NC0038377_3b-Mayo May 22, 2015 response to DENR conditional approval_20150902

DUKE
526 South Church street
Charlotte' NC 28202
ENERGY.
Mailing Address
P.O. Box 1006
Mai! Code EC13K
Charlotte, NC 28201-1006
May 22, 2015
980373.3719
704-382.6240 (fax)
Mr. Eric Rice
NC DENR Raleigh Regional Office
1628 Mail Service Center
Raleigh NC, 27699-1628
RE: Mayo Stearn Electric Plant
Revised Groundwater Assessment Work Plan
Duke Energy Progress, Inc. Response to DENR' Conditional Approval dated March 6, 2015
Dear Mr. Rice:
Duke Energy Progress, Inc. (DEP) is in receipt of the Department of Environment and Natural Resources
(DENR) Conditional Approval letter referenced above for the Mayo Steam Electric Plant. The purpose of
this letter is to provide a response to your bulleted comments within the Conditional Approval letter.
Below are DEP's responses to DENR's comments (in italics) from the Conditional Approval letter:
• Comment Section 5.3 Hydrogeologic Site Characteristics:
Information needed to develop the initial site conceptual site model was available in the
revised GAP, but for the most part data were not provided in a clear, cohesive manner to
illustrate where data gaps may exist. Duke Energy should incorporate all existing data at the
site and be prepared to collect additional data if the Division determines that additional
data gaps exist. Continued site conceptual model development should follow guidelines
similar to those presented in the American Standards Testing Measures E1689 - 95(2014)
Standard Guide for Developing Conceptual Site Models for Contaminated Sites to direct data
collection, data interpretation, and model development efforts.
The operations and processes related to building materials manufacturing at the nearby
Louisiana Pacific Corporation facility located upgradient of the Mayo Steam Electric Plant
should be considered in conceptual model development as well as groundwater flow and
transport models. Possible groundwater monitoring and water supply well production at this
facility should be documented and incorporated into the site assessment.
Response: The referenced guidance document and information requested on the adjoining
facility will be incorporated into the Comprehensive Site Assessment report (CSA) to the extent
practical.
* Comment 6.1 Compliance Monitoring Well Groundwater Analytical Results and 6.2
Preliminary Statistical Evaluation of Results
Well BG -1 and BG -2 may not be suitable locations for background wells because of their
proximity to plant activities, US Highway 501, former Highway 501, the railroad, and
Possible influence from pumping from former production wells DEP 2 and 3. The detections

Mr. Eric Rice
May 22, 2015
of constituents of potential concern in these wells, in particular well BG -1, may be related to
anthropogenic impacts rather than naturally occurring conditions. Proposed monitoring well
cluster MW-13S/BR and possibly monitoring well cluster MW-12S/BR should provide
suitable background monitoring locations, however, it should be noted at least 8 rounds of
data are needed to conduct a valid statistical evaluation of background groundwater
conditions.
Response: Agreed. It is understood that a sufficient number of sampling events for statistical
evaluation of background concentrations will not occur before the CSA report is submitted. The
goal will be to complete this activity in 2016.
• Comment 7.1.1.1 Borings Within the Ash Basin
The Division recommends that wells be installed in the partially weathered rock, or
transition zone, and bedrock at the 2 locations within the ash basin currently planned to
characterize bedrock if feasible and warranted by site conditions. The Division recommends
that wells installed through the ash basins into native materials are doubled cased to
protect well integrity.
Response: Agreed. DFP will install the wells at additional depths if there is a sufficient
saturated thickness of partially weathered rock or transition zone at these locations. A
combination of the sonic steel temporary casing and permanent PVC surface casings will be
used to protect well integrity for the wells drilled into and through the ash basins. The attached
updated Figure 5 shows the locations for additional wells ABMW-2D, ABMW-2BR, ABMW4D &
ABMW-4BR along with minor relocations of other wells which have been reviewed and
confirmed by DENR. Also note the ABMW-1 location will only have the one ash pore water well
installed using a hand auger due to the instability of the ash precluding the installation of
deeper wells below the ash. An attempt will be made to install a pore water well and a shallow
aquifer well at ABMW-3 if ash stability allows installation using a drilling rig. Alternatively, only
an ash pore water well may be installed at this location.
