land use, drainage
designs, and topographic conditions, 2) select input parameters that would represent the
different conditions, 3) make long-term DRAINMOD simulations for each field, 4)
multiply predicted flow depths by the land area to get predicted outflows (in acre inches)
for each field or combination of fields having the same soil, land use and drainage
treatment, and 5) sum all of the daily, monthly and yearly flows to obtain values for the
entire watershed.
Flatland Section Simulations. The use of DRAINMOD to simulate the hydrology
of the fields in the flatland section was routine, since the model was specifically
developed for the parallel drain conditions present in the flatland section. The flatland
section was divided into 65 fields (Figure 17). The different conditions in the fields were
various combinations of soil type, land -use, ditch (drain) depth, and ditch (drain) spacing.
July 2020 S-51 Supplement 1 2019 Data Year PCS Creeks Report

Figure 17. Discretization of Cypress Run watershed into fields
The relative areas and distributions of soil type and land use were determined from the
Soil Survey, Geographic (SSURGO) GIS database, and the 1998 color infrared digital
orthophoto quarter quadrangles (DOQQ). The relative areas and distributions of drain
depths and drain spacings were determined from field measurements and the DOQQ.
Five catagories of drain depths (0.3, 0.8, 2.0, 2.5, and 3.2 ft) and drain spacings (92, 133,
183, 233, and 467 ft) were selected to represent the drainage configurations on the
flatland section. A combination of soil type, land -use, drain depth, and drain spacing was
selected to represent each field (Table 2).
Lateral seepage from the fields to the main canals was also considered since the
main canals were much deeper (6 ft) than the field ditches (0.3 to 3.2 ft). Seepage would
occur to the deep ditches even if the water table moved below the bottom of the field
ditches. The seepage rates will depend on the depth of the main canal and the distance
from the canal to the midpoint of the field. Since field widths varied, two values were
used for the distance from the canal to the midpoint of the field. For most of the fields,
the main canal was assumed to be 6 ft deep. Two forested fields (47 and 51 in Figure 17)
were located adjacent to the 6 ft deep canals and the deeper (10 ft deep) stream channels
near the outlet of the watershed. These fields did not have field or lateral ditches and
were simulated with 6 ft deep ditches spaced 1700 ft apart and with lateral seepage to a
10 ft deep ditch (Table 2).
July 2020 S-52 Supplement 1 2019 Data Year PCS Creeks Report

The fields in Table 2 were consolidated by summing together field areas for fields
with the same land use, soil type, and drainage treatment. DRAINMOD input data sets
were prepared for each of the 25 sets of conditions that occurred on the flatland area
(Table 17). Drainage parameters and soil properties used for the DRAE MOD
simulations are shown in Appendix 5.
Scarp Section Simulations. The use of DRAP MOD to simulate the hydrology of
the fields in the scarp section was not a routine use of the model, since the land on the
scarp has a relatively constant slope of about 50 ft/mile. This condition will result in two
situations. First, groundwater in the hill slope will slowly seep from the scarp to the
flatlands. Second, surface water and shallow ground water from the upslope areas will
contribute flow to the down slope areas.
The slow seepage from the scarp to the flatland was simulated by assuming that
the scarp was drained by very widely spaced deep drains. This assumption was possible
since Durham Creek has incised a valley to the west of the scarp (see Figure 16). This
results in parallel drain situation with Durham Creek acting as one drain and the western
most ditches of the flatlands as the other. The elevation of the midpoint between the
drains is about 30 ft above the drains and the spacing between the drains is about 8000 ft.
DRAINMOD was used to simulate the hydrology of this drainage configuration over a 54
year weather record from Belhaven, NC. The average annual subsurface drainage rate
was 0.52 in/yr and this rate was assumed to be the slow seepage rate from the scarp to the
flatland. Drainage parameters and soil properties used for the DRAINMOD simulations
of the slow seepage are shown in Appendix 6.
Surface and shallow subsurface drainage from the scarp was simulated by using the
contributing area routines in DRAMMOD. The scarp was divided into two sections: a
high ground section and a low ground section. The high ground section was assumed to
be the higher ground between the natural drainage ways that carry the surface and
shallow subsurface drainage to the flatlands. The soil properties used for the high ground
were those measured for the Leon soil which occupied the higher elevations of the scarp.
The drainage configuration was assumed to be deep drains and wide spacings. Since the
drain depth and spacing could not be directly measured, they were determined by
simulating various depths and spacings until the simulated water table depths agreed with
those measured in the high ground wells on the scarp from January through June of 2005
(Figure 18). Rainfall data collected at the Jacks Creek site for the NCPC study were used
for the weather input data along with daily maximum and minimum temperature data
recorded at the Belhaven Weather station. Hourly surface and subsurface drainage rates
predicted by DRAINMOD were saved in a file and used as input for simulating the low
ground. Drainage parameters and soil properties resulting from this calibration procedure
are shown in Appendix 7.
July 2020 S-53 Supplement 1 2019 Data Year PCS Creeks Report

