NC0004987_MSS_Appendix M_20191231

Corrective Action Plan Update December 2019
Marshall Steam Station
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V
REMEDIATION ALTERNATIVE SUMMARY
SynTerra

Remediation Alternatives
Remediation Alternative 1
Monitored Natural
Attenuation
Monitored Natural Attenuation
(MNA) relies on natural
attenuation mechanisms to
reduce constituent of interest
(COI) concentrations over time
to meet corrective action goals.
For inorganic constituents,
these processes include
adsorption to soil and bedrock
surfaces, precipitation, ion
exchange, dilution and
dispersion.
K
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
Lake Norman. Human receptors are not affected by
groundwater from the Site as water supply wells are located
upgradient or outside the drainage basin.
Furthermore, 65 water supply wells within 0.5 miles of the ash
basin have either been supplied with filtration systems or
connected to the municipal supply.
Environment
An ecological risk assessment was performed for the Marshall
Steam Station (MSS) using U.S. Environmental Protection
Agency (USEPA) guidance (see Appendix E). The risk
assessment found that the ash basin does not cause an
increase in risk to aquatic wildlife receptors (mallard duck,
great blue heron, bald eagle, and river otter) evaluated for
the Lake Norman exposure area.
B. Compliance With Applicable Regulations
Federal
MNA would comply with USEPA Coal Combustion Residuals
(CCR) Rule specified in 40 Code of Federal Regulations
(CFR) § 257.
State
MNA would comply with Coal Ash Management Act of
2014 (LAMA) and 15A North Carolina Administrative Code
(NCAC) 02L .0106.(1) (See Appendix I for additional
details on MNA). If approved and subject to notification
requirements including the NC Department of
Transportation and the North Carolina Department of
Environmental Quality (NCDEQ) for Sediment and Erosion
Control associated with monitoring well installation for
effectiveness monitoring.
Local
MNA is subject to notification requirements to affected
parties and Catawba County officials per Subchapter 02L
.0409.
APPENDIX M
REMEDIAL ALTERNATIVE SUMMARY
CORRECTIVE ACTION PLAN UPDATE
MARSHALL STEAM STATION
DUKE ENERGY CAROLINAS, LLC, TERRELL, NC
C. Technical & Logistical Feasibility
Ability to construct and operate technology
There are 155 monitoring wells already installed at the MSS
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 Conceptual Site Model (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 an effectiveness
groundwater 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 in the central North Carolina area to support
effectiveness monitoring.
D. Time Required to Initiate and Implement
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 an MNA network.
Permitting
Soil Erosion and Sediment Control permits are required for any
land disturbance, including well installation activities. 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 MSS 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 for the protection of
workers and the environment. All personnel would be required
to take relevant training and supply supporting documentation
to verify competency.
Environmental Impacts
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 groundwater modeling indicates compliance to
regulatory standards at the compliance boundary in
approximately 700 years following basin closure.
F. Long-term Effectiveness
Adequacy and Reliability of Controls
Implementation and maintenance of an effectiveness monitoring
program would be in place to evaluate variations from expected
conditions. Alternative measures can be taken to address
variations, if warranted. Potential risk to groundwater users was
further controlled by the installation of water filtration systems or
connecting households to the municipal water supply for water
supply wells within 0.5 miles of the MSS ash basin.
Implementation of institutional controls (provided by the
restricted designation) will further serve to 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 risk
to groundwater use is further controlled by the connection to
municipal water or additional of water filtration systems to water
supply users within 0.5 miles of the MSS ash basin and by
institutional controls that may include a restricted designation.
Page 1 of 6

Remediation Alternatives
Remediation Alternative 1
Monitored Natural
Attenuation
Monitored Natural Attenuation
(MNA) relies on natural
attenuation mechanisms to
reduce constituent of interest
(COI) concentrations over time
to meet corrective action goals.
For inorganic constituents,
these processes include
adsorption to soil and bedrock
surfaces, precipitation, ion
exchange, dilution and
dispersion.
K
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 standards.
Volume of Materials Destroyed or Treated
None. Cols 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 about 700 years.
Irreversible Treatment
None. Natural processes are not anticipated to be reversible
based on results of extensive geochemical modeling.
