Roxboro EAB - CBE - Appendix C_20200107

Wood Environment & Infrastructure Solutions, Inc.
Duke Energy —Roxboro Plant wood.
EAB Coal Combustion Residuals Surface Impoundment Closure Plan (Excavation)
APPENDIX C: ENGINEERING EVALUATIONS AND
ANALYSES

Wood Environment & Infrastructure Solutions, Inc.
Duke Energy —Roxboro Plant wood.
EAB Coal Combustion Residuals Surface Impoundment Closure Plan (Excavation)
APPENDIX Cl: STORMWATER

wood.
November 5, 2019
Mr. Dale Smith
Project Manager
Duke Energy
526 South Church Street
Charlotte, North Carolina 28202
Subject: Roxboro East and West Ash Ponds H&H Update - Revised
Summary of Supporting H&H Analyses
Duke Energy — Roxboro Steam Station
Person County, North Carolina
Wood Project No. 7812-19-0138
Dear Mr. Smith,
As authorized by Duke Energy Carolinas, LLC (Duke Energy), Wood Environment & Infrastructure
Solutions, Inc. (Wood) has revised the Hydraulic and Hydrologic analysis (H&H) based upon a
full Probable Maximum Precipitation (PMP) rainfall event to determine if the East and West Ash
Basins located at the Roxboro Steam Station have sufficient capacity for the design storm with
the current outlet conditions.
Background Information
The Roxboro Plant is located at 1700 Dunnaway Road approximately 9 miles northeast of
Roxboro, North Carolina, and is adjacent to the Hyco Reservoir. The Roxboro Plant has four
coal-fired electric generating units. The first generating unit at the Roxboro Plant is reported to
have begun commercial operation in 1966. The four coal-fired generating units at the site are
currently in service. Flue gas desulfurization (FGD) technology, commonly referred to as a
"scrubber", has been installed to reduce SO2 emissions. The FGD Pond areas were
constructed within the West Ash Pond area to support treatment of scrubber wastewater.
All ash material was deposited within the East and West Ash Pond areas by hydraulic sluicing
operations until the plant was modified for dry fly ash handling operations in the 1990s. Most of
the fly ash material produced at the Roxboro Station is currently collected by dry handling
operations and disposed of within the ash mono -fill site located within the East Ash Pond area.
There has been no inflow to the West Ash Basin other than non -contact stormwater since April
2019.
Correspondence:
Wood Environment &Infrastructure Solutions, Inc.
4021 Stirrup Creek Drive, Suite 100
Durham, North Carolina 27703
Tel [phone]
Fax [phone]
0
Licensure NC Engineering F-1253 NC Geology C-247

Duke Energy
November 5, 2019
Page 2
East Ash Pond Main Dam and Separator Dike
Roxboro Plant
Roxboro East and West Ash Ponds H&H Update - Revised
Wood Project No. 7812-19-0138
The East Ash Pond Dam is regulated under the NCDENR Division of Energy, Mineral and Land
Resources, Land Quality Section, Dam Safety Program as a High Hazard Dam, and is identified
in the regulatory program as "Roxboro East Retired Ash Pond Dam" (State I.D. No. PERSO-
033). The East Ash Basin Dam was originally constructed between 1964 and 1965, with a
maximum embankment height of about 50 feet. In 1973, the dam was raised 20 feet to its
present configuration. The East Ash Basin became inactive following construction of the West
Ash Basin around 1986. The East Ash Basin Dam has a "Low Hazard" classification under the
regulations of the North Carolina Department of Environmental Quality (NCDEQ), Land Quality
Section, Dam Safety Program.
Beginning about 1988, the East Ash Basin was used as an unlined ash landfill area with the
conversion of the plant to dry fly ash handling. About 2001, Phases 1 through 3 of the lined ash
monofill area were permitted, which are partially located on the unlined fill area. Phases 4 and 5
of the lined monofill area were permitted in 2010, Phase 6 was permitted in 2013, which is the
first phase design with a double liner system and a leak detection layer.
Limited information regarding the construction of divider berm is available for reference. Based
on CP&L drawings dated October 22, 1990, sometime between 1987 and 1990, the divider
berm (referenced as "separating dike" in drawings) was constructed just west of the original
East Ash Basin discharge canal. It appears that the purpose of the divider berm was to provide
a cutoff for drainage between the original discharge canal and the unlined ash landfill area.
Around 1987, prior to the construction of the divider berm, a drainage system was constructed
to provide positive drainage from the east to west side of the East Ash Basin. Around 1988, the
East Ash Basin was used as an unlined ash landfill area with the conversion of the plant to dry
fly ash handling.
Based on the CP&L drawings, the divider berm was constructed using on -site borrow material
consisting of soils classified as clayey sand (SC), clay (CL) or silty sand (SM). Borrow material
areas were to be located west of the proposed divider berm location and below contour
elevation 486 feet. Notes called for placement of fill in 8-inch maximum lifts and compacted to
95% maximum standard Proctor density.
The construction sequence provided in the CP&L drawings entailed starting construction by end
dumping dry ash fill into the pond to create a stable working surface. The ash fill was to be
placed in 3-foot maximum lifts and compacted with successive passes of a dozer, sheep's foot
roller or other equipment until a stable base was established. All areas of pond ash fill were to
be capped with a 2-foot thick layer of compacted earth cover.
Currently, the stormwater derived from East Ash Pond flows to the West Ash Pond via two 30-
inch RCP culverts and one 10-foot RCP culvert beneath Dunnaway Road.
West Ash Pond Main Dam and Dikes
The West Ash Pond Dam is regulated under the NCDENR Division of Energy, Mineral and Land
Resources, Land Quality Section, Dam Safety Program as a High Hazard Dam, and is identified
in the regulatory program as "Roxboro West Ash Pond Dam" (State I.D. No. PERSO-038). The
West Ash Pond Main Dam was constructed in 1973 by Brown & Root across Sargents Creek,
which is a tributary to Hyco Reservoir. The dam is an earth fill embankment with a central low

