Mayo CBE - Closure Plan_20200107

DUKE ENERGY
MAYO STEAM ELECTRIC PLANT
COAL COMBUSTION RESIDUALS SURFACE
IMPOUNDMENT CLOSURE PLAN
CLOSURE BY EXCAVATION
Cam' :MIff
Prepared for
DUKE
ENERGY,
Duke Energy Progress, LLC
410 S. Wilmington St
Raleigh, NC 27601
December 18, 2019
Prepared by
AECOM

AECOM
Duke Energy — Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
TABLE OF CONTENTS
December 18, 2019
EXECUTIVE SUMMARY..............................................................................................................v
1. INTRODUCTION...............................................................................................................7
1.1 Background......................................................................................................................... 7
1.2 Closure Plan Objectives...................................................................................................... 7
1.3 Report Organization............................................................................................................ 8
2. GOVERNING LAWS.........................................................................................................8
3. FACILITY DESCRIPTION AND EXISTING SITE FEATURES.........................................8
3.1 Surface Impoundments Description....................................................................................
8
3.1.1
Site History and Operations...................................................................................9
3.1.2
Estimated Volume of CCR in Impoundments......................................................10
3.1.3
Description of Surface Impoundment Structural Integrity....................................10
3.1.4
Sources of Discharges into Surface Impoundments............................................12
3.1.5
Existing Liner System..........................................................................................12
3.1.6
Inspection and Monitoring Summary...................................................................12
3.2 Site Maps..........................................................................................................................
13
3.2.1
Existing CCR Impoundment -Related Structures.................................................13
3.2.2
Receptor Survey..................................................................................................13
3.2.3
Existing On -Site Landfills.....................................................................................13
3.3 Monitoring and Sampling Location Plan........................................................................... 13
4. RESULTS OF HYDROGEOLOGIC, GEOLOGIC, AND GEOTECHNICAL
INVESTIGATIONS..........................................................................................................14
4.1
Background.......................................................................................................................14
4.2
Hydrogeology and Geologic Descriptions.........................................................................
14
4.3
Stratigraphy of the Geologic Units Underlying Surface Impoundments ...........................
14
4.4
Geotechnical Properties....................................................................................................
14
4.4.1 CCR Within the Basins........................................................................................
14
4.4.2 Liner Material Properties......................................................................................
15
4.4.3 Subsurface Soil Properties..................................................................................15
4.5
Chemical Analysis of Impoundment Water, CCR, and CCR-Affected Soil .......................
15
4.6
Historical Groundwater Sampling Results........................................................................
15
4.7
Groundwater Potentiometric Contour Maps.....................................................................
15
4.8
Estimated Vertical and Horizontal Extent of CCR Within the Impoundments ...................
16
5. GROUNDWATER MODELING ANALYSIS....................................................................16
5.1 Site Conceptual Model Predictions................................................................................... 16
5.2 Groundwater Chemistry Effects........................................................................................ 16
5.3 Groundwater Trend Analysis Methods.............................................................................. 16
6. BENEFICIAL USE AND FUTURE USE.........................................................................17
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AECOM December 18, 2019
Duke Energy — Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
6.1 CCR Use........................................................................................................................... 17
6.2 Site Future Use................................................................................................................. 17
7. CLOSURE DESIGN DOCUMENTS................................................................................17
7.1 Engineering Evaluations and Analyses............................................................................ 17
7.2 Closure Plan Activities...................................................................................................... 18
7.3 Design Drawings............................................................................................................... 18
7.4 Description of a Construction Quality Assurance and Plan .............................................. 19
8. MANAGEMENT OF WASTEWATER AND STORMWATER.........................................20
8.1 Anticipated Changes in Wastewater and Stormwater Management ................................ 21
8.2 Wastewater and Stormwater Permitting Requirements.................................................... 21
9. DESCRIPTION OF FINAL DISPOSITION OF CCR.......................................................21
10. APPLICABLE PERMITS................................................................................................21
11. DESCRIPTION OF POST -CLOSURE MONITORING AND CARE................................22
11.1 Groundwater Monitoring Program..................................................................................... 22
12. PROJECT MILESTONES AND COST ESTIMATES......................................................22
12.1 Project Schedule............................................................................................................... 22
12.2 Closure and Post -Closure Cost Estimate......................................................................... 23
13. REFERENCED DOCUMENTS.......................................................................................23
PROFESSIONAL ENGINEER CERTIFICATION............................................................24
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AECOM December 18, 2019
Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
Tables
Table 2-1 NC CAMA Closure Plan Requirements Summary and Cross Reference Table
Table 4-1 Summary of Typical Geotechnical Material Properties
Table 10-1 Mayo Steam Electric Plan Regulatory Permits, Approvals, or Requirements for
Basin Closure by Excavation
Figures
Figure ES-1
Current Condition View
Figure ES-2
Post -Closure Condition View
Figure 1-1
Vicinity Map and Site Plan
Figure 3-1
Existing Conditions Plan
Appendices
Appendix A Estimated Volume of CCR in Impoundment
Appendix B Geotechnical Data and Properties
Appendix C Engineering Evaluations and Analyses
Appendix C1 Stormwater Management Calculations Memo
Appendix C2 Soil Quantities
Appendix D Closure Plan Drawings
Appendix E Final Closure by Excavation Sampling Plan