Type and Quantity of Residuals Remaining
None. The natural attenuation processes do not create additional
residuals for inorganic COIs.
APPENDIX M
REMEDIAL ALTERNATIVE SUMMARY
CORRECTIVE ACTION PLAN UPDATE
MARSHALL STEAM STATION
DUKE ENERGY CAROLINAS, LLC, TERRELL, NC
02L Standards at the Compliance Boundary
The flow and transport model predicts that concentrations of
COls would meet 02L standards at the compliance boundary in
approximately 700 years following ash basin closure.
Costs to Implement Remedial Alternative 1
Capital Costs
$734,000
Annual O&M Costs
$206,000
Total Life Cycle Costs
$3,695,000
Costs to implement MNA would be based on the assumption
Of 12 additional monitoring wells. Costs would also include the
needed labor and materials to perform groundwater sampling
on a semi-annual basis, and routine labor for annual and 5-
year reporting.
Life cycle costs are determined using a Net Present Value
(NPV) of expenditures for initial Capital costs and annual O&M
expenses for a period of 30 years. A Discount Rate of 5%
assumed in developing the cost estimate (Appendix K).
:akeholder Sentiment Regarding Implementation
is expected that there will be positive and negative
ntiment about implementation of an MNA program. No
idowner is affected and groundwater COIs do not pose an
acceptable risk to potential human or ecological receptors.
e remaining property is owned by Duke Energy, which is
ticipated to have institutional controls. Some community
Ikeholders might consider the time frame to achieve
mediation goals for boron to be unacceptable. However,
mmunity stakeholders with concerns regarding the capital
d near -term O&M costs associated with active remediation
3y favor a less costly alternative.
itil the final corrective action is developed and comments
received and reviewed, assessment of community
ceptance will not be fully informed.
Ability to Augment the Remedy, if Needed
MNA is an adaptable process. Long-term groundwater
monitoring implemented as part of MNA and can be an
effective tool in identifying the need for alternative
approaches if unexpected changes in Site conditions occur.
An MNA program would not hinder or preempt the use of
other remedial approaches in the future if conditions
change. In fact, an effectiveness monitoring program is an
essential part of any future remedial strategy. An MNA
effectiveness monitoring program would provide
information about changing Site conditions during and
after source control measures.
Environmental Footprint of the Remedy
The MNA remedy will impact the environment through energy
consumption and associated emissions associated with
installation of additional monitoring wells, periodic sampling
and analysis of groundwater.
Some clearing of wooded areas would be required to install
monitoring wells and maintain access for sampling activities.
Maintenance of access will also require energy consumption.
Alternative 1 utilizes significantly fewer resources during
construction and throughout the remedial timeframe when
compared to the other remedial alternatives. Therefore,
Alternative 1 is the least energy -intensive of the remedial
alternatives being considered, providing reduced, comparative
environmental footprint metrics in overall energy use and
across all air emission parameters.
Page 2 of 6

Remediation Alternatives
Remediation Alternative 2
Groundwater Extraction,
Infiltration and In -Situ
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 from the upper unsaturated
saprolite in order to mobilize the
Cols and effect their capture by
the extraction wells.
This remedy uses 33 extraction
wells to the south and east of the
ash basin. Clean water is infiltrated
through 7.3 acres of shallow
infiltration galleries east of the ash
basin.
Chemical amendments would be
injected into the subsurface along
the southern portion of the ash
basin dam in a grid of 143 closely
spaced boreholes to treat variably
reactive COIs in -situ.
Extracted water would be treated
and discharged through the
existing NPDES system.
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
Lake Norman. Human receptors are not affected by
groundwater from the Site as water supply wells are located
upgradient or outside the drainage basin.
Furthermore, 65 water supply wells within 0.5 miles of the ash
basin have either been supplied with filtration systems or
connected to the municipal supply.
Predictive flow and transport modeling indicate that the 02L
standard for boron could be achieved outside the compliance
boundary in approximately 30 years using active groundwater
remedial measures. Remedial Alternative 2 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).
Environment
An ecological risk assessment was performed for the Marshall
Steam Station (MSS) using U.S. Environmental Protection
Agency (USEPA) guidance (see Appendix Q. The risk
assessment found that the ash basin does not cause an
increase in risk to aquatic wildlife receptors (mallard duck,
great blue heron, bald eagle, and river otter) evaluated for
the Lake Norman exposure area.
