Marshall Attachments_20160418

Attachments

Expert Report of Douglas Cosler, Ph.D., P.E.

Expert Report of
Douglas J. Cosler, Ph.D., P.E.
Chemical Hydrogeologist
Adaptive Groundwater Solutions LLC
Charlotte, North Carolina
Marshall Steam Station Ash Basin
Terrell, North Carolina
April 18, 2016

Introduction
Site Backqround
The Marshall Steam Station is a four -unit, coal-fired generating station owned by Duke Energy and
located on a 1,446-acre site on the west bank of Lake Norman near the town of Terrell in Catawba
County, North Carolina. Coal combustion residuals ("coal ash") have historically been disposed in a
single -cell ash basin impoundment located north of the power plant. The ash basin was constructed in
1965 by building an earthen dike at the confluence of Holdsclaw Creek and the Catawba River (now Lake
Norman) and is generally located in historical depressions formed from Holdsclaw Creek and small
tributaries that discharged into the creek. Two unlined ash landfill units (Marshall dry ash landfill) are
located adjacent to the east (Phase 1) and northeast (Phase II) portions of the ash basin. A flue gas
desulfurization (FGD) landfill containing bottom ash and various other types of waste materials is located
to the west of the ash basin and is constructed with an engineered liner system. Industrial Landfill No. 1
(containing fly and bottom ash and various other types of waste materials) is located adjacent to the
northern portion of the ash basin and contains a liner and leachate collection system. The demolition
landfill (construction and demolition waste) is also located adjacent to the northern portion of the ash
basin (directly north of the dry ash landfill, Phase II). The photovoltaic farm structural fill (PV structural fill)
is constructed of fly ash and located adjacent to and partially on top of the northwest portion of the ash
basin.
Duke Energy performed voluntary groundwater monitoring at the site from November 2007 to October
2011 (nine sampling events) and NPDES permit -required compliance monitoring starting in February
2011 (sampling three times per year). Recent groundwater sampling results at Marshall indicate
exceedances of 15A NCAC 02L.0202 Groundwater Quality Standards (2L Standards). In response to
this, the North Carolina Department of Environmental Quality (NC DEQ) required Duke Energy to perform
a groundwater assessment at the site and prepare a Comprehensive Site Assessment (CSA) report. The
Coal Ash Management Act of 2014 (CAMA) also required owners of surface impoundments containing
coal combustion residuals (CCR) to conduct groundwater monitoring and assessment and prepare a CSA
report. The September 2015 CSA prepared by HDR Engineering, Inc. of the Carolinas (HDR) for the
Marshall site determined that ash handling and storage at the Marshall site have impacted soil and
groundwater beneath and downgradient from the ash basin. The CSA report identified Constituents of
Interest (COI) considered to be associated with potential impacts to soil and groundwater from the ash
basin and assessed COI concentration distributions in soil, groundwater, and seeps.
CAMA also requires the submittal of a Corrective Action Plan (CAP); the CAP for the Marshall site
consists of two parts. CAP Part 1 (submitted to DEQ in December 2015) provides a summary of CSA
findings, further evaluation and selection of COI, a site conceptual model (SCM), the development of
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groundwater flow and chemical transport models of the site, presentation and analysis of the results of
the modeling, and a quantitative analysis of groundwater and surface water interactions. The CAP Part 2
contains proposed remedial methods for achieving groundwater quality restoration, conceptual plans for
recommended corrective action, proposed future monitoring plans, and a risk assessment.
Information Reviewed
My opinions are based upon an analysis and technical review of (i) hydrogeologic and chemical data
collected at the Marshall site; (ii) the analyses, interpretations, and conclusions presented in site -related
technical documents and reports; (iii) the groundwater flow and chemical transport models constructed
for the site (including model development, calibration, and simulations of remedial alternatives); (iv) the
effectiveness of proposed remedial alternatives to achieve groundwater quality restoration; and (v)
proposed future site monitoring. These opinions are subject to change as new information becomes
available.
As a basis for forming my opinions I reviewed the following documents and associated appendices:
(1) Comprehensive Site Assessment Report, Marshall Steam Station Ash Basin (September 8, 2015);
(2) Corrective Action Plan, Part 1, Marshall Steam Station Ash Basin (December 7, 2015);
(3) Corrective Action Plan, Part 2, Marshall Steam Station Ash Basin (March 3, 2016);
(4) Miscellaneous historical groundwater and soil concentration data for the Marshall site collected
prior to the CSA; and
(5) Specific references cited in and listed at the end of this report.
Professional Qualifications
I have advanced graduate degrees in Hydrogeology (Ph.D. Degree from The Ohio State University) and
Civil and Environmental Engineering (Civil Engineer Degree from the Massachusetts Institute of
Technology), and M.S. and B.S. degrees from Ohio State in Civil and Environmental Engineering. I have
36 years of experience as a chemical hydrogeologist and environmental engineer investigating and
performing data analyses and computer modeling for a wide variety of projects. These projects include:
investigation, remediation, and regulation of Superfund, RCRA, and other hazardous waste sites involving
overburden and bedrock aquifers; ground water flow and chemical transport model development; natural
attenuation/biodegradation assessments for chlorinated solvent and petroleum contamination sites;
volatile organic compound vapor migration and exposure assessment; exposure modeling for health risk
assessments; hydrologic impact assessment for minerals and coal mining; leachate collection system
modeling and design for mine tailings disposal impoundments; and expert witness testimony and
litigation support. I also develop commercial groundwater flow and chemical transport modeling software
for the environmental industry.
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The types of sites I have investigated include: landfills, mining operations, manufactured gas plants,
wood -treating facilities, chemical plants, water supply well fields, gasoline and fuel oil storage/delivery
facilities, nuclear waste disposal sites, hazardous waste incinerators, and various industrial facilities. I
have investigated the following dissolved, nonaqueous-phase (LNAPL/DNAPL), and vapor -phase
contaminants: chlorinated solvents, various metals, gasoline and fuel oil constituents, wood -treating
products, coal tars, polychlorinated biphenyls, pesticides, dioxins and furans, phenolic compounds, flame
retardants (PBDE), phthalates, radionuclides, and biological constituents.
Summary of Opinions
The following is a brief summary of the opinions developed in my report:
• A total of 21 Compliance Boundary groundwater samples exceeded North Carolina groundwater
standards for these COI: antimony, boron, chromium, cobalt, iron, manganese, total dissolved
solids, and vanadium. Of these 21 exceedances, 19 were greater than the proposed provisional
background concentrations by HDR, which exaggerate background levels;
• The statistical analyses of historical, shallow -aquifer background groundwater concentrations at
the Marshall site (monitoring well MW-4) are invalid due to the characteristically slow rate of COI
migration in groundwater;
• There is a significant risk of chemical migration from the ash basin to neighboring private and
public water supply wells in fractured bedrock;
• Major limitations of the CAP Parts 1 and 2 groundwater flow and chemical transport models
prevent simulation and analysis of off -site migration;
• The CAP Closure Scenario simulations greatly underestimate (by factors of 10 or more) the time
frames required to achieve meaningful groundwater concentration reductions in response to
remedial actions;
• For either the Existing Condition or Cap -in -Place Scenario groundwater concentrations of many
coal -ash constituents much higher than background levels will continue to exceed North Carolina
groundwater standards at the Compliance Boundary because saturated coal -ash material and
secondary sources will remain in place;
• Source -area mass removal included in the Excavation Scenario results in COI groundwater
concentration reductions that are at least a factor of 10 greater compared to Cap -in -Place at
many locations. Additional excavation of secondary sources would further accelerate
concentration reductions;
• CSA data show 22 exceedances of groundwater standards in bedrock inside the Compliance
Boundary. However, the CAP Closure Scenarios do not address off -site chemical migration
control in the fractured bedrock aquifer;
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• Due to an incorrect boundary -condition representation of the active ash basin, the CAP models
underestimate by a factor of three or more both the mass loading of COI into Lake Norman and
the corresponding Lake Norman water concentrations (attributable to coal ash ponds) estimated
by the groundwater/surface-water mixing model;
• The CAP Part 2 geochemical modeling and monitored natural attenuation (MNA) evaluations do
not provide the required quantitative analyses of COI attenuation rates necessary to support MNA
as a viable corrective action. The CAP 2 chemical transport modeling, which included attenuation
by sorption, demonstrated that MNA is not an effective remedial option for several COI (e.g.,
antimony, beryllium, boron, chromium, cobalt, hexavalent chromium, thallium, and vanadium);
and
• Future Compliance Monitoring at the Marshall site should include much more closely -spaced
Compliance Wells to provide more accurate detection, and groundwater sampling frequency
should be re-evaluated to allow valid statistical analyses of concentration variations.
Hydrogeology of the Marshall Site
Introduction
The groundwater system at the Marshall site is an unconfined, connected system consisting of three
basic flow layers: shallow, deep, and fractured bedrock. The shallow and deep layers consist of residual
soil, saprolite (clay and coarser granular material formed by chemical weathering of bedrock), and
weathered fractured rock (regolith). A transition zone at the base of the regolith is also present and
consists of partially-weathered/fractured bedrock and lesser amounts of saprolite. The single -cell ash
basin impoundment overlies native soil and was constructed in 1965 by building an earthen dike at the
confluence of Holdsclaw Creek and the Catawba River (now Lake Norman). Most of the coal ash lies
below the groundwater table and is saturated. Groundwater flow through saturated coal ash and
downward infiltration of rainwater through unsaturated coal ash leach COI into the subsurface beneath
the basin and via seeps through the embankments.
As described by HDR, groundwater flow in all three layers within the site boundary is generally from the
northwest and north to the southeast toward Lake Norman. Vertical groundwater flow between the three
layers also occurs, and surface water ponding in the ash basin effects flow directions locally. On the
downgradient eastern site boundary the CSA and CAP Parts 1 and 2 investigations assumed that all
groundwater (overburden and bedrock aquifers) discharges into Lake Norman. However, these studies
did not collect hydrogeologic data or perform data analyses or groundwater flow modeling to support this
assumption. The CSA and CAP Parts 1 and 2 also did not analyze potential changes to site groundwater
flow directions, or the risk of off -site migration of COI in the overburden or bedrock aquifers, caused by
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groundwater extraction from numerous private and public water supply wells located close to the site
boundaries.
My report begins with a discussion of significant errors in CSA data analysis and conceptual model
development that contradict HDR's interpretation of three-dimensional groundwater flow patterns at the
Marshall site. This is followed by a presentation and discussion of measured exceedances of North
Carolina groundwater standards at multiple locations on the ash basin compliance boundary. I then
address several limitations of the CAP Parts 1 and 2 groundwater flow and chemical transport models
and identify various model input data errors. Finally, I present my evaluations of the CAP Closure
Scenario simulations and provide my opinions regarding the effectiveness of various remedial alternatives
for restoring groundwater quality to North Carolina standards.
Errors in Hydraulic Conductivity Test Analyses
Background
In the CSA and CAP reports HDR provides interpretations and conclusions regarding the horizontal and
vertical variations of groundwater flow directions and rates, and the fate and transport of COI dissolved in
groundwater. The most important site -specific parameter that controls these time -dependent flow and
transport mechanisms is the hydraulic conductivity (also referred to as "permeability") of the underlying
soils and fractured bedrock (Bear, 1979). Hydraulic conductivity (length/time) is a media -specific
measure of the rate at which water can flow through a porous (soil) or fractured (bedrock) porous
medium. Groundwater flow and chemical transport rates are directly proportional to the product of
hydraulic conductivity and the hydraulic gradient (hydraulic head difference between two points divided by
the separation distance; e.g., the water table elevation slope). Therefore, accurate measurement of
hydraulic conductivity is critical for understanding the current and future distributions of COI in soil and
groundwater and for evaluating the effectiveness (e.g., cleanup times) of alternative remedial measures.
In addition, the contrast in hydraulic conductivity between adjacent hydrogeologic units is the key factor in
determining three-dimensional groundwater flow directions and the ultimate fate of dissolved COI. For
example, at the Marshall site accurate measurement of hydraulic conductivity is critical in evaluating the
potential for: downward chemical migration into the fractured bedrock unit, off -site COI migration in the
overburden (soil) or fractured bedrock aquifers, and groundwater flow and COI transport into or beneath
Lake Norman.
A slug test is one of the standard field methods for measuring hydraulic conductivity (K) using a soil
boring or installed monitoring well. Slug tests were performed in most of the overburden and bedrock
wells at the Marshall site. In this test the static water level in the open hole (boring) or well casing is
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suddenly increased or decreased and the resulting transient change in water level is recorded. Two
commonly -used techniques for quickly changing the water level are the introduction (increases the water
level) and removal (decreases the water level) of a solid rod, or "slug" into the boring or well casing.
These tests are called "falling -head" and "rising -head" tests, respectively. Higher rates of water -level
recovery correspond to higher values of K. The measurements of water level versus time are analyzed
using mathematical models of the groundwater flow hydraulics and information regarding the well
installation (e.g., length of the slotted monitoring well screen and well casing diameter) to compute an
estimate of K.
As discussed below, HDR made significant errors in all of their analyses of field slug test data. Their
analysis errors caused the reported (CSA report) slug test hydraulic conductivity values to be as large as
a factor of 1.5 (almost 50 percent) smaller than the correct K values. I discuss the impacts of these
analysis errors on HDR's groundwater flow and chemical transport assessments and the CAP modeling
later in my report.
Overburden Slug Tests
HDR analyzed all of the CSA overburden slug tests in shallow and deep wells with the Bouwer-Rice
(1976) method using vertical anisotropy, Av = Kh,,n onrat 1 Kverticat , values that are as large as a factor of 20
lower than the values presented in the CSA report (e.g., compare geometric mean values in CSA Tables
11-9 and 11-10) and used in the CAP modeling (e.g., CAP 1 report Appendix C, Table 2), where K is
hydraulic conductivity. Comparing CSA Tables 11-9 and 11-10, the measured Av for overburden soil units
ranges from 2 to 50. In the calibrated CAP flow model Av = 10 for overburden soil. However, the
Bouwer-Rice slug test analyses assumed Av = 2 for every monitoring well (CSA Appendix H). Using the
measured M1 hydrostratigraphic vertical anisotropy, Av = 35, increases all of the M1 CSA overburden
hydraulic conductivity values (CSA Table 11-3) by almost 50 percent (factor of 1.5), depending on how
the slug -test radius of influence was computed. If the CAP 1 flow model results (Av = 10) are used in the
Bouwer-Rice analyses all of the measured overburden hydraulic conductivity values increase by almost
30 percent (factor of 1.3).
Since most of the reported overburden K values in the CSA report are up to 50 percent too low, the actual
average chemical transport rates in overburden soils are up to 50 percent greater than reported. This
site -wide data reduction error also affects the CAP flow and transport model calibrations. For example,
the transport model developers significantly reduced laboratory measurements of the soil -water partition
coefficient, Kd, for various COI during the transport model calibration based on comparisons of observed
and simulated chemical migration rates. However, if the correct (i.e., higher) overburden K values had
been used in the model calibration the Kd values would not have been reduced as much (compared to
laboratory values). The reason for this is, assuming linear equilibrium partitioning of COI with soil, the
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chemical migration rate is proportional to K/Kd (except for Kd << 1). The CAP 1 and 2 transport model
history matching indicated that the simulated transport rate was too low, so HDR reduced the model Kd.
In other words, the reductions in calibrated Kd values would not have been as great if the correct (higher)
K values were used in the first place. As discussed below, the CAP Part 1 transport modeling used Kd
values that were typically factors of 10 - 100 smaller than the measured site -specific Kd's reported in CAP
Appendix D. In contrast, the CAP Part 2 transport modeling used Kd values that are generally a factor of
about 10 larger than the CAP 1 values; however, the CAP 2 Kd's remain on the order of 10 times smaller
than the measured site -specific Kd's for many COI. COI sorption to soil is important because, as
discussed later, aquifer cleanup times (i.e., chemical flushing rates) are generally proportional to the
chemical retardation factor, which is directly proportional to Kd , except when Kd << 1 (Zheng et al., 1991).
Groundwater Flow
In the CSA and CAP reports HDR made several critical assumptions, not supported by data, regarding
the horizontal and vertical groundwater flow directions near the boundaries of the Marshall site which
impacted their conclusions regarding the ultimate discharge locations for site groundwater and dissolved
COI. Two examples discussed in this section are (i) the relationship between site groundwater and Lake
Norman and (ii) groundwater flow directions and the potential for offsite migration of COI.
Lake Norman and the LeGrand Conceptual Model
All shallow, deep, and bedrock groundwater in the downgradient areas of the site was apparently
assumed to discharge into either Lake Norman or the unnamed stream located close to the northeastern
side of the ash basin before site -specific hydrogeologic data were analyzed. The rationale that HDR used
is a generalized, theoretical conceptual model (LeGrand, 2004) that relies on land -surface topographic
elevations rather than actual groundwater flow data (i.e., hydraulic head measurements); references to
this theory were made at numerous points in the CSA and CAP reports. However, HDR did not present
any site -specific data analyses or groundwater flow modeling that would support this assumption in either
report. In fact, as discussed below, the boundary conditions for the CAP Parts 1 and 2 flow models
effectively forced downgradient site groundwater in the shallow, deep, and bedrock aquifers to discharge
into Lake Norman and the unnamed stream.
HDR continued to state this assumption in the CAP 2 report (e.g., Section 3.3.2) even though strong
measured downward groundwater flow components from deep overburden to the fractured bedrock unit
exist in the southeastern part of the site next to Lake Norman. In the CAP 2 report Executive Summary
(page 2) HDR also claims that "Groundwater at the MSS site generally flows .... to the south and
southeast beneath the source areas toward Lake Norman, which serves as the hydrologic boundary
downgradient of the CCR source areas". I demonstrate below that this interpretation is incorrect because
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CSA and CAP 2 hydraulic head data show that groundwater and dissolved COI in the fractured bedrock
aquifer flow off -site in the southeastern portion of the Marshall site toward neighboring water supply wells
The LeGrand (2004) guidance document presents a general discussion of groundwater flow patterns that
may occur near streams in the Piedmont and Mountain Region of North Carolina based on ground
surface elevations (i.e., site topography and surface watershed boundaries). However, surface water and
groundwater watersheds commonly do not coincide (Winter et al., 2003). Further, groundwater flow
patterns and rates in bedrock have been found to be poorly related to topographic characteristics (Yin
and Brook, 1992). LeGrand does not present or derive any mathematical equations or quantitative
relationships for groundwater flow near rivers or streams and does not address areally-extensive
waterbodies such as Lake Norman. The author emphasizes that site -specific data must be collected in
order to correctly evaluate river inflow or outflow. In strong contrast to the LeGrand generalizations,
numerous detailed and sophisticated mathematical (analytical and numerical) river -aquifer models and
highly -monitored field studies have been published in the scientific and engineering literature in the past
several decades. What these investigations and applied hydraulic models show is that the water flow rate
into or out of a river, stream, or lake and the depth of hydraulic influence within an underlying aquifer are
highly sensitive to several factors, including: the transient river/lake water surface elevation and slope;
river/lake bed topography; bed permeability and thickness; horizontal and vertical permeability (and
thickness) of the different hydrogeologic units underlying the river/lake; transient horizontal and vertical
hydraulic head variations in groundwater beneath and near the river/lake; and groundwater extraction
rates and screen elevations for neighboring pumping wells (e.g., Simon et al. 2015; McDonald and
Harbaugh, 1988; Bear, 1979; Hantush, 1964).
The CSA investigation did not: measure the bed permeability or thickness of Lake Norman or the
unnamed stream; characterize the lake/river bathymetry; monitor transient water surface elevation
variations at more than one location (one average value was used); collect lake/river bed hydraulic
gradient data; measure horizontal or vertical overburden or bedrock permeability beneath Lake Norman;
characterize the geology beneath Lake Norman; measure hydraulic heads in the overburden or bedrock
beneath Lake Norman or the stream; or consider the hydraulic effects of groundwater extraction from
nearby water supply wells [e.g., water supply wells NC0118676 (Duke Energy), NC0118736 (Old Country
Church), and NC0118622 (Midway Restaurant and Marina), located close to the southern section of the
ash basin compliance boundary; and the numerous private homes located south and west of the site;
see CSA Figures 4-1 and 4-5]. Well construction and well yield (gallons per minute) data for these wells
are listed in Table 1 of the 2014 receptor survey report (HDR, 2014).
Much of the CSA data contradict the LeGrand hypothesis at the Marshall site. For example, downward
flow components from deep to bedrock wells were measured at monitoring clusters AB-5 and AB-6
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located in the southeastern portion of the site close to Lake Norman during the CSA and CAP 2 (compare
CSA Figures 6-6 and 6-7 and CAP 2 Figures 2-3 and 2-4). In addition, my corrected contouring of
bedrock hydraulic head data shows that groundwater flow in the bedrock aquifer is off -site and to the
south/southeast in this portion of the site (see next section). As discussed in other parts of my report,
HDR assumed in the CSA and the CAP Parts 1 and 2 modeling that groundwater flow in all three
hydrogeologic units is directly west to east near the southern part of the Compliance Boundary and used
a no -flow boundary in this model area, which prevents off -site flow. The CSA and CAP 1 and 2 also did
not evaluate the effect of the very large constant hydraulic head in the ash basin impoundment (30 feet
greater than the Lake Norman water level and the static bedrock hydraulic head in this area) as it relates
to vertical groundwater flow from overburden to bedrock and COI transport from ash basin water to
underlying groundwater. Maps of vertical hydraulic gradient variations (e.g., contour maps) were not
generated for the CSA or CAP 2, and HDR did not discuss the significance of downward hydraulic
gradients from overburden to bedrock, or from the impounded ash basin water to the aquifer system.
These downward groundwater flow measurements are consistent with the hydraulic conductivities of the
bedrock and overburden being of similar magnitude (CSA Table 11-9).
Groundwater Flow Directions
The CSA assumptions and analysis errors discussed above have had a strong effect on: the Conceptual
Model development; the site hydrogeologic and COI transport assessment; the construction/calibration
of the CAP flow and transport models; and the simulations of CAP Close Scenarios. The hydrogeologic
assumptions should have been carefully evaluated and tested during the performance of the CSA and as
part of the CAP groundwater flow model construction and calibration to determine whether they were
valid. Instead, the hypotheses appear to have effectively guided the model development and led to
inaccurate interpretations.
A good example of this is the bedrock aquifer hydraulic head and flow direction map developed by HDR
(CSA Figure 6-7). The hydraulic head contours and inferred bedrock flow directions in Figure 6-7 are
inaccurate because HDR did not account for the hydraulic impacts of three very important influences on
horizontal and vertical groundwater flow in the fractured bedrock aquifer: the ash basin impoundment,
Lake Norman, and groundwater extraction from off -site water supply wells (e.g., the wells mentioned
above). First, the 780-foot head contour is incorrect because it cuts through the middle of the ash basin
where the constant hydraulic head is approximately 790 feet. Drawn correctly, the 780-foot head contour
should mirror the northeastern boundary of the ash basin as shown in the deep aquifer map (CSA Figure
6-6 and CAP flow model Figure 11 of Appendix C). Second, the CSA bedrock flow map does not utilize
the hydraulic information (specifically, the groundwater/surface-water interaction) associated with the
Lake Norman shoreline area to the east and southeast of the Marshall site (e.g., CSA Figure 4-1). For
example, a U.S. Geological Survey study of overburden and bedrock groundwater flow near another part
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of the Lake Norman shoreline (Pippin et al., 2008) determined that heads in bedrock were generally less
than a few feet greater than the Lake Norman water surface elevation, depending on how much rainfall
had occurred during the days and weeks preceding the measurement event (e.g., Figure 25 in the USGS
report). At the Marshall site, water -level measurements in monitoring well GWA-1 BR are consistent with
this pattern. Similarly, static water levels in the three bedrock pumping wells to the south (Duke Energy,
Old Country Church, and Midway Restaurant and Marina) are strongly influenced by hydraulic interaction
with Lake Norman. As shown in CSA Figure 4-1 these wells are located very close to the Lake Norman
shoreline. HDR (2014; Table 1) reports that the well yield for the Duke Well is 30 gallons per minute
(gpm), and Duke Energy has reported average annual water usage rates of about 10 gpm for this well in
annual water use reports submitted to the North Carolina Division of Water Resources (e.g., McGary,
2004). The reported well yields for Old Country Church and Midway Restaurant and Marina are 40 gpm
and 20 gpm, respectively.
To better understand the effects of these extraction wells on groundwater flow in the bedrock aquifer I
estimated hydraulic head reductions, relative to the Lake Norman static level, as a function of distance
from a pumping well using the exact mathematical model of Hantush (1964, Equation 73). This
analytical groundwater flow model predicts the steady-state, pumping -induced drawdown [i.e., reduction
in hydraulic head from static (non -pumping) conditions] in a confined aquifer (bedrock) overlain by a
"leaky layer", which I model as the overlying overburden aquifer (using the overburden aquifer vertical
hydraulic conductivity, as represented by data in CSA Table 11-9) and the Lake Norman water surface
elevation. I assumed a bedrock aquifer thickness of 100 feet, which is much larger than the
underestimated value used in the CAP models (i.e., 50 feet) but also is consistent with regional studies of
this bedrock aquifer system (Daniel et al., 1989). The cited depths of the Duke and Midway Marina
supply wells (HDR, 2014) are about 400 feet and 160 feet below the bedrock surface, respectively (540
and 245 feet below ground surface). For the overlying confining unit I used representative CSA values: a
50-foot thick overburden aquifer with a 0.045 feet/day vertical permeability. The following bedrock
drawdown calculations depend on the product of bedrock permeability and thickness (i.e., transmissivity);
I varied permeability by a factor of seven, which has a similar hydraulic effect on drawdown as varying the
thickness by this amount. Therefore, my calculations also represent sensitivity analyses of both the
thickness and the permeability of the fractured bedrock unit. I used a 30-gpm pumping rate, which is
representative of the well yields for any of the three supply wells. The Hantush model is conservative
(i.e., underestimates drawdown) as applied to this analysis because the model assumes that Lake
Norman covers the entire area; in actuality the lake overlies only parts of the northeastern and
southeastern quadrants of the Duke Energy supply well zone of influence.
Figure 1 is a graph of the computed steady-state drawdown versus distance for three values of bedrock
hydraulic conductivity (Kb,): 0.68 (mean site value from CSA Table 11-9), 2.0, and 4.7 feet/day
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(measured value for well GWA-1 BR, which is the Marshall -site bedrock well located closest to the Duke
Energy pumping well; CSA Table 11-3). The estimated drawdown ranges from 14 feet (higher Kb,) to 85
feet at the pumping well, and the radius of influence (e.g., drawdown = 0.01 feet) generally varies from
1800 feet (lower Kb,) to approximately 3,400 feet. Note that the distance from the Duke Energy pumping
well to monitoring well GWA-1 BR is about 2,000 feet. Therefore, these drawdown analyses indicate that
groundwater extraction from any of the supply wells NC0118676 (Duke Energy), NC0118736 (Old
Country Church), or NC0118622 (Midway Restaurant and Marina) will likely influence bedrock
groundwater flow directions in the southeastern portion of the Marshall site (as far north as the ash basin)
based on average groundwater withdrawal rates.
I used the CSA bedrock water -level data and all of the above information and analyses to re -construct the
bedrock hydraulic head map and generate groundwater pathlines, which are shown in Figure 2. 1
conservatively assumed a small 25-foot drawdown in the Duke Energy supply well, five feet of drawdown
in the Old Church well, and no pumping in the Midway Marina well. Solid black circles represent bedrock
monitoring well data. Blue circles represent inferred bedrock heads beneath Lake Norman, which I
assumed were equal to 760 feet in areas located beyond the radius of influence of any of the three supply
wells. I experimented with lake elevations that were a few feet different than 760 feet and found that
these variations had little effect on my contour map. Within the radius of influence I subtracted the
drawdowns in Figure 1 (Kb, = 2.0 feet/day curve) from the 760-foot lake level. I generated Figure 2 using
the kriging interpolation option in the Tecplot data visualization software package (Tecplot, Inc., Bellevue,
Washington). Kriging is an advanced geostatistical procedure that spatially interpolates between discrete
measurements (e.g., monitoring well water levels) by computing a weighted average of the known values
of the function (hydraulic head variation) in the vicinity of the measured value. Kriging is mathematically
closely related to regression analysis and generally gives the best unbiased prediction of interpolated
values (Deutsch and Journel, 1992).
The contours and pathlines in Figure 2 indicate that much of the bedrock groundwater flow in the
southeastern portion of the area enclosed by the ash basin compliance boundary is off -site and to the
south-southeast (e.g., areas west of GWA-1 BR and south of AB-613R). In the area generally northeast of
wells AB-5BR and GWA-1 BR groundwater in the bedrock aquifer flows to the east-northeast toward the
unnamed stream and Lake Norman. I further examined bedrock groundwater flow directions and the
hydraulic effects of off -site pumping by developing a second bedrock hydraulic head map (Figure 3) in
which the Duke Energy, Old Country Church, and Midway Restaurant and Marina water supply wells
were inactive. Without off -site groundwater extraction from these supply wells the bedrock groundwater
flow directions in the southeastern part of the Marshall site exhibit a small additional easterly component,
but overall are not significantly different than the south -southeasterly directions in this area of the site
shown in Figure 2.
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Exceedances of Groundwater Standards
In this section I compare measured groundwater concentrations in shallow, deep, and bedrock
groundwater samples to North Carolina 2L and IMAC standards and show the following: (i) 15 measured
exceedances for several COI at multiple downgradient locations on the Compliance Boundary (CB); (ii)
an additional six (6) exceedances at CB locations based on chemical transport modeling I performed; (iii)
19 of the 21 downgradient Compliance Boundary exceedances were greater than the proposed
provisional background concentrations (PPBC) by HDR; (iv) 13 of the 21 CB exceedances were greater
than the maximum background concentration in the same hydrogeologic unit (e.g., shallow, deep, or
bedrock); (v) 22 additional exceedances were observed in wells screened in the highly -permeable
fractured bedrock unit underlying the ash basin and located inside the CB; and (v) the statistical analyses
of groundwater concentrations at wells MW-4 and MW-41D for purposes of defining background levels
were performed incorrectly.
Throughout this report I reference the ash basin compliance boundary and the Duke Energy property
boundary for the Marshall site as drawn on maps developed by HDR. My reference to the "compliance
boundary" is only for identification purposes and not an opinion that this boundary as drawn by HDR is
accurate or legally correct.
Summary of Exceedances
Table 1 summarizes exceedances of 2L or IMAC standards in shallow, deep, and bedrock groundwater
samples obtained from monitoring wells located: (i) on downgradient sections of the Ash Basin
Compliance Boundary (CB) as drawn by HDR; (ii) bedrock wells (BR) located inside the CB; and (iii)
modeled Compliance Boundary concentrations (CBM), using modeling techniques described below. The
proposed provisional background concentrations (PPBC) by HDR are also listed in Table 1.
A total of 15 Compliance Boundary groundwater samples exceeded North Carolina groundwater
standards for these COI: antimony, boron, chromium, cobalt, iron, manganese, total dissolved solids, and
vanadium. I estimated an additional six (6) exceedances at downgradient CB locations based on
chemical transport modeling and measured upgradient concentrations (CBM). In addition, 22
exceedances were observed in wells screened in the highly fractured bedrock unit located inside the CB.
A total of 19 of the 21 (measured plus modeled) Compliance Boundary exceedances were greater than
the proposed provisional background concentrations (PPBC) by HDR. A total of 13 of the 21 CB
exceedances were greater than background levels from the same hydrogeologic unit (e.g., shallow, deep,
13