AECOM December 18, 2019
Duke Energy — Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
EXECUTIVE SUMMARY
Duke Energy has prepared this Closure Plan to describe the closure of the coal combustion
residuals (CCR) surface impoundments at the Mayo Steam Electric Plant (Mayo Plant). This plan
details closure by excavation of the Mayo Plant Ash Basin (Basin) and flue gas desulfurization
FGD Ponds (collectively, Basins) and placement of the excavated CCR in a new permitted, on -
site, lined CCR landfill. The excavation of CCR and the closure of the basins will be in accordance
with applicable provisions of the North Carolina Coal Ash Management Act of 2014, as amended
(CAMA), (codified at N.C.G.S. § 130A-309.200 et seq.), and the federal Disposal of Coal
Combustion Residuals from Electric Utilities rule (CCR Rule) (codified at 40 C.F.R. § 257.50 et
seq. ).
The Mayo Plant is owned and operated by Duke Energy Progress (Duke Energy) in Person
County, approximately 10 miles northeast of Roxboro, North Carolina. The Mayo Plant is a single -
unit, 727-megawatt coal-fired plant located less than one-half mile south of the North Carolina -
Virginia state line. It began commercial operation in 1983 with a single coal-fired unit, and the
plant is currently in active operation.
Duke Energy has historically operated a single impoundment for storing wet sluiced coal ash
referred to as the Basin at the Mayo Plant. The Basin was constructed during the early 1980s and
was completed in 1982. The Basin was constructed above a section of Crutchfield Branch, which
is part of the Roanoke River Basin. Based on the CCR unit boundary, the Mayo Plant Basin has
a surface area of approximately 153 acres (including the Basin Dam). Based on topographic and
bathymetric surveys performed in 2015 and updated with production data provided by Duke
Energy as of July 31, 2019, the Basin is estimated to contain approximately 5.5 million cubic yards
of CCR or an estimated 6.6 million tons as of June 2019. Two additional basins for storage of wet
sluiced FGD process residuals (also CCR) were constructed in 2009 and collectively have a
surface area of approximately 5 acres. These FGD Ponds are perched at the eastern edge of the
Basin. Process flows of CCR waste streams have ceased for all 3 basins and decanting
operations have been initiated to remove bulk water.
Closure activities for the Basin has already begun with the initiation of decanting under the Special
Order by Consent (SOC). Upon approval of a Closure Plan by NCDEQ additional actions will
commence, including; finalization of detailed designs, dewatering and removal of interstitial water,
contracting and detailed planning for the closure work, development of the new lined landfill on -
site in conjunction with excavation of the CCR, final grading of the site and landfill, and
development of stormwater features and vegetative covers.
Figures ES-1 and ES-2 illustrate the current state, and post -closure state of the Basins as detailed
by this Closure Plan.
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AECOM December 18, 2019
Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
Figure ES-1 Current View
Figure ES-2 Post Closure View
The Basin CCR would be removed to a new lined landfill within plant property, located partially
within the prior footprint of the Basin, adjacent to Boston Road. The landfill would rise
approximately 170 feet above Boston Road. Post -excavation, the Basin site will resemble the
land's valley shape before the basin was created. Soil will be graded to restore contours for
stormwater flows, then planted with native grasses for erosion control. A portion of the existing
Basin dam will be removed, and detention basins constructed for stormwater management.
Stormwater flows will then make their way into Crutchfield Branch.
This document also includes a description of the Post -Closure Plan, which provides a description
of the inspection, monitoring, and maintenance activities required to be performed throughout the
30-year post -closure care period for the closed Basins at the Mayo Plant.
This document provides a summary of properties of the site, as well as geotechnical properties
of CCR and natural soils to support engineering analyses of the closure design. These analyses
indicate that closure by excavation, as detailed in the Closure Plan, meets regulatory
requirements for the stability of the site, management of stormwater run-off, and access for
effective maintenance over the post -closure care period.
Mayo Plant is currently in compliance with North Carolina's regulations for the protection of
groundwater at 15A NCAC 02L .0202 (02L Standards). Nevertheless, in accordance with the
requirements of N.C.G.S. § 130A-309.21 1 (b)(1), Duke Energy separately submitted an updated
CAP in parallel with this Closure Plan, which CAP is herein incorporated in its entirety by this
reference. Neither the CAP nor its content is the work product of AECOM. Although the Closure
Plan contains references to the CAP, all specific relevant details to groundwater and related
actions are found in the CAP itself and not in this Closure Plan.
As detailed in the updated CAP, groundwater quality data confirm, based on one year of quarterly
monitoring results, that constituents of interest (COI) identified at the Mayo Plant do not exceed
the applicable 02L Standards at or beyond the Basin compliance boundary. Accordingly,
groundwater corrective action under 15A NCAC 02L.0106 is not triggered. However, Duke Energy
has either implemented, or will implement, source control measures at the site, including (i)
complete Basin decanting to remove the hydraulic head, thereby mitigating the risk of potential
COI migration into groundwater; (ii) complete Basin closure; and (iii) continued operation of the
dam toe -drain water collection system to reduce COI concentrations in surface water and in
groundwater proximate to the system.
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AECOM December 18, 2019
Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
1. INTRODUCTION
1.1 Background
The primary objective of this Closure Plan is to address the closure of the Basin at the Mayo Plant
which is a coal-fired electricity -generating facility owned and operated by Duke Energy Progress,
LLC (Duke Energy). The Mayo Plant is located in Person County, approximately 10 miles
northeast of Roxboro, North Carolina and is a single -unit, 727-megawatt coal-fired plant located
less than one-half mile south of the North Carolina -Virginia line. It began commercial operation in
1983 with a single coal-fired unit, and the plant is currently in active operation. CCR has
historically been managed in the Plant's on -site Basin and FGD Ponds. The Mayo Plant ceased
all waste flows to the Basins in 2019.
Figure 1-1 presents a Vicinity Map and Site Plan of the Mayo Plant.
Duke Energy uses three facilities to manage CCR at the Mayo Plant that include dams regulated
by NCDEQ and Dam Safety:
1. The Basin Dam (NCDEQ ID: PERSO-035); and
2. The flue gas desulfurization (FGD) ponds containing the integrated FGD Settling Pond
(NCDEQ ID: PERSO-036) and FGD Forward Flush Pond (NCDEQ ID: PERSO-037).
As further discussed in Section 2 below, the closure method mandated by order of the NCDEQ
for the Basins is closure by excavation.
1.2 Closure Plan Objectives
The objective of this Closure Plan is to address the closure by excavation of CCR from the
Basin and FGD Ponds as directed by order of NCDEQ. AECOM understands Duke Energy
does so without prejudice of its position that closure by excavation is neither necessary nor
appropriate for either the Basin or FGD Ponds. Duke Energy also notes that approval from
NCDEQ is required to proceed and develop the additional details as described further within this
Closure Plan to complete the necessary working documents to complete the closure actions.
Duke Energy submits this Closure Plan with the knowledge that other details will follow, as
necessary. This Closure Plan describes and communicates the key actions and activities
necessary to close the Basins in accordance with the requirements for written Closure Plans for
CCR surface impoundments presented in N.C.G.S. §130A-309.214(a)(4). Planned closure
activities include:
• Decanting the Basin;
• Construction and operation of a temporary water management system (WMS) to
manage discharges in compliance with the NPDES permit during closure;
• Dewatering to support safe excavation of CCR from the Basins;
• Excavation of the CCR and establishing post -excavation final grades using soil fill where
required;
• Breaching of the Basin dam,
• Construction of an on -site CCR landfill to permanently store the excavated CCR,
• Modification of the Basin spillway/discharge channel; and
• Restoration of disturbed areas.
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AECOM December 18, 2019
Duke Energy — Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
1.3 Report Organization
This document is structured to follow the requirements provided in CAMA (G.S. §130A-
309.214(a)(4)).
2. GOVERNING LAWS
In August 2014, the North Carolina General Assembly enacted CAMA, which contains specific
statutory requirements applicable to the CCR basins. Subsequently, in July 2016, the North
Carolina General Assembly enacted H.B. 630, Session Law 2016-95, which provides that
impoundments be classified as "low -risk" if, by certain deadlines, the owner has established
permanent alternative water supplies, as required, and has rectified any deficiencies identified by,
and has otherwise complied with requirements of, any dam safety order. NCDEQ determined
that Duke Energy met these criteria on November 14, 2018, and officially classified the Basin at
Mayo Plant as "low -risk."
On April 1, 2019, NCDEQ issued its Closure Determination mandating that the Basins be closed
by excavation of the Basins pursuant to N.C.G.S. § 130A-309.214(a)(3)a. A closure plan is
required for each CCR surface impoundment regardless of the risk classification. CAMA's closure
plan requirements and cross-referenced sections of this Closure Plan are summarized in Table
2-1. On April 26, 2019, Duke Energy filed a Petition for Contested Case Hearing before the North
Carolina Office of Administrative Hearings appealing this determination, on May 24, 2019 Duke
Energy filed amended petitions in the case. The petitions allege that in issuing its Closure
Determination, NCDEQ failed to (i) follow the mandatory process and procedure outlined in CAMA
and (ii) consider or apply the scientific and engineering evidence submitted and available to it in
reaching its decision to require the most expensive closure method available despite scientific
and engineering evidence demonstrating the availability of less expensive and more rapid closure
options that would continue to fully protect human health and the environment. Certain decisions
by the administrative law judge in that case are currently under appeal to the North Carolina
Superior Court.
In addition to the closure plan requirements, CAMA sets out groundwater assessment and
corrective action requirements. A Comprehensive Site Assessment report was submitted to
NCDEQ in September 2015, with supplemental reports submitted August 2016 and October 2017.
Duke Energy intends that a CAP will be submitted in parallel with this Closure Plan.
In addition to the above requirements, National Pollutant Discharge Elimination System (NPDES)
permit program compliance, SOC (which commits Duke Energy to initiate and complete decanting
of the Basins by dates certain) compliance, dam safety approvals for modifications to regulated
Basin dams, and environmental permitting requirements must be considered as part of closure.
3. FACILITY DESCRIPTION AND EXISTING SITE FEATURES
3.1 Surface Impoundments Description
This section provides details on the CCR-related features at the Mayo Plant.
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AECOM December 18, 2019
Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
3.1.1 Site History and Operations
Figure 1-1 shows locations of the plant, the Basin, and the Basin Dam, and the FGD Ponds.
Existing topography in the area of the Mayo Plant is presented on Figure 3-1, and also presents
overall existing conditions including topography and bathymetry of the Basin.
Basin (Dam ID, PERSO-035):
The Basin is situated north of the plant area and its CCR boundary surface area approximately
153 acres (including the Basin Dam). The Basin is unlined, impounding a former valley area and
operated at a normal pond elevation of El. 479.22. Basin Dam is approximately 2,300 ft in length,
400 ft wide at the base, with crest elevations of El. 489 ft, respectively. A survey conducted by
AECOM in 2016 identified a maximum height above downstream toe of approximately 110 ft for
the Basin Dam. The Basin was completed in October 1982. Based on the information available,
the basin appears to have been originally constructed to its present configuration and has not
been raised or expanded at any time subsequent to its original construction.
The Basin discharge flow is directed to the main cooling reservoir (Dam ID, PERSO-034) by a
channel constructed at the northeast corner of the Basin. The Basin forebay embankment is used
in the management of water quality and outflow monitoring efforts for the Basin. Three 24-inch
diameter equalization pipes were constructed in the northeast corner of the forebay embankment