B. Compliance with Applicable Regulations
Federal
The groundwater extraction, infiltration and in -situ
treatment specified in Remediation Alternative 2 would
comply with USEPA CCR Rule specified in 40 CFR § 257.
State
Alternative 2 would comply with LAMA, 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, clean water infiltration, and monitoring well
installation will be required per NCDEQ and Catawba
County regulations. Water withdrawal from Lake Norman
for use in the infiltration gallery would needed to
registered with the State. Underground infiltration of
water, or water with chemical amendments would be
designed to comply with 15A NCAC 02C .0225.
Local
Groundwater extraction, clean water infiltration, and in -
situ treatment can be implemented in compliance with
local laws and regulations.
APPENDIX M
REMEDIAL ALTERNATIVE SUMMARY
CORRECTIVE ACTION PLAN UPDATE
MARSHALL STEAM STATION
DUKE ENERGY CAROLINAS, LLC, TERRELL, NC
C. Technical & Logistical Feasibility
Ability to construct and operate technology
Technology to construct and operate a groundwater extraction,
infiltration, and treatment system proposed in Remediation
Alternative 2 is straightforward and readily 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. It 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 adding other remedial
alternatives, if warranted. Groundwater extraction or infiltration
wells can be added to the proposed system or removed from
service, as conditions dictate.
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 O&M Plan
would be implemented to track the gallons of water extracted
and the COI mass removed on a cumulative basis. Ongoing
review of data and periodic updates to the groundwater model
would be performed.
Ability to coordinate and obtain approvals from
other agencies
Soil erosion and sediment control permits are relatively
straightforward and can be obtained readily from Catawba
County. 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. Water withdrawal from Lake Norman
for use in the infiltration gallery would needed to registered with
the State.
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.
D. Time Required to Initiate and Implement
Requirements for bench scale testing
Additional hydrogeologic testing, including pilot testing, may be
required to complete the design to address heterogeneous
subsurface conditions, and confine 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.
Bench scale testing would also be conducted to verify the dosing
of chemical amendments to treat variably -reactive COIs.
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.
Water withdrawal from Lake Norman for use in the infiltration
gallery would needed to registered with the State.
An Underground Injection Control (UIC) permit for infiltration of
clean water into the subsurface would be required in accordance
with 15A NCAC 02C .0217.
E. Short-term Effectiveness
Protection of Community during remediation
The surrounding community would 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 MSS 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 the protection of
workers and the environment. All personnel would be required
to take relevant training and supply supporting documentation
to verify competency.
Environmental impacts
Remedial Alternative 2 has increased energy consumption to
operate the extraction, infiltration and treatment system. It will
also require additional energy for construction to manufacture
piping, well materials, chemical amendments and to excavate
trenches for piping and utilities. Environmental impacts
associated with clearing to install wells, infiltration galleries,
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 approximately 30
years after the system is placed into operation.
F. Long-term Effectiveness
Adequacy and reliability of controls
An extraction and infiltration system installed using predictive
modeling should be effective in reducing COI concentrations in
groundwater over time. Use of infiltration galleries will accelerate
pore volume turnover and reduce time to regulatory compliance.
Placement of chemical amendments in -situ would treat COIs in
the southern portion of the dam buttress area but may need to be
replenished over the life of the project.
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. Risk is mitigated to potential
groundwater users by the addition of water filtration systems,
connection to municipal supply, and institutional controls
(provided by the restricted designation). An Operations &
Maintenance plan would be developed and implemented to
operate the remedial system within design parameters and
document long-term effectiveness.
Magnitude of Residual Risk
The magnitude of residual risk will decrease as the remedial
program progresses over its expected 30-year timeframe.
Implementation of the groundwater extraction and clean water
infiltration system will result in a reduction of COIs in groundwater
at MSS. In -situ treatment with chemical amendments would
sequester other COIs making them immobile in groundwater.
Current state and predicted future state groundwater conditions
do not indicate unacceptable risk to human health or
environment. Potential risk is further mitigated to groundwater
users within 0.5 miles of the MSS ash basin by the addition of
water filtration systems, connection to municipal supply, and
institutional controls that may include a restricted designation.
