NC0004987_MSS_Appendix B_20191231

Corrective Action Plan Update December 2019
Marshall Steam Station
APPENDIX B
SynTerra
COMPREHENSIVE SITE ASSESSMENT UPDATE
REPORT REVIEW COMMENTS RESPONSES

CSA Update Report Review Comments and Responses December 2019
Duke Energy Carolinas, LLC - Marshall Steam Station SynTerra
COMPREHENSIVE SITE ASSESSMENT (CSA) UPDATE REPORT REVIEW
COMMENTS AND RESPONSES
CSA UPDATE REPORT COVER LETTER COMMENTS AND RESPONSES
CSA Update Report Deficiencies Comment 1
The report contents are presented in a data summary format, exhibiting a lack of conclusive data
analysis and interpretation of site conditions.
Response Summary - 1
The report contents are presented in data summary format to clearly provide the
facts regarding site characterization. Duke Energy disagrees with the comment that
data analysis conclusions and interpretation of site conditions were not provided.
However, a more thorough discussion regarding site conditions and conclusions are
provided in the CAP Update report supported with tables, figures and modeling
results as specified in the CAP Content Guidance (April 27, 2018 and September 10,
2019 NCDEQ letters).
CSA Update Report Deficiencies Comment 2
The report fails to fully integrate and evaluate data collected from the CCR monitoring program
as well as previous versions of the CSA reports for the facility.
Response Summary - 2
As indicated above, all historical and current CSA data (as of report issuance) was
provided in tabular and pictorial form for succinct definition of site conditions.
Previous CSA and CAP submittals provided detailed information that was not
deemed necessary for repetitiveness in the CSA Update report; however, the CAP
Update report incorporates pertinent information from the previous reports to fully
address site conditions for corrective action. As stated in the CSA Update Report,
CCR groundwater data was considered in data interpretations; however, the CCR
data was not fully incorporated into the analysis of the CSA Update report due to
the data only becoming available as of mid -January 2018. Additional evaluation of
data obtained for CCR Rule compliance is included in the CAP supported with
tables, figures and modeling results for corrective action planning.
CSA Update Report Deficiencies Comment 3
The distribution of constituents of interest related to coal ash sources presented in the report
Often fail, for at least some areas of the site, to fully and clearly delineate exceedances of the 15A
NCAC 2L or 2B standards above background levels.
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CSA Update Report Review Comments and Responses December 2019
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Response Summary - 3
Deficiencies regarding 02L exceedances are better defined/delineated in the CAP
Update report supported by pertinent tables and figures (Table 6-5 [mean
groundwater quality data], Figures 6-7a through 6-7c [cross -sections] and Figures 6-
13a through 6-22 [isoconcentration maps). Additional wells have been installed for
further constituent delineation in the vicinity of the coal pile, gypsum pad, PV
structural fill, Industrial Landfill No. 1 (ILF) subgrade structural fill, Dry Ash
Landfills (Phase I and II) and ash basin dam. The results of these assessments are
incorporated into the CAP Update report and flow and transport modeling results
(Appendix G) and are also included in the detailed evaluation of fractured bedrock
provided in Appendix F. Two additional bedrock wells have been installed in
December 2019 to further delineate COI occurrence with depth near the PV
Structural Fill (PVSF-2BRL) and coal pile (CP-113R). Results of these assessments will
be available at a later date, and submitted to NCDEQ in accordance with the agreed -
upon quarterly data submittal schedule. Additional sampling to assess groundwater
(02L) to surface water (02B) interaction has been conducted in accordance with a
Work Plan approved by NCDEQ and provided in Appendix J of the CAP Update
report.
CSA Update Report Deficiencies Comment 4
The characterization of other primary and secondary sources other than impoundments that
contribute to the groundwater plumes is incomplete.
Response Summary - 4
Additional evaluations/assessments, as requested by NCDEQ, have been completed
in accordance with work plans approved by NCDEQ. The results of these extensive
additional evaluations conducted at the coal pile, gypsum pad, PV Structural Fill,
ILF structural fill subgrade, and Dry Ash Landfills Phase I and Phase II are provided
in the CAP Update. An overview of primary and secondary sources is presented in
Section 3 of the CAP Update report. Historical operations, usage, and assessment
activities conducted to date related to other primary sources adjacent to the ash
basin are provided therein.
In a letter from NCDEQ to Duke Energy dated April 5, 2019, the coal pile and
gypsum pad were identified as "sources hydrologically connected to
impoundments", and are to be included in the CAP Update (Appendix A).
Additionally, unsaturated soil sampling was completed in 2019 for horizontal
delineation of constituent concentrations beyond the ash basin waste boundary.
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CSA Update Report Review Comments and Responses December 2019
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These results are presented in Table 6-3 and Table 4, Appendix C and incorporated
into the CAP approach.
CSA Update Report Deficiencies Comment 5
As detailed more fully in the attached document, additional data gaps remain concerning
impacts from coal ash at the facility.
Response Summary - 5
Responses to the detailed Site -specific comments on the CSA Update were provided
to NCDEQ Mooresville Regional Office (MRO), and were discussed in a meeting on
September 11, 2018 and documented in the NCDEQ-approved meeting minutes
(Appendix B). Concurrence on the provided responses to comments was received at
this meeting. Additional data gaps as presented in the site specific CSA comments
are addressed in the CAP Update report with appropriate references within the
document. Since the CSA Update submittal, additional assessments have been
completed including additional well installations, pumping tests, bedrock
evaluation (including geophysical borehole surveys), groundwater to surface water
interaction, soil sampling, slug testing, geochemical modeling and associated
sampling, and groundwater flow and transport modeling.
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CSA Update Report Review Comments and Responses December 2019
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CSA UPDATE REPORT COMMENTS AND RESPONSES
DEQ-MRO Marshall CSA Update Report Comment 1
The report suggests there are inadequate data in the shallow flow layer beneath ash basin. It was
not explicitly called out as a data gap in the report, however, this is a data gap that should be
addressed accordingly to complete characterization of the shallow flow layer beneath the basins
and to support CAP development.
Response Summary - 1
Since the CSA Update submittal, 6 additional wells were installed within the
saprolite beneath the ash basin. Figure 1-2 shows the location of AB-5, AB-7, AB-8,
AB-14, AB-16, and AB-18 in plan view. The well network withinibeneath the basin is
depicted on three cross -sections presented in the CAP Update (Figures 6-2 through
6-5). As discussed in Section 5 of the CAP Update, the conceptual Site model (CSM)
for Marshall details a flow -through water system with groundwater movement into
the upgradient (northern) end and flowing laterally (to the east) through the middle
regions of the basin. Supporting evidence for the CSM is provided in Table 6-1,
which indicates limited impacts to groundwater beneath saturated ash within the
basin. Dams and dikes promote downward vertical gradients into the groundwater
system, which aid the movement of COIs through the system (Figure 5-1).
DEQ-MRO Marshall CSA Update Report Comment 2
Hexavalent chromium and total radium should be considered COIs at the site. Rationale for why
those constituents were not considered COIs at Marshall Steam Station should be provided.
Response Summary - 2
Hexavalent chromium and total radium data have been carried forward as COIs in
the Marshall CAP Update report to meet DEQ MRO's consistent requests for
inclusion. Occurrences of these constituents are accounted for in corrective action
planning.
DEQ-MRO Marshall CSA Update Report Comment 3
Based on review of the isoconcentration maps (Figures 11-1 thru 11-63), it is apparent that
vertical and horizontal extent of several COIs at several GWAICCR well pair locations is
warranted (can be discussed in greater detail between North Carolina Department of
Environmental Quality (NCDEQ) Mooresville Regional Office (MRO) and Duke Energy staff
prior to completing the CAP).
Response Summary - 3
This item was discussed between MRO and Duke Energy staff and their consultants
during the CSA comments and responses meeting held in Mooresville on September
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CSA Update Report Review Comments and Responses December 2019
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11, 2018. Additional COI delineation efforts re incorporated into the CAP Update
report by utilizing a COI management process (Table 6-6). This process included
assessing all COIs listed in the 2018 CSA Update, in addition to COIs included based
on CCR Rule compliance or DEQ MRO requests, for:
• Exceedances of flow layer background at or beyond the ash basin compliance
boundary
• Exceedances of Site background at or beyond the ash basin compliance
boundary
• Exceedances of piedmont background at or beyond the ash basin compliance
boundary
• Exceedances of 02L/IMAC at or beyond the compliance boundary
Isoconcentration maps for COIs in the CAP Update are provided in Figures 6-13a
through 6-22.
As mentioned above, additional wells have been installed for further horizontal and
vertical constituent delineation in the vicinity of the coal pile, gypsum pad, PV
structural fill, ILF subgrade structural fill, Dry Ash Landfills (Phase I and II) and ash
basin dam. The results of these assessments are incorporated into the CAP Update
report, groundwater modeling and corrective action planning. Additional
assessment and delineation efforts completed since the CSA Update (e.g.,
groundwater to surface water evaluation, Appendix J) are provided in the CAP.
Two additional bedrock wells have been installed in December 2019 to further
delineate COI occurrence with depth near the PV Structural Fill (PVSF-2BRL) and
coal pile (CP-1BR). Results of these assessments will be available at a later date, and
submitted to NCDEQ in accordance with the agreed -upon quarterly data submittal
schedule.
DEQ-MRO Marshall CSA Update Report Comment 4
A letter dated June 15, 2018, was submitted to Duke Energy which detailed MRO comments
and general agreement with PBTVs (Appendix H of this report) calculated for the Marshall
Steam Station.
Response Summary - 4
The comment is noted. Duke Energy submitted updated background threshold
values in 2019, upon which DEQ replied in a letter dated August 20, 2019.
Previously approved background values, in addition to the updated background
values calculated in 2019, are provided in the CAP Update report (Table 4-2 and
Table 4-3), as an approved background threshold value is only an initial step in
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evaluating a constituent's association with a source area or as a result of naturally -
occurring concentrations or as a result of naturally -occurring concentrations.
DEQ-MRO Marshall CSA Update Report Comment 5
The report stated, "However, the CCR data has not been fully incorporated into the analysis of
this CSA due to the data only becoming available as of mid -January 2018. For example,
analytical results from CCR Rule -specific monitoring wells are included on isoconcentration
maps and analytical summary tables, but not integrated into detailed mathematical analysis,
such as piper plots, box -and -whisker plots or background statistical calculations." While it is
accurate that the CCR data collected as part of the federal CCR Rule was not publicly available
until mid -January 2018, the data was available to Duke Energy and their consultants as it was
collected between 2016 to the present. CCR data could have and should have been utilized to the
fullest extent in this report, but it appears that it was not. During review of this report, it was
unclear when CCR data was utilized and included in evaluations and the extent to which it was
utilized. CCR Groundwater data is expected to be fully incorporated into the CAP.
Response Summary - 5
Groundwater data from monitoring wells associated with the CCR Rule compliance
program are utilized and incorporated into the CAP Update report [i.e., COI
management (Table 6-6), plume stability analysis, tables, figures) and associated
geochemical modeling (Appendix H), groundwater flow and transport modeling
(Appendix G), monitored natural attenuation evaluation (Appendix I) and
groundwater to surface water interaction evaluation (Appendix J). All available
CCR Rule groundwater monitoring well data is provided in Table 1, Appendix C.
DEQ-MRO Marshall CSA Update Report Comment 6
During review of this report, it was noticed that data collected from the select wells that continue
to exhibit high pH or turbidity (likely due to grout contamination) were not presented or
included in the evaluations as they were deemed invalid. This is contrary to what was agreed
upon between MRO, Duke Energy and their consultants in a meeting on June 15, 2017. In
order to reach a compromise regarding well replacements due to grout contaminated wells,
MRO, Duke Energy and their consultants agreed that boron and sulfate were seemingly
unaffected by elevated pH and/or turbidity and instead of installing replacement wells at select
locations they would be water level monitoring and sampling of boron and sulfate. Collection of
these select parameters would allow for monitoring of flow and transport of leading edge
constituents which would also be useful for modeling. If Duke Energy and their consultants do
not support use of this data as part of the assessment, then the wells should be replaced.
Response Summary - 6
The data in question was used in the CSA Update qualitatively and to draw
isoconcentration lines, but was not posted on figures in order to avoid confusion.
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CSA Update Report Review Comments and Responses December 2019
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Figures within future submittals will include the data in question and qualify the
results with notes as appropriate.
DEQ-MRO Marshall CSA Update Report Comment 7
Upward gradients were observed within the footprint of the Phase II landfill. An evaluation of
the upward gradients and COIs (i.e., increasing boron with depth and over time) observed at this
location should be provided and should also include discussion of the relevance in terms of
contaminant movement.
Response Summary - 7
Additional evaluations of horizontal and vertical gradients are presented in the CAP
Update report (Table 5-2 and Table 5-3). Discussions of the vertical gradients are
presented in Section 5.1.2 as part of the updated conceptual site model (CSM).
Updated vertical hydraulic gradients provided in the CAP Update indicate a
generally downward vertical gradient between the shallow groundwater and wells
screened within deep (>300 ft bgs) bedrock fractures beneath the Dry Ash Landfill
Phase II.
An evaluation of the bedrock, and groundwater flow within it, underlying the Dry
Ash Landfill Phase II was conducted in 2019. This evaluation included borehole
logging with a heat -pulse flowmeter, which provide detailed borehole flow
characteristics within the bedrock beneath the landfill. The fractured bedrock
evaluation (Appendix F) provides additional detail and evaluation of the
groundwater flow system at Marshall. Additional assessments below the Dry Ash
Landfill Phase II (AL-2BRLLL) and downgradient (AB-10RBL, MW-14BRL) have
been completed since the submittal of the CSA Update.
DEQ-MRO Marshall CSA Update Report Comment 8
Concentration trends were provided graphically (Figures 14-39 thru 14-76). While these figures
did give a graphical representation of the data, there was no discussion/evaluation provided on
how hydrogeological and/or geochemical factors affect COI migration and concentrations
observed across the site and what was likely causing the trends observed.
Response Summary - 8
A detailed evaluation of temporal COI concentration trends were provided in the
2019 CAMA Annual Report (SynTerra 2019). The updated CSM for Marshall,
presented in Section 5, discusses how hydrogeological and geochemical factors
affect COI distribution across the Site. Additional COI delineation efforts are
incorporated into the CAP Update report by utilizing a COI management process, as
presented on Table 6-6. COI trend analyses were completed and supported by
analysis using Mann -Kendall methods (Section 6.1.5.1). Isoconcentration maps for
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CSA Update Report Review Comments and Responses December 2019
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COIs in the CAP Update are provided in Figures 6-13a through 6-22. Additional
discussion of site conditions and their implications on COI presence and
concentrations is discussed in Section 6.1 of the CAP Update report.
Further discussion of groundwater hydraulic gradients at Marshall is provided in
the Groundwater Flow and Transport Modeling Report (Appendix G). Geochemical
modeling results may provide the basis for explanations of COI variability
(Appendix H).
DEQ-MRO Marshall CSA Update Report Comment 9
Evaluations of groundwater data along transects were inconsistent (i.e., not using the same
wells along the transect) throughout the report. Wells should be used consistently throughout
the report to allow for a more appropriate evaluation/review of the data.
Response Summary - 9
Flow transects selected for graphical depictions of temporal COI concentration
trends in the CSA Update report were not intended as duplicates of the selected
geochemical flow transects. Flow transects utilized for geochemical modeling that
was conducted to support corrective action planning are presented in the updated
geochemical modeling report (Appendix H). The geochemical transects chosen were
selected in consultation with the groundwater flow and transport modeling team to
represent the dominant flow paths from the ash basin to potential downgradient
receptors along the flow paths. Each transect has multiple flow paths which were
determined through modeled outputs provided by the flow and transport model
(Appendix G).
DEQ-MRO Marshall CSA Update Report Comment 10
It is stated in the report that the majority of ash in the ash basin is saturated. What is the
estimated total volume of saturated ash vs. unsaturated ash? If decanting/dewatering is
anticipated, what is the estimated volume of ash that will remain saturated? What implications
does this volume of ash that will remain saturated have on contaminant concentrations and
migration if the ash will be capped -in -place as the method of source control? Cap -in -place does
inhibit infiltration, but does not account for lateral groundwater/contaminant flow and this
must be factored in during the CAP. The CAP should explain how the lateral component of
groundwater flow and resulting contaminant flux will be addressed if source material will
remain in place.
Response Summary - 10
The CAP Update report considers the effects of potential closure scenarios,
including how closure activities would affect the water table. The groundwater flow
and transport model (Appendix G) assesses pre -decanting and future Site
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conditions, including the extent of COI migration for potential closure scenarios.
Figures 5-5a through 5-5c in the CAP Update report compares hydraulic conditions
at Marshall for pre -decanting and post closure scenarios. The impact of
decanting/closure activities is discussed in Sections 5 and 6.
Estimated volumes and thicknesses of saturated source material were provided by
the closure engineers (AECOM, 2019). Estimates of potential saturated source
material left in place under a closure -in -place scenario are also addressed in the CAP
Update.
The updated Groundwater Flow and Transport Modeling Report (Appendix G)
provides an evaluation of the effects of potential remaining saturated source
material. Modeling simulations indicate very little difference in predicted boron
plumes between closure -by -excavation and closure -in -place scenarios.
Groundwater remediation designs proposed in the CAP Update could be
implemented with the same effectiveness under each potential closure scenario
(i.e., time to achieve groundwater compliance).
DEQ-MRO Marshall CSA Update Report Comment 11
It is stated in the report that, "For basin closure, reduction of infiltrating water will have the
greatest positive impact on groundwater and surface water quality downgradient of the ash
basins." This statement needs to be substantiated considering the majority of ash at Marshall
Steam Station is below the water table and will be a continued source to groundwater impacts
under this closure option.
Response Summary - 11
The CAP Update report considers the effects of potential closure scenarios,
including how closure activities would affect the water table. The groundwater flow
and transport model (Appendix G) assesses pre -decanting and future Site
conditions, including the extent of COI migration for potential closure scenarios.
Figures 5-5a through 5-5c in the CAP Update report compares hydraulic conditions
at Marshall for pre -decanting and post closure conditions. The impact of
decanting/closure activities is discussed in Sections 5 and 6.
DEQ-MRO Marshall CSA Update Report Comment 12
Based on review of Figure 14-77, delineation of soil impacts has not been completed at Marshall
Steam Station. Soil contamination should be delineated to either the site -specific PBTVs or
Protection of Groundwater (POG) Preliminary Soil Remediation Goals (PSRGs), whichever is
higher. Where appropriate, use the equation provided in the PSRG table to establish a POG
PSRG for a constituent with 02L standard that does have a PSRG established.
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CSA Update Report Review Comments and Responses December 2019
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Response Summary - 12
Since the 2018 CSA Update, additional soil sampling efforts were conducted in April
2019 and September/October 2019 to delineate concentrations of COIs detected
greater than soil background values and/or PSRG POGs, whichever is greater. These
results are presented in Table 6-3 and Appendix C, Table 4 and incorporated into
the CAP approach.
There is no potential secondary source of constituents to groundwater from leaching
of soil, and no soil concentrations are identified for corrective action at the Site. Data
indicate unsaturated soil constituent concentrations at or beyond the compliance
boundary are generally consistent with background concentrations or are less than
regulatory screening values (Table 6-3).
Where detected concentrations are greater than a comparative criteria, these
concentrations beyond the waste boundary were generally within the range of
concentrations detected in soil samples from upgradient and/or background
locations (Appendix C, Table 4). Additionally, all unsaturated soil samples with
values reported greater than the PSRG POG standard or background values are
vertically delineated by groundwater constituent concentrations less than applicable
regulatory criteria in the corresponding monitoring well (Appendix C, Table 1).
Furthermore, there is a lack of transport mechanisms by which the COI could have
migrated from the source area to the unsaturated soils. For these reasons, the soil
concentrations do not warrant consideration as potential secondary source of
constituents to the groundwater.
Additional information regarding unsaturated soils can be found in Section 6.1.1.6,
6.1.2, and 6.1.3 of the CAP Update report.
DEQ-MRO Marshall CSA Update Report Comment 13
Provide an explanation of how and why soil contamination occurs outside of the waste
boundaries, particularly soils which exhibit elevated concentrations of arsenic, barium,
chromium, iron, manganese, selenium, sulfate, strontium, and vanadium upgradient of the ash
basin.
Response Summary - 13
See response to MRO Comment 12 above. Many of the locations noted as having
elevated concentrations of select COIs are at background and/or upgradient
locations and there is no transport mechanism for these concentrations to have been
a result of migration from the source area. At downgradient locations, constituent
concentrations are predominantly similar to, or less than, values from
background/upgradient locations. The basins are surrounded by dikes or naturally
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CSA Update Report Review Comments and Responses December 2019
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elevated ground surface and there is no known pathway for COIs to migrate beyond
the waste boundary of the ash basin, except for potentially, along the flow channels
of seeps from the basins. There have been no reported releases of coal combustion
residuals from the basins. Therefore, concentrations greater than soil background
values (Table 4-2) are attributed to naturally occurring regional variability. Multiple
lines of evidence, including the natural occurrence of elements, Site groundwater
divides and flow direction, groundwater flow and transport modeling (Appendix
G), and geochemical modeling (Appendix H), the noted soil concentrations do not
suggest impacts from the ash basin. Soil concentrations do not warrant
consideration as potential secondary source of constituents to the groundwater.
DEQ-MRO Marshall CSA Update Report Comment 14
Groundwater data suggests the Phase I/Phase II Landfills and the PV Structural Fill are
contributing to groundwater impacts at the site and should be considered other primary sources,
but was not documented as such in this report. The coal pile is located west of the ash basin and
should be evaluated as another potential primary source, but was not documented as such in the
report. Further assessment is warranted in the areas mentioned above for purposes of delineation
and to understand contributions of groundwater impacts observed at the site.
Response Summary - 14
Additional assessments have been completed in accordance with NCDEQ-approved
Work Plans for the coal pile, gypsum pad, PV structural fill, ILF subgrade structural
fill, and Dry Ash Landfills (Phase I and II). An overview of additional primary
sources adjacent to the ash basin is presented in Section 3 of the CAP Update report.
A certification that consensus was reached with the NCDEQ DWR regarding
sources not considered for corrective action as part of the CAP was provided in a
letter from NCDEQ to Duke Energy dated April 5, 2019. Groundwater and soil data
from these assessments are provided in Appendix C and incorporated into
appropriate figures and tables within the CAP Update report. Evaluations of these
data are incorporated into corrective action planning.
DEQ-MRO Marshall CSA Update Report Comment 15
Duke Energy recognizes the need for additional surface water samples and submitted a proposal
to conduct 2L-2B compliance sampling at the facility. To date, only grab surface water samples
have been collected at the facility, which is not in compliance with 02B for calculating acute and
chronic values for select constituents. 2L-2B sampling is necessary to assess the leading edge of
the contaminant plume to allow for a better understanding of groundwater discharge to surface
waters. Also, it has a direct bearing on remedial technologies available for use at the site. If 2L-
2B compliance cannot be adequately demonstrated then MNA may not be considered a viable
option as a remedial technology.
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Response Summary - 15
Additional sampling and further assessment of current conditions groundwater
(02L) to surface water (02B) interaction was conducted in 2018 and submitted in
March 2019; an updated report considering regulatory revisions from 2019 is
provided in Appendix J of the CAP Update report. Furthermore, a surface water
evaluation for future conditions is also provided in Appendix J. The future
conditions evaluation utilizes components of both the geochemical and flow and
transport models for Marshall. Constituent transport related to plume movement
and potential 02B impacts are further described in the flow and transport (Appendix
G) and geochemical model (Appendix H) reports.
DEQ-MRO Marshall CSA Update Report Comment 16
Vertical gradient maps (Figure 6-11): Evaluation of upward gradients observed at the site in
respect to contaminant movement should be discussed.
Response Summary - 16
Additional evaluations of vertical gradients are presented in the CAP Update report
(Table 5-3). Discussions of the vertical gradients are presented in Section 5.1.2 as
part of the updated conceptual site model (CSM). The fractured bedrock evaluation
(Appendix F) provides additional detail and evaluation of the groundwater flow
system at Marshall. The CAP also provides an evaluation of gradients and their
effects on constituent transport from the ash basins and adjacent source areas, with
support provided by the flow and transport model (Appendix G).
DEQ-MRO Marshall CSA Update Report Comment 17
Isoconcentration maps (Figures 11-1 thru 11-63): ALL data points should be included on figures
regardless of validity of data. Maps/figures are visual representations of data, but when data is
left off it can be misleading and result informing inappropriate conclusions. Notes should be
added regarding data validity and an explanation of why better -quality data is needed to provide
a more accurate assessment of actual site conditions.
Response Summary - 17
Data presented in the CSA Update report is intended to be used to present a clear
representation of site conditions. Presenting invalid or questionable data can be
misleading and result in inaccurate interpretation of results. Therefore, data trend
analysis were performed to establish means data (Table 6-5) that is used to create
isoconcentration maps (Figures 6-13a through 6-22) in the CAP Update report.
Data included on the updated isoconcentration maps represent results of a central
tendency analysis, which was completed to capture the appropriate measure of
central tendency (arithmetic mean, geometric mean, or median) for each dataset of
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constituent concentrations. Previous Site assessments might have overrepresented
areas affected by the ash basin by posting a single data set on maps and cross -
sections that might have included isolated data anomalies. Invalid/questionable data
will continue to be carefully evaluated using professional judgement and presented
with caution, where appropriate, through the use of detailed notes to qualify
invalid/questionable data on figures within future submittals to avoid
misrepresentation of site conditions.
DEQ-MRO Marshall CSA Update Report Comment 18
Isoconcentration maps (Figures 11-1 thru 11-63): The maps indicated that data collected
between February 2015 and September 2017. It should be indicated on the map for each data
point which sampling event the data is from so that can be factored into the review/evaluation of
data provided on the maps. If the majority of the data is from the September 2017 sampling
event and a small subset is from other sampling events, simply state that in the legend and then
on the map next to the locations that differ put the date of the sampling event the data was
obtained.
Response Summary - 18
The CAP Update report evaluates groundwater data collected from January 2018
through June 2019 and more recent data, as available, from the adjacent source areas
(i.e., CP-113R). As discussed above, the data was evaluated using means analysis to
more accurately depict groundwater conditions at the Site. Isoconcentration maps
(Figures 6-13a through 6-22) reflect data presented in Table 6-5. Table 6-5 is a
summary table presenting the mean values of groundwater COIs using samples
collected between February 2018 and May 2019. A comprehensive data analytical
table for groundwater is included as Table 1, Appendix C.
DEQ-MRO Marshall CSA Update Report Comment 19
Isoconcentration maps (Figures 11-1 thru 11-63): Reporting limits should be utilized instead of
ND (non -detect). This provides meaningful information.
Response Summary - 19
Isoconcentration maps (Figures 6-13a through 6-22) presented in the CAP Update
report utilize reporting limits in place of ND (non -detect).
DEQ-MRO Marshall CSA Update Report Comment 20
Isoconcentration maps (Figures 11-1 thru 11-63): There were instances where isoconcentration
lines were not provided because it was deemed attributable to background. This is
misleading... the map should be representative of available site data and then any
evaluation/interpretation of that data should be included in the report itself.
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Response Summary - 20
The intent of isoconcentration maps is to depict plumes of COIs derived from the
ash basin. By including data attributable to background, the isoconcentration maps
would not be diagnostic of the ash basin impacts on the groundwater and would be
further misleading to the reader. Therefore, it is not appropriate to contour
background values that exhibit natural variability and are not attributable to
constituent migration from source areas.
Isoconcentration maps (Figures 6-13a through 6-22) presented in the CAP Update
report depict both 02L/IMAC and background concentration lines where the
regulatory standard is greater than the background concentration. For COIs with no
established 02L/IMAC criteria, or background values greater than the 02L/IMAC
criteria, only background concentration lines are shown. As discussed in Section 4.2
and Section 5.1.2.9 of the CAP Update report, background groundwater values are
elevated above 02L/IMAC for several COIs (Table 4-3). The elevated nature of the
COIs at background locations are likely due to naturally occurring regional
variability. Due to this regional variability, where the 02L/IMAC standards are less
than the background values, the background values are the level to which
comparisons need to be made. Therefore, 02L/IMAC concentration lines are not
included on isoconcentration maps when the background values are greater than the
02L/IMAC standards.
DEQ-MRO Marshall CSA Update Report Comment 21
Models were run out to 250 years. In previous models submitted, compliance was not achieved
for several constituents within that timeframe. It was stated in this report that simulations
would run until COI concentrations were below the 2L standard at the compliance boundary. i
would like to reiterate the necessity of this so that more informed decisions could be made
regarding what a technically feasible timeframe is, particularly in regard to metals.
Response Summary - 21
Updated groundwater flow and transport model simulations presented in the CAP
Update report and the model report (Appendix G) were run -out to a duration
beyond which simulated COI concentrations are less than the 02L/IMAC at the
compliance boundary.
DEQ-MRO Marshall CSA Update Report Comment 22
It was indicated in the report that models would only include data up to 411 quarter 2017. This is
unacceptable and MRO expects 2018 data to be incorporated into the model updates to the extent
possible (dependent upon CAP submittal deadline) and submitted as part of the CAP.
Page 14