Duke Energy
November 5, 2019
Page 3
Roxboro Plant
Roxboro East and West Ash Ponds H&H Update - Revised
Wood Project No. 7812-19-0138
permeability earth core. The original structural height of the dam was 70 feet with a crest at
Elevation 457 feet (MSL). The original normal pool was at Elevation 445 feet (MSL). Since the
dam was constructed in Hyco Reservoir, it was necessary to provide cofferdams on both sides
of the dam (The downstream area between the dam and the lake is the cofferdam which was
constructed of material consistent with the outer shell of the dam). A cutoff trench was reported
as excavated to sound rock at a depth of about 10 feet under the central earth core. A chimney
drain of sand and gravel was provided for the portion of the downstream slope of the core
between Elevation 445 (MSL) and the crest of the downstream cofferdam, Elevation 415 (MSL).
In 1986, the Main Dam was raised by 13 feet to Elevation 470 feet (MSL) and a series of new
dikes (Ash Pond Dikes No. 1, 2, 3, and 4) and channels were constructed to increase the
storage capacity of the pond and modify the circulation pattern to increase ash settling time.
The series of dikes and channels divert the natural stream flow and storm runoff around the
pond and through the spillway to Hyco Reservoir.
The Main Dam cross-section was raised toward the downstream slope using compacted
random earth with a low permeability core. A vertical chimney drain with a horizontal filter
blanket was connected with the original drain system. The downstream slope was constructed
at a slope of approximately 2(horizontal):1(vertical). The normal water level was also raised to
Elevation 463 feet (MSL), which provided a freeboard of 7 feet.
The West Ash Pond Dike No. 1 (West Ash Pond South Rock Filter, State ID No. PERSO-039) is
constructed of rock fill excavated from the nearby outlet channel. The embankment design
includes a sand filter blanket provided on the upstream slope placed below a layer of rock. The
crest of the dam is at Elevation 473 feet (MSL), and with the normal pool at Elevation 463 feet
(MSL), the available freeboard for this dam is 10 feet. A berm (buttress) approximately 20 feet
thick was constructed on the downstream slope below approximately Elevation 448 (MSL). The
maximum structural height of the Dike No. 1 is approximately 50 feet.
Dikes No. 2, 3, and 4 are placed in low areas of the original site topography along the excavated
discharge channel on the west side of the West Ash Pond area. These dikes were constructed
primarily using soil fill. For dikes 2 and 4, the fill was end -dumped into the existing water until
the soil was above the water at approximately Elevation 445 to 447 (MSL). Once the fill was out
of the water, it was placed and compacted in lifts. Dike 3 was constructed completely of
compacted soil fill above the original water level. Dike 4 was constructed across three low
areas in the pond with the shallowest in the middle. In the two deeper areas (north and south
ends), a stone berm (buttress) approximately 20 feet thick was constructed on the downstream
slope below approximately Elevation 460 (MSL). The stone berm was extended to the entire
dike in 2015. A stone berm (buttress) approximately 30 feet thick was also constructed on the
downstream slope of Dike 2 below approximately Elevation 451 (MSL). The crest of these dikes
is at approximately the same elevation as the Main Dam, Elevation 470 feet (MSL).
The maximum structural height of the Dike No. 2 is approximately 40-45 feet, for Dike No. 3 is
approximately 10 feet, and for Dike No. 4 is approximately 40-45 feet. The length of Dike No. 2
is approximately 500 feet, for Dike No. 3 is approximately 500 feet, and for Dike No. 4 is
approximately 1,000 feet. The design crest width is approximately 20 feet and the upstream
and downstream slopes are both 2(horizontal):1(vertical). From review of available design
information, there are no design provisions for internal drainage of the dikes.

Duke Energy Roxboro Plant
November 5, 2019 Roxboro East and West Ash Ponds H&H Update - Revised
Page 4 Wood Project No. 7812-19-0138
Two former discharge outlet structures for the West Ash Pond were located at Dike No. 1. The
risers for the discharge outlet structures consisted of 2-foot high sections of 48-inch diameter
RCP stacked approximately 12 feet high (to about Elevation 463.0 feet). A metal skimmer
structure was provided at the top of each structure. The risers were supported on concrete
foundations that are approximately 10 feet x 10 feet x 3.25 feet thick. The riser structures and
associated discharge piping were permanently abandoned by grouting in 2016. A new 36-inch
HDPE discharge outlet pipe was installed as a replacement, and two 400-foot overflow spillways
were constructed on the crest of the dam.
H&H Evaluation Criteria
North Carolina's Department of Environmental Quality (NCDEQ) Dam Safety has adopted the
Federal CCR Rule and per the dam safety High Hazard Classification, each ash basin is now
required to pass a full Probable Maximum Precipitation (PMP). Each basin is classified as high
hazard by NCDEQ due to the potential for environmental impacts greater than $200,000, if the
basin failed.
The computer program HydroCAD Version 10.0 was initially used to perform the H&H calculations
to determine whether the current conditions (revised per updated survey information) could safely
pass or store the revised design storm (full PMP storm event) without an uncontrolled discharge.
Previously, the design storm was listed as the 3/4 PMP in WAB, 1/3 PMP in EAB. NCDEQ has
requested that the supporting modeling information be provided in either HEC-RAS or HEC-HMS
format. In accordance with the new guidelines, the Hydrologic Engineering Center Hydrologic
Modeling System (HEC-HMS, version 4.3) computer program was used to perform the hydrologic
& hydraulic (H&H) calculations.
The existing conditions for the Ash Ponds were obtained from best available reports and
topographic data including the Wood Hydrologic and Hydraulic Evaluation Roxboro Ash Ponds,
McKim and Creed Topographic Surveys (2014), and LiDAR Topographic Survey by WSP (2015).
The Roxboro Ash Ponds are classified as high hazard, with the revised regulatory design storm
for the ponds of the full PMP storm event. Based on the Site -Specific Maximum Precipitation
Estimates, the PMP for the Roxboro site is as follows:
PMP = 17.3 inches of rainfall for 6 hours
Based on field observations and aerial imagery, each of the sub -basins within the East and West
Ash Basins were assigned appropriate curve numbers (CN) for the general condition of land
covers with an appropriate time of concentration calculated for each area by using TR-55
recommendations.
The storage for the basin was developed assuming initial conditions having water stored in the
basin at Elevation 463 feet. The storage for the basin was estimated using the prismatic volume
calculation method with the elevation -surface area input data. Storage volumes were determined
from contours derived from the existing conditions.
The H&H Analysis was conducted for the stage -storage conditions, and Table 1 provides
information on the current outlet structures.

Duke Energy
November 5, 2019
Page 5
Roxboro Plant
Roxboro East and West Ash Ponds H&H Update - Revised
Wood Project No. 7812-19-0138
Table 1. Ash Pond Outlet Existing Conditions
Ash Pond Characteristic
East Ash Basin
West Ash Basin
Dike Crest Elevation (ft)
495
470
Culvert Diameter (in)
2 x 30"
30.3
1 x 120
Culvert Elevation (ft)
471.74/471.61 (30" Culverts)
462.98
457.61 (10' Culvert)
Culvert Material
RCP
HDPE
The basin is filled with ash, and stormwater would likely infiltrate into the underlying ash material
during a storm event. However, for the purpose of this analysis, it is assumed that no infiltration
occurs. A minimum time of concentration (Tc) was calculated for the pond consistent with T-55
methods in HydroCAD. The length of the flow paths of sheet flow, shallow concentrated flow, and
channel flow as well as slope and channel characteristics were determined based on the
topography, which is consistent with TR-55 recommendations. The storage for the basin was
estimated using the prismatic volume calculation method with the elevation -surface area input
data. Storage volumes for the Ash Basins were determined from contours derived from
topographic surveys by McKim and Creed Engineers (2014, 2017), and LiDAR Topographic
Survey by WSP (2015). Wood assumed a site specific storm distribution for the 6-hr peak
hydrograph.
In order to support the request by NCDEQ to model the basin in HEC-HMS format, the existing
hydraulic models created in HydroCAD were re-created using HEC-HMS version 4.3. The HEC-
HMS models were developed using inputs from the existing HydroCAD models to the greatest
extent possible. At a minimum, the following inputs required for the development of the HEC-
HMS model were utilized:
• Rainfall data, curve numbers, time of concentration for hydrologic computations
• Stage -Storage rating curves for the ash ponds
• Outlet rating curves
H&H Summary
Using the information above and the design storm hydrograph, Wood completed the H&H
Analyses using HEC-HMS version 4.3 and ran the models for 360 hours (15 days) to allow
sufficient time for 80% drawdown. The results of the analyses are shown below in Table 2.
Analysis of the current conditions indicate both the East and West Ash Basins meet the
requirements to safely contain and pass the inflow volume through the existing discharge
structures.