or bedrock) for a particular constituent. Of the 22 bedrock exceedances, 14 were greater than PPBC
background levels.
Note that the iso-concentration contours in all of the CSA Section 10 figures and Figure ES-1 are not
consistent, and are in many cases misleading, with regard to chemical transport mechanisms in the
subsurface. For example, the iso-concentration contours in Section 10 generally closely encircle a
monitoring well and infer no subsequent transport downgradient from the well location. This contouring
problem is especially prevalent near downgradient sections of the Compliance Boundary (e.g., the
unnamed stream to the northeast and Lake Norman). Figure ES-1 is a good example of this practice.
These closed contours downgradient from the ash basin near the unnamed stream suggest that boron
transport beyond the farthest downgradient line of monitoring wells does not occur. This is not the case,
however, as demonstrated in the following section where boron exceedances at the Compliance
Boundary are demonstrated by modeling. Further, the CAP model simulated "existing conditions" plume
maps for boron and several other COI (CSA Appendix C) contain 'open contours" at these downgradient
parts of the CB, which confirm constituent transport to the boundary.
Modeled Compliance Boundary Exceedances
I computed Compliance Boundary concentrations labeled "CBM" with footnote "e" in Table 1 (wells MW-
14S,D; AL-1S,D; AB-1S; and MW-7S) using a one-dimensional, analytical chemical transport model
(van Genuchten and Alves, 1982; Equation C5) because the CB at these locations was 300-600 feet
downgradient from the wells and boron is highly mobile in the subsurface. I used site -specific
hydrogeologic data to determine input parameter values for groundwater pore velocity (Vp) and assumed
a boron retardation factor of unity (1.0), as HDR assumed in the CAP transport model. To calculate pore
velocity (Vp = K i/ne ), I used: mean hydraulic conductivity (K) values from CSA Table 11-9; average
effective porosity (ne) data in CSA Table 11-8; and measured horizontal hydraulic gradients (i) from the
hydraulic head maps in Section 6. 1 then calibrated the model to match observed 2015 boron
concentrations at the above wells. The concentrations labeled CBM in Table 1 are the modeled 2015
concentrations downgradient from each monitoring well at the Compliance Boundary.
Exceedances of Groundwater and Surface Water Standards in Seep Samples
As discussed in the introduction, the ash basin at the Marshall site was constructed above Holdsclaw
Creek and other tributaries that discharged to the Catawba River (currently Lake Norman). Seep
samples were collected during the CSA at two locations (S-2 and MSSW001 S001) on the downgradient
toe of the active ash basin dam during the CSA (CAP 1 Figure 2-2). After the CSA sample collection
HDR reported that location S-2 was not a separate seep from the ash basin, but rather pooled water from
the MSSW001 S001 seep. Nevertheless, HDR continued to show analytical results for both locations in
the CAP 1 report (Figure 2-2), and my following discussion refers to both locations.
14

Concentrations in the two seep water samples exceeded relevant NCAC 2B, 2L and/or IMAC standards
for various COI (e.g., CSA Table 7-8, CAP 1 Table 2-5, and CAP 1 Figure 2-2). Referring to my Table 1,
17 exceedances of North Carolina groundwater standards were detected in the seep samples for these
COI: arsenic, barium, beryllium, boron, chromium, cobalt, lead, manganese, selenium, thallium, total
dissolved solids, and vanadium. North Carolina surface water (2B) standards were exceeded for these
constituents: arsenic, beryllium, chromium, copper, lead, mercury, thallium, total dissolved solids, and
zinc.
Surface water sample SW-6, located in the unnamed tributary to Lake Norman immediately downgradient
from the active ash basin (CAP 1 Figure 2-2), was also considered by HDR to be representative of
groundwater quality at the site (CAP 2, Section 3.3.3). As shown in CAP 1 Table 2-6 North Carolina 2B
standards were exceeded in the July and October 2015 SW-6 samples for these COI: cobalt, iron,
manganese, sulfate, and total dissolved solids. Based on the significance of these exceedances, HDR
recommended in the CAP 2 report (Section 3.3.3) that further evaluation of the SW-6 surface-water/seep
fluid be conducted.
Statistical Analyses of Background Concentrations
Appendix G of the CSA report presents statistical analyses of historical concentrations from monitoring
wells MW-4 (shallow) and MW-41D (deep), which HDR described as following methods specified by the
U.S. Environmental Protection Agency (EPA, 2009), in an attempt to establish background groundwater
concentrations for the Marshall site. As outlined in Sections 3.2.1 and 5.5.2 of the EPA guidance
document these data must be checked to ensure that they are statistically independent and exhibit no
pairwise correlation. Groundwater sampling data can be non -independent (i.e., autocorrelated) if the
sampling frequency is too high (i.e., time interval between sampling events is too small) compared to the
chemical migration rate in the aquifer (groundwater pore velocity divided by chemical retardation factor).
Section 14 of the EPA guidance presents methods for ensuring that the data for background wells are not
autocorrelated, but the analyses in CSA Appendix G did not include evaluations for statistical
independence.
As an illustration, "slow -moving" groundwater combined with high chemical retardation (i.e., large soil -
water partition coefficients, Kd), which is the case for many COI in the shallow aquifer at the Marshall site,
can lead to the same general volume of the chemical plume being repeatedly sampled when the
monitoring events are closely spaced. Examining shallow background well MW-4, the measure hydraulic
conductivity at this location is 7.0E-5 to 3.7E-4 centimeters/sec (0.2 - 1.1 feet/day; CSA Tables 11-3 and
11-4). From CSA Table 11-8 the effective porosity at this location is about 0.25. Based on CSA Figure 6-
5 and Table 6-9 the horizontal hydraulic gradient in this area is about 0.02 feet/foot. Using these values
15

the estimated groundwater pore velocity (VP = K i/ne ) near MW-4 is on the order of 6 to 30 feet/year.
(Note that the groundwater velocities listed in CSA Table 11-12 are incorrect because this table is from
the Allen Steam Station CSA). Shallow pore velocities are generally factors of 40 to 200 greater
downgradient of the ash basin (between the ash basin and the Compliance Boundary) due to much
greater horizontal hydraulic gradients (-- 4x larger) and larger hydraulic conductivity (-- 10-50x greater) in
these areas.
The retardation factors, Rd, based on laboratory Kd measurements (Kd — 10 cm3/g, or greater) are on the
order of 100 (or greater) for many of the COI (except conservative parameters such as sulfate and
boron). Therefore, the average shallow chemical migration rate near monitoring well MW-4 (VP/Rd) is on
the order of 0.06 - 0.3 feet/year for many of the non -conservative COI, assuming linear equilibrium
sorption (refer to discussion below). With quarterly sampling, the chemical migration distance during the
time interval between sampling rounds is less than 0.1 feet (1 inch) for several COI, which is smaller than
the sand pack diameter for the monitoring wells. Therefore, based on either quarterly or annual
monitoring the shallow groundwater samples from monitoring well MW-4 are basically representative of
the same volume of the plume (i.e., the sandpack, depending on the well purge volume) for many COI,
and any measured sample concentration changes are not due to real chemical transport effects in the
aquifer. In this case, this means that the groundwater samples are non -independent and that the
statistical analyses of background concentrations do not satisfy the key requirements of the analysis
method.
CAP Groundwater Flow Model Underestimates Potential for Off -Site Chemical Migration
My discussions in this section focus on limitations of the CAP groundwater flow model. I focus specifically
on model boundary conditions representing Lake Norman; the overall size of the model grid and no -flow
boundary conditions on the western, southern, and northern grid boundaries; the misrepresentation of
groundwater flow in the fractured bedrock aquifer; and the potential for off -site groundwater flow in
relation to groundwater extraction from numerous private and public water supply wells located close to
the model boundaries, but not incorporated into the flow model.
Lake Norman and Southern No -Flow Boundary Conditions
The CAP Parts 1 and 2 groundwater flow models effectively force all groundwater (shallow, deep, and
bedrock aquifers) located beneath and downgradient from the ash basin to discharge into either Lake
Norman or the unnamed stream located close to the northeastern side of the ash basin, which discharges
as overland flow into the lake. The CAP 1 and 2 flow models also significantly underestimate the
potential for off -site flow and chemical migration in fractured bedrock. No -flow boundary conditions
16

defined along the entire western, northern, and southern model boundaries prevent any off -site
groundwater flow and chemical transport in these areas (e.g., refer to Figures 1 and 4 in Appendix C of
the CAP 1 Report). The CAP 1 and 2 models assign additional no -flow boundary conditions to all
downgradient bedrock cells located beneath Lake Norman, which prevents groundwater from flowing
beneath the lake in the bedrock aquifer. As discussed above (e.g., Figures 2 and 3), CSA hydrogeologic
data and available off -site hydraulic information clearly demonstrate that the CAP 1 and 2 models
boundary conditions are incorrect. The bottom surfaces (bedrock) of the flow models are also assumed
to be a no -flow boundary even though the hydraulic conductivity data and measured downward hydraulic
gradients at several monitoring well clusters do not support this assumption (e.g., downward flow from
deep to bedrock aquifers at well clusters AB-5D/BR and AB-6D/BR).
This hydraulic representation of Lake Norman in the flow models is inaccurate for many reasons. First,
the lake bottom is assumed to extend all the way through the overburden aquifer to the bedrock surface,
which is not the case. Second, groundwater flow beneath and adjacent to the lake is assumed to be
horizontal with zero vertical flow component. Because this boundary condition does not allow
groundwater to flow vertically in areas beneath and near the lake, the CAP models do not represent
actual site hydrologic conditions. Third, as represented in the CAP models, neither the lower -permeability
lake bed sediments nor the smaller vertically hydraulic conductivity of underlying soils restricts the
potential flow rate into or out of the lake (i.e., in the CAP models a perfect hydraulic connection exists
between the aquifer and Lake Norman). HDR did not evaluate the actual degree of aquifer -lake hydraulic
connection in the CSA or CAP 1 and 2. In summary, due to all of these factors the potential for site
groundwater and dissolved constituents to migrate off -site as underflow beneath Lake Norman and to the
south-southeast as groundwater flow cannot be evaluated with the model.
The CAP model should have represented Lake Norman using a "leaky -type" boundary condition in the top
model layer (McDonald and Harbaugh, 1988), and the model grid should have extended farther east and
south so that the above factors could have been evaluated during model calibration and sensitivity
analyses. The Electric Power Research Institute technical review committee, which included the
developer of the MT3D transport code used in the CAP modeling, made the same comment (December
02, 2015 memorandum entitled "Revised Marshall Model Review", which was submitted with the CAP
report). A leaky boundary condition incorporates the lake/river bed permeability and thickness, the
lake/river water surface elevation, and the simulated hydraulic head in the aquifer (at the base of the
lake/river bed) to dynamically specify a flux (flow rate per unit bed area) into or out of the groundwater
model depending on the head difference between the lake/river and aquifer. Typically, permeability and
vertical hydraulic gradient measurements for the lake bed (not collected in the CSA) and flow model
calibration (three-dimensional matching of simulated and measured hydraulic head measurements in the
17

