20150994 Ver 1_More Info Received_20151102

u - V-71
Eam
November 2, 2015
U.S. Army Corps of Engineers
Asheville Regulatory Field Office
151 Patton Avenue, Room 208
Asheville, NC 28801
Attention: Mr. David Brown, P.G.
N.C. Department of Environmental Quality - Division of Water Resources
Water Quality Regional Operations Section - Asheville Regional Office
2090 U.S. 70 Highway
Swannanoa, NC 28778
Attention: Mr. Andrew W. Moore, P.G.
Reference: Response to Request for Additional Information: NWP No. 12 /WQC No. 3884
Line T -01 Pipeline Replacement Project
Polk, Henderson and Buncombe Counties, North Carolina
S &ME Project No. 7335 -15 -05
DWR Project No. No. 20150994
Dear Messrs. Brown and Moore:
Please reference the September 23, 2015 Pre - Construction Notification (PCN) submitted on behalf of our
client, PSNC Energy (PSNC) for Line T -01 Pipeline Replacement project located in Polk, Henderson, and
Buncombe counties North Carolina.
On October 2, 2015, following review and evaluation of the submitted documents, the U.S. Army Corps of
Engineers (USACE) requested the following additional information in order consider the application
complete:
1. The PCN indicates trenchless methods are not feasible for the crossing at the Green River and the
applicant is proposing open trench methods at this crossing. Please provide details (narratives, drawings,
plans, etc.) for the open trench methodology at this crossing. This information should at a minimum describe
how the work will be performed in the dry, detail sediment and erosion controls, manage expected normal
river flows, restoration of the stream bed and bank, and activities to be conducted if unexpected high river
flows are encountered.
In accordance with Title 15A NCAC 02H .OS02(c), the N.C. Division of Water Resources (NCDWR) also
placed the project on hold on October 7, 2015 pending receipt of the same information.
Since that time, the Project Engineer, WBA, P.C. (WBA), along with input from S &ME Inc. (S &ME), has
continued to investigate methods of construction that would allow installation of the pipe beneath the
Green River either by "trenchless" methods, such as horizontal directional drill (HDD) or boring, or by
S &ME, Inc. 19751 Southern Pine Boulevard I Charlotte, NC 28273 1 p 704.523.4726 1 f 704.525.3953 1 www.smeinc.com

Response to Request for Additional Information: NWP No. 12 /WQC 3884 November 2, 2015
Line T -01 Replacement Project Page 2
conventional means performed "in the dry." A summary report prepared by WBA that describes the
alternatives investigated, along with reasons why such alternatives are not feasible, is attached to this
letter (Appendix I). In addition to the engineering and constructability constraints of using trenchless
means of installation, efforts to install the pipe in the dry have also been eliminated from consideration
based both on hydraulics and the integrity of the existing 12 -inch line (weight loading of the aqua dams),
which is located 25 feet downstream of the proposed 20 -inch crossing, and must remain active until the
new line is placed in service. A summary of an independent hydrologic and hydraulic analysis performed
by S &ME in is also attached (Appendix II).
As these investigations detail, pipe installation either by trenchless methods, or in- the -dry, is not
practicable nor possible when taking into consideration safety, cost, existing technology, and logistics in
light of the overall project purpose. Accordingly, PSNC requests that Condition No. 6 (Work in the Dry) of
General Water Quality Certification No. 3884 be waived for pipe installation at the Green River crossing.
A Detail Drawing of the proposed crossing as currently proposed is included in Appendix III. Prior to
installation of the pipe, PSNC plans to coordinate with Duke Energy to suspend power generation at Lake
Summit for a time sufficient to accommodate installation during low flow conditions. Prior
communication between PSNC and Duke Energy indicates that they are agreeable to suspending power
generation for up to a maximum of four -to -five days, which is sufficient time to install the pipe via an
open -cut wet crossing. A minimum of two, type -three permeable turbidity curtains will be installed
downstream of the proposed crossing location and remain during excavation and backfill operations.
The trench would then be excavated as quickly as possible using a drag -line or long reach excavator, while
stream flow at low levels continues. Excavated material would be temporarily stockpiled on high ground.
The pipe section would be pre - welded and prepared for installation ahead of time such that it could be
installed quickly once the trench is prepared. Following the pipe installation, tie -ins will be made in high
ground, and the affected stream cross - section restored to its original grade and contour.
As the attached reports indicate, installation of the pipe beneath the Green River by means other than
that which is currently proposed are not feasible, and may ultimately entail more significant
environmental impacts in order to accomplish.
Thank you for your consideration of this request. If you have questions or need additional information,
please feel free to contact us at 704.523.4726.
Sincerely,
5 &ME
Attachments
S &ME, Inc.
Joey Lawler, PWS
Patrick L. McMahon, PhD
Project Manager
Civil and Water Resources Engineer
jlawler @smeinc.com
pmcmahon @smeinc.com
Attachments
S &ME, Inc.

