Allen_AmendedClosurePlan_Rev1_20200731

DUKE ENERGY
ALLEN STEAM STATION
COAL COMBUSTION RESIDUALS SURFACE
IMPOUNDMENT CLOSURE PLAN (AMENDED)
CLOSURE BY EXCAVATION
RETIRED ASH BASIN AND ACTIVE ASH BASIN
Prepared for:
frn DUKE
ENERGY
Duke Energy (Duke)
400 South Tryon Street
Charlotte, North Carolina 28202
January 30, 2020 (Rev 0)
July 31, 2020 (Rev 1)
Prepared by
AL=com
1600 Perimeter Park Dr.
Morrisville, North Carolina 27560

AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
DESCRIPTION OF REVISIONS
The following table provides a brief description of the revisions to this Closure Plan. This Closure
Plan was originally submitted to the North Carolina Department of Environmental Quality
(NCDEQ) in January 2020 and has been modified as shown in the following table:
Revision
Date of Document
Description of Revisions
Initial Issue
January 30, 2020
Initial issuance of document.
Rev 1
July 31, 2020
Revised document to incorporate additional proposed landfill.
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AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
TABLE OF CONTENTS
EXECUTIVE SUMMARYViiiiii
1. INTRODUCTION...................................................................................................................6
1.1 Background.........................................................................................................................6
1.2 Closure Plan Objectives..................................................................................................... 6
1.3 Report Organization........................................................................................................... 7
2. GOVERNING LAWS.............................................................................................................7
3. FACILITY DESCRIPTION AND EXISTING SITE FEATURES...............................................8
3.1 Surface Impoundment Description.................................................................................... 8
3.1.1
Site History and Operations................................................................................8
3.1.2
Estimated Volume of CCR in Surface Impoundments.........................................9
3.1.3
Description of Surface Impoundment Structural Integrity ...................................
10
3.1.4
Sources of Discharges into Surface Impoundments ..........................................
11
3.1.5
Existing Surface Impoundment Liner Systems ..................................................
11
3.1.6
Inspection and Monitoring Summary................................................................
11
3.2 Site Maps
...........................................................................................................................
12
3.2.1
Existing Surface Impoundment -Related Structures ...........................................
12
3.2.2
Receptor Survey..............................................................................................
12
3.2.3
Existing On -Site Landfills.................................................................................
12
3.3 Monitoring and Sampling Location Plan.........................................................................13
4. RESULTS OF HYDROGEOLOGIC, GEOLOGIC, AND GEOTECHNICAL INVESTIGATIONS
13
4.1 Background.......................................................................................................................13
4.2 Hydrogeology and Geologic Descriptions.......................................................................13
4.3 Stratigraphy of the Geologic Units Underlying Surface Impoundments ........................13
4.4 Geotechnical Properties................................................................................................... 13
4.4.1 CCR Within the RAB and AAB....................................................................... 14
4.4.2 Liner Material Properties............................................................................... 14
4.4.3 Subsurface Soil Properties............................................................................ 14
4.4.4 AAB and RAB Dam Soil Properties............................................................... 15
4.5 Chemical Analysis of Impoundment Water, CCR, and CCR-Affected Soil ..................... 15
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AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
4.6 Historical Groundwater Sampling Results
16
4.7 Groundwater Potentiometric Contour Maps.................................................................... 16
4.8 Estimated Vertical and Horizontal Extent of CCR Within the Impoundments ................ 16
5. GROUNDWATER MODELING ANALYSIS.........................................................................16
5.1 Site Conceptual Model Predictions.................................................................................. 17
5.2 Groundwater Chemistry Effects....................................................................................... 17
5.3 Groundwater Trend Analysis Methods
17
6. BENEFICIAL AND FUTURE USE.......................................................................................17
6.1 CCR Use
6.2 Site Future Use
17
17
7. CLOSURE DESIGN DOCUMENTS....................................................................................18
7.1 Engineering Evaluations and Analyses........................................................................... 18
7.2 Closure Plan Activities..................................................................................................... 19
7.3 Design Drawings............................................................................................................... 19
7.4 Description of the Construction Quality Assurance Plan ............................................... 20
8. MANAGEMENT OF WASTEWATER AND STORMWATER................................................21
8.1 Anticipated Changes in Wastewater and Stormwater Management ............................... 22
8.2 Wastewater and Stormwater Permitting Requirements.................................................. 22
9. DESCRIPTION OF FINAL DISPOSITION OF CCR............................................................22
10. APPLICABLE PERMITS FOR CLOSURE..........................................................................23
11. DESCRIPTION OF POST -CLOSURE MONITORING AND CARE......................................23
11.1 Groundwater Monitoring Program............................................................................. 23
12. PROJECT MILESTONES AND COST ESTIMATES...........................................................24
12.1 Project Schedule........................................................................................................ 24
12.2 Closure and Post -Closure Cost Estimate.................................................................. 24
13. REFERENCED DOCUMENTS............................................................................................26
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AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
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
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AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
Tables
Table 2-1 NC CAMA Closure Plan Requirements, Summary and Cross Reference
Table
Table 4-1 Summary of Typical Geotechnical Index Properties
Table 10-1 Allen Steam Station Regulatory Permits, Approvals, or Requirements for
Basin Closure by Excavation
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AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
Appendices
Appendix A Estimated Volume of CCR in Impoundment
Appendix B Geotechnical Data and Properties
Appendix B-1 Logs of Boring and Monitoring Wells
Appendix B-2 Results of Seismic Cone Penetration Testing (SCPTu)
Appendix B-3 Results of Laboratory Testing
Appendix C Engineering Evaluations and Analyses
Appendix C1 (Reserved for Stormwater Design)
Appendix C2 Borrow Soil Quantities
Appendix D Closure Plan Drawings
Appendix E Excavation Soil Sampling Plan
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AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
EXECUTIVE SUMMARY
As required by the North Carolina Department of Environmental Quality's (NCDEQ) April 1, 2019
"Coal Combustion Residuals Surface Impoundment Closure Determination," (Closure
Determination) and Paragraph 12 of that certain Settlement Agreement by and between Duke
Energy, NCDEQ, and various community groups dated December 31, 2019 (Settlement
Agreement), Duke Energy has prepared this Closure Plan to describe the closure of the Retired
Ash Basin (RAB) and Active Ash Basin (AAB) at the Allen Steam Station (Allen Station). This plan
details closure -by -excavation of the RAB and AAB (collectively, Basins), and placement of the
excavated coal combustion residuals (CCR) in a new permitted on -site lined landfill within the
existing footprint of the AAB and two additional, new permitted on -site lined landfills within the
partial existing footprints of the RAB and AAB. The excavation of CCR and the closure of the RAB
and AAB 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 Allen Station is owned and operated by Duke Energy Carolinas, LLC (Duke Energy) and is
located in Gaston County, North Carolina along the west shore of Lake Wylie (Catawba River),
near the town of Belmont, North Carolina. Allen Station began operations in 1957 as a coal-fired
electric generating station and is currently in active operation.
The RAB was operational from 1957 until 1973 when it reached capacity and was retired. The
RAB is estimated to contain approximately 8.88 million tons of CCR (or an estimated 7.59 million
cubic yards) that are subject to this Closure Plan. The RAB includes two embankment structures
functioning as dams — RAB-North Dike and East Dike (regulated by NCDEQ as Gasto-016).
The AAB was commissioned in 1973 to divert wet sluiced CCR from the RAB after it was retired
and operated as a wet sluiced pond until flows were discontinued in February 2019. Based on
topographic and bathymetric surveys performed in July 2014 and February 2015, the AAB is
estimated to contain approximately 10.48 million tons of CCR (an estimated 8.73 million cubic
yards). The AAB includes two embankment structures functioning as dams —AAB-East Dike and
AAB-North Dike (regulated by NCDEQ as Gasto-061).
Based on CCR inventory data provided by Duke Energy as of July 31, 2019, the RAB and AAB
are estimated to contain a total of approximately 19.36 million tons of CCR (an estimated 16.33
million cubic yards). This approximate total includes all historically sluiced CCR as well as the
CCR contained within the RAB Landfill footprint (both above and below the RAB Landfill's bottom
liner system). This also includes the unlined Distribution of Residual Solids (DORS) facilities
located to the west that were constructed over the RAB.
Under this plan, all CCR except for a small amount necessary for transmission tower stability will
be removed to three new lined landfills within plant property, located partially within the prior
footprint of the Basins.
Closure activities for the Basins have 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
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Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
water, contracting and detailed planning for the closure work, development of the new lined
landfills in conjunction with excavation of the CCR, final grading of the site and landfills, and
development of stormwater features and vegetative covers.
Figures ES-1 and ES-2 illustrate the current state, and post -closure state of the RAB and AAB
as detailed by this Closure Plan.
Figure ES-1 Current View
Figure ES-2 Post Closure View
AAB and RAB CCR will be removed to three new lined landfills located within plant property — the
Ash Basin Landfill (ABLF), the North Starter Landfill (NSLF), and the South Starter Landfill
(SSLF). The ABLF will be located within the prior footprint of the AAB. The ABLF would rise
approximately 110 feet above Southpoint Road, which has an approximate elevation of 690 feet.
The smaller NSLF will be located partially within the prior footprint of the RAB, rising