aquifer) are used to determine a best -fit estimate of lake bed conductance (permeability divided by
thickness) in the model. HDR did not perform this routine analysis
Limitations of No -Flow Boundary Conditions and Small Model Domain Size
The limited areal extent and depth of the CAP Parts 1 and 2 flow and transport model grids prevent the
use of the models as unbiased computational tools that can be used to evaluate off -site migration of coal -
ash constituents. For example, the model grids should have extended farther west and incorporated
groundwater extraction from off -site private -home and public water -supply wells. The western no -flow
boundary in the current CAP models artificially prevents any off -site flow or transport to the west in either
the bedrock or overburden aquifers. The same is true for the entire northern and southern model
boundaries, as discussed above, and the artificial limitations created by the eastern Lake Norman
boundary condition. In addition, the downgradient boundaries of the CAP flow and transport models do
not extend to the Compliance Boundary along most of the Lake Norman boundary, which prevents their
use for estimating Compliance Boundary concentrations for various remedial alternatives.
The bottom boundaries of the CAP models should extend much deeper because the hydraulic
conductivity of the fractured bedrock zone is similar in magnitude to the overburden soils. In the present
configuration the lower boundary of the CAP 1 and 2 model grids is only about 50 feet below the bedrock
surface (Figure 2 in both the CAP 1 & 2 modeling appendices). Because several bedrock wells were
screened to this depth the bedrock hydraulic conductivity data collected for the CSA demonstrate that
imposing an impermeable model boundary at this depth is incorrect (compare similarities of mean
overburden and bedrock aquifer permeabilities in CSA Table 11-9).
Off -Site Groundwater Extraction Ignored
The CSA and CAP Parts 1 and 2 failed to examine the strong potential for coal -ash constituents from the
Marshall site to migrate with groundwater to private and public bedrock water supply wells located
immediately west, south, and north of the ash basin compliance boundary. CSA Figures 4-2 and 4-5
shows the locations of private and public water supply wells near the site. The basis of my opinion
includes the following: my hydraulic analyses of pumping -induced pressure reductions in the fractured
bedrock unit (Figure 1) and re-evaluation of bedrock hydraulic head variations and flow directions
(Figures 2 and 3), as discussed above; hydraulic conductivity measurements for the overburden and
bedrock formations; three-dimensional variations in measured hydraulic head in the bedrock and
overburden units; and groundwater concentration data. As discussed throughout my report, neither the
CSA nor CAP Parts 1 and 2 investigations addressed the potential for off -site migration.
COI's were detected in several water supply well samples (CSA Appendix B), but the CSA report did not
plot these detections on a map and did not discuss their possible relationship to the Marshall site.
18

Appendix B also did not present the well construction details (e.g., well diameter and elevation range of
the well screen or open bedrock interval) so that well dilution effects and potential chemical transport
pathways in the bedrock unit could be evaluated. In addition, the CSA investigations and CAP 1
modeling did not include these areas west, north, and south of the Marshall site. The CAP Part 2 flow
model did include a small number (four) of residential wells located inside the undersized model domain
(near the northern and western model domain boundaries), but the CAP 2 modeling report (CAP 2,
Appendix B) did not show simulated hydraulic head maps with these residential wells pumping and did
not provide any discussion or analyses of the potential for these wells to capture COI dissolved in
groundwater. The CAP Part 2 also did not increase the model grid size to incorporate the large number
of residential (89) and private (4) water supply wells located very close to the site boundary (CAP 2
Figure 3-3); fix the boundary condition problems; or correct the model input data errors I have outlined
so that the flow and transport models could be used to more accurately analyze the potential for off -site
chemical transport.
Another important model input data error is the bedrock hydraulic conductivity, which is assumed in the
CAP 1 flow model to be about a factor of three to five (3-5x) lower than the overburden aquifer in different
areas (Tables 2 in CAP 1 Appendix C and CAP 2 Appendix B). In the CAP 2 flow model the bedrock
permeability was further lowered to a value that is about a factor of 10 to 100 (10-100x) lower than the
overburden aquifer. However, the bedrock slug test results show that the mean bedrock permeability is
approximately the same as the overburden permeability (CSA Table 11-9). Therefore, the CAP 1 and 2
flow models significantly restrict (incorrectly) groundwater from flowing from the overburden aquifer into
the fractured bedrock unit, which causes the CAP transport models to underestimate the potential for off -
site chemical migration.
Ash Basin Hydraulic Boundary Condition and Groundwater Recharge Rates
Based on the model description in CAP 1 Appendix C [text and Figures 4 (boundary conditions) and 5
(groundwater recharge zones)] and CAP 2 Appendix B (Figure 5) the CAP 1 and 2 flow model
representations of the active ash basin are incorrect and significantly underestimate the recharge of ash
basin fluids into the underlying aquifer system (e.g., refer to my preceding discussion regarding
groundwater flow in bedrock and Figures 2 and 3). As noted in the CSA report (Section 2.6), the full
operating pond elevation (i.e., impounded fluid level) for the active ash basin is approximately 790 feet,
which is 30 feet greater than normal water level in Lake Norman. This very large hydraulic head increase
in the ash basin relative to the normal static conditions that existed in the underlying aquifer system prior
to construction creates very large downward groundwater flow components beneath areas of ponded
ash -basin fluid and causes the near -radial horizontal flow patterns observed in the bedrock (Figures 2
and 3) and overburden (CSA Figures 6-5 and 6-6) hydraulic head contour maps. The CAP 1 and 2 flow
19

models should have used constant -head or leaky -type boundary conditions in the top layer to represent
these areas of ponded fluid located inside the ash basin (e.g., McDonald and Harbaugh, 1988).
The CAP Part 2 flow model underestimates leachate discharge from the active ash basin by as much as
a factor of 34 in areas of ponded surface water (e.g., refer to CSA Figure 6-2). The CAP 1 model
underestimates active basin leakage by as much as a factor of 93. As shown in Figure 5 of CAP 1,
Appendix C, the CAP 1 flow model assumes a constant groundwater recharge rate (i.e., leakage rate)
equal to 4.5 inches/year in the active ash basin. In the CAP 2 flow model the active basin leakage rate is
assumed to be 12.3 inches/year (Figure 5 of CAP 2, Appendix B). However, CSA Figure 8-4.2 (cross-
section B-B) shows that the vertical hydraulic gradient through the coal ash in the downgradient portion of
the active ash basin is on the order of 0.5. Using Darcy's law and the mean vertical coal -ash permeability
of 6.7E-5 cm/sec in CSA Table 11-10, the approximate vertical leakage rate out of the active basin is
about 420 inches/year near Lake Norman (i.e., — 34 times greater than the specified CAP 2 recharge rate
of 12.3 inches/year; and — 93 times greater than the specified CAP 1 recharge rate of 4.5 inches/year).
Three related impacts of this incorrect active basin boundary condition are that the CAP models
significantly underestimate: (i) vertical groundwater flow rates (by up to a factor of 100) through coal -ash
source material in the vicinity of the downgradient portion of the active ash basin; (ii) horizontal
groundwater flow and chemical transport rates downgradient from the active ash basin (by at least a
factor of three; compare simulated hydraulic gradients near Lake Norman in Figure 13 of CAP 2
Appendix B with measured gradients in Figure 2-2 of the CAP 2 report); and (iii) vertical flow rates from
the overburden aquifer into the fractured bedrock unit beneath ponded areas. This incorrect boundary
condition representation of the active ash basin also causes the CAP models to significantly
underestimate (by at least a factor of three) both the mass loading of COI into the Lake Norman and the
corresponding Lake Norman surface water concentrations (attributable to coal ash ponds) that HDR
estimated with their mixing model (e.g., CAP 2 report Table 4-2 and Appendix D).
In addition, a site -specific distribution of groundwater recharge values should have been developed for
this and the other simulation scenarios to take into account site -specific topography and soil types (e.g.,
runoff estimation) and climate data (precipitation, evapotranspiration, etc.; e.g., using the U.S. Army
Corps of Engineers HELP Model; Schroeder et al., 1994). The predicted water table lowering due to
capping, discussed below, is very sensitive to the model recharge value; therefore, HDR should have
made more effort to develop a site -specific recharge -rate distribution.
20

CAP Chemical Transport Modeling
Due to model calibration, model construction, and boundary -condition and input -data errors the CAP
models significantly underestimate remediation time frames. As discussed in this section, reasons for this
include significant underestimation of the chemical mass sorbed to soil, failure to account for slow
chemical desorption rates, inaccurate analyses of water -table lowering due to capping, and flaws in the
transport model calibration.
Soil -Water Partition Coefficients and Model Calibration
The fraction of chemical mass sorbed to soil can be represented by the soil -water partition coefficient, Kd
(Lyman et al., 1982). Kd is an especially important parameter at the Marshall site because for most of the
COI the bulk of the chemical mass in the soil is associated with the solid phase (i.e., sorbed to soil grains
rather than dissolved in pore water). In effect, the solid fraction of the soil matrix acts as a large "storage
reservoir" for chemical mass when Kd is large [e.g., metals, many chlorinated solvents, and highly -
chlorinated polycyclic aromatic hydrocarbon (PAH) compounds associated with coal tars and wood -
treating fluids]. Kd is also a very important chemical transport parameter which is used to compute the
chemical retardation factor, Rd, assuming linear equilibrium partitioning of mass between the soil (solid)
and pore -water phases (Hemond and Fechner, 1994):
Rd = 1 + PbKd l ne
where Pb is the soil matrix bulk dry density and ne is the effective soil porosity. For example, the
chemical migration rate is directly proportional to hydraulic conductivity and inversely proportional to Rd .
The total contaminant mass in an aquifer is also directly proportional to Rd, as well as aquifer cleanup
times once the source is removed (e.g., Zheng et al., 1991).
Accordingly, it is very important to use accurate Kd values in the CAP Closure Scenario modeling.
Specifically, the CAP Part 1 transport modeling used Kd values that were typically factors of 10 - 100
(i.e., one to two orders of magnitude) smaller than the measured site -specific Kd's reported in CAP
Appendix D. In contrast, the CAP Part 2 transport modeling used Kd values that are generally a factor of
about 10 larger than the CAP 1 values (480x larger for arsenic; 70x larger for thallium; 25x larger for
vanadium); however, the CAP 2 Kd's remain on the order of 10 times smaller than the measured site -
specific Kd's reported in CAP 1 Appendix D and CAP 2 Appendix C for many COI. Further, soil -water
partition coefficients for the CAP Parts 1 and 2 models are much smaller than most values presented in
the literature for the COI (e.g., EPRI, 1984; Baes and Sharp, 1983). This means that, using the actual
measured Kd's for the Marshall site, the times required to reach North Carolina water quality standards at
21

the Compliance Boundary are more than a factor of 10 longer (see additional discussion below) than
cleanup times predicted by the CAP transport model.
The CAP Part 1 modeling report (CAP 1 Appendix C; Section 4.8) argues that the major Kd reductions
were needed due to the following:
"The conceptual transport model specifies that COls enter the model from the shallow saturated source
zone in the ash basin and beneath the CCR waste management units. When the measured Kd values
were applied in the numerical model to arsenic migrating from the source zones, this COI did not reach
the downgradient observation wells where it was observed in July 2015 at the end of the model simulation
period. The most appropriate method to calibrate the transport model in this case is to lower the Kd
values until an acceptable agreement between measured and modeled concentrations is achieved. Thus,
an effective Kd value results that likely represents the combined result of intermittent activities over the
service life of the ash basin, landfills, and structural fills. These may include pond dredging, dewatering
for dike construction, and ash grading and placement."
Considering the approach that HDR used to develop the chemical transport model (history matching), it is
not true that "the most appropriate method to calibrate the transport model is to lower the Kd values." The
CAP transport model used an incorrect value (2.12 g/cm3) for the bulk density of overburden materials.
The bulk density should have been computed using the total porosity (n) values in CSA Tables 11-1 and
11-7 using the following formula (e.g., Baes and Sharp, 1983):
Pb = 2.65 (1— n)
Based on the Table 11-7 mean total porosity values (--44%) Pb — 1.48 g/cm3 for overburden soil, which
means that the Rd values for the CAP 1 and 2 models were as much as a factor of 1.4 (2.12/1.48) too
high before HDR adjusted the Kd values during calibration. Also, as discussed earlier, the overburden
slug test values were about 50 percent too low due to HDR's data analysis errors. Both of these errors
(sorption rate and hydraulic conductivity) resulted in a modeled transport rate that was as much as a
factor of 2.1 too low before calibration simply due to data input errors.
At least two other important factors were not considered during the CAP 1 and 2 transport model
calibrations. First, the groundwater flow models are based on average hydraulic conductivity (K) values
within a material zone, but K distributions in aquifers are highly variable due to layering and other types of
heterogeneities (e.g., varying by factors of 3-10, or more, over distances as small as a few feet: Gelhar,
1984, 1986, 1987; Gelhar and Axness, 1983; Rehfeldt et al., 1992; Rehfeldt and Gelhar, 1992; Molz,
2015). The Marshall site hydrogeology certainly qualifies as "heterogeneous". This is very important to
consider for the CAP transport model calibrations because it is the high -permeability zones and/or layers
that control the time required (Tt,,,, l ) for a constituent to reach a downgradient observation point, and
22

HDR used differences in observed versus simulated Tt,,,,e, (i.e., time to travel from sources zones to
downgradient monitoring wells) as the justification for lowering measured Kd values.
Second, the history matching that HDR performed is very sensitive to the assumed time at which the
source (i.e., coal ash) is "turned on" and to the assumed distribution of source concentrations (fixed pore
water concentrations) in source area cells. Section 5.2 of CAP 1 Appendix C explains that different fixed
source concentration boundary conditions were specified for the Ash Basin (1965; model year 0), Dry
Ash Landfill Phases 1 & 2 (1984; model year 19), and the PV Structural Fill (2000; model year 35).
These different source concentrations were assumed to remain constant following their activation in the
model. For several reasons this source -area boundary condition approach is a major simplification and
generally inaccurate: coal ash was gradually and nonuniformly disposed of and distributed (spatially and
temporally) throughout the simulation period; it is very difficult (or not possible) to accurately extrapolate
geochemical or ash -water leaching conditions (i.e., predict COI pore -water concentrations) that existed
during the 2015 sampling round to conditions that may have existed in 1965 and thereafter; the actual
source -area concentration distributions are highly nonuniform, but it is not clear from the CAP modeling
reports how "... source concentrations were adjusted to match measured values... ", or if the source area
concentrations were nonuniform. All of these uncertainties are further magnified when using history
matching to calibrate a chemical transport model.
Based on the above model input errors and major uncertainties in hydraulic -conductivity variations and
source -term modeling, it is incorrect for HDR to simply reduce Kd values by factors of 10 to 100 below site
measurements (and the large database of literature Kd values) based only on the transport model "history
matching" exercises that HDR performed. My additional comments on the CAP Parts 1 and 2 transport
modeling of Closure Scenarios are listed in the following section.
Geochemical Modeling and Evaluation of Monitored Natural Attenuation
The CAP Part 2 geochemical modeling results do not include quantitative analyses of COI attenuation
rates at the Marshall site and are only qualitative in nature. In addition, HDR did not incorporate any
source/sink (e.g., precipitation/dissolution) terms representing geochemical reaction mechanisms in the
CAP 2 chemical transport model to evaluate whether such reactions are important compared to
groundwater concentration changes caused by advection, dispersion, and soil -water partitioning. In this
regard, HDR states in Section 2.10 of CAP 2 Appendix B : "A physical -type modeling approach was
used, as site -specific geochemical conditions are not understood or characterized at the scale and extent
required for inclusion in the model." Indeed, the Electric Power Research Institute (e.g., EPRI, 1984;
page S-8) has extensively reviewed subsurface chemical attenuation mechanisms applicable to the "utility
waste environment" and concluded: (i) precipitation/dissolution has not been adequately studied; and (ii)
"Quantitative predictions of chemical attenuation rates based upon mineralogy and groundwater
23

composition cannot be made because only descriptive and qualitative information are available for
adsorption/desorption mechanisms."
Nonetheless, HDR performed geochemical modeling to evaluate the technical basis for its monitored
natural attenuation (MNA) analysis; however, any quantitative MNA analysis must compare mass
transport rates and changes (e.g., grams/year per unit area normal to a groundwater pathline) in the
aquifer for the various active transport mechanisms in order to determine whether MNA is a viable
alternative (e.g., produces meaningful groundwater concentration reductions) at the Marshall site. In
Section 6.3.2 of the CAP 2 report HDR acknowledges that these quantitative evaluations were not
performed in CAP 2 and indicated that they would need to be completed as part of a Tier III MNA
assessment. Nevertheless, HDR suggested in the CAP 2 report that COI concentrations "will" or "may"
attenuate over time without completing the necessary evaluations to reach these conclusions. HDR also
states in CAP 2 Section 6.3.4 that ".... available assessment results indicate it is feasible that MNA can be
used partially or entirely to remediate groundwater at the MSS site .... ". HDR claims in CAP 2, Section
6.3.3 (page 47) that "The groundwater model did not allow for removal of COI via coprecipitation with iron
oxides, which likely resulted in a conservative prediction of COI transport." Finally, HDR concludes in
Section 7.2.2.1 of the CAP 2 report the following regarding the MNA assessment and Appendix H: "The
most significant finding was that the precipitation of iron and manganese serves to remove other COls
through co -precipitation and adsorption, thus confirming that attenuation is occurring." I saw no
quantitative analyses or evidence in the CAP 2 report or related appendices to support these claims. In
fact, the CAP 2 Appendix H emphasizes that much more geochemical data need to be collected and
chemical transport modeling with a source/sink term must be performed in a Tier III assessment to further
assess whether MNA is a viable remedial alternative.
Therefore, the CAP 2 report fails to provide any quantitative evidence supporting COI attenuation due to
co -precipitation with iron or manganese. The second component of COI attenuation evaluated in
Appendix H is chemical sorption to soil. It is important to note that, although the CAP models did not
incorporate a mechanism for co -precipitation with iron or manganese (or any COI sink term), the CAP
models did simulate attenuation due to sorption. Even with the sorption attenuation mechanism included,
CAP 2 Table 4-1 shows that for both the "existing conditions" and "cap -in -place" scenarios the following
COI will exceed North Carolina groundwater standards at the Compliance Boundary 100 years into the
future: antimony, beryllium, boron, chromium, cobalt, hexavalent chromium, thallium, and vanadium.
Further, my Table 1 shows that groundwater standards are currently exceeded at the Compliance
Boundary for iron, manganese, and total dissolved solids (i.e., iron, manganese, and TDS contaminant
plumes originating in the source areas have already reached the Compliance Boundary). The
conclusions of the MNA Tier I analyses (CAP 2 Appendix H, page 17) were that antimony, beryllium,
boron, cobalt, manganese, and selenium show limited evidence of attenuation and should not be
24

evaluated further for MNA. These Appendix H conclusions are consistent with the Table 4-1 results for
several of these COI (antimony, beryllium, boron, and cobalt). In addition, my Table 1 results support the
Appendix H conclusions that antimony, boron, cobalt, and manganese are not candidates for MNA
because these contaminant plumes have also already reached the Compliance Boundary. The Table 1
results contradict the Appendix H conclusion that chromium and vanadium should be further evaluated
because these COI currently exceed groundwater standards at the Compliance Boundary. All of these
data and CAP 2 modeling results strongly contradict the CAP 2 conclusion (e.g., Section 7.2.2.1) that "....
MNA is the recommended corrective action for the Marshall site."
Simulation of Closure Scenarios
As discussed below, CAP 1 Closure Scenario simulations greatly underestimate (by factors of 10 or
more) the time frames required to achieve meaningful groundwater concentration reductions in response
to remedial actions. Compared to the Cap -in -Place remedial alternative evaluated in the CAP Part 1, the
Excavation Scenario results in COI concentrations in groundwater that are in many cases at least a factor
of 10 smaller.
Although the CAP 1 modeling showed that Source Excavation outperforms CIP, the CAP 2 modeling did
not simulate an Excavation closure scenario. Nonetheless, the following comparisons between CIP and
Excavation impacts on groundwater concentrations are valid for both the CAP 1 and 2 model results.
This is because the main difference with the CAP 2 transport model (compared to CAP 1) is that
concentration changes resulting from either CIP or Excavation (if it was evaluated in CAP 2) occur much
more slowly (i.e., — 10x slower; 25-480x slower for arsenic, thallium, and vanadium) in the CAP 2 model
due to the much larger Kd (and Rd). The CAP 2 transport model also assumed uniform initial COI
concentrations equal to HDR's proposed provisional background concentrations (PPBC), even though the
PPBC exaggerate background levels (see above discussion) and there are no data to suggest that
background concentrations should be spatially uniform. Despite these changes in the CAP 1 and 2
models, the relative differences in groundwater concentrations between the two closure scenarios remain
about the same if the uniform starting (PPBC) COI concentrations are subtracted from the simulated
concentration versus time curves. For these reasons the following discussions focus on the CAP 1
modeling results.
Source Concentrations for Cap -in -Place Scenario
In this scenario the CAP 1 flow model predicts limited cap -induced water -table declines: approximately
14 feet (10 feet in the CAP 2 flow modeling) beneath the downgradient portion of the ash basin; and
about 2 feet, 3 feet, and 7 feet (about 1 foot in CAP 2) beneath the dry ash landfill (Phase 1), Phase II of
the dry ash landfill, and the PV structural fill, respectively. The geologic cross -sections presented in the
CSA show that the saturated coal ash thickness in the ash basin generally varies from 25 to 70 feet and
25