APPENDDIX I

53020 SCANA / PSNC PROJECT T -01A REPLACEMENT
Investigation of
Construction Methods for
Green River Crossing
1) CONVENTIONAL AND MODIFIED CONVENTIONAL BORING
Conventional bore- using sacrificial 20 -inch was investigated and determined infeasible due to the
following reasons:
• South side difficulties in access for pit receiving equipment.
• Dewatering receiving pit, nowhere to discharge water except into river.
• Dewatering bore pit (north side) would require deep wells and likelihood achieving well depth
required to lower ground water 15 feet is very low.
• Bore and receiving pit would have to be 21 feet (elev. 897') and 17 feet (elev. 897') respectively
to provide 5 foot clearance below river bottom and top of pipe.
• Soil conditions in boring zone, saturated alluvial sand, gravel and cobble, are not conducive to
conventional boring. Collapse of unconsolidated material around sacrificial pipe could prevent
jacking operations.
• Lake Adger normal pool elevation is between 902 to 910 mean sea level (MSL).
• Green River bottom elevation at crossing is between 905 and 906 MSL
• Water surface elevation at PSNC proposed Green River crossing is between 908 and 910 MSL
dependent on Lake Adger pool elevation.
• Top of bank elevation at PSNC proposed crossing is 919 MSL north side and 914 MSL south side.
Modified Conventional Bore — using fluid assisted (drilling mud) and guided drill head technology was
investigated and determined infeasible due to the following reasons:
• Though this method can handle gravel and cobble to some extent, ground water, especially in
sandy soils, does pose problematic for the technique.
• Pits are still required to be dry with a solid foundation for the drilling equipment.
• Site investigation determined very loose unconsolidated sands gravel and cobble and water
table to within 5 or 6 feet of surface on north side and 4 feet of surface south side.
• Lake Ager normal pool elevation is between 902 to 910 MSL.
• Water surface elevation at PSNC proposed Green River crossing is between 908 and 910 MSL.
• Top of bank elevation at PSNC proposed crossing is 919 MSL north side and is 914 MSL south
side.
53020 -PM -4 1 of 4
23 October 2015

2) HORIZONTAL DIRECTIONAL DRILLING
Four optional HDD were investigated, all of the HDDs would require purchasing completely new
rights -of -way for the length of the drill. Access for tracking the drills will be minimum and in heavy
timbered areas. Normal drill entry and exit angle from the horizontal plain are 10 degrees entry and
8 degrees exit. Due to the topography of the area, these angles proved insufficient to provide
adequate depths below the valleys encountered between proposed entry and exit points which are
situated within the existing pipeline rights -of way. The entry and exit design angle was set at 14
degrees from horizontal, considered maximum for constructability.
Three Options, 1, 2, and 3 would require the drill rig to be initially setup on the south side (lower
elevation than the exit point) approximately 809', 1,552' and 1,821' from the Green River. All three
of these drills would cross the Green River downstream from the existing T -01B 12 -inch line crossing
(623', 497', and 161' respectively) and their total lengths would be 2,111; 3,489; and 3,417 feet
respectively. The pipe pull string would be assembled south of the entry point within existing PSNC
pipeline right -of -way and would cross and block residential drives (three for Option 1 and six for
Option 2 and 3) for period of approximately 3 days prior to pulling operations until pull completed.
All three of these options would require 24/7 operation and the rig for Option 1 would be within
1,000 feet of a residence, Option 2 and 3 would be within 330 feet of a residence.
Option 1 drill entry site was determined to be on a mountain ridge with steep slope on both sides
and found unsuitable to set the rig. Options 2 and 3 were suitable sites for rig erecting and
operation, but would be too close to the residence to allow 24/7 operation for an extend period of
time of 60 -70 days. Also Options 2 and 3 were found to be unsuitable as the drill path would exit
the ground some 200 to 400 feet prior to the intended exit point due to the topography.
The remaining Option, Option 4, is 5,106 feet in length; the closest residence to the entry (rig) point
is 1,200 feet. The rig set -up area is restricted due to topography (again on top of a ridge) and is
remote and 600 feet down the existing right -of -way from the closest access road. The exit point is
the same location as Options 2 and 3 entry point. The pull string would extend southward along the
existing right -of -way and would block residential access drives to six residences and would also have
to cross Green River Cove Road if strung continuously for period of approximately three days prior
to pulling operations until pull completed. Estimated drilling time would be 85 -95 days (24/7
operation). The pull pipe section would have to be lifted 45 feet above natural ground at a point
300 feet south of the exit point to allow pipe to break over to enter at the 14 degree angle into the
drill hole, thus requiring three cranes with roller cradles to lift and hold the 46,800 Ibs of pipe in the
air. Estimated cost for this installation is $8,000,000.00 to achieve a 100' crossing.
HDD method is considered infeasible due to cost, time required, public inconvenience, and safety.
53020 -PM -4 2 of 4
23 October 2015