CSA Update Report Review Comments and Responses December 2019
Duke Energy Carolinas, LLC - Marshall Steam Station SynTerra
Response Summary - 22
The flow and transport (Appendix G) and geochemical (Appendix H) models, as
well as the associated remedial alternatives presented in the CAP Update report use
available data through June 2019, or the most current available data that was feasible
to incorporate.
DEQ-MRO Marshall CSA Update Report Comment 23
All COIs should be modeled unless rationale for why they should not be included is provided to
the Department.
Response Summary - 23
Transport of each COI was modeled for supporting efforts in the CAP Update
report, either in the geochemical (Appendix H) or flow and transport (Appendix G)
model, as appropriate.
DEQ-MRO Marshall CSA Update Report Comment 24
MRO would like to reiterate any direction given by Bill Deutsch (NCDEQ Geochemical
Advisor) is expected to be incorporated into the geochemical models.
Response Summary - 24
Duke Energy and SynTerra consulted Bill Deutsch throughout the process when
establishing guidance for the geochemical model, presented as Appendix H.
Page 15

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
The responses below were previously provided to NCDEQ Mooresville Regional Office (MRO) in September 2018. Verbal concurrence with the responses was received from
the NCDEQ MRO at a meeting held on September 11, 2018 at the MRO. Meeting minutes, along with the original responses, are provided in Attachment 1. These responses
have been bolstered where appropriate. When applicable, section references to the Corrective Action Plan (CAP) Update Report are provided.
CSA
Update
CAP Update
Report
MRO Comment
Duke Energy Response
Section
Content
Reference
1. Work Performed by Others: "...
1. What effort (if any) to make certain information being
Much effort was spent evaluating data
Not applicable
• SynTerra relied on information from the HDR reports as being correct.
utilized from the previous consultant was in fact correct prior
utilizing professional judgement in
to a specific
• The seal of the licensed geologist for this CSA applies to activities
to inclusion in this CSA Update report?
regards to identifying/flagging potentially
section,
conducted and interpretations derived after the HDR reports were
erroneous data to avoid usage of that
however, care
submitted. This submittal relies on the professional work performed
Note: There were many instances in past report
data.
was taken to
by HDR and references that work."
submittals of incorrect/erroneous data submitted.
3Q/4Q 2017 data review complete to
improve data
date. On -going efforts to review 2018
quality
data and will continue with future data
throughout the
collected.
CAP Update.
These same methods have been used as
well as others for the Corrective Action
Plan (CAP) Update to improve data
evaluation. For example, boring logs
were further evaluated to verify the flow
zone designations assigned to each well.
As presented in the 2018 CAMA Annual
Interim Monitoring Report (submitted
April 2019), 15 wells initially assigned to
the deep (transition) zone were
reclassified as bedrock wells due to wells
screens installed within competent
bedrock.
2. It is stated in the report that CCR groundwater data was
2. It is difficult to discern whether CCR groundwater data,
CCR data was utilized to inform
Not applicable
considered in data interpretations in this CSA Update report.
and to what extent the CCR groundwater data was used.
professional judgement in report
to a specific
CCR groundwater data was presented on figures, but rarely
preparation.
section.
mentioned as being incorporated in the
Groundwater data from monitoring wells
assessment/evaluation/interpretations in the report.
associated with the CCR Rule compliance
program are utilized and incorporated
into the CAP Update.
3. It was stated in ES. 1 that, "The CCR data has not been fully
3. This statement is not entirely accurate, the federal CCR
Groundwater data related to the CCR Rule
Sections 2, 4.2,
incorporated into the analysis of this CSA due to the data only
data was not PUBLICLY available until mid -January 2018, but
compliance monitoring network was used in
5, 6; Tables 4-3,
becoming available as of mid January 2018."
was available to Duke Energy and their consultants as data
the CSA Update to inform data evaluation,
5-1, 5-2, 6-5, 6-
became available between 2016 and early 2018. There was
but the data was not posted on figures or
6; Figures 6-13a
ample time and data to be incorporated, but was not at Duke
tables because it was not required to be
through 6-22,
Energy's own choosing.
made publically available until after eight
Appendices C, G,
quarters of sampling data was obtained
and H.
from the monitoring network.
Groundwater data from monitoring wells
associated with the CCR Rule compliance
program are utilized and incorporated into
the CAP Update.
Page 1 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
CSA
Update
Report
Content
MRO Comment
Duke Energy Response
CAP Update
Section
Reference
4. The report is poorly organized.
4. Poor organization of the report makes the review much
Report outline was agreed upon between
Not applicable
more cumbersome and time consuming. It requires the
NCDEQ and Duke Energy.
to a specific
reader to piece it together to get the whole picture.
The CAP Update Report is organized to
section.
align with NCDEQ CAP guidance provided
to Duke Energy.
5. Several sections of this report are still very much just data summary
S. This is a comprehensive site assessment. Data
The report contents are presented in
Sections 5, 6;
report. While Duke Energy does a good job with data presentation, the
presentation is important; however, it should not be the
data summary format to clearly provide
Tables 6-5, 6-
data evaluation/interpretations are lacking and at times non-existent.
primary focus of this report. It should instead focus heavily
factual site characterization. Data
6, 6-7; Figures
on what the data means and if there is insufficient data then
analysis and interpretation of data was
6-13a through
that should simply be stated along with what Duke Energy
presented in several sections of the
6-22;
plans to do about it. CAP development will be negatively
report (i.e., 11, 14, and 15).
Appendices E,
affected without the necessary evaluations/interpretations.
Further discussion regarding site
F, G, H, I, J
conditions and conclusions are provided
in the CAP Update report supported
with tables, figures and modeling
results as specified in the CAP Content
Guidance (April 27, 2018 and
September 10, 2019 NCDEQ letters).
Site Specific Comments
Report
Section
MRO Comment
Response to
CAP Update
I Section
Section
Content
Comment
Reference
1.2.3
"The most recent data available from the CCR
The CCR data provided as a PDF in App. B of the
Yes, CCR data was utilized to inform professional
Sections 2, 4.2, 5,
groundwater monitoring well network is
CSA Update report only presents App. III
judgement in report preparation and determination of
6; Tables 4-3, 5-
provided on isoconcentration maps and cross-
(Detection Monitoring) constituents and does not
plume geometry.
1, 5-2, 6-5, 6-6;
sections herein."
include App. IV (Assessment Monitoring)
Groundwater data from monitoring wells associated
Figures 6-13a
constituents. App. IV constituent data was
with the CCR Rule compliance program are utilized
through 6-22;
available, but was not provided. Since this data
and incorporated into the CAP Update.
Appendices C, G,
was not provided was it even considered during
H
assessment/evaluation of data? If so, to what
extent was all CCR data evaluated as part of this
report?
2.1
"The MSS ash basin, which contains ash
Figure 2-1 does not have topo lines to illustrate
Noted. Topographic contours were depicted on Figures 1-
Section 5, Figures
generated from the historic and active coal
these topographic divides as indicated in the
1 and 2-4.
ES-1, 1-1, 5-1, 5-
combustion at the Plant is situated with MSS to
report.
a-c, 6-13a
the south, topographic divides located along
Several figures within the CAP Update show topography
through 6-22
Sherrills Ford Road to the West Island Point Road
to indicate topographic divides in the vicinity of the Site.
to the north , and Duke Energy property to the
east ( Figure 2-1 ).
Page 2 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MRO Comment
Response to
CAP Update
Section
Section
Content
Comment
Reference
2.3.1
'An engineered cap would reduce infiltration
I do agree that an engineered cap would reduce
Basin decanting and dewatering would occur prior to
Sections 6.1.1.4,
through the covered area, thereby reducing the
vertical infiltration, however, as indicated in the
placement of a cap. The groundwater flow and
6.1.1.5, 6.1.1.6;
potential of leaching of Constituents of Interest
report the majority of the ash is saturated at MSS,
transport model has been updated to predict future
Table 6-1; Figure
(COIs) into the groundwater overlying the
which means a large volume of saturated source
water elevations and remediation scenarios (provided
6-5, Appendix G
closed basin."
material will remain in place. The cap does not
in CAP).
account for lateral groundwater flow. COIs will
Saturated ash thicknesses and volumes are presented
continue to be leached and continue to migrate at
in the CAP Update. As presented to NCDEQ at a
the site.
meeting held on February 05, 2019, flow and
transport modeling simulations indicate very little
difference in predicted boron plumes between closure -
by -excavation and closure -in -place scenarios.
Remediation designs proposed in the CAP Update
could be implemented with the same effectiveness
under each potential closure scenario (i.e., time to
achieve groundwater compliance).
2.3.1
" Two unlined ash landfill units, referred to as
Because the Phase I landfill is located immediately
Groundwater flow direction is understood and expected to
Sections 1.5, 3.0,
the Marshall dry ash landfill (NCDEQ Division of
adjacent/downgradient of the basin and the Phase
discharge to Lake Norman east of CCR-9 and to the
5.0, 6.0; Tables 6-
Solid Waste Permit No. 1804-INDUS), are located
II landfill is located over portions of the ash basin,
unnamed tributary east of GWA-7, MW-14, and AL-1.
5, 6-6, 6-7; Figures
adjacent to the east (Phase I) and northeast
these unlined landfills should be considered
Groundwater to surface water assessment to be included
6-13a through 6-
(Phase II) portions of the ash basin .... The
additional sources to groundwater impacts at the
in CAP.
22; Appendices C
landfill units were constructed prior to the
site.
One deep flow zone well, GWA-15D, was installed at
and F.
requirement forlining industrial landfills and were
GWA-15 location in July 2018, and associated data is
closed with a soil cover system ."
Note: Delineation is warranted east of GWA-7, MW-
included in the CAP Update. This well provides further
14 and AL-1 well clusters between the wells and
delineation of the leading edge of the plume. Additional
the stream. Delineation is also warranted
delineation was discussed at the September 11, 2018,
east/southeast of CCR-9 well cluster. Installation oi
meeting between Duke Energy and NCDEQ (final NCDEQ-
a deep well at the MW-5 location is warranted.
approved meeting minutes included in Attachment 1).
Additional deep bedrock wells were installed in late 2018
and early 2019 at the MW-14 (MW-14BRL) and AL-1 (AL-
1BRL) locations for vertical delineation of COIs and
collection of geophysical borehole information. Results of
this evaluation are presented in an Appendix of the CAP
Update.
he Dry Ash Landfill Phase I and Phase II are evaluated
as additional primary sources that are adjacent to the ash
basin, and included as components of source area 1 in
the CAP Update. Groundwater remedies presented in the
CAP Update accommodate potential impacts from these
adjacent sources. Additionally, Duke Energy is proposing
to excavate the Dry Ash Landfill Phase I and place a
geosynthetic cap on the Dry Ash Landfill Phase II. These
additional source control measures at these facilities will
be permitted through NCDEQ DWM, Solid Waste Section,
separate from the CAP Update and ash basin closure.
Page 3 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MRO Comment
Response to
CAP Update
I Section
Section
Content
Comment
Reference
2.3.4
INDUSTRIAL LANDFILL No. 1
Because the ILF was constructed over a small
The ILF subgrade structural fill is evaluated as an
Sections 1.5, 3.0,
portion of the ash basin and ash was used as
additional primary source that is adjacent to the ash
5.0, 6.0; Tables 6-
"The landfill was constructed over portions of
subgrade material, the ILF should be considered as
basin, and included as a component of source area 1 in
5, 6-6, 6-7; Figures
residual material and over portions of the ash
a potential additional source to groundwater
the CAP Update. Groundwater remedies presented in the
6-13a through 6-
basin. The subgrade for portions of this landfill
impacts at the site.
CAP Update accommodate potential impacts from this
22; Appendices C, P
were constructed of fly ash under the structural
adjacent source. Additional well installations and
rill rules found in 15A NCAC 13B .1700 et seq."
Note: AB-17 and AB-18 well clusters are slated for
sampling (soil and groundwater) north and south of the
removal to allow for construction of the a
ILF were completed in 2019 in accordance with a Work
stormwater retention basin to support closure. AB-
Plan approved by NCDEQ. Results of this evaluation are
17 well cluster should be replaced as we have
incorporated into the CAP Update. Well cluster ILF-
previously discussed. It would be beneficial to
1S/D/BR was installed as a dual-purpose cluster: to
install a well cluster off the southwest corner of
replace abandoned well cluster AB-17 and evaluate
the ILF between the landfill boundary and the
potential impacts of the ILF subgrade structural fill.
stream.
Noted.
2.3.5
PHOTOVOLTAIC FARM STRUCTURAL FILL
Because the PV structural fill was conducted
The PV Structural Fill is evaluated as an additional
Sections 1.5, 3.0,
partially on top of the NW portion of the ash basin
primary source that is adjacent to the ash basin, and
5.0, 6.0; Tables 6-
"The photovoltaic farm structural fill (PV
and does not have a liner or liner system, the PV
included as a component of source area 1 in the CAP
5, 6-6, 6-7; Figures
structural fill) was constructed of fly ash, under
structural fill should be considered an additional
Update. Groundwater remedies presented in the CAP
6-13a through 6-
the structural fill rules found in 15A NCAC 13B
source to groundwater impacts at the site.
Update accommodate potential impacts from this
22; Appendices C, P
.1700 et seq., and bottom ash, under Duke
adjacent source. Additionally, Duke Energy is proposing
Energy's Distribution of Residuals Solids Permit
Note: There are no wells drilled outside the waste
to place a geosynthetic cap on the PV Structural Fill. This
issued by NCDENR Division of Water Quality
boundary of the ash basin to monitor the PV
additional source control at this facility will be permitted
(DWQ), and is located adjacent to and partially
structural fill. Additional wells are warranted west
through NCDEQ DWM, Solid Waste Section, separate
on top of the northwest portion of the ash basin
of the PV not within the waste boundary of the ash
from the CAP Update and ash basin closure.
basin.
Four additional well clusters (PVSF-1 through PVSF-4)
were installed in 2019 along the downgradient
perimeter of the PV Structural Fill in accordance with
Work Plans approved by the NCDEQ. Additional
groundwater and soil data collected from this
evaluation is included in the CAP Update.
Noted.
2.4.2
" MSS continues to maintain a coal pile in the
Why was the coal pile not considered/identified as
The coal pile is evaluated as an additional primary source
Sections 1.5, 3.0,
area located between the coal-fired units and the
a secondary source at the site? My understanding
that is adjacent to the ash basin, and included as a
5.0, 6.0; Tables 6-
active ash basin. "
is that there will be a coal pile assessment
component of source area 1 in the CAP Update.
5, 6-6, 6-7; Figures
conducted, but it does not clearly indicate this in
Groundwater remedies presented in the CAP Update
6-13a through 6-
the report.
accommodate potential impacts from this adjacent
22; Appendix C, P
source. Additional well installations and sampling (soil
and groundwater) along the perimeter of the coal pile
were completed in 2019 in accordance with a Work Plan
approved by NCDEQ. Results of this evaluation are
incorporated into the CAP Update.
2.5
'As part of the permit renewal, the facility
Not all seeps/AOWs were covered under the
The comment is noted. The Special Order by Consent
Sections 1.5.3,
identified seeps and collected seep samples. The
current permit. The permit ONLY covers
S17-009, governing seeps at Marshall, is currently in
5.3, 6.0;
land
seeps were incorporated into the permit as
engineered seeps and they are included as
place.
Appendices C
outfalls ."
outfalls in the permits.
I
Page 4 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MRO Comment
Response to
CAP Update
Section
Section
Content
Comment
Reference
2.6.2
"The NPDES Permit NC0004987 (effective October
This permit has been updated and part of that
The comment is noted.
Not applicable to a
01, 2016), lists the groundwater monitoring wells
update included the removal of the groundwater
specific section.
to be sampled, the parameters and constituents
monitoring of compliance wells. The new permit
to be measured and analyzed, and the
was issued on 4/2/2018.
requirements for sampling frequency and
reporting results
( Table 2-2 ).
2.7
"From 1988 to 2015, several environmental
Why was this section not updated to include any
Table 2-3 was updated with information from 2015 to
Section 1.0,
incidents (i.e., releases) occurred at the site that
incidents that occurred between 2015 and
time of submittal, January 2018 (email
Table 1-1
have initiated notifications to NCDEQ or required
generation of this report? Table 2-3 does include
correspondence LaSala to Wilker, 01/08/2018).
a subsurface investigation."
some from 2016. This should have been updated
A summary of on -site environmental incidents, that
and not a regurgitation from the 2015 CSA.
received an incident reference number from the
NCDEQ, is also included in the CAP Update.
3.3
"No soil borings were advanced within the
What is the rationale for not advancing any borings
Additional subsurface investigation and well
Appendices C, F,
footprint of the dry ash landfill (Phase I) for the
within the Phase I landfill as there was at the
installation proximal to the Dry Ash Landfill Phase I
H
CSA."
Phase II landfill? Was this due to access issue or
was conducted in 2019. In addition to open borehole
merely an oversight?
analyses, one deep bedrock well (AL-1BRL) was
installed for vertical delineation. The results of this
assessment are included as an appendix in the CAP
Update.
Additionally, soil sampling was conducted at the Dry
Ash Landfill Phase I (CCR-13) for analysis of
geochemical parameters (HFO/HAO). The results of
these analyses are incorporated into the updated
geochemical model presented in the CAP Update.
Groundwater elevations along the perimeter of the Dry
Ash Landfill Phase I are monitored continuously via
pressure transducers and data recorders to monitor
the effects of ash basin decanting.
3.3
"The ash samples collected from the ash basin
Where is the interpretation/evaluation of this SPLP
Section 3.3 Chemical Properties of Ash (page 3-6)
Section 6.1.1.6,
(seven samples), the dry ash landfill (Phase II)
data and what it means in regards to contaminant
Appendix C
(two samples), and the PV structural fill (four
distribution and migration from the source?
As stated above, evaluation of the SPLP data was
samples) for SPLP testing were collected from
incorporated in the CSA Update. Verbal concurrence with
the deeper ash sample in the boring (i.e.,
the response above was received in a meeting between
approximately 2 feet to 3 feet above the ash/soil
Duke Energy and NCDEQ on September 11, 2018.
interface where field conditions allowed). Those
results are presented in Table 34.
3.3
Figure 34: Piper Diagrams
The piper diagrams are difficult to read due to the
The comment is noted. The intention of Piper diagrams
Sections 6.1.1.6,
same symbol being used for multiple samples.
was to characterize groundwater types with regards to
6.1.2.1; Figure 6-
general chemical make-up of the water rather than
11, 6-12
individual wells.
Updated Piper diagrams are provided in the CAP
Update, with water quality groupings outlined for ease
of review.
Page 5 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MRO Comment
Response to
CAP Update
I Section
Section
Content
Comment
Reference
3.3
"Chemical speciation samples were also collected
There was a small discussion of the results, but
The updated geochemical model provides more
Appendix H
from five ash pore water monitoring wells (AB-
this discussion did not include bearing this
detailed information on water geochemistry and
12S, AB-12SL, AB-15SL, AB4S, and AB4SL)
information has on COI distribution/migration at
applicable constituent species that occur, or would be
within the ash basin ( Appendix B, Table 1 )."
the site.
predicted to occur in predicted future scenarios, in the
CAP Update.
6.2.2
'Assessment results indicate the ash thickness
What is the estimated total volume of saturated ash
Estimated volumes and thicknesses of saturated source
Sections 6.1.1.4,
within the basin ranges from a few feet in
vs. unsaturated ash?
material were provided by the closure engineers (AECOM,
6.1.1.5, Table 6-1,
thickness up to 85 feet. The majority of ash
2019). Estimates of potential saturated source material
Figure 6-6;
located within the ash basin is saturated with
If dewatering is anticipated, what is the
left in place under a closure -in -place scenario are also
Appendix G
saturated ash thickness ranging from less than
estimated volume of the remaining saturated
addressed in the CAP Update.
one foot up to 52 feet. Ash contained within dry
ash?
The updated Groundwater Flow and Transport Modeling
ash landfill (Phase II) is observed to a depth of
Report provides an evaluation of the effects of potential
111 feet bgs with depth to water measured at
remaining saturated source material. As stated above,
approximately 112 feet bgs in AL-2S (shallow
modeling simulations indicate very little difference in
flow system). Ash in the PV structural fill was
predicted boron plumes between closure -by -
encountered at depths up to 71 feet bgs with
excavation and closure -in -place scenarios.
depth to water measured at approximately 61
Groundwater remediation designs proposed in the CAP
feet bgs in AB-20S (shallow flow system) ."
Update could be implemented with the same
effectiveness under each potential closure scenario
i.e. time to achieve groundwater compliance).
6.4
Table 6-10: Horizontal Groundwater Gradients
Although Table 6-10 does provide good
The comment is noted. Updated groundwater flow
Section 5.1.2.3,
and Velocities
information regarding horizontal
models provided in CAP Update will incorporate data
Table 5-2,
gradients/velocities across the site, it does not
gathered from pumping tests conducted along the
Appendix G
provide information along the major flow paths (A-
main, central flow transect across the ash basin (A-
A', B-B'). This information is most valuable in
A').
understanding groundwater flow and contaminant
Some calculations in Table 6-10 are representative of
transport at the site.
A -A' generalized flow area (AB-15S to AB-12S, AB-
16D to AB-12D, AB-15BR to AB-9BR).
Some calculations in Table 6-10 are representative of
B-B' generalized flow area (AB-5S to AB-3S, AB-31D to
GWA-11D, AB-5BR to GWA-1BR).
Pumping tests along the central transect of the ash
basin (A -A') were conducted in 2018 at three well
clusters: AB-18, AB-15, and AB-12. An in-depth
evaluation of hydraulic characteristics in the ash basin
was presented in the Ash Basin Pumping Test Report,
which was submitted to NCDEQ in January 2019. The
results of the pumping tests were used to refine
assumptions in the groundwater flow and transport
model of the Site.
Revised horizontal gradients are also provided in the
CAP Update.
Page 6 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MRO Comment
Response to
CAP Update
Section
Section
Content
Comment
Reference
6.4
"Upward vertical gradients (negative values) are
Note: upward gradients were also observed in
Vertical gradient between bedrock wells at depth (AL-2BR
Section 5.1.2.3,
observed on the eastern boundary of the ash
the Phase II landfill. This should be considered
to AL-213RL) is downward. Analysis of Q2 2018 water
Table 5-3, and
basin near Lake Norman and its tributaries.
and evaluated further since boron concentrations
level data at AL-2, AL-3, and AL-4 clusters indicate
Appendix F
Additionally, upward vertical gradients are
have been increasing over time and depth.
downward vertical gradients beneath the Phase II landfill.
predominant in the center of the historic channel
Downward vertical migration is apparent at AL-2,
of Holdsclaw Creek beneath the ash basin.
therefore additional deep bedrock assessment is pending.
Specifically, upward vertical gradients are
observed at AB- 15 location (AB-I5D/BR; -0.081
An evaluation of the bedrock, and groundwater flow
foot/foot), AB-12 location (AB- 12D/BR; -0.073
within it, underlying the Dry Ash Landfill Phase II was
foot/foot), and the AB-9 location (AB-9D/BR; -
conducted in 2019. The results of this assessment are
0.028 foot/foot). Analytical results from the
included as an appendix in the CAP Update.
bedrock wells at these locations verify that
Updated vertical hydraulic gradients are also provided
constituent migration to the bedrock flow system
in the CAP Update, which indicate a generally
is limited to specific areas identified in Section
downward vertical gradient between the shallow
groundwater and wells screened within deep (>300 ft
bgs) bedrock fractures.
6.6
"Hydraulic conductivity values for wells screened
In section 11.1.1, it was stated that the TZ is the
These are geomean values derived from many slug
Section 5.1.1.2.
in saprolite have a geometric mean of 5.50 x 10-
primary flow zone, however, section 6.6 indicates
tests, and are on the same order of magnitude (10-1
Figures 5-5a, 5-
4 centimeters per second (cm/sec). Hydraulic
the shallow flow layer has higher conductivity
cm/sec). Thus, it can be concluded that similar flow
5b, 5-5c;
conductivity values for wells screened in the TZ
than the TZ.
characteristics exist in shallow and TZ groundwater.
Appendices F, G
have a geometric mean of 4.23 x 104 cm/sec. "
Groundwater seepage velocities are presented in the
CAP Update, along with velocity vector maps for the
deep flow zone from the updated flow and transport
model. The results of the new evaluation presented in
the CAP Update indicate the greatest average
horizontal groundwater velocity is in the bedrock flow
zone (0.83 ft/day). This is likely due to the bedrock
effective porosity value derived from the flow and
transport model (0.01) being one order of magnitude
less than the corresponding value for the shallow and