in 2015. The pipes have upstream and downstream inverts of El. 477.23 ft and El. 477.03 ft,
respectively. The original 48-inch corrugated metal pipe (CMP) riser and spillway pipe between
the Basin and forebay embankment were grouted and abandoned in -place in December 2015.
There are two abandoned (grouted) 30-inch diameter CMP's through the forebay embankment
located to the south of the riser. No pipes are known to be present that penetrate through the
Basin dam structure. Toe drain collection piping was included in the original dam construction and
extends along the length of downstream toe.
Normal flow passes through the equalizer culverts located in forebay embankment. The water
level in the forebay area and the flow to the discharge channel are controlled by a submerged
fixed concrete weir with a crest at approximate El. 478.6 ft. The submerged fixed weir is a
reinforced concrete block that is keyed and doweled into the surrounding rock at the bottom and
sides of the discharge channel. Higher flows from extreme rain events would pass over the
forebay weir.
The Basin historically accepted bottom and fly ash generated from the Mayo Plant's coal
combustion operations transported to the Basin via wet sluicing, along with various other waste
water streams. Since Mayo Plant has been in operation, the Basin received fly ash, bottom ash,
ash transport water, coal pile runoff, stormwater runoff, cooling tower blowdown, and low volume
wastewater (Geosyntec, 2015). In 2013, the Plant converted from a wet to dry ash system.
Modifications were completed in 2019 to re -direct waste and process flows and all such flows to
the Basin have been ceased. In 2019, a project was also completed that re -directed a significant
amount of stormwater from other parts of the plant site away from the Basin.
FGD Settling Pond (Dam ID, PERSO-036) and FGD Forward Flush Pond (Dam ID, PERSO-037):
The FGD Ponds (FGD Ponds) were completed in 2009. From 2009 until 2019, the Mayo Plant
operated a FGD system that directed the FGD blowdown discharge to the FGD Settling Pond.
Following processing, the wastewater discharge is routed into a Thermal Evaporator system.
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AECOM December 18, 2019
Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
Normal flows did not discharge into the Basin. An emergency discharge for the FGD settling pond
discharges to the Basin (AMEC, 2015b). The FGD Ponds consist of perched soil dikes
constructed in part over a portion of the Basin and in part over natural ground. The FGD Pond
system has a combined and shared dam crest length of 2,145 ft and maximum dam height of 26
ft. Crest elevation is El. 506 ft and crest width is 15 ft. The FGD Settling Pond area is 4.36 acres
and the Forward Flush Pond area is 0.56 acres. The portion of the dike that extends over the
Basin was constructed by placing fill consisting of weathered rock and soil atop a geogrid layer.
The Forward Flush Pond is mostly excavated into the natural ground bordering the Basin and
partly on soil fill railroad embankment over natural ground. The FGD Ponds have a liner system
consisting of a 200-mil double sided geocomposite overlain by a smooth flexible 60-mil HDPE
membrane liner (FML) (Golder, 2009).
3.1.2 Estimated Volume of CCR in Impoundments
Based on CCR inventory data provided by Duke Energy as of July 31, 2019 and upon a surface
comparison calculation, performed within AutoCAD Civil 3D, comparing the approximate pre -
development topography to the existing topographic and bathymetric survey, the approximate
volume of CCR in the Basins are listed in the table below. To compute the estimated mass of CCR
in place an assumed density of 1.2 tons per CY was used, which is the Duke Energy fleet wide
assumption. See Appendix A for the Estimated Volume of CCR in Impoundment calculation.
Impoundment
Estimated CCR Volume
Estimated CCR Weight
(CY)
(Tons)
Basin*
5,500,000
6,600,000
FGD Settling
29,232
Pond**
24,360
FGD Forward Flush
2,664
Pond**
2,220
Total CCR Subject
5,526,580
6,631,896
to Closure Plan
* The Basin boundary used to estimate in -place CCR includes the current FGD Settling and
Flush Pond footprint and is based on the unit boundary as provided by Synterra, but
excluded the dam area.
**Volumes provided by Duke Energy on November 5, 2019
3.1.3 Description of Surface Impoundment Structural Integrity
The purpose of this section is to summarize the Basins' structural integrity evaluations based on
current existing information. This section includes the geotechnical, and hydrology and hydraulics
(H&H) capacity analyses results. In summary, the structural integrity of the Basins and subsequent
dam inspection reports meets the regulatory requirements of EPA's CCR Rule (40 § CFR 257.73).
Duke Energy's certifications of these requirements are available on Duke Energy's publicly -
accessible CCR Rule Compliance Data and Information website.
• Slope stability
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AECOM December 18, 2019
Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
For the Basin Dam, and FGD Pond Dams, slope stability analysis results for the existing
conditions global factors of safety for static long-term maximum storage pool, static maximum
surcharge pool, sudden drawdown conditions, and pseudo -static seismic conditions meet
regulatory and programmatic criteria. Slope stability results for the Basin Dam at four selected
sections and forebay, and at the FGD Ponds under the loading conditions mentioned above met
regulatory requirements (AECOM, 2016a).
• Liquefaction conditions (where susceptible) and Liquefaction potential
In 2016, AECOM performed a liquefaction screening analysis for the Basin Dam and the forebay
embankment. Based on the screening analyses, the Basin Dam and its foundation soils, and the
forebay discharge embankment and its foundation soils are not liquefaction -susceptible.
AECOM also evaluated seismically -induced deformations of the Basin Dam following the Makdisi
and Seed (1977) procedure. The predicted deformations from these analyses are negligible, less
than '/2 inch. Because the Basin Dam and forebay embankments and foundation soils are not
liquefaction -susceptible, AECOM expects no vertical seismically -induced settlements and
negligible seismically -induced shear at these structures from the design event which is the event
corresponding to a 2,500-year return period with a peak ground acceleration (PGA) of 0.053g and
a mean earthquake moment magnitude of 5.1.
AECOM also conducted a liquefaction screening analysis and developed a probabilistic seismic
hazard analysis (PSHA) for the Mayo Plant site. Liquefaction screening considered SPT-based,
CPT -based, shear wave -based, and state parameter methods, and finite -element analyses
utilizing ground motions from the PSHA. AECOM concluded that because the ground motions are
relatively low for the 2,500 year design event, liquefaction triggering is unlikely and the 2,500 year
MDE is unlikely to induce significant seismic deformation in the saturated ash below or adjacent
to the FGD pond.
In 2016, AECOM performed an advanced liquefaction analysis for the FGD Ponds. Based on the
advanced analysis, liquefaction triggering was calculated to be mainly in the area beyond the toe
of the FGD Pond dams towards the Basin. Post liquefaction slope stability analysis was conducted
for this condition and the calculated factor of safety met the regulatory requirements (AECOM,
2016c).
• Hydrology and hydraulics (H&H) capacity analyses
Hydrologic analysis performed by AECOM following the 2015 construction of equalization pipes
between the Basin and outfall forebay show that the Basin can convey the Inflow Design Flood
(IDF) event while maintaining adequate freeboard.
Per direction from NCDEQ, additional hydrologic modeling was conducted to evaluate whether
the existing Basin and spillway system could convey the Spillway Design Flood (SDF) generated
during the full Probable Maximum Precipitation (PMP) event without overtopping the dam. The
PMP used for this analysis was developed and provided by Applied Weather Associates (AWA)
in July 2019. The evaluation involved incorporation of updated drainage area characteristics,
including upstream stormwater ponds under construction and other storage areas. The evaluation
showed that the Basin and existing spillway system can convey the SDF generated during the full
PMP without overtopping the dam.
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AECOM December 18, 2019
Duke Energy — Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
Per direction from NCDEQ, additional hydrologic modeling was conducted to evaluate whether
the FGD Ponds could convey the SDF generated during the full PMP without overtopping the
dam. These analyses indicate that the dams will overtop during the full PMP unless the initial
water surface elevation is maintained at or below 503.3 feet using active pumping which will need
to be installed. However, the FGD Ponds are no longer in service since the water redirect project
has been implemented (AECOM, 2019). As of October 18, 2019, the FGD Ponds were in a
dewatered condition.
3.1.4 Sources of Discharges into Surface Impoundments
Process flows no longer discharge into the Basin or FGD Ponds. Process flows are directed
toward newly -constructed lined retention basins and a new FGD settling pond. The Mayo Plant
currently employs a dry ash handling system.
Historically runoff and process water streams from the coal pile, gypsum storage area, air
preheater wash, cooling tower blowdown, and stormwater runoff from plant area were discharged
into the Basin. All of these have been re-routed and no longer convey to the Basins.
3.1.5 Existing Liner System
The Mayo Plant Basin does not include a geomembrane or clay liner system and is considered
to be unlined. The Basin was constructed directly on top of the historical ground surface. The FGD
Ponds were completed in 2009 and are lined with a 200-mil double sided geocomposite overlain
by a smooth flexible 60-mil HDPE membrane liner (FML) (Golder, 2009).
3.1.6 Inspection and Monitoring Summary
Weekly Basin inspections have been on -going since 2014, and include observation of upstream
slopes and shorelines, crest, downstream slopes, toes, abutment contacts and adjacent drainage
way(s), spillway(s) and associated structure(s), and other structures and features of the dams.
Monthly inspections of the Basins include the weekly monitoring elements with the addition of
piezometer and observation well readings, and water level gauges/sensors.
Daily inspections of basins are not routinely required, however, on a case -by -case basis, the
basins may be inspected daily beginning at such times and continued for the duration as specified
by plant management. Such daily inspections might be initiated during a repair activity on the dam
or in response to a specific imposed regulatory agency requirement.
The Basins are inspected annually by an independent third -party consultant. In a letter dated
August 13, 2014, NCDEQ requires these inspections to be conducted annually at all of Duke
Energy's CCR impoundments in North Carolina. These inspections are intended to confirm
adequacy of the design, operation, and maintenance of the surface impoundments in accordance
with accepted engineering standards. Reports are to be submitted to the NCDEQ within 30 days
of the completion of the inspection.
The results of the annual inspections are used to identify needed repairs, repair schedules, to
assess the safety and operational adequacy of the dam, and to assess compliance activities
regarding applicable permits, environmental and dam regulations. Annual inspections are also
performed to evaluate previous repairs. The annual inspections of the dams/dikes have been
ongoing since 2009, with 5-year inspections conducted between 1979 and 2009.
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AECOM December 18, 2019
Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
The 2015 through 2019 annual inspections did not identify features or conditions in the Basin
dams, or their outlet structures or spillways that indicate an imminent threat of impending failure
hazard. Review of critical analyses indicated the design conforms to current engineering state of
practice to a degree that no immediate actions are required other than the recent and ongoing
surveillance and monitoring activities already underway.
Special, episodic inspections of the Basins may be performed during episodes of earthquake,
emergency, or other extraordinary events. Visual inspections are performed after a heavy
precipitation event when accumulation of four inches of rainfall or greater occurs within a 24-hour
period. An internal inspection will be performed if an earthquake is felt locally or detected by the
US Geological Survey measuring greater than a Magnitude 3 and with an epicenter within 50
miles of the dams. A special inspection would also be performed during an emergency, such as
when a potential dam breach condition might be identified or when construction activities (e.g.,
basin cleanout) are planned on or near the dams. Special inspections are also conducted when
the ongoing surveillance program identifies a condition or a trend that warrants special evaluation.
3.2 Site Maps
3.2.1 Existing CCR Impoundment -Related Structures
A site map showing property boundary, location of the Mayo Plant, Basins with their boundaries