3) DRY OPEN CUT
The hydrology plays a big part in the feasibility of a dry open cut. Duke Energy operates a
hydroelectric power plant 14.7 miles upstream of the crossing. When they are not generating
power the nominal flow of the Green River is 56 to 60 CFS and the crossing water depth is between
1 and 2 feet deep. When Tuxedo Dam is generating power the flow increases to 236 to240 CFS with
one unit on and the water level in the river raises 1.5 feet. When Tuxedo Dam runs two units the
flow increases to 416 to 420 CFS and the river water level raises 3 feet above normal flow level.
A 2 year 30 minute rain event (1.2 inches) could add as much as an additional 427 CFS and the river
water level would raise a little over 3 feet above (nominal flow). If Tuxedo Dam is generating power
with one unit during such an event, the river stage at the proposed PSNC crossing would be 4.5 to
5.5 feet (667 CFS; 299,350 gallons per minute). If two units are running during such an event, the
river stage at the proposed PSNC crossing would be 6 to 7.5 feet (847 CFS; 380,134 gallons per
minute).
A dry crossing will take approximately 5 to 6 weeks to complete: two weeks preparatory work, one
week for the crossing, and 2 weeks for restoration work depending on two separate scenarios.
Scenario one- 60% of the crossing performed in first phase (60% of crossing laid and 50%
backfilled with 30% open channel), then second phase (opposite side 40% of crossing laid and
backfilled with 30% open channel).
Scenario two- 100% channel blocked with upstream and downstream aqua dams, with flumed
pipe bypass through dams..
First scenario could handle nominal flow conditions, but any additional capacity would cause the
river banks to be breached. Additionally, the flow velocity and sandy bottom could cause the
temporary dams to be compromised and undermined. Tuxedo Dam power plant could not operate
during the in stream activities, and a 2 year 30 minute rain fall event would also compromise the
temporary dams.
The second scenario would require multiple 24" flume pipes to by -pass nominal flow and an
excessive number of flume pipes to handle one power unit running. To provide sealing area around
flume pipe four Aqua Dams (or similar product); one under the pipe upstream and downstream, and
one larger aqua dam over the pipes upstream and downstream; would be required. Each flume pipe
requires a separation of twice the diameter to allow the bottom dam to be filled with water to a
height of one -half the pipe diameter and the top bladder dam to be filled with water to fill the top
void around the pipe and provide necessary height to back up water level and provide freeboard to
prevent over breaching. The flume pipes would need to be spaced on 6 foot centers. Eighteen
flumes would be the maximum number that could be installed for a 115' high -bank to high -bank
river width. Though, more than just a small number of flumes would preclude excavation of the
trench due to the resulting restricted access to the stream bed. To achieve the maximum flow
53020 -PM -4 3 of 4
23 October 2015

through each flume, the upstream water level needs to be above the top of the flume pipe
approximately twice the flume diameter (4 feet). Upstream water levels would be 6 feet high with
nominal flow, and 8 feet high with one dam generating unit running, which would breach the top of
the south side river bank when either a power unit is running or a 2 year 30 minute rain fall event
occurs.
We have talked with Duke Energy about their power generating schedule and they implied that
possibly they could suspend power generation for up to a maximum of four to five days providing
they could draw down Lake Summit enough to handle the normal inflow to the lake and providing
there are no rain fall events that would require them to release water from the lake. Tuxedo Dam
generally operates 300 days out of a year with 64 days allowed for no power generation. They also
indicated that there would be weekends they could not allow suspension of power generation in
September, November and March during the Green River White Water Race events.
A wet stream crossing appears to be the most economical and to have the least environmental
impact. A wet crossing could be accomplished with at most three in stream days and during nominal
flow conditions. Two or more turbidity curtains would be installed downstream of the crossing to
minimize sediment from progressing downstream. Turbidity will not be completely prevented but it
should not be any more turbid than during power generation flows.
53020 -PM -4 4 of 4
23 October 2015