approximately 50 feet above Southpoint Road. The smaller SSLF will be located partially within
the prior footprint of the AAB, rising approximately 40 feet above Southpoint Road. For reference,
the existing RAB Landfill (Phase 1) is currently at an elevation of 680 feet and is permitted to a
maximum elevation of 816 feet at the final buildout of Phase 2, or approximately 126 feet above
Southpoint Road. Post -excavation, the AAB and RAB sites will restore some of the land's valley
shape before the Basins were created. Soil will be graded to restore contours for stormwater
flows, then planted with native grasses for erosion control. Portions of the existing basin dams
will be removed, pursuant to a NCDEQ Dam Safety permit approval, allowing stormwater flows
to Lake Wylie.
Excavation and placement of the ash in the originally proposed two landfills was found to be
difficult to sequence and operate. By evaluating likely excavation sequencing, it was determined
that constructing two starter landfills and one primary landfill would facilitate ash excavation, ease
staging landfill cell construction, and would reduce the overall cost of closure.
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 Allen Station.
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.
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AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
In accordance with the requirements of N.C.G.S. § 130A-309.211(b)(1), Duke Energy separately
submitted to NCDEQ an updated groundwater Corrective Action Plan (CAP) on December 31,
2019; 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 updated CAP evaluates the extent of, and remedies for, constituents of interest (COls) in
groundwater associated with the ash basins and coal pile area, focusing on constituent
concentrations detected above the applicable 02L Standards, Interim Maximum Allowable
Concentrations, or background threshold values at or beyond the Geographic Limitation (as
defined in the Settlement Agreement) to north and north-northeast of the Retired Ash Basin and
coal pile, and east of the Active Ash Basin. In addition, the updated CAP considers the federal
groundwater corrective action requirements at 40 C.F.R. §§ 257.96-.98.
As detailed in the updated CAP, Duke Energy has begun to implement, and will continue
implementing, source control measures at the site, including (i) complete decanting of the Basins
to remove the hydraulic head, thereby reducing hydraulic gradients, groundwater seepage
velocities, and COI transport potential, and (ii) complete closure of the ash basins. In addition,
Duke Energy intends to implement a robust groundwater remediation program that includes
actively addressing COI in groundwater above applicable standards at or beyond the [Geographic
Limitation] using groundwater extraction combined with clean water infiltration and removal of the
low pH area source proximate to the coal pile area. The CAP provides that these corrective action
measures will most effectively achieve remediation of the groundwater through the use of
extraction wells to the north, northeast, and east of the ash basins and coal piles, and strategically
located clean water infiltration wells. The CAP further provides that groundwater modeling
simulations indicate (i) these measures will control COI at or beyond the [Geographic Limitation];
and (ii) at such time the site -specific considerations detailed within the CAP have been satisfied,
including, but not limited to, securing all required state approvals, installing the necessary
equipment, and commencing full-scale system operation, COI at or beyond the [Geographic
Limitation] will meet the remedial objectives in nine years (SynTerra, 2019).
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Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
1. INTRODUCTION
1.1 Background
Allen Station is located at 253 Plant Allen Road in Gaston County, North Carolina. Allen Station
is a five -unit, 1,140-megawatt, coal-fired power generation facility that began commercial
operation in 1957 with Units 1 and 2. Unit 3 began operation in 1959, Unit 4 in 1960, and Unit 5
in 1961. Allen Station historically wet sluiced CCR into two surface impoundments located on the
property known as the RAB and the AAB. The RAB received CCR from initial operation for
approximately 16 years beginning in 1957 until 1973, when it reached capacity and was retired.
Allen Station then commissioned the AAB and began wet sluicing CCR into this new basin. In
2009, when Allen Station replaced its wet fly ash sluicing operation with a flue gas desulfurization
(FGD) facility, the RAB Landfill was constructed over the southeastern portion of the RAB for
placement of dry fly ash (Permit No. 3612) (NCDEQ, 2009; S&ME, 2014). Although Allen Station
previously wet sluiced bottom ash into the AAB, a dry bottom ash system is now operational and
sluicing of bottom ash and all process water to the AAB ceased in February 2019 and has been
redirected to the Lined Retention Basin (LRB) system.
Figure 1-1 presents a Vicinity Map and Site Plan of Allen Station.
Duke Energy uses two facilities to manage CCR at the Allen Station that include dams and dikes
regulated by NCDEQ:
1. The AAB-North Dike and East Dike (NCDEQ ID: GASTO-061); and
2. The RAB-North Dike and East Dike (NCDEQ ID: GASTO-016).
As further discussed in Section 2 below, the closure method mandated by order of NCDEQ for
the AAB and RAB 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 RAB
and AAB as directed by order of NCDEQ. Duke Energy 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 of the AAB;
• Construction and operation of a temporary water management system (WMS) to manage
all 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 soils where
required;
• Breaching of the Basin dams;
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Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
• Construction of three CCR landfills within plant property to permanently store the
excavated CCR; and
• Restoration of disturbed areas.
1.3 Report Organization
This document is structured to follow the requirements provided in N.C.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 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 13, 2018, and officially classified the RAB and AAB at
Allen Station as "low -risk."
On April 1, 2019, NCDEQ issued its Closure Determination mandating that the RAB and AAB be
closed by excavation 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 and on May 24, 2019
Duke Energy filed amended petitions in the case. Certain decisions by the administrative law
judge in that case are currently under appeal to the North Carolina Superior Court. On December
31, 2019, Duke Energy, NCDEQ, and certain community groups entered into a Settlement
Agreement under which the parties agreed that upon entry of a consent order in Wake County
and Mecklenburg County Superior Court in Case Nos. 13-CVS-11032 and 13-CVS-14461, the
parties would dismiss the litigation associated with the Basins.
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 August 2015 with supplemental reports submitted August 2016 and January 2018.
Duke Energy separately submitted to NCDEQ an updated Corrective Action Plan (CAP) on
December 31, 2019.
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
CCR basin dams, and environmental permitting requirements must be considered as part of
closure.
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Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
3. FACILITY DESCRIPTION AND EXISTING SITE FEATURES
3.1 Surface Impoundment Description
This section provides details on the CCR-related features at Allen Station.
3.1.1 Site History and Operations
Allen Station is located near the town of Belmont in Gaston County, North Carolina and is situated
along the west shore of Lake Wylie, a man-made reservoir created by the impoundment of the
Catawba River. A layout plan of the site is shown in Figure 1-1. The facility, which is owned and
operated by Duke Energy, is approximately 1,009 acres. CCR facilities located on -site include the
RAB, AAB and additional facilities as described in more detail below.
Retired Ash Basin
The RAB is located south of the Allen Station plant and adjacent to Lake Wylie/the Catawba River.
It is situated along Plant Allen Road to the north, Lake Wylie/the Catawba River to the east, and
the Duke Energy property boundary to the west. The natural topography at the site generally
slopes downward from the western property line to the RAB and subsequently toward Lake
Wylie/the Catawba River. The RAB includes three dams — RAB-North Dike, RAB-East Dike
(collectively GASTO-016), and RAB-South Dike (now referred to as the AAB-North Dike) — that
were constructed to form a U-shaped basin. The RAB is comprised of dikes that impound CCR
and several active and inactive CCR fill areas, which are described later in this section. The RAB
CCR boundary currently occupies an area of approximately 123 acres. The RAB received sluiced
CCR from initial operation in 1957 until 1973 when it reached capacity and was retired. The facility
no longer retains sluiced process water or free water.
Non -contact stormwater from the RAB and the RAB Landfill discharges through the primary
spillway via a headwall structure (Outfall SW015) located in the ditch in the southeast corner of
the basin. The primary spillway was constructed in 2016 as a replacement to the prior reinforced
concrete riser structure and associated reinforced concrete piping (RCP). The discharge flow is
currently conveyed through a 54-inch and 42-inch diameter high -density polyethylene HDPE pipe
system. The primary spillway ties into the existing 36-inch diameter RCP near the downstream
toe -of -slope via a reinforced concrete manhole structure (NPDES Outfall SW015). In addition to
the primary spillway, an emergency spillway was installed for the RAB in 2015 (NPDES Outfall
008).
Active Ash Basin
The AAB is located south of the Allen Station plant and adjacent to Lake Wylie/the Catawba River.
The AAB is located immediately south of the RAB and the two Basins share a dike (the AAB-North
Dike). The natural topography at the site generally slopes downward from the property line in the
west to the AAB and subsequently toward Lake Wylie/the Catawba River. The AAB includes two
dams —AAB-East Dike and AAB-North Dike (collectively GASTO-061) — that were constructed to
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Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
form an L-shaped basin. The AAB is comprised of deposited CCR and the AAB CCR boundary
currently occupies an area of approximately 170 acres. The AAB formerly received flows from the
ash removal system, coal pile runoff, landfill leachate, FGD wastewater, the station yard drain
sump, and site stormwater. Bottom ash sluicing and all other process flows to the AAB ceased in
February 2019.
Until decanting began in 2019, storm and process water from the AAB discharged through a weir
box outlet structure (Outfall 002) located in the southeast corner of the basin, which is permitted
by NCDEQ under NPDES Permit NC0004979 (NCDEQ, 2018). The weir box and spillway system
were constructed in 2016 as a replacement to the prior reinforced concrete riser structure and
associated RCP. The discharge flow is currently conveyed through a 48-inch HDPE pipe system
which ties into the pre-existing 42-inch diameter RCP near the downstream toe -of -slope via a
reinforced concrete manhole structure.
Additional Facilities
Other CCR facilities within the RAB and AAB areas are shown in the attached Figure 3-1 and are
described in more detail below.
The DORS areas (DORS 1 through DORS 4) are retired CCR stacks/fills located above the
western portion of the RAB footprint. The DORS areas, the closures of which are addressed in
this Closure Plan, will be closed by excavation in conjunction with the remainder of the RAB. CCR
was removed from the AAB and placed in the DORS fills at various times over a 10-year period
under permit W00003255. These dry CCR stacks/fills are unlined with a vegetated cover soil.
The 25-acre RAB Landfill is an active overfill landfill (NCDEQ Permit No. 3612) wholly contained
