NC0003425_Rox_Appendix B_20191231

Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant
APPENDIX B
COMPREHENSIVE SITE ASSESSMENT
SynTerra
UPDATE REPORT REVIEW COMMENTS AND
RESPONSES

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
2017 COMPREHENSIVE SITE ASSESSMENT UPDATE
NCDEQ FORMAL LETTER COMMENTS
On October 31, 2017, Duke Energy submitted a CSA Update to NCDEQ (SynTerra,
2017). In a letter from NCDEQ to Duke Energy dated May 7, 2018, NCDEQ stated that
sufficient information had been provided in the CSA Update to allow preparation of a
CAP Update. The letter also provided formal CSA-related comments and items
required to be addressed prior to or as part of the CAP Update submittal. Response to
those comments are provided in this document.
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 — 1
The CSA Update report was presented in data summary format to clearly provide
the facts regarding site characterization. Duke Energy disagrees with the contention
that data analysis conclusions and interpretation of site conditions were not
provided. The CSA Update report was provided to supplement the previously
submitted CSA Report. Data previously provided to NCDEQ was intentionally not
included so that the Update could focus on site assessment. Duke Energy now
recognizes that NCDEQ desires updates to include previously reported data and
historical information directly rather than by reference.
Comment — 2
The report fails to fully integrate and evaluate data collected from previous versions of the CSA
reports for the facility.
Response — 2
As indicated in the response to Comment 1, all historical and current CSA data (as of
the date of report submittal) was provided in tabular and graphical form for succinct
definition of site conditions. Previous CSA and CAP submittals provided detailed
information that was not deemed necessary for repetition in the CSA Update report.
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 acknowledge and delineate
exceedances of the 15A NCAC 2L or 2B standards above background levels.
Page 1

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Response — 3
Discussion regarding 02L or IMAC exceedances or exceedances above BTV, as
applicable, for constituents of interest (COI) are provided in the constituent
management process section of the CAP Update (Section 6.1.3).
Surface water associated with the West Ash Basin (WAB) are NPDES-permitted
wastewater features including the heated water discharge pond, which also receives
water from toe drains of the WAB main dam, the western discharge canal and the
extension impoundment, which are not considered waters of the state. Therefore,
the WAB was not evaluated for exceedances of 15A NCAC 02B.
Surface water associated with the East Ash Basin (EAB) include NPDES permitted
wastewater features including the Unit 3 wastewater hot pond and the Unit 3
cooling tower pond, the eastern discharge canal and the extension impoundment. A
jurisdictional intermittent stream, Stream 11A, is located southwest of the EAB. The
Intake Canal is located downgradient of the Gypsum Storage Area (GSA) and the
Dry Fly Ash (DFA) silos, transport, and handling area (DFAHA), which are
considered downgradient additional sources areas. Analytical results for surface
water samples collected from the Intake Canal and jurisdictional intermittent Stream
11A indicate that these water bodies meet 02B standards under current conditions.
The surface water evaluation was completed in accordance with NCDEQ Internal
Technical Guidance: Evaluating Impacts to Surface Water from Discharging
Groundwater Plumes provided to Duke Energy on October 31, 2017. The purpose of
the evaluation was to identify exceedances of 15A NCAC 02B present in surface
waters. Findings from the Intake Canal evaluation were submitted to NCDEQ on
March 21, 2019 (Surface Water Evaluation to Assess 15A NCAC 02B .0200
Compliance for Implementation of Corrective Action under 15A NCAC 02L .0106(k)
and (1)). Additional information for Stream 11A is provided in a revised report
provided in Appendix J of the CAP Update. Additional information can be found in
Section 6.2.1 and Section 6.18.1 of the CAP Update. An evaluation of background
surface water values is presented in Section 4.3 of the CAP Update.
Comment — 4
The characterization of other primary and secondary sources other than impoundments that
contribute to the groundwater plumes is inadequate.
Response — 4
Potential source areas combined with the East Ash Basin include the halo zone of the
industrial landfill and Land Clearing and Inert Debris (LCID) landfill. Further
discussion regarding the industrial and LCID landfill can be found in Sections 1.5.2.
Page 2

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
and Section 6.1.1 of this CAP Update. An overview of other potential source areas
independent of the Roxboro ash basins is presented in the CAP Update (Section 3.0)
and summarized in Table 3-1. Sources independent of the ash basins are not subject
to the requirements set forth in CAMA and are undergoing evaluation under a
separate process. At Roxboro, the coal pile storage area has been identified as a
source requiring evaluation and is further discussed in Section 3.0. Independent
CCR source areas downgradient from the EAB that are evaluated in this CAP
Update include the GSA and the DFAHA. Assessment of these areas have
demonstrated COI affected groundwater above regulatory or applicable background
levels along with comingled groundwater plumes associated with the EAB. The
GSA and the DFAHA are further discussed in Section 1.5.2 and Section 6.17.1 of
this CAP Update.
No potential source areas adjacent to or combined with the WAB were identified for
evaluation. There is an area identified downgradient of the WAB to have surface
releases associated with the historical operation of the now abandoned ash sluice
line system. The decommissioned sluice line corridor area is further discussed in
Section 3.0.
Comment — 5
As detailed more fully in the attached document, additional data gaps remain concerning
delineation of impacts from coal ash at the facility.
Response — 5
The NCDEQ additional data gap comments are detailed in the letter attachment
titled Comments for Roxboro Steam Electric Plant Comprehensive Site Assessment
Summary Update Submitted October 31, 2017, the responses are provided in a
section specific to that attachment (below).
Page 3

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
2017 COMPREHENSIVE SITE ASSESSMENT UPDATE
NCDEQ FORMAL ROXBORO ATTACHMENT COMMENTS
On October 31, 2017, Duke Energy submitted a CSA Update to NCDEQ (SynTerra,
2017). In a letter from NCDEQ to Duke Energy dated May 7, 2018, NCDEQ stated that
sufficient information had been provided in the CSA Update to allow preparation of a
CAP Update. The letter also provided a site specific attachment titled Comments for
Roxboro Steam Electric Plant Comprehensive Site Assessment Summary Update
Submitted October 31, 2017. Responses to that attachment are provided in this
document.
SOILS
Comment — 1
Soils: The soils investigation in the Comprehensive Site Assessment (CSA) is not sufficient
regarding the horizontal and vertical extent of soil impacts from CCR residuals.
Response — 1
Data indicate unsaturated soil COI concentrations, if present, at or beyond the EAB
and WAB compliance, boundaries are generally consistent with background
concentrations or are less than regulatory screening values. In the few instances
where unsaturated soil COI concentrations are greater than PSRG POG standards or
background values, COI concentrations are within range of background dataset
concentrations or there are no mechanisms by which the COIs could have been
transported from the ash basins to the unsaturated soils. Further discussion
regarding unsaturated soil assessments related to the EAB/GSA/DFAHA is provided
in Section 6.1.4.1 and for the WAB in Section 6.10.4.1.
Comment — 2
Soils: A significant portion of the EAB has not been assessed for coal ash constituents in soil.
Response — 2
Data indicate unsaturated soil constituent concentrations at or beyond the EAB
compliance boundary are generally consistent with background concentrations or
are less than regulatory screening values. A Technical Memorandum, Roxboro Steam
Electric Plant Ash Basin Perimeter Soil Assessment (dated February 4, 2019), was
submitted to NCDEQ Raleigh Regional Office (RRO) on February 6, 2019. The
Technical Memorandum provided objectives, methodology, and proposed locations
for the collection of unsaturated, shallow soils at targeted areas along the margins of
the ash basins. The February 4, 2019 document proposed five sample locations (PSB-
Page 4

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
1 through PSB-5) along the south-southwest perimeter of the western lobe of the
EAB and 18 locations (PSB-6 through PSB-23) along the southern perimeter of the
WAB southern extension impoundment.
Based upon review of the February 4, 2019 Technical Memo, NCDEQ provided
review comments on April 17, 2019 and requested additional samples in areas
associated with the perimeter of the WAB, and eastern extension impoundment area
of the EAB. A revised Technical Memorandum was provided to NCDEQ on June 7,
2019 which provided details for sample collection at 13 locations (PSB-37 through
PSB-49) at the margins of the EAB, including the extension impoundment area, and
13 locations (PSB-24 through PSB-36) along the margins of the WAB. In addition,
unsaturated soil samples were collected from select monitoring well locations along
the perimeters of the basins and upgradient locations during well installation for
CSA and subsequent assessments. Sample locations associated with the EAB are
provided on Figure 6-15 in the CAP Update Report. A discussion regarding COIs in
unsaturated soil related to the EAB and the eastern extension impoundment area is
provided in Section 6.1.4.1 of the CAP Update report.
Comment — 3
Soils: A significant portion of the WAB has not been assessed for coal ash constituents in soil.
Response — 3
Data indicate unsaturated soil constituent concentrations at or beyond the WAB
compliance boundary are generally consistent with background concentrations or
are less than regulatory screening values. See response for Comment 2 regarding the
objectives, methodology, and proposed locations for the collection of unsaturated,
shallow soils at targeted areas along the margins of the WAB and the southern
extension impoundment. Sample locations associated with the WAB on Figure 6-32
in the CAP Update Report. A discussion regarding COIs in unsaturated soil related
to the WAB and the southern extension impoundment area is provided in Section
6.10.4.1 of the CAP Update report.
Comment — 4
Soils: The SCSA lacks a comprehensive summation of the extent of soil impacts beyond the
compliance boundary and in the areas beyond the waste boundary.
Response
Data indicate unsaturated soil COI concentrations are generally consistent with
background concentrations or are less than regulatory screening values. In the few
instances where unsaturated soil COI concentrations are greater than PSRG POG
Page 5

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
standards or background values, COI concentrations are within range of
background dataset concentrations or there are no mechanisms by which the COI
could have been transported from the ash basins to the unsaturated soils. A
thorough evaluation of the potential nature and extent of COIs in unsaturated soil
beyond the waste boundary for the EAB and WAB was conducted by comparing
unsaturated soil concentrations with background values or PSRG POG standards,
whichever is greater, and is presented in Section 6.1.4.1 for the EAB and in Section
6.10.4.1 for the WAB in the CAP Update Report.
Comment — 5
Soils: RRO currently does not agree with Duke's PBTV soil "background" values for
Manganese and Nitrate.
Response — 5
Soil BTVs for manganese and nitrate (as N) were approved by NCDEQ in a letter
dated May 23, 2019 (Appendix A of this CAP Update). Additional information
regarding NCDEQ approved soil background values in provided in Section 4.2 of
this CAP Update.
SEDIMENT
Comment — 6
Sediment: A detailed description of sample collection methods of the sediment samples submitted
for analysis is necessary.
Response — 6
Sediment samples related to the EAB extension impoundment area and discharge
canal assessment were collected using a sample core device consisting of a 2-inch
diameter PVC pipe driver with a retractable internal 1.75-inch diameter clear acetate
sleeve coupled with a valve assembly at the top of the core device. The sampler was
manually pushed into the sediment to refusal or to a depth of at least 0.5 feet. Once
the desired depth was achieved, the valve was closed to create a vacuum for sample
retention within the sleeve and the core device removed. If an intact core sample
could not be collected, a sediment sample was manually collected by using a
decontaminated stainless steel trowel. The sediment core was extracted and
evaluated for ash content. If present, the ash material was segregated and the
sediment portion was collected and homogenized for laboratory analysis.
Sediment samples collected as part of the groundwater (02L) to surface water (02B)
evaluation for the Intake Canal and the jurisdictional stream Stream 11A (southwest
Page 6

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
of the EAB/Industrial Landfill) were collected in a similar manner. No ash material
was identified with the sediments samples collected in the Intake Canal or Stream
11A. Additional information regarding sediments associated with Intake Canal and
Stream 11A is provided in Section 6.1.2 and Section 6.17.2 of this CAP Update.
Comment — 7
Sediment: The investigation of the WAB and EAB extensions as well as the eastern and western
discharge canals, has provided evidence that the deposition of coal ash has occurred in these
features. Analytical results for the EAB detected the presence of antimony, arsenic, chromium,
cobalt, iron, manganese, selenium, and vanadium concentrations greater than the PSRG POG
and PBTV in one or more samples within the impoundment and discharge canal. Actions are
necessary to address the presence of coal ash in these locations.
Response — 7
The WAB and EAB extension impoundments are areas within the WAB and EAB.
Historical documentation was submitted to NCDEQ on October 31, 2017 (Duke
Energy to NCDEQ) related to the WAB and EAB construction, expansion, and
improvements to document the full extents of the Roxboro ash basins. Closure Plans
for the WAB and EAB, including the areas previously referred to as the WAB and
EAB extension impoundments, are submitted as separate documents in parallel with
this CAP Update.
The eastern and western discharge canals are NPDES permitted wastewater features
(effluent channels). CAMA defines closure requirements for surface impoundments.
Upon Plant retirement, the effluent channels will be decommissioned as required by
closure requirements at the time of decommissioning.
Comment — 8
Sediment: Constituents in one or more sediment sample results had detection limits that did not
comply with either the PBTV or PSRG POG.
Response — 8
Sediment samples collected after submittal of the CSA Update, as part of the surface
water evaluation in April 2018, were analyzed using detection and reporting limits
less than the PSRG POGs/background values (Appendix C, Table 5 of this CAP
Update). Additional information regarding sediments assessments is provided in
Section 6.1.2 and Section 6.17.2 of this CAP Update.
Page 7

