NC0022406_Belews Creek 60% BOD Comments_20170630

Water Resources
Environmental Quality
June 30, 2017
Ed Sullivan
Duke Energy
526 South Church Street
Mail Code EC13K
Charlotte, North Carolina 28202
Subject: 60% Basis of Design Report Comments
Belews Creek Steam Station
Dear W. Sullivan:
ROY COOPER
Governor
MICHAEL S. REGAN
Secretary
S. JAY ZMMERMAN
Director
On April 10, 2017, the North Carolina Department of Environmental Quality's Division of Water
Resources (Division) received the 60% Basis of Design (BOD) Report for the subject facility.
Division staff from the Winston-Salem Regional Office have reviewed the BOD Report and offer
the following comments:
Basis of Design 60% Submittal Comments
1) Based on the Settlement Agreement signed between DEQ and Duke Energy signed on
September 29, 2015 and test results to date, the primary objective of the interim action
conducted at the facility should be the reduction of groundwater migration of source area
constituents from the ash basin. In Section 1. 1.4 Scope and Objectives of the 60% Basis
of Design Report, the primary objective is further clarified as being "to reduce
groundwater migration of source area constituents from the ash basin towards the 2.23 -
acre parcel and remove constituent mass from the area of highest constituent
concentrations."
The information presented in the 60% BOD Report indicates the saprolite and transition
zone along the extraction well network will be dewatered, causing a gradient reversal,
and provide hydraulic control of source area constituents. Reduction of constituent mass
is unlikely due to changes in flow direction and the likely intermittent operation of the
extraction wells; however, the objective of boundary control should be achieved.
Reduction of constituent mass in groundwater should not be considered as a primary
metric for overall system effectiveness. Instead, reduction of plume distribution,
especially proximal to the extraction well network, along with confirmation of boundary
control, should be the focus for monitoring system performance. These concepts
concerning the primary objective of extraction system operation and the anticipated
resulting site conditions should be reflected in the Final BOD Report.
State of North Carolina I Environmental Quality I Division of Water Resources
Water Quality Regional Operations Section
1636 Mail Service Center I Raleigh, North Carolina 27699-1636
919-707-9129

2) Acknowledging the limitations of testing to date, the Division encourages additional
characterization and testing following Phase I implementation to evaluate concerns related
to potential preferential pathways in the study area, variable flow directions that may
develop because of pumping, and confirmation of boundary control. In summary, the
Division believes additional work is likely needed to facilitate optimization of system
operations as mentioned in the 60% BOD Report. Related information is expected in detail
as part of the Final'BOD Report
3) In -Situ Chemical Immobilization was evaluated as an effective approach in Appendix B
but was not mentioned in Section 3.2. Please expand on why this remedial alternative
would not be effective or should not be considered for the area up -gradient of Parcel A in
the Final BOD Report.
4) The report indicated that the initial extraction system will be monitored for a six-month
period after initial startup to determine system efficiency. Please provide additional
details regarding the effectiveness monitoring program (e.g. monitoring wells, monitoring
frequency, parameters, etc.) in a table in the Final BOD Report.
5) Please provide well specifications such as depth, diameter, etc., for the two proposed
observation wells and other wells if determined to be needed in the Final BOD Report.
6) Regarding Appendix C, on page 4-1, the second to last paragraph states, "The lower limit
of the model domain coincides with an assumedmaximum depth ofwater yieldingfractures
in bedrock This was estimated to be approximately 710 feet below the base of the
transition zone. " What is the basis for this specific depth selected as the base of water -
yielding fractures in the model domain?
7) Table 1-1 should list all the constituents of interest (COIs) detected in groundwater within
the study area, not just boron, chloride, and selenium. In Section 2.2.2 Summary of HDR
Recent Groundwater Quality Results, exceedances of 02LStandards provided are confined
to the upper two zones, not including reporting exceedances present in the bedrock.
Elevated concentrations of antimony, arsenic, chromium, and vanadium were detected in
downgradient bedrock well GWA-2713R. These constituents were also detected above 02L
Standards in bedrock well GWA-20 BR located between the ash basin and Parcel A.
However, there are no monitoring wells in bedrock within Parcel A, which does not mean
02L exceedances are not present in bedrock. This should be considered as part of the
modeling effort.
8) Only boron, chloride, and selenium are modeled for the interim action while there are
several other COIs that impact groundwater in the study area, including antimony, arsenic,
beryllium, chromium, hexavalent chromium, cobalt, thallium, and vanadium. These latter
COIs should also be simulated to provide predictions of site conditions resulting from this
interim action.
Paas 7 of A

