Comments on Duke Energy 10-7-19 Letter_20191024

ROY COOPER
Governor
NHCHAEL S. REGAN
Secretary
LINDA CULPEPPER,
Dlnectvr
Paul Draovitch
Senior Vice President
Environmental, Health & Safety
Duke Energy
526 South Church Street
Mail Code EC3XP
Charlotte, North Carolina 28202
NORTH CAROLINA
Environmental Quality
October 24, 2019
Subject: Comments on Duke Energy Letter dated October 7, 2019 Subject: Responses
to North Carolina Department of Environmental Quality Letter Dated August 12,
2019 - Interim Monitoring Plan Analysis for Dissolved Constituents and Metals
-Speciation
Dear Mr. Draovitch:
The objective of this letter is to provide comments in response to the October 7, 2019 Duke
Energy correspondence regarding Interim Monitoring Plan (IMP) analysis for dissolved
constituents and metals speciation and establish the North Carolina Department of
Environmental Quality (DEQ) Division of Water Resources' (Division's) position regarding data
collection and analysis requirements . The following is an outline of correspondence related to
this subject matter:
• Duke Energy submitted draft Optimized Interim Monitoring Plans (IMPs) for the 14
Duke Energy coal combustion residual (CCR) facilities in October 2018 for DEQ review.
• Discussion between Duke Energy and the respective DEQ Division regional offices
concerning Optimized IMPs commenced in October 2018 and continued through
December 2018.
• (DEQ gave approval on December 21, 2018 for Optimized IMPs to be implemented
starting on the first quarter of 2019 for the 14 Duke Energy CCR facilities. The
Optimized IMPs represented agreements between DEQ regional offices and Duke Energy
Subject Matter Experts concerning optimization of the groundwater monitoring programs
conducted' at the sites.
• On March 20, 2019, DEQ received the proposed Optimized IMP for 14 Duke Energy
Facilities - Modification Request Annual Reports - Modification Request (Modification
North Carolina Department of Environmental Quality I Division of Water Resources
512 North Salisbury Street 1 1636 Mail Service Center I Raleigh, North Carolina 27699-1636
919.707.9000 Page 1 of 4

Request) that requested changes to direction provided to Duke Energy by DEQ in the
December 21, 2018 correspondence concerning the Optimized IMPS.
• DEQ approved the Modification Request apart from some specific items subject to
approval in an April 4, 2019, letter. Duke Energy's April 25, 2019, letter provided
justification for the proposed changes to the Optimized IMPS, which was approved by the
Department in a May 20, 2019, letter.
• After review of the Optimized IMPs and remedial design considerations, DEQ provided
direction to collect additional dissolved and speciated metals samples in an August 12,
2019, letter.
• Duke Energy's October 7, 2017, letter provided responses to the Department's comments
along with discussion as to how metals speciation results are used to develop
geochemical models in Attachment A - Technical Response to the North Carolina
Department of Environmental Quality's 8/12/19 Response for Metals Speciation
Sampling and Analysis, SynTerra Corporation and Rosewater Geochemical Modeling,
LLC. 9/17/19. Limitations inherent in sample collection and analysis and the equilibrium
modeling approach were discussed in detail in Attachment A.
DEQ's review of the October 7, 2019, letter and technical position regarding its content are
provided below:
Page 3, Speciation Sampling
"Duke Energy does not believe that additional speciation sampling will be informative beyond
the extensive data already being collected at the Dube Energy coal ash sites and site -specific
geochemical modeling performed for each site. The need for speciation sampling can be
addressed again on a targeted basis should it be required to better understand changes observed
in groundwater concentrations."
Comment — Because equilibrium between redox species will be assumed by using the PHREEQC
computer code to make the speciation calculations and there is uncertainty as to whether all of
the redox-sensitive species are in equilibrium with the measured EH used for speciation (as
discussed in Attachment A to the October 19, 2019 letter), the concentrations of pairs of redox
species should be measured in selected groundwater samples to better understand the
uncertainty introduced by assuming equilibrium between the species.
Attachment A, page 1, third paragraph
"Additionally, collecting reliable field samples to preserve the oxidation/reduction (redox)
conditions and constituents of interest (COI) speciation is profoundly difficult because of the
potential exposure of the samples to atmospheric conditions during sample collection and
processing."
Comment — Although collecting groundwater samples for measurement of redox species is not a
routine process because it is not necessary at the majority of sites, the collection of such samples
is not profoundly difficult. Some commercial analytical laboratories specialize in the analysis of
such samples and will provide the necessary sample bottles with preservatives and instructions
for sample collection. At sites where, redox reactions are important processes affecting the
Page 2 of 4