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
SURFACE WATER
Comment — 9
Surface Water: The results of the investigation indicate that coal ash constituents are present in
the surface water discharge associated with the WAB and EAB extensions and respective
discharge canals.
Response — 9
Surface water discharge from the areas identified as the WAB and EAB extensions
and respective discharge canals is regulated under the Plant's NPDES permit. As
noted in Response to Comment 7 above, the WAB and EAB extensions are areas
within the WAB and EAB. The Roxboro ash basins and their respective discharge
canals (effluent channels) are NPDES permitted wastewater units.
Comment — 10
Surface Water: Additional efforts will be necessary to evaluate surface water conditions
discharging into the basins to establish whether background geochemistry has a role in the
detected concentrations of constituents.
Response — 10
The geochemical models use two main approaches to monitor the influence of
influent chemistry waters:
• PHREEQC 1-D advection modeling along four flow transects to predict
current and potential future conditions given decanting and the proposed
source control options. Three of four transects originate within the ash basins
(three in the East Ash Basin and one in the West Ash Basin) and all extend
downgradient towards a potential surface water receptor. Transects were
selected in consultation with the Flow and Transport modeling group.
• PHREEQC batch modeling that utilizes one year of data from all individual
well screen locations at the site to evaluate how the range of pH, redox
conditions (Ex), and ion concentrations effects COI mobility [quantified with
distribution coefficients (Kd) values calculated for every well screened
interval].
The batch models evaluate the influence of changing geochemical conditions by
using the measured values (pH, Ex, ion concentrations) in a model that predicts Kd
values for each COI. Therefore, the influence of an upgradient water on COI
mobility can be evaluated by monitoring how the Kd values change with changing
water chemsitry.
Page 8

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
A more direct method is taken in the transect models where the initial "Loading
Simulation" used the chemical conditions of ash pore water and were used in the
initial well in the transect which flowed downgradient to other wells and flow zones
selected based on discussions with the Flow and Transport modeling team. The
Loading Simulations are run for 500 shifts (one shift is equivalent to one pore water
exchanges which can be related to time) using the ADVECTION command in
PHREEQC and the results are a function of shifts are compared Two iteractions
were used to monitor changes in geochemical conditions in the transects:
Scenario 1: Modeling the effects of varying pH and EH values in the source
area to provide a conservative representation of changes to geochemical
conditions that could occur in the source area during decanting/closure
activities
• Scenario 2: Simulation of closure -by -excavation and mostly -unsaturated ash
closure (closure -in -place) scenario(s).
Scenario 2 simulations are the most germane to this discussion. These models start
from the end of the Loading Simulation and the initial well water is changed to that
of an upgradient unaffected well. Therefore, as DEQ is requesting in this comment,
the geochemical models are evaluating the influence of upgradient unaffected
waters to "to establish whether background geochemistry has a role in the detected
concentrations of constituents." However, the geochemical models do not explicitly
consider a surface water as the source. It is noteworthy that during the Loading
Simulations, the ash pore water is used as the initial well. The ash pore water is
created by equilibation with discharge waters into the ash basin with the ash.
Therefore, by using the ash pore water as the initial well in the model, the
geochemical models are indirectly evaluating the impact of surface water discharge
into the ash basin.
Comment — 11
Surface Water: CCR constituents have migrated adjacent to the surficial water features north of
the EAB. Additional investigation is necessary.
Response — 11
Surface water associated with the EAB include NPDES permitted wastewater
features including the Unit 3 wastewater hot pond, the Unit 3 cooling tower pond,
the eastern discharge canal and the extension impoundment. A jurisdictional
intermittent stream, Stream 11A, is located southwest of the EAB. The Intake Canal
is located downgradient of the GSA and the DFAHA, which are considered
Page 9

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
downgradient additional, sources areas. Analytical results for surface water samples
collected from the Intake Canal and jurisdictional intermittent Stream 11A indicate
that these water bodies meet 02B standards under current conditions. The surface
water evaluation was completed in accordance with NCDEQ Internal Technical
Guidance: Evaluating Impacts to Surface Water from Discharging Groundwater
Plumes provided to Duke Energy on October 31, 2017. The purpose of the
evaluation was to identify exceedances of 15A NCAC 02B present in surface waters.
Findings from the Intake Canal evaluation were submitted to NCDEQ on March 21,
2019 (Surface Water Evaluation to Assess 15A NCAC 02B .0200 Compliance for
Implementation of Corrective Action under 15A NCAC 02L .0106(k) and (1)).
Additional information for Stream 11A is provided in a revised report provided in
Appendix J of the CAP Update. Additional information can be found in Section
6.2.1 and Section 6.18.1 of this CAP Update.
GROUNDWATER
Comment — 12
Groundwater: Additional discussion is necessary regarding the groundwater chemistry observed
in MW-18D and MW-18BR.
Response — 12
The groundwater observed in MW-18D and MW-18BR generally has a neutral pH (7
to 8) and reducing conditions. As discussed in the geochemical report (Appendix H:
Section 3 and Attachments B, D, and E) reducing conditions will favor the formation
of more soluble Fe(II) and Mn(II) species, thus increasing the aqueous concentrations
as observed in MW-18D and MW-18BR. There are also some observations of Cr and
Co above 02L/IMAC levels. The co -association of cobalt and other transition metals
(including chromium) with manganese oxide minerals is discussed in the
Geochemical Report (Appendix H, Section 3.8). The known co -associations of Mn
with other transition metals along with the lack of measurements of generally
mobile COIs such as boron or sulfate, indicate that the observations of Fe, Mn, Co,
and Cr above 02L/IMAC levels in MW-18D and MW-18BR are due to background
influences and are not attributable to the ash basin.
Comment — 13
Groundwater: Various Constituents of Focus — Boron - Additional downgradient monitoring
well/s are necessary in the vicinity of existing well MW-1 for CAP monitoring purposes.
Page 10

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Response — 13
A shallow bedrock monitoring well, HWMW-1BR, was installed adjacent to MW-1
(Figure 1-3, CAP Update report). Details related to well installation are provided in
Section 2.2 of this CAP Update. Well construction information including boring
logs and well construction details are provided in Appendix Q. Groundwater
analytical results indicted no boron was detected above the laboratory reporting
limit with remaining constituents detected at concentrations below bedrock BTV.
Groundwater analytical results for HWMW-1BR are provided in Appendix C, Table
1 of this CAP Update report.
Comment — 14
Groundwater: Boron - Explain the fate/migration of the boron exceedance in the EAB, an
assessment of the source, including a comprehensive sampling effort to determine where
groundwater impacted by boron discharges into surface water.
Response — 14
Groundwater downgradient of the EAB discharges to NPDES-permitted wastewater
features including the Unit 3 wastewater hot pond and the Unit 3 cooling tower
pond, the eastern discharge canal and the extension impoundment. Groundwater
downgradient of the GSA and the DFAHA, which includes a component of
groundwater flow downgradient of the EAB (comingled zone) discharges to the
Intake Canal. A component of groundwater to the south of the EAB discharges to
the unnamed jurisdictional stream (Stream #11A). Analytical results for surface
water samples collected from the Intake Canal and Stream 11A indicate that these
water features meet 02B standards under current conditions. The surface water
evaluation was completed in accordance with NCDEQ Internal Technical Guidance:
Evaluating Impacts to Surface Water from Discharging Groundwater Plumes
provided to Duke Energy on October 31, 2017. The purpose of the evaluation was to
identify exceedances of 15A NCAC 02B present in surface waters. Findings from the
Intake Canal evaluation were submitted to NCDEQ on March 21, 2019 (Surface
Water Evaluation to Assess 15A NCAC 02B .0200 Compliance for Implementation of
Corrective Action under 15A NCAC 02L .0106(k) and (1)). Additional information
for Stream 11A is provided in a revised report provided in Appendix J of the CAP
Update. Additional information can be found in Section 6.2.1 and Section 6.18.1 of
this CAP Update.
Analytical results from the surface water evaluation indicate boron was present in
the Intake Canal with an average concentration of 650 µg/L. The presence of boron
Page 11

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
is likely attributed to groundwater discharge from the downgradient additional
source area (GSA and DFAHA).
Comment — 15
Groundwater: Hexavalent Chromium- Explain the observed concentrations of hexavalent
chromium in BG-1 (6.9 µglL) at concentrations approaching the established PBTV and also in
MW-15D (2.2 µglL) and MW-18D (2.5 µglL).
Response — 15
The highest concentrations of hexavalent chromium are found in NCDEQ approved
background monitoring wells and upgradient monitoring wells, including BG-1,
MW-15D, and MW-18D. Continued sampling has generated a more robust dataset
for hexavalent chromium. All samples downgradient of the ash basins are less than
BTV (Appendix C, CAP Update). Furthermore, the distribution of hexavalent
chromium in groundwater does not exhibit a discernable plume associated with the
ash basins. An analysis of the presence and distribution of each COI, including
hexavalent chromium, is provided in the geochemical model report (Appendix H)
with additional discussion included in Section 6.1.2.
Comment — 16
Groundwater: Cobalt - Explain the fatelmigration of the cobalt exceedance in the EAB, an
assessment of the source, including a comprehensive sampling effort to determine where
groundwater impacted by cobalt discharges into a surface water.
Response — 16
Analytical results for surface water samples collected from the Intake Canal and
jurisdictional intermittent Stream 11A indicate that these water bodies meet 02B
standards under current conditions. The surface water evaluation was completed in
accordance with NCDEQ Internal Technical Guidance: Evaluating Impacts to
Surface Water from Discharging Groundwater Plumes provided to Duke Energy on
October 31, 2017. The purpose of the evaluation was to identify exceedances of 15A
NCAC 02B present in surface waters. Findings from the Intake Canal evaluation
were submitted to NCDEQ on March 21, 2019 (Surface Water Evaluation to Assess
15A NCAC 02B .0200 Compliance for Implementation of Corrective Action under
15A NCAC 02L .0106(k) and (1)). Additional information for Stream 11A is provided
in a revised report provided in Appendix J of the CAP Update. Additional
information can be found in Section 6.2.1 and Section 6.18.1 of this CAP Update.
Analytical results from the surface water evaluation indicate cobalt was not above
the laboratory method detection limits in samples collected for the evaluation.
Page 12

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Additionally, as described in the Geochemical Modeling Report (Appendix H,
Section 3.8.3), aqueous phase concentrations of cobalt are primarily controlled by
surface complexation and ion exchange reactions, with surface complexation
becoming increasingly dominant as the pH increases. Therefore, at lower pH values,
concentrations of other soluble divalent ions can compete with cobalt for ion
exchange sites and limit cobalt sorption. The generally higher pH values of the ash
pore water and bedrock groundwater will result in higher cobalt Ka values (and
decreased mobility) when compared with the shallow and deep groundwaters.
Cobalt is also known to co -associate with manganese minerals. Therefore, increase
cobalt aqueous concentrations may also be coincident with increased aqueous
manganese concentrations. Similar to groundwaters observed in MW-18D and MW-
18BR as discussed above, groundwaters from MW-17BR and MW-25BR are
generally reducing indicating some reductive dissolution of iron and manganese
oxides is occurring. Thus, any co -associated or co -precipitated cobalt will also
dissolve from the dissolving iron and manganese oxides. However, cobalt
concentrations in these groundwaters are below detection limits.
Comment — 17
Groundwater: Manganese - Additional monitoring well1s in the area of existing well MW-1 to
monitor for manganese.
Response — 17
A shallow bedrock monitoring well, HWMW-1BR, was installed adjacent to MW-1
(Figure 1-3, CAP Update report). Details related to well installation are provided in
Section 2.2 of this CAP Update. Well construction information including boring
logs and well construction details are provided in Appendix Q. Groundwater
analytical results indicted manganese was present at concentrations ranging from
67-70 µg/L, below the bedrock BTV µg/L with remaining constituents detected at
concentrations below bedrock BTVs. Groundwater analytical results for HWMW-
1BR are provided in Appendix C, Table 1 of the CAP Update report.
Comment — 18
Groundwater: Manganese - Explain why the isoconcentration depiction for manganese does not
encompass the well locations in question for the west side of the WAB.
Response — 18
Manganese, often at concentrations greater than the 02L standard, occurs naturally
in groundwater of the Piedmont Physiographic Province, which is well documented
in literature. Manganese concentrations detected at Roxboro are isolated and
sporadic as discussed in the COI management approach provided in Section 6.1.3
Page 13

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
and in Appendix H. As noted in this CAP Update Sections 6.10.3 and 6.10.4, the
distribution of manganese in groundwater adjacent to the WAB does not exhibit a
discernable plume. Furthermore, the boron plume does not extend toward the wells
located to the west of the WAB discharge canal and groundwater flow patterns do
not demonstrate a transport pathway from the ash basin to MW-8BR and MW-12BR.
Additionally, the wells on the west side of the WAB are upgradient and analytical
data shows the manganese concentrations are within or below the range of bedrock
BTV (CAP Update Appendix C, Table 1).
Comment — 19
Groundwater: Manganese — Explain(ation) of the fate/migration of the manganese exceedance in
the EAB, an assessment of the source, coupled with a comprehensive sampling effort for a surface
water discharge.
Response — 19
Analytical results for surface water samples collected from the Intake Canal and
jurisdictional intermittent Stream 11A indicate that these water bodies meet 02B
standards under current conditions. The surface water evaluation was completed in
accordance with NCDEQ Internal Technical Guidance: Evaluating Impacts to
Surface Water from Discharging Groundwater Plumes provided to Duke Energy on
October 31, 2017. The purpose of the evaluation was to identify exceedances of 15A
NCAC 02B present in surface waters. Findings from the Intake Canal evaluation
were submitted to NCDEQ on March 21, 2019 (Surface Water Evaluation to Assess
15A NCAC 02B .0200 Compliance for Implementation of Corrective Action under
15A NCAC 02L .0106(k) and (1)). Additional information for Stream 11A is provided
in a revised report provided in Appendix J of the CAP Update. Additional
information can be found in Section 6.2.1 and Section 6.18.1 of this CAP Update.
As demonstrated in the Surface Water Evaluation, manganese was detected at levels
consistent with the range of background values for surface water with the exception
of RSW-3. The surface water sample collected on May 3, 2018 from the RSW-3
location had anomalously high concentrations of iron and manganese compared to
samples collected earlier that week at the same location. As discussed in Section 4.2
of the Surface Water Evaluation report, the anomalously high iron and manganese
concentrations might be attributable to anomalous high wind weather conditions
during the May 3, 2018 sampling event.
The Geochemical Modeling Report (Appendix H, Section 3.11), notes manganese
can exist in multiple oxidation states ranging from Mn(II) to Mn(VII). Under the Ex
Page 14