is on the order of 50 feet at many locations. Therefore, these cap -induced water table declines are about
a factor of four too small at most locations in the ash basin to dewater the source material. For example,
the CSA geologic cross -sections show saturated coal ash thicknesses in the active ash basin equal to
about 40-50 feet in cross-section A -A (northwest to southeast section generally through the middle of the
ash basin); 50-70 feet in cross-section B-B (southwest portion of the ash basin); and 25-45 feet in cross-
section C-C (north-northeast portion of the ash basin).
This means that under the simulated Cap -In -Place Scenario at the majority of locations in the ash basin
at least 75 percent of the coal ash, which is the source of dissolved COI, would remain saturated and
continue to leach constituents into groundwater. The CAP 1 simulations ignored this fact and set all
source concentrations equal to zero (i.e., assumed all coal ash was dewatered). Therefore, the simulated
Cap -in -Place concentrations should be much higher than the values presented in the CAP Part 1.
It is important to note, however, that the CAP Parts 1 and 2 groundwater flow model simulations
exaggerate the hydraulic effects of the cap (i.e., overstates water table lowering) due to the lateral no -flow
boundaries and the no -flow boundary at the base of the model, which is located only 50 feet below the
top of the highly -permeable, fractured bedrock aquifer (— 100 feet below ground surface). Note that the
depths of the neighboring Duke Energy and Midway Marina bedrock water supply wells, discussed
above, are 540 feet and 245 feet below ground surface (about 400 feet and 160 feet below the bedrock
surface), respectively, and provide high groundwater extraction yields of 30 and 20 gallons per minute,
respectively [Table 1 of the 2014 receptor survey report (HDR, 2014)]. The no -flow boundary conditions
along the entire western, southern, and northern grid boundaries prevent flow into the ash basin when
large, laterally inward hydraulic gradients are created by capping. In addition, the no -flow boundary
condition at the base of the flow model prevents upward flow from highly -permeable portions of the
bedrock aquifer that underlie the base of the CAP models, thus further exaggerating predicted water table
lowering.
Slow and Multirate Nonequilibrium Desorption of COI
Since the 1980's the groundwater industry has learned how difficult it is to achieve water quality
standards at remediation sites without using robust corrective actions such as source removal (Hadley
and Newell, 2012, 2014; Siegel, 2014). Two of the key reasons for this in aqueous -phase contaminated
soil are inherently low groundwater or remediation fluid flushing rates in low -permeability zones and slow,
nonequilibrium chemical desorption from the soil matrix (Culver et al., 1997, 2000; Zheng et al., 2010). A
good example of this is the "tailing effect" (i.e., very slow concentration reduction with time) that is
commonly observed with pump -and -treat, hydraulic containment systems. These factors are also related
to the "rebound effect" in which groundwater concentrations sometimes increase shortly after a
26

remediation system is turned off (Sudicky and Illman, 2011; Hadley and Newell, 2014; Culver et al.,
1997).
The CAP 1 and 2 flow models use different permeability (K) zones, but the scale of these zones is very
large and within each zone K is homogeneous even though large hydraulic conductivity variations (e.g.,
lognormal distribution) are known to exist at any field site over relatively small length scales (Molz, 2015).
Moreover, the CAP transport models assume linear, equilibrium soil -water partitioning which corresponds
to instantaneous COI release into flowing groundwater. The transport code (MT3D) has the capability of
simulating single -rate nonequilibrium sorption, but the Close Scenario simulations did not utilize this
modeling feature. Slow desorption of COI can also be expected at the Marshall site because sorption
rates are generally highly variable and multi -rate (Culver et al., 1997, 2000; Zheng et al., 2010), and Kd
values are nonuniform spatially (Baes and Sharp, 1983; EPRI, 1984; De Wit et al., 1995). The CAP flow
and transport models can be expected to significantly underestimate cleanup times required to meet
groundwater standards at the compliance boundary because they do not incorporate these important
physical mechanisms.
Adequacy of the Kd Model for Transport Simulation
The laboratory column experiment effluent data (e.g., CAP 1 Appendix D) generally gave very poor
matches with the analytical (one-dimensional) transport model used to compute Kd values. Since the
CAP transport models solve the same governing equations in three dimensions, the adequacy of the Kd
modeling approach for long-term remedial simulations should have been evaluated in much more detail in
the modeling appendix.
The transport modeling also did not evaluate alternative nonlinear sorption models such as the Freundlich
and Langmuir isotherms (Hemond and Fechner, 1994), which are input options in the MT31D transport
code. Several of the batch equilibrium sorption experiments (CAP 1 Appendix D) exhibited nonlinear
behavior, and such behavior is commonly observed in other studies (e.g., EPRI, 1984). However, HDR
only computed linear sorption coefficients (i.e., Kd) for the Marshall site in CAP Part 1. In CAP Part 2
HDR did fit Freundlich isotherms to the batch sorption data for selected COI (CAP 2 Appendix C, Tables
1-8) but did not use these Freundlich isotherm results in the CAP 2 transport modeling. De Wit et al.
(1995) showed that the nonlinear sorption mechanism is similar in importance to aquifer heterogeneities
in extending remediation time frames.
Closure Scenario Time Frames
Many of the simulated concentration versus time (CvT) curves presented in CAP 1 Appendix C are either
incorrect or highly misleading with respect to future groundwater concentration variations that may occur
under the Existing Conditions, Cap -In -Place (CIP), and Excavation scenarios. For example, several CvT
27

curves suggest that concentrations of several COI at various locations in the aquifer system would be as
much as factors of 10 to 100 greater if all of the ash source material is removed (Excavation) compared to
either doing nothing (Existing Conditions) or CIP for a period of 200 years into the future (e.g., arsenic,
antimony, boron, chloride, cobalt, chromium, hexavalent chromium, selenium, sulfate, thallium, and
vanadium at AB-1 BR; antimony at AB-5BR; arsenic, selenium, and vanadium at AB-6BR; barium at AL-
2D; beryllium at AB-1 S & AL-1 S; chromium at AB-3D; and selenium, sulfate, and vanadium at AL-4D).
Further, the model results for some of these CvT curves show groundwater concentrations increasing at a
dramatic rate 200 years into the future even if all source material is removed (e.g., selenium and
vanadium at AB-6BR; arsenic, cobalt, and hexavalent chromium at AB-1 BR; arsenic at AB-613R). The
CvT curves are also highly inconsistent at the same location (e.g., for the Excavation Scenario at AB-1 BR
arsenic concentrations increase significantly for 200 years, but boron concentrations decrease
significantly for the same time period) and between different locations (e.g., for the same COI the CvT
curves suggest that at some locations Excavation is much better than CIP, but at other locations CIP is
much better than Excavation).
In addition to these issues, the CAP 1 chemical transport model underestimates the time intervals
required to achieve groundwater concentration reductions (i.e., achieve groundwater quality restoration)
by a factor of 10 or more, as discussed in different parts of my report. In other words, the CAP 1 transport
model significantly overestimates the rate at which concentrations may reduce in response to remedial
actions such as capping or source removal. This is due to several factors, including major errors in model
input data, model calibration mistakes, field data analysis errors, and oversimplified model representation
of field conditions (e.g., hydraulic conductivity) and transport mechanisms (e.g., chemical
sorption/desorption). These limitations of transport models for realistically predicting cleanup times have
been recognized by the groundwater industry for the past few decades based on hands-on experience at
hundreds of extensively -monitored remediation sites.
Even if we ignore the above problems with the CvT curves in CAP 1 Appendix C and the factors of 10 or
more errors in cleanup time predictions with the CAP model, the remediation time frames for the
Excavation Scenarios are still more than two centuries for several constituents due to slow groundwater
flushing rates from secondary sources (surrounding residual soil) left in place after excavation and due to
high chemical retardation factors for most of the COI. However, excavation of secondary -source material
would further accelerate cleanup rates under this alternative. The simulated Cap -In -Place concentration
reduction rates are much slower, compared to excavation, but are also incorrect (i.e., overestimated)
because the cap -induced water -table lowering only dewaters a small percentage (— 25 percent) of the
source -area coal ash, as discussed above, and the CAP flow models overestimate cap -induced water -
table lowering due to boundary condition errors. Furthermore, these simulation time frames are well
beyond the prediction capabilities of any chemical transport model for a complex field site, especially one
28

that is as geochemically complex as the Marshall site. The historical model -calibration dataset (1965-
2015) is also significantly smaller than the predictive (remediation) time frames. In addition, the "history
matching" technique used to calibrate the transport model (e.g., major reduction in measured Kd values)
was not performed correctly by HDR.
Cap -In -Place versus Excavation Closure Scenarios
Even though the CAP 1 model significantly underestimates remediation time frames, the CAP 1 Closure
Scenario simulations (using CvT curves that do not appear to be suspect) demonstrate several significant
advantages of excavation for restoring site groundwater quality versus CIP. First, predicted COI
concentration reductions in groundwater are in many cases at least a factor of 10 greater with excavation
compared to CIP [e.g., antimony and boron (AB-31D, AB-5BR); arsenic, barium, cobalt, chromium,
hexavalent chromium, thallium (AB-3D); beryllium, cobalt, chromium, sulfate, thallium (AB-5BR); refer to
CAP Appendix C]. Further, if the cap -in -place simulations would have been performed correctly the
simulated cap -in -place concentrations would be much higher because predicted water -table lowering due
to the cap would be insufficient to dewater all of the coal ash.
Although the CAP 1 modeling demonstrated that the CIP closure alternative would be much less effective
than excavation, and that CIP would only dewater about one-fourth of the saturated coal -ash thickness in
many areas, HDR eliminated excavation from consideration in CAP 2. In Section 7.1 of the CAP 2 report
HDR assumes that "groundwater flow and geochemical modeling indicates that attenuation by a
combination of sorption, chemical precipitation, and dilution by surface water infiltration and fresh
groundwater effectively dissipates COls in groundwater beneath and downgradient of the source areas"
and that "... it is reasonable to assume that COls remaining in groundwater will decrease in concentration
overtime as upgradient non -impacted water moves through the aquifer." As discussed above, HDR
provided no quantitative analysis or evidence in the CAP 2 report or related appendices to support this
claim. Considering that up to 75 percent of the coal -ash source material would remain saturated with CIP
and that multiple exceedances of groundwater standards at the Compliance Boundary currently exist
(with no historical data to indicate that these Compliance Boundary concentrations are decreasing with
time), it is not reasonable to make sweeping assumptions about future concentration changes. Tier III
MNA analyses require rigorous quantitative evaluations using the CAP transport model with a source/sink
term that incorporates geochemical reactions to support MNA as a viable corrective action. CAP 2 did
not provide this information.
As discussed above, the CAP Part 2 flow model did include a very small number of residential wells (4 of
the 89 neighboring private wells and none of the four public water supply wells), but the CAP 2 modeling
report (CAP 2, Appendix B) did not show simulated hydraulic head maps with these residential wells
pumping and did not provide any discussion or analyses of the long-term potential for these wells to
29

capture COI dissolved in groundwater. Further, the private bedrock wells that HDR chose to include in
the CAP 2 model are located upgradient from the ash basins; HDR should have included all of the
private wells located immediately north, west, and south of the Duke Energy property boundary and the
four public water supply wells to the south (refer to my previous discussion revised maps of bedrock
groundwater flow directions). In CAP 2 section 4.1.5 HDR discusses that fact that the CAP 2 flow model
was used to compute 1-year, reverse particle pathlines for these bedrock residential wells (Figure 15 in
CAP 2 Appendix B) to determine their short-term groundwater capture zones. However, the residential
well reverse pathline tracing should have been performed for a much longer time period (e.g., from the
beginning of coal ash disposal to the present) to evaluate whether COI may have migrated from source
areas to these wells. In addition, if HDR had extended the CAP 2 model grid much farther to the north,
west, and south the capture zones for the remaining 85 private and four public water supply wells could
have been determined, as I discuss earlier in my report.
The CAP Closure Scenarios do not include hydraulic containment remedial alternatives (e.g., gradient
reversal) for the bedrock aquifer that would address the risk of off -site COI transport. As discussed
above, the CSA data show many exceedances of groundwater standards in bedrock inside the
compliance boundary. In addition, downward groundwater flow components from the deep overburden to
bedrock aquifers were measured during the CSA in the southeastern portion of the site where
groundwater flow in the bedrock aquifer is off -site (Figures 2 and 3), and ponded water in the ash basin
impoundment has historically created a large downward hydraulic gradient beneath the ash basin. The
cap -in -place alternative does not address either concentration reduction or off -site chemical migration
control in the fractured bedrock aquifer.
Conclusions
Based on my technical review and analyses of the referenced information for the Marshall site I have
reached the following conclusions:
• A total of 21 Compliance Boundary groundwater samples exceeded North Carolina groundwater
standards for these COI: antimony, boron, chromium, cobalt, iron, manganese, total dissolved
solids, and vanadium. Of these 21 exceedances, 19 were greater than the proposed provisional
background concentrations by HDR, which exaggerate background levels;
• The statistical analyses of historical, shallow -aquifer background groundwater concentrations at
the Marshall site (monitoring well MW-4) are invalid. The time periods between groundwater
sample collection from this well are too small and the concentration data are not independent;
30

• There is a significant risk of chemical migration from the ash basin to neighboring private and
public water supply wells in fractured bedrock. The design of the CAP Parts 1 and 2 flow and
transport models prevents the potential for off -site migration from being evaluated;
• The limited CAP model domain size (Parts 1 and 2); the no -flow boundary conditions along the
western, southern, and northern boundaries; the impermeable boundary at the base of the model
at a depth of only about 50 feet below the top of the fractured bedrock aquifer; the incorrect
hydraulic boundary condition representations of Lake Norman and the active ash basin; and
HDR's failure to include bedrock -aquifer groundwater extraction from most neighboring private
and public water supply wells prevent simulation and analysis of off -site COI migration;
• The CAP Closure Scenario simulations greatly underestimate (by factors of 10 or more) the time
frames required to achieve meaningful groundwater concentration reductions in response to
remedial actions. This is due to oversimplification of field fate and transport mechanisms in the
CAP Parts 1 and 2 models and several model input errors;
• The simulated water table lowering for the Cap -in -Place Scenario is about a factor of four too
small at most locations in the ash basin in order to dewater all source material. In addition, the
actual cap -induced water table elevation reduction would be much less than predicted due to the
incorrect no -flow boundary conditions (3 of 4 lateral boundaries and the bottom bedrock surface)
in the flow model. Therefore, the remediation time frames for this scenario would be much
greater because most of the source zone would still be active with the cap installed;
• For either the Existing Condition or Cap -in -Place Model Scenario groundwater concentrations of
many coal -ash constituents much higher than background levels will continue to exceed North
Carolina groundwater standards at the Compliance Boundary because saturated coal -ash
material and secondary sources will remain in place;
• Source -area mass removal included in the Excavation Scenario results in COI groundwater
concentration reductions that are at least a factor of 10 greater compared to Cap -in -Place at
many locations. Additional excavation of secondary sources would further accelerate
concentration reductions;
• Due to an incorrect boundary -condition representation of the active ash basin, the CAP models
underestimate by a factor of three or more both the mass loading of COI into Lake Norman and
the corresponding Lake Norman water concentrations (attributable to coal ash ponds) estimated
by the groundwater/surface-water mixing model;
• The CAP Part 2 geochemical modeling and monitored natural attenuation (MNA) evaluations do
not provide the required quantitative analyses (e.g., numerical transport modeling) of COI
attenuation rates necessary to support MNA as a viable corrective action and are only qualitative
in nature. The CAP 2 chemical transport modeling, which included attenuation by sorption,
31

demonstrated that MNA is not an effective remedial option for several COI (e.g., antimony,
beryllium, boron, chromium, cobalt, hexavalent chromium, thallium, and vanadium);
• The CAP Closure Scenarios do not include hydraulic containment remedial alternatives for the
bedrock aquifer and do not address the risk of off -site COI transport. CSA data show 22
exceedances of groundwater standards in bedrock inside the Compliance Boundary. The cap -in -
place alternative does not address off -site chemical migration control in the fractured bedrock
aquifer; and
• Future Compliance Monitoring at the site should include much more closely -spaced Compliance
Wells to provide more accurate detection, and the time intervals between sample collection
should be large enough to ensure that the groundwater sample data are statistically independent
to allow accurate interpretation of concentration trends.
32

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35

Figures
36

10'
10'
00 10,
C
0
i 10-1
0
10"
10'
KBR = 0.68 fWay
���• KBR=4.7fflday
Q
K,=2.0ftlday
\
i
i
i14
• i
i
• i
■ r
14 ` • r
"O
r " r ■
•
i
r
i
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Figure 1
Drawdown in Bedrock Versus Distance from Pumping Well
37
4000

BG-2BR
�r
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1 --a' AB•15BR
-..
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P tAB-GBRJ _` i 4 p
qpABABR.
` ... Lake Norman j 1
Ash Basin Waste Boundary - i, AB-5BR � e`�'. t ' r I • /' j \
1 �
F e Lake Norman
~GWA-1BR % •j• •
tr
�$ DId Country Church V/
Duke Supply Well
•1 I TI f \ 1 `v
Figure 2
Bedrock Hydraulic Head Map with Off -Site Pumping
38

GlR.I B' R� I
w AB-68R
Ash Basin Waste Boundary
BG-26R
726
MW-14BR
Ip
AB-1BR
Lake Norman
Lake Norman
BR
*I Old CouELty Church]
lre F0
Figure 3
Bedrock Hydraulic Head Map without Off -Site Pumping
39

Table
40

Table 1. Exceedances of NC Groundwater Standards at Compliance Boundary and in Bedrock
for 2015 Monitoring Well and Seep Samples
Constituent
Antimony
Background
Sample Sample Location Concentration Concentrationsc,d
Name Depth Measured PPBC
GWA-2D Deep CB 4.1
AB-6BR
Bedrock
BR
1.3
Arsenic
S-2
Seep
Ash Basin
87.1
Barium
S-2
Seep
Ash Basin
990
Beryllium
S-2
Seep
Ash Basin
15.2
Boron
MW-14S
Shallow
CB Me
2,500e
AL-1 S
CB Me
4,300e
AB-1 S
CB Me
4,500e
MW-7S
CB Me
4,400e
MW-14D
Deep
CB Me
2,500e
AL-1 D
CB Me
1,100e
AL-2BR
Bedrock
BR
2,100
S-2
Seep
Ash Basin
4,000
MSSW001
S001
6,000
41
Standard
2L IMAC
2_5 1 -
ND (BG-1 D, BG-3D), 0.33 (MW-4D)
ND (BG-2BR)
5
10 -
157.3
700 -
1
4 -
100
700 -
ND (BG-1S,-2S,-3S; MW-4)
ND (MW-4D, BG-1 D),
26 (BG-3D)
ND (BG-2BR)

Table 1. Continued
Constituent
Sample
Name
Sample
Depth
Location
Concentration'
Background
Concentrations,,d Standard'
Measured PPBC 2L IMAC
Chromium
GWA-7S
Shallow
CB
22.1
11.3 10 -
5.7 (BG-1 S), 9 (BG-2S),
2.5 (MW-4), 73.7 (BG-3S)
GWA-2D
Deep
CB
182
3.1 (BG-1 D), 6.6 (BG-3D),
1.2 (MW-4D)
AL-2BR
BR
17.5
80.4 (BG-2BR)
S-2
Seep
Ash Basin
85.7
Cobalt
GWA-2S
Shallow
CB
2.6
2.5 - 1
1.2 (BG-1 S), 0.38 (BG-2S),
ND (MW-4), 5 (BG-3S)
AB-5BR
Bedrock
BR
7.9
GWA-1 BR
BR
1.7
11.9 (BG-2BR)
S-2
Seep
Ash Basin
333
MSSW001 S001
92
Iron
GWA-7S
Shallow
CB
12,300
467.1 300 -
480 (BG-1 S), 140 (BG-2S),
510 (MW-4), 3,400 (BG-3S)
GWA-7D
Deep
CB
2,200
310 (BG-1 D), 250 (BG-3D),
77 (MW-4D)
42

