Cliffside Pilot Test WP Final 7-2-20

DUKE
ENERGY,
CAROLINAS
July 2, 2020
Mr. Ted Campbell
North Carolina Department of Environmental Quality
Water Quality Regional Operations Section
Division of Water Resources
Asheville Regional Office
2090 U.S. Highway 70
Swannanoa, North Carolina 28778
Sent via email to [e-mail]
Subject: Pilot Test Work Plan
Duke Energy Carolinas, LLC
Cliffside Steam Station
Mooresboro, NC
Mr. Campbell:
526 South Church St
Mail Code EC13K
Charlotte, NC 28202
M: 980.373.6563
On December 31, 2019, Duke Energy Carolinas LLC (Duke Energy) submitted a Corrective Action Plan (CAP)
Update Report for the Cliffside Steam Station (or Site) which included a robust groundwater corrective action
program to address constituents of interest (COI) concentrations in groundwater greater than applicable
standards at or beyond the Geographic Limitation using a combination of groundwater extraction and clean water
infiltration wells for the Active Ash Basin area, groundwater extraction at the Unit 5 Inactive Ash Basin area, and
phytoremediation using TreeWelISTm at the Former Units 1-4 Ash Basin along with groundwater monitoring in
other areas of the site.
In early 2020, Duke Energy requested the approval from North Carolina Department of Environmental Quality
(NCDEQ) to implement groundwater CAP pilot tests for five facilities, including the Cliffside Steam Station to
accelerate the overall corrective action process. On February 10, 2020, the NCDEQ approved this request with a
provision to submit a pilot test workplan to the NCDEQ. Attached is the Pilot Test Work Plan for the Cliffside
Steam Station Corrective Action Plan Remediation System.
Implementation of the groundwater CAP will be conducted in a phased approach, with the pilot test phase
implemented at the Unit 5 Ash Basin area. The pilot test will be used to optimize the full-scale corrective action
system at Cliffside, including the active ash basin area, by using adaptive design methods based on data
collected during the pilot test. The pilot test consists of installing 22 groundwater extraction wells strategically
placed based on modeling simulations and the assessment data collected at the site. The attached Pilot Test
Work Plan presents a description of the pilot test activities, along with a summary of the data collection and
analysis that will be used to refine design parameters such as well performance, flow rates, area of hydraulic
influence, and well spacing.

Pilot Test Work Plan
Cliffside Steam Station
July 2, 2020
Page 2 of 2
Per the NCDEQ's suggestion, Duke Energy will set up a follow-up meeting within the next one to two weeks to
address any questions or comments. If you have any immediate questions, please contact Mr. Ryan Czop at
Ryan.Czop(@duke-energv.com.
Sincerely,
Scott E. Davies, P.G.
Project Director
Copies:
Steve Lanter, NCDEQ Division of Water Resources, Central Office
Eric Smith, NCDEQ Division of Water Resources, Central Office
Elizabeth Werner, NCDEQ Division of Waste Management
Ryan Czop, Duke Energy
Brian Wilson, ERM
Enclosures:
Pilot Test Work Plan

14; fmak DUKE
°ENERGY
Pilot Test Work Plan
Cliffside Steam Station
July 2020
ERM Project No.: 0550577
The business of sustainability
ERM