• Comment 7.1.1.2 Borings Outside Ash Basin
The Division recommends installing a soil boring to characterize native materials in the
topographic low below the ash basin dam.
Response: Agreed, please see attached map for soil boring SB -7 in this area.
• Comment 7.1.2.3 Proposed Monitoring Wells Downgradient or Sidegradient of the Ash
Basin
Figure 5 of the report depicts MW -7S and MW-7BR located inside the compliance boundary.
The well locations should be relocated to an area at the compliance boundary or outside the
compliance boundary but in the same general location proposed in the work plan.
Response: Agreed. Attached updated Figure 5 shows the DENR agreed upon relocations for
wells MW -7S and MW-7BR. Note that saturated saprolite was not encountered at this
2

Mr, Eric Rice
May 22, 2015
location. However, saturated transition zone material was encountered. As a result, MW -7D
was installed rather than MW -7S. This is consistent with the work plan allowing adjustments
to well installations and designations based upon observed field conditions. The 'S'
designations on the work plan map are intended to be placeholders for well clusters to be
installed above competent bedrock based upon observed conditions at the time of drilling. 'S'
and/or 'D' wells may or may not be installed within these clusters depending upon the depth
of competent bedrock and the first occurrence of groundwater.
• Comment Section 7.1.4 Hydrogeologic Evaluation Testing
Since no hydraulic conductivity data is available for Mayo Plant, hydraulic tests in a subset
of existing wells is recommended. In addition, vertical hydraulic conductivities in the ash and
saprolite will be determined in accordance with ASTM Standard D-5084 from samples
collected in Shelby tubes for geotechnical analysis. The borings where these samples are
collected in Shelby tubes will be based on site-specific conditions encountered during the site
assessment. These test results will provide a more robust dataset to characterize site
conditions and refine the flow and transport models.
Response: Agreed. Initial drilling operations have indicated a very thin (< 10 —15 feet thick)
mantle of unconsolidated soil/saprolite above PWR/bedrock. This unconsolidated material is
very granular with abundant rock fragments. Initial attempts to collect Shelby Tubes in this
material have been unsuccessful. Continued attempts will be made. Considering the possibility
of limited success in acquiring Shelby Tubes in the unconsolidated material, slug tests will be
conducted for all the existing site monitoring wells (10 compliance wells and 3 voluntary wells).
• Comment Section 7.2 Ash Pore Water and Groundwater Sampling and Analysis:
Direction provided in the EPA Region 1 Cow Stress Purging and Sampling Procedure for the
Collection of Groundwater Samples from Monitoring Wells (2010) should be followed
strictly and any deviations from the procedure must be approved by the Division and
documented accordingly. For example, samples should not be collected until pH is stabilized
within f0.1 for three consecutive readings rather than # 0.2 written in the GAP.
Temperature and specific conductivity readings should stabilize within 3% for three
consecutive readings before samples ore collected instead of 10% noted in the GAP. Also
note that if the pumping rate is so low that the flow-through-cell/chamber volume cannot
be replaced in a 5 minute interval, the time between measurements should be increased
accordingly.
Speciation of inorganics from groundwater samples should be focused on wells strategically
located along flowpath transects. Collection of data along multiple flowpaths will refine the
assessment of water geochemistry and development of flow and transport models.
The Division recommends analyzing samples for radionuclides from wells CW -2 and CW -
20 instead of MW -3. Samples from these two locations will provide data from both the
transition zone and bedrock downgrodient of the facility along a flowpath transect.
3

Mr. Eric Rice
May 22, 2015
Responses: The request to strictly adhere to the EPA Region 1 sampling protocol will create
variations in protocol for the various sites since this comment has only been received for a
portion of the sites (for DEP, Raleigh Region only provided the above comment). A consistent
Protocol to be used for all sites is being developed and will be submitted under separate cover.
