NC0004979_Allen_Appendix M_20191231

Corrective Action Plan Update December 2019
Duke Energy Carolinas, LLC - Allen Steam Station
/I 9 \ O In V
REMEDIATION ALTERNATIVE SUMMARY
SynTerra

Remediation Alternatives
Remediation Alternative 1
Monitored Natural
Attenuation
Monitored Natural Attenuation
(MNA) relies on natural
attenuation mechanisms to reduce
COI concentrations over time to
meet corrective action goals. For
inorganics, these processes
include adsorption to soil and
bedrock surfaces, precipitation, ion
exchange, phyto-attenuation,
dilution and dispersion.
Q
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
A. Human Health & Environment
Human Health
There is no measurable difference between evaluated Allen Steam Station
(Allen, Station, or Site) risk and risk indicated by background concentrations;
therefore, no material increase in risks to human health related to the ash
basins have been identified. The assessment conservatively included potential
recreational receptors in Catawba River (Lake Wylie). Human receptors are
not affected by groundwater from the Site as water supply wells are located
upgradient or outside the drainage basin. Furthermore, within approximately
0.5 mile of the ash basins compliance boundary, 214 households and 2
businesses were connected to City of Belmont water supply, 10 were fitted with
water treatment systems, and three public water supply wells were abandoned
that served 77 households.
Environment
The Allen ash basins do not cause an increase in risks to ecological receptors
(mallard duck, great blue heron, muskrat, river otter, bald eagle, American
robin, meadow vole, red-tailed hawk, red fox and killdeer bird) evaluated for
the Catawba River (Lake Wylie) exposure area.
B. Compliance with Applicable Regulations
Federal
MNA complies with USEPA CCR Rule specified in 40 Code of Federal Regulations
(CFR) § 257.
State
MNA will comply with Coal Ash Management Act of 2014 and 15A NCAC 02L
.0106(I). If approved and subject to notification requirements including the NC
Department of Transportation and NCDEQ for Sediment and Erosion Control
associated with monitoring well installation for effectiveness monitoring. For
additional details on MNA see Appendix I.
Local
MNA would be subject to notification requirements to any affected parties and to
Gaston County officials per 15A NCAC 02L .0114(b).
C. Technical & Logistical Feasibility
0
Ability to construct and operate technology
There are 234 monitoring wells already installed related to the ash basin. Other than abandonment of
selected wells for basin closure and potential installation of additional monitoring wells, no significant
construction is required for implementation.
Reliability of technology
MNA has been used successfully to achieve remedial objectives for a wide range of COIs and geologic
settings either as a stand alone remedy, or in combination with other remediation approaches. The CSM
supports the reliability of an MNA approach.
Ease of undertaking additional RAs if necessary
Other remedial technologies have commonly been used in conjunction with MNA. Use of MNA will not
adversely impact the implementation of other potential remedial actions.
Ability to monitor effectiveness of remedy
Effectiveness is monitored through evaluation of COI concentrations over time in accordance with a
groundwater effectiveness monitoring program.
Ability to coordinate and obtain approvals from other agencies
MNA does not require interaction with other agencies to implement.
Availability of services and materials
An extensive groundwater monitoring well network already exists. Additional monitoring wells may be
required to complete the MNA well network. All services and materials are readily available to support
effectiveness monitoring.
Page 1 of 12

Remediation Alternatives
Remediation Alternative 1
Monitored Natural
Attenuation
Monitored Natural Attenuation
(MNA) relies on natural
attenuation mechanisms to reduce
COI concentrations over time to
meet corrective action goals. For
inorganics, these processes
include adsorption to soil and
bedrock surfaces, precipitation, ion
exchange, phyto-attenuation,
dilution and dispersion.
Q
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
D.
Requirements for bench scale testing
There are no requirements for bench scale testing to implement MNA.
Design
MNA is readily implementable. The existing monitoring well network can be
utilized to design the MNA network.
Permitting
Soil Erosion and Sediment Control permits are required for land disturbance
activities, including well installation. These permits are a straightforward to
procure.
E. Short-term Effectiveness
Protection of Community
The surrounding community would not be affected during implementation of MNA activities
performed on Duke Energy property. Any increase in traffic on roads leading to Allen due to the
nature of the work would be de minimis .
Worker Protection
Work would be performed under a Health & Safety Plan, which identifies risks and mitigation
measures to protect workers and the environment. All personal will be require relavent training
and supporting documentation to verify compentency.
Environmental Impacts
There would be Some migration of COI affected groundwater would be expected as part of the
attenuation process. However, human health and ecological risk assessments do not indicate
significant risks.
Time Until Action is Complete
Predictive modeling indicates compliance to regulatory standards at the compliance boundary
occurs approximately 320 years following basin closure.
F. Long-term Effectiveness
Adequacy and Reliability of Controls
Implementation and maintenance of an effectiveness monitoring program will be in place
to evaluate variations from expected conditions. Alternative measures can be taken to
address variations. Potential risks to groundwater users is further mitigated by the
connection of 191 households to the City of Belmont water supply, installation of water
filtration systems for water supply wells for 10 households, and abandonment of three
public water supply wells within a 0.5-mile radius of the ash basin compliance boundaries.
