20150610 Ver 3_More Info Received_20170630

/r DUKE
ENERGY.
Ms. Sue Homewood June 26, 2017
Environmental Senior Specialist NC Department of
Division of Water Resources -Water Quality Programs Environmental Quality
Winston-Salem Regional Office Received
450 Hanes Mill Road, Suite 300 JUN 3 0 2017
Winston-Salem, North Carolina 27105
Winston-Salem
RE: Response to Request for Additional Information _Regional Office
DWR # 15-0610 v3
Dan River Steam Station Stormwater Diversion Project and associated
Projects
Rockingham County, North Carolina
Dear Ms. Homewood:
Duke Energy, in consultation with Amec Foster Wheeler Environment & Infrastructure,
Inc., submitted a standard permit application to the Raleigh Regulatory Field Office of
the U.S. Army Corps of Engineers: (USACE) for issuance of Section 404 Individual
Permit for the Dan River Steam Station Stormwater Diversion Project and associated
Projects at the Dan River Steam Station in Eden, Rockingham County. The application
and supporting documents were also provided to the North Carolina Department of
Environmental Quality (NCDEQ), Division of Water Resources (DWR), requesting an
Individual Water Quality Certification from the DWR for the project. On May 2, 2017, the
DWR Water Quality Programs received the application dated April 28, 2017. Subsequent
to your review of the application and supporting documents, you presented three
requests for additional information (RAI) in a correspondence dated June 1, 2017, to
Duke Energy at the attention of Mr. Steve Cahoon. As enumerated herein for discussion
purposes, these items and respective responses are presented below with requested
materials enclosed for the DWR to consider the application to be complete.
In addition to the above request for additional information, you requested information on
the project in a May 29, 2017 email correspondence to Mr. Cahoon. Although a
response to your query was provided to you in a June 1, 2017 email correspondence
from Mr. Cahoon, that response is also included herein.
Item Number 1
This project includes a revision to impacts previously approved by the Division on May
12, 2016 (DWR#2016-0156v2). These impacts were for an access road for the Dan
River Scarp Repair and were approved as temporary impacts. The current application
for an Individual Permit requests that these impacts be approved as permanent impacts.
The original review by the Division was based on temporary impacts and therefore the
Division requires a more detailed analysis of the purpose and need for permanent
impacts as well as a more detailed analysis of avoidance and minimization measures. In
addition, this project will be placed on hold until a compliance inspection of these
culverts has been conducted. [15A NCAC 02H .0506(f) and (g)]
1

DUKE
ENERGY®
Response
Access via the two culverted stream crossings (road crossings) to the northern shoreline
of the Dan River is necessary for scarp repair. Permanent access via these two
crossings is necessary to facilitate future maintenance of the Primary and Secondary
Ash Basins embankments along the Dan River. Such maintenance would include future
scarp repair. The two road crossings will be maintained for future necessity and
emergency access to the shoreline areas along the Dan River.
If the road crossings are not permanently established (i.e., if the culverts are removed
and re -contouring is completed), future scarp repairs, as they arise, would necessitate
the reinstallation of the culverts. Such continued impacts to the stream channel would be
cumulative.
The installation is to support minimization of erosion along the Dan River. Use of rock
instead of soil to improve installation and the improvement of the existing temporary
crossings (via a change to permanent crossing) are proposed. These actions will
facilitate minimization of impacts, present and future.
Item Number 2
Your application indicates that 130 linear feet of stream stabilization will occur of location
DR -134 however Plan Sheet DR -134 Section Detail, Figure 02 shows riprap shading
throughout the entire channel bed. Please clarify whether riprap will be extended
throughout the channel bed,
Response
Riprap will be placed in the channel bed only as required to provide a working platform.
Ideally, the riprap will be placed from the top of the stream channel and the only
encroachment into the stream will be to extend the slope tie-in at the base of the
channel.
Item Number.3
As requested in the pre -application, please provide a detailed analysis of the velocity
expected at outfall SW -010, the riprap pad specifications and details, and an analysis of
the impact this additional flow and velocity may have on wetlands that are present
immediately downslope of this area.
Response
The peak flow at Outfall SW -010 is anticipated to be about 0.9 cubic feet per second
(cfs) with a velocity of about 4.5 feet per second (fps). The anticipated flow rate and
velocity is nominal as evidenced by the fact that the calculated values (0.9 cfs and 4.5
fps) are less than the minimum values shown on the riprap apron sizing nomograph. A
riprap apron will be used to further dissipate flows prior to discharge to the receiving land
area. The selected riprap apron dimensions exceed the minimum required design
dimensions. Based on these considerations, there are no anticipated negative impacts to
the receiving drainage pathway, including wetlands that are located downgradient of the
2

