2016-04-13 Amended Bedient_Exprt_Rpt_Allen

REMEDIATION OF SOIL AND GROUNDWATER
AT THE
ALLEN STEAM STATION
OPERATED BY DUKE ENERGY CAROLINAS, LLC
BELMONT, NORTH CAROLINA
Expert Opinion of:
Philip B. Bedient, Ph.D., P.E.
P.B. Bedient and Associates, Inc.
P.O. Box 1892
Houston, Texas 77251
713-303-0266
Amended
13 April 2016

13 April 2016
REMEDIATION OF SOIL AND GROUNDWATER
AT THE
ALLEN STEAM STATION
OPERATED BY DUKE ENERGY CAROLINAS, LLC
BELMONT, NORTH CAROLINA
TABLE OF CONTENTS
1.0 Introduction........................................................................................................................1
1.1 Summary of Opinions.........................................................................................................1
1.2 Qualifications......................................................................................................................2
2.0 Summary of the HDR CSA............................................................................................... 2
2.1 Physical Setting...................................................................................................................3
2.2 Hydrogeology..................................................................................................................... 3
2.3 Allen Coal Ash Basins and RAB Ash Landfill................................................................... 4
2.4 Contamination.....................................................................................................................5
3.0 Efficacy of Remedial Options for Coal Ash Contaminants Evaluated by HDR.......... 5
3.1 Excavation and Removal.................................................................................................... 5
3.2 Cap-In-place........................................................................................................................6
4.0 Opinions.............................................................................................................................. 6
4.1
Contaminants detected in groundwater at the compliance boundary exceed
applicable NCDEQ groundwater cleanup standards...........................................................
6
4.2
Groundwater contaminants are migrating in groundwater across the compliance
boundary at concentrations exceeding applicable NCDEQ groundwater cleanup
standards.............................................................................................................................
7
4.3
The groundwater flow and transport model developed by HDR to evaluate
remediation scenarios at the site is fundamentally flawed ..................................................
7
4.4
The remediation scenarios evaluated by HDR will not cause groundwater
standards to be met inside the compliance boundary, cause groundwater
standards to be met beyond the compliance boundary, or prevent coal ash
contaminants from migrating across the compliance boundary and into the
Catawba River for the foreseeable future...........................................................................
9
4.5
Successful remediation of groundwater will require excavation and removal
coupled with additional measures, such as hydraulic groundwater containment .............
10
5.0 References......................................................................................................................... 11
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC i Philip B. Bedient, Ph.D., P.E.

13 April 2016
REMEDIATION OF SOIL AND GROUNDWATER
AT THE
ALLEN STEAM STATION
OPERATED BY DUKE ENERGY CAROLINAS, LLC
BELMONT, NORTH CAROLINA
TABLE OF CONTENTS
FIGURES
Figure I Site Location and Extent of Coal Ash Requiring Excavation and Proper Disposal
Figure 2 Locations of Wells and Groundwater Standard Exceedances for Any COI
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC ii Philip B. Bedient, Ph.D., P.E.

13 April 2016
REMEDIATION OF SOIL AND GROUNDWATER
AT THE
ALLEN STEAM STATION
OPERATED BY DUKE ENERGY CAROLINAS, LLC
BELMONT, NORTH CAROLINA
1.0 Introduction
I was retained on this project for the purpose of evaluating remediation of soil and groundwater
at the Duke Energy Carolinas, LLC (Duke) Allen Steam Station (the "site") coal ash disposal
facilities. In particular, I have focused my analysis on different methods of preventing continued
transport of coal ash contaminants across the compliance boundary in groundwater at
concentrations that exceed relevant groundwater standards. The compliance boundary' is the
regulatory boundary established by the North Carolina Department of Environmental Quality
(NCDEQ) for measuring compliance with applicable water quality standards. The relevant
standards are:
• 15A NCAC 02L.0202 Groundwater Quality Standards (2L Standards); and,
• 15A NCAC 2L.0202(c) Interim Maximum Allowable Concentrations (IMACs)
established by the NCDEQ, which apply to groundwater locations beyond the limits of
the ash basins.
My opinions are based on my professional experience in hydrogeology, environmental
engineering, hydrology and hydraulics, and review of relevant data, maps, aerials, documentation
to date, and are subject to change if and when additional information becomes available.
1.1 Summary of Opinions
It is my opinion that:
• Contaminants detected in groundwater at the compliance boundary exceed applicable
NCDEQ groundwater cleanup standards.
• Groundwater contaminants are migrating in groundwater across the compliance boundary
at concentrations exceeding applicable NCDEQ groundwater cleanup standards.
• The groundwater flow and transport model developed by HDR to evaluate remediation
scenarios at the site is fundamentally flawed.
• The remediation scenarios evaluated by HDR will not cause groundwater standards to be
met inside the compliance boundary, cause groundwater standards to be met beyond the
' My references to the compliance boundary mean the compliance boundary as drawn by HDR in the CSA (HDR,
2015a). My references do not imply that I believe that the compliance boundary drawn by HDR is correct.
a
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 1 Philip B. Bedient, Ph.D., P.E.