Implementation of institutional controls may include a restricted designation to further
protect potential groundwater users.
Magnitude of Residual Risk
Implementation of MNA will not result in increased residual risk, as the current state and
predicted future state does not indicate unacceptable risk to human health or
environment. Potential risks to groundwater users is further mitigated by the connection
of 191 households to the City of Belmont water supply, installation of water filtration
systems for water supply wells for 10 households, and abandonment of three public water
supply wells within a 0.5-mile radius of the ash basin compliance boundaries.
Implementation of institutional controls may include a restricted designation to further
protect potential groundwater users.
Page 2 of 12

Remediation Alternatives
Remediation Alternative 1
Monitored Natural
Attenuation
Monitored Natural Attenuation
(MNA) relies on natural
attenuation mechanisms to reduce
COI concentrations over time to
meet corrective action goals. For
inorganics, these processes
include adsorption to soil and
bedrock surfaces, precipitation, ion
exchange, phyto-attenuation,
dilution and dispersion.
Q
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
G. Reduction of Toxicity, Mobility, & Volume
Treatment Process Used and Materials Treated
None. Relies on natural attenuation processes and mechanisms such as dispersion and dilution to
reduce COI concentrations to below 02L/IMAC or Site -specific background values, whichever is
greater.
Volume of Materials Destroyed or Treated
None. COIs are inorganic and cannot be destroyed; however, COIs will be removed from
groundwater through geochemical processes.
Degree of Expected Reductions
COI concentration reductions will occur over time and are anticipated to meet regulatory standards
in approximately 320 years.
Irreversible Treatment
None. Natural processes are not anticipated to be reversible based on results of extensive
geochemical modeling; however, variations in pH and reduction -oxidation in the geochemical
environment can change effectiveness.
Type and Quantity of Residuals Remaining
None. The natural attenuation processes do not create additional residuals for inorganic COIs.
02L Standards at the Compliance Boundary
The flow and transport model predicts that concentrations of COIs would
meet 02L standards at the compliance boundary in approximately 320
vea rs.
Page 3 of 12

Remediation Alternatives
Remediation Alternative 1
Monitored Natural
Attenuation
Monitored Natural Attenuation
(MNA) relies on natural
attenuation mechanisms to reduce
COI concentrations over time to
meet corrective action goals. For
inorganics, these processes
include adsorption to soil and
bedrock surfaces, precipitation, ion
exchange, phyto-attenuation,
dilution and dispersion.
Q
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
I K. Adaptive Site Managemer
Stakeholder Sentiment Regarding Implementation I Ability to Augment the Remedy, if Needed
It is expected that there will be positive and negative sentiment about MNA is an adaptable process. Long-term groundwater monitoring
implementation of an MNA program. No landowner is affected and implemented as part of MNA and can be an effective tool in
groundwater COIs do not pose an unacceptable risk to potential identifying the need for alternative approaches if unexpected
human or ecological receptors. changes in Site conditions occur.
The property is owned by Duke Energy, which is anticipated to have An MNA program would not hinder or preempt the use of other
institutional controls. Some community stakeholders might consider a remedial approaches in the future if conditions change. In fact, an
300-year time frame to achieve remediation goals for boron and effectiveness monitoring program is an essential part of any future
sulfate to be unacceptable. However, community stakeholders with remedial strategy. An MNA effectiveness monitoring program would
concerns regarding the capital and near -term O&M costs associated provide information about changing Site conditions during and after
with active remediation may favor a less costly alternative. source control measures.
Until the final corrective action is developed and comments are
received and reviewed, assessment of community acceptance will not
be fully informed.
Environmental Footprint of the Remedy
MNA remedy will impact the environment through energy
>umption and associated emissions associated with installation of
itional monitoring wells and sampling and analysis of groundwater
itenance of access will also require energy consumption.
rnative 1 utilizes significantly fewer resources during construction
throughout the remedial timeframe when compared to the other
edial alternatives. Therefore, Alternative 1 is the least energy-
nsive of the remedial alternatives being considered, providing
iced, comparative environmental footprint metrics in overall
rgy use and across all air emission parameters.
Rationale for Selection of Remedial Alternative
Remedial Alternative 1 is not selected at this time, due to
the relatively long-term time frame to achieve compliance,
compared to Remedial Alternative 3.
Page 4 of 12

Remediation Alternatives
Remediation Alternative 2
Groundwater Extraction and
Treatment
Groundwater extraction which relies
on purmping and removal of
groundwater to reduce COI
concentrations over time to meet
corrective action goals.
This remedy includes 87 new
vertical extraction wells located to
the north, northeast, and east of
the ash basins and in the footprint
of the coal pile and Station power
block.
Extracted water would be treated
and discharged through the existing
NPDES system.