Signature Page
July 2020
Pilot Test Work Plan
Cliffside Steam Station
Denice Nelson, Ph.D., P.E. (MN)
Partner
Jennifer Bryd, P.E.
Technical Director/Engineer-of-Record
ERM NC, Inc.
4140 Parklake Avenue
Suite 110
Raleigh, NC 27612
Brian Wilson, P.G.
Principal Geologist/Program Manager
Wesley May, P.E. (WI)
Technical Director
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PILOT TEST WORK PLAN
Cliffside Steam Station
CONTENTS
CONTENTS
1. INTRODUCTION................................................................................................................................1
1.1 Work Plan Objectives...........................................................................................................................1
2. PROJECT DESCRIPTION.................................................................................................................2
2.1 Conceptual Site Model Overview..........................................................................................................2
2.2 Corrective Action Plan..........................................................................................................................3
2.3 Pilot Test Design Overview...................................................................................................................5
3. PILOT TEST DATA COLLECTION OBJECTIVES............................................................................ 7
4. PILOT TEST IMPLEMENTATION ACTIVITIES................................................................................. 8
4.1 Pilot Test Basis of Design.....................................................................................................................8
4.1.1 Extraction Wells and Subsurface Infrastructure...................................................................8
4.1.2 Node Building....................................................................................................................10
4.1.3 Ancillary Systems...............................................................................................................11
4.1.4 French Drain and Lined Ditch............................................................................................11
4.2 Pilot Test Implementation...................................................................................................................12
4.2.1 Permitting Activities............................................................................................................12
4.2.2 Installation Activities...........................................................................................................12
4.2.3 Construction Quality Assurance.........................................................................................14
4.2.4 Data Collection Activities...................................................................................................14
4.2.5 Scale -Up Activities.............................................................................................................15
4.3 Pilot Test Implementation Schedule...................................................................................................16
TahIP_S
Table 1: Pilot Test Data Quality Objectives
Table 2: Basis of Design Summary
Table 3: Proposed Well Construction Details
Table 4: Effectiveness Monitoring Plan Summary
Figure 1:
Ash Basin Layout Map
Figure 2:
Full -Scale System Design Well Network
Figure 3:
Pilot Test Remedy and Monitoring Layout
Figure 4:
Process Flow Diagram
Figure 5:
Groundwater Extraction Well Schematic
Appendices
Appendix A: Low pH Source Area Alternative Remedial Design Summary Memo
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PILOT TEST WORK PLAN
Cliffside Steam Station
CONTENTS
Acronyms and Abbreviations
Name
Description
AAB
Active Ash Basin
bgs
below ground surface
CAP
Corrective Action Plan
CCR
Coal Combustion Residual
COI
constituent of interest
CSA
Comprehensive Site Assessment
CSM
Conceptual Site Model
DFA
Dry Fly Ash Silos, Transport, and Handling Area
EAB
East Ash Basin
EMP
Effectiveness Monitoring Plan
ft
feet
gpm
gallons per minute
G.S.
North Carolina General Statutes
GSA
Gypsum Storage Area
HASP
Health and Safety Plan
HDPE
high -density polyethylene
HMI
human -machine interface
NCAC
North Carolina Administrative Code
NCDEQ
North Carolina Department of Environmental Quality
NTU
Nephelometric turbidity units
O&M
operation and maintenance
OSHA
Occupational Safety and Health Administration
PLC
programmable logic controller
psi
pounds per square inch
PVC
polyvinyl chloride
U1-4 AB
Units 1-4 Ash Basin
U5 AB
Unit 5 Ash Basin
V
volt
WWTP
wastewater treatment plant
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PILOT TEST WORK PLAN
Cliffside Steam Station
INTRODUCTION
INTRODUCTION
ERM NC, Inc. (ERM) prepared this Pilot Test Work Plan (Work Plan) on behalf of Duke Energy Carolinas
Progress, LLC (Duke Energy) for the Rogers Energy Complex Cliffside Steam Station (the "site") located
in Rutherford and Cleveland counties (Figure 1). This Work Plan provides the details of the proposed
Unit 5 Ash Basin (U5 AB) source area groundwater extraction pilot test for remediation of groundwater as
described in the Corrective Action Plan (CAP) Update prepared by SynTerra Corporation in December
2019 (SynTerra, 2019).
Duke Energy has completed over 16 environmental site assessments of site media associated with coal
combustion residuals (CCR), the detailed findings of which are presented in the CAP. These prior site
assessments, the CAP, and this Work Plan were prepared in accordance with the requirements of
Section 130A-309.21 1 (b) of the G.S., as amended by the 2014 North Carolina Coal Ash Management
Act, and consistent with the North Carolina Administrative Code (NCAC), Title 15A, Subchapter 02L
.0106 corrective action requirements and with the written guidance provided by the North Carolina
Department of Environmental Quality (NCDEQ).
While no unacceptable environmental risk was identified, the remedial actions described herein are
intended to address the applicable North Carolina groundwater standards (NCAC, Title 15A, Subchapter
02L, Groundwater Classification and Standards 02L; Interim Maximum Allowable Concentrations; or
background values, whichever is greater) at or beyond the Geographic Limitation. Constituents of interest
(COI) were detected above the applicable standards at or beyond the Geographic Limitation at three ash
basin areas (Active Ash Basin [AAB], Units 1-4 Ash Basin [U1-4 AB], and Unit 5 Ash Basin [U5 AB]) at the
site.
The CCR impoundments identified above are classified as low -risk (pursuant to N.0 General Statue
Section 130A-309.213[d][1]) as documented by NCDEQ in a letter dated November 13, 2018. These
areas are subject to the applicable closure standards (G.S. Section 130A-309A.214[a][3]).
1.1 Work Plan Objectives
The pilot test objectives are:
Accelerate the corrective action process to meet the applicable groundwater standards at or beyond
the Geographic Limitation,
■ Optimize full-scale system performance by using adaptive design methods based on data collected
during pilot test, and
■ Focus the pilot test on the area currently available for access at the Cliffside site and thereby make
near -term progress towards achieving the applicable standards.
Additional details of pilot test objectives are presented in Section 3.
In addition, this Work Plan provides a description of the project and the planned pilot test area, a
summary of the data objectives for the pilot test, and a discussion of the pilot test design and
implementation details. Data collected from the pilot test will be used to optimize the full-scale remedy.
Parameters such as well capacity, area of hydraulic influence, and concentration reductions will be
evaluated during pilot test implementation. Design modifications will be applied to the full-scale design as
necessary to optimize system performance based on pilot test data.
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PILOT TEST WORK PLAN
Cliffside Steam Station
PROJECT DESCRIPTION
2. PROJECT DESCRIPTION
The purpose of this pilot test is to inform the design of the full-scale remedial system at the site and
achieve the objectives presented in Section 1.1 above. The following section provides a brief description
of the site and a summary of work completed to date. See the CAP for additional details (SynTerra,
2019).
2.1 Conceptual Site Model Overview
A robust Conceptual Site Model (CSM) was developed for the site, which was detailed and presented
graphically in the referenced CAP (SynTerra, 2019). Key elements of the CSM are summarized below.
The site is located in the Piedmont Physiographic Province, which conforms to the general hydrogeologic
framework for the Blue Ridge/Piedmont area, characterized by perennial flow in a slope -aquifer system
within a local drainage basin with a perennial stream (LeGrand 2004). The groundwater system
associated with the site is divided into the following three distinct hydrostratigraphic zones to distinguish
the interconnected groundwater system:
■ Shallow (surficial) flow zone is characterized by residual silty sands or clayey soils, fill and
reworked soils, alluvium, regolith, and saprolite.
■ Deep (transition) flow zone consists of a relatively transmissive zone of partially weathered and
significantly fractured bedrock as defined by drilling refusal.
■ Bedrock flow zone is characterized as slightly weathered to unweathered solid rock fractured to
varying degrees. Bedrock in the area includes volcanic and sedimentary rocks that have been
metamorphosed, intruded by coarse -grained granitic rocks, and subjected to regional structural
deformation. The dominant rock type consists of biotite gneiss and sillimanite schist.
The groundwater system in the natural materials (shallow/transition/bedrock flow zones) is consistent with
the regolith-fractured rock system and is characterized as an unconfined, interconnected groundwater
flow system indicative of the Piedmont Physiographic Province. A conceptual model of groundwater flow
in the Piedmont, which is applicable to Mooresboro, was developed by LeGrand (1988, 1989) and Harned
and Daniel (1992). In accordance with the model, groundwater is recharged by drainage and rainfall
infiltration in the upland areas followed by discharge to the perennial stream. Flow in the unconfined
regolith (shallow and deep aquifer zones) follows porous media principles, while flow in bedrock occurs in
joints and fractures. The groundwater flow direction is controlled by divides observed south, east, and
west of the site. Groundwater on the basin side of divides flows towards the ash basins, while
groundwater on the opposite side flow away from the basins. The groundwater flow direction provides
natural hydraulic control of ash basin constituent migration. The predominant site groundwater flow
direction is north toward the Broad River, with a portion, in the site center, flowing towards Suck Creek.
Calculated horizontal groundwater flow velocities are approximately 77, 93, and 84 feet (ft) per year in the
shallow, deep, and bedrock flow zones, respectively, using April 2019 groundwater elevation data
(SynTerra, 2019). The physical extent of COI migration to the north, northeast, and northwest of the AAB,
northeast of the 1_11-4 AB, and to the north and northeast of the U5 AB is limited and controlled by
hydrologic divides, dilution from unaffected groundwater, and the groundwater -to -surface -water discharge
zones. Geochemical processes stabilize and limit certain constituent migration along the flow path, and
COI in groundwater are contained within Duke Energy's property boundaries. The extents of COI -
affected groundwater associated with the ash basins have been characterized.
A brief summary of the key conclusions of the CSM presented in the CAP include:
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PILOT TEST WORK PLAN
Cliffside Steam Station
PROJECT DESCRIPTION
■ Groundwater from the ash basins and coal pile area has not and does not flow toward any water
supply wells in the area around the site due to the groundwater flow system described above;
■ No indication of completed exposure pathways that would contribute to an increase in risk to
human health based on the results of the site -specific human health risk assessment;
■ No indication of increased risk to ecological receptors based on the results of the site -specific
ecological risk evaluation;
■ Groundwater/surface water interaction has not caused, and is not predicted to cause, COI at
concentrations greater than NCAC, Title 15A Subchapter 02B, Surface Water and Wetland
Standards;
■ The aquatic systems in the Broad River adjacent to the site are healthy based on multiple lines of
evidence, including robust fish populations and species variety, based on years of sampling data.
■ Ash basin and underlying groundwater system is primarily a horizontal flow system with limited
downward COI migration;
■ Horizontal COI distribution at or beyond the Geographical Limitations is spatially limited due to
presence of hydrologic divides, dilution, and groundwater -to -surface water discharge zones; and
■ A plume stability analysis using statistical methods was performed on 61 monitoring wells in the
Unit 5 area using 1,037 individual data sets and found that 92 percent of the valid data sets had
decreasing, stable, no trend or non -detect conditions (Arcadis, 2020).
The corrective actions presented in the CAP and this Work Plan are based on the above findings.
Additional information obtained during pilot test implementation will be used to confirm and possibly
further refine the CSM in the future as appropriate.
2.2 Corrective Action Plan
The CAP identifies three source areas at the site identified for active groundwater corrective action due to
the presence of COI at or beyond the Geographic Limitation (SynTerra, 2019). These areas, as well as
the respective Geographic Limitations, are shown on Figure 1 and are described below.
■ Active Ash Basin (AAB): This area is located on the eastern portion of the site, east of Units 5
and 6.
■ Units 1-4 Ash Basin (U1-4 AB): This area is located immediately east of the retired units 1-4.
■ Unit 5 Ash Basin (U5 AB): This area is located on the western portion of the site, west and
southwest of Units 5 and 6. Pilot test activities will be conducted in this area.
The CAP summarizes a multi -component corrective action approach to address each of the above source
areas at the site that includes implementation of the following:
■ Source control (i.e., ash basin excavation and decanting);
■ An Effectiveness Monitoring Plan (EMP); and
■ A Confirmatory Monitoring Plan in areas of the site that do not have COI beyond the Geographic
Limitation.
The CAP evaluated multiple potential active groundwater corrective action technologies for the site,
assessing each based on its effectiveness in achieving the remedial objectives and constructability based
on site -specific constraints. Criteria from the NCDEQ CAP Guidance were included in the corrective
action alternative screening process (NCDEQ 2019). Site -specific groundwater modeling simulations
were performed to evaluate the effectiveness of each potential alternative to facilitate selection of the
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PILOT TEST WORK PLAN PROJECT DESCRIPTION
Cliffside Steam Station
most appropriate corrective action approach. The methodology and results of these modeling simulations
were summarized in Appendices G and H of the CAP (SynTerra 2019). A summary of the selected
groundwater corrective action technologies identified in the CAP, as well as the remedial goals for each
source area are presented below.
Source Area
Remedial Goal
Selected Remedy
Reduce COI concentrations to below
Groundwater extraction with clean water
AAB
applicable North Carolina Standards at or
infiltration
beyond Geographic Limitation.
Reduce COI concentrations to below
Phytoremediation using deep-rooted
U1-4 AB
applicable North Carolina Standards at or
TreeWellsT"'
beyond Geographic Limitation.
Reduce COI concentrations to below
U5 AB
applicable North Carolina Standards at or
Groundwater extraction
beyond Geographic Limitation.
A combination of groundwater extraction and clean water infiltration at the AAB, phytoremediation at the
U1-4 AB, and groundwater extraction with source control at the U5 AB was determined to be the most
appropriate corrective action approach for the site based on evaluation of remedial alternatives compared
to NCDEQ decision criteria. The intent of the extraction and clean water infiltration system design is to
address migration of COI -affected groundwater at or beyond the Geographic Limitation. The CAP fate
and transport modeling predicts that the clean water infiltration wells will help to address potential COI in
the vadose zone. The full-scale groundwater extraction and clean water infiltration corrective action
planned for implementation is shown on Figure 2. Currently, a total of 45 vertical extraction wells to target
the saprolite/transition/bedrock flow zone, 46 vertical infiltration wells to target the
saprolite/transition/bedrock zone, and one horizontal infiltration well to target the saprolite zone between
the AAB and the Broad River as part of the full-scale system. Additionally, 285 phytoremediation
TreeWelISTI are proposed to be installed over the 2.56 acres to the northeast of the U1-4 AB.
The remainder of this Work Plan and the pilot test activities described herein are focused on the U5 AB
groundwater extraction remedy.
Unit 5 Ash Basin Pilot Test Overview
The U5 AB received CCR from 1972 to 1980. Site operations currently consist of dry ash handling and
the ash is disposed of on -site at the Coal Combustion Products landfill. Ash within the Unit 5 basin will be
excavated as part of the basin closure program, which constitutes source removal.
The COI associated with the U5 AB appear to be related, in part, to an area of low pH surface water
located in the southern and western portions of the stormwater ditch adjacent to Cooling Tower B
identified during site assessment activities. This area may be related to the U5 AB saddle dam. See
Figure 6-73 from the CAP (SynTerra, 2019).
The CAP describes the following as the main components of the corrective action design at the U5 AB.
■ Installation of 12 vertical groundwater extraction wells screened in the saprolite (shallow) and
transition (deep) flow zones;
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PILOT TEST WORK PLAN
Cliffside Steam Station
PROJECT DESCRIPTION
■ Installation of a groundwater extraction trench to recover low pH surface water discharging south
and west of Cooling Tower B and to hydraulically control local groundwater in the shallow flow
zone; and
■ Discharging of groundwater and surface water to the plant wastewater treatment system.
ERM was tasked with preparing a detailed design of the groundwater recovery trench described in the
CAP; however, several potential issues related to safety and constructability of the deep recovery trench
were identified during preliminary design activities. The identification of these concerns led ERM to
evaluate alternative groundwater recovery systems that could effectively mitigate or reduce these safety
and constructability risks while also meeting the remedial objectives. This evaluation identified an
alternative remedial approach that meets both of these criteria, by replacing the 20-foot deep
groundwater recovery trench with installation of 10 additional vertical groundwater extraction wells
(approximately 30 to 40 ft deep) spaced linearly at approximate 25-ft intervals, a shallow French drain (up
to 6 ft deep and extending approximately 150 ft in length), and lining of the existing low pH section of the
current stormwater ditch, which is approximately 380 feet in length. A summary of this evaluation process
and the technical justification for selection of an alternate remedial design approach for the low pH source
area downgradient of the U5 AB saddle dam at the site is provided in Appendix A of this Work Plan.
The pilot test phase will consist of the installation of 12 groundwater extraction wells, as described in the
CAP, focused on reducing COI concentrations in groundwater beyond the Geographic Limitation based
on modeling simulations performed for the area. In addition, a source control system for the low pH
surface and groundwater consisting of 10 additional shallow vertical groundwater extraction wells, a
shallow French drain, and lining of the associated ditch is proposed in lieu of the groundwater extraction
trench system included in CAP. The extraction wells will provide hydraulic capture to address the area of
low pH groundwater that appears to be allowing certain COI to go into solution. Additionally, the pilot test
will include the installation of three new groundwater monitoring wells to facilitate monitoring of pilot test
system effectiveness. Locations of the proposed extraction and monitoring wells and shallow source
control area are shown on Figure 3. Results from the pilot test will be used to inform the planned full-
scale system in the AAB area and to adjust the system design in the Unit 5 area if necessary.
2.3 Pilot Test Design Overview
The U5 AB area was selected for pilot testing because it is currently available for implementation, and will
enable Duke Energy to begin making progress towards it corrective action objectives at the Cliffside
Station. The pilot test will consist of groundwater extraction from the 22 proposed vertical groundwater
extraction wells in the vicinity of the U5 AB, as well as installation of an approximate 150-ft long shallow
French drain and lining of an existing stormwater ditch to reduce low pH seep and surface water
infiltration into shallow groundwater within the source control area. Figure 3 presents the layout of the
pilot test extraction wells and conveyance systems. A Process Flow Diagram is presented as Figure 4.
Buried piping will convey extracted groundwater from the extraction well network and French drain in the
source control area to a collection point or "node." The node building will provide a location for power,
controls, communication, and subsequent extracted groundwater transfer. Extracted groundwater will be
conveyed from a holding tank within the node building into existing facility wastewater infrastructure,
ultimately reaching the existing facility wastewater treatment plant (WWTP). In the WWTP, the extracted
groundwater will combine with waste water from other areas of the facility and will be subjected to flow
equalization, pH neutralization, coagulation, flocculation, and filtration steps before being discharged
through Outfall 005 under the facility's existing National Pollutant Discharge Elimination System (NPDES)
permit.
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PILOT TEST WORK PLAN
Cliffside Steam Station
PROJECT DESCRIPTION
Extraction well arrangement and spacing has been determined based on the results of site -specific
groundwater capture zone modeling simulations presented in the CAP and Appendix A of this Work
Plan. The total anticipated groundwater flow rate for the pilot test is approximately 35 gallons per minute
(gpm). The expected contribution of groundwater from the individual pilot test extraction wells ranges from
0.6 to 2.7 gpm. The expected combined contribution from the source control area wells is approximately
10 gpm. The intent of the pilot study is to confirm that these rates are appropriate and provide sufficient
data to inform the design for the full-scale system located in the AAB area. The AAB requires excavation
of the Former Ash Storage Area to gain access for corrective action activities in this area. The final
number of wells in the full-scale system may be subject to change based on the results of the pilot study
described within this Work Plan.
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PILOT TEST WORK PLAN PILOT TEST DATA COLLECTION OBJECTIVES
Cliffside Steam Station
3. PILOT TEST DATA COLLECTION OBJECTIVES
The primary objectives of the pilot test are to:
■ Accelerate the corrective action process to meet the Consent Order obligation of meeting
applicable groundwater standards at or beyond the Geographic Limitation.
■ Focus the pilot test on the most challenging and accessible area at the Cliffside site and thereby
make near -term progress towards achieving the above -referenced standards.
■ Optimize full-scale system performance by using an adaptive design approach based on data
collected during pilot test
Pilot test data collection objectives have been defined and are presented in Table 1. The data collection
objectives include evaluation of well capacities, the area of hydraulic influence, the hydraulic connectivity,
and reductions in groundwater COI concentration. Hydrogeologic testing of extraction wells will assess
well performance, and will also advance the understanding of site hydraulic influence as part of ongoing
groundwater remediation activities. Hydrogeologic testing is discussed in more detail in Section 4.2.4.1.
Operational data will be collected from the system during the pilot test to assess performance. Extraction
well flowrates, groundwater elevations, and other operational parameters will be collected to provide
feedback for system optimization and performance. Collection of operational data is discussed in more
detail in Section 4.2.4.2.
The results of the pilot test will be used to evaluate the effectiveness of the selected remedy and
potentially provide refinement of the CSM. The results may also determine the hydrogeologic design
parameters for expansion and/or optimization of the extraction well network during subsequent phases of
the remedy.
In addition to the hydrogeologic testing and collection of operational data, Duke Energy has prepared an
EMP as discussed and presented in Appendix O of the CAP. The EMP includes groundwater monitoring
network for the AAB, 1_11-4 AB, and U5 AB source areas based on site -specific COI mobility and
distribution. The EMP is designed to be adaptable and targets key areas where changes to groundwater
conditions are most likely to occur during corrective action implementation and basin closure activities.
The EMP includes provisions for a post -closure monitoring program in accordance with G.S.
Section 130A-309.214(a)(4)k.2 upon completion of ash basin closure activities. A summary of the EMP is
presented in Table 4. A more detailed site -specific pilot test monitoring plan will be submitted to the
NCDEQ prior to pilot test implementation to augment the EMP. This monitoring plan will include details
regarding such items as sampling frequency, parameter list, and well locations that will be used to
determine the effectiveness of the pilot test program.
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PILOT TEST WORK PLAN PILOT TEST IMPLEMENTATION ACTIVITIES
Cliffside Steam Station
4. PILOT TEST IMPLEMENTATION ACTIVITIES
The following sections provide the design details and pilot test implementation activities planned to
achieve the data collection objectives described in Section 3. As previously indicated, an adaptive design
approach will be used to optimize implementation and performance of the full-scale groundwater
remediation system.
4.1 Pilot Test Basis of Design
The pilot test design incorporates approximately 30 percent of the full-scale system (including the AAB
area) and includes groundwater extraction from the U5 AB area, where COI -affected groundwater is
present in the shallow saprolite and underlying transition flow zones. The basis of design elements for the
pilot test system are summarized in Table 2. Additional details regarding pilot test system design and
construction to address COI -affected groundwater in the U5 AB are provided in the following subsections.
4.1.1 Extraction Wells and Subsurface Infrastructure
The pilot test system at the U5 AB will consist of 22 vertical extraction wells (EX-U5-1 through EX-U5-22)
installed in the vicinity of the Cooling Towers A and B area, installation of a shallow French drain south
and west of Cooling Tower B, and the lining of the stormwater ditch along the southern and western
perimeter of Cooling Tower B area. Extraction wells EX-1_15-1 through EX-1_15-12 will be installed to
approximate depths varying from 110 to 142 ft below ground surface (bgs) and will primarily consist of
boreholes screened from depths ranging from 25 to 142 ft bgs. The anticipated yield from these 12
deeper extraction wells ranges from 0.6 to 2.7 gpm, for an anticipated total combined extraction rate of
approximately 25 gpm. Shallow source area extraction wells EX-U5-13 through EX-U5-22 will be installed
in a linear spacing at approximate 25-ft intervals, parallel to the existing stormwater ditch in the source
control area, to a depth of approximately 30 ft bgs. The 10 shallow source area extraction wells are
anticipated to yield a combined total extraction rate of approximately 10 gpm based on site -specific
capture zone modeling results (Appendix A).
All extraction well pump discharge will be conveyed to a single central extraction and control compound
(i.e., node building) located south of Cooling Tower A. All extraction well conveyance lines will be
combined via a well header and directed to a small capacity (e.g., 1,000-gallon) holding tank. Extracted
groundwater pumped into the holding tank will be conveyed via an existing underground line to the
Basement Basin, where it will combine with waste water from other areas of the facility and undergo
treatment at the existing facility WWTP before ultimately discharging through Outfall 005 under the
facility's existing NPDES permit. The extraction well network will be interlinked with communications,
alarms, and controls located within the node building to synchronize groundwater extraction rates in order
to achieve the desired hydraulic capture and facilitate effluent discharge.
The layout of the pilot -scale system and source control area is shown on Figure 3. A process flow
diagram is shown on Figure 4. An example extraction well schematic is provided as Figure 5.
4.1.1.1 Extraction Wells