13 April 2016 1k,
compliance boundary, or prevent coal ash contaminants from migrating across the
compliance boundary and into the Catawba River for the foreseeable future.
• Successful remediation of groundwater will require excavation and removal coupled with
additional measures, such as hydraulic groundwater containment.
1.2 Qualifications
My educational background, research and professional experience, and the review of documents
and models provided are the basis of my opinions. I hold the Ph.D. degree from the University of
Florida in Environmental Engineering Sciences, and I have attached a curriculum vita including
a list of peer -reviewed publications. I am the professor of Civil and Environmental Engineering
at Rice University, where I have been on faculty since 1975, and teach courses in hydrology,
floodplain analysis and modeling, and courses in groundwater hydrology, contaminant transport,
and transport modeling. My textbook entitled "Hydrology and Floodplain Analysis" is one of the
top texts used at over 75 universities in the U.S. I have also written a textbook entitled "Ground
Water Contamination Transport and Remediation." I am currently the Herman Brown Professor
of Engineering, a Fellow of ASCE, and a Diplomat of the American Academy of Water
Resources Engineers. I am a registered professional engineer in Texas.
Groundwater Contamination and Remediation
I have been actively involved in groundwater contamination and remediation studies for many
years. I was principle investigator (PI) on a major EPA -funded study of Hill Air Force base in
the late 1990s where comparison tests for various remediation of Dense Non -Aqueous Phase
Liquids (DNAPLs) were performed. In the 1990s, I was a member of the EPA National Center
for Groundwater Research, and I held the Shell Distinguished Chair in Environmental Science
for my efforts in developing biodegradation models in the subsurface. Between 1999 and 2002, I
had the opportunity to work on the remediation of MTBE spills sites in Texas and California.
From 2000-2003, I worked on chlorinated solvent impacts and remediation strategies through a
study funded by EPA. More recently, I evaluated the impact of ethanol on groundwater and
various remediation methods on an API -funded study from 2003-2007.
I have worked on groundwater contamination and remediation litigation at more than 30 waste
sites nationwide. These sites include DOW Chemical and Vista Chemical in Louisiana; Conroe
Creosote, Brio, Texas Instruments and San Jacinto Waste Pits in Texas; Raytheon in Florida;
coal ash sites in North Carolina; BF Goodrich in California; and an Amoco site in Missouri.
My experience with groundwater contamination and remediation at military sites include Coast
Guard facility in Michigan, Eglin, Hill and Kelly Air Force Bases.
2.0 Summary of the HDR CSA
The information related in this summary is derived from the HDR Comprehensive Site
Assessment report (CSA; HDR, 2015a). I have noted in this section where my interpretation of
the CSA data differs from HDR's, and the basis for those differing interpretations are provided in
my technical opinions.
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 2 Philip B. Bedient, Ph.D., P.E.