deep flow zones (0.3). Additional evaluation of
fractured bedrock, and the groundwater flow within it,
is also presented in an appendix of the CAP Update.
6.7
"Bedrock fractures encountered at MSS tend to
Is there data available to support this
Additional evaluation of fractured bedrock and the
Section
be isolated with low interconnectivity."
statement? Is the interconnectivity or lack
groundwater flow within it is presented in an appendix
5.1.2.6,
thereof well understood at the site?
of the CAP Update. Great efforts were made to
Appendix F
characterize groundwater flow within bedrock fractures
with respect to depth, (300-500 feet bgs). This work
included multiple geophysical logs from six deep open
boreholes. Details of matrix diffusion within bedrock at
the Site, and its effects on groundwater flow, are also
resented in the CAP Update.
Page 7 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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7.0
SOIL SAMPLING RESULTS
How were saturated soil samples handled? Were
PBTV determination only incorporated unsaturated soil
Sections 6.1.1.6,
they included in the evaluation in this section?
samples. "The sample was collected from the
6.1.4.1, Table 6-
When reviewing Figure 7-1 it included samples
unsaturated zone, greater than 1 foot above
3; Figure 6-23;
below the water table which is fine for reference
the seasonal high water table elevation."
Appendices C, G,
purposes, but really because they are collected
and H
below the water table are likely skewed and not
Table 7-2 of the CSA Update classifies sample based
entirely representative of actual site conditions in
on saturated/unsaturated for comparative purposes.
soil.
`Saturation and other factors may also affect
constituent occurrence in the samples." For the CAP
Update, unsaturated soil will be the focus of evaluation
for potential secondary source considerations and
saturated soil will be evaluated as part of the
groundwater system in the flow and transport and
geochemical models.
Additional evaluation of COIs in unsaturated soil at the
Site is incorporated in the CAP Update. A summary
table and figure of unsaturated soil results are
presented for review of unsaturated soil
concentrations, exclusively. The updated geochemical
model incorporates soil analyses (HFO/HAO) to
evaluate COI sorption potential, as well as COI
leaching potential under various geochemical
environments.
7.0
SOIL SAMPLING RESULTS
Based on review of Figure 14-77, it is evident that
Additional soil sampling was conducted in 2018 for
Sections 6.1.1.6,
delineation of soils at the site is not complete. This
updating the geochemical model and is included in the
6.1.4.1, Table 6-
part of the assessment must be completed and
CAP Update. Additional source area investigations are
3; Figure 6-23;
included in CAP.
in progress at the site and will be presented in the
Appendices C, P
CAP. Where additional unsaturated soil samples are
needed to define the horizontal extent of COIs and of
what constituents can be discussed in the meeting
with DEQ.
Additional soil sampling was conducted in 2019 in
accordance with NCDEQ-approved work plans.
Additional assessment results for the coal pile, gypsum
pad, PV Structural Fill and ILF subgrade structural fill
are incorporated in the CAP Update.
Furthermore, a specific soil sampling plan (pre -approved
by NCDEQ) for unsaturated soils around the ash basin
and adjacent sources was conducted in 2019. A
summary table and figure of unsaturated soil results
are presented for review of unsaturated soil
concentrations, exclusively.
Unsaturated soil concentrations are generally within
range of background soil concentrations. Where there
are exceptions greater than background, those values
are delineated by groundwater concentrations less
Page 8 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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than applicable groundwater criteria. This data
indicates there is no potential secondary source to
groundwater from leaching of constituents from soil,
therefore additional soil sampling is not warranted and
no soil constituents in soil are identified for corrective
action at the Site. Additionally, there are no transport
mechanisms from the source areas for constituents in
unsaturated soil at sampling locations.
8.0
SEDIMENT RESULTS
This section simply is a data summary and in no
The comment is noted. A more robust data set was
Section 5.4, 6.1.2,
way discusses if this data has any affect on water
collected during the 2L-2B efforts, which allows for a
6.3; Appendices C
quality or potential corrective action at the site.
more thorough evaluation in CAP Update.
and E.
Additional samples are anticipated to be collected
during the 2L/2B sampling event. A more detailed
As stated above, additional sediment sampling was
evaluation is expected to be included in the CAP.
conducted in 2018 to support a groundwater to
surface water evaluation. The results of this evaluation
are presented in an appendix to the CAP, and are also
incorporated into the CAP Update.
Furthermore, the sediment data was incorporated into
an updated risk assessment for the source area, which
concluded there is no evidence of unacceptable risks
to human and ecological receptors exposed to
environmental media potentially affected by CCR
constituents at MSS. This conclusion is further
supported by multiple water quality and biological
assessments conducted by Duke Energy as part of the
NDPES monitoring program, which are also
summarized in the CAP Update.
9.0
"For this CSA, it is pertinent that a comparison
Just to clarify, even if there is an unnamed
The comment is noted.
Section 5.3.1,
with NCDENR Title 15A, Subchapter 02B. Surface
tributary does not mean that 2B standards do not
6.2.1, Figure 5-6,
Water and Wetiand Standards (2B) standards
apply. The unnamed tributary assumes whatever
An evaluation of current surface water conditions was
Appendices C and
includes only sample results from named surface
classification the water body in which the
conducted in 2018 in accordance with an approved
J
waters ."
unnamed
work plan. Results of that evaluation, along with an
tributary empties into has been designated.
evaluation of future surface water conditions, are
included as an appendix to the CAP Update. However,
it should be noted the unnamed tributary is governed
by the Special Order by Consent (SOC) 517-009
currently in place.
Page 9 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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9.0
"AOWs , wastewater and wastewater
The only AOWs regulated are the engineered
The seeps at the MSS have been extensively evaluated
Sections 6.1.2,
conveyances (effluent channels), and industrial
seeps covered by the NPDES permit and select
in the current and future conditions surface water
6.1.3, 6.2.1;
storm water are evaluated and regulated in
non -engineered seeps covered by SOC. All other
reports, which are included in an appendix to the CAP
Figure 5-6, 6-12b,
accordance with the NPDES Program
AOWs are not covered under permit or SOC. Also,
Update. Data from seeps and surface water were
and Appendices C
administered by NCDEQ DWR ."
all AOWs/seeps should be evaluated in this CSA.
incorporated into the CAP Update and considered
and J.
The information is pertinent to this assessment
during evaluation of groundwater remedial
and should be included. Just because the location
alternatives. The proposed groundwater remedial
may be covered by a permit or SOC doesn't mean
alternative accounts for potential CCR-affects in the
the data collected as part of that cannot be used
seeps. As stated above, the non -constructed seeps at
in this assessment. Please update this section
Marshall are governed by the SOC 517-009.
accordingly and submit as part of the CAP. This
information is critical in understanding areas of
groundwater discharge to surface waters.
9.0
NA
It would be beneficial to have AOW/SW results
The seeps at the MSS have been extensively evaluated
Sections 6.1.2,
depicted on a figure along with any pertinent GW
in the current and future conditions surface water
6.1.3, 6.2.1;
results to assess potential GW-SW interaction(s).
reports, which are included in an appendix to the CAP
Figure 5-6, 6-12b,
Update. Data from seeps and surface water were
and Appendices C
incorporated into the CAP Update and considered
and J.
during evaluation of groundwater remedial
alternatives. The proposed groundwater remedial
alternative accounts for potential CCR-affects in the
seeps. As stated above, the non -constructed seeps at
Marshall are governed by the SOC 517-009.
9.1
" Surface water data represents a one-time,
2L/2B evaluation is necessary and should be
Groundwater to surface water interaction at the MSS
Sections 6.1.2,
single sample; therefore, compliance with either
conducted accordingly to fully assess compliance
has been extensively evaluated in the current and
6.1.3, 6.2.1;
the acute or chronic 2B standard may not be
with 2B. (Assessment pending)
future conditions surface water reports, which are
Appendix J.
determined based on 15A NCAC 02B .0211 (11)
included in an appendix to the CAP Update. As the
(e)."
studies conclude, there are not concentrations of COIs
related to the ash basin present in surface water
greater than 02B water quality standards, nor are
there predicted to be under future conditions. Data
from seeps and surface water were incorporated into
the CAP Update and considered during evaluation of
groundwater remedial alternatives. The proposed
groundwater remedial alternative accounts for
potential CCR-affects in the seeps. As stated above,
the non -constructed seeps at Marshall are governed by
the SOC 517-009.
Page 10 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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9.2
"Discussion of Results for Constituents
Antimony - has EPA criteria to compare data.
The comment is noted.
Sections 6.1.2,
Without Established 26 Standards
Thallium - has EPA criteria to compare data.
6.1.3, 6.2.1;
A 2B value has not been established for a
Surface water at the MSS has been extensively evaluated
Appendices C and J
number of constituents. A summary of results for
in the current and future conditions surface water
select constituents without associated 2B values
reports, which are included in an appendix to the CAP
follows....."
Update. As the studies conclude, there are not
concentrations of COIs related to the ash basin present in
surface water greater than 02B water quality standards,
nor are there predicted to be under future conditions.
Applicable regulatory criteria were used in the screening
process as appropriate.
9.3
"Generally, surface water samples collected
This statement cannot be fully supported until
he statement is supported by additional surface water
Sections 6.1.2,
from Lake Norman demonstrate compliance
2L/2B compliance sampling has been conducted
data from Lake Norman that have been further
6.1.3, 6.2.1;
with 2B standards, with the occasional
at the site. (Assessment pending)
evaluated in the current and future conditions reports,
Figure 5-6;
exception of dissolved oxygen, dissolved
which are included in an appendix to the CAP Update.
Appendices C and
copper,and TDS. Additional parameters
including chloride, arsenic, selenium,
Based in the sampling results, groundwater interaction
cadmium (D), and lead (D) have been
with surface water at locations along the western edge
measured above the 2B standard at a single
of Lake Norman, immediately downgradient of the MSS
location."
Site, generally did not result in concentrations of
constituents greater than 2B standards. Dissolved
oxygen field readings were recorded in multiple sample
sets at concentrations slightly lower than the 2B
minimum concentration of 4 mg/L, but they were
consistent with background surface water
concentrations observed in Lake Norman. The surface
water evaluations concluded there are not
concentrations of COIs related to the ash basin present
in surface water greater than 02B water quality
standards, nor are there predicted to be under future
conditions.
10.1
"Monitoring well locations BG-1BR and GWA-12D
Based on review of data submitted to date, GWA-
The comment is noted. Groundwater quality data from
Section 4.2; Table
were not approved for use pending replacement
12D has not been replaced and continues to
monitoring well BG-1BPA have been incorporated into the
-3; Appendix C
and reevaluation as potential background
exhibit unacceptable water quality for inclusion
background dataset.
locations."
into background. BG-1BR was replaced with BG-
1BRA and water quality is acceptable thus this
The background dataset for groundwater in all flow zones
location is acceptable for use in the background
is sufficient for calculating background values in
evaluation.
accordance with pre -approved methodologies between
the NCDEQ and Duke Energy.
10.1.1
Background Dataset Statistical Analysis
Marshall BTV letter was submitted to Duke Energy
The comment is noted. BTVs were updated for
Section 4.0, Table
on June 15, 2018, with MRO general concurrence
groundwater during 2019 and are incorporated into the
4-2, 4-3; Appendix
and comments where appropriate.
CAP Update.
C
Page 11 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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10.1.2
Figures 10-1 thru 10-3: Piper Diagrams
The piper diagrams are difficult to read due to
The comment is noted. Piper diagrams are intended
Section
the same symbol being used for multiple
to display relative proportions of major cations and
6.1.1.6;
samples.
anions from various areas relative to source area
Figures 6-12a
(upgradient, source, downgradient).
and 6-12b.
Groundwater/source water quality signatures may
then provide some inference into potential mixing
zones/affected groundwater. Piper diagrams for
groundwater and surface water were replotted
during the CAP Update to better inform the reader.
10.2.4
"Radionuclides may exist dissolved in water
This is just data presentation. Where is the
On -going evaluation of radium at the Site.
Section 6.1.3, Table
from natural sources (e.g. soil or rock). The
evaluation/interpretation of this data as to
6-5, 6-6;
USEPA regulates various radionuclides in
why or why not radionuclides are
Appendices C and H
drinking water. Radium-226, radium-228, total
considered COIs at the site?
radium, uranium- 238, and total uranium were
analyzed in 46 wells as part of the CAMA
Based on review of data, total radium should be
The comment is noted. Total radium has been included as
sampling event in September of 2017. Results
included as a COI at the site.
a COI at the MSS site and evaluated in the CAP Update.
for radiological laboratory testing are presented
in Appendix B, Table 1. Radium and uranium
isotopes were detected at levels greater than the
USEPA MCLs at the following seven (7) locations:
Background - BG-2BR
Beneath the Ash Basin - AB-
12D/BR Downgradient - AL-
01D/BR AB-01BR MW-07D"
10.3.2
'An evaluation of data at MSS indicates
This statement is inaccurate. Based on review of
GWA-2D sample results are invalid due to grout
Section 6.1.3,
hexavalent chromium has only been detected in
data available to date, the following wells exhibit
contamination. Replacement well GWA-2DA has
Table 6-3;
one valid sample out of 867 analysis at a level
concentrations (both current and historic) above
reported concentrations two orders of magnitude less
Appendix H
greater than the 2L standard for total chromium
10 ug/L and the PBTVs:
than GWA-2D, and all below 10 ug/L.
(10 pg/L); therefore, hexavalent chromium is not
AB-20S
MW-11D, BG-2BR, and MS-15 are upgradient of the
considered as a COI ."
AB-21S
ash basin and concentrations are similar to the 2L.
AB-3D
These are interpreted to be natural variability in
BG-2BR
background concentrations.
GWA-2D
The one sample from AB-21S with detection >21-
MW-11D
(3/10/17) was invalid. Sample field preservation did
MS-15
not meet USEPA or method recommendations for
analysis, therefore, results are biased high and
should have been flagged accordingly (Pace Lab
Report317030381).
Detections at AB-3D and AB-20S appear anomalous.
Range of detected values are orders of magnitude
off, which may indicate incorrect reporting for total
chromium as hexavalent chromium. Cr(VI) has a
very limited presence in groundwater across the Site.
On -going monitoring has provided additional
information regarding whether Cr(VI) should be
considered a COI. COI management conducted
during the CAP Update indicated that no valid
hexavalent chromium results exceeded the
Page 12 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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screening criteria at or beyond the compliance
boundary and therefore, Cr(VI) has not been
included as a COI that warrants corrective action.
10.3.4
"Based on site -specific conditions, observations,
Based on review of available data to date,
This comment is noted. Cr(VI) and total radium were
Section 6.1.3 and
and findings, the following list of COIs has been
hexavalent chromium and total radium should be
added to the COI list for the MSS at the request of the
Table 6-3;
developed for MSS:
added as COIs at the site.
NCDEQ and evaluated for corrective action in the CAP
Appendices C and
Antimony
Update.
H.
Arsenic
Hexavalent Chromium was detected above 10 ug/L
As described above, detections of hexavalent chromium
Barium
and PBTVs at the following locations: AB-205, AB-
appear anomalous. COI management conducted during
Beryllium
215, AB-3D, BG-2BR, GWA-2S, MW- 11D, and MS-
the CAP Update indicated that no valid hexavalent
Boron
15 (both current and historic detections)
chromium results exceeded the screening criteria at or
Cadmium
beyond the compliance boundary and therefore, Cr(VI)
Chloride
Total Radium was detected above the Federal MCL
has not been included as a COI for corrective action.
Chromium (total)
of 5 pCi/L and PBTVs at the following locations:
Cobalt
AB-1BR, AB-9D/BR, AB-lOBR, AB- 115, AB-12D/BR,
Total radium exhibits mean concentrations in
Iron
AL-1S/D/BR, AL-2BRLL, BG-1S/D, BG-2BR, MW-
groundwater greater than background values, 02L
Manganese
7S/D, and MW-14S/D (both current and historic
standard, or IMAC downgradient of the ash basin at or
Molybdenum
detections)
beyond the compliance boundary. It has been included as
Nickel
a COI for corrective action.
Selenium
Strontium
Future monitoring and assessment of additional source
Sulfate
areas, and 2B monitoring should provide more
TDS
information as to the need to manage Cr(VI) and total
Thallium
radium as COIs for corrective action.
Vanadium
10.3.4
"COIs detected at concentrations greater than
Beryllium, cadmium, chloride, and nickel were
The comment is noted. These constituents were not
Section 6.1.3, Table
the PBTVs and associated 2L/IMACs (if
included as COIs in the list in section 10.3.4.,
'...detected at concentrations greater than the PBTVs and
6-5, Table 6-6.
applicable) for each flow unit beyond the
but are not included in this list.
associated 2L/IMACs (if applicable) for each flow unit
Appendices C, H
compliance boundary (or within bedrock
beyond the compliance boundary (or within
monitoring wells within or beyond the
bedrock monitoring wells within or beyond the
compliance boundary) are as follows:
compliance boundary)..."The refore, they are not listed
as corrective action COIs in the CSA.
Shallow - antimony, boron, chromium,
cobalt, iron, manganese, molybdenum,
In accordance with the NCDEQ-approved methodology
selenium, strontium, sulfate, TDS, thallium
presented in a meeting at the MRO, a three -step process
was used as a COI management approach in the CAP
Deep - boron, cobalt, iron, manganese,
Update. This process considers the regulatory context,
strontium, sulfate, TDS, vanadium
the mobility of constituents, and the distribution of
constituents within Site groundwater, as described in
Bedrock - antimony, barium, boron, chromium,
more detail in the CAP Update, updated geochemical
cobalt, iron, manganese, molybdenum,
model report, and additional appendices. The primary
strontium, TDS"
goal of the COI management approach is to utilize
science -based evidence to determine the realistic
distribution and behavior of coal ash -related constituents
in groundwater.
Page 13 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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10.3.4
'A constituent was not associated with a flow
If constituents were observed in upgradient and/or
If constituent concentrations were only detected greater
Section 4.0, Tables
layer in the lists above if concentrations detected
background well locations greater than PBTVS and
than PBTVs and 2L/IMACs upgradient of the identified
-2, 4-3, 4-4, 4-5,
greater than the PBTVs and associated 2L/IMACs
2L/IMAC an explanation/rationale as to why they
source area (ash basin), these concentrations are not
Appendix H
were exclusively observed in upgradient, or
were not included should be provided (i.e.,
considered to be derived from the source (i.e., the
background, locations."
groundwater flow direction, no identified source,
constituents are considered to be naturally -occurring, and
variability in background, etc.).
representative of background conditions upgradient of the
source).
10.3.4
'As directed by NCDEQ, the data with turbidity
This statement is not entirely accurate. NCDEQ
The comment is noted. Duke Energy will continue to
Not applicable to a
greater than 10 NTUs and pH greater than 8.5
directed that data with turbidity greater than 10
monitor wells in accordance with an agreed upon IMP.
specific section.
S.U. that may be a result of grout intrusion, as
NTU and pH greater than 8.5 should not be
Wells that may exhibit grout impacts, if included in the
well as data that may be auto -correlated
included in the background analysis for
agreed upon IMP, will continue to be sampled and can
because it was collected within 60 days of a
developing statistically derived BTVs. However,
provide valid boron, sulfate, and water level data.
previous sampling event, are excluded for
NCDEQ did not direct Duke Energy not to use
This data was considered and will be used for assessment
statistics and other evaluation methods."
that data as part of the assessment where
moving forward, where appropriate.
applicable. For example, boron is seemingly
unaffected by pH and turbidity and should be
included as such in this assessment.
Also, in a meeting with Duke on June 15, 2017, it
was discussed and agreed upon that in lieu of
reinstalling select wells at the site that those wells
would continue to monitored for boron, sulfate and
water levels. If Duke Energy and their consultants
do not consider this data to be valid and support
use of this data in the assessment then those
wells should be replaced so that representative
data is collected.
11.1.1
"The farthest downgradient edge (leading edge)
What about AB-1 and MW-7 well clusters
This comment is noted.
Not applicable to a
of the plume is observed at the MW-14 location.
immediately downgradient of the ash basin and
specific section.
Generally, constituents at this location occur at
immediately adjacent Lake Norman which exhibit
concentrations greater than the 2L or PBTV
similar concentrations to that observed at the MW-
while analytical results from monitoring well
14 location, except concentrations do not decrease
clusters located farther downgradient (GWA-7
with depth at the AB-1 well cluster.
and MW-10) are less than the 2L standard or
PBTVs. However, concentrations at MW-14 tend
to decrease with depth. For example, boron
concentrations decrease from 2,340 Ng/L at
MW-14S to 2,140 Ng/L at MW-14D to 53.7 Ng/L
at MW-14BR. This trend is also observed in
downgradient areas of the ash basin towards
the unnamed tributary of Lake Norman. Boron
is consistently less than or slightly over the
detection limit in GWA-11 BR, but is routinely
detected at concentrations greater than the 2L
beyond the ash basin compliance boundary in
GWA-I1S/D and GWA-15S."
11.1.1
" Migration of CCR-impacted groundwater is not
This is because it is discharging before it ever
The comment is noted.
Not applicable to a
apparent within MW-IOS/D, located in the
makes its way this far out on the little peninsula.
specific section.
eastern peninsula immediately adjacent to Lake
Norman."
Page 14 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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11.1.1
"These transects capture upgradient,
Transects A -A' and B-B' do not include upgradient
The comment is noted.
Not applicable to a
source area, and downgradient wells
locations beyond the waste boundary.
specific section.
relative to the ash basin."
11.1.1
"Thickness of the shallow flow zone varies across
In section 6.6, hydraulic conductivity was
The reported values are in the same order of magnitude;
Section 5.0, Table
the Site, however for Site assessment purposes,
reported to be higher in the shallow flow layer
conductivities are generally comparable between the
5-2.
the impacts in this zone are sufficiently
than the TZ.
shallow and TZ flow layers. Updated hydraulic
understood as the TZ is interpreted to be the
conductivities for the three flow layers beneath the MSS
primary flow zone with a predominantly
site are summarized in the CAP Update.
horizontal component of flow that would impact
receptors. "
11.1.1
"Though not captured on cross -sectional views,
Based on review of available data to date, this
The comment is noted. Deep bedrock assessment was
Sections 5.1,
vertical migration of COI concentrations into
well has been sampled 4 times since installation
completed at this location, and the results to date have
5.1.2.6; Appendices
underlying bedrock is apparent beneath the Dry
and has concentrations of boron greater than
been incorporated into the CAP Update.
C, F, G
Ash Landfill (Phase 11). A deep bedrock well (AL-
10,000 ug/L. Further assessment/evaluation is
2BRLL) for vertical delineation beneath the Dry
warranted at this location.
An evaluation of the bedrock, and groundwater flow within
Ash Landfill (Phase II) was recently installed.
it, underlying the Dry Ash Landfill Phase II was conducted
Boron was detected greater than 9,000 pg/L in
in 2019. This work included multiple geophysical logs from
this well for the first and only sample collected to
six deep open boreholes. Details of matrix diffusion within
date."
bedrock at the Site, and its effects on groundwater flow,
are also presented in the CAP Update. The results of this
assessment are included as an appendix in the CAP
Update.
Updated vertical hydraulic gradients are also provided in
the CAP Update, which indicate a generally downward
vertical gradient between the shallow groundwater and
wells screened within deep (>300 ft bgs) bedrock
fractures.
Furthermore, the Dry Ash Landfill Phase II is evaluated as
additional primary source that is adjacent to the ash
basin, and included as a component of source area 1 in
the CAP Update. Groundwater remedial alternatives
presented in the CAP Update accommodate potential
impacts from this facility. In addition, Duke Energy is
proposing to place a geosynthetic cap on the Dry Ash
Landfill Phase II. This additional source control measure
will be permitted through NCDEQ DWM, Solid Waste
Section, separate from the CAP Update and ash basin
closure.
Page 15 of 31