and topographic and bathymetric contours is shown on Figure 3-1.
3.2.2 Receptor Survey
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
3.2.3 Existing On -Site Landfills
There are two landfills at the Mayo Plant site, as identified in the table below. Figure 1-1 shows
locations of these landfills.
Landfill
Permit Number
Comment
On -site Industrial Landfill
7305-INDUS-2012
Active
1981 C&D Landfill
73-B
Non-CCR, Closed
3.3 Monitoring and Sampling Location Plan
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
Locations of the existing groundwater monitoring wells are shown in the Closure Plan Drawings,
Appendix D, but the CAP should be consulted for details of well locations, names, and status.
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CAMA Closure Plan (Closure by Excavation)
4. RESULTS OF HYDROGEOLOGIC, GEOLOGIC, AND GEOTECHNICAL
INVESTIGATIONS
4.1 Background
An overall boring and existing monitoring well location plan indicating the locations of recent and
historical borings, monitoring wells, piezometers and Cone Penetration Test (CPT) sounding
locations is shown on Drawing MAY_C999.003.005 included in Appendix D.
This chapter summarizes the site geology and hydrogeology, site stratigraphy of the geologic
units underlying the surface impoundments, hydraulic conductivity of CCR and the soils
underlying the surface impoundment, geotechnical properties of the CCRs, and the uppermost
stratigraphic unit under the surface impoundment; CCR and CCR affected soils.
4.2 Hydrogeology and Geologic Descriptions
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
4.3 Stratigraphy of the Geologic Units Underlying Surface Impoundments
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
4.4 Geotechnical Properties
This section provides a summary of geotechnical conditions and properties found from
investigations performed within the Basins and Basin dam areas. The presented information was
obtained from previous geotechnical investigations at the site and recent investigation activities
conducted to support the Closure Plan development. The geotechnical conditions within the
Basins generally consist of CCR (interbedded layers of fly ash and bottom ash) placed in the
basin primarily by hydraulic sluicing underlain by residual soil, saprolite, partially weather rock
(PWR), and bedrock. Explorations in the FGD Ponds area encountered embankment fill underlain
by CCR, residual soils, and PWR. The outlet forebay area exploration encountered embankment
fill soils underlain by residual soils and PWR.
For purposes of discussion of the geotechnical properties of the materials, the saprolite material
is described as residual material. General properties of the various materials encountered within
and surrounding the Basin are described below. A range of measured material properties of
laboratory tests performed by AECOM, SynTerra, and Mactec for the subsurface explorations
completed within the Basin is presented in Table 4-1. A summary of laboratory tests data
performed at the Mayo Plant in support of the closure design is presented in Appendix B-3.
4.4.1 CCR Within the Basins
The CCR within the Basins consists primarily of alternating layers and mixtures of bottom ash and
fly ash. Other CCR such as slag are also typically encountered. The bottom ash generally consists
14
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Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
of very loose to loose, moist to wet, dark gray to gray, silty sand (SM) or silt and sandy silt (ML).
At some drilling locations, a surficial layer of CCR fill material (SP or SW or SW-SM) was
encountered that was used for boring access road construction.
The fly ash generally consists of very soft to soft, moist to wet, light to medium gray sandy silt and
silt (ML).
The CCR within the FGD Ponds consists primarily of FGD Blowdown (primary contributor of
solids) and landfill leachate. When excavated, this material will be placed in an approved CCR
landfill.
4.4.2 Liner Material Properties
The Basin is unlined so there are no associated material properties. The FGD Ponds have a liner
system consisting of a 200-mil double sided geocomposite overlain by a smooth flexible 60-mil
HDPE membrane liner (FML) (Golder, 2009).
4.4.3 Subsurface Soil Properties
• Alluvium: Alluvial soil was encountered beneath the sluiced CCR in one boring from about
43 to 48 ft. The alluvium soil consists of very loose, wet, light grayish green, sandy silt (ML).
Alluvium was not encountered in other borings performed by AECOM within the Basins.
SynTerra reported alluvial soils in some monitoring well boring locations of sandy clay (CL)
and clayey sand (SC) to depths of about 7.5 ft.
• Residuum: The residuum (including saprolite) is the next layer encountered and generally
consists of soft to hard sandy lean clay (CL), silty sand (SM), and sandy silt (ML).
• Embankment Soil: The embankment fill generally consists of medium dense silty sand (SM)
and stiff to very stiff sandy silt (ML) with trace amounts of fine gravel and with occasional
pockets and lenses of relatively clean sand (SP) and sandy clay (CL).
4.5 Chemical Analysis of Impoundment Water, CCR, and CCR-Affected Soil
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
4.6 Historical Groundwater Sampling Results
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
4.7 Groundwater Potentiometric Contour Maps
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
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Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
4.8 Estimated Vertical and Horizontal Extent of CCR Within the Impoundments
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
5. GROUNDWATER MODELING ANALYSIS
In accordance with the requirements of N.C.G.S. § 130A-309.211(b)(1), Duke Energy separately
submitted an updated CAP in parallel with this Closure Plan; the updated CAP is herein
incorporated in its entirety by this reference. Neither the updated CAP nor its content is the work
product of AECOM. Although the Closure Plan contains references to the updated CAP, all
specific relevant details to groundwater and related actions are found in the updated CAP itself
and not in this Closure Plan.
The CAP evaluates the extent of, and remedies for, COI in groundwater associated with the Basin,
focusing on constituent concentrations detected above the applicable 02L Standards, Interim
Maximum Allowable Concentrations, or approved background threshold values at or beyond the
compliance boundary. In addition, the CAP considers the federal groundwater corrective action
requirements at 40 C.F.R. §§ 257.96-.98.
As detailed in the CAP, groundwater quality data confirm, based on one year of quarterly
monitoring results, that COI identified at the Mayo Plant do not exceed the applicable 02L
Standards at or beyond the Basin compliance boundary. Accordingly, groundwater corrective
action under 15A NCAC 02L.0106 is not triggered. However, Duke Energy has either
implemented, or will implement, source control measures at the site, including (i) complete Basin
decanting to remove the hydraulic head, thereby mitigating the risk of potential COI migration into
groundwater; (ii) complete Basin closure; and (iii) continued operation of the dam toe -drain water
collection system to reduce COI concentrations in surface water and in groundwater proximate to
the system.
5.1 Site Conceptual Model Predictions
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
5.2 Groundwater Chemistry Effects
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
5.3 Groundwater Trend Analysis Methods
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
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Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
6. BENEFICIAL USE AND FUTURE USE
6.1 CCR Use
At this time, Duke Energy has not identified a beneficial use of CCR from the Basins at Mayo
Plant.
6.2 Site Future Use
At this time Duke Energy has not identified any future use of the land reclaimed by the dewatering
and excavation of the Basins, except that a new CCR landfill is proposed to be partially built within
the western footprint of the excavated Basin.
7. CLOSURE DESIGN DOCUMENTS
7.1 Engineering Evaluations and Analyses
Engineering evaluations and analyses to support closure of the Basins at the Mayo Plant, as
detailed in this Closure Plan, are provided in Appendix C.
The FGD Ponds, including the liner material, will be fully removed down to grade. Based on the
final post closure configuration of the Basin and absence of engineered fill features, no
geotechnical calculations accompany the Closure Plan presented herein. Geotechnical
calculations for the proposed CCR landfill design will be performed separately as part of its permit
application, which will follow NCDEQ approval of this Closure Plan. Dam breach -related
calculations will be included in the dam modification permit applications, which will follow NCDEQ
approval of this Closure Plan.
Safe and effective access to the Basin is critical to CCR excavation and the completion of closure.
Access road locations into or across the Basins cannot be reliably established until detailed
phasing of closure is developed, and a contractor is selected to complete the work. A variety of
mitigation techniques can be applied, such as installation of a geogrid and crushed stone
aggregate, placement and spreading of dry CCR over the basin surface to establish access and
use of low ground pressure or light weight construction equipment.
Areas for stockpiling or conditioning (drying) of CCR are generally needed. These areas must be
established within the limits of the CCR unit and require placement or stacking of CCR excavated
from other areas of the basin. They can be established in areas where all or most of the CCR
has been removed, or on areas where a significant depth of CCR remains in place. Sluiced CCR
forming the foundation of stockpiles or conditioning areas may be subject to bearing capacity or
slope failures from the additional vertical compressive stress imparted by the stacked CCR and
hauling equipment.
During excavation of CCR, interim or temporary excavated CCR slopes are commonly created.
These slopes vary in height and the duration they will have to stand. Some slopes are subject to
potential loading from hauling or stockpiling operations. The location and geometry of such slopes
cannot be established during design. These elements depend on the means and methods
employed by the construction contractor, site conditions, schedule and other site conditions.
Excavation in a deep valley fill creates safety risks that need further evaluation and will require
the means and methods inputs from a contractor to fully address before closure excavation work
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December 18, 2019
commences. A detailed phasing and excavation plan will be developed after this Closure Plan is
approved by NCDEQ.
7.2 Closure Plan Activities
The primary activities associated with closure by excavation are as follows:
• Lower free water level through the equalization pipes in the discharge forebay outlet
under the existing NPDES permit.
• Decant by using floating pumps, screened intakes, and pumping through the discharge
forebay outlet.
• Construction and operation of a temporary WMS to manage all discharges in
compliance with the NPDES permit during closure.
• Dewater the CCR to allow for access. Excavate CCR and condition (drying) prior to
placement in the on -site landfill.
• Start CCR excavation from the Basin, with sequencing determined for optimal
progression. Manage and control of dust -generating activities through specific site
planning and mitigation. Construct landfill cells in coordination with CCR excavation.
Place the excavated CCR in the on -site landfill, and compact. Instrumentation and
monitoring requirements to be developed prior to construction will be followed to verify
construction phase stability. Construction dewatering to be used as needed to provide
stable work areas and slopes.
• Maintain required hydraulic storage capacity though the excavation process and
progressively breach the Basin Dam as excavation advances.
• Complete closure by excavation verification. Grade the area to promote positive
drainage and seed for vegetative growth.
• Sequence final dam breach with construction of proposed stormwater detention basins
and inflow design flood management.
Additional information and details pertaining to the closure design are provided in the Closure
Plan drawings, which can be found in Appendix D.
7.3 Design Drawings
The Closure Plan drawings found in Appendix D include the following:
• Cover sheet
• General notes
• Existing conditions plan with aerial photograph
• Existing conditions plan with topography
• Exploration location plan
• Demolition plan
• Estimated bottom of CCR contour plan
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Duke Energy - Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
• Final grading plan
• Final grading profiles, cross -sections and details
• Excavation plan
• Excavation profiles and details
• On -site landfill schematic plans
• On -site landfill schematic cross -sections
• Closure details
These Closure Plan drawings will be further developed and refined to develop construction level
drawings during subsequent stages following NCDEQ approval of the Closure Plan. In addition,
supplemental drawing sets will be prepared on an as needed basis to support dam modification