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
and pH conditions of the groundwater at Roxboro, Mn(II) is the dominant oxidation
state. Manganese sorption occurs through both surface complexation on ferrihydrite
and ion exchange with clay minerals. Therefore, sorption of manganese can be
strongly influenced by pH (surface complexation) and the presence of competing
divalent ions (ion exchange). The high variability in manganese Kd values in the pH
range 6 to 9 is primarily due to competition with other divalent ions (e.g., Ca+2, Mg+2)
for ion exchange sites. The high concentration of manganese, such as in ABMW-
03BR, is likely due to dissolution of manganese oxide minerals or co -precipitated
minerals under the reducing conditions frequently observed in bedrock wells.
Similarly, elevated concentrations of manganese were observed in other wells to the
east and south of the EAB (MW-18D, MW-18BR, MW-17BR, MW-25BR) which have
similar reducing conditions where soluble Mn(II) will be the dominant phase
(Appendix H, Section 3.11). These wells are all hydraulically upgradient of the ash
basin and other conservative COIs such as boron have not been observed. Thus, it
appears manganese from these deep and bedrock wells is from a naturally occurring
source. Manganese minerals and co -precipitates in the Piedmont are highly variable
in the subsurface. Due to the high variability in manganese mineral solubility, any
changes in pH (even those induced by changes in Ex) can alter the aqueous
concentration of manganese.
Comment — 20
Groundwater: Molybdenum - Explain why elevated concentrations of molybdenum are present
in deep bedrock well BG-1BRLR.
Response — 20
Monitoring well BG-1BRLR is an NCDEQ approved bedrock background
monitoring location (Figure 1-3, CAP Update Report). Initial elevated molybdenum
analytical concentrations is attributable to artificial impacts from using a packer
assembly for packer testing (used to determine the screen interval within the
bedrock boring prior to well installation) that was not properly decontaminated.
Low production/yield prevented adequately flushing of the well to remove
artificially affected groundwater during well development following installation
and purging efforts prior to field sampling Analytical results from sampling events
since January 2017 have shown a reduction of molybdenum concentrations which is
now stable and below bedrock BTV.
Page 15

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Comment — 21
Groundwater: Selenium - Explain of the fate/migration of the selenium exceedance vicinity of the
gypsum storage pad, an assessment of the source coupled with a surface water selenium
assessment in areas such as the intake canal and cooling water intake basin.
Response — 21
Analytical results for surface water samples collected from the Intake Canal and
jurisdictional intermittent Stream 11A indicate that these water features meet 02B
standards under current conditions. The surface water evaluation was completed in
accordance with NCDEQ Internal Technical Guidance: Evaluating Impacts to
Surface Water from Discharging Groundwater Plumes provided to Duke Energy on
October 31, 2017. The purpose of the evaluation was to identify exceedances of 15A
NCAC 02B present in surface waters. Findings from the Intake Canal evaluation
were submitted to NCDEQ on March 21, 2019 (Surface Water Evaluation to Assess
15A NCAC 02B .0200 Compliance for Implementation of Corrective Action under
15A NCAC 02L .0106(k) and (1)). Additional information for Stream 11A is provided
in a revised report provided in Appendix J of the CAP Update. Additional
information can be found in Section 6.2.1 and Section 6.18.1 of this CAP Update.
As described in the Geochemical Modeling Report (Section 3.14, Appendix H, CAP
Update), under the Ex -pH conditions of the Roxboro site, Se(IV) is present as HSeOs-
or SeOs 2 as the dominant species. Selenium exhibits an expected decrease in
sorption with increasing pH, consistent with many other anions. This is a
manifestation of the fact that mineral surface charge on metal oxide minerals
transitions from a net positive to a net negative charge with increasing pH.
Therefore, as the pH increases, the sorption affinity of anionic selenium species to
the more negatively charged surface decreases. In addition to the influence of pH
and Ex, competition with other anions can also influence selenium partitioning. A
wide range of Kd values were simulated in the Geochemical Modeling Report using
site specific data as the input to define the geochemical conditions. Sorption anionic
HSe03 will be in competition for sorption sites by other anionic species. Near the
GSA, there are elevated levels of sulfate in groundwaters due to the dissolution of
gypsum. Concentrations in the 1.0 to 1.4 g/L range were observed in GPMW-3 and
MW-22D and the concentrations of sulfate were found to correlate with elevated
concentrations of selenium. Thus, competition with other anions may increase
groundwater selenium concentrations.
Page 16

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Comment — 22
Groundwater: Strontium - Additional assessment is necessary in the vicinity of existing well
MW-1 for vertical extent assessment of Strontium.
Response — 22
A shallow bedrock monitoring well, HWMW-1BR, was installed adjacent to MW-1
(Figure 1-3). Details related to well installation are provided in Section 2.2 of this
CAP Update. Well construction information including boring logs and well
construction details are provided in Appendix Q. Groundwater analytical results
for HWMW-1BR are provided in Appendix C, Table 1 of this CAP Update.
Strontium was detected at concentrations ranging from 353 µg/l to 361 µg/L, which
is above the bedrock BTV but within the range of NC Piedmont regional
background values (Section 6.1.3, CAP Update).
Comment — 23
Groundwater: Strontium - Additional assessment to define the vertical and horizontal extent of
Strontium in the vicinity of wells MW-17BR and MW-25BR.
Response — 23
Bedrock groundwater monitoring wells MW-17BR and MW-25BR are located
upgradient, southeast of the EAB and south of the eastern extension impoundment.
Elevated concentrations of strontium were observed east of the EAB and the
mobility of strontium in this area may be due to the geochemical behaviors as
discussed in the Strontium Technical Memo — East Ash Basin (Appendix H). Boron
and dissolved strontium concentrations paired with 87Sr/86Sr ratios indicate there is a
component of affected groundwater flow east of the EAB because of radial flow
induced from the industrial landfill. Strontium observed in CCR-110BR and the
extension impoundment surface water has an isotopic signature indicating some
fraction is from CCR material. However, groundwaters observed in MW-17BR and
MW-25BR, which are outside the compliance boundary, have isotopic signatures of
non-CCR origin. Boron is an inorganic metal that is a sensitive indicator for other
metals leaching from CCR, and boron concentrations from MW-17BR and MW-25BR
have remained non -detect or detected below BTV over time. Thus, strontium
associated with CCRs is horizontally delineated east and south of the EAB by
locations GMW-9 and MW-24BR. Co -associated alkali earth cations (Mg, Sr, and Ba)
are likely originating from the GSA where sparsely soluble metal -sulfate phases will
control the pore water concentrations.
Comment — 24
Groundwater: Sulfate - Additional assessment in the vicinity of existing well MWA for Sulfate.
Page 17

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Response — 24
A shallow bedrock monitoring well, HWMW-1BR, was installed adjacent to MW-1
(Figure 1-3, CAP Update report). Details related to well installation are provided in
Section 2.2 of this CAP Update. Well construction information including boring
logs and well construction details are provided in Appendix Q. Groundwater
analytical results for HWMW-1BR are provided in the Appendix C, Table 1 of this
CAP Update report. Sulfate in HWMW-1BR was detected at an average
concentration of 140 mg/L, which is below the 02L value of 250 mg/L.
Comment — 25
Groundwater: Sulfate - Explain the elevated concentrations of sulfate in the vicinity of wells
MW-32BR and BG-1BRLR and why this area is considered distinct from the WAB.
Response — 25
Monitoring well BG-1BRLR is an NCDEQ approved bedrock background
monitoring location (Figure 1-3, CAP Update Report). Initial elevated sulfate
analytical concentrations is attributable to artificial impacts from using a packer
assembly for packer testing (used to determine the screen interval within the
bedrock boring prior to well installation) that was not properly decontaminated.
Low production/yield prevented adequately flushing of the well to remove
artificially affected groundwater during well development following installation
and purging efforts prior to field sampling Analytical results from sampling events
since January 2017 have shown a reduction of sulfate concentration, which is now
stable, and below bedrock BTV.
Analytical data for monitoring well MW-32BR location, the groundwater data,
presented in Appendix C, Table 1, indicated no boron concentrations above bedrock
BTV that is less than 02L. The sulfate concentrations detected at MW-32BR are
isolated and sporadic as discussed in the COI management approach provided in
Section 6.1.3 and in Appendix H. Additionally, the average calcium, sulfate, and
magnesium concentrations that gypsum is near saturation (saturation index -0.89)
which indicate that there is a sulfate bearing mineral phase there producing those
relatively high sulfate concentrations. Since those concentrations are present without
a high boron concentration, it can be concluded the sulfate minerals are naturally
occurring and not related to CCR materials.
Comment — 26
Groundwater: Sulfate — Explain(ation) of the fate/migration of the sulfate exceedance in the
EAB, an assessment of the source, including a comprehensive sampling effort to determine where
groundwater impacted by sulfate discharges into a surface water.
Page 18

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Response — 26
Analytical results for surface water samples collected from the Intake Canal and
jurisdictional intermittent Stream 11A indicate that these water bodies meet 02B
standards under current conditions. The surface water evaluation was completed in
accordance with NCDEQ Internal Technical Guidance: Evaluating Impacts to
Surface Water from Discharging Groundwater Plumes provided to Duke Energy on
October 31, 2017. The purpose of the evaluation was to identify exceedances of 15A
NCAC 02B present in surface waters. Findings from the Intake Canal evaluation
were submitted to NCDEQ on March 21, 2019 (Surface Water Evaluation to Assess
15A NCAC 02B .0200 Compliance for Implementation of Corrective Action under
15A NCAC 02L .0106(k) and (1)). Additional information for Stream 11A is provided
in a revised report provided in Appendix J of the CAP Update. Additional
information can be found in Section 6.2.1 and Section 6.18.1 of this CAP Update. As
demonstrated in the Surface Water Evaluation, sulfate was detected at levels
consistent with the range of background values for surface water
Sulfate exhibits plume like behavior in areas around the East Ash Basin and the
Gypsum Storage Area indicating conservative behavior. Sulfate concentrations in
the source wells of Transects 2 and 4 are above the NC 02L value (Transect 2
ABMW-7 = 500 µg/L; Transect 4 ABMW-03BR = 2800 µg/L, Appendix H). Due to
conservative transport of sulfate in the simulations, downgradient concentrations in
these Transects are also above the 02L values. Sulfate concentrations in
downgradient wells are accurately predicted in Transects 3 and 4 and over predicted
in Transects 1 and 2. Precipitation of sulfate minerals may be limiting sulfate
downgradient migration in Transects 1 and 2. Based on the conceptual
understanding of sulfate behavior from these transect analyses and the measured
sulfate groundwater concentrations, the GSA appears to be the source area adjacent
to the Intake Canal. This is supported by observations of sulfate concentrations in
wells surrounding the GSA (MW-22D, GPMW-01D, GPMW-02BR, GPMW-03D/BR)
are greater than upgradient wells such as GMW-11.
Comment — 27
Groundwater: TDS - Additional assessment will be necessary for TDS in the vicinity of existing
well MW-1.
Response — 27
A shallow bedrock monitoring well, HWMW-1BR, was installed adjacent to MW-1
(Figure 1-3, CAP Update report). Details related to well installation are provided in
Section 2.2 of this CAP Update. Well construction information including boring
Page 19

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
logs and well construction details are provided in Appendix Q. Groundwater
analytical results for HWMW-1BR are provided in the Appendix C, Table 1 of this
CAP Update report. TDS was detected at concentrations ranging from 475 mg/L to
505 mg/L, below the TDS BTV.
Comment — 28
Groundwater: TDS — Explain(ation) for the elevated concentrations of TDS in the vicinity of
wells MW-32BR and BG-1BRLR and why this area is not associated with the WAB.
Response — 28
For the MW-32BR location and similar to the sulfate occurrence, the groundwater
data, presented in Appendix C, CAP Update, indicated no boron concentrations
above the boron 02L and the bedrock BTV, indicating the waters have not been
affected by CCR materials. Additionally, high TDS is also likely being influenced by
the reducing conditions that facilitate formation of more soluble Mn(II) and Fe(II).
Since those concentrations are present without a high boron concentration, it can be
concluded the TDS concentrations are naturally occurring and not related to CCR
materials.
Monitoring well BG-1BRLR is an NCDEQ approved bedrock background
monitoring location (Figure 1-3, CAP Update Report). Initial elevated TDS analytical
concentrations is attributable to artificial impacts from using a packer assembly for
packer testing (used to determine the screen interval within the bedrock boring prior
to well installation) that was not properly decontaminated. Low production/yield
prevented adequately flushing of the well to remove artificially affected
groundwater during well development following installation and purging efforts
prior to field sampling Analytical results from sampling events since January 2017
have shown a reduction of TDS concentration which is now stable and below
bedrock BTV.
Comment — 29
Groundwater: TDS - Monitoring wells MW-26BR and MW-18BR have shown concentrations
of elevated TDS greater than or equal to the 2L and PBTV values but are not depicted as such on
figure 11-24. Provide an explanation why the concentrations are not depicted in the figure.
Response — 29
MW-18BR and MW-26BR are NCDEQ-approved background monitoring wells.
Multiple lines of evidence indicate that TDS detected at MW-18BR and MW-26BR
are not ash basin impacts including (1) no boron detected and wells are beyond
(upgradient) of the boron plume, and (2) flow and transport modeling supported by
Page 20