N
4
Ix
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
A. Human Health & Environment
Human Health
There is no measurable difference between evaluated Site risk and risk
indicated by background concentrations; therefore, no material increase in
risks to human health related to the ash basin have been identified. The
assessment conservatively included potential recreational receptors in the
Catawba River (Lake Wylie). Human receptors are not affected by
groundwater from the Site as water supply wells are located upgradient or
outside the drainage basin. Furthermore, within approximately 0.5 mile of the
ash basins compliance boundary, 214 households and 2 businesses were
connected to City of Belmont water supply, 10 were fitted with water treatment
systems, and three public water supply wells were abandoned that served 77
households.
Environment
The Allen ash basins do not cause an increase in risks to ecological receptors
(mallard duck, great blue heron, muskrat, river otter, bald eagle, American
robin, meadow vole, red-tailed hawk, red fox and killdeer bird) evaluated for
the Catawba River (Lake Wylie) exposure area.
B. Compliance with Applicable Regulations
Federal
The groundwater extraction and treatment specified in Remediation Alternative
2 would comply with USEPA CCR Rule specified in 40 (CFR) § 257.
State
Alternative 2 complies with the Coal Ash Management Act of 2014,15A NCAC
02L regulations and NCAC 02B regulations. NPDES permitted discharge is in
place. The NPDES Permit may need to be modified to accommodate the
discharge of treated groundwater. Procurement of Sediment and Erosion Control
permits associated with extraction and monitoring well installation is a straight-
forward process.
Local
Groundwater extraction and treatment can be implemented in compliance with
local laws and regulations.
C. Technical & Logistical Feasibility
Ability to construct and operate technology
Technology to construct and operate a groundwater extraction system is available. Technologies to
treat extracted groundwater exist, but require experience to successfully operate.
Reliability of technology
Groundwater extraction is a mature technology and has been used to implement cleanup strategies for
similar COIs, but is dependent on subsurface conditions and effectiveness of treatment approaches.
Issues such as well fouling must be considered during the detailed design process.
Ease of undertaking additional RAs if necessary
The technology doesn't preclude implementation of other remedial alternatives, if warranted.
Groundwater extraction or infiltration wells can be added to the proposed system or removed from
service, as warranted.
Ability to monitor effectiveness of remedy
Multiple methods can be used to monitor system effectiveness. An effectiveness monitoring plan would
be implemented to track changes in COI concentrations over time. A system Operations and
Maintenance (O&M) plan would be implemented to track the gallon of water extracted and the COI mass
removed on a cumulative basis. Ongoing review of data and periodic updates to the groundwater
modeling would be performed.
Ability to coordinate and obtain approvals from other agencies
Soil erosion and sediment control permits are relatively straightforward and can be readily obtained
from NCDEQ. An NPDES permit exists for the facility and currently include provisions for groundwater
remediation.
Availability of services and materials IMOM
All services and materials are readily available to support the remediation alternative. An extensive
groundwater monitoring well network already exists to support effectiveness monitoring.
Page 5 of 12

Remediation Alternatives
Remediation Alternative 2
Groundwater Extraction and
Treatment
Groundwater extraction which relies
on purmping and removal of
groundwater to reduce COI
concentrations over time to meet
corrective action goals.
This remedy includes 87 new
vertical extraction wells located to
the north, northeast, and east of
the ash basins and in the footprint
of the coal pile and Station power
block.
Extracted water would be treated
and discharged through the existing
NPDES system.
N
Q
Ix
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
D.
Requirements for bench scale testing
Additional hydrogeologic testing, including pilot testing, may be required to
complete the design, to address heterogeneous subsurface conditions, and
confirm model predictions. Collection of dynamic groundwater quality data
from wells may be required to confirm treatment options and design of any
treatment facilities if management of groundwater in the LRB, or discharge
under the existing NPDES permit is not viable.
Design
Detailed design activities would commence upon approval of the CAP Update by
NCDEQ. Full scale design is dependent on hydrogeologic testing and bench
testing, as required, to develop more accurate flow rates and estimates of
extracted groundwater quality. Final locations of extraction points, conveyance
piping, electrical service, tankage and potential treatment units would be
confirmed. Detailed design of electrical, mechanical and controls components
would then be finalized for bidding and construction.
Permitting
Soil erosion and sediment control permits are required for installation of wells
and other infrastructure that include ground disturbance (e.g., conveyance
piping). The NPDES permit can be modified if required for the discharge of
treated groundwater.
E. Short-term Effectiveness
Protection of Community during remediation
Community will not be impacted during active remediation and monitoring activities as they
would be performed on Duke Energy property. Any anticipated increase in traffic on roads
leading to Allen due to nature of the work would be de minimis .
Protection of workers during remediation
Work would be performed under a Health & Safety Plan, which identifies risks and mitigation
measures to protect workers and the environment. All personal will be require relavent training
and supporting documentation to verify compentency.