within the limits of the RAB and is constructed overthe southeastern portion of the RAB. Its permit
also includes a strip of the RAB immediately south of the landfill for management of non -contact
stormwater. (NCDEQ, 2009, S&ME, 2008). The landfill is permitted to receive residual waste,
including fly ash, bottom ash, FGD residual, boiler slag, mill rejects, and other non-CCR wastes
generated at Allen Station.
3.1.2 Estimated Volume of CCR in Surface 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 is 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, with the exception of CCR contained within the RAB Landfill above the liner, in which
case an assumed density of 1.0 tons/cy was used. See Appendix A for the Estimated Volume of
CCR in Impoundment calculation.
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AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
Impoundment
Estimated CCR Weight
Estimated CCR Volume
(Tons)
(CY)
AAB
10,480,000
8,733,300
RAB (excludes DORS)
7,893,300
6,767,900
DORS No. 1
562,800
469,000
DORS No. 2
428,400
357,000
Total CCR
19,364,500
16,327,200
Subject to Closure Plan
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
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
For the AAB and RAB embankments, 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 RAB at two selected sections and for the AAB
at six selected sections under the loading conditions mentioned above meet regulatory
requirements.
• Liquefaction conditions (where susceptible) and Liquefaction potential
Data from the PSHA and QUAD4M analyses indicate that the foundation and embankment soils
for the RAB and AAB embankments meet liquefaction screening programmatic criteria for
minimum factor of safety (FS >- 1.20). It is concluded that these soils are not subject to liquefaction
during the 2,500-year return period seismic event. Liquefaction data for the fill material placed for
the railroad tracks at the toe of the RAB east dike and the CCR in the AAB suggested that these
materials have limited susceptibility to liquefaction.
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AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
• Hydrology and Hydraulics (H&H) Capacity Analyses
The existing RAB outlet structure passes the required SDF (i.e., full Probable Maximum
Precipitation (PMP) based on NCDEQ and 1,000-year storm based on the federal CCR Rule)
without the embankment overtopping. The existing AAB outlet structure can safely pass the
required SDF (i.e., full PMP based on NCDEQ and full PMP based on the federal CCR Rule)
without the embankment overtopping. Also, a time -to -drain analysis indicates that the existing
spillway systems for the RAB and AAB are capable of removing at least 80% of the water
temporarily detained in the reservoir within 15 days following the design storm event, as required
by the North Carolina Dam Safety Regulations.
3.1.4 Sources of Discharges into Surface Impoundments
Historically, runoff and process water streams from two yard -drain sumps, the ash removal
system, the RAB Landfill leachate collection system, low volume wastes, and stormwater runoff
were discharged into the Basins. Process flows no longer discharge into the Basins. Process
flows are directed toward the newly constructed holding basin and lined retention basin. The Allen
Station currently employs a dry ash handling system. Since 2009, fly ash has been dry -handled
and disposed of in the RAB Landfill, which is constructed on the eastern portion of the RAB
(described in Section 3.1.1). The dry bottom ash system became operational in 2019.
3.1.5 Existing Surface Impoundment Liner Systems
The RAB and AAB located at the Allen Station are unlined surface impoundments and were
constructed over natural existing ground.
3.1.6 Inspection and Monitoring Summary
Weekly inspections of the AAB and RAB have been on -going since 2014, and include observation
of upstream slopes and shorelines, crest, downstream slopes, toes, abutment contacts, adjacent
drainage way(s), spillway(s), and associated structure(s), and other structures and features of the
dams.
Monthly inspections of the AAB and RAB include the weekly monitoring elements with the addition
of piezometer and observation well readings, water level gauges/sensors, and visual observations
and documentation of slopes of the dry CCR stacks.
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
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with accepted engineering standards. Reports are to be submitted to 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 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 Surface Impoundment -Related Structures
A site map showing property boundary, location of the Allen Station, 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 updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
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 is one existing on -site landfill at the Allen Station as identified in the table below, along with
the status (active/closed). The existing RAB Landfill is shown on the attached Figure 3-1 and is
described in more detail in Section 3.1.1.
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Landfill
Permit Number
Comment
RAB Landfill
NCDEQ Permit No. 3612
Active
3.3 Monitoring and Sampling Location Plan
This information is included as part of the updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
The CAP is herein incorporated by this reference but its content is not the work product of
AECOM.
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) locations is
shown on Drawing ALN_C999.001.017 and ALN_C999.001.018 included in Appendix D.
This section summarizes the site geology and hydrogeology, site stratigraphy of the geologic units
underlying the surface impoundments, geotechnical properties of the CCR, and the uppermost
stratigraphic unit under the surface impoundment.
4.2 Hydrogeology and Geologic Descriptions
This information is included as part of the updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
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 updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
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 RAB and AAB and 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
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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 weathered rock
(PWR), and bedrock.
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 in support of the closure design is presented in Appendix B-3.
4.4.1 CCR Within the RAB and AAB
The CCR encountered within the AAB complex generally consisted of dry to wet, dark gray to
gray fly ash as sandy non -plastic silt (ML), and dark blueish gray fly ash as silty sand (SM). In
recent years, bottom ash has been sluiced to the AAB area in addition to fly ash. Consequently,
samples of bottom ash were intermittently observed and collected during the AECOM
investigation.
Both stacked and sluiced CCR are present within RAB. In the DORS 1 and 2 areas, stacked CCR
primarily consists of dry to wet, dark gray to gray bottom ash as silty sand (SM), and lesser
quantities of fly ash as silt (ML), with varying quantities of sand, gravel, and slag. This stacked
CCR is underlain by sluiced CCR primarily consisting of moist to wet, dark gray to gray bottom
ash as silty sand (SM), and fly ash as silt (ML). Elsewhere in the RAB, stacked CCR within the
DORS 3 and 4 areas was classified as dry, gray and dark gray, fly ash as sandy silt (ML), and
silty sand (SM). Sluiced CCR within these areas is generally classified as dry to wet, gray and
dark gray, fly ash as sandy silt (ML), and silty sand (SM).
4.4.2 Liner Material Properties
The AAB and RAB are unlined so there are no associated material properties.
4.4.3 Subsurface Soil Properties
Alluvium: Alluvial soils were encountered in seven borings within the AAB. The alluvium generally
consisted of wet, orange or yellow silty sand (SM), and brown or red sandy clay (CUCH), with
quartz rock fragments.
Residual Soils (Residuum and Saprolite): Residual soils within the AAB were encountered in
multiple borings. This stratum generally consisted of moist to wet, reddish brown to light brown
mottled, light gray and greenish gray silty sand (SM), sand with silt (SW-SM), poorly -graded sand
(SP), and sandy non -plastic silt (ML), with varying quantities of mica and gravel. Occasionally,
soils in this stratum were classified as sandy lean clay (CL), clayey elastic silt (ML), and sandy fat
clay (CH).
Within the RAB in DORS 1 and 2, residual soils primarily consisted of wet, reddish brown to light
brown and light gray, silty sand (SM), sandy non -plastic silt (ML), and clayey sand (SC), with
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varying quantities of quartz and mica. Occasionally, soils in this stratum were classified as lean
clay (CL) and sandy fat clay (CH). Within DORS 3 and 4, the residual soils can be divided into
two distinct strata: the upper 10 to 17 ft of the residual soil stratum generally consisted of moist,
brownish yellow, reddish gray, and dark gray, native lean clay (CL) and fat clay (CH) soils,
underlain by up to 37 ft of moist to wet, yellowish brown, orange, and olive gray coarse -grained
sand with silt (SP-SM), well graded sand (SW), silty sand (SM), sand with clay (SP-SC), and non -
plastic silt (ML).
PWR: PWR was encountered within several borings in the AAB. In these locations, PWR primarily
consists of wet, light gray to reddish brown to light brown mottled sand (SP), silty sand (SM),
sandy non -plastic silt (ML), sand with clay (SP-SC), lean clay (CL), and weathered meta -quartz
diorite, meta-granodiorite, and meta-diabase bedrock.
In the RAB within DORS 1 and 2, the PWR below the residual soils primarily consists of wet, light
gray to light brown mottled coarse -grained sand (SM), greenish gray non -plastic silt (ML), and
meta -quartz diorite. Within DORS 3 and 4, PWR consisted of moist to wet, yellowish brown,
grayish brown and olive brown, silty sand (SM), well graded sand with gravel (SW), clayey sand
(SC), sandy clay with gravel (CL), sandy silt with gravel (ML), sand with clay (SP-SC) and minor
layers of fat clay (CH).
Bedrock: Bedrock was cored in four of the soil borings conducted in the interior of the AAB. The
bedrock primarily consisted of dark greenish gray, very strong, coarse grained, massive Meta -
Quartz diorite, and black and white, strong, fine to coarse grained Meta-Diabase bedrock. In the
RAB, bedrock was cored in two borings within DORS 1 and 2. The bedrock encountered in the
borings primarily consisted of light gray to dark gray, strong, massive, Meta -Quartz diorite
bedrock. Bedrock was also encountered within DORS 3 and 4 consisted of black and white to
dark gray and white, very strong, massive, moderately to slightly fractured, fresh Meta -Quartz
diorite bedrock.
4.4.4 AAB and RAB Dam Soil Properties
The RAB and AAB dam embankments consist primarily of loose to medium dense clayey to silty
sand (SC and SM), sandy silt (ML) and stiff to very stiff elastic silt with sand (MH), and sandy lean
clay to fat clay (CL and CH). The dam embankment fill was described as moist, red, and reddish
brown to brown, with varying quantities of sand and gravel.
4.5 Chemical Analysis of Impoundment Water, CCR, and CCR-Affected Soil
This information is included as part of the updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
The CAP is herein incorporated by this reference but its content is not the work product of
AECOM.
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4.6 Historical Groundwater Sampling Results
This information is included as part of the updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
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 updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
The CAP is herein incorporated by this reference but its content is not the work product of
AECOM.
4.8 Estimated Vertical and Horizontal Extent of CCR Within the Impoundments
This information is included as part of the updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
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 Corrective Action Plan (CAP) on December 31, 2019; 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 updated CAP evaluates the extent of, and remedies for, constituents of interest (COls) in