/r DUKE
ENERGY®
riprap apron. Note: the nearest wetland area to the proposed riprap apron is located
more than 50 feet from the proposed structure.
The attached document Riprap Area Calculation provides details on the analysis,
including objective, method, calculations, discussion, and references.
May 29, 2017 Email Correspondence from Ms. Homewood to Mr. Cahoon
Does SW -010 exist in your NPDES permit? If so, how will the stormwater diversion
project effect sampling with regards to that permit. If you have already been discussing
this with the stormwater unit please let me know who you've talked to so that I may
discuss this with them and make notes in my file.
Response
Outfall SW -010 is in SW Permit (NCS000572) as a future outfall. Ms. Joyce Dishmon,
Duke Energy, spoke to various NCDEQ staff. She spoke to Mr. Ken Pickle (retired) in
early 2016 and Ms. Bethany Georgoulias, Mr. Michael Randall, and Mr. Bradley Bennett
(retired) in late 2016 to discuss the future outfall. The permitted parameter list and
sampling frequency should follow requirements outlined for CCR influence in other
permits and sampled semi-annually. For illustration, the "Analytical Monitoring
Requirements for SW027" table from Permit No. NCS000573 for Craig Road Landfill
parameters is attached herein for your review.
Thank you in advance for your assistance with this project. If you have any questions or
need additional information, please contact me at telephone number [phone] or
email address [e-mail].
Sincerely,
Steve Cahoon
Enclosures
Cc: David Bailey (USACE)
Eric Kinstler (Duke Energy)
Cedric Ruhl (Amec Foster Wheeler)
Josh Bell (Amec Foster Wheeler)
Richard Harmon (Amec Foster Wheeler)
3

RIPRAP APRON CALCULATION

Riprap Apron Calculation
Duke Energy — Dan River Steam Station
Dan River Stormwater Diversion
Calculation Title:
Riprap Apron Calculation
Summary:
The peak flow at Outfall SW -010 is anticipated to be about 0.9 cfs with a velocity of about 4.5 feet per
second (fps). The anticipated flow rate and velocity is nominal as evidenced by the fact that the
calculated values (0.9 cfs and 4.5 fps) are less than the minimum values shown on the riprap apron
sizing nomograph. A riprap apron will be used to further dissipate flows prior to discharge to the
receiving land area. The selected riprap apron dimensions exceed the minimum required design
dimensions. Based on these considerations, there are no anticipated negative impacts to the receiving
drainage pathway, including wetlands that are located downgradient of the riprap apron.
Notes:
Revision Log:
No.
Description
Originator
Verifier
Technical Reviewer
00
Initial Submittal
/� A t n
i�- 1`'As
4--
C,4o*--
Cedric Ruhl
John Wrona
Chrf6 Jordan
Amec Foster Wheeler Project No. 7810-17-0895 1 of 3
6/15/17 (Initial Submittal) amec4v
foster
wheeler