Table 2. Characteristics of fields shown in Figure 17.
Field #
Area
ac
Soil
Land use
Ditch Depth
ft
Spacing
ft
0
23.79
TO
forested
2.0
467
1
69.30
RO
forested
0.3
183
2
74.86
TO
agr-corn
2.5
183
3
22.56
TO
agr-soy
3.2
233
4
2.14
TO
forested
0.3
467
5
19.75
RO
agr-soy
2.5
133
6
21.03
RO
forested
2.0
133
7
16.39
TO
forested
0.3
233
8
15.45
RO
forested
0.3
467
9
40.25
TO
agr-soy
2.5
183
10
82.07
RO
a r-corn
2.5
183
11
36.92
RO
agr-soy
2.5
133
12
5.13
RO
agr-corn
2.5
133
13
7.72
RO
forested
0.3
133
14
10.97
RO
forested
2.0
467
15
34.27
RO
agr-soy
2.5
467
16
35.81
TO
agr-soy
2.5
183
17
33.95
TO
agr-soy
2.5
133
18
36.32
TO
agr-corn
2.5
133
19
66.32
TO
agr-soy
2.5
133
20
28.82
TO
agr-soy
2.5
133
21
86.41
TO
agr-soy
2.5
133
22
7.14
TO
a r-corn
0.8
467
23
91.45
RO
a r-corn
2.5
133
24
79.81
TO
a r-corn
2.5
133
25
43.42
RO
agr-soy
2.5
133
26
110.74
RO
agr-soy
2.0
183
27
22.26
RO
agr-corn
2.0
183
28
37.07
RO
agr-soy
2.5
133
29
9.99
RO
a r-corn
2.0
133
30
26.33
RO
agr-soy
2.0
233
31
28.15
RO
agr-corn
2.5
133
32
47.89
TO
agr-corn
2.5
133
33
26.29
RO
agr-corn
2.5
467
34
54.62
TO
a r-corn
2.0
133
35
12.46
TO
a r-corn
2.5
133
36
10.35
TO
a r-corn
2.5
183
37
26.48
TO
agr-soy
2.0
133
38
14.44
RO
agr-corn
2.5
133
39
16.48
TO
agr-soy
2.5
133
40
136.61
RO
forested
0.3
467
41
41.76
TO
agr-soy
2.5
133
42
66.17
TO
agr-soy
2.0
133
43
11.73
RO
agr-corn
2.0
183
44
72.69
TO
agr-corn
2.5
133
45
20.19
TO
agr-soy
2.0
183
46
8.71
TO
agr-corn
3.2
183
47
183.67
TO
forested
0.8
183
48
16.94
TO
agr-soy
2.5
183
49
3.05
TO
forested
2.0
233
50
2.48
RO
forested
2.0
233
51
99.07
TO
forested
0.3
467
52
4.65
TO
agr-soy
0.8
467
53
5.71
RO
agr-soy
0.8
467
54
3.23
TO
forested
0.3
467
55
30.57
TO
agr-soy
3.2
92
56
38.99
TO
agr-corn
3.2
92
57
22.13
RO
agr-corn
2.0
183
58
30.36
TO
agr-corn
2.0
92
59
23.06
TO
agr-corn
2.0
133
60
10.48
TO
a r-corn
2.0
183
61
9.90
TO
a r-corn
2.5
183
62
32.68
TO
agr-corn
2.0
133
63
17.75
TO
agr-soy
2.0
133
64
5.16
TO
forested
2.0
233
65
210.52
TR
scarp -forest
0.7
667
66
1 169.01
1 LO
scarp -forest
8.3
667
67
1 150.15
1 TR
scarp-forestj
0.7
667
68
1 182.86
1 LO
scarp-forestj
8.3
667
July 2020 S-54 Supplement 1 2019 Data Year PCS Creeks Report

Table 3. Characteristics used in files that represent the consolidation of fields on the
Cypress Run watershed.
File Name
Land use
Soil
Ditch Depth
ft
Spacing
ft
Area
ac
RO60C40S
agr-corn
RO
2.0
133.3
9.99
RO60C55S
agr-corn
RO
2.0
183.3
166.87
RO75S40L
agr-soy
RO
2.5
133.3
276.36
RO75S55L
agr-soy
RO
2.5
183.3
82.08
RO75C140S
agr-corn
RO
2.5
466.7
60.56
RO25S140S
agr-soy
RO
0.8
466.7
5.71
RO60C70L
agr-corn
RO
2.0
233.3
26.33
RO10F140L
forested
RO
0.3
466.7
229.10
RO60F40L
forested
RO
2.0
133.3
21.03
RO60F70S
forested
RO
2.0
233.3
2.48
RO60F140L
forested
RO
2.0
466.7
10.97
TO25S140L
agr-soy
TO
0.8
466.7
11.80
TO60C27S
agr-corn
TO
2.0
91.7
30.36
TO60S40S
agr-soy
TO
2.0
133.3
220.78
TO60C55L
agr-corn
TO
2.0
183.3
30.68
TO75C40L
agr-corn
TO
2.5
133.3
522.96
TO75S55S
agr-soy
TO
2.5
183.3
188.12
TO95S27S
agr-soy
TO
3.2
91.7
69.56
TO95C55L
agr-corn
TO
3.2
183.3
8.71
TO95S70L
agr-soy
TO
3.2
233.3
22.56
TO180F510D
forested
TO
6.0
1700.0
183.68
TO10F70L
forested
TO
0.3
233.3
16.39
TO180F500D
forested
TO
6.0
1666.7
104.45
TO60F70S
forested
TO
2.0
233.3
8.22
TO60F140L
forested
TO
2.0
466.7
23.79
SCARPT1
scarp -forest
TR
0.71
666.7
213.09
SCARPL1
scarp -forest
LO
8.31
666.7
499.50
July 2020 S-55 Supplement 1 2019 Data Year PCS Creeks Report

10
0
P
W
~ -20
L
-30
-40
1/1 2/1 3/3 4/3 5/4 6/4 7/5
Day of Year
Figure 18. Comparison of simulated water table depth to water table depth measured in
wells HGL1 and HGL2 on the high ground Leon soil on the scarp at Cypress Run
Watershed.
The soil properties used for the low ground were those measured for the Torhunta
soil which occupied the lower elevations of the scarp. The drainage configuration was
assumed to be very shallow drains and wide spacings. As with the high ground
simulations, the drain depth and spacing were determined by simulating various depths
and spacings until the simulated water table depths agreed with those measured in the low
ground wells on the scarp from January through June of 2005 (Figure 19). Drainage
parameters and soil properties resulting from this calibration procedure are shown in
Appendix 8.
For both the high ground and low ground simulations, the parameters for lateral seepage
were set such that the average annual seepage rate equaled the slow seepage rate
calculated in the initial scarp simulations. Total flow from the scarp was calculated as the
simulated depth of flow for the combined surface and shallow subsurface drainage from
the low ground simulation (which included the surface and shallow subsurface drainage
from the high ground) multiplied by the area of the low ground section plus the slow
seepage rate multiplied by the area of the entire scarp section.
July 2020 S-56 Supplement 1 2019 Data Year PCS Creeks Report