Page 3 of 6

Remediation Alternatives
Remediation Alternative 2
Groundwater Extraction,
Infiltration and In -Situ
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 from the upper unsaturated
saprolite in order to mobilize the
Cols and effect their capture by
the extraction wells.
This remedy uses 33 extraction
wells to the south and east of the
ash basin. Clean water is infiltrated
through 7.3 acres of shallow
infiltration galleries east of the ash
basin.
Chemical amendments would be
injected into the subsurface along
the southern portion of the ash
basin dam in a grid of 143 closely
spaced boreholes to treat variably
reactive COIs in -situ.
Extracted water would be treated
and discharged through the
existing NPDES system.
G. Reduction of Toxicity, Mobility, & Volume
LLI
Treatment process used and materials treated
Treatment of affected groundwater would be performed using the
same water treatment system for the decanted water. Water
used for infiltration would be treated as necessary to ensure it
meets the requirements specified in 15A NCAC 02C .0217
(Underground Injection Control, UIC).
Chemical amendments (e.g., Meta Fix'") would be used to treat
COIs near the southern end of the dam buttress.
Volume of materials destroyed or treated
COIs would be removed from groundwater, treated and
discharged under an NPDES Permit in accordance with applicable
regulatory requirements.
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 stable site geochemical conditions.
Degree of expected reductions
COI concentration reductions are anticipated to meet regulatory
standards over time. The Flow and Transport Model predicts
concentrations of boron would be below the 02L standard at or
beyond the compliance boundary in a 30-year timeframe.
Irreversible Treatment
Mass removal would not be reversible for COIs. In -situ treatment
of COls would not be reversible under predicted stable
geochemical conditions.
Type and quantity of residuals remaining
Residuals may be present below regulatory standards as the
system would be intended to meet standards over time.
Residuals would also result from in -situ treatment of COIs by
chemical amendments (e.g., MetaFlx-),Which includes a mix of
the following: reduced iron, ferric iron, activated carbon, calcite,
and iron sulfide.
APPENDIX M
REMEDIAL ALTERNATIVE SUMMARY
CORRECTIVE ACTION PLAN UPDATE
MARSHALL STEAM STATION
DUKE ENERGY CAROLINAS, LLC, TERRELL, NC
02L Standards at the Compliance Boundary
flow and transport model predicts that concentrations of
would meet 02L standards at the compliance boundary in
oximately 30 years after implementation and ash basin
Costs to Implement Remedial Alternative 2
Capital Costs
$9,349,000
Annual O&M Costs
$670,000
Post -Remedy
$266,000
Monitoring
Well Abandonment
$138,000
Costs
Total Life Cycle Costs
$19,183,000
Costs to implement Remedial Alternative 2 would be based on
the assumption of 12 additional monitoring wells.
A network of 33 extraction wells and 7.3 acres of clean water
infiltration galleries would be installed. Chemical amendments
would be procured for infiltration into the subsurface in a grid
of 143 closely spaced boreholes along the southern end of the
dam buttress.
Costs would also include the needed labor and materials to
perform groundwater sampling on a semi-annual basis, and
routine labor for annual and 5-year reporting.
Life cycle costs are determined using a Net Present Value
(NPV) of expenditures for initial Capital costs and annual O&M
expenses for a period of 30 years; with post -remedy
monitoring for an additional 3 years. A Discount Rate of 5
assumed in developing the cost estimate (Appendix K).
akeholder Sentiment Regarding Implementation I I Ability to Augment the Remedy, if Needed
is expected that there will be positive and negative
Groundwater extraction using conventional well technology
ntiment about implementation of an active groundwater
is an adaptable process. It can be modified to address
reedy that includes extraction, infiltration and in -situ
changes to COI plume configuration or COI concentrations
�atment. No landowner is anticipated to be affected and
based on actual field data. Individual well pumping rates
aundwater Cols do not pose an unacceptable risk to
can be adjusted or eliminated or additional wells can be
tential human or ecological receptors. The remaining
installed to address COI plume changes.
'ected property is owned by Duke Energy, which is
ticipated to implement institutional controls.