Project 53020- PSNC Green River Proposed HDD's
Exits ground
before
Exit Point
Exits ground
before
Exit Point
1
Option 1
Option 2
Option 3
Option 4
Length
2,1111
Drill
Length
3,489
Drill
Length
1 3,417
Drill
Length
5,106
Drill
Station
Grd. Elev.
TOP
Cover
below
Grd.
Station
Grd. Elev.
TOP
Cover
below
Grd.
Station
Grd. Elev.
TOP
Cover
below
Grd.
Station
Grd. Elev.
TOP
Cover
below
Grd.
-300
1039
1084
45
-300
1084
-300
1084
-300
1084
Entry
0
1025
1025.8
0.8
Entry
0
1079
1079
0
Entry
0
1079
1079
0
Exit
0
1079
1079
0
246
1022
964
-58
200
1060
1029
-31
200
1066
1029
-37
200
1070
1029
-41
421
952
621
-331
400
1038
980
-58
400
1048
980
-68
400
1042
980
-62
530
1017
899.5
-117.5
600
1024
930
-94
600
1028
930
-98
600
1003
930.2
-72.8
611
1028
887
-141
800
1028
891.1
-136.9
800
1042
891.1
-150.9
800
979
891.1
-87.9
Green Rv
809
910
870.1
-39.9
1000
996
872.7
-123.3
1000
964
872.7
-91.3
1000
990
872.6
-117.4
Green Rv
873
910
870.1
-39.9
1100
963
870.9
-92.1
1200
1037
870.9
-166.1
1200
1033
870.9
-162.1
900
911
870.1
-40.9
1200
1022
870.9
-151.11
1500
1032
870.9
-161.1
1400
1065
870.92
- 194.08
921
920
870.1
-49.9
1300
1041
870.9
-170.1
Green Rv.
1821
910
870.9
-39.1
1 1600
10441
870.92
- 173.08
1000
921
870.1
-50.9
1500
923
870.9
-52.1
Green Rv.
1890
910
870.9
-39.1
1850
945
870.92
-74.08
1200
925
870.1
-54.9
Green Rv
1552
910
870.9
-39.1
1900
911
870.9
-40.1
2000
971
870.92
- 100.08
1495
939
889.6
-49.4
Green Rv
1623
910
870.9
-39.1
2029
919
870.9
-48.1
2150
941
870.92
-70.08
1700
955
929.3
-25.7
1646
913
870.9
-42.1
2400
947
881.7
-65.3
2500
971
870.92
- 100.08
1900
986
979.2
-6.8
1835
921
870.9
-50.1
2600
1000
912.7
-87.3
2700
957
870.92
-86.08
2000
1010
1004
-6
2100
925
870.9
-54.1
2800
1016
960.9
-55.1
2900
942
870.92
-71.08
Exit
2111
1031
1031.8
0.8
2400
969
878.6
-90.4
3000
975
1010
35
3000
940
870.92
-69.08
2600
994
906.49
-87.51
3080
966
1030.7
64.7
3200
936
870.92
-65.08
2800
1024
953.2
-70.8
3300
1074
1085.6
11.6
3400
919
870.92
-48.08
3000
1040
1003
-37
Exit
3417
1114
1114
0
Green Rv.
3486
911
870.92
-40.08
3200
1037
1052.9
15.9
Green Rv.
3520
911
870.92
-40.08
3400
1114
1102.8
-11.2
3600
944
870.92
-73.08
Exit
3489
1124
1124
0
3800
969
870.92
-98.08
3600
1111
4000
1000
870.92
- 129.08
4200
1021
873.6
-147.4
4400
1002
894.5
-107.5
4600
1007
935.9
-71.1
4800
1062
985.8
-76.2
5000
1074
1035.7
-38.3
Entry
5106
1061
10611
0
Notes: Option 1
Possible FRAC out last 211 feet account less than 10' deep. Rig move around is required account elevation profile and route PI will not allow pipe string to be on the north side thus rig needs to move to the north end and pipe strung on the
south end. Pull string will block three residential drives and will require lifting in the air 45 feet a distance of 300 feet from south end drill hole to allow pipe to break over and enter the 14 degree angled drill hole. Entry point is located along a
ridge with steep slopes on either side, minimal working room and no flat area for rig working room. Rig requires a 300 by 300 foot flat area for set up. Exit point is in a similar situations for rig set -up. High Risk of FRAC out and unsafe working
room on both ends.
Notes: Option 2 and 3
Both of these options will exit the ground prior to the intended exit point do to topography. Rig move around is required as no pull string room on the north end, Pull strings will block residence access on south end.
Notes: Option 4
Rig move around is not required as drill entry is required at the north end (low end). Pull string will block six residence access drives on south end as well as Green River Cove Road. Rig will require 24/7 operation and 87 days to complete drill and
ream operations because of expected base rock unconfined compressive strength of 30,000 psi (Biotite Gneiss and Schist and granitic rock).
All Optional drills are considered high risk and low probability of successful completions.

APPENDIX II

SCANA / PSNC PROJECT T -001A REPLACEMENT
Hydrologic and Hydraulic Analyses Summary
Support for Construction Methods Investigation
Green River Crossing
❖ Background
S &ME was retained by PSNC /SACNA to evaluate hydrologic and hydraulic conditions at the proposed
Green River Crossing to develop a set of specifications for the use of portable dam structures to facilitate
a dry instillation of the proposed pipeline crossing. Based on these analyses, it appears that the margin
for the opportunity to use these structures is narrowly defined at the base flow condition. The following is
a brief summary of the analyses performed and a discussion of the import of their results. These analyses
were performed independently of those performed by WBA, P.C. The datum used in this analyses differs
from the datum used by WBA, P.C. by approximately +2.5 feet. Differences between the results presented
by WBA, P.C. and results presented in this summary are primarily related to the difference between the
two datums with minor differences being related to the exact geometry of the cross - section surveyed for
each study and estimates of roughness characteristics and energy gradients and losses.
❖ Hydrologic and Hydraulic Characterization of the Green River at
the Proposed Crossing.
There are no established USGS stream gages on the Green River between the Summit Lake and Lake
Adger reservoirs. In the absence of historical gage data, a combination of regression analyses, field
measurements, and single section one - dimensional (1D) hydraulic modeling have been used to
characterize the hydrologic and hydraulic characteristics of the Green River at the proposed crossing
location. On September 17, 2015 S &ME personnel Ralf Russel and Patrick McMahon visited the site of the
proposed crossing to collect stage, cross - section, and flow velocity data and to make observations of the
existing condition of the channel bed and banks. The site visit was made during base flow conditions. A
cross - section was established perpendicular to flow and water surface and bed elevations were measured
using an auto -level and survey rod. Flow velocities were measured using a Global Water Flow Probe.
Results of these measurements are summarized in Table 1.
These data were amended using available bare ground LiDAR topographic data downloaded from the
North Carolina Flood Risk Information System website (http: / /fris.nc.gov /, BE3710053800WC20060426.txt).
The resulting cross - section is presented in Figure 1. The base flow water surface shown in Figure 1
represents the water surface at the time the field measurements were taken. According to the velocity
measurements collected during the site visit, the flow was estimated to be approximately 42 cfs. A back
calculation of the flow rate using the 1D model and an energy slope of 0.0001 ft /ft (based on gradient
information provided by Duke) suggests a flow of approximately 60 cfs at the stage observed in the field.
The discrepancy between the two values is attributed to the lack of precision of the flow probe at the low
velocities present during the field visit. The larger of these two values was chosen for use in evaluating
base flow conditions during construction.
53020 SCANA / PSNC PROJECT T -01A REPLACEMENT
Hydrologic and Hydraulic Analyses Summary Page 1 of 4