mobility of elements such as Fe, Mn, As, Se, etc., measurement of the redox species of these
elements is part of routine sampling.
Attachment A, page 2, last parag Mh
"A similar approach cannot be taken for the redox speciation. The different oxidation states of
iron, manganese, arsenic, chromium, and selenium must be coupled in the model so that the
distribution between each oxidation state can be simulated based on the total concentration in the
model."
Comment — The PHREEQC model calculations do not require the coupling of redox species for
an element. The computer code provides many different options for dealing with redox species.
In the default case, the field -measured EH and total concentration of an element is used by the
code to speciate the oxidation states of the element. A second option is to independently measure
the concentrations of the oxidation states in the groundwater sample and enter those
concentrations separately rather than the total elemental concentration in the input file. In this
case, the code conducts the ion speciation calculations on the individual redox states of the
element and does not require redox equilibrium between the pairs of species. When the
speciation calculations are complete, the code will calculate an EH based on the measured
concentrations of the redox pair in solution, which can then be compared to the field -measured
EH to evaluate equilibrium.
Attachment A, page 3, last Paragraph
"While linking this explicitly to the ferrihydrite concentration in the system could provide a more
realistic estimation of the redox potential due to the low solubility of Fe(III) species, Fe(OH)2+
was used as the aqueous species because the exact ferrihydrite concentration is not known (note
that extractable iron concentrations are available, but the fraction of a specific iron mineral is
unknown)."
Comment — Equation 1 of the Attachment should be written in terms of Fee+ and ferrihydrite for
the stated reason that the Fe(OH)2+ concentration is usually so low that it cannot be measured
but must be estimated. There is no explicit need to know the ferrihydrite concentration in the
system to use this equation to calculate EH. As with other equilibrium reactions, such as
mineral solubility, the concentration of the mineral in the system is not important as long as
some of the mineral is present. In these cases, the mineral concentration (actually activity) is set
to 1. A total ferrous iron concentration can be input into PHREEQC in a system in equilibrium
with ferrihydrite with the "redox" option set to Fe(2)/Fe(3). The code will calculate the EH
based on iron redox equilibrium. Figure 1 should be replotted based on this method of
calculating EHfrom the Fe(I&Fe(III) couple.
Since there may be difficulty collecting speciated metals samples, DEQ suggests that sampling
events for these data objectives may be conducted separately from routine monitoring to address
related quality control issues.
DEQ staff welcome the opportunity to discuss groundwater sample requirements along with
related IMP and Constituent of Interest Management Plan issues with Duke Energy. If you have
questions or comments regarding the Department's position provided in this correspondence,
Page 3 of 4

please contact Steve Lanter in the Division's Central Office at [phone] and he will
coordinate with the respective Regional Offices to initiate discussion.
Sincerely,
Jim Gregson, Deputy Director
Division of Water Resources
Attachments
Duke Energy's October 7, 2019 letter Responses to the North Carolina Department of
Environmental Quality Letter Dated August 12, 2019 — Interim Monitoring Plan Analysis for
Dissolved Constituents and Metals Speciation
cc: WQROS Regional Offices (electronic copy)
GWRS Central File Copy
Page 4 of 4