Speciation will be conducted along flowpaths as indicated.
Samples for radionuclides will be collected from wells CMW-2, CMW-2D and MW-11BR as a
background basis for comparison.
• Comment 7.9.2 Development of Kd Terms
It is expected that additional solid phase samples will be collected and analyzed for Kd
determination as well as physical properties at strategic locations along flowpath
transects. These data will refine the assessment of water geochemistry and development
of flaw and transport models.
Response: Agreed.
We also include updated Attachment 1. The included Attachment 1 may differ slightly from the version
included in the Conditional Approval. If you require any additional information or have any further
questions, please do not hesitate to contact us.
Respectfully submitted,
D. Edwin M. Sullivan
Manager, Waste & Groundwater Programs
att: Figure 5, Revision 1, Dated 4/27/15, Mayo Steam Electric Plant
Updated Attachment 1
cc: Richard Baker—Duke Energy
Herbert Lea — Duke Energy
Danny McCormick— Duke Energy
./John Toepfer— Duke Energy
Kathy Webb —SynTerra Corporation
4

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LOUISIANA PACIFIC CORPORATION
10475 BOSTON RD
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SOURCES:
1. 2010 AERIAL PHOTOGRAPH OF PERSON COUNTY,
NORTH CAROLINA WAS OBTAINED FROM NRCS
GEOSPATIAL DATA GATEWAY AT
http.//datagateway.nres. usda.goW
2. 2012 AERIAL PHOTOGRAPH OF HALIFAX COUNTY,
VIRGINIA WAS OBTAINED FROM NRCS GEOSPATIAL
DATA GATEWAY AT http.//datagateway.nres.usda.goW
3. 2014 AERIAL PHOTOGRAPH WAS OBTAINED FROM WSP
FLOWN ON APRIL 17, 2014.
4. DRAWING HAS BEEN SET WITH A PROJECTION OF
NORTH CAROLINA STATE PLANE COORDINATE SYSTEM
FIPS 3200 (NAD 83).
5. WELL SURVEY INFORMATION, PROPERTY LINE,
LANDFILL LIMITS AND BOUNDARIES ARE FROM ARCGIS
FILES PROVIDED BY S&ME AND PROGRESS ENERGY.
6. PARCEL BOUNDARIES WERE OBTAINED FROM PERSON
COUNTY (NC) GIS DATA AT http://gis.personcounty.net
7. 10ft CONTOUR INTERVALS FROM NCDOT LiDAR DATED
2007
https://connect.ncdot.gov/resources/gis/pages/cont-elev v2.aspx
8. VIRGINIA 10ft CONTOUR INTERVALS FROM USGS
TOPOGRAPHIC MAP OBTAINED FROM THE NRCS
GEOSPATIAL DATA GATEWAY AT
http.//datagateway.nres. usda.goW
NOTE:
1. CONTOUR LINES ARE USED FOR REPRESENTATIVE
PURPOSES ONLY AND ARE NOT TO BE USED FOR
DESIGN OR CONSTRUCTION PURPOSES.