10
M
-30
-40
1/1 2/1 3/3 4/3 5/4 6/4 7/5
Day of Year
Figure 19. Comparison of simulated water table depth to water table depth measured in
wells LGT1 and LGT2 on the low ground Torhunta soil on the scarp at Cypress Run
Watershed.
The hydrology of each field in the flat land and for each condition on the scarp
was simulated by DRAINMOD using the 54 year weather data set from Belhaven, NC.
The total flow from the Cypress Run watershed was calculated by summing the products
of the simulated depths of flow and the area of each condition on the flatland and then
adding the flow from the scarp determined by the method described in the previous
paragraph.
Simulations ofDifferent Mining Alternatives. The flow depth data files calculated
by the long-term simulations of each condition on the scarp and flatland were used to
determine total flow from the different mining alternatives. The proposed mining
alternatives are shown schematically in Figures 20 through 23. The mining alternatives
considered are:
1. The Intermediate Plan (Figure 20)
2. SCRA Plan (Figure 21)
3. The No Action Plan (Figure 22)
4. Preferred Plan (Figure 23)
July 2020 S-57 Supplement 1 2019 Data Year PCS Creeks Report

For each mining alternative, the undisturbed area after mining was distributed
appropriately among the drainage, soil, and land -use conditions that existed prior to
mining. The total flow from each mining alternative was determined by multiplying the
flow depth of each condition by the area of that condition existing after mining and then
summing the resulting flow volumes. Part of the scarp section was converted to a work
lot in the Preferred Plan, the SCRA Plan and the Intermediate Plan. For these plans, an
additional DRAINMOD simulation was performed to calculate flow from this new
condition. The work lot was simulated with a slowly permeable soil surface layer and no
vegetation. Drainage parameters and soil properties used for the DRAII MOD
simulations of the work lot are shown in Appendix AH.
ass Run Watershed (3046 ac)
sturbed Area after
nediate Development (1772 ac)
sturbed Area within
ass Run Watershed (531 ac)
loped Work Lot within
;ss Run Watershed (125 ac)
1.
Figure 20. South of Rt33 area map showing the undisturbed area after mining
(development) using the Intermediate Plan and the undisturbed area within the
Cypress Run Watershed.
July 2020 S-58 Supplement 1 2019 Data Year PCS Creeks Report

ess Run Watershed (3046 ac)
sturbed Area after
A Development (2631 ac)
sturbed Area within
ess Run Watershed (715 ac)
doped Work Lot within
ess Run Watershed (98 ac)
Figure 21. South of Rt33 area map showing the undisturbed area after mining
(Development) using the SCRA Plan and the undisturbed area within the
Cypress Run Watershed.
L
1
0 Cypress Run Watershed (3046 ac)
Undisturbed Area after
❑ No Action Development (3110 ac)
Isolated Areas not Included
Undisturbed Area within
❑ Cypress Run Watershed (957 ac)
Isolated Areas not Included
Figure 22. South of Rt33 area map showing the undisturbed area after mining using the
No Action Plan and the undisturbed area within the Cypress Run Watershed.
July 2020 S-59 Supplement 1 2019 Data Year PCS Creeks Report

ess Run Watershed (3046 ac)
sturbed Area after
erred Development (1475 ac)
sturbed Area within
ess Run Watershed (532 ac)
(loped Work Lot within
ess Run Watershed (98 ac)
Figure 23. South of Rt33 area map showing the undisturbed area after mining using the
Preferred Plan and the undisturbed area within the Cypress Run Watershed.
For each mining alternative, the undisturbed area after mining was distributed
appropriately among the drainage, soil, and land -use conditions that existed prior to
mining. The total flow from each mining alternative was determined by multiplying the
flow depth of each condition by the area of that condition existing after mining and
summing the resulting flow volumes. Part of the scarp section was converted to a work
lot in the Preferred Plan, the SCRA Plan and the Intermediate Plan. For these plans, an
additional DRAINMOD simulation was performed to calculate flow from this new
condition. The work lot was simulated with a slowly permeable soil surface layer and no
vegetation. Drainage parameters and soil properties used for the DRAII MOD
simulations of the work lot are shown in Appendix 8.
July 2020 S-60 Supplement 1 2019 Data Year PCS Creeks Report

Results
Huddles Cut
Flow frequency diagrams for predicted annual flows are plotted in Figure 24 for
each mining alternative. A summary of the results is given in Table 4. For current (pre -
mining) conditions, the mean predicted annual flow is 818 ac ft per year. On average
annual flows can be expected to exceed 1435 ac ft once in 10 years (90t' percentile), and
to be less than 294 ac ft per year once in 10 years (10t' percentile).
All of the mining scenarios reduce the predicted annual flows as shown in Figure 24 and
Table 4. The Dragline plan has the minimum effect with a predicted mean annual
outflow of 711 ac ft, about 86% of the annual flow before mining. The 90t' percentile
flow was 1244 ac ft, about 87% of the 1435 ac ft predicted for current conditions. These
predicted reductions are consistent with the percentage reduction in watershed area. For
the dragline plan the contributing watershed area after mining would be 610 acres which
is 86% of the current watershed area. Thus the predicted effects on annual outflows of
reducing watershed size are roughly proportional to the area reduced, as expected. The
SRA plan would reduce the contributing watershed area to 187 ac or 26% of the current
watershed area. Accordingly the predicted mean annual outflow was 217 ac ft or 27% of
that predicted for current conditions. Some of the watersheds have larger predicted
annual outflow than others, but the differences are not great, so the reduction in predicted
annual flow is nearly proportional to the reduction in watershed area. Note that the
preferred plan would result in mining nearly all of the watershed area (5 acres remaining,
Table 4) and small predicted annual outflows, compared to the pre -mined condition.
July 2020 S-61 Supplement 1 2019 Data Year PCS Creeks Report