LF DUKE
ENERGY®
October 7, 2019
Mr. Steve Lanter
North Carolina Department of Environmental Quality
1636 Mail Service Center
Raleigh, North Carolina 27699-1636
Paul Draovhch
Senior Vice President
Environmental, Health & Safety anc
Operations Support
526 S. Church Street
Mail Code: EC3XP
Charlotte, NC 28202
[phone]
Subject: Responses to North Carolina Department of Environmental Quality Letter Dated August
12, 2019 — Interim Monitoring Plan Analysis for Dissolved Constituents and Metals
Speciation
Dear Mr. Lanter:
Duke Energy is in receipt of the above -referenced letter from the North Carolina Department of
Environmental Quality (NCDEQ) which requests additional groundwater monitoring well analysis for
dissolved constituents along with metals speciation. Duke Energy and our geochemistry experts have
carefully reviewed NCDEM request in the context of the extremely large database available for each
site and the extensive geochemical modeling that has been performed in collaboration with the
NCDEQ's geochemical expert. The results of this review and discussions with NCDEQ were factored into
the Interim Monitoring Plans (IMPs), which were submitted to NCDEQ in late 2018 and updated in first
quarter 2019. Generally, the most current NCDEQ approval for the IMPs is dated April 4, 2019.
Below is the NCDEQ request from the August 12, 2019 letter in italic font along with the Duke Energy
response in normal font.
NCDEQ Comments:
DEQ conducted a review of the optimized IMPs and related submittals to determine if the necessary data are
being collected to support remedial design for corrective action. Upon review of recent submittals, DEQ staff
have identified some discrepancies between the approved IMPs and the actual data being collected and
analyzed. For example, Duke Energy is no longer collecting and analyzing dissolved samples at some wells for
some COIs included in the IMP sampling program.
Further review of the currentgroundwatermonitoring program indicates speciation ofgroundwater samples for
metals has not been performed since 2015.
Concentrations of total and dissolved constituents in combination with speciation analytes are necessary in the
development of geochemical models that will be used to understand contaminant occurrence, oxidation state, and
mobility under current (pre -closure) conditions and under the site conditions that may occur during and after decanting,
dewateting and source control measures have been implemented. To address data needs, DEQ requests the
following action to begin with the next iMP Quarterly sampling event:
Revise the existing IMPs if needed for each facility to ensure that dissolved samples are collected and
analyzed at wells along the geochemical model transects, selected background locations, and selected
downgradient wells that exhibit exceedances of the 15A NCAC 02L .0202 groundwater quality standards.

• Collect total and dissolved samples and perform speciation for the following constituents and oxidation
states: Fe(Il, 111), Mn(l1,III, IV), As(111,V), Cr(111,V1), Se (-II,IV,VI) at wells along the geochemical model
transects, selected background locations, and selected downgradient wells that exhibit exceedances of
the 15A NCAC 02L .0202 groundwater quality standards.
Duke Ene[a Response:
Potential Discrepancies in IMP Sam linC, - Duke Energy reviewed the IMPS for the individual sites and did
not identify any discrepancies between the approved IMPS and the actual data being collected, analyzed
and submitted to the NCDEQ. In some cases, Duke Energy collects additional groundwater samples on a
voluntary basis that may differ from the IMPs. These voluntary data are also submitted to the NDCEQ.
If there are any specific discrepancies that NCDEQ has observed, please provide this information to Duke
Energy so we can work with the NCDEQto resolve any issues.
Duke Energy is aware that the IMPS can be confusing to follow due to wells that are sampled at different
frequencies and for different constituent lists. Duke Energy plans to update the IMPs to make
improvements so that Duke Energy and NCDEQ are both comfortable with them. Duke Energy plans to
update the IMPS by end November 2019 so that the NCDEQ can review and approve the IMPS so they
are ready for implementation at the start of 2020.
Groundwater Sampling for Dissolved Constituents —The following summarizes Duke Energy's planned
approach in response to the NCDEQ's letter regarding sample collection and analysis for dissolved
constituents. This approach was verbally discussed with NCDEQ at a meeting at the Mooresville
Regional Office on September 4, 2019.
Duke Energy along with our consultants, SynTerra Corporation and Rosewater Geochemical Modelling,
LLC., have evaluated existing and proposed future sampling events and have determined what
additional or continued data are necessary for development of the geochemical models (e.g. collection
of both total and dissolved 10.45-micron filtered] groundwater monitoring well samples). The following
approach has been developed in response to the NCDEQ request:
• New wells (i.e., those installed after December 2018) will be sampled for a minimum of four
quarters and analyzed for total and dissolved (0.45- micron filtered) constituents for the full
CAMA parameter list (note there are other constituents that Duke Energy voluntarily samples
for to provide data to our geochemical modelling team). The four rounds of sampling assists in
the evaluation of constituent stability and provides a baseline dataset.
• Existing wells (i.e., those with historical IMP data including both total and dissolved samples) will
be sampled on a site -wide basis for total and dissolved (0.45- micron filtered) constituents
either the first or second quarter of each year to monitor potential changes in groundwater
conditions, and to accommodate any future geochemical modeling efforts, as needed. This