GRAPHIC SCALE
500 0 250 500 1000
(IN FEET)
erra
148 River Street, Suite 220
Greenville, South Carolina 29601
864-421-9999
www.synterracorp.com
DRAWN BY: J. CHASTAIN DATE: 2014-12-15
CHECKED BY: J. WYLIE I DATE: 2014-12-15
PROJECT MANAGER: KATHY WEBB
LAYOUT NAME: FIG 5 (PROP MW AND SAMP LOC MAP)
DUKE
ENERGY
PROGRESS
MAYO STEAM ELECTRIC PLANT
10600 BOSTON RD
ROXBORO, NORTH CAROLINA
FIGURE 5
PROPOSED MONITORING WELL AND
SAMPLE LOCATION MAP
REVISION 1 (2015-04-27)
LEGEND
MW -1707-1
PROPOSED SOIL BORING AND MONITORING
MW-17RR
WELL LOCATION
o ABMW-1
PROPOSED ASH BORING, PORE WATER, AND
ABMW-1S
GROUNDWATER MONITORING WELL LOCATION
® SB -2
PROPOSED SOIL BORING LOCATION
SW-CB1
PROPOSED SURFACE WATER AND
SEDIMENT LOCATION
A— —A'
PROPOSED GEOLOGIC CROSS SECTION
BG -1
BACKGROUND MONITORING WELL (SURVEYED)
MW -5
COMPLIANCE MONITORING WELL (SURVEYED)
FM—W-3-1
MONITORING WELL (APPROXIMATE)
PZ -3
PIEZOMETER (APPROXIMATE)
DEP 1
DUKE ENERGY PROGRESS PRODUCTION
WELL - NOT IN SERVICE (APPROXIMATE)
EDR 1
EDR REPORTED SUPPLY WELL (APPROXIMATE)
O S-01
SEEP LOCATION
- NPIDES
OUTFALL
OUTFALL 001
NPDES OUTFALL
DUKE ENERGY PROGRESS
500 ft COMPLIANCE BOUNDARY
MAYO CREEK
WASTE BOUNDARY
PARCEL LINES
--
FLOW DIRECTION
GENERALIZED GROUNDWATER FLOW
DIRECTION
_ p _
SUPPORTED BY GROUNDWATER ELEVATION DATA
POINTS OR TOPOGRAPHIC DATA
(o y
REVISED LOCATIONS
moil Pill 11 11
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M y
-
SOURCES:
1. 2010 AERIAL PHOTOGRAPH OF PERSON COUNTY,
NORTH CAROLINA WAS OBTAINED FROM NRCS
GEOSPATIAL DATA GATEWAY AT
http.//datagateway.nres. usda.goW
2. 2012 AERIAL PHOTOGRAPH OF HALIFAX COUNTY,
VIRGINIA WAS OBTAINED FROM NRCS GEOSPATIAL
DATA GATEWAY AT http.//datagateway.nres.usda.goW
3. 2014 AERIAL PHOTOGRAPH WAS OBTAINED FROM WSP
FLOWN ON APRIL 17, 2014.
4. DRAWING HAS BEEN SET WITH A PROJECTION OF
NORTH CAROLINA STATE PLANE COORDINATE SYSTEM
FIPS 3200 (NAD 83).
5. WELL SURVEY INFORMATION, PROPERTY LINE,
LANDFILL LIMITS AND BOUNDARIES ARE FROM ARCGIS
FILES PROVIDED BY S&ME AND PROGRESS ENERGY.
6. PARCEL BOUNDARIES WERE OBTAINED FROM PERSON
COUNTY (NC) GIS DATA AT http://gis.personcounty.net
7. 10ft CONTOUR INTERVALS FROM NCDOT LiDAR DATED
2007
https://connect.ncdot.gov/resources/gis/pages/cont-elev v2.aspx
8. VIRGINIA 10ft CONTOUR INTERVALS FROM USGS
TOPOGRAPHIC MAP OBTAINED FROM THE NRCS
GEOSPATIAL DATA GATEWAY AT
http.//datagateway.nres. usda.goW
NOTE:
1. CONTOUR LINES ARE USED FOR REPRESENTATIVE
PURPOSES ONLY AND ARE NOT TO BE USED FOR
DESIGN OR CONSTRUCTION PURPOSES.