Duke Energy
November 5, 2019
Page 6
Roxboro Plant
Roxboro East and West Ash Ponds H&H Update - Revised
Table 2. Modeling Results
Wood Project No. 7812-19-0138
Updated Results
East Ash Basin
West Ash Basin
Peak Stage during OF ft
471.5
469.1
Minimum Dike Elevation ft
476.25
470
Pond Freeboard ft
4.75
0.9
100% Inflow Volume acre-ft
369.3
893.3
80% Inflow Volume acre-ft
295.4
714.6
80% Discharge Time hr
18
145
According to Dam Safety 15A NCAC 2K.0205, the spillway system shall be capable of removing
at least 80 percent of the water temporarily detained above the elevation of the primary spillway
within 15 days following passage of the design storm peak. Based upon the existing conditions,
the East and West Ash Basins safely store and pass the design storm event. Thus, the current
structures are compliant with 15A NCAC 2K.0205.
Conclusion
Based on the results of this study and considering the conservative assumption made (no
infiltration) Wood concludes the existing conditions for the East and West Ash Basins will safely
store and pass the design storm (full PMP storm event) without an uncontrolled discharge and
meets the drawdown requirements per 15A NCAC 2K 0.0205.
Closing
Wood appreciates the opportunity to offer our services on this project. If you have any
questions concerning this response, please contact us.
Sincerely,
Wood Environment & Infrastructure Solutions, Inc.
William A. Williams, PE, PG
Senior Engineer
Attachment: HEC-HMS model results
i'`L"L�OL4d 4 i 7 4 714gi 87C
IN
438E/ti7''L�c�
Jeffery A. Mann, PE
Chief Engineer

1 J�mcppml
HEC-HMS Basin Model Diagram for Roxboro East & West Ash Basins

summary ReSurm Tor KMf W-OF-
RMjM:Ryyboro SimulationRun:PMP
ReserVarr: 6P
Start pf Run: 11
1Mar2OM WOO Basin Model: Roxboro
End of Run: 16MaF201R, 00:00 wuam"e Model: Me[ 1
Compute Time:1190ct2O19, 09:54:46 Control Sperlficatsons:Control 1
VuWme Units: 01H DAC•FT
Competed Results
Peak Lnkw: l IB2.1 (CFS) DatejTme Uf Peak Inflow: 41Mar2019, 0525
Peak Oischarge: 1956.7 (CFS) DatiaMrne oT Peak Orscharge:Ol Mar201% 05:49
tnllaw Vvlunne: 369.3 (AC -FT) Peak Slurage: 19.0 (AC -FT)
Discharge Vnlume'364-3 (AC -Fr) Peak Elewatlon: 471-5 (FT)
HEC-HMS Results at East Ash Basin for 1 PMP Storm

Reserver ^1 P^ Rewhs fa Run -PMP^
I r ,2-
,e .Itw p-Time: A — A. 09: S1:J6)
Rw:—EI—Ip Rew[9hnape Rw:Pf@flemmRlP ReafPotl Elewtlon—Rw:PYPElemxrtlPResW[Outtow---RunPIP Elemn[1PReaIHLomElnetllMar
Summary Resufts for Reservaer'1P" -1110000�q a
PrO)Ld: Raxharo simulatmn Run: PMF
RESBrvcw: 1P
Start of Run; 01Mar2019, 00;00 Basin Model: Ro-xboro
End of Run: 15MerZo19, 00;00 MeteorMingeC Model: MEL I
Compute Time:19I#c@019, 09:54:46 Control Speclftcatfans:Cwtral 1
Volume drifts: * N AC -FT
Computed Results
Peak Inflow: 2155.8 (M) 0ate�iime of Peak Wow: 01M51019, 05:14
Peak OLseharge: 1706.2 {CIS} ❑a*Trme of Peak 0+sdiarge:DIMaQ014, 05:50
FnfrowVolume; Wa Pe5k56orage: 477.7(AC•Fo
DL9drarye Volume:Mla Peak Elevation: 459.t (FT)
HEC-HMS Results at West Ash Basin for 1 PMP Storm

Roxboro Site Specific PMP - Cumulative Rainfall
//SS PMP - 6HR/PRECIP-CUM/31DEC2018/6MIN/GAGE/
Date/Time
Original
Estimate/Entry
Revised
(IN) -+
(IN)
(IN)
31Dec2018 24:00
0.00
0.00
0.09
01Jan2019 00:06
0.09
01Jan2019 00:12
0.14
0.14
01Jan2019 00:18
0.20
0.20
013an2019 00:24
0.30
0.30
013an2019 00:30
0.42
0.42
013an2019 00:36
0.54
0.54
013an2019 00:42
0.68
0.68
013an2019 00:48
0.83
0.83
013an2019 00:54
1.01
1.01
013an2019 01:00
1.21
1.21
013an2019 01:06
1.44
1.44
01Jan2019 01:12
1.68
1.68
01Jan2019 01:18
1.93
1.93
01Jan2019 01:24
2.20
2.20
01Jan2019 01:30
2.49
2.49
01Jan2019 01:36
2.78
2.78
01Jan2019 01:42
3.07
3.07
01Jan2019 01:48
3.35
3.35
013an2019 01:54
3.66
3.66
013an2019 02:00
3.95
3.95
013an2019 02:06
4.25
4.25
013an2019 02:12
4.55
4.55
013an2019 02:18
4.84
4.84
013an2019 02:24
5.12
5.12
013an2019 02:30
5.41
5.41
01Jan2019 02:36
5.70
5.70
01Jan2019 02:42
5.99
5.99
01Jan2019 02:48
6.28
6.28
01Jan2019 02:54
6.56
6.56
01Jan2019 03:00
6.84
6.84
01Jan2019 03:06
7.14
7.14
01Jan2019 03:12
7.44
7.44
013an2019 03:18
7.73
7.73
013an2019 03:24
8.04
8.04
013an2019 03:30
8.35
8.35
013an2019 03:36
8.68
8.68
013an2019 03:42
9.02
9.02
013an2019 03:48
9.37
9.37
013an2019 03:54
9.74
9.74
01Jan2019 04:00
10.13
10.13
01Jan2019 04:06
10.53
10.53
01Jan2019 04:12
11.081
11.08
01Jan2019 04:18
11.821
11.82

Date/Time
Original
Estimate/Entry
Revised
(IN)
(IN)
(IN)
01Jan2019 04:24
12.27
12.27
12.75
13.23
01Jan2019 04:30
12.75
01Jan2019 04:36
13.23
01Jan2019 04:42
13.72
13.72
01Jan2019 04:48
14.21
14.21
01Jan2019 04:54
14.69
14.69
01Jan2019 05:00
15.16
15.16
01Jan2019 05:06
15.62
15.62
01Jan2019 05:12
16.06
16.06
01Jan2019 05:18
16.44
16.44
01Jan2019 05:24
16.78
16.78
01Jan2019 05:30
17.06
17.06
01Jan2019 05:36
17.24
17.24
01Jan2019 05:42
17.30
17.30
01Jan2019 05:48
17.30
17.30
01Jan2019 05:54
17.30
17.30
01Jan2019 06:00
17.30
17.30

Final Conditions Stormwater Calculation
Duke Energy— Roxboro Steam Station
Ash Basin Closure Plan
Calculation Title:
Final Conditions Stormwater Calculation
Summary:
The existing ash basins were designed to safely contain
and discharge the runoff from 6-hour Full PMP
design storm event considering final conditions for the East Ash Basin and the West Ash Basin closure by
excavation. Stormwater channels were designed to convey stormwater for a 100 year, 24-hour design
storm event.
Notes:
_ 0 AL
— 3988r
.
19H' K H Al
\
Revision Log:
No.
Description
Originator
Verifier
Technical Reviewer
0
Initial Submittal
G'L�r
9
Ekene Okorie
Rahish Khatri
Jeff Mann
Wood Project No. 7810-18-1107 1 of 11 wood.11 /06/19