The 12 extraction wells (EX-U5-1 through -12) described in the CAP, as well as the additional 10 shallow
extraction wells (EX-1-15-13 through -22) proposed in the source recovery area (Appendix A), will be
completed to the approximate depths specified above and on Table 3. Extraction well boreholes will be a
minimum of 10 inches in diameter and may be installed using air -rotary and/or rotosonic drilling methods.
The extraction wells will be constructed of a 6-inch diameter schedule 40 or 80 polyvinyl chloride (PVC)
riser and screened using wire wrapped stainless steel, where screen slot size and filter pack will be
designed in accordance with site -collected grain size data, at the depths specified in Table 3. A 2- to
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PILOT TEST WORK PLAN PILOT TEST IMPLEMENTATION ACTIVITIES
Cliffside Steam Station
3-ft-thick layer of hydrated bentonite chips will seal the casing from the grout above, and the remainder of
the well annulus will be grouted with a neat cement grout. Adjustment to riser length and total well depths
may be made based on observed field conditions. All wells will be installed and sealed in accordance with
NCAC, Title 15A, Subchapter 2C.100 Well Construction Standards and with construction overseen by a
qualified environmental professional.
At the time of installation, all wells will be temporarily completed with a 12-inch diameter monitoring well
manhole. Well construction details for the groundwater extraction wells are shown on Figure 4.
4.1.1.2 Groundwater Extraction Pumps
Extraction well pumps will be approximately 0.5 to 1 horsepower electric submersible well pumps (e.g.,
Grundfos Redi Flo). The pumps will be a 230-volt (V) single-phase or 480-V three-phase electric multi-
stage submersible type and will discharge through a 1- to 2-inch diameter steel riser pipe. Centralizing
spacers will be placed at regular 50-ft intervals along the discharge riser to keep the pump centered in the
casing.
Each pump will be installed with in -well level controls (e.g., high and low level switches) in order to control
and protect the pump against run dry running conditions. Pump savers will also be installed to protect the
pump from dry well, over and under voltage, rapid cycling, and jammed pump conditions.
Upon system startup, extraction well performance will be evaluated to determine groundwater drawdown
shut-off points based on operating conditions to develop an operational strategy that achieves the desired
hydraulic capture. Upon refinement of the operational strategy, pumps will be operated continuously if
sufficient groundwater flow can be achieved or, if continuous flow cannot be maintained, intermittently
based on the well level switches.
4.1.1.3 Extraction Well Vaults
A concrete vault will be placed over the wellhead of each extraction for protection. The vault will be
equipped with an H-20-rated steel or aluminum access hatch. The size of the well vault will be determined
during completion of the pilot test detailed design. The bottom of the vault will be concrete to provide
containment if a leak were to occur within the vault. A float switch will be placed into each well vault to
shut down the extraction pump and alert the operators if water is present in the vault above the set point
of the level switch.
The vault will contain the transition from the riser piping to the below -grade conveyance piping. An
isolation valve and pressure gauge will be installed within the vault. In addition to the piping, electrical
junction boxes will be installed in each vault for termination of the power lead from the pump and control
wiring from the down -well level switches. Penetrations through the wall or base of the vault will be sealed
with grout or caulk.
4.1.1.4 Conveyance Piping
Each extraction well will have a dedicated conveyance pipe running from the wellhead to the designated
node building. This will allow for metering (both mechanical and digital) and well performance monitoring
in a central location and will minimize disturbance to each facility's operations during operation and
maintenance (O&M) visits. Extraction well conveyance piping will be a minimum of 2-inch nominal
diameter high -density polyethylene (HDPE) to allow for cleaning, if necessary.
Flow from the node building will discharge to the Basement Basin. The header pipe will be constructed of
four -inch -diameter HDPE and will include isolation valves and other appurtenances where appropriate.
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PILOT TEST WORK PLAN
Cliffside Steam Station
PILOT TEST IMPLEMENTATION ACTIVITIES
The conveyance and header piping will be installed within a common trench at a minimum depth of
30 inches. The trench will be backfilled with the soil excavated from the trench. If the excavated soil is
determined to be unsuitable for use as backfill, soil from other on -site location or imported fill will be used
as backfill. Backfill material will be compacted during placement.
A number of spare conveyance pipes will be included to support potential future expansion requirements
and repair in the case of pipe failure/fouling. The spare conveyance pipes will be strategically located and
stubbed up at the ground surface to facilitate potential future system modification, if necessary.
4.1.1.5 Electrical and Control Conduit
Conduit will be installed from the control building to each extraction well vault. The conduit will carry the
electrical conductors to power the submersible pumps as well as the control wiring for the controls located
in the vault and within the well. Buried conduit will be constructed of either PVC or HDPE. Handholds will
be placed as necessary to facilitate installation of the power and control wiring.
The conduit will be installed in a common trench with the conveyance and header piping. The trench will
be backfilled with the soil excavated from the trench. If the excavated soil is determined to be unsuitable
for use as backfill, soil from another on -site location or imported fill will be used as backfill. Backfill
material will be compacted during placement.
4.1.2 Node Building
The node building will consist of a manifold, flow meters, valves and gauges, sampling ports, a 500- to
1,000-gallon HDPE equalization/holding tank, transfer pump(s), and a system controls cabinet with a
programmable logic controller (PLC) and human -machine interface (HMI). All extracted groundwater will
be pumped through a manifold where it will be combined and then directed to the holding tank located at
each node building. Level switches in the holding tank will control a transfer pump, which will pump the
accumulated groundwater for conveyance to the Basement Basin via the header piping shown on
Figures 2 and 3. A high -high level switch will be installed in each holding tank to shut down the extraction
wells in the event the transfer pump fails.
4.1.2.1 Groundwater Manifold
Each leg of the groundwater manifold will convey flow from individual wells before combining. The legs
will be fitted with various components such as a pressure indicator, sample port valve, manual flow
control/isolation valve, flow meter, and check valve. Sample port valves will be placed in the manifold legs
to allow for water sample collection for observation and sampling. Flow control and isolation valves will be
utilized for preventing backflow, allowing manual throttling of flow, and isolation during service intervals.
The instantaneous flow rate and total volume of extracted groundwater for each extraction well will be
measured using a flow meter contained within each node building. The flow meters will transmit flow rate
and flow total to the PLC/HMI where it will be continuously logged, stored, and reported daily/weekly to
the system operator(s). The mechanical flow totalizers will provide redundant data in the event of data
loss or flow meter failure.
4.1.2.2 Holding Tank and Transfer Pump
All extraction wells and the French drain will discharge to a common collection header and holding tank.
The holding tank transfer pump will discharge all extracted water to the existing Basement Basin where it
would be comingled with existing facility process water. The extracted water will be treated and
discharged through the site WWTP at NPDES-permitted Outfall 005. The discharge location is shown on
Figure 3.
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PILOT TEST WORK PLAN
Cliffside Steam Station
PILOT TEST IMPLEMENTATION ACTIVITIES
The size of the header pipe and capacity of the holding tank will be determined based on actual well
yields following installation. The instantaneous flow rate and total flow will be measured with a paddle
wheel or similar flow meter. The total flow rate will also be measured using a mechanical flow totalizer.
The mechanical flow totalizer will provide redundant data in the event of data loss or flow meter failure.
The discharge from the system will be interlocked with any controls for the WWTP discharge line as
needed for safe operation.
4.1.3 Ancillary Systems
4.1.3.1 Electrical Service and Distribution
Main supply will be a 480/277 VAC, three-phase, 200 ampere service. Where possible, connections will
be made to existing facility electrical distribution and will be regulated down from a higher voltage,
3-phase service using a transformer where necessary. If connection to existing facility distribution is not
possible, a new power drop will be installed. All extraction pumps, transfer pumps, PLCs, and other
equipment will be operated on a single- or three-phase 120/240/480-V service at 60 hertz. Each node
building will include one or more 120-V power outlets and industrial -style ceiling lights.
4.1.3.2 Communications
Each pump controller will be connected to the central PLC/HMI, which will provide data logging functions.
Individual extraction well flow rates and total flows will be accessible via remote telemetry and supervisory
control and data acquisition system, minimizing the frequency of O&M visits.
The main control panel will include a PLC/HMI used to control all system operations. The PLCs from each
node building will have remote communication capabilities to facilitate intercommunication, alarms and
interlock callouts, and site -wide operational control. The system operator will be able to access the
system and data remotely through a personal computer, tablet, or smartphone interface that has the
same view, functionality, and levels of permissions as the on -site HMI touchscreen display.
4.1.4 French Drain and Lined Ditch
The French drain system designed to provide hydraulic capture to address an area of low pH surface
water and near surface groundwater proximate to the U5 AB. The system will include the installation of a
shallow French drain and lining of an existing stormwater ditch, in addition to the 10 shallow vertical
groundwater extraction wells (EX-U5-13 through -22) (see Figure 3). The French drain is planned to be
constructed roughly parallel to the existing stormwater ditch, with a geomembrane lining the base and
sidewalls, overlain by a horizontal six-inch diameter perforated HDPE pipe and drain stone to surface to
allow flow and collection of seep and surface water. The dimensions of the French drain are currently
planned to be approximately 150 ft in length and three ft in width, extending to an approximate depth of
up to six ft bgs.
Seep and surface water collected in the French drain will gravity feed to the north and collect in the
French drain sump, where it will be pumped into the source area groundwater extraction well conveyance
piping, routed through the extraction system's node building, and eventually discharged to NPDES Outfall
005 following treatment at the facility's WWTP. The existing stormwater ditch will be lined with an
impermeable material to reduce low pH seep or surface water infiltration into shallow groundwater within
the source control area. The combination of the shallow French drain, lined stormwater ditch, and shallow
vertical extraction wells will meet or exceed the modeled performance of the previously proposed deep
recovery trench, while also reducing safety and constructability risks (Appendix A).
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PILOT TEST WORK PLAN PILOT TEST IMPLEMENTATION ACTIVITIES
Cliffside Steam Station
4.2 Pilot Test Implementation
The above -referenced design elements will be incorporated with permitting, installation and construction,
start-up, and data collection activities as part of pilot test implementation. The following sections describe
each of these components planned during implementation of the pilot test phase.
4.2.1 Permitting Activities
Duke Energy is in the process preparing, or has submitted permit applications, for the NCDEQ's review
and approval necessary to implement this work. A summary of the permits required for the Cliffside
Station pilot test includes the following:
■ Groundwater Recovery Well Permit — Permit required to construct any well or well system
installed to recover COI -affected groundwater or other liquids from the subsurface. Well
construction information and a map of proposed locations was included in the permit application
submitted to the NCDEQ on July 1, 2020.
■ Erosion and Sediment Control (E&SC) Plan — Permit required for construction -related land
disturbance activities greater than one acre, which will apply to the pilot test. The E&SC Plan
express review was held on June 10, 2020 and NCDEQ's final approval was provided on June
24, 2020.
■ Existing NPDES Permit (NC0005088) — A permit modification is required to discharge extracted
treated groundwater through Outfall 005. Duke Energy submitted a permit application
amendment to NCDEQ dated May 29, 2020.
4.2.2 Installation Activities
The following sections provide brief descriptions of the anticipated activities required to implement the
pilot test. An adaptive strategy will be used to ensure flexibility in design and implementation schedule.
Installation activities will be coordinated with unrelated on -site activities to avoid conflicts.
4.2.2.1 Extraction Well Installation and Development
Prior to mobilization, an initial well location siting survey will be completed. Additionally, a thorough
evaluation of underground utilities will be completed in the vicinity of proposed activities subsurface
disturbance activities (i.e., drilling, trenching, or substantial grading) prior to initiating intrusive subsurface
work. All extraction wells will be installed by a North Carolina -licensed well driller in accordance with North
Carolina Subchapter 2C Well Construction Standards (NCDENR 2009) state regulations following the
methods described in Section 4.1.1.1 above. Well construction records for each extraction well will be
prepared and submitted to NCDEQ by the licensed well driller following installation. A qualified
environmental professional will provide field oversight of well installation activities to log subsurface
conditions and direct well construction accordingly. Proposed well construction details are provided in
Table 3.
Extraction wells will be developed no sooner than 48 hours following installation using surging, jetting,
and/or pumping techniques and shall first be pumped and surged for approximately two hours to remove
formation materials and sediment. Development progress will continue until the primary criterion for well
development, clear water and less than 10 Nephelometric turbidity units (NTU) as suspended solids, has
been achieved. The target of 10 NTU is selected based on the rationale provided in the Statistical
Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash
Facilities (Duke Energy Carolinas, LLC, 2017). If turbidity of 10 NTU cannot be achieved, well
development will be deemed complete upon stabilization of turbidity readings. Additionally, during
development, pH, specific conductivity, temperature and turbidity should be monitored frequently to
establish natural conditions and evaluate whether the well has been completely developed based on
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PILOT TEST WORK PLAN
Cliffside Steam Station
PILOT TEST IMPLEMENTATION ACTIVITIES
parameter stabilization. Following installation, the new well will be surveyed by a North Carolina -licensed
surveyor.
4.2.2.2 Waste Management Plan
Wastes generated during the remedy implementation will include concrete, asphalt, soils, drill cuttings,
groundwater, and purge water. Wastes will be managed on -site or recycled off -site. If a waste cannot be
managed on -site or recycled, the waste will be profiled according to the requirements of the approved
disposal facility prior to transportation off -site.
Excavation and drilling -derived solid waste, which may consist of soil, concrete, and asphalt, and will be
managed by the facility consistent with ongoing applicable waste management practices. Wastes deemed
not appropriate for on -site management will be stored on -site in stockpiles, 55-gallon drums, or other
Department of Transportation —regulated containers and disposed at an appropriately licensed off -site
disposal facility at the direction of Duke Energy and in accordance with local, state, and federal
regulations.
Personal protective equipment, drilling expendables (e.g., packaging, sand/cement bags, and general
refuse), plastic, and related consumable material will be disposed as municipal waste.
Liquid waste, which will consist of decontamination fluids and well development water, will be managed at
the facility's existing WWTP. Liquid wastes deemed not appropriate for on -site management will be stored
on -site in properly labelled drums or other Department of Transportation —regulated containers and
disposed off -site.
4.2.2.3 Surveying
A North Carolina —licensed surveyor will survey the locations and elevations of the new extraction and
monitoring wells following installation. The locations and elevations will be referenced to the horizontal
and vertical benchmarks established for the site (i.e. State Plane Coordinates). The survey results will be
accurate to ±0.01 ft vertically and ±0.1 ft horizontally using vertical control datum NAVD 88.
Locations of the vaults, trenches, node building, spare pipe/conduit end points, and other key buried
infrastructure will be measured in the field to develop "as -built" drawings of the pilot scale system. All field
measurements will be taken with a measuring wheel, tape measure, or other means of providing accurate
measurements. Survey data will be generated for these locations if deemed necessary and feasible. An
"as -built" set of drawings will be developed based on the measurements taken in the field during
construction.
4.2.2.4 Extraction and Node Building Installation
Node building construction details will be determined during final pilot test system design. Modular
elements of the system that can be fabricated off -site will be utilized to the extent practical. This may
include the use of 8 ft by 40 ft intermodal shipping containers (e.g., seabox). Node buildings will house
process equipment and provide a secure and climate -controlled environment. Where practical, node
building equipment (i.e., control panels, piping headers, tank connections, etc.) will be fabricated off -site,
installed within a pre -fabricated enclosure, and delivered to the site in a semi -complete condition and the
final assembling will be completed on -site.
Buried infrastructure associated with the pilot test system installation includes all conveyance pipe
(including spares), well electrical and instrumentation conduit, extraction well vaults, clean -out vaults,
electrical handholds other non -specified access vaults, and the discharge tie-in location.
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PILOT TEST WORK PLAN
Cliffside Steam Station
PILOT TEST IMPLEMENTATION ACTIVITIES
Site preparation such as grading or foundation construction may be required prior to placement of the
node buildings to provide adequate structural support. A generalized construction sequence follows:
■ Marking of utilities;
■ Site clearing and grubbing;
■ Well installation and development;
■ Trenching/buried infrastructure installation;
■ Node building site preparation;
■ Node building placement;
■ Field pipe and conduit connections to node building;
■ Wire installation;
■ Down well equipment installation;
■ Electric service installation;
■ Quality control testing; and
■ Shakedown and system startup.
Work will be performed in compliance with applicable local and county codes. In addition, work will be
performed in accordance with the latest editions of U.S. National Electrical Code of the National Fire
Protection Association, the National Electrical Safety Code, the American Institute of Steel Construction,
OSHA, and Electrical Licensing Board.
4.2.3 Construction Quality Assurance
4.2.3.1 Inspection and Testing of Conveyance Piping
Quality assurance testing of installed piping will involve visual inspection for construction defects and
quantitative hydrostatic pressure testing following standardized practices (e.g., ASTM E1003), in addition
to Duke Energy requirements. Any failed inspections or tests will result in repair and retesting.
4.2.3.2 Startup Testing
Startup testing and troubleshooting will occur following completion of construction activities and is
estimated to last approximately 2 to 4 weeks. Startup testing will include operational testing of installed
equipment and controls to confirm operation within the design parameters. Additionally, the alarm and
telemetry systems will be functionally tested to verify that data is properly recorded and communicated.
Sampling will be conducted to establish baseline COI concentrations for the system. Startup testing
results will be documented in a construction completion report.
4.2.4 Data Collection Activities
4.2.4.1 Hydraulic Testing Data Collection
In addition to the significant hydraulic data to be obtained during implementation of the pilot test,
additional short-term hydraulic testing of individual extraction wells will be performed shortly following
installation to help confirm modeling simulation results and inform full-scale system design. A sub -set of
the extraction wells will be hydraulically stress -tested to assess individual well performance respective of
expected pumping rate. Hydraulic testing will advance the data quality objectives discussed in Table 1
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PILOT TEST WORK PLAN
Cliffside Steam Station
PILOT TEST IMPLEMENTATION ACTIVITIES
such as well capacity and area of hydraulic influence. The hydraulic testing Standard Operating
Procedure is briefly summarized as follows:
■ Install a pump and transducer within a pilot test extraction well for hydraulic testing, plus
transducers in nearby extraction and/or observation wells where feasible for monitoring during
hydraulic testing;
■ Conduct a step-down and recovery test (up to 8 hours); and
■ Conduct a long-term (up to 48 hours), constant -rate pumping test.
The resulting data will be analyzed to inform decision -making for both individual well and overall system
operations. Water generated during the hydraulic testing activities will be containerized in frac tanks
temporarily placed in the vicinity of the wells, prior to being pumped into conveyance piping and treated
by the facility's existing WWTP.
4.2.4.2 System Performance Data Collection
Following system startup, select operational data will be logged on a set interval. The data will support the
criteria of Table 1. System data collection will likely consist of:
■ Instantaneous extraction flow for each well;
■ Total flow extracted from each well;
■ Operational run-time; and
■ Groundwater elevation (i.e., draw -down) in the extraction wells.
This data will be accessible through direct -read instrumentation, PLC data logging files, and remote
telemetry. The data will be used to evaluate the operational performance of the system against design
parameters.
4.2.4.3 Effectiveness Monitoring Plan Data Collection
The EMP, included in Table 4, will be followed to provide comprehensive data collection, evaluation, and
reporting on the overall effectiveness of the selected remedy. While the EMP's applicability goes beyond
the pilot test, it will provide key data to inform the requirements of the data quality objectives included in
Table 1. The EMP includes:
■ Semi-annual groundwater monitoring of the EMP Groundwater Monitoring Network and analysis
of selected field and laboratory parameters; and
■ Annual effectiveness evaluation and reporting.
To augment the EMP, a more detailed site -specific pilot test monitoring plan will be submitted to the
NCDEQ prior to pilot test implementation. This monitoring plan will include details regarding such items as
sampling frequency, parameter list, and well locations that will be used to determine the effectiveness of
the pilot test program.
4.2.5 Scale -Up Activities
Data collected as part of the hydraulic testing, system performance data collection, and EMP data
collection, will collectively inform decisions regarding scale -up of the groundwater corrective action to full-
scale in the AAB area.
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PILOT TEST WORK PLAN
Cliffside Steam Station
PILOT TEST IMPLEMENTATION ACTIVITIES
4.3 Pilot Test Implementation Schedule
The following provides the anticipated estimated schedule to complete the key milestones of this Work
Plan.
■ Permits applications (June — July 2020)
■ Begin extraction well network installation (July 2020)
■ Contracting (October 2020)
■ Extraction well network installation (October 2020)
■ Extraction well hydraulic testing (December 2020)
■ Construction of groundwater extraction system (March 2021)
■ Pilot test system startup (March 2021)
■ EMP implementation and pilot test data collection (ongoing following start-up)
■ Scale -up activities (to -be -determined)
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PILOT TEST WORK PLAN
Cliffside Steam Station
REFERENCES
5. REFERENCES
Duke Energy Carolinas, LLC. 2017. Statistical Methods for Developing Reference Background
Concentrations for Groundwater and Soil at Coal Ash Facilities. Prepared by HDR Engineering,
Inc. and SynTerra Corporation in May 2017.
Harned, D., and C. Daniel. 1992. The Transition Zone Between Bedrock and Regolith: Conduit for
Contamination. In Daniel, C.C., White, R., and Stone, P., eds., Groundwater in the Piedmont,
Proceedings of a Conference on Ground Water in the Piedmont of the Eastern United States,
Charlotte, N.C., Oct. 16-18, 1989. Clemson, SC: Clemson University (336-348).
LeGrand, H. 1988. Region 21, Piedmont and Blue Ridge. In: J. Black, J. Rosenshein, P. Seaber, ed.
Geological Society of America, 0-2, pp 201-207.
LeGrand, H. 1989. A conceptual model of ground water settings in the Piedmont region, in groundwater in
the Piedmont. In: Daniel C., White, R., Stone, P., ed. Ground Water in the Piedmont of the
Eastern United States. Clemson, SC: Clemson University, pp 317-327.
LeGrand, H. 2004. A master conceptual model for hydrogeological site characterization in the Piedmont
and Mountain Region of North Carolina: A guidance manual. North Carolina Department of
Environment and Natural Resources, Division of Water Quality, Groundwater Section Raleigh,
NC, 55.
SynTerra (SynTerra Corporation). 2019. Corrective Action Plan (CAP) Update. Prepared by SynTerra
Corporation in December 2019.
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TABLES
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Table 1 - Pilot Study Data Quality Objectives
Pilot Study Work Plan
Cliffside Steam Station
Mooresboro, North Carolina
TableData
Quality •.
Restore groundwater beyond the geographic limitation affected by the ash impoundments
State the Problem
to the applicable standards or as close to the standards as is economically feasible in
accordance with 15A NCAC 02L. 0106.
Decision Statements
Is the number of wells, well configuration, and system capacity sufficient to achieve the
design objective outlined in the problem statement?
Study Area Boundaries
Unit 5 Ash Basin
Inputs to the Decision
Decision Rules"
Compare well capacity with design.
Well capacity: calculated via flowmeters and
If well capacity is less than design and determined to be insufficient in conjunction
transducers outfitted on injection and
with other inputs, potentially increase the number of wells.
extraction wells
If well capacity is greater than design and determined to be more than sufficient
in conjunction with other inputs, potentially decrease the number of wells.
If the observed hydraulic influence is less than anticipated and other inputs and
Area of hydraulic influence: estimated via
updated modeling indicate insufficient influence to meet the problem statement, adjust
water level change measured in monitoring
the flowrates (if capacity is available). If the flowrate adjustment is insufficient,
wells in conjunction with operating flowrates
reconfigure or add to the remedial well network.
at injection and extraction wells, water level
maps, gradient analysis and modeling
results
If hydraulic influence is greater than anticipated, evaluate reducing the number of
wells and/or increasing the well spacing.
Concentration Reductions: measured via
sampling of monitoring wells in key areas
If the anticipated COI concentration trends are not achieved, first adjust flowrates
where changes/reductions in concentration is
(if capacity is available). If the flowrate adjustment is insufficient, use other inputs to
anticipated. May be of limited use during
inform reconfiguration and/or additions to the remedial well network.
short duration of pilot test.
Updated groundwater modeling: revisit
groundwater modeling only if data collected
Update modeling if calculated hydraulic conductivity or other groundwater
from the pilot study is outside of a reasonable
variation range from the inputs used in the
parameters significantly deviate from input parameters in existing numerical models.
existing modeling per decision rules.
* For the proposed hydraulic remedies at the sites, the data inputs, although listed separately here, will be used in conjunction with one another to evaluate
effectiveness of the remedy.

