20120615 Ver 1_DWR RAI Response Mayo IP Modification Application_20201211

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Mr. Rick Trone December 11, 2020
401 & Buffer Permitting Branch
NCDEQ – Division of Water Resources
1617 Mail Service Center, Raleigh, NC 27699-1617

RE: Response to Request for Additional Information
DWR # 20120615v3
Duke Energy Mayo Steam Electric Plant - Ash Basin Landfill Project
Person County, North Carolina

Dear Mr. Trone:

Duke Energy, in consultation with Wood Environment & Infrastructure Solutions, Inc. (Wood),
submitted a request for modification of the existing U.S. Army Corps of Engineers (USACE)
Individual Permit (IP) (SAW-2011-00181) for the Mayo Steam Electric Plant to the Raleigh
Regulatory Field Office of the USACE. The submittal package and supporting documents for the
IP modification were also provided to the North Carolina Department of Environmental Quality
(NCDEQ) Division of Water Resources (DWR) along with a request for a 401 Individual Water
Quality Certification for the Ash Basin Landfill Project. DWR re ceived the certification request
and supporting documents on October 26, 2020. Subsequent to review, DWR submitted three
requests for additional information (RAI) to Duke Energy in correspondence dated December 4,
2020. The RAIs are recounted herein for discussion purposes. Duke Energy’s respective
responses to the RAIs are presented below along with the enclosures for DWR’s consideration
of a 401 Individual Water Quality Certification for the Ash Basin Landfill Project.

Item Number 1

Please provide additional details on placement of Borrow Pit 3 and the haul road. Specifically,
explain why the pit and the haul road cannot be reconfigured to avoid or minimize impacts to
Streams 9 and 10. Figures provided in the application depict the haul road routed through
Borrow Pit 3. Please explain how the road will remain in this loc ation after construction of
Borrow Pit 3. Please provide detailed plan/profile drawings for these impacts. [15A NCAC 02H
.0506(b)(1)]

Response

The limits of disturbance (LOD) depicted on the referenced figure are representative of both
haul road and ash basin closure related actions. These LOD lines could lead to conflicting
interpretation and have been updated to clarify the LOD bounds for the proposed project ; please
see the enclosed plan sheet (Q-R 1).
Impacts to Streams 9 and 10, as well as Wetlands LLL and JJJ, were conservatively included in
IP modification request for potential impacts associated with clean closure activities (i.e., they
are not associated with the haul road). The impetus for their inclusion as potential areas of
impact is based on a combination of factors. Streams 9 and 10 are located approximately 27
feet from the existing ash basin limits. Duke Energy’s experience with clean closure activities
has shown that these limits can sometimes extend beyond what was mapped prior to the
initiation of construction. Following the ash lens during excavation and removal to ensure a

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clean closure has resulted in unanticipated impacts at other Duke Energy facilities (e.g.,
activities at Dan River resulted in following an ash lens upstream into wetland areas, resulting in
unanticipated impacts and after-the-fact consultation with USACE).
Though Duke Energy does not anticipate impacts to Streams 9 and 10, Duke Energy also
recognizes that clean closure activities have the potential to impact the aforementioned streams
and wetlands based on their proximity to the existing ash basin and Duke Energy’s previous
clean closure experience. If the ash lens terminates prior to reaching these areas during clean
closure, no impacts would be anticipated (i.e., jurisdictional areas will be avoided to the
maximum extent practicable). However, due to the potential for impacts and to avoid
unanticipated impacts and after-the-fact consultation , Duke Energy has conservatively included
these potential impacts in the IP modification request.

Item Number 2

Proposed impacts to Wetland OOO are indicated as a result of construction of Borrow Pit 4.
Please clearly explain why Borrow Pit 4 cannot be reconfigured/shifted to avoid impacts to
Wetland OOO. [15 A NCAC 02H .0506(b)(1)]

Response
Note that Borrow Pit 4 may no longer be used for borrow material, and instead may be utilized
as a laydown area. Regardless, the layout of Borrow Pit 4/laydown area has been reconfigured;
construction would no longer impact Wetland OOO, a previously proposed 0.1-acre impact.
Please see the enclosed plan sheet with the updated LOD (Q-R 2).
With regards to all project components and overall impacts to jurisdictional waters at the Mayo
Steam Electric Plant , the total amount of permanent impacts for the requested modification of
the USACE IP were 2.04 acres of wetlands and 1,273 linear feet of stream channel. The
primary project actions comprise the construction of the proposed Ash Basin Landfill (ABLF),
four borrow areas, haul road, dam decommission, and the previously completed construction of
the Lined Retention Basin (LRB). The elimination of the proposed 0.1-acre impact to Wetland
OOO decreases the total proposed wetland impact for the project from 2.04 acres to 1.94 acres,
as summarized in the table below.