Table 1: Cross Section Data Collected on 9/17/2015
Station
(ft)
Elevation
(ft)
Depth
(ft)
Velocity
(ft /sec)
0.0
911.10
0.00
0.00
0.0
909.89
1.21
0.00
5.0
909.18
1.92
0.10
12.0
909.18
1.92
0.10
20.0
908.44
2.66
0.20
24.0
908.49
2.61
0.20
26.0
908.31
2.79
0.20
30.0
908.34
2.76
0.30
35.0
908.76
2.34
0.30
40.0
909.02
2.08
0.30
45.0
909.18
1.92
0.40
50.0
909.04
2.06
0.40
55.0
909.31
1.79
0.40
60.0
909.40
1.70
0.30
65.0
909.34
1.76
0.40
70.0
909.01
2.09
0.30
75.0
908.97
2.13
0.10
80.0
908.95
2.15
0.10
85.0
909.12
1.98
0.00
90.0
909.13
1.97
0.00
95.0
909.64
1.46
0.00
100.0
910.14
0.96
0.00
105.0
910.85
0.25
0.00
106.0
911.10
0.00
0.00
The 2 -year and 5 -year flow rates were estimated using USGS regression equations presented in Weaver,
Et al. 2009 (Weaver, J.C.; Feaster, T.D.; and Gotvald A.J. 2009 Magnitude and frequency of rural floods in the
Southeastern United States through 2006 - Volume 2 North Carolina: U.S. Geological Survey Scientific
Investigations Report 2009 -5158, 111 p). The resulting flow estimates are 4,230 cfs and 7,000 cfs
respectively. Note that these estimates do not include the effect of the Summit Lake Dam. These results
assume negligible buffering of peak flows is provided by the dam during the 2 and 5 -year event flows.
The predicted water surface elevations during these events are illustrated in Figure 1. The predicted water
surface elevations during base flow conditions when the Summit Lake Dam is generating power on 1 and
2 units respectively are also illustrated in Figure 1.
53020 SCANA / PSNC PROJECT T -01A REPLACEMENT
Hydrologic and Hydraulic Analyses Summary Page 2 of 4

935
930
925
920
a
W
915
Figure 1 - Green River Cross Section at Proposed
Crossing, Looking Downstream
910
905
0 100
200
300 400
Station (ft)
500 600 700
Field Measurements
LiDAR
......••• Base Flow
1 Unit
2 Units
— — 2 -Year Flood
— — 5 -Year Flood
❖ Challenges Associated with using Portable Dams to Facilitate a Dry
Cut
The challenges associated with using a portable dam system to facilitate a dry open -cut and installation of
the proposed pipeline crossing generally fall into threecategories.
1. Challenges associated with cofferdam configuration
2. Challenges associated with a flume bypass configuration
3. Challenges associated with a pump around bypass configuration
At the proposed crossing location, the Green River is approximately 100 feet wide. During base flow
conditions, the freeboard to the floodplain (at 916 ft elevation) is approximately 5 feet and the average
depth of flow is approximately 2.5 feet. Allowing for a minimum of one foot of freeboard during
construction, the maximum allowable water surface elevation during construction is approximately 915
feet. The lowest point in the cross section is approximately 908.3 feet. Thus the maximum allowable
depth of water during construction is 6.7 feet. Under base flow conditions it would be conceptually
possible to use a coffer dam configuration to facilitate a dry excavation using the following general
sequence:
53020 SCANA / PSNC PROJECT T -01A REPLACEMENT
Hydrologic and Hydraulic Analyses Summary Page 3 of 4

♦ Install a horseshoe shaped coffer dam to facilitate dry excavation of 60% of the trench length;
♦ Pump water out of the work area (continuously);
♦ Excavate pipeline trench;
♦ Place the section of pipe;
♦ Backfill the pipeline trench;
♦ Remove cofferdam and install similar coffer dam on the opposite side of the river;
♦ Pump water out (continuously);
♦ Excavate pipeline trench and expose end of previously placed pipe;
♦ Install additional pipe and weld connection; and
♦ Backfill trench and remove cofferdam.
Under base flow conditions, the hydraulic influence of the coffer dams will result in a maximum increase in
flow depths to an approximate elevation of 912.5 immediately upstream of the coffer dam. When Summit
Lake is generating power on 1 unit, the hydraulic influence of the coffer dam will result in a maximum
increase in flow depths to an approximate elevation 918.1 feet (i.e. flows will be out of the channel). Thus,
the coffer dams will fail when power is generated at the Summit Lake Dam. Further challenges to the
cofferdam approach include pipe welding in a the trench sump and the potential for failure of the second
coffer dam as pore pressures in the backfilled portion of the trench may cause instability in the bed and
undermine the cofferdam.
A potential alternative to the cofferdam approach is to use portable dam structures to completely isolate
the excavation on the upstream and downstream sides and flume flows across the work area through
lengths of 20 -inch diameter steel pipe. In order to estimate the number of pipes required, U.S. Federal
Highway Administration software HY -8 (Version 7.2) was used to analyze the pipes as culverts with
projecting inlets and outlets. According to this analysis, a total of 3 pipes would be required to convey a
base flow of 60 cfs while maintaining an upstream water surface elevation of 915 feet or less. However, if
flows increase due to rainfall in the watershed or power generation at the Summit Lake Dam, the number
of required pipes increase significantly. To convey flows across the work area when a single unit is
generating power will require approximately 17 pipes. When both generators are running, it would
require 31 pipes to safely convey water across the work area.
Another alternative to the coffer dam approach would be to pump river flows around the work site. At a
base flow of 60 cfs a 30 inch DV600c suction pump from Rain for Rent (or equivalent) operating at peak
performance would be required. The published capacity of this pump will onlyjust meet the flow
requirement. Applying a factor of safety of 2, two pumps would be required to convey base flow. To
convey flows when a single unit is generating power at the dam would require as many as 8 pumps.
53020 SCANA / PSNC PROJECT T -01A REPLACEMENT
Hydrologic and Hydraulic Analyses Summary Page 4 of 4