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11.1.1
"Another area of apparent vertical migration that
This is very true. Further assessment/evaluation is
The comment is noted. Deep bedrock assessment is
Sections 5.1,
is not captured on the cross -sections is at the AB-
warranted at this location.
ongoing at this location, and the results to date have
5.1.2.6, 6.1.4 and
1 location (AB -1BR), immediately east of the ash
been incorporated into the CAP Update.
6.1.5; Figures 6-2,
basin. Several COIs in deep and bedrock
6-8a through 6-8c;
groundwater (boron, chloride, iron, manganese,
The vertical extent of the COIs have been delineated by
Appendices C, F, I.
strontium, and TOS) display increasing trends
AB-1BRLLL (which was completed 320 feet into bedrock).
over time at this location ."
An evaluation of the bedrock, and groundwater flow
within it, at the AB-1 well cluster was conducted in 2019.
This work included multiple geophysical logs from two
bedrock intervals up to a depth of 500 feet below ground
surface. Details of matrix diffusion within bedrock at the
Site, and its effects on groundwater flow, are also
presented in the CAP Update. The results of this
assessment are included as an appendix in the CAP
Update.
Updated vertical hydraulic gradients are also provided in
the CAP Update, which indicate upward vertical gradients
between the shallow groundwater and wells screened
within deep (>300 ft bgs) bedrock fractures.
Plume Stability Evaluation - Marshall Steam Station
(Arcadis, 2019) is also included as an appendix to the
monitored natural attenuation (MNA) report in the CAP
Update.
11.1.1
"Two potential scenarios could explain the
Based on review of available data to date, it is
The statement made in the CSA was not to imply that the
Not applicable to a
observation of increasing trends:
unlikely attributable to grout contamination based
cause of the increasing trends was grout contamination
specific section.
A compromised grout column at AB-IBR could
on water quality parameters collected at this
(i.e., increased pH), but rather, a compromised grout
allow overlying concentrations from the shallow
location. You typically see elevated pH (>10)
column. That is, a casing that may have been incompletely
and deep flow system to migrate downward,
associated with grout contamination, but that is
grouted in place. This would allow shallow groundwater
influencing groundwater concentrations
not the case here.
constituents to mix into the lower deep groundwater flow
measured within the vicinity of the well
zone around the well screen and therefore give non -
installation ."
representative results for the flow zone being monitored.
11.1.1
"Of the 11 wells along the centerline of this flow
MW-12 is not located along this flow transect. I
The comment is noted.
Not applicable to a
transect, MW-12BR and AB-IBRL are the only
assume this is in error and should be AB-12?
specific section.
wells with less than six valid sampling events.
Revise accordingly.
MW-12BR has three valid sampling event between
March 2017 and September 2017, and AB-1BRL
has only been sampled once."
Page 16 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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Updated December 2019
Site Specific Comments
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Section
MRO Comment
Response to
CAP Update
Section
Section
Content
Comment
Reference
11.1.1
Isoconcentration Maps: Figures 11-1 thru 11-63
Typically, only 2 contours are used, the 2L/IMAC
The comment is noted.
Sections 6.1.4,
and PBTV. It is technically appropriate to use at
6.1.5; Tables 6-5,
least 1 or 2 more contours in some instances
6-6;
where there are large gaps between the standard,
Updated isoconcentration maps of constituents selected for
Figures 6-13a
PBTV, and/or the highest or lowest concentration
mapping, in accordance with the results of the NCDEQ-
through 6-22
observed to better depict contaminant distribution.
approved constituent management evaluation, have been
This helps to better illustrate contaminant
provided in the CAP Update for each appropriate
distribution and depict areas of highest
groundwater flow zone.
concentration.
Sample locations were intentionally not included on
he comment is noted. However, if "...the map is intended
figures if it was determined to have invalid data.
to be a visual representation of data..." then using non -
This is not appropriate. All data points should be
valid data on a map may mislead the reader into drawing
included on each representative map and if data
erroneous conclusions. Additional discussions with DEQ
was not used due to validity, it should be
may be warranted to address future submittals.
indicated as such on the map so it does not appear
Updated isoconcentration maps of constituents selected for
it was just left off the map or is perceived as a
mapping, in accordance with the results of the NCDEQ-
"data gap". In a nutshell, all sampling points and
approved constituent management process, have been
data should be represented on the map. The map
provided in the CAP Update for each appropriate
is intended to be a visual representation of data
groundwater flow zone. Data included on the updated
but when data is not included it can be
isoconcentration maps represent results of a central
misleading.
tendency analysis, which was completed to capture the
appropriate measure of central tendency (arithmetic mean,
The map contains data from February 2015 to
geometric mean, or median) for each dataset of
October 2017. If the majority of the data is from
constituent concentrations. Previous Site assessments
one sampling event, for example, the October
might have overrepresented areas affected by the ash
2017 sampling, then it should be indicated in the
basin by posting a single data set on maps and cross -
title block or legend and then at locations on the
sections that might have included isolated data anomalies.
map where other data outside the October 2017
sampling event is used the date should be
indicated along with the well ID/concentration.
This allows the reader/reviewer to know which
sampling event concentrations represent.
Page 17 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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Updated December 2019
Site Specific Comments
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Section
MRO Comment
Response to
CAP Update
I Section
Section
Content
Comment
Reference
11.1.1
Isoconcentration Maps: Figures 11-1 thru 11-63
Reporting limit should be used instead of simply
The comment is noted. Updated isoconcentration maps of
Sections 6.1.4,
continued...
stating ND.
constituents selected for mapping, in accordance with the
6.1.5; Tables 6-5,
results of the NCDEQ-approved constituent management
6-6;
Figure 11-4 - the PBTV contour was not
evaluation, have been provided in the CAP Update for
Figures 6-13a
appropriately drawn. Where there were bounding
each appropriate groundwater flow zone. Where the
through 6-22
wells the contour was instead left open and on the
central tendency analysis resulted in non -detect values,
downgradient side of the basin immediately
the reporting limit is posted.
adjacent to Lake Norman the contour was a closed
solid line indicating certainty when in fact it
probably was more appropriate to leave it open
since there is no data beyond those points. This is
just one example, but this happened on several
The comment is noted. Dashed isoconcentration contours
other figures as well.
are used in the CAP Update to indicate inferred
conditions.
Figure 11-29 - the contour crosses a surface water
feature (unnamed tributary) to the east of the ash
basin. This contour was not appropriately drawn.
The contour should have not cross the surface
water feature and should instead have a contour on
The comment is noted.
its own on that side of the feature. This is just one
example, but hits happened on several other
figures as well.
11.1.1
Isoconcentration Maps: Figures 11-1 thru 11-63
It appears that certain wells that exhibit grout
The comment is noted. Updated isoconcentration maps of
Sections 6.1.4,
continued...
continued...
contamination where MRO and Duke Energy
constituents selected for mapping, in accordance with the
6.1.5; Tables 6-5,
agreed to only monitor boron and sulfate, since
results of the NCDEQ-approved constituent management
6-6;
they are seemingly unaffected by elevated pH
evaluation, have been provided in the CAP Update for
Figures 6-13a
and turbidity, were not included as having valid
each appropriate groundwater flow zone.
through 6-22
data. As discussed in previous comments, if Duke
Duke Energy continues to sample wells in accordance
Energy and their contractors do not support that
with the approved Interim Monitoring Plan (IMP), which is
data as being valid then those wells will need to be
updated annually with input and approval from the
reinstalled. The case should have been made in
NCDEQ.
this report as to why that data is valid and
supported.
All isoconcentration lines should be drawn where
he comment is noted. Isoconcentration lines were drawn
appropriate whether deemed to be attributable to
as accurately as possible, incorporating professional
background or not. A discussion regarding why
judgement, and were not intended to be misleading.
certain locations with concentrations which exceed
However, it is not appropriate to contour background
the applicable PBTV are in fact attributable to
values that exhibit natural variability and are not
background should be included in the report itself.
attributable to constituent migration from source areas.
The map should be representative of available
data; instead they are misleading.
Page 18 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MRO Comment
Response to
I
CAP Update
I Section
Section
Content
Comment
Reference
11.1.1
Isoconcentration Maps: Figures 11-1 thru 11-63
Based on review of these figures it is apparent
Global Response to Additional Delineation
Sections 5.0, 6.0;
that vertical and horizontal extent of several
Requests:
Figures 6-13a
COIs at several well pair locations is
Groundwater migration pathways/flow direction is well-
through 6-22;
warranted.
understood at the Site, therefore, additional horizontal
Appendices C, F, G,
delineation is not necessary for CAP development. A
3, P
groundwater to surface water (2L-2B) evaluation will be
conducted to determine potential surface water impacts
resulting from groundwater plume discharges.
Groundwater modeling in the CAP to provide sufficient
analysis of COI concentrations over time and depth with
various remediation scenarios. Geochemical modeling, to
be included in the CAP, may explain certain anomalous
occurrences of COIs listed here (i.e., Co, Fe, Mn, Mo, Sr,
V), where truly CCR-impacted groundwater may not be
present (non -detect boron at these locations). Also,
additional source area assessments will provide more
delineation to be included in the CAP.
Refer to responses provided above regarding extensive
additional assessments conducted since the CSA Update
to provide additional delineation at the ash basin and
adjacent source areas. Results of these assessments are
provided in the CAP Update.
Barium: AL-1D (horizontal only)
Barium: See global response above. GWA-15D installed
Sections 5.0, 6.1.4,
(July 2018) east and sidegradient of AL-1D location.
6.1.5; Figures 6-2,
6-8a through 6-8c;
Beryllium: AL-1S (horizontal only)
Beryllium: is horizontally delineated from AL -IS to the
Appendices C, F, P
north at MW-14S (non -detect) and to the south at GWA-
11S and GWA-15S (concentrations below IMAC at each of
these wells).
Boron: AL-1S/D (horizontal only, however,
Boron:
L-1: The vertical extent of COIs have been delineated by
concentrations in the BR are trending up toward 2L
AL-1BRL (which was completed 180 feet into bedrock).
and vertical delineation may be necessary in the
For shallow/deep flow zone, refer to global response
very near future),
above.
MW-14S/D (horizontal only)
MW-145 D: See global response above.
B-1BR (vertical only due to proximity of
B-1BR: Additional deep bedrock well (AB-1BRLL)
lake/river)
installed for vertical delineation. The vertical extent of
COIs have been delineated by AB-iBRLLL (which was
completed 320 feet into bedrock).
Page 19 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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Updated December 2019
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Section
MRO Comment
Response to
CAP Update
Section
Section
Content
Comment
Reference
Chloride: AL-11D (horizontal only)
Chloride: See global response above. The vertical extent
Sections 5.0, 6.0;
of COIs have been delineated by AL-1BRL (which was
Figures 6-13a
Cobalt: GWA-7S (horizontal only), MW-14S/D
completed 180 feet into bedrock).
through 6-22;
horizontal only), AL-1S (horizontal only), MW-6S
ppendices C, F, G,
(horizontal only), CCR-9S (horizontal only)
Cobalt: See global response above.
, P
MW-6S: Topography/site access prevent well installations
further downgradient toward Lake Norman from this
Iron:
location.
GWA-7S (horizontal only)
Iron:
GWA-7S: See global response above. Boron non -detect.
Background variability, not enough detections of COIs to
GWA-10D (horizontal and vertical)
warrant additional assessment.
GWA-10D: Background variability, not enough detections
AB-15BR (vertical only)
of COIs to warrant additional assessment.
B-15BR: Background variability, not enough detections
AL-2BRLL (vertically only)
of COIs to warrant additional assessment.
L-2BRLL: Additional deep bedrock well (AB-iBRLL)
installed for vertical delineation. The vertical extent of
AB-1BR (vertical only due to proximity of
COIs have been delineated by AL-2BRLLL (which was
lake/river)
completed 355 feet into bedrock).
B-1BR: Additional deep bedrock well (AB-1BRLL)
installed for vertical delineation. The vertical extent of
COIs have been delineated by AB-1BRLLL (which was
completed 320 feet into bedrock).
Manganese:
Manganese:
Sections 5.0, 6.0;
GWA-7S (horizontal only), AL -IS (horizontal only)
GWA-75 AL-1: See global response above.
Figures 6-13a
through 6-22;
GWA- 6S (horizontal only)
GWA-6S: Upgradient, background location. Verifies
Appendices C, F, G,
background variability which applies to other Fe, Mn
1, P
concentration where other COIs are not greater than
2L/IMAC.
AB-15BR (vertical only), AB-9BR (vertical only), AB-
B-5B AB-9BR AB-15BR: Background variability, not
5BR (vertical only),
enough detections of COIs to warrant additional
assessment (boron non -detect). See global response
above.
L-2BRLL (vertical only)
L-2BRLL: Additional deep bedrock well (AB-iBRLL)
installed for vertical delineation. The vertical extent of
AB-1BR (vertical only due to proximity of
COIs have been delineated by AL-2BRLLL (which was
lake/river)
completed 355 feet into bedrock).
B-1BR: Additional deep bedrock well (AB-iBRLL)
installed for vertical delineation. The vertical extent of
COIs have been delineated by AB-IBRLLL (which was
completed 320 feet into bedrock).
Page 20 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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MRO Comment
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I
CAP Update
I Section
Section
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Reference
Molybdenum:
Molybdenum:
GWA-7S (horizontal only)
GWA-7S: See global response above. Boron non -detect.
B-9BR (vertical only)
B-9BR: Not enough detections of COIs to warrant
additional assessment (boron non -detect).
11.1.1
Isoconcentration Maps: Figures 11-1 thru 11-63
Strontium:
Strontium: Regional variability in strontium likely
Sections 5.0, 6.0;
Continued...
greater than reflected by statistically -derived background
Figures 6-13a
value, therefore additional delineation solely based on
through 6-22;
strontium is not warranted. See global response above.
Appendices C, F, G,
GWA-10S D: Previous comment on isoconcentration lines
3, P
GWA-10S/D (horizontal and vertical)
crossing unnamed tributary to GWA-10 location indicated
the understanding that this tributary is a groundwater
discharge zone, and concentrations detected in these
wells are isolated from the groundwater plume associated
with the ash basin.
MW-14 AL-1: See global response above. The vertical
extent of COIs have been delineated by MW-14BRL
MW-14S/D/BR (horizontal and vertical), AL-
(which was completed 245 feet into bedrock).The vertical
1S/D/BR (horizontal and vertical)
extent of COIs have been delineated by AL-1BRL (which
was completed 180 feet into bedrock).
GWA-1D/BR (vertical only due to proximity of
lake/river)
GWA-1D BR: Other COIs non -detect at depth at this
location, therefore professional judgement suggests the
vertical extent of migration has been determined. The
geochemical model will provide more clarity with regard
MW-61D (horizontal and vertical)
to the occurrence and distribution. Strontium alone does
not warrant additional delineation, as stated above.
MW-613: Topography/site access prevent well installations
AB-15BR (vertical only), AL-4BR (vertical only),
further downgradient toward Lake Norman from this
AB-10BR (vertical only), AB-12BR (vertical only),
location. Also see global response above.
AB-5BR (vertical only)
B-5B AL-4BR AB-IOBR AB-12BR AB-15BR:
Background variability, not enough detections of COIs to
warrant additional assessment (boron non -detect). See
global response above.
Page 21 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
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Section
MRO Comment
I
Response to
CAP Update
Section
Section
Content
Comment
Reference
AL-2BRLL (vertical only)
AL-2BRLL: The vertical extent of COIs have been
Sections 5.0, 6.0;
delineated by AL-2BRLLL (which was completed 355 feet
Figures 6-13a
into bedrock).
through 6-22;
AB-1S/D/BR (vertical only due to proximity of
B-1BR: Additional deep bedrock well (AB-1BRLL)
ppendices C, F, G,
lake/river)
installed for vertical delineation. The vertical extent of
, P
COIs have been delineated by AB-1BRLLL (which was
completed 320 feet into bedrock).
MW-7S/D (vertical only due to proximity of
MW-7 8 9: Additional delineation solely based on
lake/river), MW-8S/D (vertical only due to
strontium is not warranted. Groundwater discharges to
proximity of lake/river), MW-9S/D (vertical only
identified receptors (Lake Norman, unnamed tributary)
due to proximity of lake/river)
therefore a groundwater to surface water (2L-2B)
evaluation has been conducted to determine surface
water impacts from the discharges of the groundwater
plume. That evaluation is included in Appendix J of the
CAP Update.
Sulfate: MW-14S (horizontal only)
Sulfate: See global response above.
Thallium: CCR-9S (horizontal only)Thallium:
See global response above.
DS: MW-14S (horizontal only), AL-1S/D
DS: See responses above for these locations.
(horizontal only), AB-1BR (vertical only due to
proximity of lake/river)
Vanadium: GWA-71D
Vanadium: Background variability, concentration is
(horizontal and vertical)
comparable to PBTV. See global responses above.
Page 22 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
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Section
MRO Comment
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CAP Update
I Section
Section
Content
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Reference
11.1.1
Vertical Extent Cross -Sections: Figures 11-64 thru
In review of this section of the report, it appears
The comment is noted.
Sections 5.0, 6.0;
11-120
that upgradient wells were not included on the
Figures 6-3, 6-13a
cross section line. It is most appropriate to
through 6-22;
include upgradient locations to help illustrate
Appendices C, F, G,
COI distribution (even when likely attributable
3, P
to being naturally occurring).
Why was AB-3S/D not included on the B-B' cross
Cross section B-B' was updated to include AB-3S/-3D and
section transect?
is provided in the CAP Update.
Why was AB-7S/D and SB-14 not included on the
GWA-12 was intended to provide upgradient location to
C-C' cross section transect? Note: GWA-12
help illustrate COI distribution (see comment above). AB -
location is pretty far off the cross section line and
7 was deemed to be too far off transect. SB-14 may have
is not representative of flow along that transect.
been used to help develop strata, but was not included as
it does not have a well and associated groundwater data.
Cross-section layouts were adopted from a previous HDR
submittal.
Some wells with the "D" identifier indicating they
After review of boring logs, it was determined the "D"
are TZ wells are shown on the cross section to
wells installed by a previous consultant were installed in
be in bedrock.
upper bedrock (subjectivity of TZ/bedrock interface
determination).
It is confusing as to how some of the contour lines
are drawn. Often times a 2L/IMAC/PBTV line
Contours were not drawn if there were no data to support
should be drawn but is not and there are instances
them. Much effort went into making sure the vertical
where lines just stop and are left open as if data
cross -sections matched the plan view isoconcentration
is not available. In some instances contours are
maps, therefore inferred contours may have derived from
left open and others they are inferred, it is difficult
viewing both sets of drawings together.
to understand why some are inferred and others
are not.
11.1.2
"Plume chemical characterization is detailed
Since it is not documented what other data
Majority of data (CAMA wells) used was from 3Q 2017
Sections 6.1.3,
below for each COI. Data evaluations are
outside the September 2017 sampling event was
(September) sampling event. More recent data
6.1.4, Tables 6-5,
primarily based on the September 2017
used, I cannot verify information in this section.
(October 2017) was only available and used for NPDES
6-6; Figures 6-13a
groundwater sampling event. The range of
Also, it was stated on figures that October 2017
monitoring network, as it was still active. For historic
through 6-22;
detected concentrations is presented with the
data was utilized please verify if that is correct.
wells, the most recent, valid sample was used.
Appendices C, I
number of detections for the sampling event."
Report refers to September 2017 and figures
state unto October 2017 data was used.
A measure of central tendency analysis of
groundwater COI data (February 2018 to May 2019)
was conducted and means were calculated to support
the analysis of groundwater conditions to provide a
basis for defining the extent of the COI migration at or
beyond the compliance boundary in the CAP Update. A
measure of central tendency analysis was completed
to capture the appropriate measure of central
tendency (arithmetic mean, geometric mean, or
median) for each dataset of constituent
concentrations. Constituent concentrations in a single
Page 23 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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Updated December 2019
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Report
Section
MRO Comment
Response to
CAP Update
I Section
Section
Content
Comment
Reference
well might vary over orders of magnitude; therefore, a
single sample result might not be an accurate
representation of the concentrations observed over
several months to years of groundwater monitoring.
Evaluating COI plume geometries with central
tendency data minimizes the potential for
incorporating occasions where COIs are reported at
concentrations outside of the typical concentration
range, and potentially greater than enforceable
groundwater standards. Previous Site assessments
might have overrepresented areas affected by the ash
basin by posting a single data set on maps and cross -
sections that might have included isolated data
anomalies.
11.1.2
"The majority of detections above the PBTV
Could the beryllium detections in these areas be
The two detections above the IMAC are in the vicinity of
Sections 5.0, 6.1.3,
exist in ash pore water and the shallow flow
attributable to the Phase I landfill?
the Phase I landfill. Additional source area assessments
6.1.4; Appendices
zone in the southeastern portion of the ash
have been performed and the results discussed in the
C, G, H, I
basin and limited downgradient wells east of the
CAP Update.
ash basin. "
detailed evaluation of constituent occurrence through
the NCDEQ-approved constituent management process is
presented in the CAP Update and associated appendices,
which provide multiple lines of science -based evidence to
determine which occurrences are attributable to the
source area and warrant corrective action.
11.2
'Additional HFO samples are proposed to be
In other areas of the report when discussing the
The generalized cross-section transects (Figures 6-2
Figures 6-2, 6-3, 6-
collected for the following locations within the
western transect AB- 3S/D was not utilized.
through 6-4; A -A', B-B', C-C') were selected to better
, 6-5
screened interval (* indicates an ash pore water
Instead AB-4S/D was used. Why are the wells
depict the lithology spanning the basin in several
well):
along transects not consistent throughout this
directions.
evaluation?
Western Transect-AB-5S*, AB-5D, AB-5BR,
The geochemical flow transects (Figure 11-121; western,
AB-3S, AB-3D, AB-2D, MW-9S, and MW-9D
central, eastern) were selected as flow paths and will be
the flow transects moving forward in the CAP Update.
Page 24 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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Updated December 2019
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CAP Update
I Section
Section
Content
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Reference
11.2
Pending Investigation(s)
Even though not definitively stated in this
Those assumptions are correct.
Sections 5.0, 6.0;
section, it is my understanding that the
Appendices C, E, F,
following investigations are pending:
All of the additional evaluations/assessments, as listed in
G, H, I, J, P
the MRO comment, have been completed in accordance
- 21L/213 SW/Sediment Sampling
with work plans approved by the NCDEQ. The results of
-Coal Pile Assessment
these extensive additional evaluations are provided in the
- Other primary/secondary source assessments
CAP Update and its associated appendices, or have been
(being discussed)
previously provided to the NCDEQ [i.e., Ash Basin
- Additional saprolite wells to fill data gap in
Pumping Tests Report - Marshall Steam Station
shallow flow layer beneath the basin and for
(SynTerra, 2019)].
modeling purposes.
Pump tests for modeling purposes.
Deep bedrock well assessment
-Additional HFO samples
13.1
"The flow and transport model is currently being
At this point, MRO expects 2018 data and data
The comment is noted.
Sections 5.0, 6.0,
updated as a part of the updated CAP and will
collected as part of other assessments (in
Appendices C, G, H
include: development of a calibrated steady-
particular the additional information needed for
Data considered in the CAP Update include sample results
state flow model that includes data available
the models) to be included as appropriate.
through Q2 2019. The updated groundwater flow and
through the fourth quarter of2017;
transport model provided in the CAP Update incorporated
development of historical transient model of
results from additional assessments completed in 2019
constituent transport; and predictive simulations
(i.e., PV Structural Fill, ILF structural fill subgrade, coal
ofbasin closure plus groundwater corrective
pile, and gypsum pad data).
action scenarios. "
13.1
"Predictive remedial scenarios will have
Just to reiterate, where a compliance boundary
The comment is noted.
Not applicable to a
simulation times that will continue until modeled
exists standards must be meet at the compliance
specific section.
COI concentrations are below the 2L standard at
boundary NOT the property boundary. And where
the compliance boundary."
there may not be a compliance boundary the point
of compliance is everywhere.
13.2
Summary of Geochemical Model Results
Any direction provided by B. Duetch should be
The comment is noted.
Appendix H
incorporated into the geochemical model submitted
The updated geochemical model report is included in
as part of the CAP update.
the CAP Update. The geochemical modeling efforts have
incorporated multiple iterations of comments and
meetings between Duke Energy (including SynTerra and
Rosewater Geochemical Modeling) and the NCDEQ
(including B. Deutch .
14.0
'A site conceptual model (SCM) is an
SCM was not provided in previous sections. The
Presenting the SCM as a comprehensive analysis of data
Section 5.0
interpretation of processes and characteristics
reviewer is to piece this information together from
presented in previous sections was the intended purpose
associated with hydrogeologic conditions and
various sections throughout the report instead of
of Section 14.
constituent interactions at the Site. The site
being concisely presented in one location within
assessment results provide the information to
the report.
The SCM, now referred to as the Conceptual Site Model
evaluate distribution ofconstituents with regard
(CSM), has been updated to reflect extensive additional
to site -specific geological/hydrogeological
assessment efforts at the MSS and is included in the CAP
properties. "
I
Update.
Page 25 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
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14.1
"Ash sluiced to, and accumulated
Yes for the most part, but as mentioned several
Additional evaluations/assessments, requested by
Sections 5.0, 6.0;
within, the basin is determined to be a
times in the report and suggested by groundwater
NCDEQ, have been completed in accordance with work
Appendices C, E,
source of impacts to groundwater."
data collected the unlined Phase I and II landfills
plans approved by the NCDEQ. The results of these
F, G, H, I, J, P
as well as the unlined PV structural fill are also
extensive additional evaluations are provided in the CAP
contributing to groundwater impacts observed at
Update and its associated appendices, or have been
the site.
previously provided to the NCDEQ [i.e., Ash Basin
Pumping Tests Report - Marshall Steam Station
(SynTerra, 2019)].
14.1
" The site assessment investigated the
While I agree for the most part, the horizontal and
Comment is noted. As stated above, in response to
Sections 5.0, 6.0;
Site hydrogeology, determined the
vertical extent of groundwater and soil impacts
similar repetitive comments, additional
Appendices C, E,
direction of groundwater flow from the ash
have been sufficiently determined to proceed with
evaluations/assessments, requested by NCDEQ, have
F, G, H, I, 1, P
basin, and determined the horizontal and
the CAP; horizontal and vertical delineation at the
been completed in accordance with work plans
vertical extent of impacts to groundwater
site is still incomplete and will need to addressed
approved by the NCDEQ. The results of these
and soil sufficient to proceed with
while moving to the CAP phase.
extensive additional evaluations are provided in the
preparation of a CAP.
CAP Update and its associated appendices, or have
been previously provided to the NCDEQ [i.e., Ash
Basin Pumping Tests Report - Marshall Steam Station
(SynTerra, 2019)].
14.1
"COIs identified as being associated with MSS
Hexavalent chromium and total radium should be
As discussed above, and as presented in the 2018 CAMA
Sections 5.0, 6.1.3,
ash management areas include antimony,
added to the COI list (see previous comments).
Annual Interim Monitoring Report (SynTerra, 2019), total
6.1.4; Figures 6-
arsenic, barium, beryllium, boron, cadmium,
radium and hexavalent chromium have been added to the
19a, 6-19b;
chloride, chromium, cobalt, iron, manganese,
list of COIs in the CAP Update
Appendices C, G, H,
molybdenum, nickel, selenium, strontium,
Hexavalent chromium - discussion warranted. Cr(VI)
I
sulfate, TDS, thallium and vanadium."
appears sporadically throughout the site in anomalous
detections (two exceedances at AB-31), one exceedance
at A13-20S) out of all analysis for this parameter. Cr(VI)
has a very limited presence in groundwater across the
Site. On -going monitoring has provided additional
information regarding whether Cr(VI) should be
considered a COI. Isoconcentration maps for Cr(VI)
show the very limited presence across the Site.
COI management conducted during the CAP Update
indicated that no valid hexavalent chromium results
exceeded the screening criteria at or beyond the
compliance boundary and therefore, Cr(VI) has not
been included as a COI which warrants corrective
action. However, the remedial alternative proposed in
the CAP Update would account for dissolved
constituents in groundwater.
14.1
"The unnamed tributary of Lake Norman
What about the AB-1 location? Its's downgradient
Agreed. From Section 14.iof the CSA Update -'The
Not applicable to a
immediately east of the ash basin serves as a
of the ash basin and exhibits similar concentrations
leading edge of the bedrock plume is interpreted to be
specific section.
groundwater discharge zone in the furthest
to those observed at MW-14 and should also be
atlnear the Lake Norman shoreline adjacent to SW-10
downgradient area with CCR impacts.
considered as the part of the leading edge of
sample location."
Concentrations of COIs consistently detected in
plume migration.
the shallow and deep flow zones at the MW- 14
location are interpreted as the leading edge of
the plume migration."
Page 26 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MRO Comment
Response to
CAP Update
Section
Section
Content
Comment
Reference
14.1
"Boron concentrations are non -detect at MW-
This statement is true, but it should be
The comment is noted. Statement was that groundwater
Not applicable to
10S/D, indicating CCR- impacted groundwater
understood that it is not impacted because
was not migrating beneath the peninsula, therefore
a specific
does not migrate in the peninsula located to the
impacted groundwater is discharging before it
additional delineation onto this peninsula would not be
section.
east along the shore of Lake Norman."
ever makes to the MW-10 location and not
warranted.
because it was attenuated and provides
delineation.
14.1
"In summary, the shallow and deep zone flow
This statement is not entirely accurate. Based on
Based on isoconcentration maps, COI concentrations >
Sections 5.0, 6.0,
units at MSS - beneath and downgradient of the
review of isoconcentration maps provided in this
background are consistently limited to beneath Phase II
Appendices C, F
ash basin - are impacted by CCR- derived
report and available data, it is evident that
landfill and AB-1 cluster.
constituents; however, these impacts do not
bedrock has been impacted beneath the basin as
necessarily migrate vertically in the same areas.
well as beneath the Phase I and II landfills and
Additional evaluation of fractured bedrock and the
Impact to the bedrock flow unit is confined,
downgradient of the ash basin (AB-1).
groundwater flow within it is presented in an appendix
approximately, to the Dry Ash Landfill (Phase 11)
of the CAP Update. Great efforts were made to
and immediately east of the waste boundary at
characterize groundwater flow within bedrock fractures
AB-1."
with respect to depth, (300-500 feet bgs). This work
included multiple geophysical logs from six deep open
boreholes. The locations were specifically chosen to
accommodate NCDEQ comments and requests of
vertical delineation beneath and near the Dry Ash
Landfills Phase I and Phase II as well as the ash basin
dam and downgradient areas (i.e., MW-14BRL). Details
of matrix diffusion within bedrock at the Site, and its
effects on groundwater flow, are also presented in the
CAP Update.
14.2
Maximum COI Concentrations
Hexavalent chromium and total radium should be
Refer to previous response above for the same
Sections 5.0,
added to the COI list (see previous comments).
comment.
6.1.3, 6.1.4;
Figures 6-19a, 6-
19b; Appendices C,
G, H, I
Page 27 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MRO Comment
Response to
CAP Update
Section
Section
Content
Comment
Reference
14.2
"Concentration trends at all wells, surface water,
There is no discussion/interpretation provided on
Thorough geochemical modeling of the majority of COIs
Sections 6.1.3,
and seep locations are graphically depicted in
how hydrogeological and/or geochemical factors
and their distribution has been completed and is included
6.1.4, Tables 6-5,
plan view and included as Figure 14-39 through
affect COI movement and concentrations through
in the CAP. COI not evaluated in the updated geochemical
6-6; Appendices C,
Figure 14-76. COI
out the site and why COIs are increasing at the
model report were evaluated in the groundwater flow and
G, H, I
concentrations are generally stable, often
locations identified in this section.
transport model update.
indicating slight variation which may be
attributed to natural fluctuations. However,
A Plume Stability Evaluation - Marshall Steam Station
increasing concentrations of several COIs are
(Arcadis, 2019) is also included as an appendix to the
observed in downgradient monitoring wells:
monitored natural attenuation (MNA) report in the CAP
Update.
AB-ID/BR: boron, chloride, cobalt, iron,
manganese, strontium, TDS
GWA-I1S/D: boron, TDS
GWA-ISS: boron
MW-14SID/BR : chloride
MW-1: barium, chloride
MW-6D: boron, chloride
MW-7D: boron, chloride"
14.2
Time -Series Graphs: Figures 14-1 through Figure
Why was the western transect not evaluated?
Source area and downgradient transects provided
Not applicable to a
14-38
sufficient coverage/insight to the CSA. There were
specific section.
time constraints on preparation of the CSA report.
Why was AB-9 location not included in the
evaluation? In section 11 of this report, this
Formatting of graphics were considered in order to
transect included AB-12, AB-9 and AB-1, but here
provide ease of interpretation to the reader. The
it included AB-15 and not AB-9. Why the
central source transect already contained two source
inconsistency throughout the report of wells used
area well clusters.
along transects?
These were not intended as duplicates of the selected
Why was CCR-13 location not used in the
geochemical flow transects. For reasons noted above,
evaluation as it was in other areas of the
only select locations were included in time vs
report? Again, why the inconsistency?
concentration plots. Thorough analysis of the
geochemical transects with support of modeling to be
On Figure 14-2, 14-8, and 14-24, there appeared
included in the CAP.
to be no data on the MW-1 plot. Was this an error
MW-1 is a single well (not cluster), therefore there
or does the data not exist?
were no data to support a graph of multiple flow zones
at this location.
15.0
"Receptors including water supply wells and
2L/2B evaluation is necessary to support this
Groundwater to surface water interaction at the MSS has
Sections 6.1.2,
surface water bodies were identified and found
statement and should be conducted accordingly to
been extensively evaluated in the current and future
6.1.3, 6.2.1;
to be not impacted by the ash basin and
fully assess compliance with 2B. (Assessment
conditions surface water reports, which are included in an
Appendix J
generally in compliance with applicable
pending)
appendix to the CAP Update. As the studies conclude,
regulatory standards Significant exposure
there are not concentrations of COIs related to the ash
pathways are understood and constituent
basin present in surface water greater than 02B water
concentrations detected in water supply wells
quality standards, nor are there predicted to be under
are deemed to not be from the ash basin. "
I
Ifuture conditions.
Page 28 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MRO Comment
Response to
CAP Update
I Section
Section
Content
Comment
Reference
15.0
"Impacts to groundwater in all three flow zones
Please define exactly what data collection is
Additional evaluations/assessments, requested by
Sections 5.0, 6.0;
have been identified beneath and downgradient
necessary and when these efforts are proposed
NCDEQ, have been completed in accordance with work
Appendices C, E, F,
of the ash basin at MSS. Supplemental data
to be conducted.
plans approved by the NCDEQ. The results of these
G, H, I, J, P
collection to support groundwater modeling and
extensive additional evaluations are provided in the CAP
long-term monitoring is anticipated to support
Update and its associated appendices, or have been
the CAPprocess "
previously provided to the NCDEQ [i.e., Ash Basin
Pumping Tests Report - Marshall Steam Station
(SynTerra, 2019)].
The updated groundwater flow and transport model
provided in the CAP Update incorporated results from
additional assessments completed in 2019 (i.e., PV
Structural Fill, ILF structural fill subgrade, coal pile, and
gypsum pad data).
15.2
"Surface water quality of Lake Norman adjacent
At this time 2L/2B SW sampling has not been
Groundwater to surface water interaction at the MSS has
Sections 6.1.2,
to the ash basin is generally in compliance with
conducted and this statement cannot be fully
been extensively evaluated in the current and future
6.1.3, 6.2.1;
2B standards . An evaluation of groundwater to
supported until this information has been collected.
conditions surface water reports, which are included in an
Appendix J
surface water interaction will be used to support
appendix to the CAP Update. As the studies conclude,
the CAP process."
there are not concentrations of COIs related to the ash
basin present in surface water greater than 02B water
quality standards, nor are there predicted to be under
future conditions.
15.2
Revised Site Conceptual Model
Where was the initial site conceptual model
Section 14.0 was intended as the SCM, incorporating
Section 5.0
detailed in the report?? There was no section
analysis of data that was presented in previous
dedicated to the SCM as one would typically
sections (i.e. Section 14.3 Contaminant Migration and
expect in a CSA. Instead, pieces of the SCM are
Potentially Affected Receptors).
scattered throughout the report in various
The SCM, now referred to as the Conceptual Site Model
sections and not in a single comprehensive
(CSM), has been updated to reflect extensive additional
section.
assessment efforts at the MSS and is included in the CAP
Update.
15.4
"For basin closure, reduction of infiltrating water
This needs to be substantiated considering the
The closure scenarios presented in the updated
Sections 5.0, 6.0,
will have the greatest positive impact on
majority of ash at the Marshall Steam Station is
groundwater flow and transport model included in the
Appendix G.
groundwater and surface water quality
below the water table and will be a continued
CAP Update support the conclusion.
downgradient of the ash basins."
source to groundwater contamination at the site.
Appendix
Background Determination
Based on review of data submitted to date, GWA-
Noted, as above.
Section 4.2,
H
12D has not been replaced and continues to
Table 4-3
exhibit unacceptable water quality for inclusion
into background. BG-1BR was replaced with BG-
Groundwater BTUs in each flow zone at MSS were updated
1BRA and water quality is acceptable thus this
in 2019. The updated BTVs were calculated using
location is acceptable for use in the background
concentration data from background groundwater samples
evaluation.
collected from 2010 (beginning of compliance monitoring)
to December 2018.
A letter dated June 15, 2018, was submitted
to Duke Energy regarding Marshall Steam
Station BTVs.
Page 29 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MRO Comment
Response to
CAP Update
Section
Section
Content
Comment
Reference
ES.1
"The majority of ash contained in the ash basin is
What is the estimated total volume of saturated ash
Estimates of the volumes of saturated and unsaturated
Section 6.1.1.4
saturated."
vs. unsaturated ash?
ash have been provided by the closure engineers and
Figure 6-5,
are referenced in the CAP Update.
Appendix G
If dewatering is anticipated, what is the
estimated volume of the remaining saturated
Based on topographic and bathymetric surveys, the ash
ash?
basin is estimated to contain approximately 14,033,000
cy of CCR. The vertical extent of saturated ash would be
reduced from pre -decanting conditions under a closure -
in -place scenario. Under ash basin closure by closure -
in -place, the range of potential saturated ash thickness
is between a few feet to 50 feet with greatest volume of
saturated ash remaining in the south central portion of
the ash basin near the dam. Across the basin, saturated
ash thicknesses would be reduced by approximately 10
to 20 feet as a result of decanting and dewatering
operations conducted during closure.
ES.3.3
"The surface water results collected from Lake
This statement cannot be fully supported until
Surface water at the MSS has been extensively evaluated
Sections 6.1.2,
Norman do not indicate that impacted
2L/2B compliance sampling has been conducted
in the current and future conditions surface water reports,
6.1.3, 6.2.1;
groundwater associated with the MSS ash
at the site. (Assessment pending)
which are included in an appendix to the CAP Update. As
Appendix I
basin is causing 2B exceedances in Lake
the studies conclude, there are not concentrations of COIs
Norman."
related to the ash basin present in surface water greater
than 02B water quality standards, nor are there predicted
to be under future conditions.
ES.5.2
"The following list ofgroundwater COIs has been
Hexavalent chromium and total radium should be
The comment is noted. Refer to previous responses.
Sections 5.0, 6.1.3,
developed for MSS:
added to the COI list (see previous comments).
COI management conducted during the CAP Update
6.1.4; Figures 6-
indicated that no valid hexavalent chromium results
19a, 6-19b;
Antimony Arsenic Barium Beryllium Boron
exceeded the screening criteria at or beyond the
Appendices C, G, H,
Cadmium Chloride
compliance boundary and therefore, Cr(VI) has not been
I
Chromium (total) Cobalt
included as a COI for corrective action.
Iron Manganese Molybdenum Nickel Selenium
Total radium exhibits mean concentrations in groundwater
Strontium Sulfate
greater than background values, 02L standard, or IMAC
TDS
downgradient of the ash basin at or beyond the compliance
Thallium Vanadium"
boundary. It has been included as a COI for corrective
action.
ES.5.2
"This leading edge is observed in the shallow
Why is the AB-1 location not included as being
This comment is noted. From Section 14.1 of the CSA -
Not applicable to a
and deep flow zones east of the ash basin
part of the leading edge of the plume? It should
'The leading edge of the bedrock plume is interpreted to
specific section.
between the Dry Ash Landfill (Phase I) and the
be in all flow layers.
be at/near the Lake Norman shoreline adjacent to SW-10
unnamed tributary.
sample location."
Page 30 of 31

