NC0038377_2-Groundwater Assessment Work Plan Review comments_20150902

NCDENR
North Carolina Department of Environment and Natural Resources
Division of Water Resources
Pat McCrory John E. Skvarla, III
Governor Secretary
November 4, 2014
Mr. Harry Sideris
Senior Vice -President
Environment, Health, and Safety
Duke Energy
526 South Church Street
Mail Code EC3XP
Charlotte, NC 28202
RE: Duke Energy Progress, LLC
Mayo Steam Electric Plant
NPDES Permit No. N00038377 — Person County
Review of Groundwater Assessment Work Plan
Dear Mr. Sideris:
On September 26, 2014, the Division of Water Resources (Division) received the Groundwater
Assessment Work Plan (GAP) for the subject facility. The GAP was submitted in accordance
with the August 13, 2014, Notice of Regulatory Requirements (NORR) and G.S. 130A-
309.209(a)(1). After careful review, the Division has determined that the GAP is deficient in
detailing a strategy to achieve compliance with NCAC 15A 2L .0106(g), the NORR issued to
Duke, and (or) applicable general statutes. The plan as submitted fails to provide an adequate
level of detail regarding the planned assessment activities, which if left unchanged may lead to
an inadequate assessment of environmental conditions at the site. To assist you in drafting a
complete GAP, the Division offers you the following review comments which must be addressed
and incorporated into a revised groundwater assessment work plan. This review document is
separated into comments applicable to all previously submitted plans followed by comments
applicable to the referenced facility
General Comments Applicable to All Facilities
The Site Conceptual Model (SCM) section of the work plans does not provide sufficient
detail needed for the Division to adequately review the proposed data collection efforts.
The SCM section should include an "initial conceptual model" as described in
Groundwater Modeling Policy, May 31, 2007, page 6, paragraph 2, which states, "An
initial conceptual model should be developed from available regional and local .studies
and information [existing site data], and initial site visits before significant site -specific
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November 4, 2014
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data collection efforts are undertaken. This step is necessary to assure that adequate
types and quantities of'data are collected..." The initial conceptual model will be refined
or modified later in the process as a result of data collection. The refined or modified
model, the SCM, will then be used as the foundation upon which any numerical models
are developed for the site. Importantly, the initial conceptual model should identify data
gaps and provide the context and rationale, for the types and amounts of data collection
proposed in the work plans.
Refer to the Modeling policy, the Hydrogeologic Investigation and Reporting Policy
(May 31, 2007), and other pertinent references such as ASTM E1689-95, for the elements
expected in the initial conceptual model. Ensure also that the nature, sources, and sinks
of site contaminants of concern, along with their mobility, retention, and transport
characteristics are addressed.
2. The numerical modeling description presented in the GAP is inadequate. The draft GAP
states that fate and transport modeling will be conducted using MODFLOW and MT31)
or RT31), with very little supporting rationale or information identified to justify the use
of the chosen model or approach. Explaining the rationale for the chosen model type and
design (including the inputs that will be needed for the model) will help make site
assessment data collection more efficient and may highlight deficiencies in the initial
conceptual model.
To provide context and rationale for the chosen model(s) and proposed data collection
efforts, provide in the GAP, at a minimum, the following information:
a) the purpose of any proposed numerical modeling,
b) the question(s) the model will help answer,
c) basic information about the model (type, boundaries, layers, whether/how
site heterogeneities will be modeled, etc.),
d) a description of the partition coefficient (KA how, where, and at what
depths it will be derived, and how/whether it will adequately account for
the dominant mechanisms of contaminant retention,
e) whether stream flow measurements are needed for the model and, if so,
when, where, and how those would be measured,
f) model limitations, and
g) specific data gaps (types, general locations and depths, etc) that must be
filled in order to develop the model(s).
Refer to Groundwater Modeling Policy, May 31, 2007 for the elements expected in any
numerical model developed for the site.