Table 1. Continued
Constituent
Sample
Name
Sample
Depth'
Location
Concentration`
Background
Concentrationsc,d
Measured PPBC
Standard
2L IMAC
AB-1 BR
Bedrock
BR
2,800
467.1
300 -
Iron
GWA-1 BR
BR
780
(continued)
MW-14BR
BR
320
18,200 (BG-2BR)
AB-15BR
BR
1,300
Lead
S-2
Seep
Ash Basin
227
35.9
15 -
Manganese
GWA-2S
Shallow
CB
92
48
50 -
GWA-7S
CB
510
160 (BG-1 S), 20 (BG-2S),
19 (MW-4), 180 (BG-3S)
GWA-7D
Deep
CB
76
54 (BG-1 D), 24 (BG-3D),
4.1 (MW-4D)
AB-1 BR
Bedrock
BR
54
GWA-1 BR
BR
780
380 (BG-2BR)
AB-5BR
BR
650
AB-15BR
BR
270
S-2
Seep
Ash Basin
11,600
MSSW001 S001
8,500
Selenium
AL-2BR
Bedrock
BR
24
1.6 (BG-2BR) 10
20 -
S-2
Seep
Ash Basin
25.1
43

Table 1. Continued
Constituent
Sample
Name
Sample
Depth'
Location
Concentration`
Background
Concentrationsc,d Standard
Measured PPBC 2L IMAC
Thallium
S-2
Seep
Ash Basin
8.6
0.5 - 0.2
MSSW001 S001
0.6
Total
GWA-2D
Deep
CB
650,000
85,400 500,000 -
Dissolved
142,000 (BG-1 D), 183,000 (BG-3D),
Solids
82,000 (MW-4D)
S-2
Seep
Ash Basin
892,000
MSSW001 S001
989,000
Vanadium
GWA-2S
Shallow
CB
0.33
3.9 - 0.3
GWA-7S
CB
23.7
3.8 (BG-1 S), 44 (BG-2S),
2.2 (MW-4), 14.4 (BG-3S)
GWA-7D
Deep
CB
6.1
3.5 (BG-1 D), 21.9 (BG-3D),
MW-10D
CB
3.2
2.8 (MW-4D)
GWA-2D
CB
12.2
GWA-1 BR
Bedrock
BR
3.5
100 (BG-2BR)
MW-14BR
BR
4.3
AB-6BR
BR
7.4
GWA-9BR
BR
3.9
AB-5BR
BR
0.76
AB-1 BR
BR
0.43
AB-9BR
BR
2.4
AL-2BR
BR
4.5
S-2
Seep
Ash Basin
566
44

a Refer to the CSA Report for Monitoring Well locations and screen intervals
b CB = Monitoring Well located on the Ash Basin Compliance Boundary; BR = Monitoring Well screened in Bedrock
`All values are total measured concentration in the water samples in units of micrograms per liter
d Refer to the CSA Report for information regarding placement of Background Wells.
PPBC = Proposed Provisional Background Concentration (CAP Report Table 2-2)
e CBM = Projected downgradient concentration at Compliance Boundary based on calibrated one-dimensional, analytical
chemical transport model discussed in this Report
45

DOUGLAS J. COSLER, Ph.D., P.E.
10240 Stonemede Lane
Matthews, NC 28105
EDUCATION
704-246-7702
[e-mail]
Ph.D. Chemical Hydrogeology The Ohio State University 2006
C.E.D. Civil Engineer Degree Massachusetts Institute of Technology 1987
M.S. Civil & Environmental Engineering The Ohio State University 1979
B.S. Civil & Environmental Engineering The Ohio State University 1977
Summa Cum Laude
PROFESSIONAL HISTORY
2009- Principal Hydrogeologist and Commercial Software Developer,
Adaptive Groundwater Solutions LLC, Charlotte, NC
2007-2009 Environmental Consultant, Hart Crowser, Portland, OR
2006-2007 Research Scientist and Instructor, School of Earth Sciences, The Ohio State University,
Columbus, OH
2003-2006 Research Assistant, School of Earth Sciences, The Ohio State University, Columbus, OH
1987-2003 Environmental Consultant, MACTEC (now AMEC), Nashua, NH
1984-1987 Research Assistant, Department of Civil & Environmental Engineering,
Massachusetts Institute of Technology, Cambridge, MA
1979-1984 Environmental Consultant, D'Appolonia Consulting Engineers, Pittsburgh, PA
1977-1979 Research Assistant, Department of Civil & Environmental Engineering,
The Ohio State University, Columbus, OH
REGISTRATION
Registered Professional Engineer: Pennsylvania and Vermont
HONORS AND AWARDS
Member of Tau Beta Pi
University Graduate Fellowship, The Ohio State University, 1979
The Brown Scholarship (top undergraduate in Civil Engineering), The Ohio State University, 1977
PROFESSIONAL EXPERIENCE
Environmental Consulting
1979-1984, 1987-2003, 2007-present
• Areas of Specialization: Groundwater flow and chemical transport analyses and computer modeling,
contaminant fate and transport in the environment, numerical code development, ground water and
surface water hydraulics and hydrology, contaminant fate and transport, expert witness testimony and
litigation support, hydrogeologic investigation, nonaqueous phase liquid (LNAPL/DNAPL)

Douglas J. Cosler, Ph.D., P.E. - Page 2 of 15
investigation, subsurface remediation and remedial design, natural attenuation and risk assessment, and
hydrologic and wetlands impact evaluation.
Responsibilities: Principal Hydrogeologist/Hydrologist responsible for technical aspects of a wide
variety of projects, including: investigation, remediation, and regulation of Superfund, RCRA, and
other hazardous waste sites; ground water flow and chemical transport model development for
numerous projects; expert witness testimony and litigation support for several clients and hazardous
waste sites; natural attenuation/biodegradation assessments for chlorinated solvent and petroleum
contamination sites; volatile organic compound vapor (soil gas) migration and exposure assessment;
exposure modeling for health risk assessments; hydraulic and hydrologic modeling of impoundments
and spillways for U.S. Army Corps of Engineers dam safety assessments; stream hydraulics and solute
transport modeling; hydrologic impact assessment for minerals and coal mining; leachate collection
system modeling and design for waste disposal impoundments; and design of runoff, sedimentation,
and erosion control plans.
Types of Sites and Contaminants: Sites investigated include: landfills, manufactured gas plants, wood -
treating facilities, chemical plants, water supply well fields, gasoline and fuel oil storage/delivery
facilities, nuclear waste disposal sites, hazardous waste incinerators, mining operations, and various
industrial facilities. Investigated dissolved, nonaqueous-phase (LNAPL/DNAPL), and vapor -phase
contaminants: chlorinated solvents, gasoline and fuel oil constituents, wood -treating products (e.g.,
creosote and pentachlorophenol), coal tars, polychlorinated biphenyls, pesticides, dioxins and furans,
phenolic compounds, flame retardants (PBDE), phthalates, radionuclides, biological constituents, and
various metals.
• Representative Project Experience:
Expert Witness Testimony and Litigation Support
Litigation and Expert Witness Support, Wells G&H Superfund Site, Woburn, MA (MACTEC). Doug
provided technical support for property owners involved in litigation related to economic damages
associated with groundwater contamination in a fractured bedrock aquifer resulting from upgradient sources
of chlorinated solvents (DNAPL and aqueous -phase). He completed a thorough review ofRI/FS technical
reports (including groundwater pumping tests) and performed modeling of chemical transport in the
fractured bedrock aquifer that accounted for the effects of horizontal anisotropy on transport directions.
Based on the evaluations, Doug developed an alternative site conceptual model that incorporated the effects
of bedrock fractures on solute transport in order to define probable contaminant migration pathways in
overburden and bedrock aquifers that were not identified in historical documents. He demonstrated the
existence of these pathways using two-dimensional models of groundwater flow and contaminant advection
(particle pathlines) that established a connection between DNAPL sources areas and groundwater
contamination beneath the subject properties.
Expert Witness Testimony and Litigation Support, Gasoline Remediation Site and Sewer/House Explosion
Case, Winneconne, WI (MACTEC). Doug provided expert witness testimony and investigated the potential
causes of and chemical fate and transport mechanisms responsible for a house explosion case. Plaintiffs
alleged that vadose and saturated zone petroleum remediation activities at a service station located a few
blocks from the residence and subsequent transport of gasoline vapors through a sewer line/backfill were
the fuel source for the explosion. He analyzed gasoline vapor transport rates and concentrations in the

Douglas J. Cosler, Ph.D., P.E. - Page 3 of 15
subsurface at the service station site, in the 12-inch sewer pipe, and within the sewer backfill. Doug
demonstrated that gasoline vapors could not have migrated to the residence between the time that
remediation stopped and the house exploded. He also demonstrated that gasoline vapors at explosive levels
could not have migrated up the sewer lateral and into the house. His analyses showed that sewer gas
(methane) was the likely cause of the explosion because a methane source was present in the sewer line
near the residence (sewage blockage due to tree root growth through pipe joints) and lighter -than -air
methane naturally migrates upslope along sewer lines and laterals.
Remedial Investigation and Feasibility Study (REFS) and Expert Witness Testimony for the Old
Southington Landfill Superfund Project, Southington, CT (MACTEC). Doug developed a three-
dimensional groundwater flow model (MODFLOW) to evaluate source control alternatives for a municipal
landfill that received solid and semi -solid waste materials (primarily VOC). In the vicinity of the landfill,
high -permeability deposits in the bottom portion of the aquifer and the presence of a neighboring pond
caused large downward groundwater flow components that complicated contaminant transport analysis. He
directed the site investigation that focused on the landfill and underlying and downgradient portions of the
regional aquifer. He prepared an expert report and provided expert witness testimony for insurance
litigation regarding the nature and timing of waste disposal in the landfill.
Expert Witness Testimony, Hydrogeologic Investigations of a Gasoline Station, CT (MACTEC). Doug
provided expert witness testimony regarding the results of a hydrogeologic investigation to determine the
source of petroleum contamination within a telephone company utility conduit. He provided opinions
concerning groundwater flow and chemical transport rates in the surrounding aquifer, age dating of
petroleum products, and the potential relationship of gasoline -related contaminants in a utility manhole to
historical petroleum releases at an upgradient gasoline station.
Remedial Investigation, Site Remediation and Expert Witness Testimony, FormerMGP Site, Concord, NH
(MACTEC). Historical discharges of carburetted water gas tar contaminated a 10-acre pond and the
underlying groundwater with aqueous -phase constituents and NAPL. Contaminants included PAHs and
BTEX compounds. Doug designed the hydrogeologic investigation to determine the nature and extent of
groundwater and NAPL contamination. He performed data evaluations to assess the potential for vertical
and horizontal migration of NAPL and the potential for contamination of a river adjacent to the site. He
also prepared two expert reports and provided expert witness testimony for two related insurance litigation
actions regarding the timing and ongoing nature of pond contamination and contamination from the former
MGP, located upgradient from the pond.
Remedial Design Evaluation and Expert Witness Support, Chlorinated Solvent and Petroleum
Contamination Site, MO (MACTEC). Doug served as a company expert for litigation involving a
groundwater extraction system designed to control LNAPL and aqueous -phase contaminants. Plaintiffs
(downgradient property) claimed that the extraction system was not controlling contamination. Doug
developed a hydraulic model of the site, analyzed in detail the groundwater capture zone, and demonstrated
that the system was very effective in controlling LNAPL and aqueous -phase contaminant migration.

Douglas J. Cosler, Ph.D., P.E. - Page 4 of 15
Expert Witness Testimony, Petroleum Contamination Site, Concord, NH (MACTEC). Doug served as a
hydrogeology, coal tar, and petroleum fate and transport expert for property damage litigation involving a
fuel oil distributor and former MGP site. The plaintiff claimed that coal tar contamination from the former
MGP caused environmental damage and increased construction costs for a new hotel being built at the site.
Doug performed petroleum transport and fingerprinting analyses and demonstrated that the fuel oil
distributor located immediately upgradient from the subject property was the likely source of contamination
- not coal tar.
Remedial Investigation, Design, and Expert Witness Testimony, Former MGP Site, Laconia, NH
(MACTEC). Doug reviewed site investigation reports and evaluated hydrogeologic conditions, contaminant
sources, and NAPL mobility at a former MGP site. Historical MGP waste releases (coal tar) had
contaminated soil and groundwater and dissolved -phase constituents, and NAPL had migrated into adjacent
surface water bodies. He developed conceptual remedial alternatives for the site and evaluated NAPL
containment and collection designs. He prepared an expert report and provided expert witness testimony
for insurance litigation regarding the timing and ongoing nature of pond contamination.
Expert Witness Report, Former MGP Site, Goshen, IN (MACTEC). Provided litigation support and expert
report preparation for a case involving a former MGP site. Technical aspects of the project involved
hydrogeology, coal tar, and petroleum fate and transport.
Remedial Alternatives Evaluation and Expert Witness Report Preparation, Former Electronics
Manufacturing Facility, Manchester, NH (MACTEC). Historical releases of tetrachloroethene (PCE) and
PCE dissolved in fuel oil caused soil and groundwater contamination at the site. Contaminants were
present as dissolved -phase constituents and DNAPL. Doug evaluated data regarding site hydrogeology and
contaminant fate and transport to assess the relative contributions of the PCE sources. He evaluated the
feasibility and costs of potential remedial alternatives and prepared an expert report assessing the relative
contributions of the two different sources of contamination.
Groundwater Flow and Aqueous -Phase Chemical Fate and Transport
Developed Adaptive Groundwater, a Three -Dimensional Groundwater Flow and Chemical Transport
Code based on the Adaptive Mesh Refinement Method (Adaptive Groundwater SolutionsLLC). Adaptive
Groundwater is a highly -scalable, three-dimensional numerical code for high -resolution simulation of
groundwater flow and solute transport problems. Dynamic adaptive mesh refinement (AMR) and multi-
threading are used to automatically generate unstructured grids to handle multiple scales of flow and
transport processes. This is done by translating and adding/ removing telescoping levels of progressively
finer subgrids during simulation (hiips://www.rockware.com/product/overview.php?id=329).
Groundwater Flow, Contaminant Transport, and Biodegradation Model, Feasibility Study and Natural
Attenuation Assessment, Estes Landfill Site, Phoenix, AZ (MACTEC). Doug developed three-dimensional
groundwater flow and contaminant transport models to simulate current and future, long-term TCE, cis 1,2-
DCE, and vinyl chloride (VC) concentrations in the sand and gravel, overburden aquifer at the Estes
Landfill site. He used MODFLOW and MT3D99 to simulate chemical transport and fate mechanisms,

Douglas J. Cosler, Ph.D., P.E. - Page 5 of 15
including advection, dispersion, dilution by surface water, sorption to soil, and TCE>DCE>VC
biotransformation modeled as a sequential, first -order decay -chain process. He computed site
biotransformation rates from historical chemical data and transport model calibration. He demonstrated
that natural attenuation was a viable remedial alternative, primarily due to significant source -area VOC
depletion and high biodegradation rates (reductive dechlorination and direct oxidation of DCE and VC).
Combined MTCA REFS and RCRA RFI/CMS Plus Independent Cleanup Actions, Confidential Metals
Manufacturing Facility, WA (Hart Crowser). As the Hydrogeologist and Technical Lead for PCB fate and
transport issues during work on this large metals manufacturing facility, Doug developed a three-
dimensional transport model of the PCB plume that incorporated the variation in mobility and mass fraction
of each of the 209 congeners in the PCB mixture. He constructed a three-dimensional groundwater
flow/transport model (MODFLOW/MT3D99) to analyze the capture zones and effluent concentration
variations for multiple extraction wells with various screened -interval depths. He investigated PCB
contamination sources at the site, including industrial wastewater transfer line leaks and
unsaturated/saturated zone water contact with contaminated soils.
Doug also developed an innovative two-dimensional, rate -limited PCB congener and colloid transport
model to evaluate fate and transport mechanisms at the site. The model simulates the transport of all 209
PCB congeners simultaneously, both as aqueous -phase (i.e., dissolved in groundwater) and colloidal
(sorbed to mobile colloids flowing with the groundwater) fractions. Colloid filtration due to interactions
with the porous media is included. Because of the high groundwater velocities at the site, the model also
incorporates rate -limited soil to groundwater chemical partitioning (nonequilibrium chemical sorption) and
nonequilibrium groundwater to colloid PCB sorption mechanisms.
Remedial Design and Natural Attenuation Modeling, Savage Municipal Water Supply Superfund Site,
Milford, NH (MACTEC). Doug developed three-dimensional groundwater flow and solute transport
models of this extensive drinking water aquifer using MODFLOW and MT3D. DNAPL releases (PCE and
TCA) caused groundwater contamination. Doug directed evaluation of data collected during field
permeability testing, monitoring well sampling, and extensive vertical groundwater profiling using
microwells. He modeled the effectiveness of various remedial design alternatives that included soil
excavation and hydraulic containment in the source area, hydraulic control of downgradient portions of the
PCE and TCA plumes, and natural attenuation due to biodegradation, natural groundwater flushing, and
dilution by rainwater and river recharge. Doug estimated biodegradation rates using 1) long-term
measurements of VOC concentration reductions along the plume centerline, 2) comparisons of parent to
daughter compound concentrations, and 3) computations of total VOC mass reductions in the aquifer. In
addition, the natural attenuation evaluation used other analytical parameters (e.g., electron acceptor
concentrations) to assess the strength of the biodegradation evidence based on the Technical Protocol for
Natural Attenuation of Chlorinated Aliphatic Hydrocarbons in Ground Water. He used the MODFLOW
model and the AQTESOLV software to analyze the pumping test data. He used AQTESOLV and the
Hantush solution for partially -penetrating wells to analyze the single -well tests.
Natural Attenuation Software Development, Risk -Based Correction Action (RBCA) Tier 2 Analyzer
(MACTEC). Doug authored the commercial software package RBCA Tier 2 Analyzer, a two-dimensional

Douglas J. Cosler, Ph.D., P.E. - Page 6 of 15
groundwater flow and biodegradation (transport) model. The software provides five different transport
simulation capabilities: 1) single constituent; 2) the PCE>TCE>DCE>VC sequential -decay sequence that
occurs during reductive dechlorination; 3) instantaneous BTEX biodegradation with a single electron
acceptor (oxygen); 4) instantaneous BTEX biodegradation with multiple electron acceptors (oxygen,
nitrate, iron(III), sulfate, carbon dioxide); and 5) kinetics -limited BTEX biodegradation with multiple
electron acceptors. The transport model can simulate either equilibrium or non -equilibrium (one-, two-, or
multi -site sorption) partitioning between water and soil. The software provides a design tool that can be
used for a wide variety of problems, including the analysis of remedial alternatives such as groundwater
pump and treat systems (including extraction well concentration "tailing" effects caused by slow
contaminant desorption from soil), natural attenuation evaluation, and source remediation level
determination.
Remedial Investigation and Feasibility Study (RETS) for the Gallups Quarry Superfund Site, Plainfield, CT
(MACTEC). Designed investigations of this former waste disposal site to evaluate the nature and extent of
groundwater and residual soil (source area) contamination. The initial field program included geophysical
surveys, a source -area soil vapor survey, installation and sampling of 50 microwells, wetlands delineation,
and surface water/sediment sampling. Doug performed three-dimensional computer visualization of the
contaminant plume based on microwell results to direct monitoring well installation. He performed two-
dimensional flow modeling to identify an off -site source of groundwater contamination and developed a
three-dimensional groundwater flow and chemical transport model (MODFLOW/MT3D) of the site to
facilitate the evaluation of remedial alternatives during the FS process.
Darling Hill Superfund Site Remedial Investigation and Feasibility Study (RUFS), Lyndonville, VT
(MACTEC). As Technical Leader during the Rl/FS for a municipal well field contaminated with VOCs,
Doug directed the site investigation, which focused on a disposal area upgradient of the well field and a
highly permeable sand and gravel aquifer. The investigation included geophysical investigations, a soil gas
survey, boring and well installations, groundwater sampling and analysis, air sampling, surface water and
sediment sampling, and pumping and slug tests. Doug developed a three-dimensional analytical
groundwater flow model to evaluate potential plume control at the disposal area and the municipal well
field. He also constructed a one-dimensional, numerical contaminant transport model, coupled with a
chemical leaching model of the waste disposal area, to estimate cleanup times in the regional aquifer in
response to various source control alternatives.
Evaluation ofNew Monitoring Well Design and Sampling Techniques to Determine Vertical Concentration
Variations in an Aquifer, Independent Research Project (MACTEC). Performed independent research to
determine new monitoring well designs and sampling techniques that can provide the necessary data to
evaluate vertical concentration variations in an aquifer. Doug developed two-dimensional, numerical
axisymmetric groundwater flow and chemical transport models to analyze time -dependent monitoring well
concentrations during sampling as a function of various vertical concentration distributions in the aquifer
and different well designs. The results of this research demonstrated that discrete intervals of monitoring
wells with long screens (e.g., 10 to 20 feet or more) can be sampled in a manner that allows both the
vertical plume location and concentration variation in the aquifer to be determined. The research also
showed that the time vs. concentration responses of a well during a sampling event lasting a few days