Proposed Impacts and Completed Impacts to Wetlands and Streams within the Project Site

Project Action (status) Wetland Impacts (acre) Stream Impacts (linear feet)
ABLF (proposed) 0.79 acre
(reduction of 0.1 acre from 0.89 acre) 896
LRB (completed) 1.15 377
Total 1.94 1,273

The reduction in the amount of total wetland impact for the project would correspondingly result
in a reduction in the amount of compensatory mitigation that would be required for the project.
The following table presents the compensatory mitigation summary for the project, updated with

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the elimination of the impact to Wetland OOO and the associated fee cost. The total mitigation
cost for the project would decrease from $1,329,632.36 to $1,311,421.23.

Potential Mitigation Costs for Impacts to Waters of the US within the Project Site

Item Number 3
If the U.S. Army Corps of Engineers requests a response to any comments received as a result
of the Public Notice, please provide the Division with a copy of your response to the USACE.
[15A NCAC 02H .0502(c)]

Response

Duke Energy and Wood have not received comments from the USACE or other respondents to
the Public Notice at the time of this correspondence. However, when comments are transmitted
Fee Category Features Impact Total
NCDMS
In-Lieu
Fee Unit
Cost
Total Cost¹
Wetland draining
to Ash Basin
Wetlands B, C, UU, and ZZ
– Landfill Area and
Wetlands E and MMM –
Lined Retention Basin
(NC WAM Medium Rating)
1.50 acre
(1:1 mitigation
ratio)
$91,055.65 $136,583.47
Riparian Wetland
draining to Ash
Basin
Wetlands JJJ and LLL –
Haul Road and
Wetland D – Lined
Retention Basin
(NC WAM Medium Rating)
0.31 acre
(0.62 acre at 2:1
ratio)
$91,055.65 $56,454.50
Wetland not
draining to Ash
Basin
Wetland OOO – Borrow
Area 4
(NC WAM Medium Rating)
No Impact $91,055.65 $0
Riparian Wetland
not draining to Ash
Basin (drainage to
Crutchfield Branch
via unnamed
tributary)
Wetlands F and H – Ash
Basin Dam Decommission
Area
(NC WAM Medium or High
Ratings)
0.13 acre
(0.26 at 2:1 ratio) $91,055.65 $23,674.47
Stream (unnamed
tributary) draining
to Ash Basin
Streams 9 and 10 – Haul
Road and
Streams 5 and 6 – Lined
Retention Basin
(NC SAM Medium Rating)
686 linear feet
(1,372 at 2:1
ratio)
$558.81 $766,687.32
Stream (unnamed
tributary) draining
to Crutchfield
Branch
Streams 1 and 3 – Ash
Basin Dam Decommission
Area
(NC WAM Medium Rating)
587 linear feet
(1:1 ratio) $558.81 $328,021.47
Total $1,311,421.23

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to Duke Energy and Wood by the USACE, a copy of the responses to those comments will be
provided to the DWR.

Thank you in advance for your further assistance with this project. If you have any questions or
need additional information, please contact me via phone at [phone] or email at
[e-mail].

Sincerely,

Lori W. Tollie
Duke Energy – Permitting & Compliance

Enclosures:
Q-R 1 (Plan View: Stream 9 and 10)
Q-R 2 (Plan View: Wetland OOO)

cc: Chris Hopper (USACE)
Steve Cahoon (Duke Energy)
Michae l Lazar (Duke Energy)
Mike Kendrick (Duke Energy)
Richard Harmon (Wood)

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Q-R 1: PLAN VIEW STREAMS 9 & 10