13 April 2016 i
2.1 Physical Setting
Duke Energy owns the 1,009-acre Allen Steam Station which is located on the west bank of the
Catawba River in Belmont, North Carolina. The dammed section of the Catawba River, together
with the South Fork Catawba River on the west side of the Belmont peninsula, comprise Lake
Wylie reservoir, part of the Catawba-Wateree Project and is used for hydroelectric generation,
municipal water supply, and recreation (HDR, 2015a).
The Allen Steam Station is a coal-fired electricity generating facility with a capacity of 1,155
megawatts (MW) along the Catawba River (HDR, 2015a). The Allen ash basin is situated
between the Allen powerhouse to the north and the topographic divides to the west (along South
Point Road) and the south (along Reese Wilson Road) (HDR, 2015a).
The Allen station began operation in 1957 with Units 1 and 2, each with 330 MW capacity
(HDR, 2015a; HDR, 2016). Unit 3 added an additional 257 MW, and was placed into
commercial operation in 1959. Unit 4 (275 MW) and Unit 5 (275 MW) were added in 1960 and
1961, respectively (HDR, 2015a). Coal combustion residuals from the coal combustion process
have historically been disposed of in the Allen ash basin system, which is comprised of the
inactive ash basin and the active ash basin (HDR, 2016). According to HDR, the ash basin
system waste boundary encompasses an area of approximately 322 acres. The active ash basin,
located on the southern portion of the property, is approximately 169 acres and contains an
estimated 7,700,000 tons of ash. The inactive ash basin, located between the generating units and
the active ash basin, measuring roughly 132 acres, contains approximately 3,900,000 tons of ash
(HDR, 2015a).
The inactive ash basin was commissioned in 1957 and is located adjacent to and north of the
active ash basin. According to HDR (2015a), the inactive ash basin was formed by constructing
the earthen North Dike (located along the west bank of the Catawba River), and the northern
portion of the East Dike (located between active and inactive ash basins) across drainage features
along the shore of the Catawba River. The active ash basin was constructed in 1973 and was
formed by constructing the southern portion of the East Dike (HDR, 2015a).
The coal ash basin at Allen is constructed over two streams, visible on historical topographic
maps, flowing towards the Catawba River. The lower portions of these stream channels coincide
with seeps observed flowing from the active impoundment dam face into the Catawba River.
2.2 Hydrogeology
The Allen site is located in the Charlotte terrane (HDR, 2015a). According to Hibbard et al.
(2002), the Charlotte terrane consists of an igneous complex of Neoproterozoic to Paleozoic
ages. The Charlotte terrane ranges from intermediate to mafic in composition (Butler and Secor
1999 as referenced in HDR, 2015a). The Charlotte terrane is bordered on the east and southeast
by the Carolina terrane and to the west and northwest by the Inner Piedmont and the Kings
Mountain terrane (HDR, 2015a). The structural contact of the inner Piedmont and Charlotte
terrane is the Central Piedmont Shear Zone.
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 3 Philip B. Bedient, Ph.D., P.E.

13 April 2016
The Charlotte terrane is a meta -igneous terrane consisting of volcanic and plutonic rocks that
have been subjected to deformation and high grade metamorphism due to tectonic stress during
and after intrusion of the igneous unit (HDR, 2015a).
Based on the CSA investigation, the groundwater system in the natural materials (alluvium, soil,
soil/saprolite, and bedrock) at the Allen site is consistent with the Piedmont regolith-fractured
rock system (HDR, 2015a). HDR describes the groundwater system in and around the Allen site
as an unconfined, connected system of flow layers.
Based on the available set of groundwater elevation measurements, HDR concludes in the CSA
that groundwater within the shallow and deep layers (S and D wells) and bedrock layer (BR
wells) flows from west and southwest to the east toward the Catawba River and to the north
toward Duke Energy property and the Station Discharge Canal (HDR, 2015a). I agree that this
flow pattern is generally correct for the eastern two-thirds of the property. However, as explained
in my opinions later in this report, data suggests that groundwater also flows westward from the
approximate western third of the site under the influence of the ash basins.
2.3 Allen Coal Ash Basins and RAB Ash Landfill
According to HDR (2015a), fly ash has been dry -handled and disposed of in the on -site ash
landfill, and bottom ash has continued to be sluiced to the active ash basin since 2009.
Historically, coal ash was sluiced to the inactive ash basin until the active ash basin was
constructed in 1973 (HDR, 2015a). During operations, the sluice lines discharge the water/ash
slurry into the Primary Ponds on the northern portion of the active ash basin. Primary Ponds 1, 2,
and 3 were constructed in 2004 (HDR, 2015a). HDR documents that Primary Ponds 2 and 3 are
currently utilized for settling purposes.
The Retired Ash Basin (RAB) Ash Landfill unit is located on the eastern portion of the Allen
site, on top of the inactive ash basin (HDR, 2015a). The landfill was constructed in 2009 and is
bound to the north, east, and south by earthen dikes. The RAB dam comprises the northern and
eastern boundaries of the landfill (HDR, 2015a). The lined landfill receives Coal Combustion
Residuals (CCR) materials, including fly ash, bottom ash, boiler slag, mill rejects, and Flue Gas
Desulfurization (FGD) waste generated by Duke Energy (HDR, 2015a).
According to HDR (2015a), the two unlined Distribution of Residuals Solids (DORS) structural
ash fills are located on top of the western portion of the inactive ash basin, adjacent to and west
of the RAB Ash Landfill. These fills were constructed of ponded ash removed from the active
ash basin per Duke Energy's DORS permit (HDR, 2015a). HDR documents that the placement
of dry ash in the structural fills began in 2003 and was completed in 2009. The eastern structural
fill covers approximately 17 acres and contains approximately 500,000 tons of ash; the western
structural fill covers approximately 17 acres and contains approximately 328,000 tons of ash
(HDR, 2015a). The Corrective Action Plan (CAP) Part I specifies that approximately 300,000
cubic yards of ash is stored in the ash storage areas, which encompasses an area of
approximately 15 to 20 acres of the western portion of the inactive ash basin (HDR, 2015a).
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 4 Philip B. Bedient, Ph.D., P.E.