Final Conditions Stormwater Calculation
Duke Energy — Roxboro Steam Station
OBJECTIVE:
Ash Basin Closure Plan
The objective of these calculations is to support the design of the proposed basins hydrologic and
hydraulic capacity to adequately manage runoff from the design storm event based on long-term
conditions following the decommissioning of the East Ash Basin and West Ash Basin at Roxboro
Steam Station in Semora, North Carolina (Approximate Coordinates: lat 36°28'N, long 79°04'W).
METHOD:
Stormwater flow rates will be calculated using the SCS method. The hydraulic performance of
existing and proposed outlet structures were evaluated using weir equation, culvert calculation, and
Hydrologic Modeling System (HEC-HMS) software. The proposed stormwater conveyance
channels were evaluated using Manning's equation. The existing conditions for the ash basins and
conveyance structures were obtained from best available reports and topographic data.
DEFINITION OF VARIABLES:
A =
area;
b =
bottom width;
Q =
flow;
S =
longitudinal slope;
n =
Manning's n;
V =
velocity; and
Z =
channel side slope.
t =
time;
Tc =
time of concentration;
SCS =
Soil Conservation Service;
CN =
curve number;
CFS =
Cubic Feet per Second;
PMP =
Probable Maximum Precipitation;
CCR =
Coal Combustion Residuals;
CFR =
Code of Federal Regulations;
CALCULATIONS:
1.0 Upstream Tributary Areas and Stormwater Basins
The stormwater runoff from upstream tributary areas is assumed to discharge across the closed ash
basins shown in Figures 2.
The existing ash basins are proposed to be decommissioned by excavation of CCR material and
transport to a permanent lined landfill. The existing main dam and dikes on West Ash basin will be
breached and final grades interior to the basins will be established to promote drainage. Stormwater
will be directed across vegetated finished grades and into riprap energy dissipators before
discharging into wetland areas that ultimately flow into the Hyco Lake.
The design criteria used for the basin was determined by first estimating the peak flow into the basin
using the SCS method, then evaluating the channel capacity using Manning's equation. The channels
Wood Project No. 7810-18-1107 2 of 11 ����!
11/06/19

Final Conditions Stormwater Calculation Ash Basin Closure Plan
Duke Energy — Roxboro Steam Station
were conservatively designed for capacity for the 100-year design storms and stability for the 25 year
design storm. The ash basin's storage capacity was evaluated using the prismatic volume calculation
method with the elevation -surface area input data. The Hydrologic Modeling System (HEC-HMS)
software [Ref. 1 ] was used to model the final condition of the basins and the spillways. The basins
were conservatively designed for capacity for the full PMP storm event.
1.1 Estimate drainage areas
Drainage area delineation was based on the proposed final conditions after closure of the existing
ash basins (East and West Ash Basins). The drainage areas are defined in Figure 2(a) and 2(b) and
are summarized in the following table:
Table 1: Summary of Drainage Areas
Basin ID
Drainage
Area ID
Drainage
Area
{A)
(ac)
Soil
Class
(HSG)
Curve
Number
(CN)
Total
Time of
Concentration
{TC,total)
(min)
DA-E-1
14.850
C
84
11.8
DA-E-2
23.000
C
84
7.2
DA-E-3
55.490
C
95
14.8
DA-E-4
27.630
C
84
20.9
DA-E-5
7.960
C
84
8.7
DA-E-6
9.330
C
84
10.2
East Ash
Basin
DA-E-7
13.250
C
82
10.3
DA-E-8
20.970
C
82
12
DA-E-9
2.590
C
84
7.7
DA-E-10
17.330
C/D
84
16.2
DA-E-11
69.420
C
84
39.6
11S
1.220
C
98
10.1
12S
20.670
C
88
13
West Ash
1S
381.250
C
83
41.67
17S
86.210
C
83
90.9
Basin
18S
94.980
C
82
153
19S
2190.080
C
73
1169.5
1.2 Calculate Time -of -Concentration
The time -of -concentration (Tc) is the amount of time needed for water to travel from the hydrologically
most distant point in a drainage area to the drainage area outlet. A minimum time of concentration
was calculated for the pond consistent with TR-55 methods in HydroCAD [Ref. 2]. The length of the
flow paths of sheet flow, shallow concentrated flow, and channel flow, as well as slope and channel
characteristics were determined based on the topography, which is consistent with TR-55
Wood Project No. 7810-18-1107 3 of 11 ����+
11 /06/19

Final Conditions Stormwater Calculation Ash Basin Closure Plan
Duke Energy - Roxboro Steam Station
recommendations. Channel flow in the proposed inflow channels was not included in the overall time
of concentration for the individual sub -areas. HydroCAD software [Ref. 2] was used to estimate the
total time of concentration for the drainage areas shown in Table 1.
1.3 Describe land use conditions
Land use conditions were estimated based on anticipated long-term conditions. Site soils information
for calculations were assigned based on Figure 1 which shows the site primarily consists of a mixture
of C and D soils. Given the site's soils and the final conditions, the land use was conservatively
assumed to consist of fair condition pasture, grassland, or range with CN values of 73-98. See Table
1 for CN values for each drainage area.
1.4 Stormwater Channel and Basin Design
HEC-HMS computer model was used to evaluate the final condition stormwater runoff for drainage
areas to each of the ash basins. The 25-year 24-hour storm event was based on the SCS method,
which resulted in 5.83 inch, the 100-year storm resulted in 7.38 inch for type II 24-hr rainfall [Ref 3].
The site specific PMP storm for 6-hour duration resulted in 17.3 inch. [Ref. 8]. The runoff was routed
thru the basin using the storage -indication method. Table 2 summarizes the peak flows from the
delineated catchment areas into the ash basins.
Table 2: Peak Discharges
Basin ID
Sub Basin ID
Peak Discharge
Peak Discharge
Peak Discharge
25-YR
{cfs}
100-YR
{cfs}
PMP
{cfs}
DA-E-1
82.70
111.10
92.20
DA-E-2
142.40
191.20
155.20
DA-E-3
343.50
438.60
335.60
DA-E-4
123.60
166.50
152.50
DA-E-5
47.60
63.90
52.20
DA-E-6
54.00
72.50
59.60
East Ash
Basin
DA-E-7
73.00
99.20
83.90
DA-E-8
110.90
150.80
128.90
DA-E-9
15.90
21.30
17.40
DA-E-10
86.80
116.60
100.80
DA-E-11
214.30
289.50
343.10
11S
8.60
10.90
8.00
12S
121.00
159.10
127.00
1S
1110.80
1510.30
1867.40
West
17S
1 143.90
196.20
388.80
Ash
Basin
18S
104.20
143.20
373.30
19S
366.50
1 532.60
1 1887.10
Wood Project No. 7810-18-1107 4 of 11 ����!
11/06/19