2000
1800
1600
1400
r
Drag
Figure 24. Frequency distribution of predicted annual outflows for 54 year (1951-2004)
simulations of pre -mining and four mining scenarios for the Huddles Cut Watershed.
Table 4. Frequency distribution statistics for predicted annual outflows for 54 year
(1951-2004) simulations of the pre -mined and four mining scenarios on the Huddles Cut
Watershed.
Total PreDev Pref SRA SCRA Drag
Annual Flow Volume (ac-ft)
Minimum 22 0 6 8 20
5th Percentile 194 1 50 69 169
10th Percentile 294 2 76 105 254
25th Percentile 498 3 132 182 433
Median 728 5 193 267 634
75th Percentile 1122 8 300 416 975
90th Percentile 1435 10 379 524 1244
95th Percentile 1705 11 451 624 1480
Maximum 1822 12 484 670 1582
Mean 818 5 217 300 711
Area of Watershed (ac)
707 5 187 259 610
July 2020 S-62 Supplement 1 2019 Data Year PCS Creeks Report
July 2020 S-62 Supplement 1 2019 Data Year PCS Creeks Report

Frequency distributions of predicted monthly outflows are shown in Figure 25 and
Table 5. Note that the 25t' percentile predicted flows are zero for the current condition
and for all mining scenarios (Table 5). This means that monthly outflows for these small
coastal watersheds are zero in over 25% of the months. Typically these would be
summer months when ET is greater than rainfall. The distributions plotted in Figure 25
lump predicted results for all months together. Results for specific months are discussed
subsequently.
Results for predicted daily flows are plotted in Figure 26 and summarized in Table 6.
Median daily outflows are zero for current conditions and all mining plans. This means
that predicted flows were zero for more than 50% of the days for the 54 year simulation.
Results in Figure 26 indicate that flows are expected to be close to zero for about 60 to 70
% of days for all mining plans, as well as, for current conditions.
Outflows from small coastal watershed, both naturally and artificially drained, vary
seasonally with the majority of drainage occurring in the months of December, January,
February and March. Flow frequency distributions by month, and the effect of the
various mining scenarios on predicted outflows, are shown in Figures 27-38 for the
Huddles Cut watershed. These results show that flow in January, February, and March
occurs in about 90 percent of the years. In April and December flow was predicted to
occur in about 60 percent of the years, and in only 30 to 45 percent of the years for the
months of May through November. On the other hand some of the largest monthly and
daily flows occur in August, September, and October as the result of hurricanes and
tropical storms (Figures 34-36). The effect of the various mining scenarios on outflows
during a specific month is roughly the same as predicted for annual values, with the
monthly flow, for those months in which flow occurred, being reduced by about the
percentage of land area removed from the watershed.
July 2020 S-63 Supplement 1 2019 Data Year PCS Creeks Report

1000
900
800
700
$ 600
ca
c 500
U_
400
s
o 300
200
100
0
-100
PreDev
LE ra
SCRA
SRA
Pref
0 1 10 100
Percent of Months Flow Equal or Exceeding
Figure 25. frequency distribution of predicted monthly outflows for 54 year (1951-2004)
simulations of pre -mining and four mining scenarios at Huddles Cut Watershed.
Table 5. Frequency distribution statistics for predicted monthly outflows for 54 year
(1951-2004) simulations of the pre -mining and four mining scenarios at Huddles Cut
Watershed.
Total
PreDev
Pref
SRA
I SCRA
Drag
Monthly Flow Volume (ac-ft)
Minimum
0.0
0.0
0.0
0.0
0.0
5th Percentile
0.0
0.0
0.0
0.0
0.0
10th Percentile
0.0
0.0
0.0
0.0
0.0
25th Percentile
0.0
0.0
0.0
0.0
0.0
Median
11.9
0.1
2.7
3.8
10.7
75th Percentile
105
0.7
28
38
91
90th Percentile
210
1.4
56
77
184
95th Percentile
264
1.8
69
96
228
Maximum
908
5.9
236
1 326
783
Mean
68
0.5
18
1 25
59
Area of Watershed (ac)
707
5
1 187
1 259
610
July 2020 S-64 Supplement 1 2019 Data Year PCS Creeks Report

240
200
160
0 120
u_
d
i 80
d
40
0
-40
PreDev o
b
Drag
0
0
0
SCRA o
SRA
Pref
0.001 0.010 0.100 1.000 10.000 100.000
Percent of Days Flow Equaled or Exceeded
Figure 26. Frequency distribution of predicted mean daily flow rates for 54 year (1951-
2004) simulations of pre -mining and four mining scenarios at Huddles Cut Watershed.
Table 6. Frequency distribution of predicted daily flow rates for 54 year (1951-2004)
simulations for pre -mined (PreDev) conditions and four mining scenarios at Huddles Cut
Watershed.
PreDev
Pref
SRA
SCRA
Drag
Average Daily Flow Rate (cfs)
Minimum
0.00
0.00
0.00
0.00
0.00
5th Percentile
0.00
0.00
0.00
0.00
0.00
10th Percentile
0.00
0.00
0.00
0.00
0.00
25th Percentile
0.00
0.00
0.00
0.00
0.00
Median
0.00
0.00
0.00
0.00
0.00
75th Percentile
0.32
0.01
0.19
0.28
0.31
90th Percentile
4.87
0.02
0.89
1.19
4.06
95th Percentile
5.37
0.03
1.23
1.70
4.54
Maximum
226
2
60
1 83
195
Mean
1.13
0.01
0.30
1 0.41
0.98
Area of Watershed (ac)
707
5
1 187
1 259
610
July 2020 S-65 Supplement 1 2019 Data Year PCS Creeks Report

500
450
400
350
300
3
LL 250
a
s
c 200
0
150
100
50
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 27. Distribution of predicted January outflows over a 54 year period for pre -
mining (PreDev) and four mining scenarios on Huddles Cut Watershed.
500
450
400
350
300
3
LL 250
a
r
c 200
0
150
100
50
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 28. Distribution of predicted February outflows over a 54 year period for pre -
mining (PreDev) and four mining scenarios on Huddles Cut Watershed..
July 2020 S-66 Supplement 1 2019 Data Year PCS Creeks Report