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
empirical water level data indicates groundwater from the ash basin does not flow
toward MW-18BR and MW-26BR. TDS occurs naturally in groundwater, often at
concentrations greater than the 02L standard. The occurrence of TDS in
groundwater of the Piedmont Physiographic Province is well documented in the
literature. The groundwater analytical data provided in Appendix C, Table 1,
indicates TDS concentrations in MW-18BR and MW-26BR are at or below the BTV.
Comment — 30
Groundwater: TDS - MW-2BR located between the EAB and WAB was shown to have TDS
concentrations of 570 mg1L. Figure 11-24 does not depict the concentration as being associated
with either basin. Provide an explanation why the location was not included in the depicted
figure.
Response — 30
The MW-2BR location is adjacent to the LCID landfill, which was recently
determined to overly CCR materials present in the EAB (Section 1.5.2 and Section
3.0, CAP Update). Based on flow and transport modeling supported by empirical
water level data indicates MW-2BR, positioned along a topographical ridge,
represented by Dunnaway Road, is slightly downgradient of the LCID. However,
the TDS concentrations evident in MW-2BR are at or below the bedrock BTV and
within the range of naturally occurring TDS concentrations within groundwater of
the Piedmont Physiographic Province.
Comment — 31
Groundwater: Uranium - Explain the presence of uranium (total) in BG-1BRLR at greater than
the PBTV and the 2L groundwater standard.
Response — 31
Monitoring well BG-1BRLR is an NCDEQ approved bedrock background
monitoring location (Figure 1-3). Initial elevated uranium (total) analytical
concentrations is attributable to artificial impacts from using a packer assembly for
packer testing (used to determine the screen interval within the bedrock boring prior
to well installation) that was not properly decontaminated. Low production/yield
prevented adequately flushing the well to remove artificially impacted groundwater
during well development following installation and purging efforts prior to field
sampling. Analytical results from sampling events since January 2017 have shown a
reduction of uranium (total) concentration, which is now stable, and below bedrock
BTV.
Page 21

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Additionally, there are notably high naturally occurring concentrations of uranium
in the southeastern United States, which may be contributing to the few
observations of uranium above detection at Roxboro (Hughes, 2005; UNSCEAR,
2000).
Comment — 32
Groundwater: General - Explain the presence of elevated CCR constituents in BG-1BRLR.
Response — 32
Monitoring well BG-1BRLR is an NCDEQ approved bedrock background
monitoring location (Figure 1-3). Initial elevated CCR constituent (molybdenum,
sulfate, TDS, and uranium (total)) analytical concentrations is attributable to
artificial impacts from using a packer assembly for packer testing (used to determine
the screen interval within the bedrock boring prior to well installation) that was not
properly decontaminated. Low production/yield prevented adequately flushing the
well to remove artificially impacted groundwater during well development
following installation and purging efforts prior to field sampling. Analytical results
from sampling events since January 2017 have shown a reduction of these CCR
constituent concentrations, which are now stable, and below bedrock BTV.
Comment — 33
Groundwater - Additional monitoring wells are necessary in the area of the two southern "lobes"
of the WAB extension impoundment where monitoring wells have not been installed previously.
Response — 33
Groundwater monitoring well clusters, MW-38 and MW-39, were installed in the
two lobes south of the WAB extension impoundment to access groundwater quality
in these areas (Figure 1-3). Additional information regarding well installation is
provided in Section 2.2. Well construction information, along with boring and well
construction logs, is summarized in the well construction table provided in
Appendix Q. Groundwater analytical data is not available for the MW-38 cluster;
however, analytical results for MW-39 well cluster are provided in Appendix C,
Table 1. For the MW-39 cluster, no boron was detected above the laboratory
reporting limit with remaining constituents detected at concentrations below
approved transition zone and bedrock background levels.
Comment — 34
Groundwater - Recommend that additional assessment should be conducted in the vicinity of the
Woodland School water supply well including monitoring of the school's water supply wells.
Page 22

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Response — 34
In a meeting to discuss the CSA Update comments with NCDEQ RRO, Duke Energy
and SynTerra on June 26, 2018, no additional assessment was needed in the area of
BG-1BRLR and the Woodland Elementary School based on analytical information
trends and supporting pressure transducer water level data. The discussion and
affirmation was documented in the meeting minutes, dated June 26, 2018 and
approved by NCDEQ on December 21, 2018 (Appendix A, CAP Update report).
Comment — 35
Groundwater - RRO currently does not agree with Duke's PBTV groundwater "background"
values for Aluminum and Uranium (Total) for the transition zone & Alkalinity, Aluminum,
Bicarbonate, Sulfate and Radium (Total) for bedrock.
Response — 35
A revised BTV report was submitted to DWR on May 26, 2017 and conditionally
approved July 7, 2017 with final approval on September 1, 2017 (Appendix A of this
CAP Update). Updated groundwater BTVs were calculated and are used in the
evaluation of data as discussed in Section 4.2 of this CAP Update. In addition,
groundwater BTVs were further updated for this CAP Update and are included in
the evaluation of groundwater presented in Section 4.2, Table 4-3.
SITE CONCEPTUAL MODEL
Comment — 36
Site Conceptual Model - The update to the SCM in the SCSA was lacking in detail. It was
anticipated and agreed that the latest submittal would combine the information collected in the
various reports to summarize a picture of how known site conditions relate to the initial SCM
and how the current understanding of the model provides a basis that can be beneficial for
closure/corrective action purposes. It will be necessary to enhance and refine the SCM for CAP
submittal.
Response — 36
The Roxboro CSM presented in Section 5.0 describes and illustrates hydrogeologic
conditions and constituent interactions specific to the Site. The CSM is based on
multiple lines of evidence from the large data set through numerous assessment
activities conducted at Roxboro. The CSM presents an understanding of the
distribution of constituents with regard to the Site -specific
geological/hydrogeological and geochemical processes that control the transport and
potential impacts of constituents in various media and potential exposure pathways
to human and ecological receptors. Data obtained through the second quarter of
2019 has been used to enhance and refine the CSM, Flow and Transport Model
Page 23

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
(Appendix G), and Geochemical Model (Appendix H). The revised/updated CSM is
included in this CAP Update (Section 5.0).
Page 24

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
2017 COMPREHENSIVE SITE ASSESSMENT UPDATE
RALEIGH REGIONAL OFFICE DRAFT CSA UPDATE COMPREHENSIVE
REVIEW COMMENTS
On October 31, 2017, Duke Energy submitted a CSA Update to NCDEQ (SynTerra,
2017). NCDEQ Raleigh Regional Office (RRO) comments were received in an email
from the RRO to Duke Energy on June 7, 2018. The RRO comments were noted as "draft
CSA Update Comprehensive Review Comments". Those comments are addressed in
this document.
SOILS
Comment — 1
The soils investigation in the Comprehensive Site Assessment (CSA) is not sufficient regarding
the horizontal and vertical extent of soil impacts from CCR residuals. The CSA Update does not
contain a sufficient dataset to determine whether there has been an impact to soil chemistry by
coal ash residuals and a defined area of impact. The report lacks a comprehensive summation of
the extent of soil impacts beyond the compliance boundary and in the areas beyond the waste
boundary where data has been collected. The submitted figure included in the update does not
provide a comprehensive projection of potential soil impacts. There was no recommendation for
the collection of additional soils data or a presentation of where data gaps exist. Overall, there is
an insufficient collection of soils data to determine if the ash basins have impacted areas of
regolith around the margins of the basins and other areas considered to be at potential risk.
An additional investigation of soils is recommended whether this action takes place in
conjunction with corrective action or closure activities or as a CSA amendment. In the event the
project moves on to the corrective action phase, further investigation of soils is necessary. This
expectation is independent of the type of approved corrective action (excavation, cap in place,
active remediation, other or a combination of corrective actions). The scope of the additional
investigation may be influenced by the chosen corrective actionls. If, for instance, excavation is
the method of corrective action, excavation activities will allow for the opportunity to investigate
contaminated soils around the margins including soils located beneath the basins as excavation
activities progress. If the correction action consists of a cap in place, it is recommended that soils
around the margins of the ash basin cap are further evaluated for various environmental impacts
and investigation is conducted in soils beneath the basins as necessary. It is expected that CCR
impacted soils left in place will be factored into groundwater modeling activities.
Page 25

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Response — 1
Additional assessment of soil in the vicinity of the EAB and WAB concluded there is
no impact to soil beyond the EAB and WAB waste boundaries; therefore, there is no
ash basin -related impact to soils beyond the compliance boundary. On February 6,
2019, an additional soil assessment technical memo was submitted to NCDEQ. The
technical memo focused on assessment of potential impact to soils surrounding the
periphery of western lobe of the EAB and WAB extension impoundment. On June 7,
2019, a revised technical memo was submitted to NCDEQ, which included
additional soil assessment activities related to the EAB extension impoundment and
margins of the EAB and WAB. Sample locations associated with the EAB are
provided on Figure 6-15 in the CAP Update Report. A discussion regarding COIs in
unsaturated soil related to the EAB and the eastern extension impoundment area is
provided in Section 6.1.4.1 of the CAP Update report. Sample locations associated
with the WAB on Figure 6-32 in the CAP Update Report. A discussion regarding
COIs in unsaturated soil related to the WAB and the southern extension
impoundment area is provided in Section 6.10.4.1 of the CAP Update report.
Data indicate unsaturated soil COI concentrations, if present, are generally
consistent with background concentrations or are less than regulatory screening
values (Table 6-4 (EAB) and Table 6-19 (WAB)). In the few instances where
unsaturated soil COI concentrations are greater than PSRG POG standards or
background values, COI concentrations are within range of background dataset
concentrations or there are no mechanisms by which the COI could have been
transported from the ash basins to the unsaturated soils.
Comment — 2
The constituents listed below had discrepancies between Duke -calculated Provisional
Background Threshold Values (PBTVs) and the Division of Water Resources (DWR) values. The
following constituents had the differences in calculation from Table 7-1:
• Manganese-532mglkg. Not Acceptable. RRO calculated value 405mglkg. There was no
change from Duke's previous calculation.
• Nitrate-0.945 mglkg. Not Acceptable. RRO calculated value 0.7 mglkg. There was no
change from Duke's previous calculation
The report states that the discrepancy was resolved in the meeting on October 13, 2017. This
office has no record of the resolution of this issue. It will be necessary for a more detailed review
possibly with a combination of parties to resolve the difference in calculations.
Page 26

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Response — 2
Soil BTVs for manganese and nitrate (as N) were approved by NCDEQ in a letter
dated May 23, 2019 (Appendix A of this CAP Update). Additional information
regarding NCDEQ approved soil background values in provided in Section 4.2 of
this CAP Update.
Comment — 3
The layout for Appendix B Table 4 is difficult to discern PBTV exceedances based on the color
coding. The values for Preliminary Site Remediation Goals (PSRG) Industrial Health, PSRG
Residential Health, PSRG Protection of Groundwater (POG) and the PBTV are included in the
table. It appears that no color designation was used for PBTV. The current guidance for soil
values for comparison purposes do not include PSRG Industrial and PSRG Residential Health.
The inclusion of the two values in the table results in an indistinct and unclear presentation of
exceedances. PSRG Industrial Health and PSRG Residential Health should be removed from
future submittals. The PSRGs for Protection of Groundwater are the appropriate Remediation
Goals for soil at this site.
Response — 3
CSA Update summary tables for evaluation of soil only contain the PSRGs for
Protection of Groundwater (POG) and BTVs, which are utilized as the metric for soil
remediation goals for soil in the area of the EAB and WAB (Appendix C, Table 4).
See Section 4.2 of this CAP Update for additional information.
Comment — 4
Table 7.2 does not depict PBTV exceedances for boron and nickel.
Response — 4
Boron and nickel are included in the comparisons of soil analytical results to the
appropriate PSRG POGs/background values, which are presented in Appendix C,
Table 4 of the CAP Update.
Comment — 5
The discussion in the report for chromium beneath the ash basin and outside the waste boundary
refers to the PSRG Industrial value. The value of concern that is appropriate is the PSRG
Protection of Groundwater.
Response — 5
CSA Update summary tables for evaluation of soil only contain the PSRGs for POG
and BTVs, which are utilized as the metric for soil remediation goals for soil in the
area of the EAB and WAB. See Section 4.2 of this CAP Update for additional
information.
Page 27

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Comment — 6
Section 7.2 states that concentrations of iron, manganese and vanadium are present in "site
areas not influenced by ash basins" but provides an insufficient basis for the statement or what
specific location/s this statement references. The section refers to Figure 7-1 and Appendix B
Table 4 as evidence, but these items are a presentation of data results and exceedances and does
not constitute a specific discussion of the issue and does not present an explanation of how the
iron, manganese, and vanadium are not influenced by the ash basins.
Response — 6
A thorough evaluation of the potential nature and extent of COIs, including iron,
managanese, and vanadium, in unsaturated soil beyond the waste boundary and
compliance boundary for the Roxboro ash basins is presented in Section 6.1.4.1 for
the EAB and in Section 6.10.4.1 for the WAB in the CAP Update Report.
Comment — 7
The following constituents have one of more sample results where the detection limits do not
comply with either the PBTV or PSRG POG and cannot be evaluated for possible CCR
constituent exceedances: antimony, arsenic, cadmium, chloride, molybdenum, nitrate, selenium,
sulfate and thallium.
Response — 7
Unsaturated soil samples collected after submittal of the CSA Update, were
analyzed using detection and reporting limits less than the BTV and/or PSRG POGs
values for antimony, arsenic, cadmium, chloride, molybdenum, nitrate, sulfate,
selenium and thallium (Appendix C, Table 5 of this CAP Update). The horizontal
and vertical extent of COIs in soil is presented in Section 6.1.4.1 for the EAB and in
Section 6.10.4.1 for the WAB in the CAP Update Report.
Comment — 8
In Figure 2-11 and 2-12 it appears that the most recent soil sample locations BGSB-2 and
BGSB-112 are included where location SB-31 is missing.
Response — 8
The location of SB-31, co -located with MW-31BR, is presented on Figure 6-32 of the
CAP Update report.
SEDIMENT
Comment — 9
Initial activities in the CSA consisted of the sampling of eight sediment samples. Five of the
samples (SW-1, 2, 3, 4, 5) were collected from the stream bed. Three of the samples (S-09, 13, 14)
Page 28