Appendix D Updated Geochemical Modeling Report Comments:
1) General Comments
a) The focus of the review comments provided here address Attachment A
Geochemical Model Development Focused Geochemical Modeling Report.
These comments are intended to provide a basis for revised Focused Area Model
development and reporting for Parcel A.
b) Project purpose, scope, and objectives of the geochemical modeling effort to
support the Basis of Design Report should be clearly defined in the introduction
of the revised Focused Geochemical Model Parcel A. The discussion in
subsequent sections, including the Summary section, should reflect how the
geochemical model provides information for the evaluation of remediation
options that address task objectives.
c) Geochemical modeling conducted to evaluate remedial alternatives should focus
on providing qualitative assessments of geochemical conditions and constituent
mobility that may result from implementation of the interim action using site-
specific data rather than making projections from data from other sites,
particularly those data obtained from sites with different geologic and
geochemical settings.
2) Specific Comments concerning Attachment A Geochemical Model Development
Focused Geochemical Modeling Report
a) Page A-1. "Equilibrium constants for aqueous speciation reactions were taken
from the USGS WATEQ4F database. This database contained the reactions for
most elements of interest except for Co, Sb, V, and Cr. Constants for aqueous
reactions and mineral formation for these elements were taken from the MINTEQ
v4 database which is also issued with PHREEQC." Why not just use the
MINTEQ v4 database that contains reactions for all the elements of interest?
b) Page A-1. "(Adsorption) Constants for Co, V, Cr, and Sb were added to the
modified database as well as all constants involving ion sorption to HAO". What
were the sources of these constants for BFO and HAO? The MINTEQ v4
database has sorption constants for HFO, but not HAO.
c) Page A-3. "Therefore, attempting to delineate between mineral surfaces, let alone
strong and weak sites on such surfaces, would add unnecessary uncertainty and
fitting parameters to the models. Therefore, sorption to only one site on both BFO
and HAO is considered." What type of site was considered and why?
Page 3 of 6

d) Page A-4. "This approach uses the total Fe and Al solid phase concentrations in
specific wells to identify how much sorbent is available."
L What is meant by "total Fe and Al solid phase concentrations"? Was )MF
analysis used to measure Fe and Al in the solid phase? Was an extraction
technique used to dissolve Fe and Al from the solid phase? If so, what was
the extraction method?
ii. What is the rationale for assuming that all of the solid Fe and Al is present
as ferrihydrite and gibbsite? This is unlikely to ever be the case in a
natural system.
e) Page A-4. "The utility of the EQUILUIBRIUM_PHASES command, in this case,
is that it can provide the total number of sorption sites to produce HFO and HAO,
and it is linked to the stability of the gibbsite and ferrihydrate solid phases which
are used to approximate the sorption sites." The spelling of the iron adsorbent
ferrihydrite is misspelled as ferrihydrate in this sentence and all subsequent uses
of the word.
f) Page A-4. "The utility of the EQUILUIBRIUM_PHASES command, in this case,
is that it can provide the total number of sorption sites to produce HFO and HAO,
and it is linked to the stability of the gibbsite and ferrihydrate solid phases which
are used to approximate the sorption sites. So in effect, the model is calculating
the aqueous concentrations of Fe(II), Fe(III), and AI(III) as well as moles of
gibbsite and ferrihydrate by combining the total aqueous Fe and Al concentrations
from well measurements with the total Fe and Al available as solid phases
measured from wells with solid phase data available (listed in Table A-2)." What
does it mean that the model is calculating these values? Aren't they being input by
the user? A PHREEQC input file for this calculation should be provided to clarify
how adsorption is being modeled.
g) Page A-6. "For partially weathered rock of the transition zone, the fracture's pore
volume available for adsorption surface reactions is decreased by lowering the
porosity of the material... The resulting solid phase concentration of 32 kg/L
accounts for the high density of transition zone material." This method likely
vastly overestimates the concentration of adsorption sites associated with the
fractures. Only the solid phase present along a fracture is available for adsorption,
not the entire mass of solid associated with each liter of water. Defensible
assumptions should be developed concerning modeling geochemical conditions in
the transition zone and bedrock.
h) Page A-9. Groundwater Data Used in PHREEQC Model. Why isn't inorganic
carbon included as a major ion? Bicarbonate is a common major ion in shallow
groundwater.
Page 4 of 6