GRAPHIC SCALE
500 0 250 500 1000
(IN FEET)
erra
148 River Street, Suite 220
Greenville, South Carolina 29601
864-421-9999
www.synterracorp.com
DRAWN BY: J. CHASTAIN DATE: 2014-12-15
CHECKED BY: J. WYLIE I DATE: 2014-12-15
PROJECT MANAGER: KATHY WEBB
LAYOUT NAME: FIG 5 (PROP MW AND SAMP LOC MAP)
DUKE
ENERGY
PROGRESS
MAYO STEAM ELECTRIC PLANT
10600 BOSTON RD
ROXBORO, NORTH CAROLINA
FIGURE 5
PROPOSED MONITORING WELL AND
SAMPLE LOCATION MAP
REVISION 1 (2015-04-27)

Attachment 1
Page 1 of 6
Duke Energy GAP Review Issues
The items identified in this Groundwater Assessment Plan (GAP) review summary are provided for
general discussion for the various parties to agree upon technical direction and content in the revised
GAPS, comprehensive site assessments (CSAs), and corrective action plans (CAPs).
Groundwater Monitoring
1. A schedule for continued groundwater monitoring is mandated by the Coal Ash Management
Act 2014. An interim plan should include at least two rounds of groundwater samples collected
and analyzed in 2015. The analytical results of the first round of data collected in 2015 would be
included in the CSA report, while the results of the second round would be submitted as a CSA
addendum. After CSA data can be evaluated, a plan for continued groundwater monitoring can
be developed for implementation in 2016.
2. Sites impacted by inorganics are typically managed using a tiered site analysis which includes
four elements as referenced in EPA/600/R-07/139:
Demonstration of active contaminant removal from groundwater & dissolved plume
stability;
i Determination of the mechanism and rate of attenuation;
• Determination of the long-term capacity for attenuation and stability of immobilized
contaminants, before, during, and after any proposed remedial activities; and
Design of performance monitoring program, including defining triggers for assessing
the remedial action strategy failure, and establishing a contingency plan.
This reference and the framework described above should be used as applicable to meet
the corrective action requirements found in 15A NCAC 02L.0106.
3. Because of uncertainty concerning the site's ability to attenuate contaminants over the long
term given potentially changing geochemical conditions, there is a need to address the elements
of the tiered site analysis described above and collect appropriate samples as part of the CSA,
CAP development, and continued groundwater monitoring.
4. The Division of Water Resources (Division) Director is responsible for establishing background
levels for COPCs in groundwater. This determination is based on information and data provided
by the responsible party and may include formal statistical testing using background wells with
at least four rounds of data. Wells identified as "background" are subject to periodic review
based on a refined understanding of site chemistry and hydrogeologic conditions. In general,
each facility must have a background well or wells screened or open to each of the dominant
flow systems that occur at the site and are associated with groundwater contamination. Any
questions concerning adequacy of background monitoring locations or conditions at the
facilities should be directed to the Regional offices.

Attachment 1
Page 2 of 6
5. Delineation of the groundwater contaminant plume associated with coal combustion residuals is
a requirement of the investigation and if off-site monitoring wells are ultimately required to
perform this task, then it is expected that these activities will be completed as part of the
groundwater assessment activities and included in the final report. Documentation of the effort
to gain off-site access, or right of way permits, will be provided if off-site access is denied or
alternate means of assessing the area were not available within the allocated timeframe (such
as within right-of-ways).
Site Assessment
Data Requirements and Sampling Strategy
1. Robust data collection is warranted to support timely completion of site assessments and
subsequent corrective action plans because of the impending deadlines for completion of CSAs
and CAPs, scale and geologic complexity of the sites, the challenges of modeling heterogeneous
systems, and site proximity to potential human and sensitive ecosystem receptors.
2. Robust data collection will be focused along strategically positioned flowpath transect(s) -from
ash pond source to potential receptor—as an efficient approach for model development
(analytical, geochemical, groundwater flow, and transport) in support of risk assessment and
CAP development. Data collected to support evaluation of site conditions along the flowpath
transects should be located along or defensibly proximate to the modeled transects.