Riprap Apron Calculation
Duke Energy — Dan River Steam Station
OBJECTIVE:
Dan River Stormwater Diversion
The objective of this calculation is to design the riprap apron for stormwater diversion noncontact
water pumped flow to Outfall SW -010.
METHOD:
The riprap apron was designed in accordance with the North Carolina Erosion and Sediment
Control Planning and Design Manual.
CALCULATIONS:
1.0 Calculate flow conditions
Noncontact stormwater will be pumped to Outfall SW -010 at an approximate rate of 400 gpm
through a 6 -inch diameter pipe. The peak flow rate and velocity are shown in the following table:
Table 1: Calculated Flow Conditions
Pumped
Pumped
Downstream
Pipe
Pipe
Discharge Velocity
Flow Rate
Flow Rate
Pipe Diameter
Diameter
Area
at Pipe Outlet
(gpm)
(cfs)
(in)
(ft)
(ft)
(ft/s)
400
0.89
6
0.5
0.196
4.54
2.0 Calculate minimum required riprap apron dimensions
The minimum required riprap apron dimensions and riprap median particle diameter (d50) was
designed in accordance with the North Carolina Erosion and Sediment Control Planning and
Design Manual [Ref. 1 ]. The maximum particle diameter (dmax) is 1.5 times the median particle
diameter (d50). The riprap apron thickness is 1.5 times the maximum particle diameter (dmax). The
minimum required riprap apron dimensions are shown in the following table:
Table 2: Minimum Design Riprap
Apron Size
Pumped
Downstream
Minimum
Minimum
Minimum
Apron
Minimum
Minimum
Flow
Pipe
Length of
Upstream
Downstream
Minimum dso
Minimum dso
dmax Riprap
Riprap
Rate
Diameter
Apron
Width of Apron
Width of Apron
Riprap Size
Riprap Size
Size
Thickness
(cfs)
(�n)
(ft)
(ft)
(ft)
(ft)
(�n)
(in)
(ft)
0.89
6
6
1.5
6.5
0.2
2.4
3.6
0.5
3.0 Define selected riprap apron dimensions
The riprap apron dimensions were selected to be greater than the minimum design riprap apron
sizing criteria as shown in the following table:
Table 3: Selected Riprap Apron Size
Length of
Upstream
Downstream
NCDOT Riprap
dso Riprap
dmaxRipra10.8
Apron
Width of Apron
Width of Apron
Class
Size
Size
(ft)
(ft)
(ft)
[Ref. 2]
(in)
(in)
10
2
10
A
4
6
Amec Foster Wheeler Project No. 7810-17-0895 2 of 3 "-
6/15/17 (Initial Submittal) amec
faster
wheeler

Riprap Apron Calculation Dan River Stormwater Diversion
Duke Energy — Dan River Steam Station
DISCUSSION:
The peak flow at Outfall SW -010 is anticipated to be about 0.9 cfs with a velocity of about 4.5 feet
per second (fps). The anticipated flow rate and velocity is nominal as evidenced by the fact that
the calculated values (0.9 cfs and 4.5 fps) are less than the minimum values shown on the riprap
apron sizing nomograph. A riprap apron will be used to further dissipate flows prior to discharge
to the receiving land area. The selected riprap apron dimensions exceed the minimum required
design dimensions. Based on these considerations, there are no anticipated negative impacts to
the receiving drainage pathway, including wetlands that are located downgradient of the riprap
apron.
REFERENCES:
1. North Carolina Department of Environment and Natural Resources,
Sediment Control Planning and Design Manual", Revised May 2013.
2. "Standard Specification for Roads and Structures", North Carolina
Transportation, Raleigh, January 2012.
Amec Foster Wheeler Project No. 7810-17-0895 3 of 3
6/15/17 (Initial Submittal)
"Erosion and
Department of
amec
foster
wheeler

REFERENCEI
North Carolina Department of Environment and Natural Resources, "Erosion and Sediment
Control Planning and Design Manual", Revised May 2013.

