20120615 Ver 3_USACE-DWR RAI Response - Mayo IP Mod 12-18-20_20201218

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Mr. Christopher Hopper December 18, 2020
USACE – Raleigh Regulatory Field Office
3331 Heritage Trade Drive, Suite 105
Wake Forest, North Carolina 27587

Mr. Rick Trone
NCDEQ – Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617

RE: Response to Request for Additional Information
USACE No. SAW -2011-00181; DWR No. 20120615v3
Duke Energy Mayo Steam Electric Plant - Ash Basin Landfill Project
Person County, North Carolina

Dear Mr. Hopper and 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. USACE advertised Duke Energy’s proposal by public
notice dated November 6, 2020. Subsequent to review, USACE submitted two requests
for additional information (RAI) to Duke Energy in correspondence dated December 15,
2020. In addition, a request was included in the correspondence for USACE to be copied
on Duke Energy’s responses to DWR RAIs. USACE was copied on Duke Energy’s
December 11, 2020 response to the December 4, 2020 DWR RAI; however, DWR
submitted a follow-up RAI via email on December 16, 2020.
The USACE and DWR follow-up RAIs are recounted herein for discussion purposes.
Duke Energy’s respective responses to the RAIs are presented below for USACE ’s
consideration of the approval of the Individual Permit modification for the Ash Basin
Landfill Project.
USACE Item A
The application states that the Coal Combustion Product (CCP) Monofill Alternative
would require impacts to 1,990 linear feet (lf) of intermittent stream and 84 lf of impacts
to perennial streams, with possible future impacts to 2,658 lf of streams through buildout.
The application goes on to state, “Duke Energy would not build additional phases of the
Mayo Monofill under the proposed action, but that this directive is contingent upon
obtaining all permits and approvals required to construct the proposed ABLF”. The need
for this project would be difficult to document with a viable alternative already permitted.
Please provide documentation on how the additional impacts requested meet the least
environmentally damaging practicable alternative when compared to the previously
permitted CCP Monofill.

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Response
The IP modification request package is intended to present two viable action alternatives
for ash basin closure, as described in Section 4.2.1.2 of the Environmental Report
(Report):
• Alternative 1A, construction of an industrial landfill (Ash Basin Landfill (ABLF))
under a modification to the existing IP, and
• Alternative 1B, construct Phase 2 of the existing industrial landfill (Monofill)
under the current IP.
An alternatives analysis is subsequently presented in Section 4.2.3 of the Report, along
with a summary table (Table 4-6) that is included herein for your convenience.
Table 4-6. Comparison of Impacts to Jurisdictional Waters and other Features or
Considerations among Lined Retention Basin Site Location Alternatives
Issue
(Feature or
Consideration)
Action Alternatives
Alternative 1A
Mayo ABLF Area (2020)
Alternative 1B
Mayo CCP Monofill Site (2012)
Stream impacts 896 lf
Phase I:
1,990 lf (intermittent)
84 lf (perennial)

Phase II:
2,658 lf (intermittent)
Wetland impacts 0.89 acre 0.00 acre
Transportation Potential crossing of US Route 501 US Route 501 crossing;
NCDOT Traffic Analysis
Residential and
public safety
considerations
No impacts
Disruption to local residents and
infrastructure from off-site disposal of
CCR materials

Duke Energy is proposing the selection of Alternative 1A (ABLF) as it would represent a
reduction of approximately 1,762 lf of stream impacts compared to the currently
permitted Alternative 1B (Monofill expansion). The ABLF footprint (approximately 42.2
acres) would be similar in size to Phase II of the the Monofill (approximately 43.8 acres).
Alternative 1A would potentially impact 0.89 acre of wetland. However, based on the
significant reduction in stream impac ts within a similar landfill footprint, Duke Energy
considers Alternative 1A to be the least environmentally damaging practicable
alternative. In addition, Alternative 1A is anticipated have fewer impacts to
transportation, public disturbance, and public and environmental safety.
The statement “Duke Energy would not build additional phases of the Mayo Monofill
under the proposed action, but that this directive is contingent upon obtaining all permits
and approvals required to construct the proposed ABLF” was included in the application
to convey the contingency of alternative selection. One of the two alternatives is needed