and/or decommissioning permits, erosion and sediment control permits, NPDES permit
modifications, and other related permits.
Once the excavation grades shown on the Closure Plan drawings have been achieved, the
procedures described in the Duke Energy Excavation Soil Sampling Plan (Appendix E) will be
followed to confirm that the closure by excavation has been achieved.
7.4 Description of a Construction Quality Assurance and Plan
A Construction Quality Assurance (CQA) Plan will be developed following NCDEQ approval of the
Closure Plan for closure of the Basins at Mayo Plant. The CQA Plan will be prepared to address
G.S. §130A-309.214(a)(4)(g). Its purpose is to provide a description of the CQA program to be
adhered to in execution of closure activities. The CQA Plan will present a description of the roles
and responsibilities for monitoring and testing activities and provides guidance on the
methodology to be used for evaluating whether the construction has been performed in
accordance with the approved Closure Plan. The CQA Plan will also detail the material testing
frequencies; methods for transportation, handling, and storage of materials; test methods and
verifications; manufacturer, field, and laboratory testing; field activities for construction monitoring
and oversight; and reporting and documentation requirements. Technical specifications to be
developed as part of the construction -level design packages for contractor bidding will present
specific material properties and specifications.
The CQA Plan will address materials and CQA activities associated with the following
components:
• Earthwork
■ CCR Excavation
■ Soil Fill
• HDPE Piping
• As -Built Conditions
• Record Documentation Report
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AECOM December 18, 2019
Duke Energy — Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
8. MANAGEMENT OF WASTEWATER AND STORMWATER
The Mayo Plant manages wastewater and stormwater under two separate the NPDES permits
issued by the NCDEQ that authorizes two discharge points into the Mayo Lake Reservoir. The
wastewater permit number is NCO038377 and the stormwater permit number is NCS000580.
The Basin discharge will continue to operate during closure to meet the NPDES permit discharge
requirements as it goes through the phases of decanting and dewatering. With decanting
underway discharges from the Basin via the existing passive gravity discharge system have
stopped. Decanting is proceeding via mechanical pumping. The pumping system is expected to
draw down the stored water after storm events, route it through the treatment system if necessary,
and discharge the water via the permitted outfall. When dewatering of the CCR begins, all
discharge flows are anticipated to be routed through the WMS in order to meet the permitted
discharge limits.
The Basin currently has the capacity to contain the PMP storm event by maintaining the water
surface level elevation at or below El. 486.4 ft, which provides a minimum freeboard of 2.6 ft. As
part of the closure, the Basin Dam will be removed by excavating an engineered breach in the
east portion. Under this post closure condition, there will be increased flow downstream of the
Basin Dam compared to the existing conditions. Crutchfield Branch, located downstream of the
dam, crosses the Mayo Lake Road via culvert and continues into Virginia. Additional stormwater
retention capacity will need to be provided following dam removal or the existing downstream
culverts will need to be retrofitted to increase their conveyance capacities. The closure design
proposed herein provides additional storage capacity following breach of the Basin Dam using
detention basins as described further below. The concept designs for these proposed basins
were based on limiting post -closure downstream stormwater from the 100-year storm event flows
to less than or equal to existing stormwater flows.
Dewatering is performed to remove the interstitial or pore water from the CCR to facilitate
excavation, to access in -place CCR and to establish safe slopes prior to and after CCR
excavation. It is anticipated that performance criteria will be established in the construction -level
documentation to identify required vertical and horizontal limits of interstitial water removal at
critical locations and for critical conditions during closure.
Wastewater from the Basins will be pumped, treated as needed and discharged in two phases;
the decanting phase and dewatering phase. In the decanting phase, free water above the settled
CCR layer will be removed from the Basin without the mechanical disturbance of the CCR. The
Mayo Plant WMS includes equipment that has a designed flow rate of 1,500 gpm. Following the
decanting phase and as the Closure schedule dictates, the Mayo Plant site will advance into the
dewatering phase to remove interstitial water from the Basin. During this phase, additional
physical -chemical treatment processes will be added to the WMS as necessary to maintain
compliance with the requirements of the discharge permit. During dewatering phase, the
designed flow rate may drop to 400-500 gpm.
The post -closure grades restore the historical flows from the surrounding landscape and route
that flow toward the detention basins. The detention basins will be designed with a culvert to
restrict releases under a large rain event that will result in a slower discharge release to Crutchfield
Branch but with minimal retained pooling. Up to and including the last phase of closure before the
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AECOM December 18, 2019
Duke Energy — Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
Basin Dam is breached, the Basin will maintain the capacity to contain the required storm
size/flows.
The detention basin design criteria will be further refined for the construction -level documents
based on actual field elevations reached in the excavated areas and discussions with NCDEQ
with regards to the embankment heights, which will follow NCDEQ approval of this Closure Plan.
The designs for the detention basins are limited to conceptual level at this time. These concept
designs for the detention basin are based conservatively on 100 year storms. Appendix C1
presents the results of the post -closure stormwater management calculations. Detail stormwater
design for the proposed CCR on -site landfill will be developed as part of its permit design and not
covered herein.
8.1 Anticipated Changes in Wastewater and Stormwater Management
Closure of the Basin has necessitated changes in the management of a number of wastewater
and process streams. Wastewater and process streams previously discharging to the Basin have
been rerouted to new lined retention basins as separate treatment systems.
A temporary WMS will be utilized such that the existing NPDES Outfall 002 effluent discharge
limits will be met throughout the duration of decanting/dewatering and closure.
Erosion and Sediment Control Plans for different phases of the construction will be developed as
part of the construction -level packages and formal erosion and sediment control plan permit
submittal. The details for the erosion and sediment control measures will be re-evaluated after
the specific construction phasing is established, which will follow NCDEQ approval of this Closure
Plan. In addition, erosion and sediment control measures may be installed and removed in phases
as stabilization is achieved.
8.2 Wastewater and Stormwater Permitting Requirements
Additional information on required permits is described in Section 10.
9. DESCRIPTION OF FINAL DISPOSITION OF CCR
CCR will be dispositioned by placement into an approved and permitted lined CCR landfill. Duke
Energy intends to construct a new on -site Landfill to accept CCR in completion of the NCDEQ-
mandated closure by excavation. A permit application for construction of the on -site landfill will
be prepared and submitted to NCDEQ Division of Waste Management following approval of this
closure plan.
Vegetation encountered or removed during the progression of the work will be managed in
accordance with state regulations for handling and disposal.
10. APPLICABLE PERMITS
Refer to Table 10-1 for detailed information on the potential and applicable permitting/approval
needed to implement this Closure Plan.
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CAMA Closure Plan (Closure by Excavation)
11. DESCRIPTION OF POST -CLOSURE MONITORING AND CARE
A post -closure plan will be developed following NCDEQ approval of the Closure Plan for closure
of the Basins. The purpose of the post -closure plan will be to provide a description of the
inspection, monitoring, and maintenance activities required to be performed throughout the 30-
year post -closure care period for the closed Basins at the Mayo Plant.
The post -closure care plan will be developed to meet the requirements of CAMA (G.S. §130A-
309.214(a)(4)(k)). The items that will be in the post -closure care plan for the Mayo Plant include:
• Name, address, phone number, and email address of the responsible office or person;
• Means and methods of managing affected groundwater and stormwater;
• Maintenance of the groundwater monitoring systems;
• Regular inspection and maintenance of the final cover system;
• Groundwater and surface water monitoring and assessment program (included as part
of the CAP);
• Description of planned post -closure uses; and
• Financial assurance estimates for post -closure operations and maintenance and
remedial action.
11.1 Groundwater Monitoring Program
This information is included as part of the CAP being prepared separately by SynTerra for Duke
Energy and is being submitted in parallel to this Closure Plan. The CAP is herein incorporated by
this reference, but its content is not the work product of AECOM.
12. PROJECT MILESTONES AND COST ESTIMATES
12.1 Project Schedule
A Closure project high level milestone schedule has been prepared by Duke Energy and is
provided below. The schedule defines the following anticipated activities and milestones:
Engineering, decanting, dewatering
Ongoing
Submit plan and design for landfill construction permit
Q4-2020
Start new landfill construction
Q4-2021
Start CCR excavation
Q1-2023
Complete CCR excavation
Q4-2028
Complete final closure and cover system of new landfill
Q4-2029
Site final grading and vegetative cover
Q4-2030
A detailed construction schedule will be developed following NCDEQ approval of this Closure
Plan.
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Duke Energy — Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
12.2 Closure and Post -Closure Cost Estimate
Cost estimates for closure and post -closure of the Basins at Mayo Plant were developed by Duke
Energy and provided to AECOM. These cost estimates are not a work product of AECOM. These
are Class 5 estimates as the detailed and final design is not developed at this stage of the closure
project. Following approval of this Closure Plan by NCDEQ and further development of the project
plans and engineering designs the cost estimate will be refined and updated.
The cost to complete the closure by excavation, including the new CCR landfill, is estimated to
be $249 million.
The cost to perform the 30 year post -closure activities and monitoring is estimated as $95 million
The cost estimates provided by Duke Energy include the following major activities:
• Mobilization and Site Preparation
• Dewatering, earthwork, and subgrade preparation
• CCR excavation
• Stormwater management, erosion and sediment control, and site restoration
• Engineering support (design and CQA)
• Post closure — groundwater monitoring
• Post closure — operations and maintenance
• Contingency
Corrective action costs are included as part of the CAP being prepared separately by SynTerra
for Duke Energy and is being submitted in parallel to this Closure Plan. The CAP is herein
incorporated by this reference, but its content is not the work product of AECOM.
13. REFERENCED DOCUMENTS
AECOM (2016a). Technical Memorandum -Issues MAY-119 & 122-REV01, Ash Basin Forebay
Borings and Slope Stability Analyses, Mayo Plant, Person County, NC. May 17, 2016.
AECOM (2016c). MAY-502, Fluidized Gas and Desulfurization (FGD) Ponds, Site -Specific
Seismic Analysis, Duke Energy, Person County, North Carolina, Mayo Plant. June 24,
2016.
AECOM (2019). Report for Full Probable Maximum Flood Elevation, FGD Forward Flush and the
FGD Settling Ponds, Mayo Plant, Person County, NC. June 10, 2019.
AMEC (2015b). Mayo Steam Station Water Balance Model Report, September 11, 2015.
Geosyntec (2015). Settling Features Feasibility Study Report, Mayo Steam Electric Station, June
8, 2015.
Golder (2009). Construction Certification Report, Progress Energy Mayo Facility, FGD Waste
Pond. June 29, 2009.
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Duke Energy — Mayo Steam Electric Plant
CAMA Closure Plan (Closure by Excavation)
PROFESSIONAL ENGINEER CERTIFICATION
I, Douglas Wilson Carr, being a registered Professional Engineer in the state of North Carolina,
do hereby certify to the best of my knowledge, information, and belief, that the information
contained in this Closure Plan dated December 18, 2019, was developed pursuant to the
requirements of N.C.G.S. § 130A-309-214(a)(4) and has been prepared pursuant to recognized
and generally accepted good engineering practices.
SIGNATURE DATE 12 he ko is
AECOM Technical Services of North Carolina, Inc. (License: F-0342)
/.�M 24