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3. The proposed borings, core, and well installation work are inadequate to understand,
characterize, and (or) model subsurface conditions at the sites. For piedmont and
mountain sites, the GAP shall propose field work necessary to evaluate and document the
following:
a) presence/absence,
b) areal extent and depth/thickness,
c) flow and transport properties, and
d) heterogeneity of the following groundwater flow zones: alluvial/fluvial,
fill/residuum/saprolite, weathered rock (transition zone), and fresh,
competent fractured bedrock. Specifically, continuous core shall be
collected from land surface to a depth of at least 50 feet into fresh,
competent bedrock at a sufficient number of locations inside and outside
of ash basins to understand the flow system in areas proposed for
modeling and (or) areas of contaminant concern. All cores shall be
described/logged, photographed, and retained.
Data previously obtained from existing voluntary and compliance well borings and wells
shall also be used to understand and characterize the multipart flow system. Data
collection should also be sufficient for the development of any proposed numerical
models.
Note: Drilling and coring methods shall be used to prevent potential cross
contamination of flow zones, as stipulated in 15A NCAC 02C, and, where
applicable, to maintain structural integrity of dam.
4. Rather than abandoning the cored locations, consideration should be given to converting
borings to either a well nest/cluster or a piezometer nest/cluster. Nested/clustered wells
shall be open to each of the dominant flow zones through the use of appropriately sized
screens and discreet screened intervals and shall be installed to measure groundwater
quality and properties that may affect contaminant mobility and transport. If the boring is
not of sufficient diameter to install all of the necessary nested wells/piezometers, the
remaining wells/piezometers should be installed in the immediate vicinity.
In addition to the logging described in comment 3 above, each core location shall include
the collection of a solid phase sample at the following intervals:
a) immediately above the water table,
b) immediately below the water table,
c) within the saturated upper transition zone material (if not already included
in a) or b) above), and
d) from a primary, open, stained fracture within fresh bedrock, if these zones
exist.

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The sample(s) 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, organic carbon
content, organic carbonate content, cation exchange capacity, anion exchange
capacity, surface area, moisture content; particle size analysis, Atterberg limits,
specific gravity, porosity, permeability, and any other physical properties or
analyses that may be required to estimate a batch partition coefficient Kd or
otherwise serve as input to a chosen model.
In addition, total analytes (see comment 412), SPLP analytes (see comment # 12), and
speciation of selected inorganics shall be conducted for selected sample locations in
sufficient quantity and distribution to characterize the solid and aqueous chemistry and
geochemistry in locations and depths of contaminant concern, and this work shall be
clearly defined in the GAP. Inorganic speciation typically will include Fe and Mn, along
with others that may shed light on contaminant toxicity, mobility, and (or) prevailing
geochemical conditions. Sulfide and methane shall also be collected at selected locations
to evaluate geochemical conditions. Water and bed sediment samples from seeps and
streams shall be treated and analyzed in a manner consistent with the description above.
If a given analysis is believed to be unnecessary at a given location or depth based on site
conditions or assessment objectives, provide a detailed rationale for its omission for the
Division's consideration. In general, the collection strategy for ash samples from cores
inside of ash basins as described in the GAP appear to be adequate, along with the
proposed total and SPLP analyses. The need for additional core locations, where
applicable, is provided in the site -specific comment section below. Note that the chosen
numerical model(s), extent of contamination, and size of site shall drive the number,
distribution, and type of solid phase sample collection and analyses needed to understand
the retention and mobility of constituents of concern.
5, Duke shall describe the batch partition coefficient Kd, the individual inorganics that will
be tested, and whether multi -metals will be co -tested. Duke shall identify the
approximate number, distribution, and depths/flow zones of solid phase samples used to
derive the Kd(s) across the site.
6. The term "deep" as it relates to a well is subjective. For consistency and to avoid
confusion as to whether a deep well is open to transition zone material or competent
bedrock, please refer in all descriptions to each well as alluvial/fluvial, saprolite,
transition zone, or bedrock. If one or more of these zones are relatively thick, contain
more than one discreet flow zone, and should be thought of as "upper" and "lower", that
qualifying designation is also appropriate (for example, upper transition zone and lower
transition zone if the two intervals represent discreet flow intervals).
7, Surface water and bed sediment sampling are limited or are not proposed in the GAP.
The Division expects base flow surface water and bed sediment sampling to be included
in the site assessment and the GAP. These data will provide information on surface water

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quality and will be useful in efforts to understand the interaction of ground and surface
water at the site. Sample locations and distribution shall be based on site specific
considerations, but seepage areas, key tributaries, and ash ponds should be given special
emphasis. Surface water data collected by the Division during the March 2014 sampling
event, and existing ground and surface water data collected by Duke should be used in
the, sample design and site assessment.
It is expected that Duke conduct assessment work, including borings, wells, and surface
water/bed sediment sampling, ojfsite (outside of property boundaries) as needed for
adherence to 15A NCAC 02L.0106 (g)(4) and (or) for the evaluation of background
conditions. The plans as submitted do not adequately account for offsite assessment
work or provide a justification that offsite work is not needed. Proposed offsite
assessment locations should be described in the GAP.
9. It is expected that as data from wells, borings, and water samples are derived and
evaluated, Duke will identify and sample additional locations as needed to complete the
horizontal and vertical extent of impacts associated with coal ash to subsurface soils,
saprolite, bedrock, and the ground and surface water resources. These activities and
anticipated locations shall be proposed in the GAP and included in the assessment.
10. Please note that wells identified as "background" are subject to periodic review based on
an increased understanding of site chemistry and hydrogeologic conditions. If a well
currently identified or otherwise labeled as background does not, in fact, represent
background conditions, it shall be excluded from further consideration as "background".
The need for additional or replacement background wells shall be considered during site
assessment and (or) as outlined in the site specific comment section below. However, 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 that are associated with groundwater
contamination (e.g., alluvium, fluvial deposits, saprolite, transition zone, and (or)
competent bedrock). Each of these wells must represent ambient background conditions
unaffected by site or offsite activities. Offsite well placement will, in some cases, be
expected depending on the position and proximity of waste, compliance, and property
boundaries. At least four independent sampling events generally are needed for a well to
be used in formal statistical testing.
11. Quality control samples shall be proposed in the GAP. These shall include but are not
limited to, descriptions of field calibration procedures, collection of replicate
measurements, use of field blanks, use of "blind" quality control samples, etc.