APPENDIX III

POLK COUNTY, NORTH CAROLINA
! I /BAC UP TURBUIDITY CURTAIN /
B_ A
ATW /
5' Xi282'
PERMANENT EASEMENT E PRIMARY TURBIDITY CURTAIN
EXISTING PIPELINE T -001B
122.42' ;
1 ;
P/L
i
P/L ONE UNIT RUNNING
n WATER LEVEL 85.15' PROPOSED 20" PIPELINE T -001A
(NORMAL WAT R LEVEL)
_ PERMANENT EASEMENT
_T_EA ORARY_w RKSPAC i
WAO
i
in P�� i
0� WA08
gK
TE P`ORARY OSPACE — — — — — /
ONE UNIT RUNNING WATER EL
C B A \
—Fl nW
—Fl nW
LEGEND
—FI nw
COBBLE T— i z" 01B SECTION C —C
SCALES N.T.S.
990
980
970
960
950
940
930
920
910
900
890
880
870
A
COBBLE i T z" —018 SECTION 13-13 13-13
SCALE N.T_S-
COBBLE ;z °'a SECTION A —A
SCALE. N.T.S.
%I
115T �/
-- x-- - -x - -- EROSION & SEDIMENTARY CONTROL DEVICE,
p �
-
/! ', _ PROPOSED
Of
j
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RIVER
TEMPORARY SPOIL PILE
cl
l CROSSING
WOOD MATS
ro
3� 3�
08° ENERGY DISSIPATION MATERIAL
3m
�JUa
- - -- TURBIDITY CURTAINS
° AWN
Ery
SJS
Ua
zW
w
vJi
—FI nw
COBBLE T— i z" 01B SECTION C —C
SCALES N.T.S.
990
980
970
960
950
940
930
920
910
900
890
880
870
A
COBBLE i T z" —018 SECTION 13-13 13-13
SCALE N.T_S-
COBBLE ;z °'a SECTION A —A
SCALE. N.T.S.
%I
245 +50 245 +00
I I I I 1 1
244 +50 244 +00 243 +50 243 +00 242 +50 242 +00
990
980
970
960
950
940
930
920
910
900
890
880
870
GREEN RIVER
SITE SPECIFIC PROJECT NOTES:
1. ALL CONSTRUCTION AND MAINTENANCE ACTIVITIES WILL BE PERFORMED IN ACCORDANCE
WITH PSNC ECS.
2. CROSSING INSTALLATION SHALL BE THE WET DITCH CROSSING METHOD AND SHALL BE
IN ACCORDANCE WITH APPLICABLE PERMITS AND REGULATIONS.
3. CONSTRUCTION DATES ARE UNLIMITED BUT NOT EXCEEDING 1 JUNE 2016.
4. NC DENR SHALL BE NOTIFIED 5 DAYS PRIOR TO CONSTRUCTION AS PER 401 PERMIT
CONDITIONS.
5. LOCATE EXTRA WORK AREAS AT LEAST 10 FEET FROM EDGE OF WATER.
6. GRADE AND TRENCH SPOIL WILL BE STOCKPILED IN SEDIMENT CONTROLLED AREA
ADJACENT TO RIVER BANKS IN EXTRA WORK AREAS.
7. TURBIDITY CURTAINS (TWO OR MORE) SHALL BE INSTALLED DOWNSTREAM IN ORDER
TO TRAP ANY SEDIMENTS FROM MIGRATING DOWNSTREAM.
8. WETLAND BOUNDARIES AND OTHER AREAS OF ENVIRONMENTAL CONCERN WILL BE FIELD
MARKED BY THE ENVIRONMENTAL INSPECTOR PRIOR TO CONSTRUCTION.
9. REMOVE AND STOCKPILE TOP 12 INCHES OF TOPSOIL FOR SPOIL PILE AREAS LOCATED
IN WETLANDS.
10. CONCRETE COATED PIPE SHALL BE INSTALLED UNDER THE STREAM TO A MINIMUM OF
5 FEET OF COVER AND EXTEND AT LEAST 15 FEET PAST TOP OF BANK TO OUTSIDE OF
TOP BANK.
11. PIPE SHALL BE INSTALLED LEVEL UNDER STREAMS LESS THAN 100' WIDE TO A
MINIMUM OF 5 FEET COVER EXCEPT IN ROCK FORMATIONS WHERE TOP OF PIPE MAY BE
LAID TO A MINIMUM OF 2.0 FEET BELOW ADJACENT ROCK.
12. FULL JOINTS OF PIPE SHALL BE USED UNLESS OTHERWISE DIRECTED BY THE
CONSTRUCTION ENGINEER.
13. ALL GIRTH WELDS SHALL BE 100% RADIOGRAPHICALLY INSPECTED.
14. CONCRETE COATED PIPE, FIELD SAG BENDS, AND RELATED CROSSING PIPE SHALL BE
STAGE, ASSEMBLED, AND PRE - INSTALLED TESTED ON THE NORTH SIDE RIGHTS -OF THE