TABLES

AECOM Table 2-1: NC CAMA Closure Plan Requirements September 20, 2019
Summary and Cross Reference Table
Duke Energy, Mayo Steam Electric Plant
No.
Description
Corresponding
Closure Plan Section
Part II.
Provisions for Comprehensive Management of Coal Combustion Residuals
§ 130A-309.214(a)(4) Closure Plans for all impoundments shall include all of the following:
a. Facility and coal combustion residuals surface impoundment description. — A description of the operation of the site that shall include, at a minimum, all of the following:
1
Site history and history of site operations, including details on the manner in which coal combustion residuals have been stored and disposed of historically.
3.1.1
2
Estimated volume of material contained in the impoundment.
3.1.2
3
Analysis of the structural integrity of dikes or dams associated with impoundment.
3.1.3
4
All sources of discharge into the impoundment, including volume and characteristics of each discharge.
3.1.4
5
lWhether the impoundment is lined, and, if so, the composition thereof.
7.1
6
JA summary of all information available concerning the impoundment as a result of inspections and monitoring conducted pursuant to this Part and otherwise available.
3.1.6
b. Site maps, which, at a minimum, illustrate all of the following:
1
All structures associated with the operation of any coal combustion residuals surface impoundment located on the site. For purposes of this sub -subdivision, the term "site" means the land or waters within the property boundary of the
applicable electric generating station.
3.2.1
2
All current and former coal combustion residuals disposal and storage areas on the site, including details concerning coal combustion residuals produced historically by the electric generating station and disposed of through transfer to
structural fills.
3.3
3
The property boundary for the applicable site, including established compliance boundaries within the site.
3.3
4
All potential receptors within 2,640 feet from established compliance boundaries.
3.2.2
5
Topographic contour intervals of the site shall be selected to enable an accurate representation of site features and terrain and in most cases should be less than 20-foot intervals.
3.3
6
Locations of all sanitary landfills permitted pursuant to this Article on the site that are actively receiving waste or are closed, as well as the established compliance boundaries and components of associated groundwater and surface
water monitoring systems.
3.2.3
7
All existing and proposed groundwater monitoring wells associated with any coal combustion residuals surface impoundment on the site.
3.3
8
JAII existing and proposed surface water sample collection locations associated with any coal combustion residuals surface impoundment on the site.
3.3
c. The results of a hydrogeologic, geologic, and geotechnical investigation of the site, including, at a minimum, all of the following:
1
A description of the hydrogeology and geology of the site.
4.1
2
A description of the stratigraphy of the geologic units underlying each coal combustion residuals surface impoundment located on the site.
4.2
3
The saturated hydraulic conductivity for (i) the coal combustion residuals within any coal combustion residuals surface impoundment located on the site and (ii) the saturated hydraulic conductivity of any existing liner installed at an
impoundment, if any.
4.3
4
The geotechnical properties for (i) the coal combustion residuals within any coal combustion residuals surface impoundment located on the site, (ii) the geotechnical properties of any existing liner installed at an impoundment, if any,
and (iii) the uppermost identified stratigraphic unit underlying the impoundment, including the soil classification based upon the Unified Soil Classification System, in -place moisture content, particle size distribution, Atterberg limits,
specific gravity, effective friction angle, maximum dry density, optimum moisture content, and permeability.
4.4
S
A chemical analysis of the coal combustion residuals surface impoundment, including water, coal combustion residuals, and coal combustion residuals -affected soil.
4.5
6
Identification of all substances with concentrations determined to be in excess of the groundwater quality standards for the substance established by Subchapter L of Chapter 2 of Title 15A of the North Carolina Administrative Code,
including all laboratory results for these analyses.
4.6
7
Summary tables of historical records of groundwater sampling results.
4.6
8
A map that illustrates the potentiometric contours and flow directions for all identified aquifers underlying impoundments (shallow, intermediate, and deep) and the horizontal extent of areas where groundwater quality standards
established by Subchapter L of Chapter 2 of Title 15A of the North Carolina Administrative Code for a substance are exceeded.
4.7
9
Cross -sections that illustrate the following: the vertical and horizontal extent of the coal combustion residuals within an impoundment; stratigraphy of the geologic units underlying an impoundment; and the vertical extent of areas
where groundwater quality standards established by Subchapter L of Chapter 2 of Title 15A of the North Carolina Administrative Code for a substance are exceeded.
4.8