Environmental impacts
Remedial Alternative 2 has increased energy consumption to operate the extraction and
treatment system and will require additional energy for construction to manufacture piping, well
materials, pumps, and to excavate trenches for piping and utilities. Environmental impacts
associated with clearing to install wells and supporting infrastructure would be minimal and
work would be performed with a soil erosion and sediment control permit.
Time Until Action is Complete
Predictive modeling indicates compliance to regulatory standards at the compliance boundary in
500+ years after the system is placed into operation.
F. Long-term Effectiveness
Adequacy and reliability of controls
An extraction system installed using predictive modeling should be effective in reducing
COI concentrations in groundwater over time. Implementation and maintenance of an
effectiveness monitoring program would be in place to evaluate variations in water quality
from expected conditions. Alternative measures can be taken to address variations, if
warranted. Potential risks to groundwater users is further mitigated by the installation of
water filtration systems for water supply well within a 0.5-mile radius of the ash basin
compliance boundaries. Implementation of institutional controls may include a restricted
designation to further protect potential groundwater users. An Operations & Maintenance
plan will be developed and implemented to operate the remedial system within design
parameters and document long-term effectiveness.
Magnitude of Residual Risk
Implementation of a groundwater extraction and treatment system will not result in
increased residual risk, as the current state and predicted future state does not indicate
unacceptable risk to human health or environment. Potential risks to groundwater users is
further mitigated by the connection of 191 households to the City of Belmont water supply,
installation of water filtration systems for water supply wells for 10 households, and
abandonment of three public water supply wells within a 0.5-mile radius of the ash basin
compliance boundaries. Implementation of institutional controls may include a restricted
designation to further protect potential groundwater users.
Page 6 of 12

Remediation Alternatives
Remediation Alternative 2
Groundwater Extraction and
Treatment
Groundwater extraction which relies
on purmping and removal of
groundwater to reduce COI
concentrations over time to meet
corrective action goals.
This remedy includes 87 new
vertical extraction wells located to
the north, northeast, and east of
the ash basins and in the footprint
of the coal pile and Station power
block.
Extracted water would be treated
and discharged through the existing
NPDES system.
N
Q
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
G. Reduction of Toxicity, Mobility, & Volume
Treatment process used and materials treated
Treatment of the affected groundwater would be performed using the same water treatment system
used for the decanted water.
Volume of materials destroyed or treated
COIs would be removed from the groundwater, treated and discharged under an NPDES permit in
accordance with applicable regulatory requirements.
Degree of expected reductions
COI concentration reductions are anticipated to meet regulatory standards in a 500+ year
ti mefra me.
Irreversible Treatment
Mass removal would not be reversible for COIs. In -situ treatment of COIs would not be reversible
under stable geochemical conditions.
Type and quantity of residuals remaining
Residuals may be present below regulatory standards as the sysstem would be intended to meed
standards over time. Residuals removed through groundwater treatment for COIs would be
managed in accordance with applicable regulatory requirements.
02L Standards at the Compliance Boundary
he flow and transport model predicts that concentrations of boron and
ulfate would meet 02L standards at the compliance boundary in
pproximately 500+ years after implementation.
Costs to Implement Remedial Alternative 2
Capital Costs
$6,806,000
Annual Costs
$9,106,000
Total Life
$15,912,000
C
Cycle Costs
Costs to implement Remedial Alternative 2 would be based on the assumption installing a
network of 87 vertical extraction wells and associated piping and control system.
Costs would also include the needed labor and materials for redevelopment of wells, as
necessary, and routine labor for annual and 5-year reporting. pH Adjustment costs are also
included.
Life cycle costs are determined using a Net Present Value (NPV) of expenditures for initial
Capital costs and annual O&M expenses for the duration of the remedy. A Discount Rate of
5% assumed in developing the cost estimate.
Page 7 of 12

Remediation Alternatives
Remediation Alternative 2
Groundwater Extraction and
Treatment
Groundwater extraction which relies
on purmping and removal of
groundwater to reduce COI
concentrations over time to meet
corrective action goals.
This remedy includes 87 new
vertical extraction wells located to
the north, northeast, and east of
the ash basins and in the footprint
of the coal pile and Station power
block.
Extracted water would be treated
and discharged through the existing
NPDES system.
N
Q
Ix
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
Stakeholder Sentiment Regarding Implementation
It is expected that there will be positive and negative sentiment about
implementation of an active groundwater remedy that includes
extraction and treatment. No landowner is anticipated to be affected
and groundwater COIs do not pose an unacceptable risk to potential
human or ecological receptors. The remaining affected property is
owned by Duke Energy, which is anticipated to implement institutional
controls.
It is anticipated that the treated groundwater would be discharged
through a NPDES permitted outfall that flows to the Catawba River
(Lake Wylie) and the discharge would be treated as necessary to meet
permit limits.
An expanded groundwater extraction system that addresses the COI
plume across the east and northeastnortheast perimeter of the ash
basins and coal pile area may improve public perception. It is
anticipated that groundwater extraction and treatment would generally
receive more positive community acceptance than MNA since it
involves more active measures to extraction and reduce COI mass
from groundwater. This alternative would likely be percieved as more
robust than MNA in addressing groundwater impacts even if human
health and ecological risks are essentially the same between MNA and
groundwater extraction.