Douglas J. Cosler, Ph.D., P.E. - Page 7 of 15
exhibit characteristic shapes that can be directly related to aquifer properties and well design parameters
and the vertical concentration distribution. He computed a series of concentration vs. time "type curves,"
analogous to time-drawdown type curves for aquifer permeability tests, that can be matched with measured
time -concentration responses.
Evaluation and Recommendation of Hydrologic Models for the Department of Natural Resources,
Commonwealth ofKentucky (D'Appolonia). Doug performed an extensive analysis of hydraulic/hydrologic
simulation models for the Department of Natural Resources, Commonwealth of Kentucky. He evaluated
more than 60 hydrologic (i.e., watershed), surface water, and groundwater computer models for simulating
flow and contaminant transport that could be used in determining the potential hydrologic and
environmental impacts of coal mining operations at various locations in Kentucky. He made several code
modifications to the USACE's STORM, Stream Hydraulics Package (SHP), and Water Quality for
River/Reservoir Systems (WQRRS) models.
Mine Inflow Evaluation for the Shell Minerals Company, IN (D'Appolonia). To evaluate groundwater
inflow rates into a 30-square mile underground coal mine in southwestern Indiana during a 30-year mine
life, Doug developed a three-dimensional computer model to simulate groundwater flow into various mine
panels from an overlying sandstone aquifer by three processes: (1) artesian flow from portions of the
aquifer outside of the mine plan area, (2) gravity drainage of water from the voids in the overlying
sandstone, and (3) infiltration through a shale layer separating the aquifer and coal seam.
Site Investigation and Hydrogeologic Study, Massachusetts Contingency Plan (MCP), Manufacturing
Facility (MACTEC). Designed an investigation to characterize the nature and extent of VOC contamination
in a shallow overburden -bedrock aquifer system underlying a manufacturing facility. The investigation
included soil vapor analysis, overburden and bedrock monitoring well installation, and permeability testing.
Doug designed an interim pump and treat system to control contaminant migration from a source area
containing PCE in the form of a NAPL.
Hydrogeologic Study and Groundwater Remediation for an Industrial Facility, NH (MACTEC). Served as
the Technical Leader during the Phase I investigation and performed data evaluation for this 70-acre
salvage yard site. The investigation included evaluation of VOC contamination in the groundwater and the
design, installation, and operation of a pump and treat system. Doug developed a two-dimensional,
axisymmetric groundwater flow model to evaluate the data from a pumping test involving a large -diameter,
partially penetrating water supply well. He performed groundwater flow modeling for the final engineering
design of the pump and treat system.
Design of Waste Disposal Facility for the U.S. Department of Energy, WV (D'Appolonia). Doug designed
the leachate collection system for a waste disposal facility that contained process waste from a proposed
solvent -refined coal preparation plant near Morgantown, West Virginia. The 800-acre-foot impoundment
consisted of two embankments approximately 60 feet in height constructed from coarse refuse, a primary
spillway system, a 5-foot clay liner beneath the impoundment, and an underdrain system directly above the
liner to reduce the liquid content of the waste and thereby decrease seepage of contaminants through the
clay blanket. He performed a detailed computer simulation of the underdrain system performance to

Douglas J. Cosler, Ph.D., P.E. - Page 8 of 15
determine the hydrostatic pressure reduction above the clay liner as a function of waste permeability, drain
spacing, ground slope, saturated waste depth, and drain dimensions.
Remediallnvestigation/Feasibility Study (RI/FS) forAllied Chemical Company, OH(D'Appolonia). Doug
performed a groundwater contamination evaluation and remedial design study for a chemical plant
bordering the Ohio River. He developed two-dimensional groundwater flow and chemical transport models
to evaluate migration beneath a stream to a local municipal well field and computed a groundwater mass
balance to determine the percentage of site groundwater flow reaching the well field, the Ohio River, a
neighboring stream, and an adjacent property. He used the calibrated model to screen remedial alternatives
and determine cleanup levels.
Vadose Zone Flow and Transport
Vadose Zone and Hydrogeologic Modeling of Storm Water Detention Facilities, Vancouver, WA (Hart
Crowser). Doug developed a three-dimensional saturated/unsaturated groundwater flow model of a storm
water detention facility using the USGS computer program SUTRA (Saturated -Unsaturated Transport). He
dynamically linked the SUTRA code with watershed hydrology (i.e., runoff hydrograph) and detention
basin (storage and discharge rate vs. elevation) models. He modified the SUTRA code to incorporate the
hydrologic and hydraulic models as subroutines, which provided storm water runoff inflow rates and time -
dependent water elevations in the detention basins. Water elevations were converted to time -dependent
specified pressure node values in SUTRA. He added transient discharge rates through the porous
boundaries of the detention facilities (computed by SUTRA) to the outflow hydrographs. Doug used the
models to evaluate the impacts of several factors on the storm water detention facility performance and
design, including groundwater table mounding, hydraulic conductivity (K) heterogeneity, the ratio of
vertical to horizontal K, detention basin storage capacity, and storm event recurrence interval.
Hydrologic Impact Assessment at a Waste Isolation Pilot Plant for the U.S. Department of Energy, NM
(D'Appolonia). Evaluated potential salt removal from beneath a radioactive waste disposal facility
enclosed in a 2,000-foot-thick salt formation in southeastern New Mexico. The objective was to determine
the size and geometry of a dissolution cavity that could form beneath the facility in the next 10,000 years
due to hydraulic interaction with a water -bearing unit located 1,000 feet below. Doug evaluated potential
mechanisms for salt dissolution and migration to the underlying unit (e.g., diffusion or advection currents
produced by density differences), derived analytical equations to quantify the salt removal rate and cavity
geometries, and developed a computer model of salt transport in the water -bearing unit.
Hydrologic Impact Assessment and Vadose Zone Modeling for the Exxon Minerals Company, WI
(D'Appolonia). Evaluated potential hydrologic impacts on the groundwater and surface water regimes due
to minerals mining and the related disposal of inorganic wastes at a 400-acre site. Doug developed
site -specific computer models of saturated/unsaturated flow and transport to predict changes in groundwater
flow rates, water quality, and water levels in hydraulically -connected lakes. He used predictions
encompassing an estimated 100-year mine life to negotiate a work plan with the Wisconsin DNR.

Douglas I Cosler, Ph.D., P.E. - Page 9 of 15
Remedial Investigation/Feasibility Study, Vadose Zone Modeling, and Remedial Design for a Former
Wood -Treating Facility, Olympia, WA (MACTEC). Doug directed the hydrogeologic investigation and
remedial design for this wood -treating site. The site involved tidally influenced groundwater contaminated
with polynuclear aromatic hydrocarbons (PAH), chlorinated dibenzo-p-dioxins, pentachlorophenol (PCP),
LNAPL (PCP carrier oil), and DNAPL (creosote). The investigation consisted of installation of monitoring
wells specifically designed to detect LNAPL and DNAPL, aquifer tests, long-term tidal monitoring, salt
water intrusion evaluation, aquifer water budget (infiltration) modeling, and treatability studies for
bioremediation of soil and groundwater. Doug designed a NAPL and groundwater extraction system and
developed a two-dimensional, numerical groundwater flow model as part of the groundwater extraction
system design. He performed one-dimensional unsaturated zone vapor transport modeling to estimate
leachate and soil gas flux loadings to groundwater. He used the AquiferTest software to analyze the
pumping test data and analyzed tidal variations in water -level amplitude and phase lag to evaluate hydraulic
conductivity variations.
Vapor -Phase Transport Modeling, Lipari Landfill Superfund Site, NJ (MACTEC). Doug constructed a
vertical, one-dimensional vapor (soil gas) flux model to calculate VOC emission rates from contaminated
soil downgradient of the landfill. He used the emission estimates as source terms in an atmospheric
dispersion model to compute air concentrations in the immediate vicinity of the contaminated soil and at
several downgradient receptors and used the results to estimate health risks caused by inhalation exposure.
These modeling results and health risk estimates provided the necessary data to determine excavation
depths for contaminated soil and the thickness of a soil cap that would reduce future exposures to
acceptable levels.
Health Risk Assessment, Massachusetts Contingency Plan (MCP), Auto Auction Facility (MACTEC).
Doug performed the exposure assessment for potential exposure to VOC contamination resulting from a
leaking underground fuel tank. He developed a one-dimensional, unsaturated zone, soil gas flux model for
estimating indoor air concentrations in domestic buildings overlying subsurface areas contaminated by the
spill. He also developed a two-dimensional groundwater transport model for estimating downgradient
concentrations beyond the existing monitoring network.
Development of Performance Goals for Remedial Measures, a Risk -Based Approach for a Manufacturing
Facility, OH (MACTEC). Computed exposure point concentrations for a health risk assessment to
determine performance goals for soil and groundwater remediation at a 2-acre site contaminated with
several organic chemicals. Doug was responsible for the exposure assessment that involved the
development of a groundwater transport model to perform two basic calculations: 1) rate of chemical
removal from the contaminated areas of the unsaturated zone soil, and 2) two-dimensional chemical
advection and dispersion in the shallow groundwater unit downgradient from the source area. The
computation of contaminant removal from the unsaturated zone involved a one-dimensional (vertical)
analysis of advection due to infiltration and molecular diffusion through the water and air phases of the soil.
He also calculated contaminant dilution in the sand layer using a calibrated two-dimensional (horizontal)
transport model.

Douglas J. Cosler, Ph.D., P.E. - Page 10 of 15
NAPL Characterization and Modeling
Petroleum Extraction System Optimization, Former Manufacturing Facility, MA (MACTEC). Developed
and calibrated a two-dimensional fuel oil flow model using the SPILLCAD software to evaluate historical
free product recovery volumes and optimize extraction well locations and oil and groundwater pumping
rates. He used the calibrated oil flow model to (i) demonstrate the effectiveness of the recovery system in
minimizing the future risk of off -site free product transport and (ii) estimate the time period required to
obtain the remedial goals for the site.
Remedial Design and Investigation, Former Manufactured Gas Plant (MGP) Site, Fort Wayne, IN
(MACTEC). Doug designed a groundwater and NAPL (coal tar) containment and collection system for this
former MGP site adjacent to a river. A sheet pile wall provided containment along the perimeter of the site,
and a trench system with collection pipes and wells collected groundwater and NAPL. Doug developed a
three-dimensional groundwater model (MODFLOW) to determine the required water levels in the various
collection trench segments to provide hydraulic control of the groundwater plume and optimize NAPL
recovery.
Remedial Design and Investigation, Former MGP Site, Hammond, IN (MACTEC). Doug designed a
NAPL (coal tar) containment system at this former MGP site to prevent NAPL migration into a river that
formed the downgradient site boundary. Doug evaluated slurry wall and sheet piling designs. He
developed a three-dimensional groundwater model (MODFLOW) of the site to evaluate optimal
containment wall designs (e.g., wing wall orientation and length) for minimizing off -site groundwater
transport of contaminants. In addition, he used the model to evaluate water level increases on the
upgradient side of the wall and potential design options (e.g., gates) to mitigate this effect.
Surface Water Modeling
Evaporation Prediction for Heated Water Bodies, Research Project for the Electric Power Research
Institute, GA (Massachusetts Institute of Technology). Evaluated the evaporative heat loss from a series of
heated (70 degrees Celsius) cooling ponds (1 to 5 acres) and canals. Doug developed a one-dimensional
hydrothermal model to evaluate the temperature distribution and the energy budgets for the system of water
bodies. He performed a literature review of evaporation prediction methods, emphasizing methods capable
of predicting combined free (thermally induced) and forced (wind) evaporative heat loss. The research
resulted in the formulation of a new evaporation equation that more accurately predicts heat loss from water
bodies for conditions, such as high water temperature, where both free and forced evaporation are
important.
Site Evaluation of Two Nuclear Power Plants for Northeast Utilities, New England (Massachusetts
Institute of Technology). Doug evaluated waste heat transport from two nuclear power generation facilities
located along the coast of New England. He developed two-dimensional numerical tidal hydrodynamic and

Douglas J. Cosler, Ph.D., P.E. - Page 11 of 15
thermal transport models to evaluate temperature increases in adjacent estuaries. He used the temperature
simulations to locate new water intakes and to determine heat effects on sediment biota.
Sewage Disposal Outfall Siting Study for the Massachusetts Water Resources Authority, Boston, MA
(Massachusetts Institute of Technology). Doug evaluated tidal hydrodynamics and contaminant transport in
Boston Harbor as part of the design of the new Deer Island sewage treatment plant. He used mass loading
data at the existing Deer and Nut Island treatment plants in conjunction with measured concentration
distributions for six chlorinated VOCs to calibrate dispersion coefficients and first order surface
volatilization rates for the compounds. He used current meter measurements for calibration of the two-
dimensional, harmonic hydrodynamic model. He simulated harbor concentrations for several planned
diffuser outfall locations using a two-dimensional, transient contaminant transport model that was linked
with the hydrodynamic model.
Estimate of Toxic Chemical Loadings to Puget Sound, Washington State Department of Ecology Toxics
Cleanup Program, WA (Hart Crowser). Doug was the Technical Director assisting Ecology with a multi-
year effort to develop strategies, remedial actions, and performance measures to protect and restore the
overall health of the Puget Sound ecosystem. He identified toxic chemicals of concern and characterized
contaminant sources and pathways (e.g., stormwater runoff, municipal/industrial wastewater effluents,
groundwater discharge, chemical spills, and atmospheric deposition). For each of the 17 chemicals of
concern, Doug estimated average annual rates of mass loading (runoff rates and stormwater concentrations)
to Puget Sound via each pathway. He developed a probabilistic approach to characterizing data uncertainty
that involved computing cumulative probability distributions for each mass loading pathway.
Surface Water Quality Impact of Treatment System Effluent, In dus tri-Plex Trust, Sup erfund Site, Woburn,
MA (MACTEC). Developed two-dimensional hydrodynamic and contaminant transport models of a 10-acre
impoundment to evaluate water quality impacts of the treatment system effluent from a series of
groundwater extraction wells. Both organic (VOC) and inorganic contaminants were present in the waste
stream. Steady-state hydrodynamic simulations, qualitatively verified by field observations, provided an
understanding of the velocity distribution in the impoundment that was a function of both tributary and
treatment system inflows and large water depth variations of 5 to 20 feet. Doug incorporated depth -
averaged contaminant concentration distributions computed using the transport model in an aquatic impact
assessment designed to determine preferred effluent discharge locations and rates.
Surface Water Quality Impact of Dam Breach, Bangor Hydroelectric, ME (MACTEC). Doug developed a
numerical, one-dimensional dissolved oxygen transport model to evaluate receiving water quality impacts
from hydrodynamic changes caused by the breaching of a dam in a large river system. He used the
USACE's stream hydraulics model HEC-1 to simulate river stage and velocity for a range of breach
elevations and stream flow rates. For each flow field the transport model provided estimates of dissolved
oxygen changes in the river system. These results demonstrated the beneficial effects of leaving the dam in
place.
Sedimentation and Erosion Control Plan Design for DuPont, SC (D'Appolonia). Designed the
sedimentation and erosion control plan for a 200-acre site disturbed during construction of a waste

Douglas J. Cosler, Ph.D., P.E. - Page 12 of 15
processing facility. Evaluations included calculation of storm runoff hydrographs, the design of three
sedimentation basins with heights ranging from 10 to 20 feet and storage capacities of 3 to 5 acre-feet,
hydraulic design of primary and emergency spillways for the basins, specification of diversion ditch
locations and sizes, and design of various other erosion control measures.
Research
Research Assistant, School of Earth Sciences, The Ohio State University, Columbus, OH, 2003 — 2006.
• Dissertation: Numerical Investigation of Field -Scale Convective Mixing Processes in Heterogeneous,
Variable -Density Flow Systems Using High -Resolution Adaptive Mesh Refinement Methods.
Advisor: Motomu Ibaraki.
• Ph.D. Research: Developed new adaptive simulation software for high -resolution, field -scale modeling
of non -linear, variable -density ground water flow systems. Examined practical problems such as in situ
chemical oxidation of contaminants by dense treatment fluids, water supply applications such as
freshwater storage and recovery in coastal aquifers, and saltwater intrusion assessments. The software
automatically adjusts to multiple scales of convective mixing processes by translating and
adding/removing telescoping levels of progressively finer subgrids to maintain a specified numerical
accuracy throughout the global simulation domain. Adaptive mesh refinement methods and higher -
order Eulerian-Lagrangian discretization schemes were used to construct a three-dimensional flow and
transport code capable of simulating fine -scale (-1-10 cm) instability development and resulting
convective mixing in field -scale variable -density ground water flow systems. Because the flow and
transport solutions for each subgrid are computed independently, field -scale simulations are broken into
multiple smaller problems that can be modeled more efficiently and with finer detail.
Convective mixing in heterogeneous porous media is shown to be more amenable to prediction than
previously concluded. Convective mixing rates are related to the geostatistical properties of the aquifer
(variance and mean of the log permeability distribution, horizontal and vertical correlation scales), the
fluid density difference, the magnitude of local small-scale dispersion, the effects of different
permeability field realizations, the injection well size and orientation, hydraulic parameters such as
injection rate and regional hydraulic gradient, and the spatial resolution. Further, three-dimensional
fluid mixing rates are related to mathematical expressions for density -dependent macrodispersivity that
are based on stochastic flow and solute transport theory.
Colloid transport modeling: Simulated colloid and radionuclide injection experiments for fractured -
rock test site in Switzerland. Used two-dimensional finite element code COLFRAC (flow and transport
of colloids and contaminants in discretely -fractured porous media) to perform sensitivity analyses
involving: fracture aperture, spacing, connectivity; secondary permeability and diffusion rate in rock
matrix; equilibrium and kinetic radionuclide sorption parameters for colloids and fracture walls;
longitudinal dispersivity; colloid filtration coefficient; and radionuclide decay rate.
Research Assistant, Department of Civil & Environmental Engineering, Massachusetts Institute of
Technology, Cambridge, MA, 1984 — 1987.
• Areas of Specialization: Hydraulics/hydrology, surface water heat transport mechanisms, heat transfer
in unstable atmospheric boundary layers, tidally- and density -driven flow/transport, chemical
fate/transport, numerical methods (finite element, finite difference, Eulerian-Lagrangian).
• Thesis: Evaporation from Heated Water Bodies, Predicting Combined Forced Plus Free Convection.
Advisor: Eric Adams. Constructed hydrothermal model to compute evaporative heat loss from 70' C
cooling ponds and canals based on simulated temperature distributions and energy budgets.

Douglas J. Cosler, Ph.D., P.E. - Page 13 of 15
Formulated new evaporation equation that more accurately predicts heat loss from heated water bodies
for conditions where both free and forced evaporation are important.
• Surface water modeling: Analyzed tidal hydrodynamics and contaminant transport in Boston Harbor
and Massachusetts Bay for design of new Deer Island sewage treatment plant. Constructed two-
dimensional, finite element hydrodynamic (harmonic) flow and Eulerian-Lagrangian transport models
to evaluate mixing of treatment plant effluent for alternative multi -port diffuser designs and locations.
• Hydrothermal modeling: Developed two-dimensional finite element, tidal hydrodynamic and thermal
transport models to evaluate waste heat transport in estuaries for two nuclear power generation
facilities.
Research Assistant, Department of Civil & Environmental Engineering, The Ohio State University,
Columbus, OH, 1977 — 1979.
• Areas of Specialization: Turbulent transport processes, hydraulics/hydrology, numerical methods.
• Thesis: Numerical Simulation of Turbulence in a Wind -Driven, Shallow Water Lake. Advisor: Keith
Bedford. Developed three-dimensional hydrodynamics code (finite difference) using large -eddy
simulation techniques. Evaluated energy cascade process for turbulent flows in lakes through spectral
analysis of velocity fluctuation time series.
Independent Research, 1990 — 2002.
• Effects of Rate -Limited Mass Transfer, Vertical Concentration Distribution, and Well Design on
Ground -Water Sampling and Remediation: Constructed numerical axisymmetric flow and
nonequilibrium (multi -rate) transport models to simulate monitoring/extraction well concentrations as a
function of plume shape and well design. Showed how sample concentration variations with time can
be used to determine vertical concentration distributions in plumes and aquifer properties such as
vertical anisotropy ratio, porosity, retardation factor, and soil -water mass transfer parameters.
• Commercial Contaminant Transport and Biodegradation Modeling Software: Author of the Risk -
Based Correction Action (RBCA) Tier 2 Analyzer, a two-dimensional ground water flow,
nonequilibrium (multi -rate) transport, and biodegradation model. Software is based on Eulerian-
Lagrangian solution of transport equation with alternating direction implict (ADI) technique for
dispersion, and fourth -order Runge-Kutta scheme for PCE decay chain and BTEX biodegradation
terms.
Teaching
Instructor, School of Earth Sciences, The Ohio State University, Columbus, OH, 2006.
• Instructor for graduate -level courses in hydrogeology and environmental risk assessment, and
undergraduate courses in hydrology and water resources.
Teaching Assistant, School of Earth Sciences, The Ohio State University, Columbus, OH, 2003-2006.
• Taught several class sessions of graduate -level courses in hydrogeology and environmental risk
assessment, and an undergraduate course in water resources. Assisted in the preparation of lecture
materials and homework assignments, developed class projects involving field applications, and guided
group discussions among students during classes.
• Instructor for laboratory sessions of class in earth sciences and water resources. Prepared review
materials and lectured on fundamental concepts, and directed students during laboratory exercises.
Mathematics Tutor, Boston Partners in Education, Boston, MA, 2001.