Appendices
Riprap (large stones of various sizes) is often used to prevent erosion at the ends
of culverts and other pipe conduits. It converts high -velocity, concentrated
pipe flow into low-velocity, open channel flow. Stone should be sized and the
apron shaped to protect receiving channels from erosion caused by maximum
pipe exit velocities. Riprap outlet structures should meet all requirements in
Practice Standards and Specifications: 6.41, Outlet Stabilization Structure.
Several methods are available for designing riprap outlet structures. The
method presented in this section is adapted from procedures used by the USDA
Soil Conservation Service. Outlet protection is provided by a level apron of
sufficient length and flare to reduce flow velocities to nonerosive levels.
Design Procedure for The following procedure uses two sets of design curves: Figure 8.06a is used
Riprap Outlet for minimum tailwater conditions, and Figure 8.06b for maximum tailwater
conditions.
Protection
Step 1. Determine the tailwater depth from channel characteristics below the
pipe outlet for the design capacity of the pipe. If the tailwater depth is less
than half the outlet pipe diameter, it is classified minimum tailwater condition.
If it is greater than half the pipe diameter, it is classified maximum condition.
Pipes that outlet onto wide flat areas with no defined channel are assumed
to have a minimum tailwater condition unless reliable flood stage elevations
show otherwise.
Step 2. Based on the tailwater conditions determined in step 1, enter Figure
8.06a or Figure 8.06b, and determine d50 riprap size and minimum apron length
(La). The d50 size is the median stone size in a well -graded riprap apron.
Step 3. Determine apron width at the pipe outlet, the apron shape, and the
apron width at the outlet end from the same figure used in Step 2.
Step 4. Determine the maximum stone diameter:
dmax = 1.5 x d50
Step 5. Determine the apron thickness:
Apron thickness =1.5 x dmax
Step 6. Fit the riprap apron to the site by making it level for the minimum
length, La, from Figure 8.06a or Figure 8.06b. Extend the apron farther
downstream and along channel banks until stability is assured. Keep the
apron as straight as possible and align it with the flow of the receiving stream.
Make any necessary alignment bends near the pipe outlet so that the entrance
into the receiving stream is straight.
Rev. 12/93 8.06.1

Appendices
A
3 5 10 20 50 100 200 500 1000
Discharge (ft3/sec)
Curves may not be extrapolated.
Figure 8.06a Design of outlet protection protection from a round pipe flowing full, minimum tailwater condition (Tw < 0.5 diameter).
Rev. 12/93 8.06.3

REFERENCE
"Standard Specifications for Roads and Structures", North Carolina Department of
Transportation, Raleigh, January 2012.