3. The dataset developed along proposed flowpath transects shall include any information needed
to determine constituent concentrations, conduct Kd tests, and perform batch geochemical
modeling in multiple flow horizons as appropriate. This data will include a) solid phase sample
collection for Kd measurement and batch geochemical modeling, inorganic analysis and
speciation, and other parameters identified in General Comment #4 of the November 4, 2014
GAP comments issued by DWR, b) solution phase sample collection for total and dissolved
inorganic analysis of total concentrations, small pore filtration for dissolved samples, etc., and c)
slug, constant/falling head, and packer testing. The solid phase sample mineralogy, total
concentration results, re-dox measurements, and other geochemical parameters will be used as
input for equilibrium speciation calculations of redox sensitive constituents calculated by
PHREEQC or similar program (EPA/540/S-92/018). This geochemical modeling will be performed
to identify potential mineral phases, estimated species speciation and concentrations, and will
be performed varying key solubility controlling ,parameters to predict mineral phases,
speciation, and concentrations under varying conditions. Solid samples for Kd tests collected
from along from proposed flowpath transects will be handled and preserved in order to
eliminate exposure to ambient air in the field. Kd samples should be collected in plastic bags
and sealed with a conventional vacuum plastic bag sealer. The samples will be then placed on
ice in a cooler for transport and kept out of direct sunlight. Once received by the analytical
laboratory, the Oxidation -Reduction Potential (ORP) of the sample will be measured using an
ORP probe and meter in accordance with ASTM method G200-19 (Reapproved 2014). Based on
this ORP measurement, either normal or "glove -box" processing of a sample will be applied

Attachment 1
Page 3 of 6
(EPA/600/R-06/112). An additional sample will be retained, pending confirmation of subsequent
ORP and DO testing. ORP and dissolved oxygen will be measured in the groundwater monitoring
wells subsequently installed at these sample locations. In the event that the groundwater field -
measured ORP and DO reveal reducing conditions, the additionally -retained sample will be
subject to glove box processing for the Kd analyses. Refer to EPA/600/R-07/139 Section III for
the data collection and characterization needed to support the four -tiered analysis discussed
above.
4. Speciations for groundwater and surface water samples should include Fe, Mn, and any COPCs
whose speciation state may affect toxicity or mobility (e.g. As, Cr, Se, or others if applicable).
This speciation will apply for groundwater samples collected at wells located along proposed
flowpath transects and in wells where these constituents exceed 2L groundwater standards as
well as for surface water samples collected within ash impoundments.
5. Solid phase samples shall be analyzed for: minerals present, chemical composition of oxides,
hydrous Fe, Mn, and AL oxides content; moisture content; particle size analysis; plasticity;
specific gravity; porosity; permeability, or other physical properties or analyses needed to
provide input to a chosen model. These analyses for physical properties will be conducted at up
to 15 locations along proposed flowpath transects where Kd samples are collected. Solid phase
samples at up to 15 additional locations will be collected and analyzed for hydrous ferric oxide
(HFO) content. At these additional locations where HFO content is analyzed, analyses for
physical properties will not be performed. Solid phase samples will be analyzed for total organic
content from the same locations where samples are collected for Kd determination. Solid phase
samples will be analyzed for total organic carbonate content from the same locations where
samples are collected for Kd determination only at facilities located in the coastal plain.
6. In addition to conducting the SPLP leachable inorganic compounds analysis for selected ash
samples to evaluate the potential for leaching of constituents to groundwater, the leachable
analysis should also be conducted for some soil samples from locations beneath the ash ponds,
within the plume, and outside the plume to evaluate potential contributions from native soils.
7. In addition to collecting solid phase samples onsite for Kd procedures, soil samples should be
also collected from unaffected soils within groundwater flow pathways to evaluate Kd(s) or
hydrous ferrous oxide.
8. Rock samples for laboratory analyses should be collected as commented in General Comment 4
of the November 4, 2014 GAP comments issued by DWR. This GAP review comment indicated
that the sample(s) collected from bedrock well soil and rock cores shall be analyzed, at a
minimum, for the following: type of material, formation from which it came, minerals present,
chemical composition as oxides, hydrous Fe, Mn, and Al oxides content, surface area, moisture
content, etc.; however, these analyses were not mentioned in the GAP. The Division reserves
the right to request analysis for organic carbon content, organic carbonate content, and ion
exchange capacity if needed to complete the site assessment process.