groundwater associated with the ash basins and coal pile area, focusing on constituent
concentrations detected above the applicable 02L Standards, Interim Maximum Allowable
Concentrations, or background threshold values at or beyond the Geographic Limitation (as
defined in the Settlement Agreement) to north and north-northeast of the Retired Ash Basin and
coal pile, and east of the Active Ash Basin. In addition, the updated CAP considers the federal
groundwater corrective action requirements at 40 C.F.R. §§ 257.96-.98.
As detailed in the updated CAP, Duke Energy has begun to implement, and will continue
implementing, source control measures at the site, including (i) complete decanting of the Basins
to remove the hydraulic head, thereby reducing hydraulic gradients, groundwater seepage
velocities, and COI transport potential; and (ii) complete closure of the Basins. In addition, Duke
Energy intends to implement a robust groundwater remediation program that includes actively
addressing COI in groundwater above applicable standards at or beyond the [Geographic
Limitation] using groundwater extraction combined with clean water infiltration and removal of the
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low pH area source proximate to the coal pile area. The CAP provides that these corrective action
measures will most effectively achieve remediation of the groundwater through the use of
extraction wells to the north, northeast, and east of the Basins and coal piles, and strategically
located clean water infiltration wells. The CAP further provides that groundwater modeling
simulations indicate (i) these measures will control COI at or beyond the [Geographic Limitation];
and (ii) at such time the site -specific considerations detailed within the CAP have been satisfied,
including, but not limited to, securing all required state approvals, installing the necessary
equipment, and commencing full-scale system operation, COI at or beyond the [Geographic
Limitation] will meet the remedial objectives in nine years.
5.1 Site Conceptual Model Predictions
This information is included as part of the updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
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 updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
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 updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
The CAP is herein incorporated by this reference but its content is not the work product of
AECOM.
6. BENEFICIAL AND FUTURE USE
6.1 CCR Use
At this time, Duke Energy has not identified a beneficial use of CCR from the Basins at Allen
Station.
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 AAB and RAB, except that the proposed new CCR landfills are proposed
to be built partially within the footprints of the excavated RAB and AAB.
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7. CLOSURE DESIGN DOCUMENTS
7.1 Engineering Evaluations and Analyses
Engineering evaluations and analyses to support closure of the AAB and RAB at the Allen Station,
as detailed in this Closure Plan, are provided in Appendix C.
Geotechnical calculations for the proposed CCR landfill designs will be performed separately as
part of their permit application(s), which will follow NCDEQ approval of this Closure Plan. It is
noted that the conceptual layout of the landfills may be optimized during subsequent design
analysis and that the permit submittals may vary in some respects from that proposed in this Plan.
Dam removal -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.
For closure by excavation of the RAB and AAB, all CCR will be removed, with the exception of
CCR integral with the foundations of overhead transmission line support towers currently located
within or adjacent to the RAB limits. Ash will remain for structural stability around the supporting
structures of these transmission towers and will be capped with geomembrane. The estimated
volume of ash that will remain surrounding the overhead transmission line towers is approximately
20,000 tons (16,600 cubic yards). The ash to remain in place at the towers is and would continue
to be unsaturated based on comparing historical bottom of ash elevations and groundwater
elevations.
Areas for stockpiling or conditioning 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
means and methods inputs from a contractor to fully address before closure excavation work
commences. A detailed phasing and excavation plan will be developed after this Closure Plan is
approved by NCDEQ.
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7.2 Closure Plan Activities
The primary activities associated with closure by excavation are as follows:
• Reduce free/surface water volume via discharge to existing NPDES-permitted Outfall 002.
• Decant by using floating pumps, screened intakes, and pumping.
• 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, CCR excavation and conditioning (drying) prior to
placement in the proposed on -site landfills.
• Start CCR excavation from the basins, with sequencing determined for optimal
progression. Manage and control 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 landfills 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 AAB and RAB dams as excavation advances.
• Complete closure by excavation verification. Grade the area to promote positive drainage
and seed for vegetative growth.
• Sequence final dam breaches 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 plans with topography
• Subsurface exploration location plans
• Estimated bottom of CCR contour plans
• Demolition plans
• Final closure grading plans
• Final surface water management plan
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• Final closure grading cross section layout plan
• Final closure grading cross sections
• Final closure grading details
• On -site landfill schematic plan
• On -site landfill schematic cross sections
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 closure by excavation has been achieved.
7.4 Description of the Construction Quality Assurance Plan
A Construction Quality Assurance (CQA) Plan will be developed following NCDEQ approval of the
Closure Plan for closure of the Basins at the Allen Station. The CQA Plan will be prepared to
address N.C.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 properties and specifications; 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
o CCR Excavation
o Structural Soil Fill
• HDPE Piping
• Vegetation
• As -Built Conditions
• Record Documentation Report
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8. MANAGEMENT OF WASTEWATER AND STORMWATER
The Allen Station manages wastewater and stormwater under two NPDES permits issued by
NCDEQ. Permit number NC0004979, issued on July 13, 2018 (NCDEQ, 2018), permits the
discharge of various process -related wastewaters in accordance with specified limits and
monitoring requirements. Permit number NCS000546, issued May 15, 2015 (NCDEQ, 2015),
provides monitoring and best management practice requirements for industrial stormwater
discharges from the Allen Station. Discharges of stormwater and treated process -related
wastewaters flow directly or indirectly to Lake Wylie/the Catawba River.
Plant discharges to the AAB have stopped as of February 2019. The AAB will continue to operate
during closure to meet the NPDES permit discharge requirements as it goes through the phases
of decanting and dewatering. The AAB must continue to safely pass the SDF to meet dam safety
requirements.
Decanting of the AAB has been completed. Because tthe free water has been completely drawn
down, discharges from the basin via the passive weir box outlet gravity discharge system are not
expected to occur. The pumping system is expected to draw down the stored water after storm
events, route it through the WMS, and discharge the water via the permitted outfall. Dewatering
began on June 2, 2020. All discharge flows are being routed through the water management
process and meet the permitted discharge limits.
The AAB currently has the capacity to contain the PMP storm event by maintaining the water
surface level elevation at or below El. 641.63 ft (given a starting elevation of 634.8 ft), which
provides a minimum freeboard of 2.6 ft. As part of closure, a new, deeper stormwater outfall
channel will be created to Lake Wylie/the Catawba River, but the final connection to the
stormwater outlet channeling will be timed to avoid exposure to contact wastewater leaving the
AAB work site.
Dewatering is currently being 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 ash 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 basins without the mechanical disturbance of the
CCR. The Allen WMS includes equipment that has a designed flow rate of 650 gpm. The
decanting phase was completed on June 2, 2020, and the Allen site is currently in the dewatering
phase to remove interstitial water from the Basins. During this phase, additional physical -chemical
treatment processes may be added to the WMS as necessary to maintain compliance with the
requirements of the discharge permit. Additionally, during the dewatering phase, the designed
flow rate may drop to 250-500 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
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restrict releases under a large rain event that will result in a slower discharge release to Lake
Wylie/the Catawba River. Up to and including the last phase of closure before the AAB and RAB
dams are breached, the Basins 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. Detailed
stormwater design for the proposed CCR on -site landfills will be developed as part of their permit
designs and is not covered herein.
8.1 Anticipated Changes in Wastewater and Stormwater Management
All CCR and wastewater flows historically sent to the AAB have been diverted to the holding basin
and lined retention basin in the coal pile area and to the north of the station.
A temporary WMS will be utilized such that the NPDES Outfall 002 effluent discharge limits will
be met throughout the duration of 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 depicted on the drawings in
this Closure Plan submittal 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 three proposed lined CCR landfills located on plant
property. Duke Energy intends to construct three new on -site landfills to accommodate CCR
dispositioned in completion of the NCDEQ-mandated closure by excavation. Permit applications
for construction of the on -site landfills will be prepared and submitted to NCDEQ Division of Waste
Management following approval of this Closure Plan. The permitting process may begin earlier
for the NSLF and SSLF than the ABLF permitting, since ABLF construction will begin much later
in the CCR excavation process.
Vegetation encountered or removed during the progression of the work will be managed in
accordance with state regulations for handling and disposal.
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10. APPLICABLE PERMITS FOR CLOSURE
Refer to Table 10-1 for detailed information on the potential and applicable permitting/approval
needed to implement this Closure Plan. Development of permitting package submittals and/or
regulatory approval requests would follow NCDEQ approval of the Closure Plan.
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 AAB and RAB. 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 AAB and RAB.
The post -closure care plan will be developed to meet the requirements of N.C.G.S. §130A-
309.214(a)(4)(k). The items that will be in the post -closure plan for the Allen site 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 of the on -site landfills;
• Groundwater and surface water monitoring and assessment program (included as a
part of the CAP);
• Post -closure inspection checklist to guide post -closure inspections;
• 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 updated CAP that was prepared separately by SynTerra
for Duke Energy. Duke Energy submitted the updated CAP to NCDEQ on December 31, 2019.
The CAP is herein incorporated by this reference but its content is not the work product of
AECOM.
23

AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
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 and dewatering
Ongoing
Submit plan and design for NSLF/SSLF construction permits
Q4-2020
Start CCR excavation
Q1-2021
Landfill permit approvals
Q2-2021
Start new landfill construction
Q3-2021
New landfill in service (NSLF)
Q3-2022
Complete CCR excavation
Q4-2037
Complete final closure and cover system of new landfills
Q4-2038
Site final grading and vegetative cover
Q4-2039
A detailed construction schedule will be developed following NCDEQ approval of this Closure
Plan.
12.2 Closure and Post -Closure Cost Estimate
Cost estimates for closure and post -closure of the Basins at Allen Station 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 closure by excavation, including the new CCR landfills, is estimated to be
$744 million .
The cost to perform the 30-year post -closure activities and monitoring is estimated to be $82
million.
The cost estimates prepared by Duke Energy includes the following major activities:
• Mobilization and Site Preparation
• Dewatering, earthwork, and subgrade preparation
• On -site landfill construction
• CCR excavation
• Stormwater management, erosion and sediment control, and site restoration
• Engineering support (design and CQA)
• Post closure — groundwater monitoring
I

AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
• Post closure — operations and maintenance
• Contingency
Corrective action costs are included as part of the CAP that was prepared separately by SynTerra
for Duke Energy and was submitted to NCDEQ on December 31, 2019. The CAP is herein
incorporated by this reference, but its content is not the work product of AECOM.
99

AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
13. REFERENCED DOCUMENTS
Duke Energy Corporation (Duke Energy), Misc. Dates. Allen Steam Station Design Plans.
Drawing numbers A-3330, A-3350, A-3350-01, A-3350-02, A-3350-03, A-3350-A-01, A-
3350-B-01, A-3352-01, A-3352-02, A-3352-03, A-3350-2014-0507. 1965, 1972, 1973,
1975, 1983 and 2014.
NCDEQ, 2009. Industrial Solid Waste Landfill Facility Permit No. 3612, Issued December 2009.
NCDEQ, 2015. Permit No. NCS000546 to Discharge Stormwater under the National Pollutant
Discharge Elimination System. May 15, 2015.
NCDEQ, 2018. Permit No. NC0004979 to Discharge Wastewater under the National Pollutant
Discharge Elimination System. July 13, 2018.
S&ME, 2008. Engineering Plan, Retired Ash Basin (RAB) — Ash Landfill, Permit to Construct
Application, Allen Steam Station, March 26, 2008.
S&ME, 2014. Operations Plan — Revision 7, Duke Energy Carolina, LLC —Allen Steam Station,
Retired Ash Basin (RAB) Ash Landfill — Phase 1, Permit No. 3612, Gaston County,
Belmont, North Carolina. June 2014.
SynTerra Corporation (SynTerra), 2019. Corrective Action Plan Update. December 31, 2019
9.1

AECOM July 31, 2020
Duke Energy —Allen Steam Station
CAMA Closure Plan (Closure by Excavation) — Retired Ash Basin and Active Ash Basin
PROFESSIONAL ENGINEER CERTIFICATION
I, Jay Mokotoff, 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 July 31, 2020, 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 �t Mck 00 DATE
AECOM Technical Services of North Carolina, Inc. (License: F-0342)
OA
7/31 /2020

FIGURES

FIGURE 1-1
mv• A
iT # ALLEN STEAM STATION
■ 1
bm
ar
I
* •
' �` `� ` r� • PLANT ALLEN RD f r • COAL YARD
41
hp
��r' I r L i •yiL S I Iz; +Ia===aa 1 JED _
HOLDING
ok
BASINS
Ell -dm
ro
ASH M �I '� ' _ ; •
�- STORAGE 1 ■ 1 I l
RETIRED ASH BASIN
RETIRED ASH BASIN DIKE
■• _ _ _ +i� FR �� '',a♦ �; ; ; ,I r� ' (GASTO-016)
f
f
91
p ASH
I I I + I
j �..►;� FILL i
i I ASH + _ RETIRED ASH BASIN i '
,
��I 1
FILL 1 I ♦oft-_w-ft --- ft_% I F�.__
LL LL LL LL LL
' � • �� ; ; ; I1 I r I
' : y 1 i ■I�I 1 iI
mmY I I I
60
- ASH
* RETIRED ASH BASIN STORAGE RETIRED ASH BASIN LANDFILL r
_ _ T go � I �I!+ � _j PERMIT NO. 36-12 �
y��+ 7 I 'tr I I� I� IIl I I
1A 1 1 1 1 I I+r rl
-, � I� I 1 III I r1 I1
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or
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ti II --
1! ACTIVE AS
NORTH DIKE­
440 i
r + %ok.
Ill-
' �
_ PRIMARY POND 3 r
APPROX.
* PRIMARY PRIMARY POND 2 �L PRE -DECANTING
' IFF POND 1 APPROX. WSE 640.0'
1 } f :1111 - - PRE -DECANTING _ '*
• �� _ �+■ WSE 640.0'
ai
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-in -8
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i
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1 f
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-
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LAKE WYLIE/
CATAWBA RIVER
NORMAL W.S.E.
565.7 FT.
YLIE/
CATAWBA RIVEI
NORMAL W.S.E
565.7 FT.
N
0 300 600 900
GRAPHIC SCALE (IN FEET)
0,
RAB
I
CATAWBA RIVER/
°`���" �L�� •� �_ :\� a LAKE WYLIE
AAB
"
IM
0 2000 4000 6000 N
GRAPHIC SCALE (IN FEET)
LEGEND
DUKE ENERGY PROPERTY BOUNDARY
APPROXIMATE LIMITS OF IMPOUNDED ASH
APPROXIMATE ASH BASIN WASTE BOUNDARY
•________________• ASH STORAGE BOUNDARY
W.S.E. WATER SURFACE ELEVATION
TITLE
FIGURE 1-1 VICINITY MAP AND SITE PLAN
ALLEN STEAM STATION
CCR SURFACE IMPOUNDMENT CLOSURE PLAN DRAWINGS - CIP
GASTON COUNTY, NORTH CAROLINA
N.C. ENGINEERING LICENSE NO. FOR F-0342 ISSUED FOR APPROVAL
S SCALE: DES: ANR
DUKE DWG TYPE : • DWG DFTR : AMC
JOB NO: 60603204 CHKD: JDM
ENERGY® DATE: 12-12-19 ENGR: JDM
FILENAME: FIGURE 1-1 SITE LAYOUT PLAN . DWG APPD: JDM
DWG SIZE DRAWING NO. REVISION
ANSI FIGURE 1 -1
22.0"x34.0" A
9 10
Fl
C
m
i