population of wells will include all wells along geochemical transects (i.e., those included in or
associated with the PHREEQCII-D advection models).
Speciation Sampling —This request was reviewed by Duke Energy's geochemistry experts and the
following response is provided. Additional technical details in support of this response is provided in
Attachment A to this letter. Speciation sampling was completed during 2015 as part of the groundwater
assessment plan. Duke Energy does not believe that additional speciation sampling will be informative
beyond the extensive data already being collected at the Duke Energy coal ash sites and site -specific
geochemical modeling performed for each site. The need for Speciation sampling can be addressed
again on a targeted basis should it be required to better understand changes observed in groundwater
concentrations. This approach was shared with the NCDEQ and their geochemical expert during our
meeting at the Mooresville Regional Office on September 4, 2019.
If you have any questions on the enclosed information, please contact Ed Sullivan at 980-373-3719.
Sincerely,
Pa Draovitch
Senior Vice President
Environmental, Health & Safety
Attachment: Geochemical Modeling Discussion on Metals Speciation — September 2019
cc: Ed Sullivan — Duke Energy
Scott Davies — Duke Energy
Kathy Webb — SynTerra Corp.
Jim Wells - Duke Energy
Matt Hanchey — Duke Energy
PHREEQC- United States Geologic Survey (USGS) equilibrium modeling program with the original
acronym pH-REdox-EQuilibrium written in C programming language

ATTACH M ENT A
Technical Response to the North Carolina Department of Environmental Quality's 8/12/19 Response for
Metals Speciation Sampling and Analysis
Prepared by: SynTerra Corporation and Rosewater Geochemical Modeling, LLC.
9/17/19
On August 3.2.2019, the North Carolina Department of Environmental Quality (NCDEQ) sent a letter to
Duke Energy requesting, in part, groundwater sampling and analysis for metals speciation, specifically
for: Fe(II, III), Mn(II, III, IV), As(III, V), Cr(III, VI), Se( -II, IV, VI).
In this Attachment, metals speciation is discussed in terms of how results are used in the development
of the geochemical model as well as the limitations inherent in sample collection and analysis and the
equilibrium modeling approach.
The structure of the current geochemical model - using the aqueous speciation and surface
complexation modeling program, PHREEQC—was developed assuming that the groundwater system
being modeled is in equilibrium (Note: the second "E" in PHREEQC denotes equilibrium and the model
assumes equilibrium conditions are present). Often, geochemical systems are not present at
equilibrium but are along a reaction path towards an equilibrium state (Zhu, 2009: Stumm and Morgan,
1996; Tinnacher and Honeyman, 2010). This summary describes how potential non -equilibrium
conditions can be accounted for using PHREEQC predictive models. Additionally, collecting reliable field
samples to preserve the oxidation/reduction (redox) conditions and constituents of interest (COI)
speciation is profoundly difficult because of the potential exposure of the samples to atmospheric
conditions during sample collection and processing. Therefore, redox speciation is best evaluated from
expert judgement using a combination of;1) the geochemical models to see the constituents and likely
species present and note the thermodynamic driving forces and direction of change of the system, and;
2) observations of changes in constituent concentrations and geochemical conditions overtime.
Therefore, collection of total and dissolved constituent concentrations periodically is important and is
supported by Duke Energy as described in the letter response for this attachment. If there are observed
changes in constituent concentrations, the geochemical models can be utilized to determine if the
change in concentration is consistent with the predicted chemical speciation. Further field data
collection may occur if the model simulations cannot explain the observed data.
The geochemical models use an equilibrium -based aqueous speciation and surface complexation model
(PHREEQC) to simulate the geochemical behavior of multiple constituents related to the coal ash
impoundments. The geochemical model can be used to evaluate the behavior of COls in terms of the
likely chemical species, dominant attenuation mechanisms, and overall potential for groundwater
migration for current, and estimated future conditions at each site. Site -specific data have been
evaluated to identify trends in geochemical behavior for each COI, including:
• Aqueous concentration of constituents in both ash pore water and groundwater;
• Total digested and extractable solid phase concentrations of constituents for each flow
zone (e.g., ash, shallow/surficial, deep/transition zone, and bedrock for the Piedmont
physiographic region);
• Solid phase mineralogy/lithology data; and
• Leaching potential from source material or coal ash using the United States
Environmental Protection Agency (USEPA) Method 1313 and Method 1316 analysis
included in the USEPA-Leaching Environmental Assessment Framework (LEAF) to