500
450
400
350
300
3
LL 250
a
s
c 200
0
150
100
50
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 29. Distribution of predicted March outflows over a 54 year period for pre -mining
(PreDev) and four mining scenarios on Huddles Cut.
500
April
450
400
350
6 300
3
LL 250
a PreDev
r
c 200
0
150
Drag
100
SC
50
S
=Pref
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 30. Distribution of predicted April outflows over a 54 year period for pre -mining
(PreDev) and four mining scenarios on Huddles Cut Watershed.
July 2020 S-67 Supplement 1 2019 Data Year PCS Creeks Report

500
May
450
400
350 PreDev
300
3
LL 250
a
s
c 200
0 Dra
150
SCRA
100
SR
50
Pre
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 31. Distribution of predicted May outflows over a 54 year period for pre -mining
(PreDev) and four mining scenarios on Huddles Cut Watershed.
500
450
PreDev
400
350
300
3
LL 250
a
s
c 200
0
150
100
SCRA
50
June
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 32. Distribution of predicted June outflows over a 54 year period for pre -mining
(PreDev) and four mining scenarios on Huddles Cut Watershed.
July 2020 S-68 Supplement 1 2019 Data Year PCS Creeks Report

500
July
450
400
PreDev
350
300
3 Dra
�—°° 250
a
c 200
0
SCRA
150
S
100
50
Pref
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 33. Distribution of predicted July outflows over a 54 year period for pre -mining
(PreDev) and four mining scenarios on Huddles Cut Watershed.
500
PreDev = 539 August
450
400
PreDev
350
R 300
3 Dra
�° 250
a
c 200
SCRA
150
100 - �% A
S
50
Pref
0
!LN
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 34. Distribution of predicted August outflows over a 54 year period for pre -
mining (PreDev) and four mining scenarios on Huddles Cut Watershed.
July 2020 S-69 Supplement 1 2019 Data Year PCS Creeks Report

500
PreDev = 764
Drag =661 September
450
400 PreDev
350
Dra
Y
W
R 300
0
LL 250
21
s SCRA
c 200
0
150
100
ESRA50
Pref
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 35. Distribution of predicted September outflows over a 54 year period for pre -
mining (PreDev) and four mining scenarios on Huddles Cut Watershed.
500
PreDev = 908
Drag = 783 October
450
PreDev
400
Drag
350
300
3
LL 250
a
r
c 200
0
150
100 ��scal
s
50
Pref
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 36. Distribution of predicted October outflows over a 54 year period for pre -
mining (PreDev) and four mining scenarios on Huddles Cut Watershed.
July 2020 S-70 Supplement 1 2019 Data Year PCS Creeks Report

500
November
450
400
350
PreDev
6300
3
LL 250
21
s
0 200 raajn
150
SCRA
100
50 S
Pref
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 37. Distribution of predicted November outflows over a 54 year period for pre -
mining (PreDev) and four mining scenarios on Huddles Cut.
500
December
450
400
PreDev
350
6300
3
LL 250
s Drag
c 200
0
150
SCRA
100
50
S0
Pref
0
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 38. Distribution of predicted December outflows over a 54 year period for pre -
mining (PreDev) and four mining scenarios on Huddles Cut Watershed.
July 2020
S-71 Supplement 1 2019 Data Year PCS Creeks Report

Cypress Run.
Pre -Mining Conditions. Average annual results for the Cypress Run watershed
are summarized in Table 7. These results show that predicted total annual outflow from
the Cypress Run watershed is 17.5 inches. This means that the predicted average annual
outflow from the Cypress Run watershed is 53300 acre -inches, or 4440 acre-feet, or 193
million cubic feet per year. Because of somewhat higher ET on the scarp, average
predicted outflow was 15.3 inches as compared to 18.2 inches for the flatland (Table 3).
Table 7. Simulated water balance components for the mostly agricultural flatland, the
forested scarp and the total Cypress Run Watershed.
Component
Flatland Scarp I Total
------------- - inches ---------------
Rainfall
50.8
50.8
50.8
Infiltration
42.7
36.4
41.2
Evapotranspiration
32.7
35.6
33.3
Subsurface Drainage
9.6
0.3
7.4
Surface Runoff
8.2
14.4
9.6
Lateral Seepage
0.4
0.5
0.4
Total Outflow
18.2
15.3
17.5
In some respects the annual summaries mask more than they reveal. Outflows
from the watershed are extremely variable temporally. Outflow rates are high during
large storms and during wet periods. They are also affected by evapotranspiration (ET).
For example, drainage rates in response to relatively large rainfall events may be small or
nil if preceded by long dry periods of high ET which dry out the profile and create
storage for rainfall that follows. Drainage from the flat agricultural fields may be nil
during dry periods during the summer and fall, sometimes lasting into winter. On the
other hand, large summer storms, tropical storms and hurricanes may cause very large
outflows during the summer months. Predicted daily flow rates at the watershed outlet in
cubic feet per second (cfs) are plotted for the 54-yr period in Figures 39-44. These
results show that the average daily outflow rates are generally between 0.1 and 100 cfs,
with maximum flow rates of several hundred cfs in some years. Predicted monthly flows
(in inches) are plotted in Figures 45-50. Volumes (in acre -inches) can be obtained from
these data by multiplying the plotted values by the area of the watershed (3046 acres).
July 2020 S-72 Supplement 1 2019 Data Year PCS Creeks Report

10000.00
1000.00
o
100.00
a�
r
NN�
a: 10.00
A
c0 1.00
N
0.10
0.01
1951 1952 1953 1954 1955 1956 1957 1958 1959 1960
Date
Figure 39. Simulated mean flow rate from Cypress Run Watershed for each day from
Jan. 1, 1951 to Dec. 31, 1959.
10000.00
1000.00
a
100.00
a�
r
NN�
LL
10.00
A
c0 1.00
N
0.10
0.01
1960 1961 1962 1963 1964 1965 1966 1967 1968 1969
Date
Figure 40. Simulated mean flow rate from Cypress Run Watershed for each day from
Jan. 1, 1960 to Dec. 31, 1968.
July 2020 S-73 Supplement 1 2019 Data Year PCS Creeks Report