AECOM Table 2-1: NC CAMA Closure Plan Requirements September 20, 2019
Summary and Cross Reference Table
Duke Energy, Mayo Steam Electric Plant
Corresponding
No.
Description
Closure Plan Section
d.
The results of groundwater modeling of the site that shall include, at a minimum, all of the following:
An account of the design of the proposed Closure Plan that is based on the site hydrogeologic conceptual model developed and includes (i) predictions on post -closure groundwater elevations and groundwater flow directions and
velocities, including the effects on and from the potential receptors and
1
(ii) predictions at the compliance boundary for substances with concentrations determined to be in excess of the groundwater quality standards for the substance established by Subchapter L of Chapter 2 of Title 15A of the North
5.1
Carolina Administrative Code.
Predictions that include the effects on the groundwater chemistry and should describe migration, concentration, mobilization, and fate for substances with concentrations determined to be in excess of the groundwater quality standards
2
for the substance established by Subchapter L of Chapter 2 of Title 15A of the North Carolina Administrative Code pre- and post -closure, including the effects on and from potential receptors.
5.2
A description of the groundwater trend analysis methods used to demonstrate compliance with groundwater quality standards for the substance established by Subchapter L of Chapter 2 of Title 15A of the North Carolina Administrative
3
Code and requirements for corrective action of groundwater contamination established by Subchapter L of Chapter 2 of Title 15A of the North Carolina Administrative Code.
5.3
A description of any plans for beneficial use of the coal combustion residuals in compliance with the requirements of Section .1700 of Subchapter B of Chapter 13 of Title 15A of the North Carolina Administrative Code
e
(Requirements for Beneficial Use of Coal Combustion By -Products) and Section .1205 of Subchapter T of Chapter 2 of Title 15A of the North Carolina Administrative Code (Coal Combustion Products Management).
6.1
f
All engineering drawings, schematics, and specifications for the proposed Closure Plan. If required by Chapter 89C of the General Statutes, engineering design documents should be prepared, signed, and sealed by a professional
7 1 7 2
engineer.
A description of the construction quality assurance and quality control program to be implemented in conjunction with the Closure Plan, including the responsibilities and authorities for monitoring and testing activities, sampling
g
strategies, and reporting requirements.
7.3
h.
A description of the provisions for disposal of wastewater and management of stormwater and the plan for obtaining all required permits.
8
A description of the provisions for the final disposition of the coal combustion residuals. If the coal combustion residuals are to be removed, the owner must identify (i) the location and permit number for the coal combustion
residuals landfills, industrial landfills, or municipal solid waste landfills in which the coal combustion residuals will be disposed and (ii) in the case where the coal combustion residuals are planned for beneficial use, the location and
manner in which the residuals will be temporarily stored. If the coal combustion residuals are to be left in the impoundment, the owner
L
must (i) in the case of closure pursuant to sub -subdivision (a)(1)a. of this section, provide a description of how the ash will be stabilized prior to completion of closure in accordance with closure and post -closure requirements
9
established by Section .1627 of Subchapter B of Chapter 13 of Title 15A of the North Carolina Administrative Code and (ii) in the case of closure pursuant to sub -subdivision (a)(1)b. of this section, provide a description of how the
ash will be stabilized pre- and post -closure. If the coal combustion residuals are to be left in the impoundment, the owner must provide an estimate of the volume of coal combustion residuals remaining.
j.
A list of all permits that will need to be acquired or modified to complete closure activities.
10
A description of the plan for post -closure monitoring and care for an impoundment for a minimum of 30 years. The length of the post -closure care period may be (i) proposed to be decreased or the frequency and parameter list
modified if the owner demonstrates that the reduced period or modifications are sufficient to protect public health, safety, and welfare; the environment; and natural resources and (ii) increased by the Department at the end of
k
the post -closure monitoring and care period if there are statistically significant increasing groundwater quality trends or if contaminant concentrations have not decreased to a level protective of public health, safety, and welfare;
the environment; and natural resources. If the owner determines that the post -closure care monitoring and care period is no longer needed and the Department agrees, the owner shall provide a certification, signed and sealed by
11
a professional engineer, verifying that post -closure monitoring and care has been completed in accordance with the post -closure plan. If required by Chapter 89C of the General Statutes, the proposed plan for post -closure
monitoring and care should be signed and sealed by a professional engineer. The plan shall include, at a minimum, all of the following:
1
A demonstration of the long-term control of all leachate, affected groundwater, and stormwater.
11.1
A description of a groundwater monitoring program that includes (i) post -closure groundwater monitoring, including parameters to be sampled and sampling schedules; (ii) any additional monitoring well installations, including a map
2
with the proposed locations and well construction details; and (iii) the actions proposed to mitigate statistically significant increasing groundwater quality trends.
11.2
I.
An estimate of the milestone dates for all activities related to closure and post -closure.
12.1
M.
JProjected costs of assessment, corrective action, closure, and post -closure care for each coal combustion residuals surface impoundment.
12.2

AECOM Table 2-1: NC CAMA Closure Plan Requirements September 20, 2019
Summary and Cross Reference Table
Duke Energy, Mayo Steam Electric Plant
Corresponding
No.
Description
Closure Plan Section
A description of the anticipated future use of the site and the necessity for the implementation of institutional controls following closure, including property use restrictions, and requirements for recordation of notices
6.2
n
documenting the presence of contamination, if applicable, or historical site use.
§ 130A-309.214(b)(3)
No later than 60 days after receipt of a proposed Closure Plan, the Department shall conduct a public meeting in the county or counties proposed Closure Plan and alternatives to the public.

Table 4-1. Summary of Typical Geotechnical Material Properties
Properties
Within Ash Basin
Dam and outside Ash basin Area
CCR/Ash
Alluvium
Residuum
Embankment Fill
Residual Soil
Soil Type
Silt (ML) and Sandy Silt
(ML)
Sandy Silt (ML)*
Sandy Lean Clay (CL), Silty
Sand (SM), and Sandy Silt
(ML)
Silty Sand (SM) and Sandy
Silt (ML)
Silt (ML), Sandy Silt (ML), and
Sandy Clays (CL)
Color
Dark Gray to Gray
Light Grayish Green*
Light Brown, Red, Grayish
Green
Light Brown, Red Brown,
Gray, White, Tan
Brown, Red Brown, White,
and Black
Plasticity
Predominantly non -plastic
Non Plastic*
Predominantly non -plastic
Non plastic to
Predominantly non -plastic
Liquid Limit
NP to 30
NP*
NP to 44
NP - 44
Predominantly non -plastic
Plasticity Index
NP to 4
NP*
NP to 19
NP - 16
Predominantly non -plastic
Representative Range
Natural Moisture Content (°o)
6% - 53%
14%*
8% - 19%
11% - 35%
9% - 28%
Fines Content
11% - 99%
32%*
17% - 41%
27% - 73%
16% - 38%
Clay Content
1% - 13%
11%*
1% - 4%
3% - 25%
3% - 11%
Blow Count - Uncorrected N value (bpf)
WOR - 12 bpf
WOH*
10 to 50+ bpf
7 - 25 bpf
21 to 50+ bpf
Moist Unit Weight - y,,, (pcf)
89 - 111 pcf
134 pcf*
---
118 - 130 pcf
122 - 126 pcf
Dry Unit Weight - yd (pcf)
58 - 84 pcf
117 pcf*
---
89 - 114 pcf
90 - 95 pcf
Specific Gravity
2.15 - 2.78
2.66*
---
2.62 - 2.74
2.63 - 2.70
Horizontal Hydraulic Conductivity (cm/sec)
1.5E-3 - 1.7E-5
6.1E-06 - 8.5E-6
---
---
---
Vertical Hydraulic Conductivity (cm/sec)
6.6E-08 - 7.9E-04
---
---
---
1.1E-06 - 1.0E-05
Notes:
Outlier values are not included in the table above
WOR: Weight of Rod, WOH: Weight of Hammer
bpf: Blows per foot
* Only one test was performed