Marshall Steam Station - 2018 CSA Update Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
Site Specific Comments
Report
Section
MIRO Comment
Response to
CAP Update
I Section
Section
Content
Comment
Reference
ES.5.2
'7t is anticipated that additional monitoring wells
Additional monitoring wells for purposes of
Additional evaluations/assessments, requested by
Sections 5.0, 6.0,
for vertical delineation may be installed to
vertical delineation is necessary to complete
NCDEQ, have been completed in accordance with
Appendices C, F,
support the groundwater corrective action
delineation at the site. This is a must to comply
work plans approved by the NCDEQ. The results of
P
planning process."
with 2L.
these extensive additional evaluations are provided in
the CAP Update and its associated appendices.
Additional evaluation of fractured bedrock and the
groundwater flow within it is presented in an appendix
of the CAP Update. Great efforts were made to
characterize groundwater flow within bedrock fractures
with respect to depth, (300-500 feet bgs). The
locations were specifically chosen to accommodate
NCDEQ comments and requests of vertical delineation
beneath and near the Dry Ash Landfills Phase I and
Phase II as well as the ash basin dam and
downgradient areas. Details of matrix diffusion within
bedrock at the Site, and its effects on groundwater
flow, are also presented in the CAP Update.
ES.6
"The assessment investigated the Site
Groundwater and soil delineation is incomplete,
See responses above in regards to the same comment.
Not applicable to a
hydrogeology, determined the direction of
however, I do agree that it is sufficient enough to
specific section.
groundwater flow from the ash basin, and
proceed with CAP preparation.
determined the horizontal and vertical extent of
impacts to groundwater and soil sufficient to
proceed with preparation of a corrective action
plan (CAP). "
ES.6
"Surface water receptors downgradient of the
This statement cannot be fully supported until
Groundwater to surface water interaction at the MSS has
Sections 6.1.2,
ash basin (e.g. Lake Norman) demonstrate
2L/2B compliance sampling has been conducted
been extensively evaluated in the current and future
6.1.3, 6.2.1;
compliance with 2B standards, with the
at the site. (Assessment pending)
conditions surface water reports, which are included in an
Appendix J
occasional exception of dissolved oxygen,
appendix to the CAP Update. As the studies conclude,
chloride, TDS, arsenic, selenium, cadmium (D),
there are not concentrations of COIs related to the ash
copper (D), and lead (D)."
basin present in surface water greater than 02B water
quality standards, nor are there predicted to be under
future conditions.
ES.6
'A "Low" risk classification and closure via a cap-
Just to note, per HB 630, you not only have to
The comment is noted. Pursuant to G.S. Section 130A-
Appendix A
in place scenario are considered appropriate as
provide alternate, but you have to comply with all
309.213(d)(1), a November 14, 2018 letter from NCDEQ
alternative water supplies are being provided in
dam safety requirements to be considered for a
to Duke Energy, documented the classification of the CCR
accordance with G.S. 130A- 309.213.(d)(1) of
"low" risk classification.
surface impoundment at MSS as low -risk. The letter cited
House Bill 630."
that Duke Energy has "established permanent water
supplies as required by G.S. Section 130A-309.211(cl)"
and has "rectified any deficiencies identified by, and
otherwise complied with the requirements of, any dam
safety order issued by the Environmental Management
Commission... pursuant to G.S. Section 143-215.32."
Page 31 of 31