10000.00
1000.00
a
100.00
a�
r
NN�
LL
10.00
A
c0 1.00
N
0.10
0.01
1969 1970 1971 1972 1973 1974 1975 1976 1977 1978
Date
Figure 41. Simulated mean flow rate from Cypress Run Watershed for each day from
Jan. 1, 1969 to Dec. 31, 1977.
10000.00
1000.00
o
100.00
a�
r
NN�
0 10.00
LL
A
.5
c0 1.00
N
0.10
0.01
1978 1979 1980 1981 1982 1983 1984 1985 1986 1987
Date
Figure 42. Simulated mean flow rate from Cypress Run Watershed for each day from
Jan. 1, 1978 to Dec. 31, 1986.
July 2020 S-74 Supplement 1 2019 Data Year PCS Creeks Report

10000.00
1000.00
o
100.00
a�
r
NN�
a: 10.00
A
c0 1.00
N
0.10
0.01
1987 1988 1989 1990 1991 1992 1993 1994 1995 1996
Date
Figure 43. Simulated mean flow rate from Cypress Run Watershed for each day from
Jan. 1, 1987 to Dec. 31, 1995.
10000.00
1000.00
o
100.00
a�
r
NN�
0 10.00
LL
A
.5
c0 1.00
N
0.10
0.01
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005
Date
Figure 44. Simulated mean flow rate from Cypress Run Watershed for each day from
Jan. 1, 1996 to Dec. 31, 2004
July 2020 S-75 Supplement 1 2019 Data Year PCS Creeks Report

15
12
c
9
3
0
LL
A
L
06
3
0
04 c W � CO a) o
m m m m m m m m m m
Figure 45. Simulated monthly flow from Cypress Run Watershed for each month from
Jan. 1, 1951 to Dec. 31, 1959.
15
12
c
3
0
LL
_A
L
06
3
0
O N M O W h CO T
W f0 W W W f0 W W W W
T T T T T T T T T T
Figure 46. Simulated monthly flow from Cypress Run Watershed for each month from
Jan. 1, 1960 to Dec. 31, 1968.
July 2020 S-76 Supplement 1 2019 Data Year PCS Creeks Report

15
12
c
9
3
0
LL
A
L
06
3
0
T O N M O W h CO
f0 h h h h h h h h h
T T T T T T T T T T
Figure 47. Simulated monthly flow from Cypress Run Watershed for each month from
Jan. 1, 1969 to Dec. 31, 1977.
15
12
c
3
0
LL
_A
L
06
3
0
00 T O N M O f0 h
h h 00 00 00 00 00 00 00 00
T T T T T T T T T T
Figure 48. Simulated monthly flow from Cypress Run Watershed for each month from
Jan. 1, 1978 to Dec. 31, 1986.
July 2020 S-77 Supplement 1 2019 Data Year PCS Creeks Report

15
12
c
9
3
0
LL
A
L
06
3
0
h CO T O N M O W
CO CO CO T T T T T T T
T T T T T T T T T T
Figure 49. Simulated monthly flow from Cypress Run Watershed for each month from
Jan. 1, 1987 to Dec. 31, 1995.
15
12
c
3
0
LL
_A
L
06
3
0
f0 h CO T O N M O
T T T T O O O O O O
N N N N N N
Figure 50. Simulated monthly flow from Cypress Run Watershed for each month from
Jan. 1, 1996 to Dec. 31, 2004.
July 2020 S-78 Supplement 1 2019 Data Year PCS Creeks Report

40
35
30
25
0
LL
20
L
L
d
R 15
10
OO
OpO
QOOQ /�
QQV
OpQQQo�Q
O
OOp0000
10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
Figure 51. Distribution of predicted annual outflows for the 54 year period (1951-2004)
on the Cypress Run Watershed.
As with the Huddles the principle results are presented using flow frequency
diagrams which show the temporal variability of outflows. Results for annual predicted
outflows are given in Figure 51 for the entire Cypress Run Watershed. These results
indicate that the medium annual outflow is about 17 inches, which is very close to the
mean of 17.5 inches (Table 7). This means that the outflow in half of the years is greater
than 17 inches and in half of the years is less than 17 inches. These results further show
that outflows greater than 30 inches should be expected in 10% of the years and less than
9 inches in 10% of the years.
The flow frequency diagram for all monthly flows is given in Figure 52. These
results indicate that the median monthly flow is just less than 1 inch, and that expected
monthly flows are greater than about 4 inches in 10% of the months and less than 0.1
inches in about 13% of the months. In contrast to the Huddles Cut watershed, no
monthly flows from the Cypress Run watershed are zero. This is mostly due to seepage
from the scarp and from seepage from the flatland fields to the deep canals and streams.
Distributions for each month are quite different (Figure 53 and Table 8). For
example, the median predicted outflow for the month of January was 2.55 inches with
10% of the January months having more than 5.1 inches and 10% having less than 0.79
inches. By comparison the month of May had a median of 0.26 inches with 10% of the
May months having outflows greater than 2.4 inches and 10% having less than 0.04
inches.
July 2020 S-79 Supplement 1 2019 Data Year PCS Creeks Report

100
10
c
0
0
0.1
0.01 ' '
0 10 20 30 40 50 60 70 80 90 100
Percent of Months Flow Equal or Exceeding
Figure 52. Distribution of predicted monthly outflows for a 54 year period(1951-2004)
on the Cypress Run Watershed.
100
c
3
O
10
0.1
Jan
Mar
Oct
May
0.01 ' '
0 10 20 30 40 50 60 70 80 90 100
Percent of Months Flow Equaled or Exceeded
Figure 53. Distribution of predicted monthly outflows by month for a 54 year period
(1951-2004) on the Cypress Run Watershed.
July 2020 S-80 Supplement 1 2019 Data Year PCS Creeks Report