13 April 2016
2.4 Contamination
According to the HDR CSA and CAP Part I and II (HDR, 2015a; HDR, 2015b; HDR, 2016),
groundwater constituent of interest (COI) exceedances were determined to be the result of both
source related materials contained within the ash basins and ash storage area as well as naturally
occurring conditions within the Duke Energy property boundary and surrounding vicinity. The
CSA identified the horizontal and vertical extent of groundwater contamination at the Allen site
and found it is limited to within the compliance boundary (HDR, 2015a). HDR indicated that
additional assessment and monitoring is required offsite as well as west of the ash basin to
further evaluate groundwater quality and groundwater flow west of the ash basin. According to
HDR, where soil impacts were identified beneath the inactive ash basin and the active ash basin,
the vertical extent of contamination beneath the ash/soil interface is generally limited to the
uppermost soil sample collected beneath the ash.
According to HDR (2016), analytical results from background monitoring wells indicated the
presence of naturally occurring metals and other COIs at concentrations that exceeded their
respective regulatory standards or guidelines. These COIs included: antimony, barium,
chromium, cobalt, iron, manganese, pH, total dissolved solids (TDS), and vanadium.
The CAP Part I and II (HDR, 2015b; HDR, 2016) maintains that the geologic conditions present
beneath the inactive ash basin and active ash basin generally impede the vertical migration of
contaminants. The direction of contaminant transport is generally in a northeast and east
direction towards the Catawba River, as anticipated, and not toward off -site receptors such as
private drinking water wells to the west.
As explained in my opinions below, I do not agree with the CSA's contention that groundwater
standards and/or background concentrations are not currently exceeded at the compliance
boundary. Furthermore, if groundwater is flowing west from the western site boundary, COIs
contained in the groundwater are also being transported to drinking water wells west of the site.
3.0 Efficacy of Remedial Options for Coal Ash Contaminants Evaluated by
HDR
In its CAP, HDR evaluates the effects of two remedial options on groundwater concentrations at
the compliance boundary: (1) excavation of the coal ash material, and (2) the use of a cap to
isolate the coal ash and reduce leaching of contaminants to groundwater. The efficacy of these
two remediation options for the COIs present in groundwater at the Allen Station site is
discussed below.
3.1 Excavation and Removal
Excavation and removal would remove the source of the contamination (coal ash in all of the
basins) entirely in order to end the contamination of underlying groundwater. This process would
entail excavating coal ash from the site, loading it onto trucks or rail cars, and sending it off to be
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 5 Philip B. Bedient, Ph.D., P.E.