evaluate the leaching potential of inorganic constituents over a range of pH values (pH 3
to pH 11) and liquid-to=solid ratios (ranging from 0.5 to 10 mL/g-dry ash).
Model simulations are performed using both the batch and the 1-D advective transport modes available
in PHREEQC. As discussed in detail below, the inherent assumption of equilibrium in the PHREEQC
simulations may lead to differences between predicted and observed oxidation/reduction conditions. An
example of this disequilibrium is provided in this attachment. Despite this potential limitation, the
model provides an assessment of the equilibrium conditions of the system that can be used in
conjunction with observations from actual site field data to assess deviations from equilibrium. This
concept and approach was discussed between Duke Energy and our Geochemical Modelling Team along
with staff from the North Carolina Department of Environmental Quality (NCDEQ) and Mr. William
Deutsch (external reviewer for NCDEQ) in meetings dating back to 2015 and have acknowledged
agreement with this approach.
The question of evaluating speciation can be complicated, but it is also not always necessary to predict
the concentrations of a specific COL As an equilibrium -based model PHREEQC does not consider
reaction kinetics. Therefore, all chemical reactions are assumed to reach equilibrium, including
oxidation-reduction and mineral precipitation -dissolution reactions, which can be kinetically limited in
many cases. For example, naturally occurring pyrite (FeS2) is commonly found in surface water streams.
When in contact with atmospheric 02(g) which can dissolve in water to form dissolved oxygen (O2(aq)),
an equilibrium model would predict that essentially all the pyrite would oxidize to form ferric iron
(Fe(III)) and sulfate (SO4 2), leaving no pyrite in the system. In a surface water where pyrite minerals are
observed, this reaction is clearly not reaching the predicted equilibrium state. The equilibrium model
provides information on the expected equilibrium endpoint of the system but does not provide
information on how quickly it will reach that state.
The aqueous complexation, sorption/desorption, oxidation/reduction, and precipitation/dissolution
reactions considered in the PHREEQC model all occur at different rates, and therefore, will take different
times to reach equilibrium. Aqueous complexation and sorption reactions are commonly observed to
reach equilibrium on time scales of minutes to hours. Therefore, equilibrium -based models are
appropriate in many cases, particularly where groundwater flow rates are slow and the system has
longer time to reach equilibrium on a local level. In contrast, oxidation-reduction reactions may occur at
slower rates because they,involve complete electron transfer during the chemical interactions and
potentially structural rearrangement of the species [Example: addition of oxygen to hexavalent
chromium (CrO4-') during oxidation of trivalent chromium (Cr")). The structural rearrangement of
mineral phases is a potential rate limiting step that will cause a system not to reach equilibrium in
relevant time scales. For example, in a PHREEQC simulation initially containing aqueous ferric iron
(Fe(IIII), the system will predict the mineral hematite ((x-Fe2O3) to be the most thermodynamically
stable, and therefore, predominant phase instead of the more soluble minerals ferrihydrite (a-
Fe(OH)3)(s)) and goethite ((x-FeOOH). However, under the conditions in the coal ash impoundments;
ferrihydrite is often found to be the dominant iron mineral because of the additional energy and time
required to form goethite or hematite. Therefore, the model simulations are written using a feature in
PHREEQC to not allow goethite or hematite to form so that constraint provides a better description of
the actual system. This minimizes the influence of the equilibrium assumptions for mineral
precipitation/dissolution.
A similar approach cannot be taken for the redox speciation. The different oxidation states of iron,
manganese, arsenic, chromium, and selenium must be coupled in the model so that the distribution
N