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
were collected from seep locations. In addition to the preceding, sediment samples were collected
from the Southern Extension Impoundment (CF-01, 03, 05, EF-01, 03, WF-01, 03) and Western
Discharge Canal (WDC-01, 02, 03, 04, 05, 06). Samples were collected from the Eastern
Extension Impoundment (CL-02, 04, 06, 07, CV-01, 02, NL-04, 08) and Eastern Discharge
Canal. (EDC-00, 01, 02, 03, 05). Sample EDC-04 identified in Figure 5-3 of the Ash Basin
Extension and Discharge Canal Assessment Report was missing from the Appendix B Table 5 of
the CSA Update.
Response — 9
As noted by the symbol reference for location EDC-04 in Figure 5-3 of the Ash Basin
Extension and Discharge Canal Assessment Report, only surface water was sampled
at that location. Location EDC-04 is in a concrete channel extending 100 feet
upstream and downstream of the sample location.
Comment — 10
Table 5-1 and 5-2 in the Ash Basin Extension and Discharge Canal Assessment Report in
conjunction with the CSA Update (Page 8-3) does not clearly define what collected sediment or
ash interval was analyzed. Intervals are provided for total sediment core and for the interval of
ash encountered at each location, but the report does not specify what interval of sediment was
analyzed and/or if the material discrete sample location was analyzed as a composite or discrete
sample. The report indicates that shallow sediment samples from the EAB were collected from the
top six (6) inches of sediment. A detailed description of sample collection methods of the sediment
samples submitted for analysis is necessary.
Response — 10
Sediment samples related to the Ash Basin Extension and Discharge Canal
assessment were collected using a sample core device consisting of a 2-inch diameter
PVC pipe driver with a retractable internal 1.75-inch diameter clear acetate sleeve
coupled with a valve assembly at the top of the core device. The sampler was
manually pushed into the sediment to refusal or to a depth of at least 0.5 feet. Once
the desired depth was achieved, the valve was closed to create a vacuum for sample
retention within the sleeve and the core device removed. If an intact core sample
could not be collected, a sediment sample was manually collected by using a
decontaminated stainless steel trowel. The sediment core was extracted and
evaluated for ash content. If present, the ash material was segregated and the
sediment portion was collected and homogenized for laboratory analysis.
Comment — 11
The following constituents in one or more sediment sample results had detection limits that did
not comply with either the PBTV or PSRG POG and cannot be evaluated for possible CCR
Page 29

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
constituent exceedances: antimony, arsenic, cadmium, chloride, molybdenum, nitrate, selenium,
sulfate and thallium.
Response — 11
Sediment samples collected after submittal of the CSA Update, as part of the surface
water evaluation in April 2018, were analyzed using detection and reporting limits
less than the PSRG POGs/background values (Appendix C, Table 5 of this CAP
Update). Additional information regarding sediments assessments is provided in
Section 6.1.2 and Section 6.17.2 of this CAP Update.
SURFACE WATER
Comment — 12
Some additional sampling of surface waters is anticipated given the current data that
demonstrates 2L groundwater exceedances adjacent to surface waters north of the EAB. It is not
clear if the exceedance are in part associated with non DWR permitted activities (i.e. structural
fill at gypsum pad or DWM Landfill). Also, additional efforts will be necessary to evaluate
surface water conditions discharging into the basins to establish whether background
geochemistry has a role in the detected concentrations of constituents.
Response — 12
Surface water associated with the EAB include NPDES permitted wastewater
features including the Unit 3 wastewater hot pond, the Unit 3 cooling tower pond,
the eastern discharge canal and the extension impoundment. A jurisdictional
intermittent stream, Stream 11A, is located southwest of the EAB. The Intake Canal
is located downgradient of the GSA and the DFAHA, which are considered
downgradient additional, sources areas. Analytical results for surface water samples
collected from the Intake Canal and jurisdictional intermittent Stream 11A indicate
that these water bodies meet 02B standards under current conditions. The surface
water evaluation was completed in accordance with NCDEQ Internal Technical
Guidance: Evaluating Impacts to Surface Water from Discharging Groundwater
Plumes provided to Duke Energy on October 31, 2017. The purpose of the
evaluation was to identify exceedances of 15A NCAC 02B present in surface waters.
Findings from the Intake Canal evaluation were submitted to NCDEQ on March 21,
2019 (Surface Water Evaluation to Assess 15A NCAC 02B .0200 Compliance for
Implementation of Corrective Action under 15A NCAC 02L .0106(k) and (1)).
Additional information for Stream 11A is provided in a revised report provided in
Appendix J of the CAP Update. Additional information can be found in Section
6.2.1 and Section 6.18.1 of this CAP Update.
Page 30

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Analytical results from the surface water evaluation indicate boron was present in
the Intake Canal with an average concentration of 650 µg/L. The presence of boron
is likely attributed to groundwater discharge from the downgradient additional
source areas (GSA and DFAHA).
GROUNDWATER
Comment — 13
The CSA Update focused on the following constituents of interest (COI) regarding groundwater:
• Antimony, Boron, Chromium (hexavalent), Chromium (total), Cobalt, Iron, Manganese,
Molybdenum, pH, Selenium, Strontium, Sulfate, Total Dissolved Solids (TDS),
Vanadium, and Uranium (total)
Section 10.3 states that site specific COIs were developed by evaluating groundwater sampling
results with respect to PBTVs, applicable regulatory standards, and additional regulatory
input/requirements. The Raleigh Regional Office found the description of criteria used to
establish COI's for the facility to be vague.
Response — 13
A constituent management process was developed by Duke Energy at the request
and acceptance of NCDEQ (NCDEQ letter dated October 24, 2019; Appendix A,
CAP Update), to gain a thorough understanding of constituent behavior and
distribution in site groundwater and to aid in identifying unit -specific COIs. The
constituent management process consists of three steps:
1. Perform a detailed review of the applicable regulatory requirements under
NCAC, Title 15A, Subchapter 02L
2. Understand the potential mobility of unit -related constituents in
groundwater based on Site hydrogeology and geochemical conditions
3. Determine the constituent distribution at the unit under current and
predicted future conditions.
The COI management process is supported by multiple lines of evidence including
empirical data collected at the Site, geochemical modeling, and groundwater flow
and transport modeling. The management process uses a matrix evaluation to
identify those constituents that have migrated downgradient of the source unit, in
the direction of groundwater flow at concentrations greater than
02L/IMAC/background value with a discernable plume. This approach has been
used to understand and predict COI behavior in the subsurface related to the ash
Page 31

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
basin or COIs that are naturally occurring. Details on the COI management
approach are presented in Section 6.1.3 and Appendix H of this CAP Update.
Comment — 14
Section 10.1.2 is a presentation using some of the groundwater sampling results in piper
diagrams to explain site geochemistry and background conditions. The section predominantly
discusses the general use for piper diagrams and cites Orange County, NC groundwater quality
data as a comparison to the conditions at the Roxboro plant. The discussion contains little detail
regarding an interpretation of the data. A statement in the section about background wells MW-
18D and MW-18BR speak to the higher concentration of calcium without providing a discussion
of what meaning that may have. The MW-18 well set has been included in the background
dataset and so it is important that the current information demonstrate that the wells' location is
appropriate for inclusion in the groundwater background dataset. The RRO request that Duke
Energy provide additional discussion regarding the groundwater chemistry observed in MW-
18D and MW-18BR.
Response — 14
The referenced information was not used in developing this CAP Update; therefore,
the reference is not included.
Modified piper diagrams for the background wells as well as bar graphs comparing
the anion and cation concentrations indicate that the MW-18 well set is slightly
different than other background wells (Figure 6-28, CAP Update Report). The
primary difference is in the chloride ion concentration rather than the calcium
concentration. The calcium concentrations are comparable in MW-18D/BR with
concentrations in other wells with calcium concentrations in MW-19BR, MW-26BR,
and MW-30BR greater than those found in MW-18D/BR. The chloride concentrations
are 1.5 to 10 times greater than other background wells and the source of chloride is
unclear which may be attributable to upgradient off -site agricultural practices.
However, the pH and Ex as well as concentrations of other major ions (calcium,
magnesium, potassium, sodium, sulfate) are comparable to other background wells.
Additionally, there have been no measurements of boron or other conservative COIs
in the MW-18 well cluster. Therefore, MW-18D/BR indeed appears to be a
background, unaffected well.
Comment — 15
Groundwater: Boron - WAB, elevated boron (six times 2L standard) is present at ABMW-3BR
which is adjacent to the dam that separates the basin from the heated water discharge pond. The
vertical extent well did not detect boron greater than PQL. Migration of boron from this location
through the "shallow" bedrock is expected to discharge to the heated water discharge pond.
Page 32

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Additional monitoring wellls will be necessary in the area down gradient of this location in the
vicinity of existing well MW-1 for CAP monitoring purposes. Excluding the preceding area
near the dam, the WAB has been reasonably defined.
Response — 15
The vertical and horizontal extent of boron near ABMW-3BR has been delineated.
Groundwater analytical results shown no boron was detected greater than the
laboratory reporting in the deeper monitoring well, ABMW-3BRL, at this location.
A shallow bedrock monitoring well, HWMW-1BR, was installed downgradient of
ABMW-3BR, adjacent to MW-1 (Figure 1-3, CAP Update report). Details related to
well installation are provided in Section 2.2 of this CAP Update. Well construction
information including boring logs and well construction details are provided in
Appendix Q. Groundwater analytical results indicted no boron was detected above
the laboratory reporting limit with remaining constituents detected at concentrations
below bedrock BTV. Groundwater analytical results for HWMW-1BR and ABMW-
313RL are provided in Appendix C, Table 1 of this CAP Update report.
Comment — 16
Groundwater: Boron - EAB, elevated concentrations of boron greater than 2L standard have been
noted adjacent to the cooling water intake pond, unit #3 cooling tower intake pond, Plant intake
pond and intake canal. The shallow and deep bedrock flow regimes have concentrations of boron
several times the 2L standard (TZ: GPMW-3D two times, GPMW-ID 96l yg/L, GPMS-1S two
times, bedrock: MW-3BR four times, GPMW-2BR three times, GPMW-1BR two times). It
should be noted that the vertical extent is not defined in this location, however deeper flow paths
for groundwater would be expected to discharge to one or more of the previous named features. A
comprehensive sampling effort for a surface water discharge is necessary to track the fate of
elevated boron in this area. Additionally, it is unclear, given the presence of the coal ash
structural fill located in the gypsum pad storage area, what part, if any, the structural fill has in
the contribution of the observed boron concentrations. Request an explanation of the
fatelmigration of the boron exceedance in the EAB, an assessment of the source, including a
comprehensive sampling effort to determine where groundwater impacted by boron discharges
into surface water.
Response — 16
Groundwater downgradient of the EAB discharges to NPDES-permitted wastewater
features including the Unit 3 wastewater hot pond and the Unit 3 cooling tower
pond, the eastern discharge canal and the extension impoundment. Groundwater
downgradient of the GSA and the DFAHA, which includes a component of
groundwater flow downgradient of the EAB (comingled zone) discharges to the
Page 33

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Intake Canal. A component of groundwater to the south of the EAB discharges to
the unnamed jurisdictional stream (Stream #11A). Analytical results for surface
water samples collected from the Intake Canal and Stream 11A indicate that these
water features meet 02B standards under current conditions. The surface water
evaluation was completed in accordance with NCDEQ Internal Technical Guidance:
Evaluating Impacts to Surface Water from Discharging Groundwater Plumes
provided to Duke Energy on October 31, 2017. The purpose of the evaluation was to
identify exceedances of 15A NCAC 02B present in surface waters. Findings from the
Intake Canal evaluation were submitted to NCDEQ on March 21, 2019 (Surface
Water Evaluation to Assess 15A NCAC 02B .0200 Compliance for Implementation of
Corrective Action under 15A NCAC 02L .0106(k) and (1)). Additional information
for Stream 11A is provided in a revised report provided in Appendix J of the CAP
Update. Additional information can be found in Section 6.2.1 and Section 6.18.1 of
this CAP Update.
Analytical results from the surface water evaluation indicate boron was present in
the Intake Canal with an average concentration of 650 µg/L. The presence of boron
is likely attributed to groundwater discharge from the downgradient additional
source area (GSA and DFAHA).
Comment — 17
Groundwater: Hexavalent chromium - Hexavalent chromium has been detected in the shallow
TZ wells (BG-1 6.9 µg/L) at concentrations approaching the established PBTV and has also been
detected in MW-15D (2.2 µg/L) and MW-18D (2.5 µg/L). Most ash basin wells and monitoring
wells near the basins (excluding ABMW-5D) do not have elevated concentrations comparable to
the detections in BG-1. Also, the bedrock wells BG-1, MW-15 and MW-18 do not appear to
demonstrate elevated concentrations of hexavalent chromium as has been detected in the more
shallow wells. The CSA Update does not discuss what conditions may be responsible for the
concentrations. Request an explanation for the observed concentrations of hexavalent chromium.
Response — 17
The highest concentrations of hexavalent chromium are found in NCDEQ approved
background monitoring wells and upgradient monitoring wells, including BG-1,
MW-15D, and MW-18D. Continued sampling has generated a more robust dataset
for hexavalent chromium. All samples downgradient of the ash basins are less than
BTV (Appendix C, CAP Update). Furthermore, the distribution of hexavalent
chromium in groundwater does not exhibit a discernable plume associated with the
ash basins. An analysis of the presence and distribution of each COI, including
Page 34