9. The coal ash and soil analyte lists should match the groundwater analyte lists.
10. Total uranium analysis should be analyzed where total radium is analyzed for groundwater.

Attachment 1
Page 4 of 6
11. If analytical results from a seep sample exceed 2L standards, then the area in the vicinity of the
sample location should be investigated for groundwater contamination. If analytical results
from a surface water sample exceed 2B standards, then the area in the vicinity of the sample
location should be investigated for groundwater contamination.
12. Surface water/seep samples should be collected during baseflow conditions and the
groundwater monitoring (water levels and sampling) should occur at about the same time.
13. Measurement of streamflow in selected perennial streams is expected as needed in support of
simulation/calibration of flow and transport models; major rivers that serve as groundwater
divides are not included in this expectation.
Conceptual Model Elements
1. In the CSA report, data gaps remaining should be specifically identified and summarized.
2. Site heterogeneities should be identified and described with respect to: a) their nature, b)
their scale and density, c) the extent to which the data collection successfully characterizes
them, d) how the modeling accounts for them, e) and how they affect modeling uncertainty.
3. The impact of data gaps and site heterogeneities should be described in relation to the
elements developed in the Site Hydrogeologic Conceptual Model and Fate and Transport
Model subsections.
4. For sites in the Piedmont or Mountains, the CSA Report should include a subsection within the
Site Geology and Hydrogeology Section titled `Structural Geology'. This section should
describe. a) foliations, b) shear zones, c) fracture trace analysis, and d) other structural
components anticipated to be relevant to flow and contaminant transport at the site.
5. Duke Energy will include a poster -sized sheet(s) (ANSI E) combining tabulated analytical
assessment results (groundwater, surface water, and leachate samples); multiple sheets may
be needed to present the data. This should be provided in addition to the individual analytical
results tables that will be prepared for the CSA reports. Any questions concerning format or
content of the analytical result summaries should be directed to the Regional offices.
Geochemical Modeling
1. The Division agrees that a geochemical model "coupled" to a 3-D fate and transport model is
inappropriate given the size and complexity of the sites and the extremely large amount of data
required to calibrate such a model. Rather, a "batch" geochemical model approach should be
sufficient for successfully completing the site assessment and/or corrective action plan.
2. Samples collected for "batch" geochemical analysis should be focused along or defensibly
proximate to flowpath transects.
3. To support successful batch geochemical modeling, dissolved groundwater samples collected
along a contaminant flowpath transect should be obtained using a 0.1 um filter. This will help
ensure a true dissolved phase sample. Note that the dissolved samples are for assessment
purposes only and may not be used for purposes of compliance monitoring. If there is
uncertainty about which areas/wells will be used in the batch geochemical modeling, the initial
round of assessment sampling at the facility can utilize the 0.45 um filter until the contaminant

Attachment 1
Page 5 of 6
flow path transects are selected. Once determined, Duke Energy can go back and re -sample the
wells needed for geochemical modeling using the 0.1 um filter. It is recognized that the use of a
0.1 um filter will be difficult for wells with elevated turbidity; in this case, it is recommended
that Duke Energy use two filters in series (the water initially passes through a 0.45 um filter to
remove larger particles prior to passing through the 0.1 um filter). Information for a disposable
0.1um field filter designed specifically for sampling groundwater for metal analysis is provided at
the following link: http://www.vosstech.com/index.php/products/filters. If field comparisons of
0.1 versus 0.45 micron filtration at several transect wells at a given site show no significant
differences between the two methods, then 0.45 micron filters may be used for evaluating the
dissolved phase concentrations at that site.
4. In support of the objectives of General Comment #2 of the November 4, 2014 GAP comments
issued by DWR, Duke Energy should add a column titled 'relative redox' to the analytical results
tables to record the geochemical conditions for that location/sample date. The redox
determination should be based on observed DO, ORP, and any other relevant measures and
presented for historic and new samples (wells, ash pore water, surface waters, etc.). Relative
redox designations may include "iron reducing", "sulfate reducing", mildly oxidizing, moderately
oxidizing, etc. and should be footnoted with a statement about the degree of confidence in the
designation based on amount and quality of available data.