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12. The analyte list for supply well sampling, compliance well sampling, and site assessment
sampling shall include, but is not limited to, the following:
Al, Sb, As, Ba, B, Be, Ca, Cd, Co, Cr, Cu, Fe, K, Pb, Mg, Mn, Mo, Hg, Na, Ni,
Se, Sr, Tl, V, Zn, Cl, SO4, total dissolved solids (TDS), alkalinity, bicarbonate,
carbonate, total suspended solids (TSS), turbidity, pH; temperature, specific
conductance (SC), dissolved oxygen (DO), oxidation reduction potential (ORP),
and water level (water level measurements in supply wells may be omitted if well
head hardware prevents ready access). In addition, total combined radium (Ra-
226 + Ra-228) shall be measured on at least one occasion in selected compliance
wells of highest concern at each facility. Note that 15A NCAC O2H. 0804 requires
certification for f eld parameters.
The GAP shall include the sampling frequency for each sample type. Justification must
be provided for Division consideration for any sample types/locations in which a sample
frequency of one is proposed.
13. Duke shall list and provide a detailed description of each coal combustion residuals
(CCR) waste storage or disposal area (unit) at each facility. This description shall state
the following:
a) known or approximate quantities of CCR waste stored in the unit(s);
b) details of the operational history of the unit(s), including years of use, all
known waste types, methods of emplacement, rationale for formal or
informal closure, and methods of closure or abandonment;
c) whether the unit is already included in the facility's current NPDES
permit;
d) whether the unit was permitted and managed by an agency other than the
Division and pertinent details of that permit;
e) whether there are additional permitted or unpermitted waste storage areas
within CCR waste storage areas;
f) the location and distribution of any coal ash used as structural fill or other
construction (i.e. roadbeds, storage pads, berms, etc,) both on and offsite
(proximal to the site); and
g) whether the existing compliance boundary captures all the CCR waste
storage areas or if revisions need to be made.
Based on requirements specified in 15A NCAC 02L .0107 and a review of the
information discussed in a) to g) above, the Division will determine whether additional
units or areas need to be included in an existing or a new compliance boundary.
14. It is expected that the reporting limits associated with all analytical methods proposed in
the GAP be EPA approved and be at or below the state groundwater standards at 15A
NCAC 2L or surface water standards at 15A NCAC 2B.

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15. 15A NCAC 02C .0108(p) specifies that each non -water supply well be developed such
that the level of turbidity or settleable solids does not preclude accurate chemical
analyses of any fluid samples collected. The GAP shall acknowledge and state that well
construction design will be based on site specific conditions and shall be actively
modified in the field (alternate screen slot size, use of well sock, or others, for example)
to accommodate the grain size of the formation, as needed to minimize turbidity or
address other unforeseen issues. Any deviations from originally proposed protocols shall
be fully documented and provided to the Division.
16. The GAP shall state that well development and purging protocols will be based on site
specific conditions and shall be actively modified in the field as needed to minimize
turbidity or address other unforeseen issues. In all cases, well development and purging
prior to sample collection shall be conducted to specific field standards which shall be
clearly stated in the GAP. Deviations from this protocol or from other proposed
development and purging protocols shall be fully documented and provided to the
Division. If the Division concludes that turbidity is impacting analytical results for any
reason, a replacement well will, in some cases, be required.
17. Duke shall contact adjacent property owners for site access as needed to complete the
assessment activities. If Duke is unable to obtain access from an owner, Duke shall
request liaison assistance from the Division in writing. This request shall include all
contact information, details of all prior discussions regarding access to the property for
purposes of conducting site assessment, and results of those discussions. Duke shall
provide the Division a copy of any formal access agreements proposed for use.
18. The statewide 1:500,000 geologic map is not a substitute for local, larger scale geologic
mapping and site scale geologic information where available. The GAP shall propose the
use of fracture trace analysis (where applicable) and onsite/near-site geologic mapping to
better understand site geology. The scope of these efforts shall depend upon site
conditions and existing geologic information.
19. If proposed, please provide a detailed rationale for the use of Rotosonic or similar drill
method and why it is appropriate for use in the site assessments. Please address any
potential issues (such as the consolidation of aquifer material in the vicinity of the well
screen) that could affect aquifer or groundwater analyses.
20. The purpose, methods, and numbers (including anticipated depths/flow zone(s) and,
where known, locations) of packer testing shall be clearly detailed in the GAP.
21, The use of statistics to help establish background concentrations of specific parameters
shall be based on site -specific data and shall follow the methods approved for use by the
Division. In most cases, the methods outlined in RCRA Unified Guidance (U.S. EPA,
2009, EPA 530/R-09-007) are considered to be appropriate for use at these sites.
Background wells deemed appropriate for use in statistical analyses must be approved by
the Division. Final background determinations are made by the Division Director based
on available data and information.