WAY PRIOR TO COMMENCING TRENCHING OPERATIONS.
15. NC DENR SHALL BE NOTIFIED 7 DAYS PRIOR TO RESTORATION AS PER PERMIT
CONDITIONS.
16. RESTORATION SHALL COMMENCE IMMEDIATELY AFTER TRENCH IS BACKFILLED.
17. EXISTING T -01 B 12 -INCH PIPELINE WILL REMAIN ACTIVE AND SHALL BE PROTECTED
AGAINST DAMAGE THROUGHOUT THE CROSSING CONSTRUCTION.
18. MAINTAIN 10.0 FOOT UN- GRUBBED BUFFER ZONE ON EACH SIDE UNTIL TRENCH
CONSTRUCTION BEGINS.
19. CONTRACTOR TO PROVIDE OIL BOOMS AND SHEEN CONTROL DEVICES ON PROXIMAL
STAND -BY DURING CROSSING CONSTRUCTION.
20. BENDS SHALL BE INSTALLED NO CLOSER THAN 10.0 FEET OUTSIDE OF TOP OF BANKS.
21. CONTRACTOR TO COORDINATE IN RIVER CONSTRUCTION EFFORTS WITH DUKE ENERGY'S
TUXEDO POWER SCHEDULE. DUKE ENERGY IS WILLING TO WORK WITH PSNC TO SUSPEND
POWER GENERATION FOR UP TO FOUR DAYS SO THAT CROSSING CAN OCCUR DURING
NORMAL FLOW CONDITIONS (60 CFS) RATHER THAN 240 CFS WHEN ONE POWER UNIT IS
RUNNING. CONTRACTOR SHALL EXCAVATE (WORK) WITHIN RIVER ONLY DURING NORMAL
FLOW CONDITIONS AND SHALL BE VIGILANT OF ANY IMPENDING RAIN FORCAST WHICH MAY
CAUSE RIVER TO FLOOD.
RIVER FLOW RATES
NOMINAL FLOW : 42 -60 CFS
ONE TUXEDO UNIT RUNNING : 222 -240 CFS
TWO TUXEDO UNITS RUNNING : 402 -420 CFS
2 YEAR 30
INCHES, 38,400 ACRE DRAINAGE ADDS 427 CFS
WBA, P, C,
FIRM REGISTRATION NUMBER: NC C -2618
PSIICENE/;GI:
PROJECTION SYSTEM: NAD83 STATE PLANE,
NORTH CAROLINA (U.S. SURVEY FEET)
R/W INGRESS F ED FOR
X= 588523.9600' RMIT
Y= 1031736.4737'
OBER -201 5
R/W EGRESS
Q X= 588659.9957'
j
Y= 1031677.8121'
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NATURAL G
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WATER ELEV. WITH
WATER
POWER GENERATION
LEV. LOW WATER 90
911.178
.653
NATURAL GRADE
\\�\
PROPOSED 20" PIPELINE T -001A
175 FT.
CONCRETE COATED PIPE
245 +50 245 +00
I I I I 1 1
244 +50 244 +00 243 +50 243 +00 242 +50 242 +00
990
980
970
960
950
940
930
920
910
900
890
880
870
GREEN RIVER
SITE SPECIFIC PROJECT NOTES:
1. ALL CONSTRUCTION AND MAINTENANCE ACTIVITIES WILL BE PERFORMED IN ACCORDANCE
WITH PSNC ECS.
2. CROSSING INSTALLATION SHALL BE THE WET DITCH CROSSING METHOD AND SHALL BE
IN ACCORDANCE WITH APPLICABLE PERMITS AND REGULATIONS.
3. CONSTRUCTION DATES ARE UNLIMITED BUT NOT EXCEEDING 1 JUNE 2016.
4. NC DENR SHALL BE NOTIFIED 5 DAYS PRIOR TO CONSTRUCTION AS PER 401 PERMIT
CONDITIONS.
5. LOCATE EXTRA WORK AREAS AT LEAST 10 FEET FROM EDGE OF WATER.
6. GRADE AND TRENCH SPOIL WILL BE STOCKPILED IN SEDIMENT CONTROLLED AREA
ADJACENT TO RIVER BANKS IN EXTRA WORK AREAS.
7. TURBIDITY CURTAINS (TWO OR MORE) SHALL BE INSTALLED DOWNSTREAM IN ORDER
TO TRAP ANY SEDIMENTS FROM MIGRATING DOWNSTREAM.
8. WETLAND BOUNDARIES AND OTHER AREAS OF ENVIRONMENTAL CONCERN WILL BE FIELD
MARKED BY THE ENVIRONMENTAL INSPECTOR PRIOR TO CONSTRUCTION.
9. REMOVE AND STOCKPILE TOP 12 INCHES OF TOPSOIL FOR SPOIL PILE AREAS LOCATED
IN WETLANDS.