5. Duke Energy shall also evaluate: a) spatial geochemical trends across the facility and along
selected flow paths, b) temporal geochemical trends where observable (such as for compliance
boundary wells), along with the likely reason for the change (e.g. increase in seasonal recharge,
pond de -watering and subsequent reversal of groundwater flow direction, inundation of well
from river at flood stage, etc.) in support of the CAP. This evaluation step will require a
comparison of geochemical conditions overtime with rainfall data, notable ash capping,
dewatering, disposal/removal, or other plant operations, etc. The quality of existing
geochemical data will be evaluated using field notes, calibration records, and consistency in
redox measurements (e.g. eH vs. raw ORP).
Groundwater Models
1. The technical direction for developing the fate and transport modeling will follow guidelines
found in Groundwater Modeling Policy, NCDENR DWQ, May 31, 2007, and discussions
conducted between Duke Energy and their consultants with the Division. Ultimate direction for
completion of fate and transport models will be provided by the Division.
2. The CAP Report should include a subsection within Groundwater Modeling Results titled 'Site
Conceptual Model' that succinctly summarizes, for purposes of model construction, the
understanding of the physical and chemical setting of the site and shall include, at a
minimum: a) the site setting (hydrogeology, dominant flow zones, heterogeneities, areas of
pronounced vertical head gradients, areas of recharge and discharge, spatial distribution of
geochemical conditions across the site, and other factors as appropriate), b) source areas and
estimated mass loading history, c) receptors, d) chemical behavior of COPCs, and e) likely

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retention mechanisms for COPCs and how the mechanisms are expected to respond to changes
in geochemical conditions.
3. Modeling will be included in the Corrective Action Plan (CAP). The four -tiered analysis
previously referenced and appropriate modeling should be conducted, and the mass flux
calculations described in the EPA/600/R-07/139 should be performed.
4. The CAP Report shall provide separate subsections for reporting groundwater flow models and
fate and transport models.
5. The CAP Report should include subsections within Groundwater Modeling Results titled
'Groundwater Model Development' that describes, for each chosen model: a) purpose of model,
built-in assumptions, model extent, grid, layers, boundary conditions, initial conditions, and
others as listed in Division guidance. Include in this section a discussion of heterogeneities and
how the model(s) account for this (e.g. dual porosity modeling, equivalent porous media
approach, etc.). Separate subsections should be developed for the groundwater flow model,
fate and transport model, and batch geochemical models, respectively.
6. CAP Reports should include a subsection within Groundwater Modeling Results titled
'Groundwater Model Calibration' that describes, for each model used, the process used to
calibrate the model, the zones of input and calibration variables (for example, hydraulic
conductivities) that were used, the actual (measured) versus modeled results for all key
variables, and others. Separate subsections should be developed for the groundwater flow
model, fate and transport model, and batch geochemical models), respectively.
7. CAP Reports should include a subsection within Groundwater Modeling Results titled
'Groundwater Model Sensitivity Analysis' that describes, for each model used, the process used
to evaluate model uncertainty, variable ranges tested, and the key sensitivities. Separate
subsections should be developed for the groundwater flow model, fate and transport model,
and batch geochemical model(s), respectively.
Development of Kd Terms
1. Kd testing and modeling in support of CAP development should include all COPCs found above
the NCAC 15A 02L .0106(8) standards in ash leachate, ash pore water, or compliance boundary
well groundwater samples.
2. The selected Kd used in transport modeling often will profoundly affect the results. Duke
Energy should acknowledge this concept and document within the transport modeling section(s)
of the CAP all widely recognized limitations inherent in the estimation of the Kd term.
Risk Assessment
1. Provide references for guidance and potential sampling methodology related to conducting a
baseline ecological risk assessment or habitat assessment, if warranted.