The available land area for infiltration of clean water is
limited. If additional flow is determined to be needed to aid
is anticipated that the treated groundwater would be
in flushing of the saprolite, augmentation of this portion of
;charged through a NPDES permitted outfall that flows to
the remedial system would be limited if flow to the existing
ke Norman and the discharge would be treated as
system cannot be increased.
cessary to meet permit limits.
expanded groundwater extraction system that addresses
COI plume across the entire south and east perimeter of
basin may improve public perception. This alternative
iuld likely be perceived as more robust than MNA in
dressing groundwater affects, even if human health and
ological risks are essentially the same between MNA and
aundwater extraction and in -situ treatment.
me community stakeholders might consider the time frame
achieve remediation goals for boron preferable to the
adicted time under an MNA scenario.
infiltration of large quantities of chemical amendments to
t in -situ groundwater remediation may receive negative
iment from some stakeholders since residuals from these
nicals, and the COIs that they will treat, will remain in the
it the final Site remedy is developed and comments are
rived and reviewed, assessment of community acceptance
not be fully known.
Infiltration of amendments should not be a limiting factor if
it is later determined that alternative technologies should
be employed to augment the remedy.
An effectiveness monitoring program would provide
information about changing Site conditions during and
after source control measures.
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
Sustainability analysis was conducted to quantify the
environmental footprint of each remedial alternative based on
energy use and associated emissions, during the construction
phase, active remediation, and groundwater monitoring
activities.
The environmental footprint of Alternative 2 is the most
emission -intensive remedial alternative being considered.
Alternative 1 (MNA) requires significantly less materials and
energy than Alternative 2 and is therefore characterized by a
dramatically smaller environmental footprint. Conversely,
Alternative 2 generates a dramatically larger environmental
footprint than Alternative 3. Compared to Alternative 3,
Alternative 2 utilizes 13 fewer extraction wells, does not
employ 24 infiltration wells, but does propose the use of a 7-
acre infiltration gallery and the in -situ placement of
approximately 60 tons of reactive media through drilled
boreholes. The additional remediation system components
required by Alternative 2 will generate higher material -related
environmental footprint emissions for the construction phase
than Alternative 3. Additionally, the increased timeframe of
remediation system operation for Alternative 2 (30 years)
when compared to Alternative 3 (9 years) produces air
emissions more than five times the levels of Alternative 3. The
quantitative analysis of the environmental footprints of the
remedial alternatives under consideration for this CAP
indicates Alternative 2 to be the least sustainable option.
Page 4 of 6

Remediation Alternatives
Remediation Alternative 3
Groundwater Extraction
With Clean Water
Infiltration and 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
Flush residual concentrations of
COIs from the upper unsaturated
saprolite in order to mobilize the
COI and effect their capture my
the extraction wells.
Based on groundwater modeling
simulations, this remedy uses up
to 66 extraction wells to the south
and east of the ash basin. Clean
water is infiltrated into the
unsaturated saprolite along the
northeast portion of the ash basin,
between the basin and the
tributary through a series of up to
24 vertical clean water infiltration
Extracted water would be treated
and discharged through the
existing NPDES permit.
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
Lake Norman. Human receptors are not affected by
groundwater from the Site as water supply wells are located
upgradient or outside the drainage basin.
Furthermore, 65 water supply wells within 0.5 miles of the ash
basin have either been supplied with filtration systems or
connected to the municipal supply.
Predictive flow and transport modeling indicate that the 02L
standard for boron could be achieved outside the compliance
boundary in approximately 9 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
An ecological risk assessment was performed for the Marshall
Steam Station (MSS) using U.S. Environmental Protection
Agency (USEPA) guidance (see Appendix Q. The risk
assessment found that the ash basin does not cause an
increase in risk to aquatic wildlife receptors (mallard duck,
great blue heron, bald eagle, and river otter) evaluated for
the Lake Norman exposure area.
B. Compliance With Applicable Regulations
Federal
The groundwater extraction, infiltration and treatment
specified in Remediation Alternative 3 would comply with
USEPA CCR Rule specified in 40 CFR § 257.