Final Conditions Stormwater Calculation Ash Basin Closure Plan
Duke Energy - Roxboro Steam Station
The proposed basins were designed to collect and convey the full PMP storm event. The conveyance
channels were sized to convey the 100-year storm runoff from the contributing areas.
The interior channel dimensions are presented in the following table:
Table 3: Channel Dimensions
Channel
ID
Channel
Type
Bottom
Width
{b}
(ft)
MIN.
Depth
{D}
(ft)
Left
Side
Slope
{ZlH:V}
Right
Side
Slope
{Z2H:V}
Top
Width
{T}
(ft)
Upstream
Invert
(ft)
Downstream
Invert
(ft)
Length
{L}
(ft)
Longitudinal
Slope
{S}
(ft/ft)
R DA-E-1
DIV
25
6
4
4
73
459.37
455.00
964.5
0.0045
R DA-E-2
DIV
10
3
4
4
34
465.00
457.29
1,319.0
0.0058
R DA-E-3
DIV
10
3
3
3
28
474.00
460.00
514.0
0.0272
R DA-E-4
DIV
25
4
4
4
57
464.56
459.37
1,047.7
0.0050
R DA-E-5
DIV
6
2
4
4
22
470.00
467.42
488.0
0.0053
R DA-E-6
DIV
25
4
4
4
57
467.76
464.56
605.5
0.0053
R DA-E-7
DIV
10
3
4
4
34
471.00
467.51
677.5
0.0052
R DA-E-8
DIV
10
2.5
4
4
30
473.00
469.50
484.3
0.0072
R DA-E-9
DIV
15
3
4
4
39
471.37
469.00
317.0
0.0075
R DA-E-10
DIV
15
2
4
4
31
474.00
471.37
241.5
0.0109
R DA-E-11
DIV
15
3
4
4
39
474.00
471.37
480.2
0.0055
R 12s
DIV
15
3
3
3
33
478.00
459.37
261.8
0.0712
The capacity of the proposed stormwater channels was evaluated using Manning's equation
presented as:
V _ 1.49 R2/3S1/2 [Ref. 4]
n
and
Q = AV [Ref. 4]
The flow area "A" and wetted perimeter "F were calculated using the following relationships based
on the geometry of a trapezoidal channel with a flow depth "d", bottom width "b", left side slope "21",
and right side slope "22":
A = bd + 0.5Z1d2 + O.5Z2d2
P = b + [(Z1d)2 + d2] + [(Z2d)2 + d2]
The proposed stormwater channel capacities were evaluated for the 100-year storm and the
stormwater channel linings were evaluated for the 25-year storm. The trial flow depths were iteratively
modified until the channel capacity exceeded the peak runoff for the conditions modeled. The
Manning's n for each channel was determined based on the permissible velocity. The permissible
velocity for a channel with grass lining (tall fescue), slope of 0% to 5%, and easily erodible soils is 4.5
feet per second [Ref. 4]. Originally, the channels were analyzed as grass lined channels with a
Wood Project No. 7810-18-1107 5 of 11 ����!
11/06/19

Final Conditions Stormwater Calculation
Duke Energy - Roxboro Steam Station
Ash Basin Closure Plan
Manning's n of 0.035. The channel capacity was estimated based on the appropriate Manning's n
and flow depth as shown in the following table:
Table 4: Channel Capacity -100yr
TrialFlow
Manning's
Wetted
Hydraulic
Trial
Peak
Trial
Flow
Velocity
Channel
Channel
n
Area
Perimeter
Radius
Flow
Runoff
Flow >
Freeboard
De
Depth
p
{V }
ID
Lining
{n}
{A}
{P}
{R}
{q}
{g100}
Peak
(in)
(f O
[Ref.41
;d;
(ft2)
(ft)
(ft)
(cfs)
(cfs)
Runoff?
Grassed
R DA-E-
-
/ Straw
0.035
5.3
244.9
68.7
3.6
6.7
1,637.10
1,593.40
yes
8.4
1
Net
Grassed
R DA-E-
/ Straw
0.035
2.3
44.2
29.0
1.5
4.3
190.39
186.70
yes
8.4
2
Net
Grassed
R DA-E-
-
/ Straw
0.035
2.55
45.0
26.1
1.7
10.1
454.40
438.80
yes
5.4
3
Net
Grassed
R DA-E-
-
/ Straw
0.035
3.6
141.8
54.7
2.6
5.7
802.28
797.50
yes
4.8
4
Net
Grassed
R DA-E-
-
/ Straw
0.035
1.8
23.8
20.8
1.1
3.4
80.26
63.20
yes
2.4
5
Net
Grassed
R DA-E-
-
/ Straw
0.035
2.8
101.4
48.1
2.1
5.1
515.66
498.60
yes
14.4
6
Net
Grassed
R DA-E-
-
/ Straw
0.035
1.7
28.6
24.0
1.2
3.4
97.94
97.80
yes
15.6
7
Net
Grassed
R DA-E-
/ Straw
0.035
2
36.0
26.5
1.4
4.4
159.85
150.10
yes
6.0
8
Net
Grassed
R DA-E-
-
/ Straw
0.035
2.7
69.7
37.3
1.9
5.6
389.11
342.80
yes
3.6
9
Net
Grassed
R_DA-E-
/ Straw
0.035
1.32
26.8
25.9
1.0
4.5
121.63
116.50
yes
8.2
10
Net
Grassed
R_DA-E-
/ Straw
0.035
2.55
64.3
36.0
1.8
4.6
297.77
289.00
yes
5.4
11
Net
Grassed
R-12s
/ Straw
0.035
1.25
23.4
22.9
1.0
11.5
270.26
159.10
yes
21.0
Net
Wood Project No. 7810-18-1107 6 of 11 ����!
11/06/19

Final Conditions Stormwater Calculation
Duke Energy - Roxboro Steam Station
Ash Basin Closure Plan
Channel stability is determined based on the shear strength of the channel lining. The shear force
for each of the channels was calculated using the following equation:
T = YwaterdS
[Ref. 5]
Channel lining was chosen by comparing the calculated shear versus the minimum permissible shear
for various form of liners. The minimum permissible shear for each of the proposed forms of channel
lining is shown in the following table.
Table 5: Channel
Stability - 25-yr Storm
Unit
Storm
Flow
Longitudinal
Shear
Permissible
WeightDepth
Recurrence
Slope
Stress
Shear
Channel Lining
of Water
Safe
Interval
{d}
{5}
{ti}
{Tperm}
(years)
ate
{Ywr}
(ft)
(ft/ft)
(psf)
(psf)
(patecf)
R_DA-E-
25
Grassed / Straw Net
62.4
4.60
0.0045
1.30
1.45
Yes
1
R_DA-E-
25
Grassed / Straw Net
62.4
2.00
0.0058
0.73
1.45
Yes
2
R_DA-E-
25
rock riprap -d50: 12
62.4
2.25
0.0272
3.82
4.20
Yes
3
R_DA-E-
25
Grassed / Straw Net
62.4
3.10
0.0050
0.96
1.45
Yes
4
R-DA-E-
25
Grassed / Straw Net
62.4
1.50
0.0053
0.49
1.45
Yes
5
R_DA-E-
25
Grassed / Straw Net
62.4
2.35
0.0053
0.77
1.45
Yes
6
R_DA-E-
25
Grassed / Straw Net
62.4
1.60
0.0052
0.51
1.45
Yes
7
R_DA-E-
25
Grassed / Straw Net
62.4
1.70
0.0072
0.77
1.45
Yes
8
R_DA-E-
25
Grassed / Straw Net
62.4
2.20
0.0075
1.03
1.45
Yes
9
R_DA-E-
25
Grassed / Straw Net
62.4
1.10
0.0109
0.75
1.45
Yes
10
R-DA-E-
25
Grassed / Straw Net
62.4
2.20
0.0055
0.75
1.45
Yes
11
R 12s
25
rock riprap-d50: 12
62.4
0.80
0.0712
3.55
4.20
Yes
The proposed basins capacity was determined by developing a stage -storage relationship utilizing
contours derived from the final conditions of the basin. Excavated areas upstream of the spillway and
outlet structures were accounted as reservoirs. The storage volume was estimated using the
prismatic volume calculation method with the elevation -surface area input data. Ponding area details
can be found in the modeling results. The proposed basins dimensions are presented in the following
tables:
Wood Project No. 7810-18-1107 7 of 11 ����!
11/06/19