Table 8. Distribution of monthly outflows predicted in a 54-year DRAINMOD simulation
of the Cypress Run watershed.
Predicted Monthly Outflow for a 54 year Simulation (in)
Percent of
Months with
10th 25th 75th 90th
Minimum
Percentile
Percentile
Median
Percentile
Percentile
Maximum
flow < 0.1"
JAN
0.38
0.79
1.56
2.55
3.54
5.10
6.94
0
FEB
0.14
0.43
1.07
1.92
3.34
4.31
6.40
0
MAR
0.24
0.42
0.82
1.62
3.15
3.81
5.36
0
APR
0.04
0.06
0.20
0.56
1.44
2.01
4.19
17
MAY
0.02
0.04
0.07
0.26
1.22
2.42
6.78
28
JUN
0.02
0.02
0.09
0.33
1.55
2.59
11.88
30
JUL
0.02
0.06
0.15
0.40
1.63
3.54
6.73
20
AUG
0.02
0.06
0.10
0.62
3.27
5.38
10.00
26
SEP
0.03
0.07
0.16
0.41
2.15
5.15
13.80
20
OCT
0.02
0.07
0.15
0.23
0.91
2.78
15.94
17
NOV
0.03
0.17
0.26
0.57
1.41
2.33
5.33
2
DEC
0.15
0.28
0.63
1.45
2.83
3.65
6.85
0
Flow frequency data on a daily basis is given in Figure 54 and Table 9. These
results indicate that the median predicted daily outflow is about 1 cfs. Based on these
data, average predicted daily flow rates were greater than 10 cfs in 10% of the days
during the 54 year simulation period and less than about 0.11 cfs in 10% of the days.
1000
100
0.1
0.01 '
0 10 20 30 40 50 60 70 80 90 100
Percent of Days Flow Equaled or Exceeded
Figure 54. Distribution of predicted mean daily flow rates for a 54 year (1951-2004)
simulation at Cypress Run Watershed.
July 2020
S-81 Supplement 1 2019 Data Year PCS Creeks Report

Table 9. Distribution of predicted mean daily flow rates for 54 year (1951-2004)
simulations of the mostly agricultural flatland, the forested scarp, and the total Cypress
Run Watershed
Flatland
Scarp
Total
cfs
Minimum
0.03
0.04
0.07
5th Percentile
0.06
0.04
0.10
10th Percentile
0.07
0.04
0.12
25th Percentile
0.12
0.05
0.19
Median
0.82
0.08
1.07
75th Percentile
2.52
0.62
3.66
90th Percentile
7.07
2.78
9.95
95th Percentile
17.4
5.67
20.8
Maximum
1053
289
1342
Flow frequency data on a daily basis in given in Figure 54 and Table 9. These
results indicate that the median predicted daily outflow is about 1 cfs. Based on these
data, average predicted daily flow rates were greater than 10 cfs in 10% of the days
during the 54 year simulation period and less than about 0.11 cfs in 10% of the days. In
contrast to the Huddles Cut watershed, no daily flows from the Cypress Run watershed
are zero. Seepage from the scarp and from the flatland fields to the deep canals and
streams occurs every day. Results in Table 9 break the results into predicted daily flow
rates from the scarp and the flatland.
Effects of Different Mining Alternatives. Under current pre -mining conditions
the median predicted annual flow is 4151 acre ft. per year (Table 10). On average, the
flow exceeds 7074 ac. ft. per year once in 10 years (90th percentile). Likewise it is less
than 2064 ac ft per year once in 10 years (1 Oth percentile).
All of the mining scenarios dramatically reduce the predicted annual flows as
shown in Figure 56 and Table 10. For example the Intermediate Plan had a predicted
median annual outflow of 912 ac ft, about 22% of the annual flow before mining. The
90th percentile flow was 1603 ac ft, about 23% of the 7074 ac ft predicted for current
conditions. These predicted reductions are consistent with the percentage reduction in
watershed area. For the intermediate plan the contributing watershed area after mining
would be 731 acres which is 24% of the current watershed area. Thus the predicted
effects on annual outflows of reducing watershed size are roughly proportional to the area
reduced.
July 2020 S-82 Supplement 1 2019 Data Year PCS Creeks Report

Table 10. Distribution statistics for predicted annual outflows for 54 year (1951-2004)
simulations of the pre -mining (PreDev) and four mining scenarios at Cypress Run
Watershed.
Total
PreDev
Pref
I Inter
I SCRA
NoAct
Annual
Flow Volume (ac-ft)
Minimum
1284
340
382
355
425
5th Percentile
1837
394
455
474
548
10th Percentile
2064
424
497
511
584
25th Percentile
3046
566
663
705
811
Median
4151
781
912
974
1118
75th Percentile
5508
1064
1237
1365
1606
90th Percentile
7074
1378
1603
1758
2061
95th Percentile
8178
1543
1807
2022
2341
Maximum
8882
1 1648
1 1924
1 2125
2491
Mean
4444
846
1 987
1 1071
1242
Area of Watershed (ac)
3046
630
731
813
957
10000
9000
8000
7000
6000
0
5000
d
s
4000
3000
2000
1000
0
O
00
00°0000'
Oa000OOp0
°❑❑❑O 000:
00
0 10 20 30 40 50 60 70 80 90 100
Percent of Years Flow Equaled or Exceeded
♦ PreDev ❑ Pref ♦ Inter O SCRA ❑ NoAct
Figure 56. Distribution of predicted annual outflows for 54 year (1951-2004) simulations
of pre -mining (PreDev) and four mining scenarios on Cypress Run Watershed.
July 2020 S-83 Supplement 1 2019 Data Year PCS Creeks Report