Until the final Site remedy is developed and comments are received
and reviewed, assessment of community acceptance will not be fully
known.
Ability to Augment the Remedy, if Needed
Groundwater extraction using conventional well technology is an
adaptable process. It can be easily modified to address changes to
COI plume configuration or COI concentrations based on actual field
data. Individual well pumping rates can be adjusted or eliminated,
or additional wells can be installed to address COI plume changes.
While it is not expected, treatment of the groundwater discharge
can be modified to address changes in COI concentrations or permit
limits.
Environmental Footprint of the Remedy
iinability analysis was conducted to quantify the environmental
rint of each remedial alternative based on energy use and
:iated emissions, during the construction phase, active
diation, and groundwater monitoring activities.
he Groundwater Extraction remedy will impact the environment
trough energy consumption associated with the installation of wells
)r monitoring and extraction as well as operating mechanical
umping for the lifespan of the project. If treatment further
'eatment is required, additional impact will be associated with
instruction and operation of a treatment facility as well as any
ssociated further disposal of treatment residuals. Groundwater
xtraction will also remove water from the subsurface at a rate less
ian anticipated basin recharge. Minor reductions in flow to surface
ater bodies are anticipated. Final design may include beneficial
:use of extracted groundwater or discharge of groundwater under
PDES permit.
Rationale for Selection of Remedial Alternative
Remedial Alternative 2 is not selected at this time, due to
the relatively long-term time frame to achieve compliance,
compared to Remedial Alternative 3.
Page 8 of 12

Remediation Alternatives
Remediation Alternative 3
Groundwater Extraction ith
Clean Water Infiltration
Treatment
Groundwater extraction relies on
pumping and removal of
groundwater to reduce
concentrations of COIs over time to
meet corrective action goals.
Infiltration of clean water is used to
flush residual concentrations of
COIs in order to mobilize the COI
and effect their capture my the
extraction wells.
The system would be implemented
north, northeast and east of the ash
basins and in the coal pile area and
Station power block. The remedy
includes 87 vertical extraction wells
with either 76 vertical clean water
infiltration wells or 48 vertical clean
water infiltration wells combined
M
with 22 horizontal clean water
Q
infiltration wells. Extracted water
would be treated and discharged
through the existing NPDES permit.
Extracted water would be treated
and discharged through the existing
NPDES permit. Water for infiltration
would be obtained through the fire
suppression system already in place
at the Site. The fire suppression
system obtains water from the
Catawa River through an on -Site
intake.
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
A. Human Health & Environment
Human Health
There is no measurable difference between evaluated Site risk and risk
indicated by background concentrations; therefore no material increase in risks
to human health related to the ash basin have been identified. The
assessment conservatively included potential recreational receptors in the
Catawba River (Lake Wylie). Human receptors are not affected by
groundwater from the Site as water supply wells are located upgradient or
outside the drainage basin. Furthermore, within approximately 0.5 mile of the
ash basins compliance boundary, 214 households and 2 businesses were
connected to City of Belmont water supply, 10 were fitted with water treatment
systems, and three public water supply wells were abandoned that served 77
households.
Predictive flow and transport modeling indicate that the 02L standards for
boron and sulfate could be achieved outside the compliance boundary in
approximately 10 years using active groundwater remedial measures.
Remedial Alternative 3 will achieve a higher degree of protection for human
health and the environment in a much shorter time -frame when compared to
Remedial Alternative 1 (MNA) or Remedial Alternative 2.
Environment
The Allen ash basins do not cause an increase in risks to ecological receptors.
The ecological risk assessment did not indicate an increase of risks to aquatic
wildlife receptors (mallard duck, great blue heron, bald eagle, river otter, and
killdeer bird) evaluated for the Catawba River (Lake Wylie) exposure area.
Notes:
CCR - coal combustion residuals
CFR - Code of Federal Regulations
COI - constituent of interest
CSM - conceptual site model
LRB - Lined Retention Basin
MNA - monitored natural attenuation
NCAC - North Carolina Administrative Code
NCDEQ - North Carolina Department of Environmental Quality
NPDES - National Pollution Discharge Elimination System
NPV - net present value
O&M - operation and maintenance
UIC - Underground Injection Control
USEPA - U.S. Environmental Protection Agency
B. Compliance with Applicable Regulations
Federal
The groundwater extraction, infiltration and in -situ treatment specified in
Remediation Alternative 3 would comply with USEPA CCR Rule specified in 40
(CFR) § 257.
State
Alternative 3 complies with the Coal Ash Management Act of 2014,15A NCAC
02L (groundwater standards) and NCAC 02B (surface water standards). NPDES
permitted discharge is in place. The NPDES Permit may need to be modified to
accommodate the discharge of treated groundwater. Procurement of Sediment
and Erosion Control permits associated with extraction and monitoring well
installation is a straight -forward process. Underground injection of water, or
water with chemical amendments would be designed to comply with 15A NCAC
02C .0225.