Douglas J. Cosler, Ph.D., P.E. - Page 14 of 15
• Served as volunteer tutor for high school students in Boston Public School system. Taught individual
studies mathematics course in preparation for Massachusetts Comprehensive Assessment System
(MCAS) proficiency tests.
Teaching Assistant, Department of Civil & Environmental Engineering, Massachusetts Institute of
Technology, Cambridge, MA, 1984 — 1987.
• Instructed laboratory sessions of undergraduate fluid mechanics course. Conducted laboratory
demonstrations and directed students during experiments using various fluid mechanics apparatus. Led
field trip to conduct a stream tracer study and evaluate stream hydraulics and dispersion characteristics.
Engineering Tutor and Coordinator, College of Engineering, The Ohio State University, 1974 — 1977.
• Tutored undergraduate engineering students in mathematics, physics, chemistry, and engineering
mechanics. Served as student program coordinator responsible for evaluating undergraduate
educational requirements, and tutor assignments and schedules.
PUBLICATIONS
Cosler, D.J. 2006. Numerical Investigation of Field -Scale Convective Mixing Processes in
Heterogeneous, Variable -Density Flow Systems Using High -Resolution Adaptive Mesh Refinement
Methods. Ph.D. Dissertation, The Ohio State University, School of Earth Sciences, Columbus, Ohio.
Cosler, D.J. 2004*. Effects of Rate -Limited Mass Transfer on Water Sampling with Partially Penetrating
Wells. Ground Water 42, no. 2: 203-222.
Cosler, D.J. 2000. Risk -Based Correction Action (RBCA) Tier 2 Analyzer, Two -Dimensional
Groundwater Flow and Biodegradation Model, Ref. Manual. Waterloo Hydrogeologic, Inc., Waterloo,
Ontario, Canada.
Cosler, D.J. 1997*. Ground -Water Sampling and Time -Series Evaluation Techniques to Determine
Vertical Concentration Distributions. Ground Water 35, no. 5: 825-841.
Adams, E.E. and Cosler, D.J. 1990*. Evaporation from Heated Water Bodies: Predicting Combined
Forced Plus Free Convection. Water Resources Research 26, no. 3: 425-435.
Adams, E., Kossik, R., Cosler, D., MacFarlane, J., and Gschwend, P. 1990. Calibration of a Transport
Model Using Halocarbons. Estuarine and Coastal Modeling, M.L. Spaulding, ed., ASCE, New York,
N.Y., pp. 380-389.
Andrews, D.E. and Cosler, D.J. 1989*. Preventing and Coping with Water Pollution. Journal of Testing
and Evaluation, ASTM 17, no. 2: 95-105.
Walton, R., Kossik, R., Adams, E., and Cosler, D. 1989. Far -Field Numerical Model Studies for Boston's
New Secondary Treatment Plant Outfall Siting. Third National Conference on Hydraulic Engineering,
New Orleans, Louisiana, August 14-18.
Adams, E.E. and Cosler, D.J. 1988*. Density Exchange Flow Through a Slotted Curtain. Journal of
Hydraulic Research 26, no. 3: 261-273.
Adams, E.E. and Cosler, D.J. 1987. Predicting Circulation and Dispersion Near Coastal Power Plants:
Applications Using Models TEA and ELA. Massachusetts Institute of Technology Energy Laboratory
Report No. MIT -EL 87-008, 113.
Adams, E.E., Cosler, D.J., and Helfrich, K.R. 1987. Evaporation from Heated Water Bodies: Analysis of
Data from the East Mesa and Savannah River Sites. Civil Engineer Degree Thesis, Massachusetts
Institute of Technology, Cambridge, Massachusetts.
Cosler, D.J. and Snow, R.E. 1984*. Leachate Collection System Performance Analysis. Journal of
Geotechnical Engineering, ASCE 110, no. 8: 1025-1041.
Snow, R.E. and Cosler, D.J. 1983. Computer Simulation of Ground Water Inflow to an Underground
Mine. In Proceedings of the First Conference on Use of Computers in the Coal Industry, AIMS, (Y.J.
Wang and R.L. Sanford editors), pp. 587-593. W. Virginia University, August 1-3.

Douglas J. Cosler, Ph.D., P.E. - Page 15 of 15
Cosler, D.J. 1979. Numerical Simulation of Turbulence in a Wind -Driven, Shallow Water Lake. M.S.
Thesis, The Ohio State University, Columbus, Ohio.
* Denotes peer -reviewed journal.
PRESENTATIONS
Cosler, D.J. 2015. An Intelligent Graphical User Interface for MODFLOW and MT31) based on
Dynamic Adaptive Mesh Refinement Methods. MODFLOW and More 2015 Conference.
Colorado School of Mines, Golden, Colorado, May 31 - June 3.
Cosler, D.J. 2013. Numerical Simulation of Multiscale Transport Processes in Variable -Density Flow
Systems Using High -Resolution Adaptive Mesh Refinement Methods. MODFLOW and More 2013
Conference. Colorado School of Mines, Golden, Colorado, June 2-5.
Cosler, D.J. 2006. Numerical Investigation of Field -Scale Convective Mixing Processes in Heterogeneous,
Variable -Density Flow Systems Using High -Resolution Adaptive Mesh Refinement Methods.
Geological Society of America Annual Meeting, October 22-25, Philadelphia, Pennsylvania.
Cosler, D.J. and Ibaraki, M. 2006. Numerical Investigation of Multiple-, Interacting -Scale Variable -
Density Ground Water Flow Systems. American Geophysical Union, Western Pacific Geophysics
Meeting, July 24-27, Beijing, China.
Cosler, D.J. and Ibaraki, M. 2005. Numerical Investigation of Multiple-, Interacting -Scale Variable -
Density Ground Water Flow Systems. Geological Society of America Annual Meeting, October 16-19,
Salt Lake City, Utah.
Cosler, D.J. 2003. Modeling the Effects of Multirate Mass Transfer on Water Sampling with Partially -
Penetrating Wells. Geological Society of America Annual Meeting, November 2-5, Seattle,
Washington.

Duke Energy Memorandum Regarding CAMA
Requirements

Introduction
The purpose of this document is (1) to establish Duke Energy's compliance with the groundwater
assessment and corrective action requirements of the North Carolina Coal Ash Management Act
("CAMA"), and (2) to identify information relevant to the Department's assessment and prioritization of
coal ash surface impoundments for closure under CAK8A. Asexplained further below, Duke Energy has
submitted all groundwater information required by CAMA to date and will continue to submit information
required bythe Department pursuant ioCAK0Aauthority. /\maresult, there ionnbasis for any finding by
the Department that Duke Energy has failed tocomply with CAMA. Further, the information submitted by
Duke Energy, supplemented by other available, relevant information, is sufficient for the Department to
make an evidence -based assessment of the factors that CAMA requires for impoundment prioritization;
as a result, it would be legal error for the Department to prioritize the surface impoundments without full
consideration of, and findings offact on, each ofthe factors.
U. Compliance with Groundwater Assessment and Corrective Action
CAMA's groundwater assessment and corrective action provisions are located at North Carolina
General Statutes § 130A-309.211. Duke Energy has complied with subsections (a) and (b)aefollows:
A. Suboection(o)-GmnundvvoterAmomaament
Subsection (a) requires Duke Energy to, at each of its surface impoundments, do three things..
(1) submit a proposed Groundwater Assessment Plan for approval by the Department, (2) begin
implementing a Groundwater Assessment Plan approved by the Department, and (3) submit a
Groundwater Assessment Report describing all exceedances of groundwater quality standards
associated with the impoundment. Duke Energy has moteach ofthese requirements.
As you are aware, Duke Energy submitted draft Groundwater Assessment Plans for all of its
surface impoundments inNorth Carolina onSeptember 26.2014. The Department provided comments
on November 5, 2014, and Duke Energy submitted revised Groundwater Assessment Plans on
December 30.2D14. The Department conditionally approved the Plans on various dates earlier this year,
NCOENRO194488

and Duke Energy began implementing each plan within 1Ddays ufapproval. Groundwater Assessment
Reports describing all exceedances of groundwater quality standards associated with the various surface
impoundments were submitted tothe Department inAugust and September. The Department's approval
of the plans reflected a determination that the plans met CAMA requirements. Duke Energy's
implementation of the plans, including the conditions of approval, under the Department's close oversight,
further supports a conclusion that the requirements of Subsection (a) were met.
Aoonrdingto8)ep|ain|anguagenf8ubaaodon(a).Ouk*EnerAy'snom[dkannewbh8)o
requirements does not depend on the substantive content of the Groundwater Assessment Reports.
Duke Energy was required to make plans to assess various groundwater factors, which it did. The
Department approved the plans, thereby determining that the Plans would assess those groundwater
factors. Duke Energy diligently implemented the Plans. There isnofurther requirement inSubsection
(a), or anywhere else in CAMA, that the results of the groundwater assessments definitively establish or
disprove the existence ofany condition otasite. |nfact, CAK8Aanticipates that groundwater
assessments performed under Subsection (a) may not supply all the information desired by the
Department —Subsection (b)(a) requires Duke Energy to include in a proposed Groundwater Corrective
Action Plan ^[a]nyother infonnationne|atodtogroundvvaderauooaoman{naquirodbythaDepartmont.^
Had the General Assembly anticipated that Groundwater Assessment Reports would be definitive
documents, there would have been no need to authorize the Department to request additional information
in the proposed Corrective Action Plans.
B. Submeudon(b)-CorrectivaAction
Similarly, Subsection (b)requires Duke Energy Lodntwo things: (1)submit aproposed
Groundwater Corrective Action Plan, and (2) begin implementing the Groundwater Corrective Action Plan
once i1has been approved bythe Department. The deadline for completion ofthe first requirement has
not yet passed. The Department and Duke Energy agreed that the Corrective action plans would be
submitted in two parts, and Duke Energy has submitted the first part for all fourteen sites with surface
impoundments The deadline for submission ofthe second part has not yet arrived.
NCOENRO194489

The Corrective Action Plans contain each of the elements from Subsection (b)(1) that were to be
included inthe first part submittals. The Corrective Action Plans were prepared byqualified professionals
and contain work performed tothe industry standard. Additional information will besubmitted inthe part
two submittals. It is premature to evaluate Duke Energy's compliance with this requirement until the
submittals are complete.
Ui Prioritization mfSurface Impoundments
Under CAMA, the Department is charged with developing proposed classifications of
surface impoundments according tothe procedures in Worth Carolina General Gtututea§ 13OA,300.213.
The prioritization must be based on "a site's risks to public health, safety, and welfare; the environment;
and natural resnuroes.^ N.C.Gen. Gtat. §13OA-30Q213(a). |nassessing the risks, the Department must
evaluate groundwater data submitted under § 13OA-309.21 1, discharge information submitted under §
130A,38Q.212.and any other information deemed relevant. Further, the Department must consider all of
the following:
no Any hazards topublic health, safety, orwelfare resulting from the impoundment.
"o The structural condition and hazard potential nfthe impoundment.
uo The proximity of surface waters to the impoundment and whether any surface waters are
contaminated or threatened by contarnination as a result of the impoundment.
co Information concerning the horizontal and vertical extent of soil and groundwater
contamination for all contaminants confirmed to be present in groundwater in exceedance
of groundwater quality standards and all significant factors affecting contaminant
transport.
on The location and nature of all receptors and significant exposure pathways.
oo The geological and hydroOnn|oOira|features influencing the movement and chemical and
physical character ofthe contaminants.
oo The amount and characteristics of coal combustion residuals in the impoundment.
on Whether the impoundment is located within an area subject to a 1 00-year flood.
'o Any other factor the Department deems relevant tuestablishment ofrisk.
The Department must issue written declarations, including findings uffact, documenting
proposed risk classification.
NCOENRO194490

This section requires the Department to make decisions based on the available evidence
regarding each ofthe listed factors.' hwould not boconsistent with this requirement for the Department
to make a classification decision based solely on one factor and disregard valid information about the
others. Further, the section anticipates that the Department will make decisions before complete
information about a site is available. For example, it does not require the Department to oump|o{o|y know
the vertical and horizontal extent of soil and groundwater contamination for each site; rather it requires
that the Department consider infort'nation conceming the vertical and horizontal extent. Similarly, i1does
not require the Department to know all factors that might conceivably affect contaminant transport orall
conceivable exposure pathways, it requires the consideration only of significant factors affecting
contaminant transport and significant exposure pathways.
Additional support for this conclusion is found in the fact that this section defines an iterative
process by which evolving data, review, and commentary are used to classify surface impoundments as
|ow, intennediate, or high risk. This iterative process begins with e provisionally proposed classification by
the Department by December 31, 2015 and extends for a minimum (no maximum) of six months while
feedback and additional data are received and evaluated by the Department and the Coal Ash
Management Commission.
Taken as a whole, this section requires the Department to make evidence -based decisions using
the best available information inthe record. Duke Energy has submitted substantial evidence into the
administrative record. Any classification should be based on this evidence, with the understanding that
additional information requests may be relevant to the degree of certainty in the classification but do not
undermine the validity ofthe classification.
IV. Conclusion
The Groundwater Assessment Plans, Groundwater Assessment Reports, and Groundwater
Corrective Action Plans submitted by Duke Energy to the Department meet the requirements of CAMA
and provide vast data, analysis, and findings. Chief among the findings inadetermination bylicensed
1 Aside from CAMA, the North Carolina Administrative Procedure Act requires that agency decisions be
supported "by substantial evidence ... in view of the entire record as submitted." G.S. 1 50B-51 (b)(5).
NCOENRO194491

environmental geologists that none of the sites pose an imminent hazard to human health or the
environment.
Duke Energy is committed to meeting the Department's expectations by providing additional data,
fully leveraging the time provided by CAMA's iterative process to ensure final classifications reflect the
best science and engineering. Nonetheless, Duke Energy has complied with all ofCAMA'srequirements
to date, and available information is sufficient for the Department to develop classifications as required by
CAK4A.
NCOENRO194492

3 -12-15 NCDENR Conditional Approval of Revised
Groundwater Assessment Work Plan

AFFFA
74i'AT
NR
North Carolina Department of Environment and Naturai Resources
Pat McCrory
Governor
March 12, 2015
Mr. Harry Sideris
Senior Vice -President
Environment, Health, and Safety
Duke Energy
526 South Church Street
Mail Code EC3XP
Charlotte, NC 28202
Re: Marshall Steam Station
NPDES Permit No. NCO0O4987 — Catawba County, North Carolina
Conditional Approval of Revised Groundwater Assessment Work Plan
Dear Mr. Sideris:
Donald R. van der Vaart
Secretary
On December 31, 2014, the Division of Water Resources (Division) received the revised.
Groundwater Assessment Plan (GAP) for the above listed facility. The revised GAP was submitted
in response to the DWR's Review of Groundwater Assessment Work Plan letter dated November 4,
2014. A review of the plan has been completed and several deficiencies or items requiring
clarification were noted. Therefore, in order to keep the site assessment activities on a timely
schedule, the Division has approved the revised GAP under the condition that the following deficient
items are addressed in the Groundwater Assessment Report;
• Comment Section 5.3 Hydrogeologic Site Characteristics:
The initial site conceptual model (ISCM) section of the revised GAP does not provide a
clear, cohesive description of how constituents of potential concern (CQPCs) may migrate
from the source(s) to the receptors through various pathways. It is acknowledged that there
is information available to develop an ISCM, but the data are not presented in a manner such
as groundwater elevation maps, geologic maps, cross -sections that depict detailed site
conditions, flow diagrams, or in a tabulated format 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.
1611 Maid Service Center, Raleigh, North Carolina 27699-1611
Phone: [phone] Internet: http:Nwww.ncwater,orgi
An Equal Opportunity' Affrrnatwc Action Employer — Made in part by recycled paper
NCDENROO68627

Marshall Steam Station
March 12, 2015
Page 2 of 3
a Comment 7.1.4 Bedrock Monitoring Wells:
The Division suggests installing bedrock monitoring wells at several locations in order to
provide data for assessment of multiple flowpath transects across the site, A bedrock
monitoring well is recommended near the compliance boundary in the vicinity of well cluster
MW-14S/D based on analytical results obtained from those locations that suggest a possible
coal ash signature. Installation of a bedrock monitoring well in the vicinity of the MW-7S/D,
MW-8S/D, and MW-9S/D well clusters is recommended in order to provide a monitoring
location downgradient of the active ash basin adjacent to Lake Norman, In addition, bedrock
monitoring wells are recommended in the immediate vicinity of proposed well clusters at
AB-6S/D, AB-15S/SL/D, and AL-2S/D so bedrock groundwater can be characterized in the
ash basins and landfill.
0 Con-iment Section 7.2 Groundwater Sampling and Analysis:
Direction provided in the EPA Region I Low 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 ± 0,1 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 be -fore samples are 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 Qannot 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. transpo.1.1 models.
The Division recommends analyzing samples for radionuclides from wells monitoring well
locations MW-14S/D because of elevated concentrations of boron, iron, manganese and
sulfate detected during previous sampling events. Other well locations recommended for
collecting and analyzing samples for radionuclides include MW-6S and MW-7S so
groundwater can be assessed for these constituents beneath the landfill and doNAMgradient of
the active ash basin, respectively.
Comment Table 5 — Groundwater, Surface Water, and Seep Parameters and Constituent
Analytical Methods:
Low level Vanadium listed as having a detection limit unit of mg/L. This is likely just a
typographical error but the units should be in gg/L rather than mg/.L.
Comment Section 7.3.1 Surface Water Samples, 73.2 Seep Samples and 7.2.2 Speciation
of Select Inorganics:
The GAP text indicates that review of the NCDENR. March 20:14 seep and surface water
sampling analytical data will be incorporated into assessment plans to evaluate seep and
surface water sample locations at the facility,
NCDENR0068628

Marshall Steam Station
March 12,2015
Page 3 of 3
s Comment 7.9.2 Development of Kd Terms
It is expected that additional solid phase samples will be collected and analyzed for lid
determination as well as physical pro -per -ties at strategic locations along flowpath
transects. These data will refine the assessment of water geochemistry and development
of flow and transport models.
Locations where NCDENR's March 2014 seep and surface water sampling data indicated
exceedances or elevated concentrations of iron, manganese and other constituents of
concern should be incorporated into the assessment's seep/surface water sampling plans
with speciation of analytical data sufficient to support delineation and modeling efforts.
In addition, technical direction that will serve as the basis of expectations for completion of the site
assessment is provided at Attachment 1. Failure to address the deficient items stated above will
result in Duke Energy not being in compliance with the stated statutes. Per G.S. 130A-309.209(a)
(3) and (4), you must begin implementation of the revised GNP on March 22, 2015 and the
Groundwater Assessment Report is due on September 8, 2015, It is our understanding that Duke
Energy may have to obtain additional permits to facilitate installation of certain monitoring wells. In
the event permits are needed for this purpose, Duke Energy should take all steps necessary consistent
with the law to avoid delaying completion of the assessment report.
If you have any questions, please contact Bruce Paiiis at (704) 2' ) 5 -2185,
Sincerely,
're"Y 4ZeZman, P.G.,
Director, Division of Water Resources
cc: WQROS — MRO
WQROS Central Files
DENR Secretary - Don van der Vaart
HDR (Attn: William Miller) 440 South Church Street, Suite 1000, Charlotte, NC 28202
NCDENR0068629

Attacrtment 1
Page 1 of 6
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 4CSAsj, and corrective action plans (OAPs).
is ; � _ '•.
a.
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 submittedas 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 EPAJ600/R-07/139:
Demonstration of active contaminant removal from groundwater & dissolved prime
stability;
* Determination of the mechanism and rate of attenuation;
8 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 pl'an,.
This reference and the framework described above should' be used as applicable to meet
the corrective action requirements found' in 1 aA NCAC 02L .0106..
3.. Because of uncertainty concerning the site's ability to attenuate contaminants over the long
terra given potentially changing geochernical 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,
GAP development, and continued groundwater monitoring.
4. The Division of Water Resources (Division) Director is responsible for establishing background
levels for CQPCs 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 roust 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.
NCDENR0068630