Final Conditions Stormwater Calculation Ash Basin Closure Plan
Duke Energy — Roxboro Steam Station
Table 6: Proposed East Ash Basin
Dimensions
Contour
Elevation
Area
(ft)
(Acre)
457.6
0.66935
458
0.8501
459
1.2259
460
1.6701
461
2.2936
462
3.0595
463
4.1438
464
6.0399
465
8.6182
466
11.971
467
14.534
468
18.987
469
25.727
470
28.784
471
32.101
472
35.12
473
38.411
474
41.702
475
45.381
480
45.382
490
45.383
Table 7: Proposed West
Ash Basin Dimensions
Contour
Elevation
Area
(ft)
(Acre)
405
28.555
406
29.967
408
33.716
410
38.165
410.5
39.12
412
41.988
413
43.862
414
45.736
416
49.808
418
57.979
420
62.498
424
76.214
428
89.542
The spillway system for the West Ash Basin is primarily the breached main dam. The existing West
Ash Basin main dam crest will be lowered, and the embankment breached as required for dam
decommissioning. The spillway has a control section approximately 540 feet wide at the bottom
elevation of 405.00 feet and rises at 4H:1 V side slope up to elevation 470 feet. The average spillway
width is used in the analysis. Flows through the spillway are discharged directly to the downstream
canal and ultimately discharges into Hyco Lake. The tailwater condition at the spillway is assumed to
be the water surface elevation at Hyco Lake during the PMP storm. With a starting water surface
elevation controlled by Hyco Lake, the spillway opening hydraulic ratings, and the basins storage
capacity were evaluated using HEC-HMS computer model. The hydraulic analysis consisted of those
elements necessary to account for all inflows to the ash basins including inflow from the East Ash
Basin that passes through the culvert under Dunnaway road. The basins performance was analyzed
during and after the design storm for 360 hours (15 days). The result of the analysis is shown below
in Table 8.
Wood Project No. 7810-18-1107 8 of 11 ����+
11 /06/19

Final Conditions Stormwater Calculation
Duke Energy — Roxboro Steam Station
Ash Basin Closure Plan
1.5 Stormwater analysis of the Probable Maximum Precipitation (PMP)
Although the dams that impound the West Ash Basins will be breached it is necessary to show that
stormwater basin is capable of safely retaining and conveying the stormwater runoff of the design
storms according to the dam classifications. According to the North Carolina Department of
Environmental Quality (NCDEQ) — Dam Safety regulations the West Ash Pond (State I.D. No.
PERSO-038) is classified as a large high hazard, and the 1 /3 PMP being the minimum spillway design
storm [Ref. 9]. For the Final Environmental Protection Agency Coal Combustion Residuals
(CCR) Rule, the requirements for the initial and periodic (every 5 years) OF evaluation are
provided in 40 CFR 257.82. The inflow design flood for a CCR surface impoundment, as
determined under 40 CFR is the Probable Maximum Flood (PMF). The PMP is used to estimate
the PMF inflow hydrograph and peak spillway discharge capacity needed at a dam. Since the CCR
is more conservative than the state criteria, the PMF is used as the inflow design storm. In addition,
a site -specific study of the PMP/PMF using current techniques can result in a more appropriate
estimate of the PMF for consideration as the OF [Ref. 9].
Based on the Site -Specific Probably Maximum Precipitation Study for Hyco Reservoir [Ref. 8], the
rainfall depth of the full PMP for 6 hours duration is 17.3 inches. Though the rainfall depth of the site
specific PMP is greater than 100-year storm event and results in more volume of water, shown in the
figure below, the rainfall distribution is flat compared with Type II distribution. This leads to less
intensity of rainfall, therefore the peak discharge of the site PMP storm is not much higher than 100-
year storm. The results show the site specific PMP storm event will remain within the basin storage
capacity and not overtop the impoundment. With the proposed removal of the main dam, the new
spillway opening can safely pass the PMP storm. The results from the PMP storm event on the
proposed ash basins is shown in the following table.
Table 8: PMP Routing Results for Proposed Basin
Roxboro
PROP.
Top of
Peak
Freeboard
Peak
Peak
Peak
Plant
BOTTOM
Embankment El
Water
(ft)
Inflow
Outflow
Storage
El(ft)
(ft)
Surface
(cfs)
(cfs)
(AC -FT)
Elevation
(ft)
East Ash
455.00
476.25
470.30
5.95
1540.80
936.60
121.80
Basin
West Ash
405.00
470.00
424.13
45.87
3557.20
3558.00
944.40
Basin
Wood Project No. 7810-18-1107 9 of 11 ����!
11/06/19

Final Conditions Stormwater Calculation
Duke Energy — Roxboro Steam Station
1
0.9
+L
0.8
a
0 0.7
0.6
c
0.5
0.4
0
u 0.3
co
L
LL 0.2
0.1
0
Rainfall Distribution
Site Specific PMP Type II Storm
0 1 2 3
Time (hr)
Ash Basin Closure Plan
Figure 3 Rainfall Distribution of Type II and Site Specific PMP
DISCUSSION
The results from the analysis show that the proposed stormwater basin for the West Ash Basin and
East Ash Basin has sufficient storage capacity and spillway opening to adequately manage flow into
the ash basins during and following the peak discharges of the PMP storm event. The peak water
surface elevation is below the proposed impoundment crest elevation. Therefore, overtopping is not
expected.
FIGURES:
1. Soil Map
2(a) East Ash Basin Catchment Areas; 2(b) West Ash Basin Catchment Areas
3. Rainfall Distribution of Type II and Site Specific PMP
4. HEC-HMS Routing Diagram for Roxboro Ash Basins and Spillway Parameters
5. West Ash Basin Drainage profile and Cross Section
6. Spillway Cross Section Details
Wood Project No. 7810-18-1107 10 of 11 ����+
11 /06/19

Final Conditions Stormwater Calculation
Duke Energy — Roxboro Steam Station
Ash Basin Closure Plan
REFERENCES:
1. HEC-HMS 4.3 (build 96), Hydrologic Modeling System U.S. Army Corps of Engineers, 2018.
2.
3.
4.
5.
6.
7.
8.
9.
10
HydroCAD 10.00 (build 9), HydroCAD Software Solutions LLC, 2013.
Bonnin, G.M. et. al., "NOAA Atlas 14, Volume 2, Version 3, Point Precipitation Frequency
Estimates", NOAA National Weather Service, obtained May 16, 2016.
North Carolina Department of Environment and Natural Resources, "Erosion and Sediment
Control Planning and Design Manual", Revised May 2013.
"Standard Specification for Roads and Structures", North Carolina Department of
Transportation, Raleigh, January 2012.
United States Department of Agriculture, "Urban Hydrology for Small Watersheds", Technical
Release 55, June 1986.
NCAC — Title 15A, Department of Environmental Quality, Subchapter 2K, Dam Safety, Section
.0100
Hydrometeorological Report No. 51, Probable Maximum Precipitation Estimates, United
States East of the 105th Meridian, National Weather Service, June 1978.
EPA, Selecting and Accommodating Inflow Design Floods for Dams, Federal Emergency
Management Agency, August, 2013.
Applied Weather Associates, Roxboro Site Specific PMP, January 2018.
Wood Project No. 7810-18-1107 11 of 11 ����!
11/06/19