Section 1043
1 All stone shall meet the approval of the Engineer. While no specific gradation is required,
2 there shall be equal distribution of the various sizes of the stone within the required size
3 range. The size of an individual stone particle will be determined by measuring its long
4 dimension.
5 Stone or broken concrete for rip rap shall meet Table 1042-1 for the class and size
6 distribution.
TABLE 1042-i i
ACCEPTANCE CRITERIA FOR RIP RAP AND STONE FOR EROSION CONTROL ?
Required Stone Sizes, inches
Class Minimum Midrange i Maximum i
_. A 2 4 6
_.
B 5 8 12
. 17
_.
9. . ;., ,. _.,..14. _.._.__... 23
7 No more than 5.0% of the material furnished can be less than the minimum size specified nor
8 no more than 10.0% of the material can exceed the maximum size specified.
9 SECTION 1043
10 AGGREGATE FROM CRUSHED CONCRETE
11 1043-1 GENERAL
12 Aggregate from crushed concrete is a recycled product made by crushing concrete obtained
13 from concrete truck clean out, demolition of existing concrete structures or pavement, or
14 similar sources and transported from a crushing facility. It does not include concrete
15 pavements that are rubblelized, broken or otherwise crushed in place on the roadway.
16 The crushed material must meet all sources approval requirements described in Sections 1005
17 and 1006 with the exception of the sodium sulfate test requirement. Deleterious materials
18 shall not be more than 3%.
19 Sampling and acceptance for the determination of gradaction, LL and PI will be performed as
20 described in the Aggregate QC/QA Program Manual and the Aggregate Sampling Manual.
21 1043-2 AGGREGATE BASE COURSE
22 The material shall meet the ABC gradation. The LL of the material shall be raised 5 points to
23 no more than 35.
24 1043-3 AGGREGATE SHOULDER BORROW
25 The material shall meet Section 1019.
26 1043-4 CLEAN COARSE AGGREGATE FOR ASPHALT
27 The material shall meet the gradation of a standard size in Table 1005-1. Use of the material
28 shall be approved by the Engineer, and the mix shall meet all requirements.
29 1043-5 CLEAN COARSE AGGREGATE FOR CONCRETE
30 The material shall meet the gradation of a standard size in Table 1005-1. Use of the material
31 is restricted to Class B concrete mixes only. Use of the material shall be approved by the
32 Engineer, and the concrete shall meet all requirements.
33 SECTION 1044
34 SUBSURFACE DRAINAGE MATERIALS
35 1044-1 SUBDRAIN FINE AGGREGATE
36 Subdrain fine aggregate shall meet No. 2S or 2MS in Table 1005-2.
10-62 NCDOT 2012 Standard Specifications

ANALYTICAL MONITORING REQUIREMENTS TABLE

Permit No. NCS000573
The permittee's application reports that no industrial activity takes place in the drainage
area south of the FGD Residuals Landfill discharging via outfall SW026. A stormwater
discharge permit is not required under the reported site conditions and operating mode.
The following parameters shall be monitored during a measurable storm event discharging
from the Craig Road Landfill via outfall SW027 into West Belews Creek/Belews Lake.
Table 4 Analvtical Monitorine Reauirements for SW027
= Discharge;
Measurement
Sample
Sample
Characteristics
Units
Fre 'uenc ;1-
T e2
Location3
Total Suspended Solids TSS
m L
semi-annual
Grab
SDO
H
standard
semi-annual
Grab
SDO
40 CFR Part 423 Appendix A:
Additional Priority Pollutant Metals -
mg/L
semi-annual
Grab
SDO
Ag, As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb,
Se, Tl, Zn5
Boron
m L
semi-annual
Grab
SDO
Total Rainfa114
inches
semi-annual
Rain
_
gauge
Footnotes:
1 Measurement Frequency: Twice per year (unless other provisions of this permit prompt monthly sampling)
during a measureable storm event, until either another permit is issued for this facility or until this
permit is revoked or rescinded. If the facility is monitoring monthly because of Tier Two or Three response
actions under the previous permit, the facility shall continue a monthly monitoring and reporting
schedule in Tier Two or Tier Three status until relieved by the provisions of this permit or the
Division.
2 Grab samples shall be collected within the first 30 minutes of discharge. When physical separation between
outfalls prevents collecting all samples within the first 30 minutes, sampling shall begin within the first 30
minutes, and shall continue until completed.
3 Sample Location: Samples shall be collected at each stormwater discharge outfall (SDO) specified above
unless representative outfall status (ROS) has been granted. The permittee may petition the Director for
ROS using DEMLR's ROS Request Form. DEMLR may grant ROS if stormwater discharges from a single
outfall are representative of discharges from multiple outfalls. Approved ROS will reduce the number of
outfalls where the analytical sampling requirements apply and will be documented in a letter to the
permittee. A copy of the Division's letter granting ROS shall be kept on site.
4 For each sampled measureable storm event, the total precipitation must be recorded. An on-site rain gauge
is required. Where isolated sites are unmanned for extended periods of time, a local rain gauge reading
may be substituted for an on-site reading.
5 Mercury shall be measured by EPA Method 1631E.
Part II Page 10 of 20