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to close the ash basin by excavation. Key p ermit s and approvals are pending for
preferred Alternative 1A whereas key permits and approvals have been received for
Alternative 1B resulting in either the
• preferred outcome (Alternative 1A); the USACE approves the IP modification
request and Duke Energy secures all regulatory permits and approvals for the
ABLF), then Duke Energy will construct the ABLF resulting in no need to expand
the Monofill for ash basin closure by excavation or;
• the less preferred outcome (Alternative 1B); if Duke Energy is unable to secure
all regulatory permits and approvals for the ABLF, then Duke Energy will proceed
with expansion of the Monofill (construction of Phase II)
Duke Energy is currently working with various regulatory agencies to secure permits and
approvals required to construct the ABLF. Duke Energy hopes approvals for Alternative
1A are obtained so that closure activities are maintained in addition to reducing potential
impacts to the public and environment.
USACE Item B
The MOA [February 6, 1990; between USACE and U.S. Environmental Protection
Agency] requires that appropriate and practical mitigation will be required for all
unavoidable adverse impacts remaining after all appropriate and practical minimization
has been employed. Please provide a Statement of Availability from the NCDEQ
Division of Mitigation Services (DMS) to mitigate for the projected, unavoidable loss of
waters or wetlands or provide information as to the absence of any such appropriate and
practical measures.
Response
Duke Energy requested a Statement of Availability and received response from DMS on
December 17, 2020. The DMS response, attached to this letter, stated that to meet the
proposed mitigation need with the Roanoke 03010104 Hydrologic Unit Code (HUC),
DMS would utilize assets in the Roanoke 03010102, 03010103, or 03010104 HUCs, and
noted that the premium wetland rate for the 03010104 HUC will be applied for the
credits. The mitigation would be performed in accordance with the In-Lieu Fee Program
instrument dated July 28, 2010.
DWR Item 1, Part 1
Table 5-3 lists proposed impacts to Wetlands LLL and JJJ and streams 9 and 10 to be a
result of the haul road and Borrow Area 3. A review of impact maps submitted in the
application do not clearly indicate how the haul road and Borrow Area 3 are impacting
these stream and wetland features. Based on the RAI response received by this office, it
may be more appropriate to classify these proposed impacts as resulting from clean
closure activities. Please revise table 5-3 to indicate ex actly what impacts to Streams 9
and 10 and Wetlands JJJ and LLL are proposed to result from.

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Response
Tables 5-3 (wetland impacts) and 5-4 (stream impacts) have been updated to
appropriately indicate that the proposed impacts to Wetlands LLL and JJJ and streams 9
and 10 would result from ash basin closure by excavation activities. The wetland impacts
in Table 5-3 have also been updated to reflect the avoidance of Wetland OOO, per Duke
Energy’s December 11, 2020 response to DWR. Revised Tables 5-3 and 5 -4 are
attached.
DWR Item 1, Part 2
Please explain how the haul road will be utilized and if the road will remain in place
permanently. Impact maps depict the haul road routed through Borrow Area 3. Please
explain how the road will be configured once Borrow Area 3 becomes active. Will the
haul road be moved at a later date to make room for the borrow pit?
Response
The haul road will serve as a permanent access road in order to maintain internal site
access to the landfill following construction. During construction, the road will provide
access, internal to the Mayo property, between Borrow Area 3 and the ABLF for the
transportation of materials and equipment. Please note that the area known as Borrow
Area 3 has been identified for use as a laydown area during the construction process.
The area will be graded to create a useable work laydown area. If the area is utilized for
borrow material, the construction of borrow pits is not expected to impact or change the
alignment of the road (i.e., Borrow Area 3 usage or the phase of landfill construction will
not dictate a change of the roadway alignment).
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 Tollie
Duke Energy – Permitting & Compliance

Enclosures:
Statement of Availability
Table 5-3
Table 5-4

cc: Michael Lazar (Duke Energy)
Mike Kendrick (Duke Energy)
Steve Cahoon (Duke Energy)
Richard Harmon (Wood)
Chris Keenan (Wood)

Table 5-3. Proposed Impacts and Completed Impacts to Wetlands within the
Project Site
Wetland ID Total Area (acres) Impact Area (acres)
ABLF Area (Proposed Impacts)
Wetland B 0.1 0.1
Wetland C 0.04 0.04
Wetland UU 0.02 0.02
Wetland ZZ 0.3 0.3
Borrow Area 1 (Proposed Impacts)
Wetland JJ 0.1 No Impact
Wetland KK 0.2 No Impact
Ash Basin Clean Closure (Proposed Impacts)
Wetland JJJ 0.1 0.1
Wetland LLL 0.1 0.1
Borrow Area 4 (Proposed Impacts)
Wetland NNN 0.1 No Impact
Wetland OOO 0.1 No Impact
Plant Facility (Proposed Impacts)
Wetland VVVa 0.4 No Impact
Wetland VVVb 0.1 No Impact
Ash Basin Dam Decommission Footprint (Proposed Impacts)
Wetland F 0.03 0.03
Wetland G 0.1 No Impact
Wetland H 0.1 0.1
Lined Retention Basin (Completed Impacts)
Wetland D 0.11 0.11
Wetland E 0.76 0.76
Wetland MMM 0.28 0.28

Total (all project components) 3.04 1.94

Table 5-4. Proposed Impacts and Completed Impacts to Streams within the Project
Site
Stream ID Total Length (linear feet) Impact Length (linear feet)
Ash Basin Clean Closure (Proposed Impacts)
Stream 9 218 218
Stream 10 91 91
Ash Basin Dam Decommission Footprint (Proposed Impacts)
Stream 1 322 322
Stream 2 878 Not Impacted
Stream 3 485 265
Lined Retention Basin (Completed Impacts)
Stream 5 148 148
Stream 6 229 229

Total (all project components) 2,371 1,273