between each oxidation state can be simulated based on the total concentration in the model.
Therefore, the redox speciation is included as part of the PHREEQC simulations and is evaluated with
expert judgement in comparison with observations of total and dissolved constituent concentrations
over time.
Conclusion
The above discussion shows the geochemical modeling approach used is very useful to understand site
groundwater conditions, but the model results do not comprehensively provide all the answers. Expert
judgment is required in many cases to interpret the results. As long as the PHREEQC model simulations
are combined with expert judgment (based on existing empirical evidence and extensive literature
review) are acceptably predicting the concentrations of redox active constituents, there is no need for
additional speciation sampling. Speciation information was useful in original model development and
site characterization, but the use of this data in our future models is not required unless site
measurements cannot be adequately explained with the current approach. Therefore, additional
speciation sampling is not proposed.
Supplemental Information
Example of redox diseguilibrium using data from Sutton rPowell. 2016)
To evaluate the potential for redox disequilibrium in the field samples, the expected redox potential
(Le., pe and E„) for each groundwater sample was calculated based on the Fe(II) and Fe(III) ratios. Using
the reaction shown in Equation 1 for Fe(II) oxidation to Fe(III) and the equilibrium expression shown in
Equation 2.
Fe++ + 2H20 H Fe(OH)2+ + 2H+ + e- log — 18.78
[Fe(OH)2 ] [H+]z [e-] = equilibrium constant (K) = log —18.78
[Fe ++]
Equation 1
Equation 2
where [e ] is the electron concentration in the system which is more commonly noted as pe (pe = -log[e
]). This reaction has been written in terms of Fe++ oxidation to Fe(OH)2+ which are the expected aqueous
species at the pH values under consideration. While linking this explicitly to the ferrihydrite
concentration in the system could provide a more realistic estimation of the redox potential due to the
low solubility of Fe(III) species, Fe(OH)2+ was used as the aqueous species because the exact ferrihydrite
concentration is not known (note that extractable iron concentrations are available but the fraction of a
specific iron mineral is unknown). Iron speciation is used for this calculation because the dissolved iron
concentrations are relatively high compared to other redox active species and it is likely that iron would
be a significant redox buffer in these systems. Also, this iron couple is known to be more likely at or near
equilibrium than many other couples. Taking the log of the Equation 2, the expected pe value based on
the ratio of Fe(II) to Fe(III) can be calculated as (Equation 3):
Equation 3
[Fe(OH)Z ]
log [Fe++] — 2pH + 18.78 = pe
3

The calculated and measured EH values are shown in Figure 1. From these data, it is clear that the
expected EH values based on the iron redox couple are greater than the measured values in many cases
and lower in some. Thus, iron is either 1) not the dominant redox buffer in this system causing the
measured EH values, or 2) iron speciation is not present under equilibrium conditions.
700
,-% 600
E
j W111H
X
W
400
L
300
200
100
C�7
0 100 200 300 400 500 600 700 800
Estimated EH (mV) based on Fe(II)/Fe(III) couple
Figure 1: Estimated EH values based on the Fe(II)/Fe(III) redox couple compared with the measured
values in groundwater samples from the L.V. Sutton site (Powell, 2016). The solid black line represents
the location where measured and estimated values would plot if in perfect agreement.
4

References
Powell, B. A. (2016). Analysis of geochemical phenomena controlling mobility of ions from coal ash
basins at the Duke Energy L. V. Sutton Energy Complex. Wilmington, NC.
Summ, W.; Morgan, J.J., Aquatic Chemistry: Chemical Equilibria and Rates in Natural Waters. 3" ed.;
Wiley-Interscience: Chicago, 1996; P 1040.
Tinnacher, R.M.; Honeyman, B.D., Theoretical analysis of kinetic effects on the quantitative comparison
of K-d values and contaminant retardation factors. Journal of Contaminant Hydrology 2010, 118,
(1-2), 1-12.
Zhu, C., Geochemical Modeling of Reaction Paths and Geochemical Reaction Networks. Reviews in
Mineralogy and Geochemistry 2009, 70, 533-569.
0