13 April 2016
disposed of in a secure landfill that is equipped with a proper liner and leachate collection
system. Alternatively, the coal ash could be excavated in phases and stored on -site while
multiple cells of an on -site, secure landfill are constructed. This remediation technique is
underway at other contaminated coal ash sites in North Carolina. While there is precedent for
complete removal of the coal ash, additional, temporary protective measures, such as the
construction of sheet piles and coffer dams, would be necessary on this site to prevent influx of
groundwater and river water during excavation.
Ultimately, this remedial approach is feasible and the most effective remediation measure due to
permanent source removal. Even with coal ash removal, however, the current impacted
groundwater will exist as a constant source of contamination within the transmissive zones
beneath and adjacent to the site and to the Catawba River. Additional measures will be needed to
address this residual contamination at the site. Nevertheless, excavation and removal stands as
the only remediation measure that completely removes the source of contamination and, in
conjunction with other measures described below, safeguards against future contamination.
3.2 Cap -In -place
A cap -in -place remedy utilizes a cap of low -permeability material, including clay and/or
synthetic liners, to reduce the rate of water infiltration into the underlying coal ash. The cap may
be equipped with an underdrain system to capture even small amounts of water that infiltrates
through the cap material. In systems where contaminants are relatively fast-moving or
biodegradable, capping provides more time for the chemicals to become diluted or degraded,
protecting potential receptors downgradient.
Cap -and -treat technology is also limited, however. Where contaminants exist in thick material
that contains substantial water, continued leaching of contaminants to groundwater may occur,
even with reduced infiltration. These materials can serve as a long-term source of groundwater
impacts.
4.0 Opinions
Based on my review of the available reports and analysis of other data received to date, my
opinions are, to a reasonable scientific certainty, the following:
4.1 Contaminants detected in groundwater at the compliance boundary exceed
applicable NCDEQ groundwater cleanup standards.
As acknowledged in the CAP (HDR, 2015b), several COIs have been detected in groundwater at
the compliance boundary that exceed background and 2L or IMAC standards. These locations
are shown on Figure 2. As seen in the figure, groundwater COIs are present in groundwater on or
outside of the compliance boundary.
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 6 Philip B. Bedient, Ph.D., P.E.

13 April 2016 k,
4.2 Groundwater contaminants are migrating in groundwater across the compliance
boundary at concentrations exceeding applicable NCDEQ groundwater cleanup
standards.
The potentiometric surface contours depicted by HDR in the CSA (HDR, 2015a) suggest that
groundwater flows only east. This flow pattern results from the presumption that a groundwater
divide exists along the ridge west of the site, so that groundwater elevations of background wells
west of the site and south of the Station Discharge Canal are not included in the contouring.
However, as discussed below, the presumption of a groundwater divide along the ridge west of
the site is not justified by the stratigraphy and measured groundwater elevations.
When the background wells are included in the groundwater elevation contouring along with the
rest of the monitoring wells, the groundwater elevation data can be interpreted to indicate that
groundwater in the shallow, deep, and bedrock zones is flowing west as well as east to the
Catawba River. This westward flow component has been confirmed by the additional data from
the HDR CAP Part 2 report (HDR, 2016), indicating that groundwater is transporting
contaminants across the compliance boundary to both the east and west, and almost certainly
north toward the Station Discharge Canal as well.
4.3 The groundwater flow and transport model developed by HDR to evaluate
remediation scenarios at the site is fundamentally flawed.
The groundwater flow model developed for Duke by HDR (HDR, 2015b; HDR, 2016) has been
constructed so that only one pattern of groundwater flow is possible; flow from the western site
boundary eastward to the Catawba River. This effect is the result of the choice of hydraulic
boundary conditions in the model, which can only result in this groundwater flow pattern. The
flow pattern is inconsistent with groundwater elevation measurements in the southwestern corner
of the site.
No flow boundaries to the north and south are not realistic and pre -define the groundwater flow
direction.
The flow model developed for Duke allows groundwater to flow only generally eastward, from
the coal ash basins into the Catawba River. The no -flow boundaries to the north and south pre-
suppose that groundwater flow paths have no strong northerly and no strong southerly
components. This assumption is not justified by the potentiometric surface contours, which
suggest a strong northerly component caused by the Station Discharge Canal and a substantial
southerly component caused by radial flow from the interior of the Belton Peninsula. The flow
paths predicted by the model are likely incorrect and do not represent actual site conditions. The
inaccurate flow paths also lead to erroneous expectations of contaminant migration pathways and
mass loading to the Catawba River.
The western boundary condition in the flow model is not technically supported.
The no -flow boundary to the west presumes that there is a groundwater divide that follows the
north -south trending ridge that roughly divides the Belton Peninsula into eastern and western
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 7 Philip B. Bedient, Ph.D., P.E.