FIGURE 3-1 1 mv. A
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3G-2D
G-2 /
3G-2BR BG-2BRA-2
ro-�j
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GWA-16D
GWA-16S
INCHES
G
0
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GWA-7D ALLEN STEAM STATION
\\\ / -, ,`I �� \ E \ 0 GWA-7S
I / ` \ �11 r\ , \`\ _ _,__� . , GW��Ay-8S ��
J
I \ _ r \., ._ - I � d� � \ GWA-7 J i I iii `-- _ _ BGSB-GW-8 NA-8 w ' 3Q \ \ \ 1 I\
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t 1�` 1 / \\
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— 30 — / / iii' _ - \ r ` ` 4 \ / I \ r \\1
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_�
nY - /
--- -- - -- RD 3fl _ _ l GWA-6 r rr-/,Y�/yr Irlr\_ I �I,\�� ` r�
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' / GWA-18D 1 ,� \ _ , / COAL YARD "111 II N\\r 0 �C 1
1 1 c \ _ . �_ \ GWA-6DA.
r � I \ I , i - N I i♦l%i-:� ,�, ; \✓,� � \ may,. , l , / rllr ,, I
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I \ . / -- . I CCR_ 1 / l rbl l II
�'' /' ` / I I ` ` I '� i i�--- .,• /I"I;fii.� / \ \ CR-4D' GWA-6D ✓" r It/ 1 I a
l � � z, nl„ � r l I v , I HOLDING
GWA-18 /- I • CCR-2S _ 1 \ 4, }� r \ h „✓ Ji I Ili„ \\\ of
/ !, i .' ; f .. I I ( ,�i/, ■ �� i 1� /'%�. ,i \ ) \\ i \\\ ` I Ili/ BASIN �\\
ASH STORAGE ,
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EX. SLUICE //- \\ \
/ a\
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I r, AB-39S I 41! I� t''II'
I t� I lol to CCR-5S \ / p �1 r-- ►, _ _ - h^ I
RETIRED ASH IAB-38BR
�Io / 1 r/ I Icfll ico \C\ ``CCR-7D <- - ��^ '=
BASIN I� r I III I IIII \� �`\ -____' . r CPT-URS-5-S
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� � �I I B- - � c CCR-9D
1AB-38S' / , AB-39D 1 I AB-39 IIIII I \\`� CCR-Fn� CCR-7 ` , I .-
I AB-38 0 "I ' \ 1� �I li II I B 4 = _3 RETIRED ASH BASIN DIKE =_
\\\
Ir ',( I ,!I11 II 1 I� ��II I� Illii TL 1A482 — �
I \ 11 r f- , II 111 foil I / (GASTO-016 DW-5�\\\\�\\cl CCR-9S
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rl I CCR-BG-1S\ 1 100kV ` I I ` f 1 II 'I�• II I III i " `'�
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BG-1 D' ► 11 OW-7 — P.I: �, - ► / nll II
\ (500kV) I _/ /' IIIIII I I III I /~ \ \\ // III I I
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I I III I !�� � \ . �
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%1 � I r �_________ = RETIRED ASH BASIN AB-32D p,l
II �ti/ __/ ./ \6 `� / � TL 2A10 ` �( \11 w ASH FILL 1 I� --- ��— �� Ilion B-11
0� ._ \ � co, � `-- ---- %''�= `:\ OW-10 II toll GWA-SBRA
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i' / / \ / / / ���\ I I �' I �yaaaaaaaa \ -- Saar- -- \\I �\ _ I I
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I -- �' — I ' �l 1 I I IIII �`� ��� ,�'1'Mlaa-- �sa� PZ-26-3 IIIIIIII
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ASH FILL I I I i Jr -----� L 1 , — _ I
I lil 1 I I I I OW�8— - ` ---- ------ - I I I I
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I I II III II 11 I I I--_ ----__---- _ �\��______- — — — — — — — = - -� I IIII III CCR-11 DA
/ 1 1 0 0 i DRAIN I IIII IIIIII I / I I ----------- I I ft I I IIIIII =--------------- �__----__--------------- ---- III III I I
1l �I Ir� 1I lI,II(III II (TYIlII lI iIIlI I��Ia lIIlII IIllI — I 1 �`I��IIII lIjlIIIIIIII IIIIII1rj�I IIIIl ITIIl i1 IjIlI r IlI Il!I —
-- 13iF AB-37D.' 11 )
woo'1I j
`' _ \ 1IIIIIIIIIIIII IIII I 1 AB-37S RETIRED ASH RETIRED ASH BASIN LANDFILL
PERMIT NO. 36-12 1III III PInIIIIIIIIIZ
IIB IuII �I-1I'
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e AB-37 *I ASH STORAGL1y vl I'll rl - _OW
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I. O O 11 I I AB3515SII1-II I SR
I I III, I II II I (TYP., LOCATION TWIN EX.
AB-36,i APPROXIMATE) PIPES TWIN EX. PIPES
-36S woLO AB 1I`-GWA-15� o O101I 101-714 1101, .1 I II B-21
M
100-YEAR
FLOOD
ELEVATION:
571.3 FT.
-to WA - IOU \ _\ ` 1� - I I I I CO III LtO - �,1 ma 1 TWIN EX. 36 RCP PIPES \\II PZ-2B-1 �l,l r 1111.11 EMERGENCY
\ \ IIII \\ ' I I I ® — — — —= 675 --\I l\__ -- n I I �I i
\ I \ I III II //// II I II it _ _ _ — _______--___ _-` _r0 �i I
11 , IIIIII I I I �___.__ _� Fj CV'IO� SPILLWAY
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' � / \ . +III // // , I I I____
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o \ \ \�� r i \I� :! i _ OW-18 __a -_ _ AB-__29S_L_ _-' Ilnlli� AB-9S
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— GWA-1_ % GWA-14D - _ ; �� {I \ ~ / "' 1 AB-30 AB-30S (TYP., LOCATIONS ;-26- — - , / ; AB-9
APPROXIMATE) rOW- I,+
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-',/ B-23 v I r_7 II i i i I I I
\ \ i L�i' / ~� I I NPDES
i \ \ �-'� I OW-22 ' OW- i i AB28 B-28 i , , AB- 7S I- Milli fill
AB-28D - �./
n , ` I / —Al I ' 1111 III OUTFACE
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GWA-20 I\\ _ i GWA-22S ' c --- /� �` .rJ ,ti ✓. 1 +IICCR-14S l
\ /. - — — — — _ \\ r• B-30 / / ,/ �, 1 1 1 1 IIII I I
OW-21 I p
-2D- OW-1 l I II . �C7 ��®
LAKE WYLIE/
CATAWBA RIVER
NORMAL W.S.E. 565.7 FT.
`--- r PN-1 D i I EX. SLUICE \ g® ��� III i 1 IIIII 11 1 COAL YARD SUMP
\ I \ o Ii I—CCR-14DIiI DISCHARGE
GWA-21BR PIPES B-31 PRIMARY POND 3
(ABANDONED)
—
GWA-21
APPROX. r \
\ \ I I
PRIMARY POND 2 / / PRE -DECANTING 1 1 II I IIII! I
/ PRIMARY I I I I Ito
GWA-1 1S I��3 I �, APPROX. t r q WSE 640�0' i i III I IN tlol
4 f-fir, POND 1 I Ill 11:11! .-
1 650 �v PRE -DECANTING AB-25 _�_ __AB-26
GWA-21D / ` c3 'AB-24S 1 - - _ , II i III I�AB-26D GWA-3BRA
l a` -_-t� __• o r // -WSE 640.0'-- ,
\ , - / / AB-13S " � r AB-25SL Ip I I IIII GWA-3S
\ GWA-21 DA ( - -- \ B-24 /�'~' i / I I I r
.r� i I I 1 tlil GWA-313R
AB-26S III II I
AB-25BRU _ I IIIIII
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~I
OW-
6Ol'/j/ W
I _�' �• LAKE WYL4RRIE/AB-�Ail \// CATAWBA RIVER
r•///NORMAL W.S.E.AB-4D ��•
oU1 P3 z 565.7 FT.CHEMICAL j
S� �mAB-23,BUILDING ` >Lu
II it AB-4S__�'�- r/•�0;`V
F_' o
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o 11
'cn o s\ >
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i
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�i —� -- �— '/ \�\ / / \\___\_/, i''�'' ,�� % l I r 1 , Illll+II \��. \
/cr r� / , , _ �l I POLISHING POND I !I I IIIII III CCR,-1 \7D
' I I `•� '/ 1 l /� I '/i/ �•r l l \ APPROX.\\. \
i /IIIr /GWA-9D, , 1 \ ,,, ► / I /' / j \ L
/ GWA-24i l i t r .►Ire % 1 _ _-- -''/�, ': / /L, / �/ ,/ • 1 \ PRE -DECANTING N I� c,l Ili II
r GWA-9BR I I-� // _r ,/ y . \� c0 I m
--GWA-24D, / GWA-9„� r/ m - ,� „? `% / I / ,� ,� \" ,, \ I III II II I AB-10
� / \ I' / r •\ WSE 635.0 t{I�Ui,I llt III �_.� \
r AB-20S` r \ / 1 \ r1 • ' \ lJ ~ 1 �1 t I IIII lllllll
GWA 24S/ / / / AB-20D o o ; 1 / / I/ I� • • ��. \\ \ i� AB-22S \\ /JI I Iilli i!
AB-20 rn I� + l i \\I'• ' ACTIVE ASH BASIN \ \\ / i> - , I I �_ I AB-10S
GWA-24BR / o GWA � 9S f o AB-21 BRL ' // i / AB-21 S'� `\ J/�\ AB / 22 5 r \\ t I ABI 22BR
o; III ; ,,, o > r \ �►• -- �/OW_81 II i IIIII itl ip� g
�A<0 cat?/ \ co co /f`�i '"'` r7u� , '"'` ''` �h / ,� AB-21SL '"'` ''I'`\\ ,/ 'OW-121
o o �, Il B-21 �,�� `'� i`--� /' P-7 l ll� I lii I II�IIiI!I i
/ / / m ~ � `I � \ /— OW-10 `l ll III OW-11
' I
AB-21 BR J IIIII II n �►
r/ o , /, AB-21 D \ . 1 I�I III I AB-6A
GWA-25. / `--/ 1\ I , \` " \ AB-� 6 l ll I IIIIII V I _1
`'1� I CCR-18D
JURISDICTIONAL STREAM
100-YEAR
FLOOD
ELEVATION:
571.3 FT.
i J w i, / CHEMICAL 1\ .� \ =-"�\ 1 �i I� IIIII dill PERMITTED SPILLWAY
00
11 k- w - ` — ``` `_! CCR-1 8S
BUILDING rr /
xllc • yl�c xllc xllc xllc — — =!i- / j -�
• ,v \\ - EXISTING'/�--//i
cn h \ AB-12S _-- -.\�-' _ — �\ `� WTS PAD
_��j// ��\ \`�` \`\ ` ylic �lic \ ' CCR-21 S I
A13-12,
'AB-12D,/ / _ \ \ \� _ -- - - ---' // r= \ ` \\ \ \ 1 CCR-21 D/'CCR/ 20D CCR-20S
_ \
\ � \ \ \\ \
1 /- 'CCR-22SJ, / l I l
\` \ I ` /% / I / IF
� l GWA-2S/
GWA-26 - - 1 r / \ \ I , �i / / / _ �p
/ / � / CCR-22DA, / / co /
c�s� ~---- ��'' �61 GWA-26S rr `r cfl ; 1 \\ r_`\\ \\\\�\ I \ / ��_--- ,',/ / / I \ , / /' WA-2D,/
\\ \ GWA-26D,?
-\ \
\\\ iG/W/
A-2,/
' 1 / =i BGSB-GWA-26, �\k CC-23S\GWA-I 1D
_ _ 10
i
THS10
t
NPDES
OUTFALL
002
JURISDICTIONAL STREAM
LEGEND
—
— — - 625 - — — —
EXISTING MAJOR CONTOUR (25 FOOT)
EXISTING MINOR CONTOUR (5 FOOT)
DUKE ENERGY PROPERTY BOUNDARY
APPROXIMATE LIMITS OF IMPOUNDED ASH
LIMITS OF EXISTING RAB LANDFILL LINER
LL
------------------
ASH STORAGE BOUNDARY
APPROXIMATE ASH BASIN WASTE BOUNDARY
LIMITS OF WATER
100-YR
100 YR FLOOD LINE
HDR SOIL BORING/GROUNDWATER
AB-X/GWA-X/BG-X
MONITORING WELL LOCATION (2015)
S&ME SOIL BORING/MONITORING WELL
B-X
LOCATION (2010)
S&ME SOIL BORING/MONITORING WELL
TT
B-x/OW-x
LOCATION (2007)
T
AB-x
S&ME EXISTING ASH BASIN VOLUNTARY
GROUNDWATER MONITORING WELL LOCATION (2004)
MACTEC EXISTING ASH BASIN COMPLIANCE
AB-X
GROUNDWATER MONITORING WELL LOCATION (2010)
4
Ow-x
DUKE EXISTING OBSERVATION WELL (1983)
x
P_x
DUKE EXISTING PIEZOMETERS WELL (1983)
CCR-x
CCR MONITORING WELL
HATCH LEGEND
WETLAND (SEE NOTE 5)
POTENTIAL HABITAT - SCHWEINITZ'S
SUNFLOWER (SEE NOTE 4)
NOTES
71-1
1. LIMITS OF IMPOUNDED ASH ARE APPROXIMATE.
2. VOLUME OF FREE STANDING WATER WITHIN THE AAB SHOWN IN THE DRAWING IS
C
APPROXIMATELY 92 MILLION GALLONS BASED ON FEBRUARY 2015 SURVEY BY WSP.
m
3. REFER TO DRAWING SHEET ALN_C901.021.002 FOR REFERENCES.
W
4. POTENTIAL HABITAT FOR SCHWEINITZ'S SUNFLOWER WAS IDENTIFIED BY AMEC'S JUNE
1
24, 2015 NATURAL RESOURCES TECHNICAL REPORT. PRIOR TO LAND DISTURBANCE,
-.JL
THE U.S. FISH AND WILDLIFE SERVICE MAY REQUIRE A BIOLOGICAL SURVEY OF THESE
AREAS.
5. POTENTIAL JURISDICTIONAL WATERS (STREAMS/WETLANDS) WERE IDENTIFIED BY
AMEC'S JUNE 24, 2015 NATURAL RESOURCES TECHNICAL REPORT AND SURVEYED BY
MCKIM & CREED IN FEBRUARY 2016. CONFIRMATION IS PENDING U.S. ARMY CORPS OF
0
ENGINEERS REVIEW.
0 300 600 900
NOT FOR CONSTRUCTION
GRAPHIC SCALE (IN FEET)
TITLE
P"=com
N.C. ENGINEERING LICENSE NO.
F-0342
EXISTING CONDITIONS PLAN
ALLEN STEAM STATION
CCR SURFACE IMPOUNDMENT CLOSURE PLAN DRAWINGS - CIP
GASTON COUNTY, NORTH CAROLINA
FOR ISSUED FOR APPROVAL
SCALE: AS SHOWN DES: ANR
DUKEDWG TYPE :. DWG DFTR : AMC
JOB
�. ENEENERGY®[DATE. 12-12-119 ENGR: JDM
FILENAME: FIGURE 3-1 EX TOPO AND BATHYMETRY.D PPD: JDM
DWG SIZE DRAWING NO. REVISION
ANSI FIGURE 3 -1
22.0"x34.0" Q
10