Table 2 - Basis of Design Summary
Pilot Test Work Plan
Cliffside Steam Station
Mooresboro, North Carolina
Approximately 25 gpm from pilot test extraction wells and 10 gpm from source control area based on modeling. Total flow is 35 gpm.
Design • • Arsenic, Chromium, Strontium, Vanadium, Hexavalent Chromium, Cobalt, Iron, Manganese, Radium, Thallium, Boron, Lithium, Sulfate, TDS
Groundwater Draw -Down Wells EX-U5-1 to EX-U5-12: 679 to 697 ft AMSL (average = 691 ft AMSL ; Wells EX-u5-13 to EX-u5-22: 685 to 695 ft AMSL
Modelingcurrent) beingprepared to define capture zone.
Ranges from 70 to 150 feet on -center for pilot test wells. Source Control Area wells spaced approximately 30 feet.
Discharge Location Dischar a to existingwaste water conveyance at "Basement Basin" located near the CoolingTowers.
Generalized Well water pumps within extraction well network dewater wells to targeted depth, inducing groundwater capture zone. A source control trench with sumps will
eneral - capture water from the southern cooling towers. Extracted water conveyed to existing central discharge point for combined flow to facility waste water
DescriptionProcess
treatment )ant.
Due to extended distances, collection points, referred to as "Node Buildings", will combine the flow from a localized group of extraction wells into a common
Collection Points/Node Buildings header. Several collection points will be located to minimize the length of total piping required and to maximize pumping efficiency. Node Building discharges
will combine to form a single final discharge. All instrumentation and controls will be at the Node Buildings
Equipment must be commonly available, serviceable, and universally compatible with system controls.
Well Pump Control Extraction well pumps will cycle on/off within targeted draw -down depth range (target range set per well).
Flow rates will be controlled manually using a control valve.
Water levels will be periodicallychecked manually. Water level intrumentation will control um and water level within well.
Instantaneous and totalizing flow measurement for individual wells prior to discharge to the manhole.
Conveyance All exterior conduit/pipe to be buried whenever possible. Minimize road crossing and overall trenching work. Oversize piping to allow for cleanouts (buried pipe
size 2-inch diameter minimum). Incorporate Node Buildings as common control, metering, and discharge collection centers. Size headers for expansion.
Desi n to integrate discharge into existing systems, without impacting functionality of existing s stems.
Secondary Containment Not required for conveyance pipe, but required for holding/equalization tanks and leak detection/sump in collection buildings.
Seconds containment 110% of the hold in /e ualization tank maximum capacity.
Flexibility Include water storage, pump, conveyance, and electrical/controls capacity for future expansion.
Includes are conveyance pipe/conduit where appropriate for future expansion.
Operation & Maintenance Design for maximum automation and remote monitoring. Design for full serviceability of all major components (e.g., tru-union fittings, clean -outs, etc.).
Winterization Desi n for all -season operation, including electric heat tracing and insulation where required.
Minimize complexity, include Fail -Safes to prevent spills, to protect the operating equipment, and to allow for automated operation with minimal operator input.
Remote Monitoring Remote monitoring capabilities, allow full remote operation of all systems by approved operator personnel, and monitoring -only option available.
• • No controls integration anticipated.
Each Node building o contain dedicated/independent control, but include inter -node communication if required for alarm interlocks.
Number of Wells 22 lot -scale 45 total full-scale
Vertical Extraction Wells Flow RateAvers a Flow Rate: 25 qpmpilot-scale
Schedule 40 PVC riser and 304L stainless steel screen.
E.r Varies
1 /2 to 1 HP electric submersible well pump (e.g. Grundfos Redi-Flo 4 or similar).
Drillers to install with temporary well box to be modified during system equipment installation.
Precastsquare concrete vault box with lids (Duty -ratings to be determined during design). Shut-off valve at wellhead.
Carbon steel pipe. Riser pipe 1 to 1.25-inch diameter sized to match pump outlet).
Groundwater extraction controlled by a PLC with HMI.
Page 1 of 2