Table 10-1 Mayo Steam Electric Plant Regulatory Permits, Approvals, or Requirements for Basin Closure by Excavation
Permit/Approval
Existing
Regulating
Permit No.
Type of Regulatory Approval
General Permit Name or Subject
Agency
(if applicable)
Mechanism or Not Required
Comments
Permit modification likely due to the increased heavy
Air Quality
NCDEQ
Permit modification likely
equipment vehicle traffic and potential dust generated
during closure activities
Person
A local building permit is required for installation of
Building Permit
County
New Permit
construction trailers
Modification or abandonment of CAMA program monitoring
CAMA Monitoring Plan
NCDEQ
Written NCDEQ DWR approval
wells require the approval of the Division of Water Resources
(DWR)
CCR Impoundment Closure
US EPA
Self Regulating
Required postings to Public Record
CCR Rule
CCR Impoundment Monitoring Network
US EPA
Self Regulating
Maintain CCR GW monitoring network and requirements as
CCR Rule
stated in 257.90 - 257.98
Clean Water Act 401
NCDEQ
IP permit
IP likely to be required for impacts to jurisdictional areas
Clean Water Act 404
USACOE
IP permit
IP likely to be required for impacts to jurisdictional areas
Closure Plan
NCDEQ
Per CAMA
Cutting Trees
DEMLR
E&SC plan
include in E&SC plan approval
PERSO-035,
Permitting is required to modify or abandon wells and
Dam Safety
NCDEQ
PERSO, 036,
Certificate of Approval to
instrumentation on regulatory dams through the Division of
PERSO-037
Modify
Energy, Mineral, and Land Resources (DEMLR)
Ash Basin Dam - Permitting is required to modify the dam in
Dam Safety
NCDEQ
PERSO-035
Certificate of Approval to
accordance with the Dam Safety Law of 1967, 15A NCAS
Modify
02K.0201 (b)(2); an application must be filed with the
Division of Energy, Mineral, and Land Resources (DEMLR)
FGD Settling Pond Dam - Permitting is required to remove
Certificate of Approval to
the dam in accordance with the Dam Safety Law of 1967, 15A
Dam Safety
NCDEQ
PERSO-036
Modify
NCAS 02K.0201 (b)(2); an application must be filed with the
Division of Energy, Mineral, and Land Resources (DEMLR)
FGD Flush Pond Dam - Permitting is required to remove the
Certificate of Approval to
dam in accordance with the Dam Safety Law of 1967, 15A
Dam Safety
NCDEQ
PERSO-037
Modify
NCAS 02K.0201 (b)(2); an application must be filed with the
Division of Energy, Mineral, and Land Resources (DEMLR)
Utilization of or modification to state or federal highways to
DOT - General
Not anticipated at this time
transport CCR will require consultation or notification to
relevant DOT agency
Driveway Permit
NCDOT
Potential
Temporary access or driveway permits as needed
Land disturbance activities outside of the ash basin will
NCDEQ and
exceed one acre, therefore in conformance with 15A NCAC
Erosion and Sediment Control (E&SC)
Person
New Permit
04, an E&SC Permit is required from Land Quality prior to
commencement of construction in those areas. Note that
County
land disturbance includes tree clearing and grubbing and
vehicular wheel or tracking as disturbance.
Removal from or import of material could be restricted
Fire Ants
Restriction not likely
dependent on the potential for fire ants and geographic
regions involved
Flood Damage Prevention Ordinance of Person County,
Article 3 General Provisions, Section C, requires a Floodplain
Floodplain Development
Person
New Permit
Development Permit prior to any development activities
County
within FEMA mapped Special Flood Hazard Areas for the
Flood Insurance Rate Maps
Permits are required to construct any water supply well or
Large Capacity Water Supply Well
NCDEQ
Not anticipated at this time
water well system with a design capacity equal to or greater
than 100,00 gallons per day - for dewatering outside of the
ash basin
Multi -State Agreement
Not anticipated at this time
If movement of CCR will cross state lines, multi -state
regulations might apply
NPDES (National Pollution Discharge
odification of NPDES may be necessary if new source or
Elimination System)
NCDEQ
NCO038377
Permit modification likely
ttfallis created.

Permit/Approval
Existing
Regulating
Permit No.
Type of Regulatory Approval
General Permit Name or Subject
Agency
(if applicable)
Mechanism or Not Required
Comments
NPDES (National Pollution Discharge
Revision to existing sitewide permit or new permit may be
Elimination System) Industrial
NCDEQ
Permit revision likely
required for access roads, staging areas, etc.
Stormwater
NPDES (National Pollution Discharge
NCDEQ
New Permit possible
Permit required for temporary and permanent stormwater
Elimination System) Stormwater
rerouting.
Removal from or import of vegetated material could be
Noxious Weeds
Not anticipated at this time
restricted dependent on the vegetation and geographic
regions involved
Railroad Easement, Access, or Crossing
Construction activities adjacent to tracks/ballast or a new
Not anticipated at this time
Permit
railroad crossing require an agreement or permit
SPCC (Spill Prevention Control and
In accordance with the Federal Water
Countermeasure) Plan
NCDEQ
Modification of existing plan
Pollution Control Act (Clean Water Act) of 1974, Title 40,
Code of Federal Regulations, Part 112.
Threatened or Endangered Species:
Federal and/or state regulations may apply including agency
Candidate Conservation Agreement
consultation and performing site -specific surveys within the
Avian Protection Plan(s)
NCDEQ and
Consultation will be covered in
proper survey period (e.g., flowering period for listed plant)
Bird and Bat Conservation Strategies
EPA
the 404/401 permitting process
to determine if Threatened or Endangered Species or their
Eagle Conservation Plan
habitat exist within the limits of disturbance
Eagle Take Permit
Solid Waste Site Suitability
NCDEQ
Approval by Letter
New CCR Landfill
Solid Waste Permit to Construct
NCDEQ
Permit
New CCR Landfill
Solid Waste Permit to Operate
NCDEQ
Permit
New CCR Landfill
County Approval - zoning
Person
New CCR Landfill, requires Special Use Permit
County

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— — — APPROXIMATE ASH BASIN WASTE BOUNDARY
DUKE ENERGY PROPERTY BOUNDARY
ADJACENT PROPERTY BOUNDARY
— — RIGHT OF WAY
— — — — — EXISTING MINOR CONTOURS (5 FT)
— - EXISTING MAJOR CONTOURS (25 FT)
® GROUNDWATER MONITORING WELL
IK SEEPS (APPROX. LOCATION SEE REF. 6)
EXISTING PIEZOMETER
+ + + + + + + + + EXISTING WETLANDS
+++++++++
- EXISTING STREAM
TITLE
F AREAS UNDER WATER DURING BATHYMETRY
NO BATHYMETRY AVAILABLE
\
COMPLIANCE MONITORING WELL
ABMW 2BR
WELL IN COMPETENT BEDROCK
ABMW 2
WELL IN ASH PORE WATER
s MW-16D
WELL IN TRANSITION ZONE
e MW 16S
WELL IN ALLUVIUM MATERIAL
c Mw-8S
WELL IN SAPROLITE MATERIAL
REFERENCE
1. TOPOGRAPHIC DATA PRESENTED IN THIS DRAWING IS TAKEN
FROM "AERIAL TOPOGRAPHIC SURVEY - MAYO PLANT" DATED
OCTOBER 31, 2015 PREPARED BY WSP FOR DUKE ENERGY.
2. APPROXIMATE ASH BASIN WASTE BOUNDARY PRESENTED IN THIS
DRAWING IS PREPARED BY SYNTERRA FOR DUKE ENERGY.
UPDATED SEPTEMBER 2018
3. BATHYMETRIC SURVEYS CONDUCTED BY WSP IN AUGUST 2014 &
FEBRUARY 2015. ISOLATED PONDS AROUND THE ASH BASIN ARE
INACCESSIBLE FOR SURVEY.
4. NO UNDERGROUND UTILITIES HAVE BEEN LOCATED OR MAPPED
FOR THIS PROJECT. THE LOCATION OF ANY AND ALL UTILITIES
SHOWN HEREON WHETHER PUBLIC/PRIVATE, ARE BASED ON
PHOTOGRAMMATIC MAPPING AND ARE APPROXIMATE ONLY.
5. BASIS OF BEARINGS: NC GRID NAD83/2011,ELEVATIONS ARE
BASED ON NAVD88.
6. SEEP LOCATIONS DEPICTED ARE APPROXIMATE AND BASED ON
"COMPREHENSIVE SITE ASSESSMENT REPORT - MAYO STEAM
ELECTRIC PLANT " PREPARED BY SYNTERRA FOR DUKE ENERGY
AND SUBMITTED TO NCDEQ (NPDES PERMIT NO. NCO038377) ON
SEPTEMBER 2, 2015.
7. THE WATERS OF THE US HAVE NOT BEEN APPROVED BY THE US
ARMY CORPS OF ENGINEERS AT THE TIME OF THE MAP
CREATION. THIS MAP IS A PRELIMINARY JURISDICTIONAL
DETERMINATION ONLY. THE PRELIMINARY WETLANDS AND
STREAMS BOUNDARIES WERE OBTAINED FROM AMEC FOSTER
WHEELER ENVIRONMENTAL & INFRASTRUCTURE, INC. NATURAL
RESOURCE TECHNICAL REPORT FOR MAYO STEAM ELECTRIC
PLANT DATED JANUARY 20, 2014.
NOT FOR CONSTRUCTION
EXISTING CONDITIONS PLAN WITH
TOPOGRAPHIC MAP
MAYO STEAM ELECTRIC PLANT
CLOSURE BY EXCAVATION CLOSURE PLAN
PERSON COUNTY, NORTH CAROLINA
FOR ISSUED FOR APPROVAL
D���
ENERGYC
SCALE: 1" = 300'
DES: DMS
DWG TYPE :.DWG
DFTR : DMS
:60/20/2019
DATE:
ENGR: DMS
FILENAME: 004-EXISTING CONDITION.DWG
APPD: DWC
DWG SIZE
DRAWING NO.
REVISION
ANSI D
22.0"x34.0" FIGURE 3-1 A
0
Z)
m
<
0 1 2 8 L ITENTHS 10 20 30

APPENDICES

APPENDIX A
ESTIMATED VOLUME OF CCR IN IMPOUNDMENT

APPENDIX B
GEOTECHNICAL DATA AND PROPERTIES

APPENDIX C
ENGINEERING EVALUATIONS AND ANALYSES

APPENDIX Cl
STORMWATER MANAGEMENT CALCULATION MEMO

APPENDIX C2
SOIL QUANTITIES

APPENDIX D
CLOSURE PLAN DRAWINGS

APPENDIX E
FINAL CLOSURE BY EXCAVATION SAMPLING PLAN