Local
Groundwater extraction, infiltration and in -situ treatment can be implemented in
compliance with local laws and regulations.
C. Technical & Logistical Feasibility
Ability to construct and operate technology
Technology to construct and operate Remediation Alternative 3 is straightforward and available.
Technologies to treat extracted groundwater exist but are less straight -forward to operate.
Reliability of technology
Groundwater extraction and clean water infiltration is a mature technology and has been used to
implement cleanup of similar COIs. It is strongly dependent on subsurface conditions and effectiveness
of treatment approaches.
Ease of undertaking additional RAs if necessary
The technology doesn't preclude implementation of other remedial alternatives. Groundwater extraction
or infiltration wells can be added to the proposed system or removed from service, as warranted.
Ability to monitor effectiveness of remedy
Effectiveness is monitored through changes in COI concentrations (decreases) and system operations.
Periodic review of data and revised predictive modeling can be used to evaluate optimization
opportunities. A system operation and maintenance plan would be implemented to track gallons of
water extracted and the COI mass removed on a cumulative basis.
Ability to coordinate and obtain approvals from other agencies
Soil erosion and sediment control permits are relatively straightforward and can be obtained readily. An
NPDES permit exists for the facility but may need to be modified for the discharge of treated
groundwater, which is a straight -forward process.
Availability of services and materials
All services and materials are readily available to support the remediation alternative and effectiveness
monitoring in the central North Carolina area.
Page 9 of 12

Remediation Alternatives
Remediation Alternative 3
Groundwater Extraction ith
Clean Water Infiltration
Treatment
Groundwater extraction relies on
pumping and removal of
groundwater to reduce
concentrations of COIs over time to
meet corrective action goals.
Infiltration of clean water is used to
flush residual concentrations of
COIs in order to mobilize the COI
and effect their capture my the
extraction wells.
The system would be implemented
north, northeast and east of the ash
basins and in the coal pile area and
Station power block. The remedy
includes 87 vertical extraction wells
with either 76 vertical clean water
infiltration wells or 48 vertical clean
water infiltration wells combined
M
with 22 horizontal clean water
Q
infiltration wells. Extracted water
would be treated and discharged
through the existing NPDES permit.
ad
Extracted water would be treated
and discharged through the existing
NPDES permit. Water for infiltration
would be obtained through the fire
suppression system already in place
at the Site. The fire suppression
system obtains water from the
Catawa River through an on -Site
intake.
Notes:
CCR - coal combustion residuals
CFR - Code of Federal Regulations
COI - constituent of interest
CSM - conceptual site model
LRB - Lined Retention Basin
MNA - monitored natural attenuation
NCAC - North Carolina Administrative Code
NCDEQ - North Carolina Department of Environmental Qualit
NPDES - National Pollution Discharge Elimination System
NPV - net present value
O&M - operation and maintenance
UIC - Underground Injection Control
USEPA - U.S. Environmental Protection Agency
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
D.
Requirements for bench scale testing
Additional hydrogeologic testing may be required to complete the design, to
address heterogeneous subsurface conditions, and confirm model predictions.
Collection of dynamic groundwater quality data from wells may be required to
confirm treatment options and design of any treatment facilities if management
of groundwater in the LRB or discharge under the existing NPDES permit is not
viable.
Design
Design activities would commence upon approval of the CAP Update by NCDEQ.
Full scale design is dependent on hydrogeologic testing and bench testing, as
required, to develop more accurate Flow rates and estimates of extracted
groundwater quality. Final locations of extraction points, conveyance piping,
electrical service, tankage and potential treatment units would be confirmed.
Detailed design of electrical, mechanical and controls components would then
be finalized for bidding and construction.
Permitting
Soil erosion and sediment control permits are required for installation of wells
and other infrastructure that include ground disturbance (e.g., conveyance
piping). The NPDES permit can be modified if required for the discharge of
treated groundwater.
An Underground Injection Control (UIC) permit for injection of clean water into
the subsurface will be required.
E. Short-term Effectiveness
Protection of Community during remediation
Community will not be impacted during active remediation and monitoring activities as they
would be performed on Duke Energy property. Any anticipated increase in traffic on roads
leading to Allen due to nature of the work would be de minimis .
Protection of workers during remediation
Work would be performed under a Health & Safety Plan, which identifies risks and mitigation
measures for workers and the environment. All personnel will be required to participate in
relevant training with supporting documentation to verify competency.
Environmental impacts
Remedial Alternative 3 has increased energy consumption to operate the system and will
require additional energy for construction to manufacture piping, well materials, pumps,
chemical reagents and to excavate trenches for piping and utilities. Waste streams may be
generated by the treatment approach requiring off -site disposal. Environmental impacts
associated with clearing to install wells and supporting infrastructure would be minimal and
work would be performed with a soil erosion and sediment control permit.