TABLES

AECOM Table 2-1: NC CAMA Closure Plan Requirements September 20, 2019
Summary and Cross Reference Table
Duke Energy, Allen Steam Station
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
Whether 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
IAII 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
5
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
Page 1

AECOM Table 2-1: NC CAMA Closure Plan Requirements September 20, 2019
Summary and Cross Reference Table
Duke Energy, Allen Steam Station
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
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
f
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
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;
k
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.
Projected costs of assessment, corrective action, closure, and post -closure care for each coal combustion residuals surface impoundment.
12.2
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
n
documenting the presence of contamination, if applicable, or historical site use.
6.2
Page 2

AECOM Table 2-1: NC CAMA Closure Plan Requirements September 20, 2019
Summary and Cross Reference Table
Duke Energy, Allen Steam Station
Corresponding
No.
Description
Closure Plan Section
§ 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.
Note 1
Reports Prepared by Other Consultants Include:
1 Synterra Groundwater Assessment Work Plan
2 HDR Groundwater Assessment Work Plan
Page 3

AECOM
Duke Allen Steam Station
Closure Plan
Table 4-1 - Summary of Geotechnical Index Properties'
Ash Within Ash Basin
Properties
(RAB and AAB)
Foundation Soil below Ash Basin
Embankment Fill Soil
Foundation Soil below Embankment Dam
Partially Weathered Rock (PWR)
Silt (ML), Silty Sand (SM), Sandy Silt (ML), and
Sandy Silt (ML / MH), Sandy Clay (CL / CH),
Silty Sand (SM), Sand (SW), Clayey Sand
Silty Sand (SM), Sandy Silt (ML), Sand (SC),
Soil Type
Silt/Sandy Silt (ML) - Predominantly Fly Ash,
Clay (CH)
Silt (ML), Silty Sand (SM), and Clayey Sand
(SC), Sandy Clay (CL / CH), Clayey Silt (ML),
and Clay (CL)
(SC)
and Sandy Silt (ML)
Liquid Limit
Non -Plastic
NP - 49%
NP - 73%
NP - 68%
NP - 33%
Plasticity Index
Non -Plastic
NP - 35%
NP - 39%
NP - 35%
NP - 8%
Representative
Geometric Mean
Representative
Geometric Mean
Representative
Geometric Mean
Representative
Geometric Mean
Representative
Geometric Mean
Range
Range
Range
Range
Range
Natural Moisture Content (%)
18 - 66
39
11 - 68
29
12 - 69
27
4 - 67
30
11 - 24
16
Fines Content
15 - 98
68
17 - 89
50
13 - 81
57
19 - 90
49
21 - 64
34
Moist Unit Weight - y,n (pcf)
72 - 120
92
74 - 113
98
115 - 149
126
115 - 133
124
---
---
Dry Unit Weight - 7a (pcf)
57 - 92
68
55 - 86
71
87 - 119
99
91 - 114
103
---
Specific Gravity
1.95 - 2.81
2.23
2.53 - 2.95
2.75
2.59 - 2.79
2.68
2.66 - 3.08
2.76
2.68 - 2.94
2.78
Notes:
NP: Classification of Non -Plastic
*Only one lab test data available
Data obtained from lab tests performed on material obtained from within the Ash Basins for the Closure Design, Phase 2 Reconstitution of Ash Pond Designs Report (AECOM, 2016a), Allen Geotechnical and Design Services Report (S&ME, 2010), Site Suitability
Study Retired Ash Basin (S&ME, 2007), Comprehensive Site Assessment Study by (HDR, 2015a), and Historical geotechnical data provided by Duke Energy.

Table 10-1
Allen Steam Station Regulatory Permits, Approvals, or Requirements for Ash
Basin Closure by Excavation
Permit/Approv
al
Type of
Existing
Regulatory
Permit
Approval
General Permit
Regulating
No.
Mechanism or
Name or Subject
Agency
applicable)
Not Required
Comments
Permit modification likely due to the
Permit
increased heavy equipment vehicle
Air Quality
NCDEQ
modification
traffic and potential dust generated
likely
during closure activities
Gaston
A local building permit is required for
Building Permit
New Permit
County
installation of construction trailers
Modification or abandonment of CAMA
CAMA Monitoring
Written NCDEQ
program monitoring wells require the
Plan
NCDEQ
DWR approval
approval of the Division of Water
Resources (DWR)
CCR
Impoundment
US EPA
Self -Regulating
Required postings to Public Record
CCR Rule
Closure
CCR
Maintain CCR GW monitoring network
Impoundment
US EPA
Self -Regulating
and requirements as stated in 257.90 -
Monitoring
CCR Rule
Network
257.98
USACE
and
NCDEQ
It is anticipated that an individual
Clean Water Act
DWR 401
Individual
permit will be required in relation to
401
Water
Permit
dam breaching and associated
Quality
downstream impacts.
Permitting
Section
It is anticipated that an individual
Clean Water Act
Individual
permit will be required in relation to
404
USACE
Permit
dam breaching and associated
downstream impacts.
Applicable and
Erosion and sediment controls, natural
to be covered
Cutting Trees
habitat, and endangered species
as part of other
considerations.
permits

AAB Dam - Permitting is required to
Certificate of
modify or abandon wells and
Dam Safety
NCDEQ
GASTO-
Approval to
instrumentation on regulatory dams
061
Modify
through the Division of Energy, Mineral,
and Land Resources (DEMLR)
AAB Dam - Final approval after
abandoning wells and instrumentation
Certificate of
on regulatory dams through the
Dam Safety
NCDEQ
GASTO-
Final Approval
Division of Energy, Mineral, and Land
061
(COFA)
Resources (DEMLR) in accordance with
the Dam Safety Law of 1967, 15A WAS
02K.0220.
AAB Dam - Permitting is required to
modify and remove the dam in
Certificate of
accordance with the Dam Safety Law of
GASTO-
Approval to
1967, § 143-215.27 and § 143-215.27A
Dam Safety
NCDEQ
061
Modify and
(where applicable) and the Dam Safety
General Provisions, 15A WAS 02K.0201
Remove
(b)(2); an application must be filed with
the Division of Energy, Mineral, and
Land Resources (DEMLR)
AAB Dam - Final approval after
Certificate of
modifying to remove the Ash Basin
Dam Safety
NCDEQ
GASTO-
Final Approval
Dam through the Division of Energy,
061
(COFA)
Mineral, and Land Resources (DEMLR)
in accordance with the Dam Safety Law
of 1967, 15A WAS 02K.0220.
RAB Dam - Permitting is required to
Certificate of
modify or abandon wells and
Dam Safety
NCDEQ
GASTO-
Approval to
instrumentation on regulatory dams
016
Modify
through the Division of Energy, Mineral,
and Land Resources (DEMLR)
RAB Dam - Final approval after
abandoning wells and instrumentation
Certificate of
on regulatory dams through the
Dam Safety
NCDEQ
GASTO-
Final Approval
Division of Energy, Mineral, and Land
016
(COFA)
Resources (DEMLR) in accordance with
the Dam Safety Law of 1967, 15A WAS
02K.0220.
RAB Dam - Permitting is required to
Certificate of
modify and remove the dam in
GASTO-
Approval to
accordance with the Dam Safety Law of
Dam Safety
NCDEQ
016
Modify and
1967, § 143-215.27 and § 143-215.27A
(where applicable) and the Dam Safety
Remove
General Provisions, 15A WAS 02K.0201
(b)(2); an application must be filed with

the Division of Energy, Mineral, and
Land Resources (DEMLR)
RAB Dam - Final approval after
Certificate of
modifying to remove the Ash Basin
Dam Safety
NCDEQ
GASTO-
Final Approval
Dam through the Division of Energy,
016
(COFA)
Mineral, and Land Resources (DEMLR)
in accordance with the Dam Safety Law
of 1967, 15A NCAS 02K.0220.
Utilization of or modification to state or
DOT - General
Not anticipated
federal highways to transport CCR will
at this time
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 exceed one acre,
therefore in conformance with 15A
Erosion and
NCAC 04, an E&SC Permit is required
Sediment Control
NCDEQ
New Permit
from Land Quality prior to
(E&SC)
commencement of construction in
those areas. Note that land
disturbance includes tree clearing and
grubbing and vehicular wheel or
tracking as disturbance.
Removal from or import of material
Fire Ants
Restriction not
could be restricted dependent on the
likely
potential for fire ants and geographic
regions involved
Gaston County Floodplain Development
Regulations Section 16.3.3 require a
Floodplain
Gaston
Floodplain Development Permit prior to
Development
County
New Permit
the start of construction within FEMA-
mapped Special Flood Hazard Areas
indicated on Flood Insurance Rate
Maps.
Permits are required to construct any
water supply well or water well system
Large Capacity
NCDEQ
New Permit
with a design capacity equal to or
Water Supply Well
possible
greater than 100,00 gallons per day -
for dewatering outside of the ash basin
Multi -State
If movement of CCR will cross state
Not required
lines, multi -state regulations might
Agreement
apply

NPDES (National
Pollution
Permit
Modification of NPDES may be
Discharge
NCDEQ
NC0004
modification
necessary if new source or outfall is
Elimination
979
likely
created.
System)
NPDES (National
Pollution
Discharge
NCS000
Permit revision
Revision to existing sitewide permit or
NCDEQ
new permit may be required for access
Elimination
546
likely
System) Industrial
roads, staging areas, etc.
Stormwater
Removal from or import of vegetated
Not anticipated
material could be restricted dependent
Noxious Weeds
at this time
on the vegetation and geographic
regions involved
Railroad
Not
Construction activities adjacent to
Easement, Access,
anticipated at
tracks/ballast or a new railroad crossing
or Crossing Permit
this time
require an agreement or permit
SPCC (Spill
In accordance with the Federal Water
Prevention
Modification of
Pollution Control Act (Clean Water Act)
Control and
EPA
Countermeasure)
existing plan
of 1974, Title 40, Code of Federal
Regulations, Part 112.
Plan
Threatened or
Endangered
Species:
Candidate
Federal and/or state regulations may
Conservation
apply including agency consultation and
Agreement
performing site -specific surveys within
Avian Protection
NCDEQ
the proper survey period (e.g.,
Plan(s)
and EPA
flowering period for listed plant) to
Bird and Bat
determine if Threatened or Endangered
Conservation
Species or their habitat exist within the
Strategies
limits of disturbance
Eagle
Conservation Plan
Eagle Take Permit
Solid Waste Site
Approval by
NCDEQ
New CCR Landfill
Suitability
Letter
Solid Waste
Permit to
NCDEQ
Permit
New CCR Landfill
Construct
Solid Waste
NCDEQ
Permit
New CCR Landfill
Permit to Operate