State
Alternative 3 would comply with LAMA, 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, clean water infiltration, and monitoring well
installation will be required per NCDEQ and Catawba
County regulations. Water withdrawal from Lake Norman
for use in the infiltration well network would needed to
registered with the State. Underground infiltration of
water would be designed to comply with 15A NCAC 02C
.0225.
Local
Groundwater extraction, clean water infiltration, and
treatment can be implemented in compliance with local
laws and regulations.
APPENDIX M
REMEDIAL ALTERNATIVE SUMMARY
CORRECTIVE ACTION PLAN UPDATE
MARSHALL STEAM STATION
DUKE ENERGY CAROLINAS, LLC, TERRELL, NC
C. Technical & Logistical Feasibility
Ability to construct and operate technology
Technology to construct and operate a groundwater extraction,
infiltration, and treatment system proposed in Remediation
Alternative 3 is straightforward and readily available.
Technologies to treat extracted groundwater exist, but require
experience to successfully operate.
Reliability of technology
Groundwater extraction and clean water infiltration is a mature
technology and has been used to implement cleanup strategies
for similar COIs. It 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 from being implemented, if warranted.
Groundwater extraction or infiltration wells can be added to the
proposed system or removed from service, as conditions
dictate.
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 O&M Plan
would be implemented to track the gallons of water extracted
and the COI mass removed on a cumulative basis. Ongoing
review of data and periodic updates to the groundwater model
would be performed.
Ability to coordinate and obtain approvals from
other agencies
Soil erosion and sediment control permits are relatively
straightforward and can be obtained readily from Catawba
County. 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. Water withdrawal from Lake Norman
for use in the infiltration well network would needed to
registered with the State.
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.
D. Time Required to Initiate and Implement
Requirements for bench scale testing
Additional hydrogeologic testing, including pilot testing, may be
required to complete the design, to address heterogeneous
subsurface conditions, and confine 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.
An Underground Injection Control (UIC) permit for infiltration of
clean water into the subsurface would be required in accordance
with 15A NCAC 02C .0217.
Water withdrawal from Lake Norman for use in the infiltration
well network would needed to registered with the State.
E. Short-term Effectiveness
Protection of Community during remediation
The surrounding community would 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 MSS 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 the protection of
workers and the environment. All personnel would be required
to take relevant training and supply supporting documentation
to verify competency.
Environmental impacts
Remedial Alternative 3 has increased energy consumption to
operate the groundwater extraction, infiltration and treatment
system and will require additional energy for construction to
manufacture piping, well materials, 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 RA objectives are achieved
Predictive modeling indicates compliance to regulatory
standards at the compliance boundary in approximately 9 years
after the system is placed into operation.
F. Long-term Effectiveness
Adequacy and reliability of controls
An extraction and infiltration system installed using predictive
modeling should be effective in reducing COI concentrations in
groundwater over time. Use of infiltration wells will accelerate
pore volume turnover and reduce time to regulatory compliance.
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. Risk is mitigated to potential
groundwater users by the addition of water filtration systems,
connection to municipal supply, and institutional controls
(provided by the restricted designation). An Operations &
Maintenance plan would be developed and implemented to
operate the remedial system and document long-term
effectiveness.
Magnitude of Residual Risk
The magnitude of residual risk will decrease as the remedial
program progresses over its expected 9-year timeframe.
Implementation of the groundwater extraction and clean water
infiltration system will result in a reduction of COIs in groundwater
at MSS. Current state and predicted future state groundwater
conditions do not indicate unacceptable risk to human health or
environment. Potential risk is further mitigated to groundwater
users within 0.5 miles of the MSS ash basin by the addition of
water filtration systems, connection to municipal supply, and
institutional controls that may include a restricted designation.
Page 5 of 6

Remediation Alternatives
Remediation Alternative 3
Groundwater Extraction
with Clean Water
Infil ion and Treat ent
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 from the upper unsaturated
saprolite in order to mobilize the
COI and effect their capture my
the extraction wells.
Based on groundwater modeling
simulations, this remedy uses up
to 66 extraction wells to the south
and east of the ash basin. Clean
water is infiltrated into the
unsaturated saprolite along the
northeast portion of the ash basin,
between the basin and the
tributary through a series of up to
24 vertical clean water infiltration
wells.
Extracted water would be treated
and discharged through the
existing NPDES permit.