Attachment I
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 requiredto
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).
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) a 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.
transacts should be located along or defensibly proximate to the modeled transects.
I The dataset developed along proposed flowpath transects will 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/540/5-92%018). This geochemical modeling will: be performed'
to identify potential mineral phases, estimated species speclation 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 transacts 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), Rased on
this ORP measurement, either normal or "glove -box" processing of a sample will be applied
NCDENR0068631

Attachment 1
Page 3 of 6
(EPA1600/R-06/112). An additional sample will be retained, pending confirmation of subsequent
©RP 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 speclation 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 transacts 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 conductedi at up
to 15 locations along proposed flowpath transacts 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 SPILP 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,
NCDENR0068632

Attachment I
Page 4 of 6
IL 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 that the
groundwater monitoring (water levels and sampling) should occur at about the same time.
13. Measurement of strearnflow 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
In the CSA report, data gaps remaining should be specifically identified and: summarized.
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,
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,
S. 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 Towpath 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 urn filter until the contaminant
NCDENR0068633

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 over time 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 f) likely
NCDENR0068634

Attachment I
Pace 6 of 6
Z3
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 geochernical model(s), 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(g) standards in ash leachate, ash pore water, or compliance boundary
well groundwater samples.
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.
Provide references for guidance and potential sampling methodology related to conducting a
baseline ecological risk assessment or habitat assessment, if warranted.
NCDENR0068635

10-2-15 NCDENR Draft Comprehensive Site Assessment
Comments

Pat McCrory
Governor
October 2, 2015
Mr. Harry Sideris
Senior Vice -President
Environment, Health, and Safety
Duke Energy
526 South Church Street
Mail Code EC3XP
Charlotte, NC 28202
Re: Marshall Steam Station
NPDES Permit No. NC0004987 — Catawba County, North Carolina
Comprehensive Site Assessment Comments
Dear Mr. Sideris:
Secretary
On September 8, 2015, the Division of Water Resources (Division) received the Comprehensive Site
Assessment (CSA) Report for the above listed facility. A preliminary review of the CSA has identified
data gaps and deficiencies that require clarification. As the Division continues its review of the
assessment report, additional data gaps and deficiencies may be identified. Resolution of data gaps and
deficiencies are needed in order to refine remedial design and are expected to be addressed in the CSA
Supplemental Report. Please be advised the CAP Report is due on November XX, 2015 per the Coal
Ash Management Act (CAMA).
General Comments
While the CSA Report provides data to develop a general understanding of site conditions, the report
fails to fully explain groundwater exceedances of groundwater quality standards as required by CAXIA
§ 130A-309.211. The relationship of the distribution of constituents of interest (COIs) with respect to
the coal ash basins is not well discussed or evaluated in the report. Understanding, using site data, and
communicating why a contaminant is elevated in one area (or location) and low in another, is essential
to assessing fate, transport, and risk to receptors prior to the development of a CAP.
The CSA Report generally fails to quantitatively estimate background concentrations in soil and
groundwater and use these estimates as a basis for delineating constituents. The CSA Report should
provide provisional estimates of constituent concentrations using site data. The estimates are needed to
compare ash leachate-impacted groundwater to background levels.
1636 Mail Service Center, Raleigh, North Carolina 27699-1636
Phone: [phone]Internet: http://www.ncwater.org
An Equal Opportunity 1 Affirmative Action Employer —Made in part by recycled paper
NCDENRO193372

Marshall Steam Station
Page 2 of 8
Specific Comments
The data gaps and deficiencies noted during review of the CSA Report include the following:
• The Division expects "provisional estimates for purposes of assessment (PEPA)" of background
concentration levels for constituents of interest (COIs) in groundwater to be established in order
to evaluate the results of the CSA Report consistent with CSA Guidelines and CAMA
requirements to describe all exceedances of North Carolina Administrative Code (NCAQ Title
15A Chapter 02L.0202 groundwater quality standards (2LStandards). Although various ranges
of background concentrations (regional, MW-7D/SR, and BG series wells) were provided in the
report, overall site provisional estimates of background levels for the COI are needed as a basis
for comparison of CSA data and determination of the nature and extent of contamination. The
PEPA determinations should be made using background data from relevant compliance wells
(historic and current data) as well as background data from relevant assessment wells. Data
outliers influenced by turbidity should be removed prior to the PEPA. determination. The
methodology used to determine the PEPA and a list of removed outliers should be included in
the CSA supplement.
0 It is indicated throughout the CSA that there are constituents that are naturally -
occurring. Naturally -occurring constituents are generally in equilibrium in water/rock
geochernical systems. Contamination disturbs the equilibrium by increasing
concentration in one of the phases and the systems reacts by transferring some of the
contaminant to the other phase until equilibrium is re-established. Concentrations in
solution above the 2L Standards of naturally -occurring constituents may be an indication
that equilibrium between phases has been altered. This has not been noted in the CSA
Report.
0 If contamination associated with the site is determined to be the ultimate cause of
naturally -occurring constituents above the 2L Standards, these constituents should be
considered contaminants of interest (COIs). Therefore, the Division emphasizes that
background concentrations of all constituents with concentrations above the 2L
standards must be determined, and that those constituents be included in the geochernical
modeling for the CAP.
0 For some naturally occurring COIs, their naturally occurring levels will be the site
cleanup levels. The background levels for COIs that are naturally occurring but also
whose concentrations include contributions by coal ash or whose concentrations are
effected by geochernical conditions related to the ash management basin should be
determined in the CSA report and CAP,
0 COI determinations should consider hexavalent chromium.
• Concentrations of COIs exceeding the 2L/IMAC and likely background ranges were detected in
monitoring wells installed close to, or beyond, the compliance boundary on the hydraulically
up -gradient (west, south, northwest) and down -gradient (east) sides of the site. Immediately
downgradient of the site is a major hydraulic discharge zone. Immediately upgradient of the site
is a topographic high which the report proposes restricts the flow of groundwater to the west
(upgradient direction). Although groundwater flow does typically follow the Slope -Aquifer
model in piedmont settings under natural flow conditions, the high concentration of residential
NCDENR0193373

Marshall Steam Station
Page 3 of 8
water supply wells immediately adjacent and west of the ash basins and those to the northwest,
combined with the long history of hydraulic sluicing into the ash basins, may cause or have
previously caused variances of groundwater flow from the traditional Slope -Aquifer model.
0 Although current groundwater flow measurements support general flow patterns to
the east/southeast toward the Catawba River/Lake Norman from the topographic divides
roughly Sherrills Ford Rd and Island Point Rd, the planned hydraulic modeling should
include an evaluation of whether collective private water supply well pumping and
previous mounding and geochemical conditions in the ash storage areas may have
affected historic contaminant migration and constituent concentrations now observed in
upgradient wells GWA-2S/D, MW-llS/D, MW-1.2S/D, GWA-9BR, MW-13S/D, GWA-
3S/D, GWA-4S/D, and GWA-8S/D. Additional off -site upgradient monitoring wells
may be needed to fully delineate the extent of COIs that exceed the PEPA background
concentrations which are proposed.
0 Some of the groundwater constituent isoconcentration maps in Figures 10-75
through 10-122 show closed boundaries delineating the extent of 2L/lMAC exceedances
where no data has been collected beyond the exceedances detected in monitoring wells.
While it is understood that several COI appear to have background concentrations that
exceed the 2L/L'vIACs, proposed PEPA background concentrations need to be well
defined to demonstrate that the COI have been fully delineated in groundwater. Areas of
uncertainty with respect to isoconcentration delineation of COI on figures should be
clearly designated. Any areas where delineation of exceedances has not been achieved
will require additional monitoring well nest installation and assessment. If a monitor
well (data point) does not exist between a known 2L (or background) exceedance and a
receptor (stream or supply well, e.g.), a monitor well should be installed and sampled to
fill this data gap. If there is uncertainty about local flow directions due to an insufficient
number or placement of monitor wells, additional monitor wells should be installed and
sampled. The horizontal extent of a contaminant plume must be based on concentration
data rather than inferences about groundwater flow and contaminant concentrations
downgradient; local flow directions and concentrations must be known.
o Although Total Chromium concentrations at MW-1 ID are below 2L limits,
compliance monitoring data show concentrations have been increasing in this location
since February 2013. Vanadium was detected at 23.8 ug/L at MW-1 ID in the July, 2015
assessment sample. Hexavalent chromium was detected at 4.6 ug/L in the July, 2015
samples from MW- I I D. Additional assessment to west of MW- I I D is encouraged to
develop more off -site data to characterize groundwater hydraulic and geochemical
conditions.
C, Exceedances of the 2L/IMAC for Cobalt, Vanadium and Iron were reported in the
MW-12 well nest. Additional off -site assessment and evaluation to the west of MW-12
is encouraged.
0 Exceedances of the 2L/1MAC for Antimony, Chromium, Vanadium and Manganese
were reported in the GWA-3 well nest. Additional off -site assessment and evaluation to
the northwest of GWA-_3 ) is encouraged.
0 CS.A. Section 10.2 discusses the background wells BG-1 S/D, BG-2S/BR and BG-3S/D. The text
indicates that there is currently insufficient data to statistically qualify the BG series wells as
NCDENR0193374

Marshall Steam Station
Page 4 of 8
background but that they are likely representative of upgradient conditions. MW-4 and MW-4D
were historically used as upgradient monitoring well locations.
0 Previous historic data from existing background wells MW-4 and MW-4D did not
include all COIs being evaluated in the CSA. (vanadium and cobalt are examples).
0 The CSA report Section 10.2 indicates an additional bedrock and deep background
monitoring well will be considered in a location south of Lake Norman and east of the
Marshall Station. The Department supports the installation of an additional background
well nest. Samples from the background well should also include speciation.
0 CSA report Section 10.2 and Appendix G discuss prediction limits for comparing
whether historical data from background well MW-4 & MW-4D are statistically valid
for determining site specific background concentrations because there are currently
insufficient data sets from the BG series wells to use in statistical analyses. There are
insufficient data sets from MW-4S & MW-4D for vanadium, cobalt and hexavalent
chromium for statistical analyses however, PEPA background concentrations will need
to also be proposed for these constituents.
0 Given the number of tested private water supply wells which have been designated
by NCDHHS as unsafe for potable use due to hexavalent chromium and vanadium
concentrations, it is important that groundwater from the background wells also be
speciated and a thorough understanding of chromium species distribution at and around
the site be developed to determine if the ash basins are fully or partially influencing the
concentrations of contaminants observed in the residential water supply wells.
0 While assessing the significance and extent of hexavalent chromium, please speciate
groundwater samples from the additional background monitoring well nest and BG-
2S/BR, BG-3S/D, MW-13D, GWA-9BR, GWA-3S/D, GWA-8S/D, and GWA-2S/D.
CSA report Section 3.0 discusses source characteristics and volumes. Of the unlined features
containing coal combustion residuals (CCRs), the report does not specifically reference the
volume of CCRs in the 394 acre unlined ash basin or the structural fill underneath the
photovoltaic farm. The report indicates that there are 280,000 tons of CCRs in the Division of
Waste Management permitted Phase I unlined landfill and 2,515,000 tons of CCRs in the
unlined Phase 11 landfill. Duke Energy's website lists the volume in the ash basin as 16,020,000
tons, the volume of CCRs in "fills" as 7,360,000 tons. Based on these numbers, the combined
volume of unlined CCR storage at the facility is approximately 26,175,000 tons. Please verify
and list the volumes of CCRs in the unlined and lined site storage features in the supplement and
CAP.
• CSA Section 4.0 discusses pertinent structures located proximal to ash management features
illustrated in Figure 4-3. Please show the flow directions through pipes illustrated in Figure 4-3.
1
CSA report section 4.3 discusses NCDENR's Well Water Testing Program of drinking wells
adjacent to the facility. Appendix B provides tabulated sampling results provided by Duke
Energy from NCDENR. The CSA does not discuss and evaluate the detections of COls found
in residential water supply wells and provide explanations as to their presence and whether or
not they fall within expected background ranges. Evaluation and discussion of the sample
results from adjacent water supply wells relative to COls associated with the site should be
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conducted in the CSA Supplement and CAP along with provisions for alternate water required
under CAMA.
• The CSA. report evaluates COIs in soil and sediment relative to the NC Preliminary Soil
Remediation Goals (PSRGs) for Industrial Health and/or the Protection of Groundwater. These
values come from a table maintained by the Division of Waste Management- Superfund Section -
Inactive Hazardous Sites Branch (IHSB) and are used to evaluate assessment and remediation
benchmarks which should be achieved in soils and sediments. The IHSB PSRGs are used by
that program to regulate sites and include a component of risk based evaluation of soil
contamination during assessment and remediation. The 2L rules, which apply to the permitted
coal ash facilities, require assessment and remediation of soils so that they will not be a
continuing source for groundwater contamination. There is no specific component related to
"health based" direct contact standards in the 2L rules for evaluating soil contamination.
Assessment of soil impacts should only be measured against the Protection of Groundwater
goals in the referenced table and not the Industrial Health PSRGs.
• It was noted that the detection limits associated with some solid phase (soil) constituents
(Antimony, Arsenic, Cobalt, Selenium, Thallium) were higher than the Protection of
Groundwater goals to which they were being compared in the CSA tables. It may be necessary
to resample or collect additional samples.
• CSA Section 7.3.1 indicates that samples collected from boring SB-9, located approximately
900 ft northwest of boring SB-8, were not analyzed due to a laboratory error. Data from this
source area location should be recollected and analyzed or a justification provided as to why this
data point is no longer necessary.
• In various tables in the CSA which list solids analytical data (7-2 Cation/Anion Sample Results,
8-2 Total Inorganic Results -Background Soil, 8-3 Total Inorganic Results — Background and
PRW, 8-4 Total Inorganic Results -Soil, 8-5 Total Inorganic Results -Rock, 9-2 Sediment Sample
Results -Total) only total chromium results are available. Sections 7.1, 7.2, 7.2, 8.3, and 9.2 of
the CSA also discusses comparison of the soil results to applicable levels. The PSRG Protection
of Groundwater values used in the referenced IHSB table only have separate values for trivalent
and hexavalent chromium due to the large differences in toxicity between these two compounds.
The CSA tables use the PSRG Protection of Groundwater values for trivalent chromium as
surrogate regulatory comparison for solids analytical results from the site rather than the more
restrictive PSRG Protection of Groundwater table values for hexavalent chromium. For the
purposes of delineating exceedances of contaminants in soils and sediments to develop a
remediation plan, solids samples from the site should be speciated for chromium to evaluate
whether there are exceedances of the PSRG Protection of Groundwater values for the purposes
of delineation of soil and sediment contamination. The referenced IHSB PSRG table also
includes a formula which can be used to calculate a value for total chromium which would be
protective of the state's 2L groundwater quality standard.
• Although the geochernical site conceptual model (GSCM) presented in section 13.3 provides a
"bullet list" of factors that may affect leaching, sorption and desorption, and precipitation and
dissolution, the list is so generic that it is of limited value and says nothing about what is being
observed geochernically at the site. While the CSA includes raw contaminant concentrations,
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selected valence state data, pH, dissolved oxygen, eH, TDS, alkalinity, and other data in various
tables and figures throughout the report, these were not used or interpreted to develop a
conceptual understanding of contaminant mobility and transport at CSS. The GSCM section
13.3 should provide a summary narrative of the current understanding of geochemical
conditions across the site (different areas will be characterized by different conditions and
should be described accordingly) and how they are expected to affect individual contaminant
mobility and transport. Specifically, the GSCM narrative should describe, based on site data: a)
the source of iron and manganese in groundwater (coal ash versus native soil) and how these
constituents are solubilized/mobilized and (or) precipitated at the site, b) the source of each of
the other COls (coal ash versus native soil), c) the mechanism(s) and conditions under which
each COI would be expected to be mobilized or attenuated at the site, d) prevailing geochemical
conditions (i.e. pH and eH) in COI source areas and along identified flow paths, and e) any
other factors relevant to the occurrence and mobility of contaminants at the site. Information in
the GSCM narrative should explain what is known about why a COI is found at elevated
concentrations in one area of CSS and at very low concentrations in another. It is understood
that geochemical modeling will be performed as part of the CAP and that the GSCM will
undergo revisions as part of that process.
• Because the mobility of iron and manganese is controlled by geochemically-mediated (pH, eH)
precipitation rather than sorption onto iron hydroxides (and Kd measurements are not
particularly relevant to Fe and Mn concentrations along a flow path), a separate sub -section
should be provided in section 1.3 that describes how the fate and transport of these constituents
will be modeled.
• Although data needed to develop a hydrogeologic site conceptual model (HSCM) are provided
in various tables, figures, and appendices throughout the CSA, there is not the GAP -required
section that interprets this information in a summary narrative needed to evaluate CSA results of
contaminant extent and movement, ensure compliance with CSA guidelines and LAMA, and
assess modeling results and CAP. Section 6.2.4, Hydrogeologic Site Conceptual Model, is the
section that is supposed to provide this narrative; instead it lists the types of data that comprise
the HSCM and the sections in which these data may be found. Section 6.2.4 should include a
stand-alone narrative for each area and its corresponding downgradient footprint for which a
coal ash source has been identified. The narrative should summarize the current conceptual
hydrogeologic understanding of that area of the site. Each narrative should succinctly describe:
a) the character of the connected three-part groundwater system in which flow occurs and where
units are particularly thick or thin, b) how, where, and how much recharge occurs in that area, c)
horizontal and vertical flow directions in that area, d) the areas of discharge, e) locations in that
area that do not follow the HSCM for the area and why, and f) data gaps that affect the ability to
understand a) through e) above. Areas of the site that do not fit the generalized HSCM should
be discussed in the narrative.
• CSA report Section 2.2 refers to Figure 2-3 which depicts the site prior to construction of the
ash basins on a USGS 1954 topographic map. Figure 2-3 has a note indicating that the source
map is a USGS 1981 topographic map. It appears the text reference is accurate and not the note
on Figure 2-3.
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CSA report Section 2.7 discusses permitted activities and waste at the site with site features
illustrated on Figure 2-4. Please illustrate the locations and flow directions of Internal Outfall
004, Yard Sump Overflow Outfalls 002A and 002B, and Non -contact cooling water Outfall 003
on Figure 2-4.
Cross -Section C to C', Figures 8-5.1, 8-5.2 and 8-5.3 are incorrectly labeled as to their
orientation. The transect starts with GWA-6S/D which is illustrated on Figure 8-5.1 at the west
side of the transect, however, this monitoring well nest it is actually located on the northeastern
side of the transect. MW-I I S/D is illustrated as the eastern end of the transect when it is
actually the southwestern end.
CSA report Section 9.1. discusses one surface water sample (SW-6) which was collected from an
unnamed tributary to Lake Norman adjacent to the unlined dry ash landfill (Phase 1, DWM
permit 1804-ES-DUS). Cobalt was detected above the 2B standards. Although SW-6 is a
surface water sample, the report noted that Boron, Manganese, and Vanadium exceeded the
2L/E\4AC standards. Monitoring wells MW-145, MW-14D, AL -IS, AL -ID, located between
the Phase I landfill and the unnamed tributary, also exhibited 2L/IMAC exceedances of Boron
and various other metals. Additional assessment of the extent of surface water impacts to the
unnamed tributary and Lake Norman should be conducted. Additional delineation of the
groundwater exceedances to the north-northeast of the unnamed tributary should be conducted.
An understanding of the groundwater/surface water interactions in this area should be included
in the site conceptual model.
CSA report Section 10.9 and Table 1.0-17 discuss radionuclide testing in limited monitoring
well locations at the site. Radium 226 was detected in monitoring well MW -14D with an
activity level of 96.1 J pCi/L. Please collect and evaluate additional samples for radionuclides
from downgradient flow paths in this area to include monitoring wells AB -ID, AB-IBR, AL -
IS, AL -ID, AB-IIS, andAB-IID.
No surface water samples were collected from the Catawba River/Lake Norman as part of the
CSA investigation even though exceedances of the 2B stream standards were detected in SW-6
from the unnamed tributary that flows into Lake Norman. Exceedances of the 2L standards,
which also would exceed the 2B stream standards in surface water, were noted in monitoring
wells located immediately adjacent to Lake Norman. Sampling and assessment of impacts to
the Catawba River/Lake Norman should be included in the assessment. An understanding of
the groundwater/surface water interactions (hydraulic and geochemical) should be included in
the site conceptual model.
The above comments were based on a preliminary review of the CSA Report. The Division is
continuing to review the report and may provide additional comments in subsequent letters, if
appropriate. Failure to address the deficient items stated above may result in the assessment of civil
penalties and/or the use of other enforcement mechanisms available to the State. If you have any
questions, please contact Bruce Parris at [phone].
Sincerely,
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S. Jay Zimmerman, P.G., Director
Division of Water Resources
cc: WQROS — MRO
WQROS Central Files
DENR Secretary — Don van der Vaart
HDR (Attn: William Miller) 440 South Church Street, Suite .1000, Charlotte, NC 28202
NCDENR0193379