Table 2 - Basis of Design Summary
Pilot Test Work Plan
Cliffside Steam Station
Mooresboro, North Carolina
Acronyms:
amsl = above mean sea level
bgs = below ground surface
CAP = Corrective Action Plan
ft = feet
gpm = gallons per minute
HMI = human -machine interface
HP = horsepower
HPDE = high density polyethylene
PLC = programmable logic controller
PVC = polyvinyl chloride
SS = stainless steel
TDS = total dissolved solids
Page 2 of 2

Table 3 - Proposed Well Construction Details
Pilot Test Work Plan
Cliffside Steam Station
Mooresboro, North Carolina
Well I.D.
Well Purpose
Type of Well
Location
Fasting
(NAD 83)
Northing
(NAD 83)
Screen
Material
Riser
Material
Borehole
Diameter
(inches)
Well Screen
and Riser
Diameter
inches
Well Screen
Interval
(ft bgs)
Sand Pack
Interval
(ft bgs)
Bentonite
Seal
(ft bgs)
Grout
Slurry
Interval
(ft bgs(ft
Cement and
Flushmount
bgs)
Total
Depth
(ft bgs))
Additional
Notes
Vertical
North of Cooling
Wire Wrapped
EX-U5-1
Saprolite/Transition Zone
1174126.90
545805.10
Sch 80 PVC
10 - 12
6
25 - 118
22 - 118
19 - 22
2 - 19
0-2
118
Unit 5 Area
Extraction
Tower A
304L SS
Vertical
North of Cooling
Wire Wrapped
EX-U5-2
Extraction
Saprolite/Transition Zone
Tower A
1174180.80
545752.90
304L SS
Sch 80 PVC
10 - 12
6
25 - 118
22 - 118
19 - 22
2 -19
0-2
118
Unit 5 Area
Vertical
North of Cooling
Wire Wrapped
EX-U5-3
Saprolite/Transition Zone
1174241.40
545707.50
Sch 80 PVC
10 - 12
6
25 - 126
22 - 126
19 - 22
2 - 19
0-2
126
Unit 5 Area
Extraction
Tower A
304L SS
Vertical
North of Cooling
Wire Wrapped
EX-U5-4
Extraction
Saprolite/Transition Zone
Tower A
1174000.70
545764.70
304L SS
Sch 80 PVC
10 - 12
6
25 - 118
22 - 118
19 - 22
2 -19
0-2
118
Unit 5 Area
Vertical
North of Cooling
Wire Wrapped
EX-U5-5
Saprolite/Transition Zone
1173854.20
545720.90
Sch 80 PVC
10 - 12
6
25 - 126
22 - 126
19 - 22
2 - 19
0-2
126
Unit 5 Area
Extraction
Tower A
304L SS
Vertical
South of Cooling
Wire Wrapped
EX-U5-6
Saprolite/Transition Zone
1173945.10
545512.20
Sch 80 PVC
10 - 12
6
25 - 110
22 - 110
19 - 22
2 -19
0-2
110
Unit 5 Area
Extraction
Tower A
304L SS
Vertical
South of Cooling
Wire Wrapped
EX-U5-7
Saprolite/Transition Zone
1174014.10
545517.20
Sch 80 PVC
10 - 12
6
25 -118
22 -118
19 - 22
2 - 19
0-2
118
Unit 5 Area
Extraction
Tower A
304L SS
Vertical
South of Cooling
Wire Wrapped
EX-U5-8
Saprolite/Transition Zone
1174093.30
545524.00
Sch 80 PVC
10 - 12
6
25 - 134
22 - 134
19 - 22
2 -19
0-2
134
Unit 5 Area
Extraction
Tower A
304L SS
Vertical
South of Cooling
Wire Wrapped
EX-U5-9
Saprolite/Transition Zone
1174201.00
545547.50
Sch 80 PVC
10 - 12
6
25 - 134
22 - 134
19 - 22
2 -19
0-2
134
Unit 5 Area
Extraction
Tower A
304L SS
Vertical
South of Cooling
Wire Wrapped
EX-US-10
Saprolite/Transition Zone
1174148.80
545466.70
Sch 80 PVC
10 - 12
6
25 - 142
22 - 142
19 - 22
2 -19
0-2
142
Unit 5 Area
Extraction
Tower A
304L SS
Vertical
South of Cooling
Wire Wrapped
EX-U5-11
Saprolite/Transition Zone
1174249.80
545401.00
Sch 80 PVC
10 - 12
6
25 - 142
22 - 142
19 - 22
2 - 19
0-2
142
Unit 5 Area
Extraction
Tower A
304L SS
Vertical
South of Cooling
Wire Wrapped
EX-U5-12
Saprolite/Transition Zone
1174259.90
545337.10
Sch 80 PVC
10 - 12
6
25 - 142
22 - 142
19 - 22
2 -19
0-2
142
Unit 5 Area
Extraction
Tower A
304L SS
Vertical
West of Cooling
Wire Wrapped
EX-U5-13
Saprolite/Transition Zone
1174353.06
544907.98
Sch 80 PVC
10
6
20-35
17-35
14-17
2-17
0-2
35
Unit 5Area
Extraction
Tower B
304L SS
Vertical
West of Cooling
Wire Wrapped
EX-US-14
Saprolite/Transition Zone
1174319.49
544919.74
Sch 80 PVC
10
6
20-35
17-35
14-17
2-17
0-2
35
Unit 5Area
Extraction
Tower B
304L SS
Vertical
West of Cooling
Wire Wrapped
EX-U5-15
Saprolite/Transition Zone
1174297.95
544947.48
Sch 80 PVC
10
6
20-35
17-35
14-17
2-17
0-2
35
Unit 5Area
Extraction
Tower B
304L SS
Vertical
West of Cooling
Wire Wrapped
EX-US-16
Saprolite/Transition Zone
1174289.43
544982.27
Sch 80 PVC
10
6
20-35
17-35
14-17
2-17
0-2
35
Unit Area
Extraction
Tower B
304L SS
Vertical
West of Cooling
Wire Wrapped
EX-U5-17
Saprolite/Transition Zone
1174285.46
545018.05
Sch 80 PVC
10
6
20-35
17-35
14-17
2-17
0-2
35
Unit 5Area
Extraction
Tower B
304L SS
Vertical
West of Cooling
Wire Wrapped
EX-US-18
Saprolite/Transition Zone
1174281.48
545053.83
Sch 80 PVC
10
6
20-35
17-35
14-17
2-17
0-2
35
Unit 5Area
Extraction
Tower B
304L SS
Vertical
West of Cooling
Wire Wrapped
EX-U5-19
Saprolite/Transition Zone
1174277.50
545089.61
Sch 80 PVC
10
6
20-35
17-35
14-17
2-17
0-2
35
Unit 5Area
Extraction
Tower B
304L SS
Vertical
West of Cooling
Wire Wrapped
EX-U5-20
Saprolite/Transition Zone
1174273.53
545125.39
Sch 80 PVC
10
6
20-35
17-35
14-17
2-17
0-2
35
Unit 5Area
Extraction
Tower B
304L SS
Vertical
West of Cooling
Wire Wrapped
EX-U5-21
Saprolite/Transition Zone
1174269.36
545161.15
Sch 80 PVC
10
6
20 - 35
17 - 35
14- 17
2 - 17
0-2
35
Unit 5 Area
Extraction
Tower B
304L SS
Vertical
West of Cooling
Wire Wrapped
EX-U5-22
Saprolite/Transition Zone
1174264.97
545196.88
Sch 80 PVC
10
6
20-35
17-35
14-17
2-17
0-2
35
Unit 5Area
Extraction
Tower B
304L SS
West of Cooling
PVC Slotted
GWA-4BR
Monitoring
Bedrock
Tower B
1174247.23
545093.95
Screen
Sch 40 PVC
6
2
112 - 122
109 - 122
106 - 109
2 - 109
0-2
122
Unit 5 Area
South of Cooling
PVC Slotted
GWA-36BR
Monitoring
Bedrock
Tower A
1174219.86
545364.74
Screen
Sch 40 PVC
6
2
112 - 122
109 - 122
106 - 109
2 - 109
0-2
122
Unit 5 Area
North of Cooling
PVC Slotted
GWA-37BR
Monitoring
Bedrock
Tower A
1174067.95
545729.32
Screen
Sch 40 PVC
6
2
88 - 98
85 - 98
82 - 85
2 - 82
0-2
98
Unit 5 Area
Notes:
Ft bgs: Feet below ground surface
NAD: North American Datum

Table 4 - Effectiveness Monitoring Plan Summary
Pilot Test Work Plan
Cliffside Steam Station
Mooresborc, North Carolina
0
Table 4 - Effectiveness Monitoring Plan Summary
Source - Table 6-40 from CAP Update
Effectiveness Monitoring Plan (EMP) Post -Closure Monitoring Plan (PCMP)
Implemented 30 days after CAP Approval Implemented after completion of ash basin closure activities
EMP Groundwater Well Monitoring Network
(background, downgradient of source
areas)
Performance Monitoring Network
CCR-U5-6S
GWA-36S
GWA-37BR*
CCR-U5-6DA
GWA-36D
MW-38S
GWA-4S
GWA-36BR*
MW-38D
GWA-41D
GWA-37S
MW-38BR
GWA-4BR*
GWA-37D
Continued Monitoring Network
CCR-U5-3S
GWA-2S
GWA-35D
CCR-U5-3D
GWA-2BRU
GWA-35BR*
CCR-U5-4S
GWA-2BRA
GWA-67BR
CCR-U5-4D
GWA-3D
MW-36S
CCR-U5-4BR
GWA-3BR*
MW-36BRU
CCR-U5-5D
GWA-35S
MW-36BR*
Background Monitoring Wells'
GWA-30S
MW-30DA
MW-32D
GWA-30BR
MW-32S
MW-32BR
MW-30S
EMP Groundwater Quality3' 4
(Semi -Annual Sampling Frequency)
Alkalinity Cobalt' Potassium
PCMP Groundwater Well Monitoring Network
(background, downgradient of source areas)
A PCMP will be implemented at the Site in accordance with
G.S. 130A-309.214(a)(4)k.2 after completion of
ash basin closure activities.
PCMP Groundwater Quality
(Sampling frequency to be determined)
Aluminum
Ferrous Iron
Sodium
Bicarbonate Alkalinity
Iron'
Strontium'
z
z
2
Parameters and sampling frequency to be included in the PCMP in
Boron
Lithium
Sulfate
accordance with G.S. 130A-309.214(a)(4)k.2 when submitted.
Calcium
Magnesium
Total Dissolved Solids'
Chromium (Total)'
Manganese'
Total Organic Carbon
Chromium (VI)'
Nitrate + Nitrite
Total Radium'
CMP and PCMP Groundwater Field Parameters
Water Level
Specific Conductivity Temperature
pH
Oxidation Reduction Potential Dissolved Oxygen
EMP Review
1) Summary of annual groundwater monitoring results
2) Evaluate statistical concentration trends
2) Comparison of observed concentrations to model predictions
3) Evaluation of compliance with applicable Standards
4) Evaluation of system performance and effectiveness
4) Recommend plan adjustments, if applicable, to optimize the remedial
action
5-Year Performance Review Reporting
1) Update background analysis
2) Confirm Risk Assessment assumptions remain valid
3) Re-evaluate effectiveness of technology
4) Verify modeling results, update model if needed
5) Modify corrective action approach, as needed, to achieve compliance
30 days after CAP approval, the EMP will be implemented at the Site
and will continue until there is a total of three years of data confirming
COIs are below applicable Standards at or beyond the compliance
boundary, at which time a request for completion of active remediation
will be filed with NCDEQ.
If applicable standards are not met, the EMP will continue and transition
to post -closure monitoring if necessary.
PCMP Review
Annual Evaluation and Reporting:
1) Summary of annual groundwater monitoring results
2) Evaluate statistical concentration trends
2) Comparison of observed concentrations to model predictions
3) Evaluation 02L compliance
4) Recommend plan adjustments, if applicable
At a frequency no greater than 5 years:
1) Update background analysis
2) Confirm Risk Assessment assumptions remain valid
3) Verify model results, update if needed
After ash basin closure and following ash basin closure certification,
a PCMP will be implemented at the Site for a minimum of 30 years in
accordance with G. S. 130A-309.214(4)(k)(2).
Early termination:
If groundwater monitoring results are below applicable Standards at
the compliance boundary for three years, Duke Energy will request
completion of corrective action in accordance with G.S. 130A-
309.214(a)(3)b. If groundwater monitoring results are above
applicable Standards, the PCMP will continue.
' Approved background groundwater monitoring locations
' Corrective action COIs to monitor plume stability and physical attenuation either from active remedy or natural dilution/dispersion
3 The number of monitoring wells and parameters may be adjusted based on additional data and the effects of corrective action.
4 Groundwater standards may be modified over time in accordance with 02L .0106(k)
* Proposed new well
Italicized parameters - parameters for general water quality to evaluate monitoring data quality
Wells indicated in red will have geochemical sondes placed to monitor geochemical conditions
Prepared by: TJG Checked by: SAS
Page 1 of 1