10. CONCRETE COATED PIPE SHALL BE INSTALLED UNDER THE STREAM TO A MINIMUM OF
5 FEET OF COVER AND EXTEND AT LEAST 15 FEET PAST TOP OF BANK TO OUTSIDE OF
TOP BANK.
11. PIPE SHALL BE INSTALLED LEVEL UNDER STREAMS LESS THAN 100' WIDE TO A
MINIMUM OF 5 FEET COVER EXCEPT IN ROCK FORMATIONS WHERE TOP OF PIPE MAY BE
LAID TO A MINIMUM OF 2.0 FEET BELOW ADJACENT ROCK.
12. FULL JOINTS OF PIPE SHALL BE USED UNLESS OTHERWISE DIRECTED BY THE
CONSTRUCTION ENGINEER.
13. ALL GIRTH WELDS SHALL BE 100% RADIOGRAPHICALLY INSPECTED.
14. CONCRETE COATED PIPE, FIELD SAG BENDS, AND RELATED CROSSING PIPE SHALL BE
STAGE, ASSEMBLED, AND PRE - INSTALLED TESTED ON THE NORTH SIDE RIGHTS -OF THE
WAY PRIOR TO COMMENCING TRENCHING OPERATIONS.
15. NC DENR SHALL BE NOTIFIED 7 DAYS PRIOR TO RESTORATION AS PER PERMIT
CONDITIONS.
16. RESTORATION SHALL COMMENCE IMMEDIATELY AFTER TRENCH IS BACKFILLED.
17. EXISTING T -01 B 12 -INCH PIPELINE WILL REMAIN ACTIVE AND SHALL BE PROTECTED
AGAINST DAMAGE THROUGHOUT THE CROSSING CONSTRUCTION.
18. MAINTAIN 10.0 FOOT UN- GRUBBED BUFFER ZONE ON EACH SIDE UNTIL TRENCH
CONSTRUCTION BEGINS.
19. CONTRACTOR TO PROVIDE OIL BOOMS AND SHEEN CONTROL DEVICES ON PROXIMAL
STAND -BY DURING CROSSING CONSTRUCTION.
20. BENDS SHALL BE INSTALLED NO CLOSER THAN 10.0 FEET OUTSIDE OF TOP OF BANKS.
21. CONTRACTOR TO COORDINATE IN RIVER CONSTRUCTION EFFORTS WITH DUKE ENERGY'S
TUXEDO POWER SCHEDULE. DUKE ENERGY IS WILLING TO WORK WITH PSNC TO SUSPEND
POWER GENERATION FOR UP TO FOUR DAYS SO THAT CROSSING CAN OCCUR DURING
NORMAL FLOW CONDITIONS (60 CFS) RATHER THAN 240 CFS WHEN ONE POWER UNIT IS
RUNNING. CONTRACTOR SHALL EXCAVATE (WORK) WITHIN RIVER ONLY DURING NORMAL
FLOW CONDITIONS AND SHALL BE VIGILANT OF ANY IMPENDING RAIN FORCAST WHICH MAY
CAUSE RIVER TO FLOOD.
RIVER FLOW RATES
NOMINAL FLOW : 42 -60 CFS
ONE TUXEDO UNIT RUNNING : 222 -240 CFS
TWO TUXEDO UNITS RUNNING : 402 -420 CFS
2 YEAR 30
INCHES, 38,400 ACRE DRAINAGE ADDS 427 CFS
WBA, P, C,
FIRM REGISTRATION NUMBER: NC C -2618
PSIICENE/;GI:
PROJECTION SYSTEM: NAD83 STATE PLANE,
NORTH CAROLINA (U.S. SURVEY FEET)
R/W INGRESS F ED FOR
X= 588523.9600' RMIT
Y= 1031736.4737'
OBER -201 5
R/W EGRESS
Q X= 588659.9957'
j
Y= 1031677.8121'
0 25 50
a RMSCAM' 1' -50, Sa
PN ME (N) SCME: 1- -50'
0 25 50
PROFLE (V) SCALE. 1- -50'
I
SCANA - T -001A REPLACEMENT
GREEN RIVER CROSSING
WET DITCH CROSSING METHOD
POLK COUNTY NORTH CAROLINA
° AWN
Ery
SJS
NOTED ATe 0059354
DATE
D,,,,,,,,,
09 -18 -15
DRAWING NO.
53020 -34 -051
A
A
EaR veR1tT
20 -31 -011
AUGNMENT SFEET
C1ECKm
CAF
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ORAWNING N0.
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DRAWN DATE
ar REVISED
C mm
ar
PROJECT
ENGINEER
APPROVm
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PROJECT
EN6RiEER
DEM
REFERENCE DRAWINGS
I ISSUE RECORD
I ''PPuRaym
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Oa b. X 2015 - 10:41—