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
hexavalent chromium, is provided in the geochemical model report (Appendix H)
with additional discussion included in Section 6.1.2.
Comment — 18
Groundwater: Cobalt - WAB, elevated concentrations were observed in ABMW-3BR at twenty
times the PBTV. The vertical extent well at this location did not detect boron greater than the
PQL. Cobalt from this location is expected to migrate through the "shallow" bedrock and
discharge to the heated water discharge pond. Additional groundwater assessment will be
necessary in the area downgradient of this location in the vicinity of existing well MW-1.
Excluding the preceding area, located near the dam, the WAB has been reasonably defined.
Response — 18
The vertical and horizontal extent of cobalt near ABMW-3BR has been delineated.
Groundwater analytical results shown no cobalt was detected greater than the
laboratory reporting in the deeper monitoring well, ABMW-3BRL, at this location.
A shallow bedrock monitoring well, HWMW-1BR, was installed downgradient of
ABMW-3BR, adjacent to MW-1 (Figure 1-3, CAP Update report). Groundwater
analytical results indicate no cobalt was detected above the laboratory reporting
limit with remaining constituents detected at concentrations below bedrock
background values. Groundwater analytical results for ABMW-3BRL and HWMW-
1BR are provided in the Appendix C, Table 1 of this CAP Update report.
Comment — 19
Groundwater: Cobalt - EAB, elevated concentrations of cobalt greater than the PBTV have been
noted in the TZ adjacent to the cooling water intake pond and intake canal. The cooling water
intake pond and intake canal discharge to Hyco Lake. Cobalt in the shallow groundwater flow
regime has been detected at several times the PBTV (GPMW-3D- nine times, GPMW-1S - nine
times, GPMW-2D - eight times). Bedrock well MW-22BR had detections of cobalt greater than
the PBTV. A comprehensive assessment effort for surface water discharge is necessary to track
the fate of elevated cobalt in this area. Additionally, it is unclear, given the presence of the coal
ash structural fill located in the gypsum pad storage area, what part, if any, of the structural fill
has contributed to the observed concentrations. Request an explanation of the fatelmigration of
the cobalt exceedance in the EAB, an assessment of the source, including a comprehensive
sampling effort to determine where groundwater impacted by cobalt discharges into a surface
water.
Response — 19
Analytical results for surface water samples collected from the Intake Canal and
jurisdictional intermittent Stream 11A indicate that these water bodies meet 02B
standards under current conditions. The surface water evaluation was completed in
Page 35

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
accordance with NCDEQ Internal Technical Guidance: Evaluating Impacts to
Surface Water from Discharging Groundwater Plumes provided to Duke Energy on
October 31, 2017. The purpose of the evaluation was to identify exceedances of 15A
NCAC 02B present in surface waters. Findings from the Intake Canal evaluation
were submitted to NCDEQ on March 21, 2019 (Surface Water Evaluation to Assess
15A NCAC 02B .0200 Compliance for Implementation of Corrective Action under
15A NCAC 02L .0106(k) and (1)). Additional information for Stream 11A is provided
in a revised report provided in Appendix J of the CAP Update. Additional
information can be found in Section 6.2.1 and Section 6.18.1 of this CAP Update.
Analytical results from the surface water evaluation indicate cobalt was not above
the laboratory method detection limits in samples collected for the evaluation nor is
it anticipated to be in the future (Appendix J).
Comment — 20
EAB, elevated iron is present in the TZ wells GPMW-2D at approximately sixty times the
PBTV and ABMW-5D at approximately thirty times the PBTV. GPMW-2D is located adjacent
to the intake canal and water intake basin. ABMW-5D is an ash basin well located upgradient of
the unit #3 intake tower cooling. A comprehensive sampling effort for these surface water
features is necessary to track any migration of elevated iron into the surface water features.
Response — 20
Analytical results for surface water samples collected from the Intake Canal and
jurisdictional intermittent Stream 11A indicate that these water bodies meet 02B
standards under current conditions. The surface water evaluation was completed in
accordance with NCDEQ Internal Technical Guidance: Evaluating Impacts to
Surface Water from Discharging Groundwater Plumes provided to Duke Energy on
October 31, 2017. The purpose of the evaluation was to identify exceedances of 15A
NCAC 02B present in surface waters. Findings from the Intake Canal evaluation
were submitted to NCDEQ on March 21, 2019 (Surface Water Evaluation to Assess
15A NCAC 02B .0200 Compliance for Implementation of Corrective Action under
15A NCAC 02L .0106(k) and (1)). Additional information for Stream 11A is provided
in a revised report provided in Appendix J of the CAP Update. Additional
information can be found in Section 6.2.1 and Section 6.18.1 of this CAP Update.
The Unit 3 Heated Water Discharge Pond and Unit 3 Cooling Tower Pond are
permitted NPDES wastewater treatment units therefore were not included in the
surface water evaluation.
Page 36

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
As demonstrated in the Surface Water Evaluation report (Appendix J, CAP Update),
iron was detected in the Intake Canal samples ranging from approximately 200
mg/L to 300 mg/L, consistent with the background sample concentrations.
Based on lithological information observed during the installation of GPMW-2D,
silty clay with remnant sediment was noted to a depth of approximately 34.5 feet
bgs. The screen interval for GPMW-2D is 36-46 feet bgs. The well is installed in a
former swale where remnant sediment and organic material is likely present
creating a reducing environment as noted by negative ORP and low Ex values in the
groundwater samples.
The low Ex conditions will favor formation of Fe(II) which is more soluble than
Fe(III). Given that iron is ubiquitous in the subsurface, decreased EH is expected to
increase groundwater iron concentrations. Ferrous iron (Fe(II)) may be attenuated
by sorption and ion exchange as described in the Geochemical Modeling Report
(Section 3.9.3, Appendix H, CAP Update) where the total iron Kd generally increases
with increasing pH. The widest variations in Kd values are found for the transition
zone and bedrock zones, which also have the widest variation in Ex. This is a critical
consideration because the reduction potential determines the concentration of Fe(II)
available for sorption, ion exchange, or precipitation. Aqueous concentrations of
Fe(III) are primarily controlled by solubility. Therefore, discussion of a Ka value for
Fe(III) is somewhat irrelevant due to the solubility limitations. The higher Kd values
in the ash and transition zones flow zones are primarily due to the higher clay
content, which provides significant cation exchange of Fe(II) and promotes
decreased aqueous phase concentrations.
Comment — 21
Groundwater: Manganese - WAB, elevated manganese (thirteen times the PBTV) is present at
ABMW-3BR which is adjacent to the dam that separates the basin from the heated water
discharge pond. The vertical extent well did not detect manganese greater than the PBTV
(ABMW-3BRL 180 µg/L). The manganese from this well location migrating through the
"shallow" bedrock is expected to discharge to the heated water discharge pond. Additional
monitoring well/s will be necessary in the area downgradient of this location in the vicinity of
existing well MW-1.
Response — 21
The vertical and horizontal extent of manganese near ABMW-3BR has been
delineated. Groundwater analytical results shown no manganese was detected
greater than bedrock BTV in the deeper monitoring well, ABMW-3BRL, at this
location. A shallow bedrock monitoring well, HWMW-1BR, was installed
Page 37

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
downgradient of ABMW-3BR, adjacent to MW-1 (Figure 1-3, CAP Update report).
Groundwater analytical results indicate no manganese was detected above bedrock
BTV with remaining constituents detected at concentrations below bedrock
background levels. Groundwater analytical results for ABMW-3BRL and HWMW-
1BR are provided in Appendix C, Table 1 of this CAP Update report.
Comment — 22
Groundwater: Manganese - In Figure 11-12, the depicted isoconcentration map for manganese
did not include the elevated concentrations detected in MW-12BR and MW-8BR. It was noted
that ABMW-1BR had a detection of 966 µg/L and is located in the approximate middle of the
basin. It would appear that this points to a correlation with the observed concentrations in MW-
12BR and MW-8BR. An explanation is necessary why the isoconcentration depiction for
manganese does not encompass the well locations in question for the west side of the WAB.
Response — 22
Manganese, often at concentrations greater than the 02L standard, occurs naturally
in groundwater of the Piedmont Physiographic Province, which is well documented
in literature. Manganese concentrations detected at Roxboro are isolated and
sporadic as discussed in the COI management approach provided in Section 6.1.3
and in Appendix H. As noted in this CAP Update Sections 6.10.3 and 6.10.4, the
distribution of manganese in groundwater adjacent to the WAB does not exhibit a
discernable plume. Furthermore, the boron plume does not extend toward the wells
located to the west of the WAB discharge canal and groundwater flow patterns do
not demonstrate a transport pathway from the ash basin to MW-8BR and MW-12BR.
Additionally, the wells on the west side of the WAB are upgradient and analytical
data shows the manganese concentrations are within or below the range of bedrock
BTV (CAP Update Appendix C, Table 1).
Comment — 23
Groundwater: Manganese - EAB, elevated concentrations of manganese greater than the PBTV
have been noted in the TZ adjacent to the cooling water intake pond and intake canal. The
shallow groundwater flow regime has detected concentrations of manganese several times the
PBTV (GPMW-3D -four times, GPMW-IS - nine times, GPMW-2D -fourteen times). In the
bedrock aquifer, MW-23BR was observed to have detections of manganese approximately four
times the PBTV. ABMW-5D is an ash basin well located upgradient of the unit #3 intake tower
cooling where manganese was detected at fourteen times the PBTV. A comprehensive surface
water assessment is necessary to track the fate of the elevated manganese in this area.
Additionally, it is unclear, given the presence of the coal ash structural fill located in the gypsum
pad storage area, what part, if any of the structural fill has contributed to the observed
Page 38

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
concentrations. Request an explanation of the fate/migration of the manganese exceedance in the
EAB, an assessment of the source coupled with a comprehensive sampling effort for a surface
water discharge.
Response — 23
Analytical results for surface water samples collected from the Intake Canal and
jurisdictional intermittent Stream 11A indicate that these water bodies meet 02B
standards under current conditions. The surface water evaluation was completed in
accordance with NCDEQ Internal Technical Guidance: Evaluating Impacts to
Surface Water from Discharging Groundwater Plumes provided to Duke Energy on
October 31, 2017. The purpose of the evaluation was to identify exceedances of 15A
NCAC 02B present in surface waters. Findings from the Intake Canal evaluation
were submitted to NCDEQ on March 21, 2019 (Surface Water Evaluation to Assess
15A NCAC 02B .0200 Compliance for Implementation of Corrective Action under
15A NCAC 02L .0106(k) and (1)). Additional information for Stream 11A is provided
in a revised report provided in Appendix J of the CAP Update. Additional
information can be found in Section 6.2.1 and Section 6.18.1 of this CAP Update.
As demonstrated in the Surface Water Evaluation, manganese was detected at levels
consistent with the range of background values for surface water with the exception
of RSW-3. The surface water sample collected on May 3, 2018 from the RSW-3
location had anomalously high concentrations of iron and manganese compared to
samples collected earlier that week at the same location. As discussed in Section 4.2
of the Surface Water Evaluation report, the anomalously high iron and manganese
concentrations might be attributable to anomalous high wind weather conditions
during the May 3, 2018 sampling event.
The high concentration of manganese, such as in ABMW-03BR, is likely due to
dissolution of manganese oxide minerals or co -precipitated minerals under the
reducing conditions frequently observed in bedrock wells. Similarly, as described in
the Geochemical Modeling Report (Section 3.11, Appendix H, CAP Update)
manganese can exist in multiple oxidation states ranging from Mn(II) to Mn(VII).
Under the Ex and pH conditions of the groundwater at Roxboro, Mn(II) is the
dominant oxidation state. Mn(II) is highly soluble and mobile under low pH
conditions. Under the reducing conditions observed at upgradient wells of the EAB,
Mn(II) is stable and soluble. Thus, concentrations of manganese with in the EAB are
likely from ash leaching as well as upgradient naturally occurring inputs. It is
noteworthy that in many cases, measured aqueous manganese concentrations are
variable, particularly in the bedrock flow zone. A likely underlying cause for this
Page 39

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
effect is the presence of naturally occurring manganese minerals and co -precipitates,
which are highly variable in the subsurface. Due to the high variability in
manganese mineral solubility, any changes in pH (even those induced by changes in
Ex) can alter the aqueous concentration of manganese.
Comment — 24
Groundwater: Molybdenum - WAB, elevated concentrations of molybdenum have been detected
in deep bedrock well BG-1BRLR at as much as twice the PBTV value. Request an explanation
why the elevated concentration is present in the bedrock well at this location.
Response — 24
Monitoring well BG-1BRLR is an NCDEQ approved bedrock background
monitoring location (Figure 1-3, CAP Update Report). Initial elevated molybdenum
analytical concentrations is attributable to artificial impacts from using a packer
assembly for packer testing (used to determine the screen interval within the
bedrock boring prior to well installation) that was not properly decontaminated.
Low production/yield prevented adequately flushing of the well to remove
artificially affected groundwater during well development following installation
and purging efforts prior to field sampling Analytical results from sampling events
since January 2017 have shown a reduction of molybdenum concentrations which is
now stable and below bedrock BTV.
Comment — 25
Groundwater: Selenium - EAB, an area of elevated concentrations greater than the
PBTV and four to five times the 2L standard is present in the vicinity of the gypsum
storage pad and downgradient of the ash basin. Request an explanation of the
fate/migration of the selenium exceedance for this area, an assessment of the source
coupled with a surface water selenium assessment in areas such as the intake canal and
cooling water intake basin.
Response — 25
Analytical results for surface water samples collected from the Intake Canal and
jurisdictional intermittent Stream 11A indicate that these water features meet 02B
standards under current conditions. The surface water evaluation was completed in
accordance with NCDEQ Internal Technical Guidance: Evaluating Impacts to
Surface Water from Discharging Groundwater Plumes provided to Duke Energy on
October 31, 2017. The purpose of the evaluation was to identify exceedances of 15A
NCAC 02B present in surface waters. Findings from the Intake Canal evaluation
were submitted to NCDEQ on March 21, 2019 (Surface Water Evaluation to Assess
15A NCAC 02B .0200 Compliance for Implementation of Corrective Action under
Page 40