Marshall Steam Station - 2018 CSA Update
Report Comments - Response to Comments
Previously Submitted September 2018
Updated December 2019
ATTACHMENT 1
CSA UPDATE REPORT COMMENTS, CAP FRAMEWORK,
AND IMP OPTIMIZATION MEETING MINUTES -
SEPTEMBER 11, 2018

Project: Duke Energy
Subject: Marshall CSA Update Report Comments, CAP Framework, and IMP Optimization
Date: September 11, 2018
Meeting Minutes
Project: Duke Energy Carolinas - Marshall Steam Station
Subject: CSA Update Report Comments, CAP Framework, and IMP Optimization
Date: Tuesday, September 11, 2018
Location: NC DEQ Mooresville Regional Office (MRO)
Meeting Attendees
Duke Energy
DEQ
SynTerra
John Toepfer phone
Steve Lanter
KathyWebb
Tyler Hardin
Elizabeth Werner
Brian Wilker
Courtney Murphy
Joanna Harbison
Brandy Costner
Andrew Pitner
Meeting Purpose
The purpose of the meeting was to discuss the North Carolina Department of Environmental
Quality's (DEQ's) comments regarding the Marshall Comprehensive Site Assessment
(CSA)Update. In addition to reviewing the DEQ January 2018 CSA Update Report comments
and responses, the purpose of the meeting was also to discuss the Corrective Action Plan
(CAP) framework and agree on a path forward for the Interim Monitoring Plan (IMP) optimization
at the Marshall Steam Station (Site).
The CSA Update Report was submitted January 31, 2018. DEQ presented its comments in a
letter dated August 17, 2018. That letter included the following categories:
• Delineation of Groundwater Contamination
• Groundwater Flow, Contamination Flow and Transport
• Other Potential Primary and Secondary Sources
• 02L/02B Surface Water Sampling
• Maps, Figures, and Tables
• Modeling
B. Costner submitted detailed comments in an email also dated August 17, 2018 to T. Hardin.
Prior to this meeting, T. Hardin sent, as an attachment to an invitation for this meeting, a
summary of responses to all comments from the August 17, 2018 letter and email. The
invitation was dated September 7, 2018 and also included Duke's proposed IMP optimization.
DEQ review of these responses and proposed optimized IMP prior to this meeting streamlined
Page 1
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594\Meeting Minutes\DEQ MRO_Marshall CSA Update Meeting Minutes_Final.docx

Project: Duke Energy
Subject: Marshall CSA Update Report Comments, CAP Framework, and IMP Optimization
Date: September 11, 2018
the meeting discussion, specifically with regard to concurrence on the IMP list, which Duke
expects to receive from DEQ in October.
DEQ stated that responses to comments received in the September 7, 2018 meeting invitation
(Attachment 1) were generally agreed upon, and that only comments warranting further
discussion would be addressed in this meeting.
These meeting minutes are summarized into the following sections: CAP Framework, CSA
Update, IMP Optimization, and On-going/Upcoming Work. The CSA Update section includes
subsections, as listed above, to address each of the categories from DEQ's comments
summarized in the August 17, 2018 letter.
DEQ approves these notes as presented at the time and date of the specified meeting. Any
policy, guidance, or direction given or approved subsequent to this meeting may supersede the
actions and/or decisions agreed upon during this meeting.
Meeting Summary
Marshall CAP Framework
• The Marshall CAP Framework was presented by Duke in a Power Point
presentation.
• Ongoing site evaluations were included in the presentation.
• The CAP submittal schedules are currently being discussed by others within Duke
and DEQ.
• DEQ confirmed Marshall background threshold values (BTVs) are resolved and
Duke should have written notification of concurrence by the end of the month.
o DEQ suggested that having a background data summary table for all NC
sites would be helpful to have a greater understanding of background
concentration variability.
o It was stated that BTVs may be re-evaluated at some time following the CAP
Update submittals but should not be revised before.
o DEQ asked about the strategy (especially regarding soil) in BTV evaluation.
DEQ requested documented explanation of their use to facilitate clarification
to stakeholders.
o It was mutually agreed that small exceedances of BTVs, within regional
background value ranges or with no source for presence, does not indicate
impacted soil or groundwater.
o DEQ stated an expectation that a clear, defensible explanation be provided in
the upcoming CAP Update documents how reasonable background ranges
will be determined
• It was discussed that data evaluation, as being requested by DEQ, takes time
(requiring approximately a 6-month lead time) and that reports with significant
data evaluations may not include the most recent available data.
Page 2
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594\Meeting Minutes\DEQ MRO_Marshall CSA Update Meeting Minutes_Final.docx

Project: Duke Energy
Subject: Marshall CSA Update Report Comments, CAP Framework, and IMP Optimization
Date: September 11, 2018
CSA Update
Delineation of Groundwater Contamination
• DEQ presented observations of concentrations greater than background values.
• It was discussed that additional monitoring well(s) east of MW-14 may not be
necessary if the 2L-2B evaluation addresses potential surface water impacts due
to groundwater discharge in the tributary.
• DEQ stated that multiple lines of evidence are needed to provide more
explanation for results greater than background where potential impacts to
groundwater may not exist.
• DEQ stated it would be helpful to have groundwater data to define the area north
of ILF for cross -sections and transects.
• DEQ noted that boron was not delineated to the east of AL-1 (GWA-10 cluster on
far side of tributary/draw).
o Duke stated that the 2L-2B evaluation would help confirm delineation in
this area; extremely difficult access exists further east of AL-1, which
limits potential additional well installation (very steep, wooded slope).
• Further discussion is needed to determine if hexavalent chromium needs to be
added as a constituent of interest (COI).
• Total radium was added as a COI.
• For groundwater samples with pH and turbidity concerns, it was mutually agreed
upon to use professional judgement along with documented justification to
determine validity of data to be used for assessment purposes.
• DEQ asked when data from new wells AB-1 BRLL and GWA-15D will be
available.
o Duke responded they may have been sampled in Q3 2018.
• Duke stated that Work Plans for additional source wells and potential data gaps
are pending.
• DEQ was not aware of any additional work requests pending beyond what was
discussed at this meeting.
• A need to plan for long term monitoring post -closure was discussed.
o DEQ recommended tracking potential data gaps during and post -closure
activities to have an optimal effectiveness monitoring plan in the future.
Groundwater Flow, Contamination Flow and Transport
• DEQ agrees with the response to comment regarding calculated vertical
gradients.
Page 3
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594\Meeting Minutes\DEQ MRO_Marshall CSA Update Meeting Minutes_Final.docx

Project: Duke Energy
Subject: Marshall CSA Update Report Comments, CAP Framework, and IMP Optimization
Date: September 11, 2018
Other Potential Primary and Secondary Sources
• Duke stated that Work Plans are pending for potential additional source
evaluations
• It was mutually agreed upon that adequate coverage exists upgradient of the
photovoltaic (PV) structural fill and that the primary source is characterized.
• DEQ noted that monitoring wells are needed downgradient of the PV structural
fill, outside of the ash basin waste boundary, for future long-term monitoring.
DEQ stated the shallow groundwater in this area is likely impacted, however data
is limited.
• The AB-17/18 monitoring well clusters are scheduled to be abandoned in
January 2019. Duke is likely to be conducting additional source evaluations in
Q1-Q2 2019. Duke noted that the AB-17 cluster could be potentially replaced at
that time.
02L/02B Surface Water Sampling
• DEQ suggested providing the 2L-2B evaluation report in a stand-alone document
prior to the CAP submittal.
• DEQ stated the value of AOW data and recommended that the information be
used for evaluation and corrective action planning, even though seeps are
currently covered under the Special Order by Consent (SOC).
• Duke agreed to follow up with details about the timeframe for the 2L-2B
evaluation and potential stand-alone report.
Maps, Figures, and Tables
• Figure 14-77 was discussed. DEQ noted that background soil data outside of the
ash basin is lacking.
• DEQ noted that many background soil samples have reporting limits greater than
soil BTVs. DEQ noted that the soil samples collected from three background
locations (BGSB-GWA-02, BGSB-GWA-04, BGSB-GWA-06) in August 2017 had
reporting limits below the soil BTVs (preferable).
• DEQ requested that more background samples should be collected. DEQ agreed
to provide a list of desired soil sampling locations.
• Cross Sections:
o DEQ noted some detections greater than background in bedrock beneath
western and central portions of the ash basin.
o Duke stated contours were drawn using the statistically derived
background values in the CSA. Closing contours, particularly with depth
on cross -sections, is also an area where professional interpretation was
used during the preparation of the CSAs.
Page 4
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594\Meeting Minutes\DEQ MRO_Marshall CSA Update Meeting Minutes_Final.docx

Project: Duke Energy
Subject: Marshall CSA Update Report Comments, CAP Framework, and IMP Optimization
Date: September 11, 2018
o DEQ agreed on the need for using professional judgement with
documented explanation/justification regarding how constituents are
contoured.
o Duke stated that many previously designated "D" wells were completed in
competent bedrock based on review of boring logs.
• It was mutually agreed upon that isoconcentration figures (plan view or cross
section) are meant as conceptual figures and should not be interpreted literally.
DEQ noted the CSA Update Report needs more discussion explaining the
conceptual nature of the CSA figures to help provide clarification to stakeholders.
Modeling
• It was mutually agreed that groundwater flow and transport or geochemical
modeling in the CAP Update would answer the majority of questions regarding
presence and concentrations of constituents.
• DEQ agreed that items requested in an email sent to J. Toepfer on 9/10/18 would
not be feasible to include in the November 2018 model report. DEQ agreed to
follow up with Duke to further discuss these comments.
• Duke stated that the November 2018 model submittal will incorporate Q2 2018
data. DEQ stated that this submittal would facilitate decisions regarding source
control.
• Closure options were discussed (e.g., landfills and structural fill would not be
included in closure construction activities).
o DEQ noted that groundwater impacts cannot be discerned between the
landfills and structural fill areas and the ash basin.
o DEQ noted something needs to be done to help discern comingled
sources.
o DEQ noted these landfills were closed but reiterated that does not
mitigate potential impacts to groundwater.
o The DEQ Regional office comments/concerns regarding the proposed
closure options have been sent to J. Risgaard.
iMP Optimization
• DEQ agreed to finalize agreement on the optimized IMP by end of October 2018 if
Duke Energy provides the needed information in a timely manner.
• DEQ has reviewed and is in general agreement Duke's proposed IMP optimization
and associated rationale.
o Duke stated that revisions to the proposed optimized IMP revisions, as
discussed between DEQ and Duke on a conference call 9/5/18, have been
incorporated. Specifically, DEQ-requested wells in the vicinity of the PV
structural fill were added.
• It was decided that the CCR-9 monitoring well cluster will be added to the IMP
quarterly schedule.
Page 5
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594\Meeting Minutes\DEQ MRO_Marshall CSA Update Meeting Minutes_Final.docx

Project: Duke Energy
Subject: Marshall CSA Update Report Comments, CAP Framework, and IMP Optimization
Date: September 11, 2018
• DEQ stated areas near site activities may be eligible for reduced monitoring once
stable conditions are verified after activities are completed.
• DEQ proposed caveats to the IMP agreement (i.e., new wells will be automatically
added to quarterly sampling).
o DEQ suggested a contingency plan may be written into IMP and likely a
review of the optimized IMP on an annual basis would be appropriate in the
future.
• Parameter reduction:
o It was mutually agreed upon that further discussion is warranted regarding
inclusion of hexavalent chromium as a COI.
o It was mutually agreed upon to add total radium as a COI.
o Duke proposed to remove mercury, total uranium, and other non -COI
parameters.
o DEQ requested additional time to review the proposed parameters for
elimination.
• Duke agreed to submit a formal IMP optimization plan including well list and
parameters to DEQ for written approval.
On-going/Upcoming Work
• Duke presented DEQ with a Work Plan for proposed pumping test planned at AL-
2BRLL.
• Deep bedrock evaluation/well installation:
o DEQ Solid Waste has been notified of the pending evaluation and drilling on
the Phase II landfill.
o Duke proposed, and DEQ provided concurrence with, moving one deep
bedrock location from GWA-11 to AL-1.
Attachments:
Attachment 1 Marshall CSA Update Report — DRAFT Response to DEQ Comments
Page 6
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594\Meeting Minutes\DEQ MRO_Marshall CSA Update Meeting Minutes_Final.docx

Project: Duke Energy
Subject: Marshall CSA Update Report Comments, CAP Framework, and IMP Optimization
Date: September 11, 2018
ATTACHMENT 1
MARSHALL CSA UPDATE REPORT - DRAFT RESPONSE TO
DEQ COMMENTS
P:\Duke Energy Carolinas\18. MARSHALL\06.EHS CAMA Compliance Support\06BB. 2018 NCDEQ Meetings - PCR
594\Meeting Minutes\DEQ MRO_Marshall CSA Update Meeting Minutes_Final.docx

DRAFT - Marshall Steam Station - CSA Update Report Comments -
Report
Content
1. Work Performed by Others: "...
• SynTerra relied on information from the HDR reports as being correct.
• The seal of the licensed geologist for this CSA applies to activities
conducted and interpretations derived after the HDR reports were
submitted. This submittal relies on the professional work performed by
HDR and references that work. "
It is stated in the report that CCR groundwater data was
isidered in data interpretations in this CSA Update report
It was stated in ES. 1 that, "The CCR data has not been fully
orporated into the analysis of this CSA due to the data only becoming
3ilable as of mid January 2018. "
The report is poorly organized.
Response to Comments
8/31/2018
M RO
Comment
1. What effort (if any) to make certain information
being utilized from the previous consultant was in fact
correct prior to inclusion in this CSA Update report?
Note: There were many instances in past report
submittals of incorrect/erroneous data submitted.
2. It is difficult to discern whether CCR groundwater
data, and to what extent the CCR groundwater data
was used. CCR groundwater data was presented on
figures, but rarely mentioned as being incorporated in
the assessment/evaluation/interpretations in the
3. This statement is not entirely accurate, the federal
CCR data was not PUBLICLY available until mid-Januai
2018, but was available to Duke Energy and their
consultants as data became available between 2016
and early 2018. There was ample time and data to be
incorporated, but was not at Duke Energy's own
choosing.
4. Poor organization of the report makes the review
much more cumbersome and time consuming. It
requires the reader to piece it together to get the
. Several sections of this report are still very much just data summary 5. This is a comprehensive site assessment. Data
2port. While Duke Energy does a good job with data presentation, the presentation is important; however, it should not be
ata evaluation/interpretations are lacking and at times non-existent. the primary focus of this report. It should instead
focus heavily on what the data means and if there is
insufficient data then that should simply be stated
along with what Duke Energy plans to do about it.
CAP development will be negatively affected without
the necessary evaluations/interpretations.
Report
Section
1.2.3
Section
Content
"The most recent data available from the CCR
groundwater monitoring well network is provided on
isoconcentration maps and cross -sections herein."
M RO
Comment
The CCR data provided as a PDF in App. B of the CSA
Update report only presents App. III (Detection
Monitoring) constituents and does not include App. IV
(Assessment Monitoring) constituents. App. IV
constituent data was available, but was not provided.
Since this data was not provided was it even
considered during assessment/evaluation of data? If
so, to what extent was all CCR data evaluated as part
of this report?
Page 1 of 19
Response to
Comment
Much effort was spent evaluating data utilizing
professional judgement in regards to
identifying/flagging potentially erroneous data to avo
usage of that data.
3Q/4Q 2017 data review complete to date. On -going
efforts to review 2018 data and will continue with
future data collected.
CCR data was utilized to inform professional
judgement in report preparation.
l evaluation of data obtained for CCR Rule
ce will be included in the CAP.
Report outline was agreed upon between NCDEQ and
Duke Energy.
The report contents are presented in data summary
format to clearly provide factual site
characterization. Data analysis and interpretation of
data was presented in several sections of the report
(i.e. 11, 14, 15). A more thorough discussion
regarding site conditions and analysis will be
provided in the CAP supported with tables, figures,
and modeling results as specified in the CAP Content
Guidance (April 27, 2018 DEO letter).
Response to
Comment
Yes, CCR data was utilized to inform professional
judgement in report preparation and determination of
plume geometry.
P:\Duke Energy Carolinas\ 18. MARSHALL \ CSA Update January 2018 \ NCDEQ Comments —August 2018 \ Marshall CSA Update Report - DRAFT Response to NCDEQ Comments.docx

DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
2.1
"The MSS ash basin, which contains ash generated
Figure 2-1 does not have topo lines to illustrate these
Noted. Topo depicted on Figure 1-1 and 2-4.
from the historic and active coal combustion at the
topographic divides as indicated in the report.
Plant, is situated with MSS to the south, topographic
divides located along Sherrills Ford Road to the West
Island Point Road to the north , and Duke Energy
property to the east Figure 2-1 .
2.3.1
'An engineered cap would reduce infiltration
I do agree that an engineered cap would reduce
Basin decanting and dewatering to occur prior to
through the covered area, thereby reducing the
vertical infiltration, however, as indicated in the report
placement of cap. Groundwater flow and transport
potential of leaching of Constituents of Interest
the majority of the ash is saturated at MSS, which
model currently being updated to predict future water
(COIs) into the groundwater overlying the closed
means a large volume of saturated source material
elevations and remediation scenarios (provided in
basin."
will remain in place. The cap does not account for
CAP).
lateral groundwater flow. COIs will continue to be
leached and continue to migrate at the site.
2.3.1
Two unlined ash landfill units, referred to as the
Because the Phase I landfill is located immediately
Additional source area assessments to be included in
Marshall dry ash landfill (NCDEQ Division of Solid
adjacent/downgradient of the basin and the Phase II
CAP.
Waste Permit No. 1804-INDUS), are located adjacent
landfill is located over portions of the ash basin, these
to the east (Phase I) and northeast (Phase II)
unlined landfills should be considered additional
Groundwater flow direction is understood and expected
portions of the ash basin .... The landfill units were
sources to groundwater impacts at the site.
to discharge to Lake Norman east of CCR-9 and to the
constructed prior to the requirement for lining
unnamed tributary east of GWA-7, MW-14, and AL-1.
industrial landfills and were closed with a soil cover
Note: Delineation is warranted east of GWA-7, MW-14
Groundwater to surface water assessment to be included
system ."
and AL-1 well clusters between the wells and the
in CAP.
stream. Delineation is also warranted east/southeast
of CCR-9 well cluster. Installation of a deep well at the
GWA-15D (deep well) installed at GWA-15 location in July
MW-5 location is warranted.
2018.
2.3.4
INDUSTRIAL LANDFILL No, 1
Because the ILF was constructed over a small portion
Additional source area assessments to be included in
of the ash basin and ash was used as subgrade
CAP.
"The landfill was constructed over portions of residual
material, the ILF should be considered as a potential
material and over portions of the ash basin. The
additional source to groundwater impacts at the site.
subgrade for portions of this landfill were constructed
of fly ash under the structural fill rules found in 15A
Note: AB-17 and AB-18 well clusters are slated for
NCAC 138 .1700 et seq."
removal to allow for construction of the a stormwater
Noted.
retention basin to support closure. AB-17 well cluster
should be replaced as we have previously discussed. It
would be beneficial to install a well cluster off the
southwest corner of the ILF between the landfill
boundary and the stream.
2.3.5
PHOTOVOLTAIC FARM STRUCTURAL FILL
Because the PV structural fill was conducted partially
Additional source area assessments to be included in
on top of the NW portion of the ash basin and does
CAP.
"The photovoltaic farm structural fill (PV structural fill)
not have a liner or liner system, the PV structural fill
was constructed of fly ash, under the structural fill
should be considered an additional source to
rules found in 15A NCAC 138 .1700 et seq., and
groundwater impacts at the site.
bottom ash, under Duke Energy's Distribution of
Residuals Solids Permit issued by NCDENR Division of
Note: There are no wells drilled outside the waste
Noted.
Water Quality (DWQ), and is located adjacent to and
boundary of the ash basin to monitor the PV structural
partially on top of the northwest portion of the ash
fill. Additional wells are warranted west of the PV not
basin ."
within the waste boundary of the ash basin.
Page 2 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
2.4.2
" MSS continues to maintain a coal pile in the area
Why was the coal pile not considered/identified as a
Additional source area assessments to be included in
located between the coal-fired units and the active
secondary source at the site? My understanding is that
CAP.
ash basin."
there will be a coal pile assessment conducted, but it
does not clearly indicate this in the report.
2.5
'As part of the permit renewal, the facility identified
Not all seeps/AOWs were covered under the current
Noted. Special Order by Consent (SOC) currently in
seeps and collected seep samples. The seeps were
permit. The permit ONLY covers engineered seeps
place.
incorporated into the permit as outfalls ."
and they are included as outfalls in the permits.
2.6.2
"The NPDES Permit NC0004987 (effective October 01,
This permit has been updated and part of that update
Noted.
2016), lists the groundwater monitoring wells to be
included the removal of the groundwater monitoring
sampled, the parameters and constituents to be
of compliance wells. The new permit was issued on
measured and analyzed, and the requirements for
4/2/2018.
sampling frequency and reporting results
( Table 2-2 ).
2.7
"From 1988 to 2015, several environmental incidents
Why was this section not updated to include any
Table 2-3 was updated with information from 2015 to
(i.e., releases) occurred at the site that have initiated
incidents that occurred between 2015 and generation
time of submittal, January 2018 (email
notifications to NCDEQ or required a subsurface
of this report? Table 2-3 does include some from
correspondence LaSala to Wilker, 01/08/2018).
investigation."
2016. This should have been updated and not a
regurgitation from the 2015 CSA.
3.3
"No soil borings were advanced within the footprint
What is the rationale for not advancing any borings
Majority of ash (source) sampling was conducted as
of the dry ash landfill (Phase I) for the CSA."
within the Phase I landfill as there was at the Phase II
part of the initial CSA investigation. Additional soil
landfill? Was this due to access issue or merely an
analysis (HFO/HAO) to be included within an updated
oversight?
geochernical model in the CAP.
3.3
"The ash samples collected from the ash basin (seven
Where is the interpretation/evaluation of this SPLP
Section 3.3 Chemical Properties of Ash (page 3-6)
samples), the dry ash landfill (Phase II) (two
data and what it means in regards to contaminant
samples), and the PV structural fill (four samples) for
distribution and migration from the source?
SPLP testing were collected from the deeper ash
sample in the boring (i.e., approximately 2 feet to 3
feet above the ash/soil interface where field
conditions allowed). Those results are presented in
Table 34.
3.3
Figure 34: Piper Diagrams
The piper diagrams are difficult to read due to the
Noted. Intention of Piper diagrams was to characterize
same symbol being used for multiple samples.
groundwater types with regards to trends rather than
individual wells.
3.3
"Chemical speciation samples were also collected from
There was a small discussion of the results, but this
Updated geochemical model to provide more
five ash pore water monitoring wells (AB-12S,
discussion did not include bearing this information
detailed information in the CAP.
AB-12SL, AB-15SL, AB4S, and AB4SL) within the ash
has on COI distribution/migration at the site.
basin Appendix B, Table 1
6.2.2
'Assessment results indicate the ash thickness within
What is the estimated total volume of saturated ash vs.
Updated groundwater flow and transport model to predict
the basin ranges from a few feet in thickness up to
unsaturated ash?
potentiometric surfaces post -closure. On -going
85 feet. The majority of ash located within the ash
coordination with closure engineering.
basin is saturated with saturated ash thickness
If dewatering is anticipated, what is the estimated
ranging from less than one foot up to 52 feet. Ash
volume of the remaining saturated ash?
contained within dry ash landfill (Phase II) is
observed to a depth of 111 feet bgs with depth to
water measured at approximately 112 feet bgs in
AL-2S (shallow flow system). Ash in the PV structural
fill was encountered at depths up to 71 feet bgs with
depth to water measured at approximately 61 feet
bgs in AB-20S (shallow flow system) ."
Page 3 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
6.4
Table 6-10: Horizontal Groundwater Gradients and
Although Table 6-10 does provide good information
Noted. Updated groundwater flow models to be
Velocities
regarding horizontal gradients/velocities across the
provided in CAP will incorporate data gathered from
site, it does not provide information along the major
pumping tests conducted along the main, central flow
flow paths (A -A', B-B'). This information is most
transect (A -A').
valuable in understanding groundwater flow and
Some calculations in Table 6-10 are representative of
contaminant transport at the site.
A -A' generalized flow area (AB-15S to AB-12S, AB-
16D to AB-12D, AB-15BR to AB-9BR).
Some calculations in Table 6-10 are representative of
B-B' generalized flow area (AB-5S to AB-3S, AB-3D to
GWA-1D, AB-5BR to GWA-1BR).
6.4
"Upward vertical gradients (negative values) are
Note: upward gradients were also observed in the
Vertical gradient between bedrock wells at depth (AL-2BR
observed on the eastern boundary of the ash basin
Phase II landfill. This should be considered and
to AL-2BRL) is downward. Analysis of Q2 2018 water
near Lake Norman and its tributaries. Additionally,
evaluated further since boron concentrations have
level data at AL-2, AL-3, and AL-4 clusters indicate
upward vertical gradients are predominant in the
been increasing over time and depth.
downward vertical gradients beneath the Phase II landfill.
center of the historic channel of Holdsclaw Creek
beneath the ash basin. Specifically, upward vertical
Downward vertical migration is apparent at AL-2,
gradients are observed atAB-15 location
therefore additional deep bedrock assessment is pending.
(AB-15D/BR; -0.081 foot/foot), AB-12 location (AB-
12D/BR; -0.073 foot/foot), and the AB-9 location
(AB-9D/BR; -0.028 foot/foot). Analytical results from
the bedrock wells at these locations verify that
constituent migration to the bedrock flow system is
limited to specific areas identified in Section 11.1.1. "
6.6
"Hydraulic conductivity values for wells screened in
In section 11.1.1, it was stated that the TZ is the
These are geomean values, and are on the same
saprolite have a geometric mean of 5.50 x 104
primary flow zone, however, section 6.6 indicates the
order of magnitude (10-4). Similar flow characteristics
centimeters per second (cm/sec). Hydraulic
shallow flow layer has higher conductivity than the
exist in shallow and TZ groundwater.
conductivity values for wells screened in the TZ have
TZ.
a geometric mean of 4.23 x 104 cm/sec. "
6.7
"Bedrock fractures encountered at MSS tend to be
Is there data available to support this statement?
Deep bedrock assessment to be included in CAP.
isolated with low interconnectivity."
Is the interconnectivity or lack thereof well
understood at the site?
7.0
SOIL SAMPLING RESULTS
How were saturated soil samples handled? Were they
PBTV determination only incorporated unsaturated soil
included in the evaluation in this section? When
samples. "The sample was collected from the
reviewing Figure 7-1 it included samples below the
unsaturated zone, greater than 1 foot above
water table which is fine for reference purposes, but
the seasonal high water table elevation."
really because they are collected below the water
table are likely skewed and not entirely representative
Table 7-2 classifies sample based on
of actual site conditions in soil.
saturated/unsaturated for comparative purposes.
`Saturation and other factors may also affect
constituent occurrence in the samples." For the CAP,
unsaturated soil will be the focus of evaluation for
potential secondary source considerations and
saturated soil will be evaluated as part of the
groundwater system in the flow and transport model.
7.0
SOIL SAMPLING RESULTS
Based on review of Figure 14-77, it is evident that
Additional soil sampling has been conducted in 2018
delineation of soils at the site is not complete. This
for updating geochemical model to be included in the
part of the assessment must be completed and
CAP. Additional source area investigations are pending
included in CAP.
and will be presented in the CAP. Where additional
unsaturated soil samples are needed to define the
horizontal extent and of what constituents can be
discussed in the meeting with DE .
Page 4 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
8.0
SEDIMENT RESULTS
This section simply is a data summary and in no way
Noted. A more robust data set collected during 2L-2B
discusses if this data has any affect on water quality or
efforts will allow for thorough evaluation in CAP.
potential corrective action at the site. Additional
samples are anticipated to be collected during the
2L/2B sampling event. A more detailed evaluation is
expected to be included in the CAP.
9.0
"For this CSA, it is pertinent that a comparison with
Just to clarify, even if there is an unnamed tributary
Noted.
NCDENR Title 15A, Subchapter 02B. Surface Water
does not mean that 2B standards do not apply. The
and Wetland Standards (2B) standards includes only
unnamed tributary assumes whatever classification
sample results from named surface waters ."
the water body in which the unnamed
tributary empties into has been designated.
9.0
"AOWs , wastewater and wastewater conveyances
The only AOWs regulated are the engineered seeps
2L-2B evaluation to be included in the CAP.
(effluent channels), and industrial storm water are
covered by the NPDES permit and select
evaluated and regulated in accordance with the
non -engineered seeps covered by SOC. All other
NPDES Program administered by NCDEQ DWR ."
AOWs are not covered under permit or SOC. Also, all
AOWs/seeps should be evaluated in this CSA. The
information is pertinent to this assessment and should
be included. Just because the location may be covered
by a permit or SOC doesn't mean the data collected as
part of that cannot be used in this assessment. Please
update this section accordingly and submit as part of
the CAP. This information is critical in understanding
areas of groundwater discharge to surface waters.
9.0
NA
It would be beneficial to have AOW/SW results
2L-2B evaluation to be included in the CAP.
depicted on a figure along with any pertinent GW
results to assess potential GW-SW interaction(s).
9.1
" Surface water data represents a one-time, single
2L/2B evaluation is necessary and should be
2L-2B evaluation to be included in the CAP.
sample; therefore, compliance with either the acute
conducted accordingly to fully assess compliance with
or chronic 2B standard may not be determined based
2B. (Assessment pending)
on 15A NCAC 02B .0211 (11) (e)."
9.2
"Discussion of Results for Constituents
Antimony - has EPA criteria to compare data.
Noted. May be on -going discussions between NCDEQ and
Without Established 2B Standards
Thallium - has EPA criteria to compare data.
Duke Energy.
A 2B value has not been established for a number of
constituents. A summary of results for select
constituents without associated 2B values follows....."
9.3
"Generally, surface water samples collected from
This statement cannot be fully supported until
Noted.
Lake Norman demonstrate compliance with 2B
2L/2B compliance sampling has been conducted at
standards, with the occasional exception of
the site. (Assessment pending)
dissolved oxygen, dissolved copper,and TDS.
Additional parameters including chloride, arsenic,
selenium, cadmium (D), and lead (D) have been
measured above the 2B standard at a single
location. "
Page 5 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
10.1
"Monitoring well locations BG-1BR and GWA-12D were
Based on review of data submitted to date, GWA-12D
Noted.
not approved for use pending replacement and
has not been replaced and continues to exhibit
reevaluation as potential background locations."
unacceptable water quality for inclusion into
background. BG-1BR was replaced with BG-1BRA and
water quality is acceptable thus this location is
acceptable for use in the background evaluation.
10.1.1
Background Dataset Statistical Analysis
Marshall BTV letter was submitted to Duke Energy on
Noted.
June 15, 2018, with MRO general concurrence and
comments where appropriate.
10.1.2
Figures 10-1 thru 10-3: Piper Diagrams
The piper diagrams are difficult to read due to the
Noted. SynTerra's use of Piper diagrams were
same symbol being used for multiple samples.
intended to display relative proportions of major
cations and anions from various areas relative to
source area (upgradient, source, downgradient).
Groundwater/source water quality signatures may
then provide some inference into potential mixing
zones/affected groundwater.
10.2.4
"Radionuclides may exist dissolved in water from
This is just data presentation. Where is the
On -going evaluation of radium at the Site.
natural sources (e.g. soil or rock). The USEPA
evaluation/interpretation of this data as to why
regulates various radionuclides in drinking water.
or why not radionuclides are considered COIs
Radium-226, radium-228, total radium, uranium-
at the site?
238, and total uranium were analyzed in 46 wells as
part of the CAMA sampling event in September of
Based on review of data, total radium should be
Noted.
2017. Results for radiological laboratory testing are
included as a COI at the site.
presented in Appendix B, Table 1. Radium and
uranium isotopes were detected at levels greater than
the USEPA MCLs at the following seven (7) locations:
Background - BG-2BR
Beneath the Ash Basin - AB-12D/BR
Downgradient-AL-01D/BR, AB-0IBR,
MW-07D"
10.3.2
'An evaluation of data at MSS indicates hexavalent
This statement is inaccurate. Based on review of
GWA-2D sample results are invalid due to grout
chromium has only been detected in one valid sample
data available to date, the following wells exhibit
contamination. Replacement well GWA-2DA has
out of 867 analysis at a level greater than the 2L
concentrations (both current and historic) above 10
reported concentrations two orders of magnitude
standard for total chromium (10 pg/L); therefore,
ug/L and the PBTVs:
less than GWA-2D, and all below 10 ug/L.
hexavalent chromium is not considered as a COI.
AB-20S
MW-11D, BG-2BR, and MS-15 are upgradient of the
AB-21S
ash basin and concentrations are similar to the 2L.
AB-3D
These are interpreted to be natural variability in
BG-2BR
background concentrations.
GWA-2D
The one sample from AB-21S with detection >2L
MW-11D
(3/10/17) was invalid. Sample field preservation
MS-15
did not meet EPA or method recommendations for
analysis, therefore results are biased high and
should have been flagged accordingly (Pace Lab
Report 317030381).
Detections at A113-3113 and AB-20S appear
anomalous. Range of detected values are orders of
magnitude off which may indicate incorrect
reporting for total chromium as hexavalent
chromium. On -going monitoring will provide
Page 6 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
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Site Specific Comments
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Section
MRO
Response to
Section
Content
Comment
Comment
additional information regarding whether Cr(VI)
should be considered a COI.
MS-15 sampled for hex chrome once in September
2017 - errata- not included in IMP.
Isoconcentration maps for Cr(VI) show the very
limited presence across the Site.
10.3.4
"Based on site -specific conditions, observations, and
Based on review of available data to date, hexavalent
findings, the following list of COIs has been developed
chromium and total radium should be added as COIs at
for MSS:
the site.
Antimony
Arsenic
Hexavalent Chromium was detected above 10 ug/L and
Detections appear anomalous - future monitoring,
Barium
PBTVs at the following locations: AB-205, AB-215,
additional source area assessments, and 2L-2B
Beryllium
AB-3D, BG-2BR, GWA-2S, MW- 11D, and MS-15 (both
assessment should provide more evaluation of
Boron
current and historic detections)
hexavalent chromium as a potential COI.
Cadmium
Chloride
Total Radium was detected above the Federal MCL of
Chromium (total)
5 pCi/L and PBTVs at the following locations: AB-1BR,
Cobalt
AB-9D/BR, AB-IOBR, AB- 11S, AB-12D/BR,
Noted.
Iron
AL-1S/D/BR, AL-2BRLL, BG-1S/D, BG-2BR, MW-7S/D,
Manganese
and MW-14S/D (both current and historic detections)
Molybdenum
Nickel
Selenium
Strontium
Sulfate
TDS
Thallium
Vanadium
10.3.4
"COIs detected at concentrations greater than the
Beryllium, cadmium, chloride, and nickel were
Noted. These constituents were not "...detected at
PBTVs and associated 2L/IMACs (if applicable) for
included as COIs in the list in section 10.3.4., but
concentrations greater than the PBTVs and associated
each flow unit beyond the compliance boundary (or
are not included in this list.
2L1IMACs (if applicable) for each flow unit beyond the
within bedrock monitoring wells within or beyond the
compliance boundary (or within bedrock
compliance boundary) are as follows:
monitoring wells within or beyond the compliance
boundary)...'
Shallow - antimony, boron, chromium, cobalt
iron, manganese, molybdenum, selenium,
strontium, sulfate, TDS, thallium
Deep - boron, cobalt, iron, manganese,
strontium, sulfate, TDS, vanadium
Bedrock - antimony, barium, boron, chromium,
cobalt, iron, manganese, molybdenum, strontium,
TDS"
Page 7 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
10.3.4
'A constituent was not associated with a flow layer in
If constituents were observed in upgradient and/or
If constituent concentrations were only detected greater
the lists above if concentrations detected greater than
background well locations greater than PBTVS and
than PBTVs and 2L/IMACs upgradient of the identified
the PBTVs and associated 2L/IMACs were exclusively
2L/IMAC an explanation/rationale as to why they were
source area (ash basin), these concentrations are not
observed in upgradient, or background, locations."
not included should be provided (i.e., groundwater
considered derived from the source (naturally -occurring,
flow direction, no identified source, variability in
upgradient of source).
background, etc.).
10.3.4
"As directed by NCDEQ, the data with turbidity
This statement is not entirely accurate. NCDEQ
Noted. Duke Energy will continue to monitor wells in
greater than 10 NTUs and pH greater than 8.5 that
directed that data with turbidity greater than 10 NTU
accordance with an agreed upon IMP. Wells that may
may be a result of grout intrusion, as well as data
and pH greater than 8.5 should not be included in the
exhibit grout impacts, if included in the agreed upon IMP,
that may be auto -correlated because it was
background analysis for developing statistically
will continue to be sampled and will provide valid boron,
collected within 60 days of a previous sampling
derived BTVs. However, NCDEQ did not direct Duke
sulfate, and water level data.
event, are excluded for statistics and other
Energy not to use that data as part of the
This data was considered and will be used for assessment
evaluation methods."
assessment where applicable. For example, boron is
moving forward, where appropriate.
seemingly unaffected by pH and turbidity and should
In the future, it needs to be agreed upon by both Duke
be included as such in this assessment.
and DEQ before only sampling for B and sulfate.
Also, in a meeting with Duke on June 15, 2017, it was
discussed and agreed upon that in lieu of reinstalling
select wells at the site that those wells would continue
to monitored for boron, sulfate and water levels. If
Duke Energy and their consultants do not consider
this data to be valid and support use of this data in
the assessment then those wells should be replaced
so that representative data is collected.
11.1.1
"The farthest downgradient edge (leading edge) of
What about A13-1 and MW-7 well clusters immediately
Additional investigation on -going at A13-1 cluster (AB -
the plume is observed at the MW-14 location.
downgradient of the ash basin and immediately
1BRLL installed July 2018). Potential deep bedrock well
Generally, constituents at this location occur at
adjacent Lake Norman which exhibit similar
planned for 4Q2018, based on pending analytical results
concentrations greater than the 2L or PBTV while
concentrations to that observed at the MW-14 location,
from AB-1BRLL. From Section 14.1 -'The leading edge
analytical results from monitoring well clusters
except concentrations do not decrease with depth at
of the bedrock plume is interpreted to be at/near the
located farther downgradient (GWA-7 and MW-10)
the A13-1 well cluster.
Lake Norman shoreline adjacent to SW-10 sample
are less than the 2L standard or PBTVs. However,
ocation."
concentrations at MW-14 tend to decrease with
depth. For example, boron concentrations decrease
Deep well (upper bedrock) was installed at GWA-15
from 2,340 pg/L at MW-14S to 2,140 pg/L at
location in July 2018 for vertical delineation in
MW-14D to 53.7 pg/L at MW-14BR. This trend is also
downgradient area near unnamed tributary.
observed in downgradient areas of the ash basin
towards the unnamed tributary of Lake Norman.
Vertical delineation established at MW-7, significant
Boron is consistently less than or slightly over the
decrease in boron concentrations with depth (below 2L in
detection limit in GWA-11BR, but is routinely
MW-7D).
detected at concentrations greater than the 2L
beyond the ash basin compliance boundary in
GWA-I1S/D and GWA-15S."
11.1.1
" Migration of CCR-impacted groundwater is not
This is because it is discharging before it ever makes
Agreed.
apparent within MW-10S/D, located in the eastern
its way this far out on the little peninsula.
peninsula immediately adjacent to Lake Norman. "
11.1.1
"These transects capture upgradient,
Transects A -A' and B-B' do not include upgradient
Noted.
source area, and downgradient wells
locations beyond the waste boundary.
relative to the ash basin."
Page 8 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
11.1.1
"Thickness of the shallow flow zone varies across the
In section 6.6, hydraulic conductivity was reported
Same order of magnitude; conductivities are generally
Site, however for Site assessment purposes, the
to be higher in the shallow flow layer than the TZ.
comparable between the shallow and TZ flow layers.
impacts in this zone are sufficiently understood as the
TZ is interpreted to be the primary flow zone with a
predominantly horizontal component of flow that
would impact receptors."
11.1.1
"Though not captured on cross -sectional views,
Based on review of available data to date, this well
Noted. Deep bedrock assessment currently pending at
vertical migration of COI concentrations into
has been sampled 4 times since installation and has
this location, and will be included in CAP.
underlying bedrock is apparent beneath the Dry Ash
concentrations of boron greater than 10,000 ug/L.
Landfill (Phase 11). A deep bedrock well (AL-2BRLL)
Further assessment/evaluation is warranted at this
for vertical delineation beneath the Dry Ash Landfill
location.
(Phase II) was recently installed. Boron was detected
greater than 9,000 pg/L in this well for the first and
only sample collected to date."
11.1.1
'Another area of apparent vertical migration that is
This is very true. Further assessment/evaluation is
Noted. Deep bedrock assessment currently pending at
not captured on the cross -sections is at the AB-1
warranted at this location.
this location, and will be included in CAP.
location (AB-1 BR), immediately east of the ash basin.
Several COIs in deep and bedrock groundwater
(boron, chloride, iron, manganese, strontium, and
TDS) display increasing trends over time at this
location ."
11.1.1
"Two potential scenarios could explain the observation
Based on review of available data to date, it is
Agreed.
of increasing trends:
unlikely attributable to grout contamination based on
A compromised grout column at AB-1 BR could allow
water quality parameters collected at this location.
overlying concentrations from the shallow and deep
You typically see elevated pH (>10) associated with
flow system to migrate downward, influencing
grout contamination, but that is not the case here.
groundwater concentrations measured within the
vicinity of the well installation . "
11.1.1
"Of the 11 wells along the centerline of this flow
MW-12 is not located along this flow transect. I
Yes.
transect, MW-12BR and AB-IBRL are the only wells
assume this is in error and should be AB-12? Revise
with less than six valid sampling events. MW-12BR has
accordingly.
three valid sampling event between March 2017 and
September 2017, and AB-IBRL has only been sampled
once."
Page 9 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
11.1.1
Isoconcentration Maps: Figures 11-1 thru 11-63
Typically, only 2 contours are used, the 2L/IMAC and
Noted.
PBTV. It is technically appropriate to use at least 1 or
2 more contours in some instances where there are
large gaps between the standard, PBTV, and/or the
highest or lowest concentration observed to better
depict contaminant distribution. This helps to better
illustrate contaminant distribution and depict areas of
highest concentration.
Sample locations were intentionally not included on
Noted. Discussion warranted.
figures if it was determined to have invalid data. This
is not appropriate. All data points should be included
on each representative map and if data was not used
due to validity, it should be indicated as such on the
map so it does not appear it was just left off the map
or is perceived as a "data gap". In a nutshell, all
sampling points and data should be represented on
the map. The map is intended to be a visual
representation of data but when data is not included it
can be misleading.
The map contains data from February 2015 to
Noted.
October 2017. If the majority of the data is from one
sampling event, for example, the October 2017
sampling, then it should be indicated in the title block
or legend and then at locations on the map where
other data outside the October 2017 sampling event is
used the date should be indicated along with the well
ID/concentration. This allows the reader/reviewer to
know which sampling event concentrations represent.
11.1.1
Isoconcentration Maps: Figures 11-1 thru 11-63
Reporting limit should be used instead of simply
Noted.
continued...
stating NO.
Figure 11-4 - the PBTV contour was not appropriately
drawn. Where there were bounding wells the contour
Noted. Could use more dashed contours for inferred
was instead left open and on the downgradient side of
conditions.
the basin immediately adjacent to Lake Norman the
contour was a closed solid line indicating certainty
when in fact it probably was more appropriate to leave
it open since there is no data beyond those points.
This is just one example, but this happened on several
other figures as well.
Figure 11-29 - the contour crosses a surface water
feature (unnamed tributary) to the east of the ash
Noted.
basin. This contour was not appropriately drawn. The
contour should have not cross the surface water feature
and should instead have a contour on its own on that
side of the feature. This is just one example, but hits
happened on several other figures as well.
Page 10 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
11.1.1
Isoconcentration Maps: Figures 11-1 thru 11-63
It appears that certain wells that exhibit grout
Noted.
continued...
continued...
contamination where MRO and Duke Energy agreed
to only monitor boron and sulfate, since they are
seemingly unaffected by elevated pH and turbidity,
were not included as having valid data. As discussed
in previous comments, if Duke Energy and their
contractors do not support that data as being valid
then those wells will need to be reinstalled. The case
should have been made in this report as to why that
data is valid and supported.
All isoconcentration lines should be drawn where
Noted. Isoconcentration lines were drawn as accurate as
appropriate whether deemed to be attributable to
possible, incorporating professional judgement, and were
background or not. A discussion regarding why certain
not intended to be misleading. However, it is not
locations with concentrations which exceed the
appropriate to contour background values that exhibit
applicable PBTV are in fact attributable to background
natural variability and are not attributable to constituent
should be included in the report itself. The map should
migration from source areas.
be representative of available data; instead they are
misleading.
11.1.1
Isoconcentration Maps: Figures 11-1 thru 11-63
Based on review of these figures it is apparent that
Global Response to Additional Delineation
vertical and horizontal extent of several COIs at
Requests:
several well pair locations is warranted.
Groundwater migration pathways/flow direction is well -
understood at the Site, therefore additional horizontal
delineation is not necessary for CAP development. A
groundwater to surface water (2L-2B) evaluation will be
conducted to determine potential surface water impacts
resulting from groundwater plume discharges.
Groundwater modeling in the CAP to provide sufficient
analysis of COI concentrations over time and depth with
various remediation scenarios. Geochemical modeling, to
be included in the CAP, may explain certain anomalous
occurrences of COIs listed here (i.e., Co, Fe, Mn, Mo, Sr,
), where truly CCR-impacted groundwater may not be
present (non -detect boron at these locations). Also,
additional source area assessments will provide more
delineation to be included in the CAP.
Page 11 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
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Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
Barium: AL-1D (horizontal only)
Barium: See global response above. GWA-15D installed
(July 2018) east and sidegradient of AL -ID location.
Beryllium: AL -IS (horizontal only)
Beryllium: is horizontally delineated from AL-1S to the
north at MW-14S (non -detect) and to the south at GWA-
11S and GWA-15S (concentrations below IMAC at each
of these wells).
Boron: AL-SS/D (horizontal only, however,
Boron:
POTENTIALLY DISPOSITION PROPOSED DEEP
concentrations in the BR are trending up toward 2L and
BEDROCK
ROCK INVESTIGATION FROM GWA-11 TO AL-1. For
ertical delineation may be necessary in the very near
shallow/deep flow zone, refer to global response above.
future),
MW-145 D: See global response above.
MW-14S/D (horizontal only)
B-1BR: Additional deep bedrock well (AB-1BRLQ
installed for vertical delineation. Additional deep bedrock
AB-IBR (vertical only due to proximity of lake/river)
assessment pending analytical results.
Chloride: AL -SD (horizontal only)
Chloride: See global response above.
Cobalt: GWA-7S (horizontal only), MW-14S/D
Cobalt: See global response above.
horizontal only), AL -IS (horizontal only), MW-6S
MW-6S: Topography/site access prevent well installations
(horizontal only), CCR-9S (horizontal only)
further downgradient toward Lake Norman from this
location.
Iron:
Iron:
GWA-7S (horizontal only)
GWA-7S: See global response above. Boron non -detect.
Background variability, not enough detections of COIs to
warrant additional assessment.
GWA-10D (horizontal and vertical)
GWA-10D: Background variability, not enough detections
of COIs to warrant additional assessment.
AB-15BR (vertical only)
B-15BR: Background variability, not enough detections
of COIs to warrant additional assessment.
L-2BRLL (vertically only)
L-2BRLL: Additional deep bedrock evaluation pending.
B-1BR (vertical only due to proximity of lake/river)
B-1BR: Additional deep bedrock well (AB-1BRLQ
installed for vertical delineation. Additional deep bedrock
assessment pending analytical results.
Page 12 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
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Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
Manganese:
Manganese:
GWA-7S (horizontal only), AL -IS (horizontal only)
GWA-7S AL-1: See global response above.
GWA- 6S (horizontal only)
GWA-6S: Upgradient, background location. Verifies
background variability which applies to other Fe, Mn
concentration where other COIs are not greater than
2L/IMAC.
AB-15BR (vertical only), AB-9BR (vertical only), AB-5BR
B-5BR AB-9BR AB-15BR: Background variability, not
(vertical only),
enough detections of COIs to warrant additional
assessment (boron non -detect). See global response
above.
L-2BRLL (vertical only)
L-2BRLL: Additional deep bedrock evaluation pending.
B-1BR (vertical only due to proximity of lake/river)
B-iBR: Additional deep bedrock well (AB-1BRLQ
installed for vertical delineation. Additional deep bedrock
assessment pending analytical results.
Molybdenum:
Molybdenum:
GWA-7S (horizontal only)
GWA-7S: See global response above. Boron non -detect.
B-9BR (vertical only)
B-9BR: Not enough detections of COIs to warrant
additional assessment (boron non -detect).
11.1.1
Isoconcentration Maps: Figures 11-1 thru 11-63
Strontium:
Strontium: Regional variability in strontium likely
Continued...
greater than reflected by statistically -derived background
value, therefore additional delineation solely based on
strontium is not warranted. See global response above.
GWA-10S/D (horizontal and vertical)
GWA-IOS D: Previous comment on isoconcentration lines
crossing unnamed tributary to GWA-10 location indicated
he understanding that this tributary is a groundwater
discharge zone, and concentrations detected in these
wells are isolated from groundwater plume.
MW-14S/D/BR (horizontal and vertical), AL-1S/D/BR
MW-14 AL-1: See global response above.
(horizontal and vertical)
GWA-iD BR: Other COIs non -detect at depth at this
GWA-iD/BR (vertical only due to proximity of
location, therefore professional judgement suggests the
lake/river)
vertical extent of migration has been determined. The
geochemical model will provide more clarity with regard
o the occurrence and distribution. Strontium alone does
not warrant additional delineation, as stated above.
MW-61D (horizontal and vertical)
MW-61): Topography/site access prevent well
installations further downgradient toward Lake Norman
from this location. Also see global response above.
AB-15BR (vertical only), AL-4BR (vertical only),
AB-10BR (vertical only), AB-12BR (vertical only),
B-5BR AL-4BR AB-10BR AB-12BR AB-15BR:
AB-5BR (vertical only)
Background variability, not enough detections of COIs to
warrant additional assessment (boron non -detect). See
global response above.
Page 13 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
L-2BRLL (vertical only)
L-2BRLL: Additional deep bedrock evaluation pending.
AB-1S/D/BR (vertical only due to proximity of
B-1BR: Additional deep bedrock well (AB-1BRLQ
lake/river)
installed for vertical delineation. Additional deep bedrock
assessment pending analytical results.
MW-7S/D (vertical only due to proximity of lake/river),
MW-7 8 9: Additional delineation solely based on
MW-8S/D (vertical only due to proximity of lake/river),
strontium is not warranted. Groundwater discharges to
MW-9S/D (vertical only due to proximity of lake/river)
identified receptors (Lake Norman, unnamed tributary)
therefore a groundwater to surface water (2L-2B)
evaluation will be conducted to determine surface water
impacts of the groundwater plume discharges and that
evaluation will be incorporated in the CAP.
Sulfate: MW-14S (horizontal only)
Sulfate: See global response above.
Thallium: CCR-9S (horizontal only)Thallium:
See global response above.
DS: MW-14S (horizontal only), AL-1S/D (horizontal
DS: See responses above for these locations.
only), AB-1BR (vertical only due to proximity of
lake/river)
Vanadium: GWA-7D (horizontal
Vanadium: Background variability, concentration is
and vertical)
comparable to PBTV. See global responses above.
11.1.1
Vertical Extent Cross -Sections: Figures 11-64 thru
In review of this section of the report, it appears
Noted.
11-120
that upgradient wells were not included on the cross
section line. It is most appropriate to include
upgradient locations to help illustrate COI
distribution (even when likely attributable to being
naturally occurring).
Additional geochemical evaluation pending along western
Why was AB-3S/D not included on the B-B' cross
flow transect, incorporating AB-3 location (Figure 11-
section transect?
121).
Why was AB-7S/D and SB-14 not included on the C-C'
GWA-12 intended to provide upgradient location to help
cross section transect? Note: GWA-12 location is
illustrate COI distribution (comment above). AB-7 too far
pretty far off the cross section line and is not
off transect. SB-14 may have been used to help develop
representative of flow along that transect.
strata, but was not included as it does not have a well
and associated groundwater data. Cross-section layouts
Some wells with the "D" identifier indicating they are
were from adopted from previous HDR submittal.
TZ wells are shown on the cross section to be in
bedrock.
After review of boring logs, it was determined the "D"
wells installed by previous consultant were installed in
It is confusing as to how some of the contour lines are
upper bedrock (subjectivity of TZ/bedrock interface
drawn. Often times a 2L/IMAC/PBTV line should be
determination).
drawn but is not and there are instances where lines
just stop and are left open as if data is not available.
Contours were not drawn if there were no data to support
In some instances contours are left open and others
hem. Much effort went into making sure the vertical
they are inferred, it is difficult to understand why
cross -sections matched the plan view isoconcentration
some are inferred and others are not.
maps, therefore inferred contours may have derived from
viewing both sets of drawings together.
Page 14 of 19
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DRAFT - Marshall Steam Station - CSA Update Report Comments -
Report
Section
11.1.2
11.1.2
11.2
11.2
13.1
Section
Content
"Plume chemical characterization is detailed below for
each COI. Data evaluations are primarily based on the
September 2017 groundwater sampling event. The
range of detected concentrations is presented with
the number of detections for the sampling event."
"The majority of detections above the PBTV exist in
ash pore water and the shallow flow zone in the
southeastern portion of the ash basin and limited
downqradient wells east of the ash basin."
"Additional HFO samples are proposed to be collected
for the following locations within the screened
interval (* indicates an ash pore water well):
Western Transect-AB-5S*, AB-5D, AB-5BR, AB-3S,
AB-3D , AB-2D, MW-9S, and MW-9D
ding Investigation(s)
"The flow and transport model is currently being
updated as a part of the updated CAP and will
include: development of a calibrated steady-state
Flow model that includes data available through the
fourth quarter of 2017; development of a historical
transient model of constituent transport; and
predictive simulations ofbasin closure plus
qroundwater corrective action scenarios."
Response to Comments
8/31/2018
M RO
Comment
Since it is not documented what other data outside
the September 2017 sampling event was used, I
cannot verify information in this section. Also, it was
stated on figures that October 2017 data was utilized
please verify if that is correct. Report refers to
September 2017 and figures state unto October 2017
Could the beryllium detections in these areas be
attributable to the Phase I landfill?
In other areas of the report when discussing the
western transect AB- 3S/D was not utilized. Instead
AB-4S/D was used. Why are the wells along transects
not consistent throughout this evaluation?
Even though not definitively stated in this
section, it is my understanding that the following
investigations are pending:
-2L/2B SW/Sediment Sampling
-Coal Pile Assessment
- Other primary/secondary source assessments (being
discussed)
-Additional saprolite wells to fill data gap in
shallow flow layer beneath the basin and for
modeling purposes.
Pump tests for modeling purposes.
Deep bedrock well assessment
-Additional HFO samples
At this point, MRO expects 2018 data and data
collected as part of other assessments (in particular
the additional information needed for the models) to
be included as appropriate.
Page 15 of 19
Response to
Comment
Majority of data (CAMA wells) used was from 3Q
2017 (September) sampling event. More recent data
(October 2017) was only available and used for
NPDES monitoring network, as it was still active. For
historic wells, the most recent, valid sample was
used.
e two detections above the IMAC are in the vicinity of
Phase I landfill. Additional source area assessments
be included in CAP.
he generalized cross-section transects (Figures 6-2
trough 6-4; A -A', B-B', C-C') were selected to better
epict the lithology spanning the basin in several
irections.
geochemical flow transects (Figure 11-121; western,
:ral, eastern) were selected as flow paths and will be
flow transects moving forward in the CAP.
are correct.
2L/2B SW/Sediment Sampling
Data gap saprolite wells beneath basin
Ash basin pumping tests
Additional HFO samples
Additional vertical delineation wells (CCR dual-purpose)
ep bedrock evaluation/investigation
al pile assessment
ditional source assessments
P:\Duke Energy Carolinas\ 18. MARSHALL \ CSA Update January 2018 \ NCDEQ Comments —August 2018 \ Marshall CSA Update Report - DRAFT Response to NCDEQ Comments.docx

DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
13.1
"Predictive remedial scenarios will have simulation
Just to reiterate, where a compliance boundary exists
Noted.
times that will continue until modeled COI
standards must be meet at the compliance boundary
concentrations are below the 2L standard at the
NOT the property boundary. And where there may not
compliance boundary."
be a compliance boundary the point of compliance is
everywhere.
13.2
Summary of Geochemical Model Results
Any direction provided by B. Duetch should be
Noted.
incorporated into the geochemical model submitted as
part of the CAP update.
14.0
"A site conceptual model (SCM) is an interpretation
SCM was not provided in previous sections. The
Presenting the SCM as a comprehensive analysis of data
of processes and characteristics associated with
reviewer is to piece this information together from
presented in previous sections was the intended purpose
hydrogeologic conditions and constituent interactions
various sections throughout the report instead of
of Section 14.
at the Site. The site assessment results provide the
being concisely presented in one location within the
information to evaluate distribution of constituents
report.
with regard to site -specific geological/hydrogeological
properties. "
14.1
'Ash sluiced to, and accumulated within,
Yes for the most part, but as mentioned several times
Additional source area assessments to be included in
the basin is determined to be a source of
in the report and suggested by groundwater data
the CAP.
impacts to groundwater."
collected the unlined Phase I and II landfills as well as
the unlined PV structural fill are also contributing to
groundwater impacts observed at the site.
14.1
" The site assessment investigated the Site
While I agree for the most part, the horizontal and
Some additional investigations have already been
hydrogeology, determined the direction of
vertical extent of groundwater and soil impacts have
completed and others are pending, as noted above.
groundwater flow from the ash basin, and
been sufficiently determined to proceed with the CAP;
determined the horizontal and vertical extent
horizontal and vertical delineation at the site is still
of impacts to groundwater and soil sufficient to
incomplete and will need to addressed while moving
proceed with preparation of a CAP. "
to the CAP phase.
14.1
"COIs identified as being associated with MSS ash
Hexavalent chromium and total radium should be
Radium - agree.
management areas include antimony, arsenic, barium,
added to the COI list (see previous comments).
beryllium, boron, cadmium, chloride, chromium,
Hexavalent chromium - discussion warranted. Cr(VI)
cobalt, iron, manganese, molybdenum, nickel,
appears sporadically throughout the site in anomalous
selenium, strontium, sulfate, TDS, thallium and
detections (two exceedances at AB-3D, one exceedance
vanadium."
at AB-20S) out of all analysis for this parameter. Please
see responses to other exceedances above.
Isoconcentration maps for Cr(VI) show the very limited
presence across the Site.
14.1
"The unnamed tributary of Lake Norman immediately
What about the AB-1 location? Its's downgradient of
Agreed. From Section 14.1 - "The leading edge of the
east of the ash basin serves as a groundwater
the ash basin and exhibits similar concentrations to
bedrock plume is interpreted to be at/near the Lake
discharge zone in the furthest downgradient area with
those observed at MW-14 and should also be
Norman shoreline adjacent to SW-10 sample location."
CCR impacts. Concentrations of COIs consistently
considered as the part of the leading edge of plume
detected in the shallow and deep flow zones at the MW-
migration.
14 location are interpreted as the leading edge of the
plume migration."
14.1
"Boron concentrations are non -detect at MW-10S/D,
This statement is true, but it should be understood
Noted. Statement was that groundwater was not
indicating CCR- impacted groundwater does not
that it is not impacted because impacted
migrating beneath peninsula, therefore additional
migrate in the peninsula located to the east along the
groundwater is discharging before it ever makes to
delineation onto this peninsula would not be
shore of Lake Norman."
the MW-10 location and not because it was
warranted.
attenuated and provides delineation.
Page 16 of 19
P: \ Duke Energy Carolinas\ 18. MARSHALL \ CSA Update January 2018 \ NCDEQ Comments -August 2018 \ Marshall CSA Update Report - DRAFT Response to NCDEQ Comments.docx

DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
14.1
"In summary, the shallow and deep zone flow units
This statement is not entirely accurate. Based on
Based on isoconcentration maps, COI concentrations >
at MSS - beneath and downgradient of the ash basin
review of isoconcentration maps provided in this
background are consistently limited to beneath Phase II
- are impacted by CCR- derived constituents;
report and available data, it is evident that bedrock
landfill and AB-1 cluster.
however, these impacts do not necessarily migrate
has been impacted beneath the basin as well as
vertically in the same areas. Impact to the bedrock
beneath the Phase I and II landfills and downgradient
flow unit is confined, approximately, to the Dry Ash
of the ash basin (AB-1).
Landfill (Phase II) and immediately east of the waste
boundary atAB-1."
14.2
Maximum COI Concentrations
Hexavalent chromium and total radium should be
Refer to previous responses.
added to the COI list (see previous comments).
14.2
"Concentration trends at all wells, surface water, and
There is no discussion/interpretation provided on how
Thorough geochemical modeling of the majority of COIs
seep locations are graphically depicted in plan view
hydrogeological and/or geochemical factors affect COI
and their distribution to be included in the CAP.
and included as Figure 14-39 through Figure 14-76.
movement and concentrations through out the site and
COI
why COIs are increasing at the locations identified in
concentrations are generally stable, often indicating
this section.
slight variation which may be attributed to natural
fluctuations. However, increasing concentrations of
several COIs are observed in downgradient
monitoring wells:
AB-ID/BR: boron, chloride, cobalt, iron, manganese,
strontium, TDS
GWA-IIS/D: boron, TDS
GWA-15S: boron
MW-14SID/BR : chloride
MW-1: barium, chloride
MW-6D: boron, chloride
MW-7D: boron, chloride"
14.2
Time -Series Graphs: Figures 14-1 through Figure 14-38
Why was the western transect not evaluated?
Source area and downgradient transects provided
sufficient coverage/insight. There were time
Why was AB-9 location not included in the evaluation?
constraints on preparation of this report.
In section 11 of this report, this transect included
AB-12, AB-9 and AB-1, but here it included AB-15 and
Formatting of graphics were considered in order to
not AB-9. Why the inconsistency throughout the report
provide ease of interpretation to the reader. The
of wells used along transects?
central source transect already contained two source
area well clusters.
Why was CCR-13 location not used in the
evaluation as it was in other areas of the report?
These were not intended as duplicates of the selected
Again, why the inconsistency?
geochemical flow transects. For reasons noted above,
only select locations were included in time vs
On Figure 14-2, 14-8, and 14-24, there appeared to be
concentration plots. Thorough analysis of the
no data on the MW-1 plot. Was this an error or does
geochemical transects with support of modeling to be
the data not exist?
included in the CAP.
MW-1 is a single well (not cluster), therefore there
were no data to support a graph of multiple flow zones
at this location.
Page 17 of 19
P: \ Duke Energy Carolinas\ 18. MARSHALL \ CSA Update January 2018 \ NCDEQ Comments -August 2018 \ Marshall CSA Update Report - DRAFT Response to NCDEQ Comments.docx

DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments AL
Report
Section
MRO
Response to
Section
Content
Comment
Comment
15.0
"Receptors including water supply wells and surface
2L/2B evaluation is necessary to support this
2L-2B evaluation to be included in the CAP.
water bodies were identified and found to be not
statement and should be conducted accordingly to
impacted by the ash basin and generally in
fully assess compliance with 2B. (Assessment
compliance with applicable regulatory standards
pending)
.Significant exposure pathways are understood and
constituent concentrations detected in water supply
wells are deemed to not be from the ash basin. "
15.0
"Impacts to groundwater in all three flow zones have
Please define exactly what data collection is
Completed and pending investigations are listed above,
been identified beneath and downgradient of the ash
necessary and when these efforts are proposed to
as previously discussed.
basin at MSS. Supplemental data collection to
be conducted.
support groundwater modeling and long-term
monitoring is anticipated to support the CAP process "
15.2
"Surface water quality of Lake Norman adjacent to the
At this time 2L/2B SW sampling has not been
Noted.
ash basin is generally in compliance with 28 standards
conducted and this statement cannot be fully supported
. An evaluation of groundwater to surface water
until this information has been collected.
interaction will be used to support the CAP process. "
15.2
Revised Site Conceptual Model
Where was the initial site conceptual model detailed in
Section 14.0 was intended as the SCM, incorporating
the report?? There was no section dedicated to the
analysis of data that was presented in previous
SCM as one would typically expect in a CSA. Instead,
sections (i.e. Section 14.3 Contaminant Migration and
pieces of the SCM are scattered throughout the report
Potentially Affected Receptors).
in various sections and not in a single comprehensive
section.
15.4
"For basin closure, reduction of infiltrating water will
This needs to be substantiated considering the majority
Updated groundwater flow and transport modeling to
have the greatest positive impact on groundwater
of ash at the Marshall Steam Station is below the water
be included in CAP.
and surface water quality downgradient of the ash
table and will be a continued source to groundwater
basins."
contamination at the site.
Appendix H
Background Determination
Based on review of data submitted to date, GWA-12D Noted, as above.
has not been replaced and continues to exhibit
unacceptable water quality for inclusion into
background. BG-iBR was replaced with BG-1BRA and
water quality is acceptable thus this location is
acceptable for use in the background evaluation.
A letter dated June 15, 2018, was submitted to
Duke Energy regarding Marshall Steam Station
BTVs.
ES.1
"The majority of ash contained in the ash basin is
What is the estimated total volume of saturated ash vs.
See response above.
saturated."
unsaturated ash?
If dewatering is anticipated, what is the estimated
volume of the remaining saturated ash?
Page 18 of 19
P: \ Duke Energy Carolinas\ 18. MARSHALL \ CSA Update January 2018 \ NCDEQ Comments —August 2018 \ Marshall CSA Update Report - DRAFT Response to NCDEQ Comments.docx

DRAFT - Marshall Steam Station - CSA Update Report Comments -
Response to Comments
8/31/2018
Site Specific Comments
Report
Section
MRO
Response to
Section
Content
Comment
Comment
ES.3.3
"The surface water results collected from Lake
This statement cannot be fully supported until
21L-213 evaluation to be included in the CAP.
Norman do not indicate that impacted groundwater
21-/213 compliance sampling has been conducted at
associated with the MSS ash basin is causing 2B
the site. (Assessment pending)
exceedances in Lake Norman. "
ES.5.2
"The following list of groundwater COIs has been
Hexavalent chromium and total radium should be
Refer to previous responses.
developed for MSS:
added to the COI list (see previous comments).
Antimony Arsenic Barium Beryllium Boron Cadmium
Chloride
Chromium (total) Cobalt
Iron Manganese Molybdenum Nickel Selenium
Strontium Sulfate
TDS
Thallium Vanadium"
ES.5.2
"This leading edge is observed in the shallow and
Why is the AB-1 location not included as being part
From Section 14.1 - "The leading edge of the bedrock
deep flow zones east of the ash basin between the
of the leading edge of the plume? It should be in all
plume is interpreted to be at/near the Lake Norman
Dry Ash Landfill (Phase I) and the unnamed
flow layers.
shoreline adjacent to SW-10 sample location."
tributary. "
ES.5.2
"It is anticipated that additional monitoring wells for
Additional monitoring wells for purposes of vertical
Additional deep bedrock investigation pending.
vertical delineation may be installed to support the
delineation is necessary to complete delineation at
groundwater corrective action planning process."
the site. This is a must to comply with 2L.
ES.6
"The assessment investigated the Site hydrogeology,
Groundwater and soil delineation is incomplete,
Additional investigations have been completed and are
determined the direction of groundwater flow from the
however, I do agree that it is sufficient enough to
pending, as discussed above.
ash basin, and determined the horizontal and vertical
proceed with CAP preparation.
extent of impacts to groundwater and soil sufficient to
proceed with preparation of a corrective action plan
(CAP). "
ES.6
"Surface water receptors downgradient of the ash
This statement cannot be fully supported until
21--213 evaluation to be included in the CAP.
basin (e.g. Lake Norman) demonstrate compliance
2L/2B compliance sampling has been conducted at
with 2B standards, with the occasional exception of
the site. (Assessment pending)
dissolved oxygen, chloride, TDS, arsenic, selenium,
cadmium (D), copper (D), and lead (D). "
ES.6
'A "Low" risk classification and closure via a
Just to note, per HB 630, you not only have to provide
Noted.
cap -in -place scenario are considered appropriate as
alternate, but you have to comply with all dam safety
alternative water supplies are being provided in
requirements to be considered for a "low" risk
accordance with G.S. 130A - 309.213, (d)(1) of House
classification.
Bill 630. "
Page 19 of 19
P:\Duke Energy Carolinas\ 18. MARSHALL \ CSA Update January 2018 \ NCDEQ Comments -August 2018 \ Marshall CSA Update Report - DRAFT Response to NCDEQ Comments.docx