FIGURES
www.erm.com Project No.: 0550577 Client: Duke Energy Carolinas, LLC July 1 2020

� ' 1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
= 1
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1
:1
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I
I
iH BASIN '
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AREA
Pr UNITS 1-4 ASH BASIN
r (U1-4 AB)
. f SOURCE AREA
Ki
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0
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ter.
r
- ,
r :%
♦ -......................
�-
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0 300 600 1,200 .
tt
Feet ,
Y
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2
Legend
Approximate Ash Basin Waste Source Area
Y Boundary Source Area DUKE
U -
—• Geographic Limitation 40)ENERGY
t Source Area
mi Cliffside Steam Station Property
i Line
@BOBO"
N
♦
1
r
1
' 1
1
1
1
1
1
1
1
1
1
. 1
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1
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1
r
ACTIVE ASH BASIN
(AAB) •
SOURCE AREA
1
4
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1
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1
1
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V
a
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41
♦ TAYL
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CHECKED
DIE
DITLERE
Ash Basin Layout Map
No.
BW
6/30/2020
Pilot Test Work Plan
Duke Energy
Cliffside Steam Station
PROJECT MANAGER
DIE
ENVIRONMENTAL RESOURCES MANAGEMENT, INC.
E1ZM
JFt/gV\/
6/30/2020
MOoresboro, North Carolina
PRo�Eo
WM
TE
6/30/2020
c�Nav S.Vickery
6/30/2020
s 1 " = 600 '
MPRo�EETNo
ER 0550577
IEV 1

Legend
Proposed Monitoring Well
Existing Monitoring Well
Proposed Full Scale Extraction Well
Proposed Pilot Test Extraction Well
Proposed Clean Water Infiltration Well
Proposed Source Control Area Extraction
Well
—Approximate Ash Basin Waste Boundary
• • Geographic Limitation
Cliffside Steam Station Property Line
(' DUKE
ENERGY.
CHECKED
DATE
TITLE
Full -Scale System Design Well Network
FIGURE NO.
BW
6/30/2020
Pilot Test Work Plan
Duke Energy
Cliffside Steam Station
2
PROJECT MANAGER
DATE
ENVIRONMENTAL RESOURCES MANAGEMENT, INC.
M
E�y
JP/Byy
I
6/30/2020
I
MOoresboro, North Carolina
I
PPFROVER WM
DAT6/30/2020
HEl S. Vickery
6/30/2020
5
1 " = 600 '
ERMEPROJECTNO
0550577
REV 1

Legend
Proposed Monitoring Well
Existing Monitoring Well
Proposed Pilot Test Extraction Well
Proposed Source Control Area
Extraction Well
Existing 18" Discharge Line
O Proposed Node Building
Proposed French Drain
— Extraction Well Conveyance Path
— Source Control Conveyance Path
Source Control Area
•- Geographic Limitation
Proposed Node Building Disturbance
Area
V
DUKE
ENERGY.
CHECKED
DATE
TITLE
FIGURE NO.
Pilot Test Remedy and Monitoring Layout
BW
6/30/2020
Pilot Test Work Plan
Duke Energy
Cliffside Steam Station
3
PROJECT MANAGER
DATE
ENVIRONMENTAL RESOURCES MANAGEMENT, INC.
ERM �.
JP/BW
6/30/2020
MOoresboro, North Carolina
APPROVED WM
DAT6/30/2020
DRAWN BY S. Vickery
6/30/2020
5
1 " = 110 '
ERMEPROJECT NO
0550577
EV 1

N
0
Lo
0
0
LO
D
0
0
a
2
w
PROCESS STREAM CHARACTERISTICS
Stream
Description
Flow Conditions
A
GW Extraction Wells (EX-1.15-1 to -12)
0.6 - 2.7 gpm ea.
B
Source Control Extraction Wells (EX-1.15-13 to -22)
0.4 - 2 gpm ea.
C
Total Combined Pilot Test Discharge
—35 gpm
gpm - gallons per minute
ea. - each
ft - feet
P-313 TO P-322
SOURCE CONTROL
EXTRACTION WELLS
EX-1.15-13 TO EX-1.15-22
0
P-101 TO P-112
GW EXTRACTION WELLS
EW-U5-1 TO EW-U5-12
— — — — — — — — — — — — — — —
I I
I
T-201
HOLDING
TANK
I � I
P-201
TRANSFER PUMP
L----------------I
LIMITS OF NODE BUILDING
EXISTING
BASEMENT BASIN
(HOLDING CELL)
1 r/' r-K I
EXTRACTION PUMP
r TRANSFER PUMP
HOLDING TANK
NOTE: ALL EXTRACTION WELL
INSTRUMENTATION AND CONTROLS,
INCLUDING FLOW METERS,
TOTALIZERS, FLOW CONTROL
VALVES, AND PRESSURE GAUGES,
WILL BE CONTAINED WITHIN EACH
NODE BUILDING.
WASTEWATER
TREATMENT
SYSTEM
(WWTS)
NPDES
OUTFALL 005
Figure 4
Process Flow Diagram
Pilot Test Work Plan
Cliffside Steam Station
Mooresboro, North Carolina
Environmental Resources Management
www.erm.com
ERM

LEVEL SWITCHE
CONTROL WIRIN
1.25-INCH TO 1.5 IN(
STILLING WE
HIGH LEVEL SWITCH
BENTONITE 1
MIN. 2 FE
}
CASING CENTRALIZER
6" WELL SCREEN
(WIRE WRAPPED SS)
LOW LEVEL SWITCH
NOT TO SCALE
4 'NCH TO 1.Or- -INCH
;OP PIPE (GALV. STEEL)
EXTRACTION PUMP
POWER LEAD
10-INCH TO 12-INCH BOREHOLE
NEAT CEMENT GROUT
IN CASING ANNULUS
6-INCH WELL CASING
THREADED JOINTS
BENTONITE CHIP SEAL
SAND PACK
CHECK VALVE
ELECTRIC SUBMERSIBLE
WELL PUMP
Figure 5
Groundwater Extraction Well Schematic
Pilot Test Work Plan
Cliffside Steam Station
Mooresboro, North Carolina
Environmental Resources Management
www.erm.com
ERM

APPENDIX A
www.erm.com Project No.: 0550577 Client: Duke Energy Carolinas, LLC July 1 2020

ERM 4140 Parklake Avenue relehone: [phone]
Suite 110
Raleigh, NC
27612 erm.com
Memo
To Scott Davies ERM
From Brian Wilson and Wes May
Date 1 July 2020
Reference ERM PN 0550577
Subject Cliffside Steam Station — Low pH Source Area Alternative Remedial Design
Summary Memo
Duke Energy Carolinas, LLC (Duke Energy) retained ERM NC, Inc. (ERM) to prepare a work plan
and a constructible design for the Unit 5 Ash Basin (U5 AB) source area groundwater extraction
pilot test at the Cliffside Steam Station in Rutherford and Cleveland Counties in North Carolina
(the Site). The U5 AB and conceptual design for source control is described in the Corrective
Action Plan (CAP) Update prepared by SynTerra Corporation in December 2019 (SynTerra,
2019). Coal ash from the U5 AB will be excavated. In addition, the conceptual design presented in
the CAP included a groundwater recovery trench to facilitate hydraulic recovery of low pH
groundwater downgradient of the U5 AB Saddle Dam. The low pH groundwater is suspected to
cause the mobilization of constituents (strontium, iron and manganese) with seep water and
shallow and deep groundwater at concentrations greater than other areas at the Site.
ERM was tasked with preparing a detailed design of the groundwater recovery trench; however,
several potential issues related to construction of the deep recovery trench in this area of the Site
were identified during preliminary design activities. These concerns are summarized as follows,
and are discussed in greater detail in subsequent sections of this memo.
Safety — The depth of the trench (including installation of a perforated pipe in the bottom of
the trench), the close proximity of Cooling Tower B to the trench, and the presence of a
steep slope at the southern end of the trench, all pose a considerable safety risk to Site
personnel, construction workers, and the structural integrity of Cooling Tower B.
Constructability — The northern extent of the proposed location of the deep trench is
bounded to the east by Cooling Tower B and to the west by the U5 AB Saddle Dam, while
the curved southern extent of the proposed deep trench location is bounded to the south
by a steep, near -vertical slope and to the north by Cooling Tower B. These Site
constraints, along with the 20-foot depth of the trench, pose constructability issues due to
inaccessibility by large construction equipment, laydown/stockpile storage requirements,
adequate shoring of excavation to depth, management of shallow groundwater, and
diversion and management of stormwater.
The identification of these concerns led ERM to evaluate alternative groundwater recovery
systems that could effectively mitigate or reduce these safety and constructability risks while
Page 1 of 10
© Copyright 2020 by ERM Worldwide Group Limited and/or its affiliates ('ERM'). All Rights Reserved. No part of this work may be
reproduced or transmitted in any form or by any means, without prior written permission of ERM.

1 July 2020
ERM PN 0550577
Page 2 of 10
effectively meeting the remedial objectives. ERM's evaluation identified an alternative remedial
approach that meets both of these criteria. This memorandum has been prepared to document the
evaluation process and present the technical justification for selection of this alternate remedial
design approach for the low pH source area downgradient of the U5 AB Saddle Dam at the Site.
Background and Remedy Objectives
The CAP prepared by SynTerra proposed hydraulic recovery of groundwater to mitigate low pH
groundwater downgradient of the U5 AB Saddle Dam at the Site. In the CAP, the remedial
alternative selected to address the low pH groundwater at the Site included installation of vertical
recovery wells to the to the north and south of Cooling Tower A, and the installation of a hydraulic
recovery trench in the low pH source area downgradient of the U5 AB Saddle Dam located west of
Cooling Tower B. The low pH source area hydraulic recovery concept included construction of a
trench along an existing ditch carrying acidic water from the southern end of Cooling Tower B to
the west and then north, parallel to and beyond Cooling Tower B (Figure 1). A conceptual layout
included installation of a hydraulic recovery trench lined with a geotextile and subsequently filled
with stone that was approximately 380 feet long, 20 feet deep, and 2 to 6 feet wide. The proposed
trench would capture and collect low pH groundwater via collection sump(s), which would then be
conveyed through the existing storm sewer system to the Cliffside wastewater treatment plant
(WWTP) to be treated and discharged through Outfall 005. In addition to the trench, it was also
proposed that the stormwater ditch have an impermeable liner placed along the length of the
trench to limit the potential for infiltration into shallow groundwater.
The primary objectives of the low pH source remedy are to hydraulically:
(1) Prevent low pH groundwater/seeps from discharging into the ditch carrying acidic water from
the southern end of Cooling Tower B;
(2) Control/minimize the infiltration of acidic storm water present in the ditch into groundwater;
and
(3) Reduce the migration of low pH groundwater away from the source area.
Remedial Alternatives Evaluation
The source area remedial alternatives evaluation conducted by ERM included a review of potential
remedies that could meet the remedial objectives with a standalone remedy or a combination of
individual remedial components. The remedial options evaluation included review and risk ranking
of the following scenarios:
Deep Trench and Lined Ditch: Construction of a deep groundwater recovery trench (20
feet deep) with surface completion as a lined channel (replacement of low pH section of
current drainage ditch). Construction options:
a. Excavation with shoring
b. Continuous trencher (i.e., One -Pass Trenching Technology)
2. Extraction Well(s), French Drain and Lined Ditch: Installation of extraction wells
(approximately 30 to 40 feet deep), a shallow French drain (up to 6 feet deep) and surface