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
15A NCAC 02L .0106(k) and (1)). Additional information for Stream 11A is provided
in a revised report provided in Appendix J of the CAP Update. Additional
information can be found in Section 6.2.1 and Section 6.18.1 of this CAP Update.
As described in the Geochemical Modeling Report (Section 3.14, Appendix H, CAP
Update), under the Ex -pH conditions of the Roxboro site, Se(IV) is present as HSe03
or SeOs 2 as the dominant species. Selenium exhibits an expected decrease in
sorption with increasing pH, consistent with many other anions. This is a
manifestation that mineral surface charge on metal oxide minerals transitions from a
net positive to a net negative charge with increasing pH. Therefore, as the pH
increases, the sorption affinity of anionic selenium species to the more negatively
charged surface decreases. In addition to the influence of pH and Ex, competition
with other anions can influence selenium partitioning. A wide range of Ka values
were simulated in the Geochemical Modeling Report using site specific data as the
input to define the geochemical conditions. Sorption anionic HSe03 will be in
competition for sorption sites by other anionic species. Near the GSA, there are
elevated levels of sulfate in groundwaters due to the dissolution of gypsum.
Concentrations in the 1.0 to 1.4 g/L range were observed in GPMW-3 and MW-22D
and the concentrations of sulfate were found to correlate with elevated
concentrations of selenium. Thus, competition with other anions may increase
groundwater selenium concentrations.
Comment — 26
Groundwater: Strontium - WAB, detections of strontium are observed in the TZ and bedrock
flow regimes. The concentrations in the TZ do not appear to exceed (approximately) the PBTV.
In the bedrock flow regime concentrations that are close to or exceeding the PBTV are present in
various locations. The ABMW-3 well set has detections of strontium that exceed the PBTV. Nine
times the PBTV was detected in ABMW-3BR and four times the PBTV in deeper bedrock well
ABMW-3BRL. Downgradient of the ABMW-3, well set CW-2D (327 µg/L) has detections
greater than the PBTV. The vertical extent of strontium has not been defined in the
downgradient area. Strontium migrating through bedrock is expected to discharge into the
heated water discharge pond. Additional assessment will be necessary in the area downgradient
of this location in the vicinity of existing well MW-1 for vertical extent assessment and CAP
monitoring purposes. Request an explanation for the elevated concentrations (about four times
PBTV) in BG-1BRLR.
Response — 26
A shallow bedrock monitoring well, HWMW-1BR, was installed adjacent to MW-1
(Figure 1-3). Details related to well installation are provided in Section 2.2 of this
Page 41

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
CAP Update. Well construction information including boring logs and well
construction details are provided in Appendix Q. Groundwater analytical results
for HWMW-1BR are provided in Appendix C, Table 1 of this CAP Update.
Strontium was detected at concentrations ranging from 353 µg/1 to 361 µg/L, which
is above the bedrock BTV but within the range of NC Piedmont regional
background values (Section 6.1.3, CAP Update).
Monitoring well BG-1BRLR is an NCDEQ approved bedrock background
monitoring location (Figure 1-3, CAP Update Report). Initial elevated strontium
analytical concentrations is attributable to artificial impacts from using a packer
assembly for packer testing (used to determine the screen interval within the
bedrock boring prior to well installation) that was not properly decontaminated.
Low production/yield prevented adequately flushing of the well to remove
artificially affected groundwater during well development following installation
and purging efforts prior to field sampling Analytical results from sampling events
since January 2017 have shown a reduction of strontium concentration, which is
now stable, and below bedrock BTV.
Comment — 27
Groundwater: Strontium - EAB, elevated concentrations of strontium greater than the PBTV
have been noted in the TZ and bedrock flow regimes adjacent to the cooling water intake pond
and intake canal. The shallow flow regime has observed concentrations of strontium several
times the PBTV (GPMW-3D - two times, GPMW-IS - three times, GPMW-ID - two times,
GPMW-2D exceeds PBTV). Strontium concentrations in the bedrock flow regime were detected
at several times the PBTV (GPMW-1BR -five times, GPMS-2BR - six times, GPMW-ID - two
times, GPMW-3BR -four times, MW-3BR - six times). Request an explanation of the
fatelmigration of the strontium exceedance in the EAB adjacent to the surface water features,
along with a comprehensive sampling effort to evaluate any surface water discharge. Elevated
concentrations have been detected at four and nine times the PBTV in wells MW-17BR and
MW-25BR respectively in the bedrock flow regime. The vertical and horizontal extent of
strontium impacts has not been defined in this location near the facility property boundary.
Additional assessment is necessary to define the vertical and horizontal extent in the vicinity of
wells MW-17BR and MW-25BR.
Response — 27
Elevated concentrations of strontium were observed east of the EAB and the
mobility of strontium in this area may be due to the geochemical behaviors as
discussed in the Strontium Technical Memo — East Ash Basin (Appendix H). Boron
and dissolved strontium concentrations paired with 87Sr/86Sr ratios indicate there is
Page 42

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
a component of affected groundwater flow east of the EAB because of radial flow
induced from the industrial landfill. Strontium observed in CCR-110BR and the
extension impoundment surface water has an isotopic signature indicating some
fraction is from CCR material. However, groundwaters observed in MW-17BR and
MW-25BR, which are outside the compliance boundary, have isotopic signatures of
non-CCR origin. Boron is an inorganic metal that is a sensitive indicator for other
metals leaching from CCR, and boron concentrations from MW-17BR and MW-25BR
have remained non -detect or detected below BTV over time. Thus, strontium
associated with CCRs is horizontally delineated east and south of the EAB by
locations GMW-9 and MW-24BR. Co -associated alkali earth cations (Mg, Sr, and Ba)
are likely originating from the GSA where sparsely soluble metal -sulfate phases will
control the pore water concentrations.
Comment — 28
Groundwater: Sulfate - WAB, sulfate concentrations were observed in ABMW-3BR at ten times
the PBTV. Sulfate concentrations in the vertical extent well at this location were less than twice
the 2L standard. Sulfate from this location is expected to migrate through the "shallow" bedrock
aquifer and discharge into the heated water discharge pond. Additional assessment will be
necessary in the area downgradient of this location in the vicinity of existing well MW-1.
Excluding the preceding area near the dam, the WAB has been reasonably defined.
Response — 28
A shallow bedrock monitoring well, HWMW-1BR, was installed adjacent to MW-1
(Figure 1-3, CAP Update report). Details related to well installation are provided in
Section 2.2 of this CAP Update. Well construction information including boring
logs and well construction details are provided in Appendix Q. Groundwater
analytical results for HWMW-1BR are provided in the Appendix C, Table 1 of this
CAP Update report. Sulfate in HWMW-1BR was detected at an average
concentration of 140 mg/L, which is below the 02L value of 250 mg/L.
Comment — 29
Groundwater: Sulfate - An area of elevated sulfate has been designated in the vicinity of wells
MW-32BR and BG-1BRLR. This area is represented as being distinct from the WAB. Request
an explanation for the elevated concentrations of sulfate and why this area is not associated with
the WAB.
Response — 29
Monitoring well BG-1BRLR is an NCDEQ approved bedrock background
monitoring location (Figure 1-3, CAP Update Report). Initial elevated sulfate
analytical concentrations is attributable to artificial impacts from using a packer
Page 43

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
assembly for packer testing (used to determine the screen interval within the
bedrock boring prior to well installation) that was not properly decontaminated.
Low production/yield prevented adequately flushing of the well to remove
artificially affected groundwater during well development following installation
and purging efforts prior to field sampling Analytical results from sampling events
since January 2017 have shown a reduction of sulfate concentration, which is now
stable, and below bedrock BTV.
Analytical data for monitoring well MW-32BR location, the groundwater data,
presented in Appendix C, Table 1, indicated no boron concentrations above bedrock
BTV that is less than 02L. The sulfate concentrations detected at MW-32BR are
isolated and sporadic as discussed in the COI management approach provided in
Section 6.1.3 and in Appendix H. Additionally, the average calcium, sulfate, and
magnesium concentrations that gypsum is near saturation (saturation index -0.89)
which indicate that there is a sulfate bearing mineral phase there producing those
relatively high sulfate concentrations. Since those concentrations are present without
a high boron concentration, it can be concluded the sulfate minerals are naturally
occurring and not related to CCR materials.
Comment — 30
Groundwater: Sulfate - EAB, elevated concentrations of sulfate greater than 2L standard have
been noted adjacent to the cooling water intake pond and intake canal. The shallow and deep
bedrock flow regimes have concentrations of sulfate several times the 2L standard (TZ: GPMW-
3D -five times, GPMW-ID -four times, GPMS-1W -four times, bedrock: MW-3BR >2L,
GPMW-2BR -four times, GPMW-1BR -four times). It should be noted that the vertical extent
of elevated sulfate is not defined in this location, however deeper flow paths for groundwater
would be expected to discharge to one or more of the previous named features or Hyco Lake. A
comprehensive surface water sampling effort is necessary to track the fate of elevated sulfate
water in this area. Additionally, it is unclear, given the presence of the coal ash structural fill
located in the gypsum pad storage area, what part, if any, the structural fill and/or gypsum pad
has in the contribution of the observed sulfate concentrations. Request an explanation of the
fate/migration of the sulfate exceedance in the EAB, an assessment of the source, including a
comprehensive sampling effort to determine where groundwater impacted by sulfate discharges
into a surface water.
Response — 30
Analytical results for surface water samples collected from the Intake Canal and
jurisdictional intermittent Stream 11A indicate that these water bodies meet 02B
standards under current conditions. The surface water evaluation was completed in
Page 44

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
accordance with NCDEQ Internal Technical Guidance: Evaluating Impacts to
Surface Water from Discharging Groundwater Plumes provided to Duke Energy on
October 31, 2017. The purpose of the evaluation was to identify exceedances of 15A
NCAC 02B present in surface waters. Findings from the Intake Canal evaluation
were submitted to NCDEQ on March 21, 2019 (Surface Water Evaluation to Assess
15A NCAC 02B .0200 Compliance for Implementation of Corrective Action under
15A NCAC 02L .0106(k) and (1)). Additional information for Stream 11A is provided
in a revised report provided in Appendix J of the CAP Update. Additional
information can be found in Section 6.2.1 and Section 6.18.1 of this CAP Update. As
demonstrated in the Surface Water Evaluation, sulfate was detected at levels
consistent with the range of background values for surface water.
Comment — 31
Groundwater: TDS - WAB, elevated concentrations were observed in ABMW-3BR at eight
times the PBTV. TDS concentrations in the vertical extent well at this location are greater than
the PBTV. TDS from this location is expected to migrate through the "shallow" bedrock and
discharge into the heated water discharge pond. Additional assessment will be necessary in the
area downgradient of this location in the vicinity of existing well MW-1. Excluding the
preceding area near the dam, the WAB has been reasonably defined.
Response — 31
A shallow bedrock monitoring well, HWMW-1BR, was installed adjacent to MW-1
(Figure 1-3, CAP Update report). Details related to well installation are provided in
Section 2.2 of this CAP Update. Well construction information including boring
logs and well construction details are provided in Appendix Q. Groundwater
analytical results for HWMW-1BR are provided in the Appendix C, Table 1 of this
CAP Update report. TDS was detected at concentrations ranging from 475 mg/L to
505 mg/L, below the TDS BTV.
Comment — 32
Groundwater: TDS - An area of elevated TDS greater than the 2L standard and the PBTV is present in
the vicinity of wells MW-32BR and BG-1BRLR, as depicted in figure 11-24. This area of elevated TDS is
represented as being distinct from the area of elevated TDS in the vicinity of the WAB. Request an
explanation for the elevated concentrations of TDS and why this area is not associated with the
WAB.
Response — 32
For the MW-32BR location and similar to the sulfate occurrence, the groundwater
data, presented in Appendix C, CAP Update, indicated no boron concentrations
above the boron 02L and the bedrock BTV, indicating the waters have not been
Page 45