13 April 2016 i
halves. There is not enough evidence to support this assumption, and some groundwater
elevation data contradicts the assumption of a groundwater divide.
Groundwater elevation measurements depicted in figures from the HDR CAP Part 2 report
(HDR, 2016) indicate a westward -directed groundwater flow direction in the shallow and deep
groundwater zones. For example, in Figure 2-2, groundwater elevations in shallow zone wells
A1320S, GWA9S, and A1312S indicate that groundwater flows radially from the western edge of
the coal ash. Wells AB20D, GWA91), and AB 12D show a similar flow pattern in the deep zone.
These flow directions are not consistent with a groundwater divide.
The Duke flow model reverses these observed groundwater flow directions. Table 3 in Appendix
B of the CAP Part 2 (HDR, 2016) report compares observed heads to heads predicted by the
model. The measured head in AB20S is higher than the head in GWA9S, indicating groundwater
flow to the west. The heads predicted by the Duke model reverse these elevation differences,
predicting a head in AB20S that is lower than the head in GWA9S, thereby incorrectly predicting
groundwater flow to the east instead of to the west. The Duke flow model similarly
misrepresents the flow direction between A1312S, A 35, and BG1S. These three wells indicate
that groundwater flows southwest. However, the Duke model predicts flow directed toward the
east in these wells, as shown in Figure 14 of the CAP Part 2.
Examination of the groundwater elevation contours of the shallow, deep, and bedrock zones
provided by HDR in the CSA (HDR, 2015a) and in the CAP Part 2 report (HDR, 2016) also
show that groundwater contours do not closely follow the topography. For example, the contours
for the shallow zone illustrated on Figure 3-3 of the CSA indicates groundwater flow north
toward the Station Discharge Canal beneath the ridge at the north edge of the site, and
groundwater contours at left center of the site that flow perpendicular to the ridge elevation
slope. These flow lines indicate that natural topography alone is not driving groundwater flow,
and do not support a north -south groundwater divide along the west edge of the site.
Finally, the assumption of a groundwater divide along the western ridge is also not supported by
the stratigraphy as presented by HDR (2015a). The CSA east -west cross sections C-C', D-D', and
E-E' all show that to the west, groundwater elevations are 60 to over 100 feet above the bedrock,
so that groundwater flow across the ridge is not cut off by underlying, relatively impermeable
layers.
There is a sound technical reason for the lack of a divide along the ridge. Prior to site
development, and in the absence of any pumping west of the site, a groundwater divide likely did
exist because ground surface elevations trended toward the Catawba River on each side of the
ridge. The relative uniformity of the undeveloped land surface would have allowed a roughly
equally distributed amount of recharge through the natural surface. After coal ash disposal,
however, the ground surface elevation was greatly increased on the eastern side of the ridge
across the site. This elevation change serves to reduce the tendency of groundwater to flow from
the ridge toward the Catawba River to the east. In addition, the unconsolidated coal ash is much
more permeable and homogeneous than the natural land surface, so that a greater amount of
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 8 Philip B. Bedient, Ph.D., P.E.