ERM [ERM
July 2020
PN 0550577
age 3 of 10
completion as a lined channel (replacement of low pH section of current drainage ditch).
Construction options for the extraction wells:
a. Vertical extraction wells
b. Horizontal extraction well(s)
The potential risks associated with each alternative were evaluated with respect to overall safety,
constructability, and impact to Site operations. A summary of the evaluation is presented in Inset 1
(below), with a more detailed discussion of the options provided in attached Table 1.
Inset 1. Remedial Alternative Evaluation Summary
Green = Lower Risk, Yellow = Medium Risk, Red = Higher Risk.
Remedial
Alternative
Deep Trench and
Lined Ditch
Extraction Wells,
Shallow French
Drain and Lined
Ditch
U)
Installation
Description Method °' N y
> iY
d
0 W
Installation of a 20-ft deep
trench for hydraulic
capture of shallow
groundwater, and a lined
ditch to limit infiltration of
low pH surface water
Installation of wells for
hydraulic capture of
shallow groundwater, a
shallow French drain to
capture seep and surface
water, and a lined ditch to
limit infiltration of low pH
surface water
Excavation
Continuous
Trenching
Vertical
Wells
Horizontal
Wells
The evaluation summarized in Inset 1 indicates implementation of a combination of hydraulic
capture of shallow groundwater (via vertical extraction wells) combined with a shallow French
drain (Figure 2) and lining the ditch is the preferred option, providing the same relative
effectiveness in achieving the stated remedial objectives, while also having both lower relative
safety risk and a lower relative constructability risk.
Based on this analysis, ERM recommends installation of vertical extraction wells combined with a
shallow French drain and lining of the ditch, rather than installation of a deep recovery trench in

T1M
1 July 2020
ERM PN 0550577
Page 4 of 10
the source area. A technical evaluation and expanded justification for the change in the source
area remedy is discussed below.
Technical Justification
There are multiple lines of evidence that support a change in the source area remedial approach,
including relative safety of implementation, ability of meeting design objectives, and promoting
sustainable long-term performance.
Safety Risk — As shown in Inset 1, installation of the deep recovery trench presents a high safety
risk, while the Dewind One Pass Trenching approach poses a medium safety risk compared to the
installation of horizontal and vertical wells. The workspace limitations and depth of trench have
clear safety considerations, particularly with the deeper trenches initially proposed for the Site.
Accessing any portion of a 20-foot deep trench or working anywhere near the top edge of such a
trench would require substantive and potentially prohibitive safety measures. The Dewind One
Pass Trenching approach has definite advantages over the deep trench concept from the
standpoint of safety and potentially eliminating the need to access the trench at all except in an
extreme event or failure of a component during installation. However, considerable safety risks to
Site personnel, construction workers and the structural integrity of Cooling Tower B are posed by
the depth of the deep recovery trench, along with the close proximity to Cooling Tower B and
adjacent steep slope along the southern end of the trench.
Constructability Risk — As shown in Inset 1, excavation of a deep recovery trench presents a
high implementation risk when compared to the other potential alternatives included in the
evaluation. These risks range from Site constraints restricting equipment access required for
installation, particularly along the curved portion of the proposed trench layout south of Cooling
Tower B, to worker safety and structural safety of the adjacent cooling tower during construction.
Site Constraints — The proposed location for the deep recovery trench installation is within
the footprint of an existing surface drainage ditch, with the curved southern extent located
between Cooling Tower B to the north and a steep slope to the south. This ditch receives
stormwater from both sides and is situated adjacent to a paved roadway that provides
maintenance access around the cooling tower. Stormwater runoff diversion away from any
open trenching (including the proposed engineered channel) will be crucial during
construction; however, a significantly larger laydown area would be required for spoils
excavated from the deep trench and for stockpiled backfill material. A 20-foot deep trench is
anticipated to require stockpiling of a significantly greater volume of soil and stone (anticipated
to be approximately four times as large) compared to the shallower 5-foot deep trench
associated with an engineered lined channel. This necessary laydown area will be challenging
to accommodate at the Site given the space constraints, and a more significant volume of
waste requiring disposal would be generated.
Equipment Access Limitations — The use of large excavators or trenchers with longer reach
compared to more commonly used equipment will be required for installation of the deep
trench. In addition, there is potential for encountering more substantial partially weathered rock
(PWR) or shallow bedrock during excavation, which will could require excavators/trenchers
with specialty buckets or teeth. Shoring for a 20-foot deep excavation will require site -specific

1 July 2020
ERM PN 0550577
Page 5 of 10
structural engineering to verify adequacy of trench box use to ensure construction is
completed in accordance with Occupational Safety and Health Administration (OSHA)
mandates. The large excavators will also have difficulty in negotiating the curved section of the
trench without widening to accommodate the longer reach needed. As a result, ERM also
considered the use of a Dewind One Pass Trencher rather than excavators with shoring to
excavate and backfill the trench in a single pass. ERM determined this approach holds merit
for the straight section of the alignment; however, there would still be significant challenges to
accommodate trenching of the curved section, which may not be possible with the One Pass
Trencher. The Dewind approach may instead require two or more setups to navigate the
curved section of the trench and may also have limited access to the southern extent of the
ditch due to the near -vertical slope immediately south of the ditch and Cooling Tower B to the
north of the ditch. The One Pass Trencher also has potentially limited availability and higher
mobilization costs given the limited number of machines with this capability.
Relative Effectiveness — As shown in Inset 1, extraction using vertical wells would have the same
effectiveness in meeting the remedial objectives as the use of a deep recovery trench. This
assessment is based on an evaluation of hydraulic capture of the shallow groundwater, the ability
to optimize the system through adaptable design, and long-term operations and maintenance
(O&M)/performance.
Shallow Groundwater Hydraulic Capture —Given the constructability concerns associated
with the deep recovery trench outlined above, ERM evaluated whether a series of vertical
extraction wells would be capable of meeting the objectives for capture of the shallow
groundwater within the source area. ERM performed calculations to evaluate the drawdown
potential for vertical wells installed in the source area using hydraulic conductivity ranges
presented in the CAP (estimated from 0.5 feet per day [ft/d] to 10 ft/d). The evaluation
indicated that installation of 10 vertical extraction wells, placed along the proposed trench
alignment, can achieve sufficient drawdown to capture shallow groundwater when pumped at
an individual flowrate of 0.5 gallons per minute (gpm), with a total flow of 5 gpm (Inset 2). After
passing this initial screening, Duke Energy commissioned SynTerra to update the existing
groundwater model for the Site using the above information to compare the predicted
performance of the proposed vertical extraction well alternative option to that of the previously
proposed recovery trench. The results of SynTerra's predictive site -specific modeling effort
confirmed that the capture zone created by the 10 vertical extraction wells proposed to be
placed in a line approximately parallel to the existing stormwater ditch is expected to
sufficiently capture shallow groundwater within the source area to meet the remedial
objectives. The inputs and results of the site -specific modeling effort conducted by SynTerra
are summarized in the slides provided as Attachment 1.

�i
1 July 2020
ERM PN 0550577
Page 6 of 10
Inset 2. Drawdown Approximation for different hydraulic conductivities for 10 wells
pumping at 0.5 gpm along the proposed trench alignment.
Groundwater Drawdown iK = 0.48 Red. Q = 0.5 9pml Groundwater Drawdown fK = 1.0 M. Q = 0.5 9p" Gmundwaw Drawdown {K = 10 M. ❑ = 0.5, gpm)
brawdowndtl O.61 Drawdow lV
545300 -10 MOW -12 0 515300 -2.00
-R
615100 -26 W%2W -144 54S1p0 ^232
-T 56
545300 -� 3a5100 -160 545100
-34 -19 2 -T !0
_ 545000 34 WOO545000
-21 6 -; DA
544900 -A¢900 -2e0 54a900 -329
6
-3 92
7W 500 .100 300 200 300 400 500 ....30p i0p 500
♦l ] la.... +t 114e6 +1 11445
Adaptability/adaptive design — Use of vertical extraction wells rather than a deep recovery
trench or horizontal wells will allow for adaptive operation over time. Once installed, the trench
would be a static feature at the Site, with little to no ability to optimize pumping within the
trench. Horizontal wells have similar drawbacks, if not positioned perfectly, they will not
effectively contain the targeted zone or discrete interval in which they are pumping from. It is
possible to construct different segments of the horizontal wells to allow for different pumping
regimes; however, they are also static features once installed, similar to trenches. Conversely,
vertical wells allow much more adaptability to optimize performance, including individual flow
controls to allow for optimization of pumping at different rates, and the ability to vary screen
lengths across large vertical intervals (to mirror recovery across that vertical interval, similar to
a trench), increases the potential of vertical capture compared to horizontal wells. The vertical
extraction well system is less constrained than recovery trench or horizontal well systems, in
that additional vertical wells can be added to the system to enhance capture in targeted areas,
if necessary, based on performance of the initial system. Use of vertical wells provides
flexibility in operation that is not possible with a deep recovery trench or horizontal well
system, thereby increasing certainty associated with meeting remedial objectives.
Long-term O&M/Performance — The ability to perform long-term maintenance to keep the
recovery system operating as designed is critical to meeting performance objectives given the
anticipated long-term operation of the remedy. The combination of a shallow French drain and
lining of the ditch, paired with vertical extraction wells balances the short-term needs/risks with
reasonable maintenance requirements to maximize system up time and allow remedial
objectives to be met in a sustainable manner. The lined ditch is shallow enough that periodic
cleanout, repair or replacement can occur quickly and efficiently. The vertical wells can
undergo preventative maintenance (e.g., redevelopment, etc.) at a frequency that can be
customized based on groundwater extraction rates and associated capture zone estimates.
These same preventative actions are not possible with a deep trench, and are limited in nature
for horizontal wells. Lastly, key extraction wells can be replaced and additional wells
connected to the system if significant performance issues are observed, whereas significant
performance issues with horizontal wells or deep trenches are not readily mitigated and, in
some cases, may require full replacement. All of these factors contribute to added uncertainty
with respect to long-term sustained performance following installation of a deep recovery
trench or horizontal recovery well system when compared with the proposed vertical extraction
well system.

ERM [ERM
July 2020
PN 0550577
age 7 of 10
Summary
During preliminary design, ERM identified issues related to safety and constructability of a deep
recovery trench that could meet the Site remedial objectives. ERM performed a remedial
alternatives evaluation for the low pH source area to evaluate options that would reduce the safety
and constructability risks while still effectively meeting the remedial objectives in this area. As a
result of this evaluation, ERM proposes replacement of the deep recovery trench with a remedial
alternative combining the following:
Ditch to capture low pH storm water runoff to prevent infiltration into shallow
groundwater, and a shallow (approximately 150 feet long, up to 6 feet deep, and 3 feet
wide) French drain to capture shallow groundwater/seeps prior to discharging into the
ditch.
2. Vertical extraction wells along the previously proposed recovery trench alignment to
capture low pH groundwater already present in the shallow water -bearing unit.
ERM believes the combination of these two remedies, depicted on Figure 1, will meet or exceed
the modeled performance of the previously proposed deep recovery trench. ERM also believes
this combination will be as or more effective in both long-term and short-term performance, will
provide adaptability that is not possible with the recovery trench, and can be constructed to meet
remedial objectives while allowing for safer installation.
Attachments:
Table 1 — Comparative Analysis of Source Control Trench Alternatives
Figure 1 — Source Area Layout
Attachment 1 — Flow and Transport Model Revision Technical Memorandum, Groundwater
Remediation Compliance Progress — Cliffside U5 AB (SynTerra, 2020)

ERM
1 July 2020
ERM PN 0550577
Page 8 of 10
Table 1 — Comparative Analysis of Source Control Trench Alternatives