i) Page A-9. "A second modeling effort was undertaken to examine general
behavior of several constituents of interest under changing geochemical
conditions. This modeling effort is referred to as a global model because it
considers the range of ion concentrations, pH, Eh, and extractable Fe and Al
concentrations from seven coal ash disposal sites in NC. The results of this model
remain applicable to Belews Creek because nearby sites, Roxboro and Mayo,
used in the Global Model have similar onsite geology and geochemistry as
Belews Creek." The global model is setup in Section A.3 and parameters are
discussed in Section A.4, which includes data from the Weatherspoon, Sutton,
and H.F. Lee facilities located in the coastal plain in addition to data from the
Cape Fear facility that is in a Triassic Basin. Data from these four sites do not
represent those site conditions representative of the geology and geochemistry of
Piedmont crystalline bedrock and do not enhance model results. Geochemical
model development at this point should be focused on site-specific data.
j) Page A-11. "This is the approach used in the global model and the assumed solid
phase concentration was 50 g-solid/L-volume." What is the source of this value?
Why aren't the calculated values of 8 kg-solid/L-solution (unconsolidated
material) and 32kg-solid/L-solution (transition zone fractured material) on page
A-6 used in this equation? .
k) Page A-12. Note the large differences (> 1 Ox) in AI and Fe concentrations in
Table A-6 compared to Table A-2. Why were total concentrations used for the
Model 1 Belews Creek adsorption site concentrations, while extractable
concentrations were used in the global model? Comparing Tables A-3 and A-6;
the Al and Fe site concentrations for Model 1 are on the order of 100,000 times
greater than those for the global model. How were the "extractable"
concentrations of Fe and Al measured?
1) Page A-18. "The concentrations of major ions (e.g., Ca2+, Na+, Fe (IUIII), Cl-,
SO4 2-) were varied to consider the range of potential values. The concentrations
of several trace ions and constituents of interest were not varied so that the model
could examine the potential for competition for sorption sites between the varying
major ion concentration conditions and a fixed condition for the trace elements
(Table A-8)."
i. Trace ion adsorption maybe more competitive for the COI than major
ion adsorption.
ii. Also, why not use the actual trace concentrations for Belews Creek,
instead of an average for seven other sites?
m) Page A-22. "To gain an understanding of the aqueous chemical species of each
constituent of interest, Pourbaix diagrams were generated using Geochemist
Workbench (GWB) version I O.vlO. Instead of using generic groundwater data for
the missing plots, why not use specific Belews Creek data?
Page 5 of 6

If you have any questions, please feel free to contact Shuying Wang, Winston-Salem Regional
Office, at [phone] or Steve Lanter at [phone].
Sincerely,
4S26t, P.G., Director
Division of Water Resources
cc: Sherri Knight — WSRO Regional Office Supervisor
WQROS Central File Copy
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