9
EXISTING DUKE
10
LLL
JJJ
0
+
9
2
0
+
0
0
0+000+950+001+001+000+9
9
0+0
0
ASH BASIN
-FIGURE 1FIGURE 1
DWG SIZE REVISION
FOR
DRAWING NO.
TITLE
FILENAME:
DWG TYPE:
JOB NO:
DATE:
SCALE:DES:
DFTR:
CHKD:
ENGR:
APPD:
A
F
E
D
C
B
2 3 4 5 7 86
4 5 7 8 9 106
A
F
C
B
11"x17"
ANSI C
SEAL
321
Environment & Infrastructure Solutions
4021 STIRRUP CREEK DRIVE, SUITE 100
DURHAM NC 27703
TEL: [phone]
FAX: [phone]
LICENSURE:
NC ENG: F-1253
NC GEOLOGY: C-247
REV DATE JOB NO.PROJECT TYPE DES DFTR CHKD ENGR APPD DESCRIPTION
12/10/2020
7812-20-0451
DWG
AS SHOWN
RH
RH
JC
SM
SM
MAYO ASH BASIN LANDFILL
MAYO STEAM ELECTRIC STATION
PERSON COUNTY, NORTH CAROLINA
PLAN VIEW 1 --FIGURE 1
-MATCH LINE - FIGURE 2N
EXISTING ASH BASIN BOUNDARY
PROPOSED LANDFILL BOUNDARY
STREAM - IMPACTED
STREAM - NOT IMPACTED
WETLAND - IMPACTED
WETLAND - NOT IMPACTED
LIMITS OF DISTURBANCE
CROSS SECTION
EXISTING MAJOR ROAD
EXISTING RAILROAD
LEGEND
STREAM 9
485'
490'
495'
500'
505'
510'
485'
490'
495'
500'
505'
510'
0+00 0+10 0+20 0+30 0+40 0+50 0+60 0+70 0+80 0+90 1+00 1+05
STREAM 10
475'
480'
485'
490'
495'
500'
475'
480'
485'
490'
495'
500'
0+00 0+10 0+20 0+30 0+40 0+50 0+60 0+70 0+80 0+90 1+00
-FIGURE 14FIGURE 14
DWG SIZE REVISION
FOR
DRAWING NO.
TITLE
FILENAME:
DWG TYPE:
JOB NO:
DATE:
SCALE:DES:
DFTR:
CHKD:
ENGR:
APPD:
A
F
E
D
C
B
2 3 4 5 7 86
4 5 7 8 9 106
A
F
C
B
11"x17"
ANSI C
SEAL
321
Environment & Infrastructure Solutions
4021 STIRRUP CREEK DRIVE, SUITE 100
DURHAM NC 27703
TEL: [phone]
FAX: [phone]
LICENSURE:
NC ENG: F-1253
NC GEOLOGY: C-247
REV DATE JOB NO.PROJECT TYPE DES DFTR CHKD ENGR APPD DESCRIPTION
12/10/2020
7812-20-0451
DWG
AS SHOWN
RH
RH
JC
SM
SM
MAYO ASH BASIN LANDFILL
MAYO STEAM ELECTRIC STATION
PERSON COUNTY, NORTH CAROLINA
CROSS-SECTIONS --FIGURE 14
-
LOCATION OF STREAM 9
STA: 0+50.00
ELEV: 494.65
LOCATION OF STREAM 10
STA: 0+58.61
ELEV: 484.32

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Q-R 2: PLAN VIEW WETLAND OOO

BOSTON ROAD (US. RT. 501)OOO
-FIGURE 5FIGURE 5
DWG SIZE REVISION
FOR
DRAWING NO.
TITLE
FILENAME:
DWG TYPE:
JOB NO:
DATE:
SCALE:DES:
DFTR:
CHKD:
ENGR:
APPD:
A
F
E
D
C
B
2 3 4 5 7 86
4 5 7 8 9 106
A
F
C
B
11"x17"
ANSI C
SEAL
321
Environment & Infrastructure Solutions
4021 STIRRUP CREEK DRIVE, SUITE 100
DURHAM NC 27703
TEL: [phone]
FAX: [phone]
LICENSURE:
NC ENG: F-1253
NC GEOLOGY: C-247
REV DATE JOB NO.PROJECT TYPE DES DFTR CHKD ENGR APPD DESCRIPTION
12/10/2020
7812-20-0451
DWG
AS SHOWN
RH
RH
JC
SM
SM
MAYO ASH BASIN LANDFILL
MAYO STEAM ELECTRIC STATION
PERSON COUNTY, NORTH CAROLINA
PLAN VIEW 5 --FIGURE 5
-
N
EXISTING ASH BASIN BOUNDARY
PROPOSED LANDFILL BOUNDARY
STREAM - IMPACTED
STREAM - NOT IMPACTED
WETLAND - IMPACTED
WETLAND - NOT IMPACTED
LIMITS OF DISTURBANCE
CROSS SECTION
EXISTING MAJOR ROAD
EXISTING RAILROAD
LEGEND
MATCH LINE - FIGURE 6