Table 1 - Comparative Analysis of Source Control Trench Alternatives
Duke Energy
Cliffside Steam Electric Plant
Mooresboro, North Carolina
Technology Process
Installation Method
Description
Safety Risk
Constructability Risk
Effectiveness
Option
Deep Trench and Lined
Excavation
A groundwater recovery trench (approx. 385 ft long x 20
Higher - This option would represent the highest
Higher - Constructability risk is associated with site constraints and limitations on equipment access. The
Higher - The use of >10 feet of stone in the bottom of
Ditch
ft deep x 4 ft wide) with three sumps (spaced out across
relative safety risk due to the depth of trenching and
proposed deep trench location is along an existing ditch, including a portion that wraps around the southern
the excavation will provide a high contact area with the
trench length), each outfitted with a submersible pump
need for shoring, particularly when installing the section
end of Cooling Tower B, and is located between a steep slope and the cooling tower. Site constraints include
aquifer and will transect areas of both high and low
to capture low pH groundwater.
of trench located along the toe of the slope south of
adequate diversion and management of stormwater coming from steep slope and from the U5 AB Saddle
permeability within the water bearing unit. This method
Cooling Tower B. Additional concerns include
Dam during construction of the deep trench, and accomodating the large laydown area required for
will have a higher potential effectiveness.
The existing ditch along the length of the proposed
undermining of the foundation of Cooling Tower B, the
stockpiling soils and stockpiled backfill materials. Equipment access limitations include the use of a larger
trench would be lined with geomembrane and overlain
operation of multiple pieces of construction equipment
long -reach excavator that can handle the 20-foot depth of the trench, the potential for the presence of
with concrete.
in close proximity to Cooling Tower B (especially within
partially weathered bedrock (PWR) and competent bedrock and ability to excavate material with standard
the narrow area along the southern end of Cooling
equipment, and the design of a shoring system adequate to meet Occupational Safety and Health
Tower B), and the operation of equipment within an
Administration (OSHA) requirements. Finally, excavation of a deep trench would be disruptive to facility
active operations area.
operations and would limit access to the eastern and southern sides of Cooling Tower B for an extended
period of time.
Deep Trench and Lined
DeWind One Pass
A groundwater extraction trench (approx. 385 ft long x
Moderate - This option would represent a moderate to
Medium - Constructability risk is associated with site constraints and limitations on equipment access. The
Higher - The use of >10 feet of stone in the bottom of
Ditch
Trenching
20 ft deep x 2 ft wide) with three sumps (spaced out
high relative safety risk due to the operation of the
proposed deep trench location is along an existing ditch, including a portion that wraps around the southern
the excavation will provide a high contact area with the
across trench length), each outfitted with a submersible
trenching machine in close proximity to Cooling Tower
end of Cooling Tower B, and is located between a steep slope and the cooling tower. Site constraints include
aquifer and will transect areas of both high and low
pump to capture low pH groundwater.
B and within the narrow area south of Cooling Tower B.
adequate diversion and management of stormwater coming from steep slope and from the U5 AB Saddle
permeability within the water bearing unit. This method
Additionally, movement of materials and trenching
Dam during construction of deep trench, and accomodating the large laydown area required for stockpiling
will have a higher potential effectiveness.
The existing ditch along the length of the proposed
would be within active operations areas.
soils and stockpiled backfill materials. Equipment access limitations include the use of a large chain trencher
trench would be lined with geomembrane and overlain
capable of reaching 20 feet in depth. It would be particularly difficult, if not impossible, for the trencher to
with concrete.
install the curved portion of the trench located to the south of Cooling Tower B. In addition, the One Pass
Trencher has potentially limited availability and construction may be delayed while waiting for the equipment.
Finally, using One Pass Trenching to install the deep trench would be disruptive to facility operations and
would limit access to the western and southern sides of Cooling Tower B for an extended period of time.
Vertical Extraction
Drilling
Ten (10) vertical groundwater extraction wells installed
Lower - This option would represent a lower to
Lower - Preliminary groundwater modelling results indicate that a 25-foot radius of influence (ROI) is
Higher - The installation of closely spaced wells to an
Wells, Shallow French
to an approximate depth of 30 to 40 feet blow grade
moderate relative safety risk. Trenching would be
sufficient to capture and contain shallow groundwater. Low pH surface water seepage would be addressed
approximate depth of 30 to 40 feet below grade to
Drain and Lined Ditch
along the proposed source control trench footprint.
limited to the depth necessary to install piping and
using a shallow French drain and by lining the existing ditch. The possibility of encountering bedrock at
maximize drawdown would be sufficient to capture the
Wells would be installed on 25 foot centers and would
conduit to wells. Equipment would need to be operated
proposed terminal depths of extraction wells may add complexity and cost to installation efforts; however,
low pH plume. If sufficient drawdown could not be
be screened across the saturated zone. Each well
in close proximity to Cooling Tower B and within areas
this can be mitigated with drilling methodology. Installation of vertical extraction wells may limit access to
established between two wells, an additional well could
would be equipped with a submersible pump to
of active operation, but size and quantities would be
portions of the western and southern sides of Cooling Tower B, but access limitations would be localized and
be installed between them, giving them a higher relative
capture low pH groundwater.
significantly less than those required for installation of a
relatively short in duration. Movement of excavated and imported soil would be limited compared to deep
effectiveness ranking.
deep trench.
trench options, as it would only be associated with shallow trenches for the French drain, piping and conduit.
A shallow French drain would be installed on the
upgradient side of the existing ditch.
The existing ditch along the length of the proposed
trench would be lined with geomembrane and overlain
with concrete.
Horizontal Extraction
Drilling
One (1) approximately 385 linear foot long horizontal
Lower - This option would represent a lower to
Medium - More robust groundwater modelling would likely be required to determine whether a horizontal
Moderate - The installation of a horizontal well at an
Well(s), Shallow
well installed at approximately 25 to 30 ft below grade.
moderate relative safety risk. Trenching would be
extraction well would be sufficient to capture and contain shallow groundwater; however, the potential exists
approximate depth of 25 to 30 feet below grade would
French Drain and
Well would be equipped with one to two submersible
limited to the depth necessary to install piping and
for multiple horizontal wells to be required to meet remedial objectives. Horizontal wells require high certainty
generally be sufficient to capture the low pH plume. If
Lined Ditch
pumps to capture low pH groundwater.
conduit to well pump(s). Equipment would need to be
in placement to ensure capture given their construction (discrete intervals associated with their diameter).
sufficient drawdown could not be established in a
operated in close proximity to Cooling Tower B and
The presence of PWR and/or competent bedrock near the proposed installation depth may limit efficacy.
section of the wells, additional vertical wells could be
A shallow French drain would be installed on the
within areas of active operation, but size and quantity of
Installation of horizontal extraction well(s) may limit access to portions of the western and southern sides of
installed. The horizontal well, however, would provide
upgradient side of the existing ditch.
equipment would be significantly less than those
Cooling Tower B, but access limitations would be localized. Movement of excavated and imported soil would
the least amount of flexibility of the four options with
required for installation of a deep trench.
be limited compared to deep trench options, as it would only be associated with shallow trenches for the
respect to optimization and proactive maintenance.
The existing ditch along the length of the proposed
French drain, piping and conduit.
trench would be lined with geomembrane and overlain
with concrete.
Page 1 of 1

iu►�i I
Figure 1 — Source Area Layout
1 July 2020
ERM PN 0550577
Page 9 of 10

Proposed Monitoring Well
Existing Monitoring Well
Proposed Full Scale Extraction
Well
Proposed Pilot Test Extraction Well
Proposed Source Control Area CAP -Proposed Source Control
Extraction Well Trench {(
Existing 18" Discharge Line Proposed French Drain DUKE
QProposed Node Building E1 7ERVY-
—•— Geographic Limitation
ENVIRONMENTAL RESOURCES MANAGEMENT, INC.
ER �.
■■■1•yI' M
BIN
6/30/2020
Source Area Layout
Duke Energy
Cliffside Steam Station
Mooresboro, North Carolina
o E TM�gGER
JR/BW
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6/30/2020
PPFROVER
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DATDRAWN
6/30/2020
BY S. Vickery
6/30/2020
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1 " = 110 '
ERI1111T NO.
0550577
EV
1

ERM
1 July 2020
ERM PN 0550577
Page 10 of 10
Attachment 1 — Flow and Transport Model Revision Technical Memorandum, Groundwater
Remediation Compliance Progress — Cliffside U5 AB (SynTerra, 2020)

IC7
synTerra TECHNICAL MEMORANDUM
Date: July 1, 2020 File: 1026.600.06A
To: Scott Davies (Duke Energy)
Ryan Czop (Duke Energy)
From: Regina Graziano (SynTerra)
Eric Hicks, PG (SynTerra)
Johnathan Ebenhack (SynTerra)
Subject: Flow and Transport Model Revision Technical Memorandum
Groundwater Remediation Compliance Progress - Cliffside U5 AB
SynTerra prepared this technical memorandum for Duke Energy as an update to the
Technical Memorandum: Modeling Evaluation of Extraction Wells and Trench, Unit 5 inactive
Ash Basin developed for the Duke Energy Rogers Energy Complex formerly Cliffside
Steam Station (CSS, Plant, or Site) provided in the Corrective Action Plan (CAP) Update
report (SynTerra, 2019). Specifically, this report is intended to present findings that
show that 10 vertical extraction wells are as effective as the originally proposed
extraction trench at capturing groundwater from the sluice discharge delta. The sluice
discharge delta is described in detail in the Technical Memorandum: Modeling Evaluation
of Extraction Wells and Trench, Unit 5 inactive Ash Basin provided in the Corrective Action
Plan (CAP) Update report (SynTerra, 2019).
Current Model Revision
The updated numerical model (updated U5 AB model) used for this evaluation is based
on the original numerical flow model (original U5 AB model) that is presented in the
Technical Memorandum: Modeling Evaluation of Extraction Wells and Trench, Unit 5 inactive
Ash Basin provided in the Corrective Action Plan (CAP) Update report (SynTerra, 2019).
The original U5 AB model was refined to improve the numerical model accuracy. The
numerical grid was refined west and south along the Unit 5 cooling tower B where the
proposed 10 extraction wells will be installed. Grid sizes were reduced from up to 40
feet in the original U5 AB model to 25 feet in the updated U5 AB model. The original
grid contained 159 rows and 217 columns. The revised grid contains 183 rows and 230
columns. The model layers were not changed. The refinement increased the total
number of active grid cells in the revised model from 731,868 cells to 900,272 cells. The
original U5 AB model design included a 380-foot long shallow groundwater extraction
trench and 12 vertical extraction wells (SynTerra, 2019). The extraction trench is located
west of the Unit 5 cooling tower B (Figure 1). The 12 vertical extraction wells proposed
in the original U5 AB model design included five wells north of Unit 5 cooling tower A,
Page 1

Flow and Transport Model Revision Technical Memorandum - U5 AB July 1, 2020
Rogers Energy Complex SynTerra
five wells south of Unit 5 cooling tower A, and two wells northwest of Unit 5 cooling
tower B (Figure 1).
The updated U5 AB model includes a remedial design proposed by Environmental
Resources Management, Inc. (ERM). This remedial design includes 10 vertical extraction
wells that replace the original 380-foot long groundwater extraction trench (Figure 1).
The updated U5 AB model also includes the original 12 vertical extraction wells
proximate to U5 cooling tower A described above (Figure 1).
The 10 vertical extraction wells designed by ERM are simulated using a vertical series of
MODFLOW DRAIN points. The method to simulate wells using MODFLOW DRAIN
points is described in the Technical Memorandum: Modeling Evaluation of Extraction Wells
and Trench, Unit 5 inactive Ash Basin (SynTerra, 2019). The 10 extraction wells are
installed approximately 35 feet below ground surface (bgs) with a constant drawdown
head of 25 feet bgs.
Groundwater Simulation Results
MODPATH particle tracking, with forward tracking, was used to evaluate the
performance of the 10 vertical extraction wells designed by ERM compared to the
extraction trench proposed in the 2019 CAP (SynTerra, 2019). The method to simulate
particle tracking is described in the Technical Memorandum: Modeling Evaluation of
Extraction Wells and Trench, Unit 5 inactive Ash Basin (SynTerra, 2019). Particles with
starting locations in the sluice discharge delta were tracked forward in time until they
discharged from the groundwater system. All particles simulated discharged to
extraction features (i.e., vertical extraction wells or the extraction trench) in both the
original and updated U5 AB models.
The original U5 AB model predicts that particles along the west side of the sluice
discharge delta are captured by extraction wells near the Unit 5 cooling tower A and
particles along the east side of the delta are captured by the extraction trench and
extraction wells near Unit 5 cooling tower B (Figure 1). The updated U5 AB model
predicts similar results; however additional particles from the east side of the sluice
discharge delta are captured by the newly proposed 10 vertical extraction wells
compared to the original extraction trench (Figure 1). Results from the updated U5 AB
model show that the 10 vertical extraction wells proposed by ERM are as effective as the
extraction trench at capturing groundwater from the sluice discharge delta.
REFERENCES:
SynTerra (2019). Corrective Action Plan Update. Cliffside Steam Station, Mooresboro, NC,
December 2019.
Page 2

Flow and Transport Model Revision Technical Memorandum - U5 AB July 1, 2020
Rogers Energy Complex
LIST OF FIGURES:
Figure 1 Particle Tracking Comparison of Extraction Trench and 10 Vertical
Extraction Wells
SynTerra
Page 3

Flow and Transport Model Revision Technical Memorandum - U5 AB July 1, 2020
Rogers Energy Complex
FIGURES
SynTerra

ORIGINAL 2019 CLIFFSIDE CAP
CORRECTIVE ACTION DESIGN
UNIT 5
INACTIVE
ASH BASIN
ERM PROPOSED
10 VERTICAL
EXTRACTION WELL DESIGN
1
♦• . �,
lb
.4-
• cw
GRAPHIC SCALE
LEGEND
270 0 270 540
1 10 ERM PROPOSED EXTRACTION WELLS
EXTRACTION WELLS
synTena
(IN FEET)
PARTICLE PATH
DRAWN BY: R. GRAZIANO DATE: 6/30/2020
-UNIT 5 TRENCH DRAIN
> DUKE
CHECKED BY: J. EBENHACK DATE: 07/01/2020
APPROVED BY: K. WEBB DATE: 07/01/2020
-SLUICE DISCHARGE DELTA
ENERGY-
PROJECT MANAGER: S. SPINNER
ASH BASIN WASTE BOUNDARY
C,' ..5
ASH BASIN COMPLIANCE BOUNDARY
www.synterracorp.com
NOTES:
ALL BOUNDARIES ARE APPROXIMATE.
FIGURE 1
THE 12 EXTRACTION WELLS SIMULATED IN THE ORIGINAL US AS MODEL AND THE UPDATED U5 AS MODEL HAVE
PARTICLE TRACKING
AN TOTAL SIMULATED FLOW RATE OF 24 GPM.
UPDATED MODEL EVALUATION COMPARING
THE EXTRACTION TRENCH IN THE ORIGINAL US AS MODEL HAS ATOTAL SIMULATED FLOW RATE OF 5 GALLONS
PER MINUTE (GPM). THE TRENCH DEPTH IS APPROXIMATELY 20 FEET BGS AND HAS A CONSTANT HEAD OF 15
EXTRACTION TRENCH DESIGN AND
FEET BELOW GROUND SURFACE (BGS).
10 VERTICAL EXTRACTION WELL SYSTEM DESIGN,
THE 10 WELLS PROPOSED BY ERM HAVE A TOTAL OF 10 GPM.
CALES
UNIT
UNIT 5 INACTIVE ASH BASIN
APPROXIIM AT 35 FEET BGS WITH A CONS ANTTXTRACTION
THE WELL DEIPTH HEAD OF 25 FEET BGSIMULATED S.
CLIFFSSIDE STEAM STATION
AERIAL PHOTOGRAPHY OBTAINED FROM ESRI ON DECEMBER 4, 2019. AERIAL WAS COLLECTED ON MAY 8, 2015.
MOORESBORO, NORTH CAROLINA
DRAWING HAS BEEN SET WITH A PROJECTION OF NORTH CAROLINASTATE PLANE COORDINATE SYSTEM FIPS
3200 (NAD83).

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