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NOTE: THIS FIGURE IS FOR REFERENCE ONLY.
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0 860 1,720 Feet
Airbus ON z DA. U�
EAB CATCHMENTS
ROXBORO STREAM STATION �' DUKE
PERSON COUNTY, NORTH CAROLINA ENERGY®
PROJECT NO: 7810-18-1107 1 FIGURE NO: 2 (a)

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Hydrologic Element 11P-19P] — ❑
U Reservoir Options
Basin Name: Roxboro CBE
Element Name: 1P-19P
Description: lip-19P a]
Dovmstream: ]unction-1 L'i
Method: loutt€ow Structures
Storage Method: ELuation-Area
"Elev-Area Function: 1P-17P Combined
Initial Condition: 1nf6ow = Out€tow
Main Taihr,,ater; Fixed Stake
"Stage (FT 424.13
ALIlllarf; --E—
Time Step Method; Automatic A p bn
Outlets:
I
i
Spill -ways:
1
Dam Tops:
D
Pumps:
0:
Dam Break:
NO
Dam Seepage:
w
Release:
No
Evaporation:
I NO
Apply Close

Components Compute Results
1 1 Reservoir Spillv,,'dY 1 Options
Basin Harne: Roxboro CBE
Element Name: 1P-19P
Ni eth o d : I Broad-Cr-estad SpAvay
Direction: b1a15
"Elevation (FT) 405
"Length (FT) 785
"Coefficient (FT" 0.5/5) 7.7
Gates: 0

EAST ASH BASIN - Stage Storage Table
//6P ELEV-AREA/ ELEVATION -AREA///TABLE/
Ordinate
ELEVATION
6P ELEV-AREA
AREA
TABLE
Labels
FT
Linear
ACRE
Linear
0.66935
Units
Type
1
457.60
2
458.00
0.85010
3
459.00
1.22590
4
460.00
1.67010
5
461.00
2.29360
6
462.00
3.05950
7
463.00
4.14380
8
464.00
6.03990
9
465.00
8.61820
10
466.00
11.97100
11
467.00
14.53400
12
468.00
18.98700
13
469.00
25.72700
14
470.00
28.78400
15
471.00
32.10100
16
472.00
35.12000
17
473.00
38.41100
18
474.00
41.70200
19
475.00
45.38100
20
480.00
45.38200
21
490.00
45.38300
Roxboro Steam Station

West Ash Basin
Stage Storage Table
Ordinate
ELEVATION
1P-17PCOMBINED
AREA
TABLE
Labels
Units
FT
Linear
ACRE
Type
Linear
1
405.0
28.555
2
406.0
29.967
3
408.0
33.716
4
410.0
38.165
5
410.5
39.120
6
412.0
41.988
43.862
45.736
7
413.0
414.0
8
9
416.0
49.808
10
418.0
57.979
11
420.0
62.498
12
424.0
76.214
131
428.0
89.542
Roxboro Steam Station

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//SS PMP - 6HR/PRECIP-CUM/31DEC2018/6MIN/GAGE/
Date/Time
Original
Estimate/Entry
Revised
(IN) -+
(IN)
(IN)
31 Dec2018 24:00
0.0 0
0.09
0.00
01Jan2019 00:06
0.09
01Jan2019 00:12
0.14
0.14
01Jan2019 00:18
0.20
0.20
01Jan2019 00:24
0.30
0.30
01Jan2019 00:30
0.42
0.42
01Jan2019 00:36
0.54
0.54
01Jan2019 00:42
0.68
0.68
01Jan2019 00:48
0.83
0.83
01Jan2019 00:54
1.01
1.01
01Jan2019 01:00
1.21
1.21
01Jan2019 01:06
1.44
1.44
01Jan2019 01:12
1.68
1.68
01Jan2019 01:18
1.93
1.93
01Jan2019 01:24
2.20
2.20
01Jan2019 01:30
2.49
2.49
01Jan2019 01:36
2.78
2.78
01Jan2019 01:42
3.07
3.07
01Jan2019 01:48
3.35
3.35
01Jan2019 01:54
3.66
3.66
01Jan2019 02:00
3.95
3.95
01Jan2019 02:06
4.25
4.25
01Jan2019 02:12
4.55
4.55
01Jan2019 02:18
4.84
4.84
01Jan2019 02:24
5.12
5.12
01Jan2019 02:30
5.41
5.41
01Jan2019 02:36
5.70
5.70
01Jan2019 02:42
5.99
5.99
01Jan2019 02:48
6.28
6.28
01Jan2019 02:54
6.56
6.56
01Jan2019 03:00
6.84
6.84
01Jan2019 03:06
7.14
7.14
01Jan2019 03:12
7.44
7.44
01Jan2019 03:18
7.73
7.73
01Jan2019 03:24
8.04
8.04
01Jan2019 03:30
8.35
8.35
01Jan2019 03:36
8.68
8.68
O1Jan2019 03:42
9.02
9.02
01Jan2019 03:48
9.37
9.37
01Jan2019 03:54
9.74
9.74
01Jan2019 04:00
10.13
10.13
01Jan2019 04:06
10.53
10.53
01Jan2019 04:12
11.081
11.08
01Jan2019 04:18
11.821
11.82

Date/Time
Original
Estimate/Entry
Revised
(IN)
(IN)
(IN)
01Jan2019 04:24
12.27
12.27
12.75
01Jan2019 04:30
12.75
01Jan2019 04:36
13.23
13.23
13.72
01Jan2019 04:42
13.72
01Jan2019 04:48
14.21
14.21
01Jan2019 04:54
14.69
14.69
01Jan2019 05:00
15.16
15.16
01Jan2019 05:06
15.62
15.62
01Jan2019 05:12
16.06
16.06
01Jan2019 05:18
16.44
16.44
01Jan2019 05:24
16.78
16.78
01Jan2019 05:30
17.06
17.06
01Jan2019 05:36
17.24
17.24
01Jan2019 05:42
17.30
17.30
01Jan2019 05:48
17.30
17.30
01Jan2019 05:54
17.30
17.30
01Jan2019 06:00
17.30
17.30