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22. As part of the GAP, provide an oversized summary table of all existing compliance and
voluntary well data collected to date at the site. Please place all constituents, including
DO, SC, ORP, and turbidity, as headings across the top of the table, and all wells and
sample dates as rows along the left side of the table. Highlight in yellow those values
that exceed a 2L standard. Please also include on this table any surface water, ash, and
(or) ash leachate data relevant to the site. This table should be included in the GAP and
also made available in electronic (Excel or similar) format.
23. As part of future site assessment reporting deliverables, provide at a minimum the
following tables, graphs, and maps:
a) box (whisker) plots, for locations sampled on four or more events (show
min, 25, 50, 75, max); align plots for multiple locations on one chart;
construct a similar chart for each constituent of concern (COC),
b) stacked time -series plots (for each COC, stack multiple wells/locations
using same x-axis to discern seasonal trends; construct similar chart for
each COC; consider also showing turbidity, DO, ORP, or other constituent
on plot to demonstrate influence,
c) piper and (or) stiff diagrams showing selected monitor wells, supply wells,
surface water locations, ash leachate as separate symbols,
d) correlation charts, where applicable,
e) orthophoto potentiometric maps for "like" flow zones (maps for bedrock
wells likely will be plotted on a different map than maps for transition
zone wells),
f) orthophoto potentiometric difference maps, showing the difference in
vertical heads between selected flow zones,
g) orthophoto iso-concentration maps for selected COCs and flow zones,
h) orthophoto map showing relationship between ground and surface water
samples for selected COC(s),
i) geologic cross sections,
j) photographed borings/core for each boring location, and
k) others as appropriate.
For summary statistics tables, avoid presenting "average" value(s) unless the
constituent(s) at the location in question is (are) normally distributed, in which case a
mean and standard deviation are acceptable. For non -normal data, use of the median
value is more appropriate. In either case, use of the maximum value is often misleading
if it is a formally -tested outlier or is associated with high turbidity; footnote maximum
values as appropriate.
24. With respect to the use of the terms "may" versus "will", the GAP shall use the term
"will" or clearly state, in detail, why the qualifying term "may" is used. In either case,
the Division reserves the right to request at any time additional work needed to meet site
assessment objectives. During the assessment, if Duke decides that additional work is

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needed at a facility, the Division shall be contacted immediately with a description of the
proposed work and timeline.
25. Any assumptions or timelines stated in the GAP shall not be used as justification to
circumvent the mandatory deadlines established by legislative order, Governor's
Executive Action, or NORR.
Additional Comments Specific to the Referenced Facility
26. Relocate proposed well set AW-1 and AW-1D approximately two hundred and fifty feet
South- Southeast of anticipated location.
27. Install a vertical extent monitoring well at CW-3 location.
28. Install a vertical extent monitoring well at CW-6 location.
29. Place an additional potential background well set at a location approximately one
thousand five hundred feet Southwest of BG-2.
30. Place an additional well set at a location approximately six hundred feet Northeast of
CW-3.
31. PIace an additional well set at a location approximately seven hundred feet Northeast of
CW-2 and CW-2D.
32, Relocate proposed background wells BG-4 and BG-4D.
Your assessment plan must be submitted to the DWR Raleigh Regional Office and Central
Oltice for review within 30 days of the receipt of this letter. A revised plan must be submitted
that fully incorporates the responses to the above comments rather than a letter response
intended to supplement the previously submitted plans.
Please note that failure to conduct a complete assessment pursuant to the above referenced rule
and statute will be considered a violation, subject to potential enforcement actions by the
Division.

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We appreciate your attention and prompt response in this matter. If you have questions, please
do not hesitate to call Rick Bolich at 919-791-4200.
Sincerely,
S. Ja Li�,Merman, P.G., Chief
Water Quality Regional Operations Section
Cc: WQROS — RRO
WQROS — Central Office
Don van der Vaart
Synterra (Attn: Kathryn Webb) —148 River Street, Suite 220, Greenville, SC 29601