Time until RA objectives are achieved
Predictive modeling indicates compliance to regulatory standards at the compliance boundary in
10 years after the system is placed into operation.
F. Long-term Effectiveness
Adequacy and reliability of controls
Use of infiltration wells will accelerate pore volume turnover and reduce time to regulatory
compliance. Use of infiltration wells will accelerate pore volume turnover and reduce time
to regulatory complience. Implementation and maintenance of an effectiveness monitoring
program would be in place to evaluate variations in water quality from expected
conditions. Alternative measures can be taken to address variations, if needed. Potential
risks to groundwater users is further mitigated by the connection of 191 households to the
City of Belmont water supply, installation of water filtration systems for water supply wells
for 10 households, and abandonment of three public water supply wells within a 0.5-mile
radius of the ash basin compliance boundaries. An Operations & Maintenance plan will
be developed and implemented to operate the remedial system within design parameters.
Magnitude of Residual Risk
The magnitude of residual risk will decrease and the remedial program progresses over its
expected 9-year timeframe. Implementation of the groundwater extraction, infiltration,
and in -situ treatment system will result in a reduction of COIs in groundwater. Current
state and predicted future state groundwater conditions do not indicate unacceptable risk
to human health or environment. Potential risks to groundwater users is further
mitigated by the connection of 191 households to the City of Belmont water supply,
installation of water filtration systems for water supply wells for 10 households, and
abandonment of three public water supply wells within a 0.5-mile radius of the ash basin
compliance boundaries.
Page 10 of 12

Remediation Alternatives
Remediation Alternative 3
Groundwater Extraction ith
Clean Water Infiltration
Treatment
Groundwater extraction relies on
pumping and removal of
groundwater to reduce
concentrations of COIs over time to
meet corrective action goals.
Infiltration of clean water is used to
flush residual concentrations of
COIs in order to mobilize the COI
and effect their capture my the
extraction wells.
The system would be implemented
north, northeast and east of the ash
basins and in the coal pile area and
Station power block. The remedy
includes 87 vertical extraction wells
with either 76 vertical clean water
infiltration wells or 48 vertical clean
water infiltration wells combined
M
with 22 horizontal clean water
Q
infiltration wells. Extracted water
would be treated and discharged
through the existing NPDES permit.
Extracted water would be treated
and discharged through the existing
NPDES permit. Water for infiltration
would be obtained through the fire
suppression system already in place
at the Site. The fire suppression
system obtains water from the
Catawa River through an on -Site
intake.
Notes:
CCR - coal combustion residuals
CFR - Code of Federal Regulations
COI - constituent of interest
CSM - conceptual site model
LRB - Lined Retention Basin
MNA - monitored natural attenuation
NCAC - North Carolina Administrative Code
NCDEQ - North Carolina Department of Environmental Qualit
NPDES - National Pollution Discharge Elimination System
NPV - net present value
O&M - operation and maintenance
UIC - Underground Injection Control
USEPA - U.S. Environmental Protection Agency
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
G. Reduction of Toxicity, Mobility, & Volume
Treatment process used and materials treated
Treatment to the affected groundwater flow zones will be through removal of COI mass east and
northeast of the ash basins and coal pile area.
Volume of materials destroyed or treated
COIs will be removed from the groundwater flow zones in those areas where active groundwater
extraction is proposed. COI's will not be destroyed in the areas proposed for in -situ treatment but
would be sequestered in place and not be mobile under site geochemical conditions. COIs removed
by pumping would be transferred to another waste stream and disposed in accordance with
applicable regulatory requirements.
Degree of expected reductions
COI concentration reductions are anticipated to meet regulatory standards in a 9-year timeframe.
Irreversible Treatment
Mass removal would not be reversible for COIs. In -situ treatment of COIs would not be reversible
under stable geochemical conditions.
Type and quantity of residuals remaining
Residuals removed through groundwater treatment for COIs would be managed in accordance with
applicable regulatory requirements.
02L Standards at the Compliance Boundary
The flow and transport model predicts that concentrations of COIs would
meet 02L standards at the compliance boundary in approximately 10 years
after implementation.
Costs to Implement Remedial Alternative 3
Vertical Wells Only
Horizontal and Vertical Wells
Capital Costs
$11,819,000
$14,509,000
Annual Costs
$4,367,000
$4,367,000
Post -Remedy
$386,000
$386,000
Monitoring
Well
Abandonment
$82,000
$72,000
Costs
Total Life
$16,654,000
$19,334,000
Cycle Costs
Costs to implement Remedial Alternative 3 would be based on the assumption installing a
network of 87 vertical extraction wells and either 76 vertical clean water infiltration wells or
48 vertical clean water infiltration wells combined with 22 horizontal clean water infiltration
wells, and associated piping and control system.
Costs would also include the needed labor and materials for redevelopment of wells, as
necessary, and routine labor for annual and 5-year reporting. pH Adjustment costs are also
included.