2
3 4
5
6
7
8
ROX C901-039.012
REV.
B
520.00
520.00
500.00
\� \�
500.00
__
% 1
/ //
EXISTING GRADE
EXISTING
WEST ASH BASIN MAIN DAM
CREST DESIGN EL. 470'
(TO BE REMOVED)
/ `
\
EXISTING
A
480.00
-
\
WEST ASH BASIN NO.1
480.00
A
/
\
/
\
CREST EL
\ \
(TO BE REMOVED)
`�-
--------
--- - -
- -
----------
----
--�
460.00
- - -
- -�
460.00
\\
U_
U_
z
\ /
z
0 440.00
440.00
0
LJ
100 YEAR FLOOD
J
LU
LAKE ELEVATION 413'
W
420.00
REMOVE DAM
NORMAL LAKE ELEVATION
420.00
B
(CUT DOWN TO ELEV. 405')
410.5'
TIE INTO ORIGINAL
CREEK BED
400.00---
400.00
woo
BOTTOM OF ASH GRADE
380.00
380.00
360.00
360.00
C
-2+00
0+00 2+00
4+00 6+00 8+00
10+00 12+00 14+00 16+00 18+00
20+00 22+00 24+00 26+00 28+00
30+00
32+00
34+00
36+00 38+00 40+00
42+00 44+00 46+00
48+00 50+00 52+00 54+00 56+00
C
PROFILE A
HORIZONTAL SCALE: 1 "=200'
VERTICAL SCALE: 1 "=20'
520.00
520.00
500.00
500.00 LEGEND
0
- - - - - - - EXISTING GRADE
IX
EXISTING GRADE
- BOTTOM OF ASH
^
500.00
���
//
500.00
480.00
\ \
480.00 PROPOSED GRADES
O
_
\
LAKE ELEVATION
C)
- J \
- - - - - -/ \\
\\
/
100 YEAR FLOOD ELEVATION
O
480.00
/
/
// \�
EXISTING GRADE
480.00
460.00
_ /
FEATURE TO BE REMOVED
460.00
Cfl
\
\
N
J
/
460.00
/
460.00
440.00
/
440.00 0
i
I
J
z
O
440CD
.00
/
440.00
z
O
420.00
100 YEAR FLOOD
LAKE ELEVATION 413'
LL1
420.00
m
<
Q
Q
BOTTOM OF ASH
NORMAL LAKE ELEVATION
4
E
\
/
>
410.5'
J
100 YEAR FLOOD
J
LLI
LAKE ELEVATION 413'
LLI
420.00
NORMAL LAKE ELEVATION
420.00
400.00
400.00
410.5'
2,
BOTTOM OF ASH GRADE
0 200' 400' 600'
400.00
400.00
380.00
380.00
-2+00
0+00 2+00 4+00
6+00 8+00 10+00
12+00
0
PROFILE C
TITLE
ROXBORO WEST ASH BASIN
HORIZONTAL SCALE: 1"=200'
wood
380.00
380.00
VERTICAL SCALE: 1"=20'
CLOSURE PROJECT
ROXBORO STEAM STATION
F
Environment &Infrastructure Solutions
F
4021 STIRRUP CREEK DRIVE, SUITE 100 DURHAM
PERSON COUNTY, NORTH CAROLI NA
NC27703
TEL: [phone]
CROSS -SECTIONS
FAX: [phone]
360.00
360.00
LICENSURE:
FOR
NCENG:F-1253
ISSUED FOR REVIEW - 60%
-2+00
0+00 2+00
4+00 6+00 8+00
10+00 12+00 14+00 16+00 18+00
20+00 22+00 24+00 26+00 28+00
30+00
NC GEOLOGY: C-247
SEAL
SCALE: AS SHOWN DES:
DUKE DWG TYPE: DWG DFTR:
JL
VD
PROFILE B
HORIZONTAL SCALE: 1 "=200'
��
ENERGY JOB NO: 7812190186 CHKD:
AP
VERTICAL SCALE: 1 =20
[DATE: 08/30/2019 ENGR:
SA
FILENAME: ROX-C901.039.011B.dwg APPD:
CK
DWG SIZE DRAWING NO. REVISION
B 08/30/2019 7812190186
A 06/26/2019
DESIGN PLAN
DESIGN PLAN
JL VD
JL VD
AP SA
AP SA
CK ISSUED FOR REVIEW - 60%
CK ISSUED FOR REVIEW 30%
ANSI D
ROX C901.039.012
B
7812190186
-
22"x34"
REV DATE JOB NO.
PROJECT TYPE
DES DFTR CHKD ENGR
APPD DESCRIPTION
TENTHS 10 20
30 4
5
6
7
8
9 10
INCHES 1 2 3
Plotted By: Deberardinis, Victoria Sheet Set: 7812190186 - Roxboro CAMA Closure Plans Layout: CROSS -SECTIONS August 27, 2019 01:16: 54pm Q:\Duke Energy\Roxboro\7812190186 - CAMA Closure Plan\Issued for Review \60%\sheets\ROX-C901.039.011 B.dwg

2 3 4 5
6 7
8
ROX C901.039.013
REV.
B
EXISTING GROUND
A
A
490.00
490.00
STA: 0+00.00
STA:10+46.55
480.00
ELEV. 472.50
ELEV: 472.25
480.00
470.00
------------------------------------------------------------------------------------------------------------------------------------------
470.00
460.00
460.00
.-.
LL
450.00
4
4
.-.
450.00
1
PROPOSED MAIN DAM BREACH
1
Z
Z
0
440.00
440.00 0
B
430.00
430.00 J
i
W
SURFACE WATER
W
420.00
ELEV 410.5'
420.00
410.00
410.00
400.00
STA: 2+65.79
STA: 8+02.91
400.00
ELEV:405.41 PROPOSED BOTTOM OF BREACH
ELEV.405.00
390.00
390.00
1+00 2+00 3+00 4+00 5+00
6+00 7+00
8+00 9+00
10+00 10+50
C
C
0
N
MAIN DAM BREACH
PROFILE VIEW
1
013 SCALE: 1" = 40'
O
40
0
40 80 FT
X
o
IN
O
D
O
GJ
C�
O
GJ
m
DO
E
TITLE
ROXBORO WEST ASH BASIN
wood
CLOSURE PROJECT
ROXBORO STEAM STATION
F
Environment &Infrastructure Solutions
F
4021 STIRRUP CREEK DRIVE, SUITE 100 DURHAM
PERSON COUNTY, NORTH CAROLINA
NC 27703
TEL: [phone]
DETAILS
FAX: [phone]
LICENSURE:
FOR
NC ENG: F-1253ISSUED
FOR REVIEW - 60%
NC GEOLOGY:: C-247 C-
SEAL
SCALE: AS SHOWN DES:
DFTR:
DUKE
JL
DWG TYPE: DWG
VD
O CHKD:
E N E RGY
AP
DATE 08/ 0/20196 ENGR:
SA
FILENAME: ROX—C901.039.012B.dwg APPD:
CK
DWG SIZE
DRAWING NO.
REVISION
B 08/30/2019 7812190186
06/26/2019
DESIGN PLAN JL VD AP SA CK
DESIGN PLAN JL VD AP SA CK
ISSUED FOR REVIEW - 60%
ISSUED FOR REVIEW 30%
ANSI D
ROX C901.039.013
B
A 7812190186
-
22"x34"
REV DATE JOB NO.
PROJECT TYPE DES DFTR CHKD ENGR APPD
DESCRIPTION
TENTHS 10 20 30 4 5
6 7
8
9
10
INCHES 1 2 3
Plotted By: Deberardinis, Victoria Sheet Set: 7812190186 — Roxboro CAMA Closure Plans Layout: CLOSURE DETAILS August 30, 2019 10: 35: 48am Q: \Duke Energy\Roxboro\7812190186 — CAMA Closure Plan\Issued for Review\60%\sheets\ROX_C901.039.012B.dwg

Wood Environment & Infrastructure Solutions, Inc.
Duke Energy —Roxboro Plant wood.
EAB Coal Combustion Residuals Surface Impoundment Closure Plan (Excavation)
APPENDIX C2: BORROW SOIL QUANTITIES
EAB ESTIMATED QUANTITIES
DESCRIPTION
UNITS
ESTIMATED QUANTITY
SOIL FILL VOLUME
CU. YARDS
1,938,400