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
affected by CCR materials. Additionally, high TDS is also likely being influenced by
the reducing conditions that facilitate formation of more soluble Mn(II) and Fe(II).
Since those concentrations are present without a high boron concentration, it can be
concluded the TDS concentrations are naturally occurring and not related to CCR
materials.
Monitoring well BG-1BRLR is an NCDEQ approved bedrock background
monitoring location (Figure 1-3, CAP Update Report). Initial elevated TDS analytical
concentrations is attributable to artificial impacts from using a packer assembly for
packer testing (used to determine the screen interval within the bedrock boring prior
to well installation) that was not properly decontaminated. Low production/yield
prevented adequately flushing of the well to remove artificially affected
groundwater during well development following installation and purging efforts
prior to field sampling Analytical results from sampling events since January 2017
have shown a reduction of TDS concentration which is now stable and below
bedrock BTV.
Comment — 33
Groundwater: TDS - EAB, concentrations greater than the PBTV have been noted adjacent to
the cooling water intake pond, #3 cooling towers pond, the plant intake pond and intake canal.
The shallow and deep bedrock groundwater flow regimes have concentrations of TDS several
times the PBTV (TZ: GPMW-3D - three times, GPMW-ID - three times, GPMW-IS - three
times, GPMW-2D >PBTV, bedrock: MW-3BR -four times, GPMW-2BR -four times, GPMW-
IBR - three times, GPMW-3BR -four times). It should be noted that the vertical extent of
elevated TDS is not defined in this location, however deeper flow paths for groundwater would
be expected to discharge to one or more of the previous named features. A comprehensive
assessment of surface water discharges is necessary to track the fate of elevated TDS in this area.
Additionally, it is unclear, given the presence of the coal ash structural fill located in the gypsum
pad storage area, what part, if any, the structural fill and/or gypsum pad has in the contribution
of the observed TDS concentrations. Request an explanation of the fate/migration of the TDS
exceedance in the EAB, assessment of the source(s) of TDS, and the technical basis if no
additional vertical delineation is considered necessary.
Response — 33
Analytical results for surface water samples collected from the Intake Canal and
jurisdictional intermittent Stream 11A indicate that these water bodies meet 02B
standards under current conditions. The surface water evaluation was completed in
accordance with NCDEQ Internal Technical Guidance: Evaluating Impacts to
Surface Water from Discharging Groundwater Plumes provided to Duke Energy on
Page 46

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
October 31, 2017. The purpose of the evaluation was to identify exceedances of 15A
NCAC 02B present in surface waters. Findings from the Intake Canal evaluation
were submitted to NCDEQ on March 21, 2019 (Surface Water Evaluation to Assess
15A NCAC 02B .0200 Compliance for Implementation of Corrective Action under
15A NCAC 02L .0106(k) and (1)). Additional information for Stream 11A is provided
in a revised report provided in Appendix J of the CAP Update. Additional
information can be found in Section 6.2.1 and Section 6.18.1 of this CAP Update. As
demonstrated in the Surface Water Evaluation, TDS was detected at levels consistent
with the range of background values for surface water.
Comment — 34
Groundwater: TDS - Monitoring wells MW-26BR and MW-18BR have shown concentrations
of elevated TDS greater than or equal to the 2L and PBTV values but are not depicted as such on
figure 11-24. Provide an explanation why the concentrations are not depicted in the figure.
Response — 34
MW-18BR and MW-26BR are NCDEQ-approved background monitoring wells.
Multiple lines of evidence indicate that TDS detected at MW-18BR and MW-26BR
are not ash basin impacts including (1) no boron detected and wells are beyond
(upgradient) of the boron plume, and (2) flow and transport modeling supported by
empirical water level data indicates groundwater from the ash basin does not flow
toward MW-18BR and MW-26BR. TDS occurs naturally in groundwater, often at
concentrations greater than the 02L standard. The occurrence of TDS in
groundwater of the Piedmont Physiographic Province is well documented in the
literature. The groundwater analytical data provided in Appendix C, Table 1,
indicates TDS concentrations in MW-18BR and MW-26BR are at or below the BTV.
Comment — 35
Groundwater: TDS - MW-2BR located between the EAB and WAB was shown to have TDS
concentrations of 570 mg1L. Figure 11-24 does not depict the concentration as being associated
with either basin. Provide an explanation why the location was not included in the depicted
figure.
Response — 35
The MW-2BR location is adjacent to the LCID landfill, which was recently
determined to overly CCR materials present in the EAB (Section 1.5.2 and Section
3.0, CAP Update). Based on flow and transport modeling supported by empirical
water level data indicates MW-2BR is positioned along a topographical ridge,
represented by Dunnaway Road, and is slightly downgradient of the LCID.
However, the TDS concentrations evident in MW-2BR are at or below the bedrock
Page 47

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
BTV and within the range of naturally occurring TDS concentrations within
groundwater of the Piedmont Physiographic Province.
Comment — 36
Groundwater: Uranium - Explain the presence of uranium (total) in BG-1BRLR at greater than
the PBTV and the 2L groundwater standard.
Response — 36
Monitoring well BG-1BRLR is an NCDEQ approved bedrock background
monitoring location (Figure 1-3). Initial elevated uranium (total) analytical
concentrations is attributable to artificial impacts from using a packer assembly for
packer testing (used to determine the screen interval within the bedrock boring prior
to well installation) that was not properly decontaminated. Low production/yield
prevented adequately flushing the well to remove artificially impacted groundwater
during well development following installation and purging efforts prior to field
sampling. Analytical results from sampling events since January 2017 have shown a
reduction of uranium (total) concentration, which is now stable, and below bedrock
BTV.
Additionally, there are notably high naturally occurring concentrations of uranium
in the southeastern United States, which may be contributing to the few
observations of uranium above detection at Roxboro (Hughes, 2005; UNSCEAR,
2000).
SPECIAL AREAS OF CONCERN
Comment — 37
The recent investigation of the eastern and western extension impoundments has detected
impacts from coal ash constituents and the presence of coal ash. Considering this data, it will be
necessary to install additional monitoring wells in the area of the two southern "lobes" of the
WAB extension impoundment where monitoring wells have not been installed previously.
Particular attention should be given to offsite water supply wells or other sensitive receptors
when locating the wells. Pending regulatory/permit decisions may have some bearing on what
assessment is considered necessary.
Response — 37
Groundwater monitoring well clusters, MW-38 and MW-39, were installed in the
two lobes south of the WAB extension impoundment to access groundwater quality
in these areas (Figure 1-3). Additional information regarding well installation is
provided in Section 2.2. Well construction information, along with boring and well
Page 48

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
construction logs, is summarized in the well construction table provided in
Appendix Q. Groundwater analytical data is not available for the MW-38 cluster;
however, analytical results for MW-39 well cluster are provided in Appendix C,
Table 1. For the MW-39 cluster, no boron was detected above the laboratory
reporting limit with remaining constituents detected at concentrations below
approved transition zone and bedrock background levels.
Comment — 38
Special Areas of Concern - The assessment of the EAB was influenced by the presence of several
characteristics. A lined DWM permitted landfill has been constructed in the EAB. Also, present
adjacent to the EAB is the gypsum storage pad which was partly constructed with coal ash fill. A
number of CCR constituents have been detected in groundwater at concentrations greater than
the 2L standards and/or PBTV in the area between the gypsum pad and the intake canal. It is not
clear whether the structural fill, the stored gypsum or some other source/s besides the coal ash
associated with the NPDES permit are contributing to the observed CCR groundwater
concentrations in this area. It is important that the additional information is collected as
necessary, so that a model of site conditions can be established that explains whether CCR
sources (other than the basins or secondary sources that are required to be addressed by CAMA)
are significant contributors to the observed groundwater exceedances. It will be necessary for
Duke Energy to address the details by providing a summary description and conclusion.
Conduct additional assessment as necessary to identify source locations in the effort to
distinguish areas required to be addressed by CAMA from other sources.
Response — 38
This CAP Update assesses the GSA and DFAHA independent of the EAB.
Analytical data in addition to Flow and Transport model simulations indicate that
the GSA and DFAHA are the primary source contributors of the elevated COIs
present in the area adjacent to the Intake Canal. The GSA and DFAHA, referred to
as downgradient additional source areas, are referenced as "Source Area 3". Details
for Source Area 3, including proposed corrective action are provided in Section 6.17
of this CAP Update.
Comment — 39
Special Area of Concern - It should be noted that the Woodland Elementary School is
located in the vicinity of the WAB extension where additional assessment is necessary.
Given that the Woodland School utilizes groundwater for potable water needs, the RRO
recommends that additional assessment should be conducted in the vicinity of the
school as well as monitoring of the school's water supply wells.
Page 49

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
Response — 39
A revised BTV report was submitted to DWR on May 26, 2017 and conditionally
approved July 7, 2017 with final approval on September 1, 2017 (Appendix A of this
CAP Update). Updated groundwater BTVs were calculated and are used in the
evaluation of data as discussed in Section 4.2 of this CAP Update. In addition,
groundwater BTVs were further updated for this CAP Update and are included in
the evaluation of groundwater presented in Section 4.2, Table 4-3.
Comment — 40
The evolving nature of the groundwater investigation efforts have contributed to the area in the
vicinity of the WAB extension impoundment not having been fully assessed for CCR
constituents. Given the discovery of coal ash and CCR in the WAB extension impoundment it is
necessary to install monitoring wells to assess any impacts to groundwater around the feature. It
is recommended that soil samples are collected at the time of well installation. The pending
classification of this unit may have an influence on what additional investigation is necessary.
Response — 40
Groundwater monitoring well clusters, MW-38 and MW-39, were installed in the
two lobes south of the WAB extension impoundment to access groundwater quality
in these areas (Figure 1-3). Additional information regarding well installation is
provided in Section 2.2. Well construction information, along with boring and well
construction logs, is summarized in the well construction table provided in
Appendix Q. Groundwater analytical data is not available for the MW-38 cluster;
however, analytical results for MW-39 well cluster are provided in Appendix C,
Table 1. For the MW-39 cluster, no boron was detected above the laboratory
reporting limit with remaining constituents detected at concentrations below
approved transition zone and bedrock background levels.
The area referenced as the "WAB Extension Impoundment" is not a separate
impoundment "pending classification" as noted in this comment. On October 31,
2017 Duke Energy submitted a letter to NCDEQ titled Response to August 25 Letter
Regarding Compliance Boundaries. The letter included exhibits in response to
NCDEQ's request for additional information related to certain Roxboro NPDES
waste units. Exhibits included:
• Historic drawings and other information demonstrating the historic role of
EAB Eastern Extension Impoundment (EAB EEI) and the WAB Southern
Extension Impoundment (WAB SEI); and
Page 50

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
An analysis of the jurisdictional status of Sargents Creek, the Western
Discharge Canal, the Eastern Discharge Canal, and the Heated Water
Discharge Pond.
SITE CONCEPTUAL MODEL (DRAFT)
Comment — 41
Section 15 Site Conceptual Model -.The update to the SCM was limited in discussion. It was
anticipated that the latest submittal would work towards 1) combining the information collected
in the various reports 2) summarize a picture of how known site conditions relate to the initial
SCM and 3) explain how the current conceptual model understanding will influence actions
moving forward towards closure/corrective action. The section does not provide a detailed
discussion of how the present understanding of site conditions will have an influence on future
actions.
Response — 41
The Roxboro CSM presented in Section 5.0 describes and illustrates hydrogeologic
conditions and constituent interactions specific to the Site. The CSM is based on
multiple lines of evidence from the large data set through numerous assessment
activities conducted at Roxboro. The CSM presents an understanding of the
distribution of constituents with regard to the Site -specific
geological/hydrogeological and geochemical processes that control the transport and
potential impacts of constituents in various media and potential exposure pathways
to human and ecological receptors. Data obtained through the second quarter of
2019 has been used to enhance and refine the CSM, Flow and Transport Model
(Appendix G), and Geochemical Model (Appendix H). The revised/updated CSM is
included in this CAP Update (Section 5.0).
ADDITIONAL COMMENTS (DRAFT)
Comment — 42
Section 11 Hydro Investigation - States that the horizontal and vertical extent of the plume has
been defined and that monitoring wells are appropriate placed and constructed to monitoring
groundwater quality. The section in the CSA Update continues to describe individual COIs and
general information regarding occurrence of the constituents. General statements are made
without applying the information presented to site specific conditions or examples.
Response — 42
The COI management process is supported by multiple lines of evidence including
empirical data collected at the Site, geochemical modeling, and groundwater flow
and transport modeling. The management process uses a matrix evaluation to
Page 51

Appendix B: Comprehensive Site Assessment Update NCDEQ Comments and Responses
Corrective Action Plan Update December 2019
Roxboro Steam Electric Plant SynTerra
identify those constituents that have migrated downgradient of the source unit, in
the direction of groundwater flow at concentrations greater than
02L/IMAC/background value with a discernable plume. This approach has been
used to understand and predict COI behavior in the subsurface related to the ash
basin or COIs that are naturally occurring. Details on the COI management
approach are presented in Section 6.1.3 and Appendix H of this CAP Update.
The vertical and horizontal extent of the EAB and WAB plumes are then defined,
based on the unit specific COIs. Discussions regarding the vertical and horizontal
extent of COIs for the EAB are presented in Section 6.1.4 and for the WAB in
Section 6.10.4 of the CAP Update.
Comment — 43
Section 11.2 Pending Investigation - The CSA Update indicates that additional investigation
will be conducted to collected data for metal oxy-hydroxide iron (HFO) and aluminum (HAO) to
support geochemical model for the CAP. Soil and rock samples from previously installed borings
or from new installations along groundwater flow transects will be used.
Response — 43
Ash samples were analyzed for extractable metals analysis, including HFO (hydrous
ferric oxide)/HAO (hydrous aluminum oxide), using the Citrate-Bicarbonate-
Dithionite (CBD) method. Leaching environmental assessment framework (LEAF) is
a leaching evaluation framework for estimating constituent release from solid
materials. Leaching studies of consolidated ash samples from the EAB and the WAB
were conducted using two LEAF tests, EPA methods 1313 and 1316 (USEPA, 2012a,
b). The data are presented and discussed in the Geochemical Modeling Report in
Appendix H, Attachment C. The HFO and HAO data were used as input values for
the batch and 1D transect PHREEQC models. The HFO and HAO values were used
to determine the concentration of ferrihydrite and gibbsite minerals, which are the
primary sorbents for many, COIs in the geochemical models.
A revised and updated Geochemical Modeling Report that incorporates various
geochemical data types and datasets collected throughout the Roxboro EAB and
WAB assessment since 2015 is included in this CAP Update (Appendix H). The
report provides conclusions concerning partitioning properties that affect
constituent migration, conclusions concerning constituent mobility, and evaluation
of source control options on current and future Site geochemical characteristics.
Page 52