The mining scenarios also dramatically reduce the predicted monthly flows (Table
I I and Figure 57). Percent flow reductions for the monthly flows correlate fairly well to
percent area reductions for the median and higher percentiles, however they do not
correlate well for the lower percentiles. For example the Intermediate Plan with a 24%
reduction in area had a predicted median monthly outflow of 54 ac ft, about 27% of the
annual flow before mining. The 90th percentile flow was 195 ac ft, about 2 1 % of the 929
ac ft predicted for current conditions. Flow at the 5t' percentile, however, was 2.6 ac-ft
which is about 37% of the 7.0 ac-ft predicted for current conditions. The lack of
correlation at the lower percentiles in the monthly flows is caused by the fact that a much
lower percentage of the scarp area was lost to the mining compared to percentage of
flatland area lost to mining. The slow seepage from the scarp makes up a larger
proportion of the total flow for low flow periods. Another observation resulting from the
slow seepage from the scarp is that monthly flow volumes never equal zero as they did in
the Huddles Cut watershed.
Average daily flow rates were also reduced for the different mining scenarios
(Table 12 and Figures 58 and 59). The effect of the scarp seepage is also evident in the
daily flow values in that the percent reductions in the lower percentile flows are less than
the reductions in area. Percent reduction in the 5t' percentile daily flow rate was 40% for
the Intermediate Plan. The distributions of daily flow rates for the scarp and flatland for
each scenario are also shown with the total daily flow rates (Table 12). These show that a
much greater flow and area reductions occurred on the flatland than on the scarp.
Table 11. Distribution statistics for predicted monthly outflows for 54 year (1951-2004)
simulations of the pre -mining and four mining scenarios on Cypress Run Watershed.
Total
PreDev
Pref
Inter
I SCRA
NoAct
Monthly Flow Volume (ac-ft)
Minimum
4.8
2.0
2.3
2.2
2.5
5th Percentile
7.0
2.3
2.6
2.6
3.0
10th Percentile
10.4
2.5
2.9
3.0
3.7
25th Percentile
42.0
13.6
15.2
14.8
18.6
Median
197
47
54
54
63
75th Percentile
577
97
116
129
143
90th Percentile
929
168
195
218
257
95th Percentile
1241
220
260
294
336
Maximum
3775
779
904
1008
1190
Mean
370
71
82
89
103
Area of Watershed (ac)
3046
630
1 731
1 813
957
July 2020 S-84 Supplement 1 2019 Data Year PCS Creeks Report

4000
3500
3000
r
2500
R
3
c 2000
a_
2,
t
c 1500
0
Z
1000
500
0.1 1.0 10.0 100.0
Percent of Months Flow Equal or Exceeding
♦ PreDev -Pref - - - - - - Inter SCRA NoAct
Figure 57. Distribution of predicted monthly outflows for 54 year (1951-2004)
simulations of predevelopment and four development scenarios at Cypress Run
Watershed.
July 2020 S-85 Supplement 1 2019 Data Year PCS Creeks Report

1400
1200
1000
w
0 800
LL
d
600
d
400
200
0
•
•
•
0.001 0.010 0.100 1.000 10.000 100.000
Percent of Days Flow Equaled or Exceeded
♦ PreDev Pref ...... Inter SCRA NoAct
Figure 58. Distribution of predicted mean daily flow rates for 54 year (1951-2004)
simulations of pre -mining (PreDev) and four mining scenarios at Cypress Run.
1000
M
100
0.1
0.01 ' '
0 10 20 30 40 50 60 70 80 90 100
Percent of Days Flow Equaled or Exceeded
• PreDev -Pref ------ Inter SCRA NoAct
Figure 59. Distribution of predicted mean daily flow rates for 54 year (1951-2004)
simulations of pre -mining (PreDev) and four mining scenarios at Cypress Run. Y-axis is
changed to emphasize low flow rates.
July 2020 S-86 Supplement 1 2019 Data Year PCS Creeks Report

Table 12. Distribution of predicted mean daily flow rates for 54 year (1951-2004)
simulations of the pre -mining (PreDev) conditions and the four mining scenarios at
Cypress Run Watershed. Distributions are also shown for the Scarp and Flatland
sections of the watersheds.
Total
PreDev Pref Inter I SCRA NoAct
Average Daily Flow Rate (cfs)
Minimum
0.07
0.03
0.04
0.04
0.04
5th Percentile
0.10
0.04
0.04
0.04
0.05
10th Percentile
0.12
0.04
0.04
0.04
0.05
25th Percentile
0.19
0.04
0.05
0.05
0.07
Median
1.07
0.07
0.09
0.13
0.19
75th Percentile
3.66
0.49
0.57
0.62
0.91
90th Percentile
9.95
2.29
2.64
3.26
3.71
95th Percentile
20.8
5.48
6.32
6.35
7.13
Maximum
1342
265
308
330
386
Mean
6.14
1.17
1.36
1.48
1.71
Area of Watershed ac
3046 630 1 731 1 813 957
Scarp
PreDev Pref Inter I SCRA NoAct
Average Daily Flow Rate cfs
Minimum
0.04
0.03
0.04
0.03
0.04
5th Percentile
0.04
0.04
0.04
0.04
0.04
10th Percentile
0.04
0.04
0.04
0.04
0.04
25th Percentile
0.05
0.04
0.04
0.04
0.04
Median
0.08
0.07
0.08
0.07
0.08
75th Percentile
0.62
0.48
0.52
0.48
0.61
90th Percentile
2.78
2.28
2.46
2.26
2.74
95th Percentile
5.67
5.45
6.09
5.38
5.59
Maximum
289
263
292
260
285
Mean
1.25
1.16
1.29
1.15
1.23
Area of Watershed ac
713 626 1 691 1 619 702
Flatland
PreDev Pref Inter I SCRA NoAct
Average Daily Flow Rate (cfs)
Minimum
0.03
0.00
0.00
0.00
0.00
5th Percentile
0.06
0.00
0.00
0.01
0.01
10th Percentile
0.07
0.00
0.00
0.01
0.01
25th Percentile
0.12
0.00
0.00
0.01
0.01
Median
0.82
0.00
0.01
0.05
0.08
75th Percentile
2.52
0.01
0.02
0.08
0.20
90th Percentile
7.07
0.01
0.12
0.54
0.75
95th Percentile
17.4
0.03
0.42
1.96
2.53
Maximum
1053
2
16
70
102
Mean
4.88
0.01
0.07
0.33
0.48
Area of Watershed ac
2333 4 1 41 1 194 256
July 2020 S-87 Supplement 1 2019 Data Year PCS Creeks Report