G. Reduction of Toxicity, Mobility, & Volume
Treatment process used and materials treated
Treatment of affected groundwater would be performed using the
same water treatment system for the decanted water. Water
used for infiltration will be treated as necessary to ensure it
meets the requirements specified in 15A NCAC 02C .0217 (UIC).
Volume of materials destroyed or treated
COIs would be removed from groundwater by pumping, 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 over time. The Flow and Transport Model predicts
concentrations of boron would be below the 02L standard at or
beyond the compliance boundary in a 9-year timeframe.
Irreversible Treatment
Mass removal would not be reversible for COIs.
Type and quantity of residuals remaining
Residuals may be present below regulatory standards as the
system would be intended to meet standards over time.
APPENDIX M
REMEDIAL ALTERNATIVE SUMMARY
CORRECTIVE ACTION PLAN UPDATE
MARSHALL STEAM STATION
DUKE ENERGY CAROLINAS, LLC, TERRELL, NC
02L Standards at the Compliance Boundary
ow and transport model predicts that concentrations of
would meet 02L standards at the compliance boundary in
ximately 9 years after implementation and ash basin
Costs to Implement Remedial Alternative 3
Capital Costs
$8,419,000
Annual O&M Costs
$690,000
Post -Remedy
$266,000
Monitoring
Well Abandonment
$109,000
Costs
Total Life Cycle Costs
$13,158,000
Costs to implement Remedial Alternative 3 would be based on
the assumption of 12 additional monitoring wells.
A network of 66 groundwater extraction wells and 24 clean
water infiltration wells would be installed.
Costs would also include the needed labor and materials to
perform groundwater monitoring on a semi-annual basis, and
routine labor for annual and 5-year reporting.
Life cycle costs are determined using a Net Present Value
(NPV) of expenditures for initial Capital costs and annual O&M
expenses for a period of 9 years; with post -remedy
monitoring for an additional 3 years. A Discount Rate of 5
assumed in developing the cost estimate (Appendix K).
Sentiment Regarding Implementation I (Ability to Augment the Remedy, if Needed
is expected that there will be positive and negative
ntiment about implementation of an active groundwater
nedy that includes groundwater extraction and clean water
filtration. No landowner is anticipated to be affected and
aundwater Cols do not pose an unacceptable risk to
tential human or ecological receptors. The remaining
'ected property is owned by Duke Energy, which is
ticipated to implement institutional controls.
is anticipated that the treated groundwater would be
;charged through a NPDES pennitted outfall that flows to
ke Norman and the discharge would be treated as
cessary to meet permit limits.
expanded groundwater extraction system that addresses
COI plume across the entire south and east perimeter of
basin may improve public perception. This alternative
iuld likely be perceived as more robust than MNA in
dressing groundwater impacts even though human health
d ecological risks are essentially the same between MNA
d groundwater extraction and infiltration.
me community stakeholders might consider the time frame
achieve remediation goals for boron preferable to the
adicted times under MNA and Remedial Alternative 2.
it the final Site remedy is developed and comments are
-ived and reviewed, assessment of community acceptance
not be fully known.
Groundwater extraction and clean water infiltration using
conventional well technology are adaptable processes.
They can be modified to address changes to COI plume
configuration or COI concentrations based on actual field
data. Individual well pumping/infiltration rates can be
adjusted or eliminated or additional wells can be installed
to address COI plume changes.
An effectiveness monitoring program would provide
information about changing Site conditions during and
after source control measures.
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
Sustainability analysis was conducted to quantify the
environmental footprint of each remedial alternative based on
energy use and associated emissions, during the construction
phase, active remediation, and groundwater monitoring
activities.
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.
Altemative 3 utilizes twice the extraction wells (66) than
Altemative 2 and a clean water infiltration system consisting
of 24 wells not planned for Alternative 2. However, Alternative
2 utilizes a 7-acre infiltration gallery and the in -situ placement
of approximately 60 tons of reactive media, through
boreholes, which Alternative 3 does not employ. As a result,
Alternative 3 will generate a lower material -related
environmental footprint for the construction phase.
Additionally, the smaller timeframe of remediation system
operation for Alternative 3 (9 years) when compared to
Alternative 2 (30 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.
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