Life cycle costs are determined using a Net Present Value (NPV) of expenditures for initial
Capital costs and annual O&M expenses for the duration of the remedy. A Discount Rate of
5% assumed in developing the cost estimate.
Page 11 of 12

Remediation Alternatives
Remediation Alternative 3
Groundwater Extraction ith
Clean Water Infiltration
Treatment
Groundwater extraction relies on
pumping and removal of
groundwater to reduce
concentrations of COIs over time to
meet corrective action goals.
Infiltration of clean water is used to
flush residual concentrations of
COIs in order to mobilize the COI
and effect their capture my the
extraction wells.
The system would be implemented
north, northeast and east of the ash
basins and in the coal pile area and
Station power block. The remedy
includes 87 vertical extraction wells
with either 76 vertical clean water
infiltration wells or 48 vertical clean
water infiltration wells combined
M
with 22 horizontal clean water
Q
infiltration wells. Extracted water
would be treated and discharged
through the existing NPDES permit.
ad
Extracted water would be treated
and discharged through the existing
NPDES permit. Water for infiltration
would be obtained through the fire
suppression system already in place
at the Site. The fire suppression
system obtains water from the
Catawa River through an on -Site
intake.
Notes:
CCR - coal combustion residuals
CFR - Code of Federal Regulations
COI - constituent of interest
CSM - conceptual site model
LRB - Lined Retention Basin
MNA - monitored natural attenuation
NCAC - North Carolina Administrative Code
NCDEQ - North Carolina Department of Environmental Qualit
NPDES - National Pollution Discharge Elimination System
NPV - net present value
O&M - operation and maintenance
UIC - Underground Injection Control
USEPA - U.S. Environmental Protection Agency
APPENDIX M - REMEDIATION ALTERNATIVES SUMMARY
CORRECTIVE ACTION PLAN UPDATE
ALLEN STEAM STATION
DUKE ENERGY CAROLINAS, LLC, BELMONT, NC
Stakeholder Sentiment Regarding Implementation
It is expected that there will be positive and negative sentiment about
implementation of an active groundwater remedy that includes
groundwater extraction and clean water infiltration. No landowner is
anticipated to be affected and groundwater COIs do not pose an
unacceptable risk to potential human or ecological receptors. The
remaining affected property is owned by Duke Energy, which is
anticipated to implement institutional controls.
Extracted groundwater would be discharged through a NPDES
permitted outfall that Flows to the Catawba River (Lake Wylie) and the
discharge would be treated as necessary to meet permit limits.
An expanded groundwater extraction system that addresses the COI
plume across the entire south and east perimeter of the basin may
improve public perception. It is anticipated that groundwater
extraction and treatment would generally receive more positive
community acceptance than MNA since it involves more active
measures to attempt physical extraction of COI mass from
groundwater. Some community stakeholders might consider a 9-year
time frame to achieve remediation goals for boron preferable to the
predicted time under an MNA scenario or 500+ years predicted for
Remedial Alternative 2.
Until the final Site remedy is developed and comments are received
and reviewed, assessment of community acceptance will not be fully
known.
Ability to Augment the Remedy, if Needed
Groundwater extraction and infiltration using conventional well
technology are adaptable processes. They can be easily modified to
address changes to COI plume configuration or COI concentrations.
Individual well pumping/infiltration rates can be adjusted or
eliminated or additional wells can be installed to address COI plume
changes.
While it is not expected, treatment of the groundwater discharge
can be modified to address changes in COI concentrations or permit
limits.
Environmental Footprint of the Remedy
The environmental footprint of Alternative 3 is the second -most
emission -intensive remedial alternative being considered. Alternative
1 (MNA) requires significantly less materials and energy than
Alternative 3 and is therefore characterized by a dramatically smaller
environmental footprint. Alternative 2 presents marginally higher
energy -consumption metrics when measured against Alternative 3.
Alternative 3 uses additional wells for infiltration wells not planned for
Alternative 2. The shorter timeframe of remediation system operation
for Alternative 3 (10 years) when compared to Alternative 2 (500+
years) produces air emissions far less than the levels of Alternative 2.
The quantitative analysis of the environmental footprints of the
remedial alternatives under consideration for this CAP indicates
Alternative 3 to be the second -most sustainable option after MNA.
Opportunities for system optimization and energy savings could be
pursued throughout the remediation timeframe, as conditions change
and component technologies possibly evolve.
Rationale for Selection of Remedial Alternative
Remedial Alternative 3 is selected as preferred groundwater
corrective action option for Allen. This alternative meets the
corrective action objectives described in Section 1.2 and
Section 6.6 of this CAP Update at or beyond the compliance
boundary in the most expeditious timeframe through the
flushing effect of clean water infiltration combined with
extraction. Although there are no significant risks to human
or ecological receptors, Alternative 3 will meet the
regulatory requirements most effectively and provids frther
protections for downgradient surface water. This alternative
is readily implementable although it is the most costly
alternative due to the addition of infiltration wells. The
system would also be adaptable based on field data results.
Page 12 of 12