13 April 2016 i
infiltration occurs east of the ridge. The increased infiltration causes groundwater to mound east
of the ridge, in essence shifting the groundwater divide to the east.
The Duke model does not account for the significant pumping from wells west of the coal ash
ponds, which would serve to divert groundwater flow to the west.
A further factor that does not support the presence of a groundwater divide along the ridge is the
pumping of the four water supply wells and the 217 private wells west of the ridge. Along with
the coal ash disposal, pumping of these wells are likely responsible for groundwater flow to the
west along the western site boundary.
The Duke model includes 44 residential pumping wells, but it is not clear how they affect
groundwater flow patterns in the model. Figure 16 of Appendix B of the CAP Part 2 report
(HDR, 2016), for example, shows 1-year reverse flow particle tracks from the water supply
wells. Some of these particle tracks indicate that groundwater flowing to these wells originates
from the beneath the adjacent coal ash basins. However, groundwater elevation contours are not
drawn with sufficient precision to judge the effect of these wells on flow patterns along the
western boundary. Furthermore, because predicted groundwater flow direction south of these
water supply wells is incorrect, the effect of these pumping wells on flow patterns is probably
underestimated.
The Duke model does not account for the hydraulic influence of the Station Discharge Canal.
The Station Discharge Canal to the north and northwest of the site should exert a large effect on
groundwater flow in all three groundwater zones. This effect is evident when the background
wells west of the site are used to generate potentiometric surface contours. However, because of
the no -flow boundaries to the west and north, the Station Discharge Canal is excluded from the
groundwater flow model. Thus, the potential effect of the canal on groundwater flow is not
accounted for in the Duke model. Because of the canal's location west and north of the site, the
canal would be expected to have a profound influence on groundwater flow patterns, directing
groundwater westward from the western half of the site.
4.4 The remediation scenarios evaluated by HDR will not cause groundwater standards
to be met inside the compliance boundary, cause groundwater standards to be met
beyond the compliance boundary, or prevent coal ash contaminants from migrating
across the compliance boundary and into the Catawba River for the foreseeable
future.
The CAP Part 1 prepared for Duke by HDR (HDR, 2015b) is not effective in addressing or
mitigating the groundwater contamination occurring at this site as a result of the leakage of coal
ash contents from coal ash disposal at the Allen Station. In Appendix C of the CAP Part 1 report
(HDR, 2015b), Duke acknowledges that under the cap -in -place scenario, antimony, arsenic,
chromium, cobalt, selenium, and vanadium will all remain above groundwater cleanup standards
inside the compliance boundary and beyond the Catawba River compliance boundary after 250
years. This conclusion is reached even when the soil -water partitioning coefficient (Kd) values
for metals were significantly reduced during model calibration. Setting the Kd values equal to
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 9 Philip B. Bedient, Ph.D., P.E.

13 April 2016 1k,
those determined in laboratory studies would result in much slower contaminant migration and
more persistent exceedances at all compliance boundaries because of the much slower release of
adsorbed COIs into groundwater.
In the CAP Part 2 report (HDR, 2016), Duke indicates that with the exception of sulfate and
hexavalent chromium, capping in place will not reduce any COI concentration to below
groundwater standards within 100 years. As referenced from the results in Table 4-1 within the
CAP Part 2 report, the refined model predicts that under both the Existing Conditions and Cap-
in -Place scenarios, the following COIs are predicted to exceed their respective 2L standards at
the Catawba River: antimony, arsenic, cobalt, boron, chromium, barium, selenium, and sulfate
(HDR, 2016). While the model used to develop the results for Table 4-1 does not take into
account natural attenuation, this does not change the fact that HDR has already concluded that
four of the COIs do not naturally attenuate, as referenced in Appendix H of the CAP Part 2
report (HDR, 2016). Therefore, contamination from four of the COIs will persist with capping in
place due to the fact that these constituents do not attenuate.
The excavation and removal option would perform better than the cap -in -place option, as
acknowledge by HDR in the CAP Part 1 report (HDR, 2015b). However, even under the
excavation and removal scenario, antimony, chromium, and hexavalent chromium are all
projected to remain above cleanup standards at the Catawba River compliance boundary after
250 years. With a more appropriate value of Kd, it is likely that other constituents would also
exceed groundwater cleanup levels at the Catawba River compliance boundary.
4.5 Successful remediation of groundwater will require excavation and removal coupled
with additional measures, such as hydraulic groundwater containment.
A cap -in -place remedy, even if augmented by a groundwater extraction hydraulic control system,
would not be a feasible method of groundwater remediation, nor would it maintain groundwater
concentrations below 2L or IMAC standards at the compliance boundary. To eliminate ongoing
migration of COIs across the compliance boundary, full excavation and removal of the ash from
the landfill and the underlying unlined coal ash pit is necessary as a first step. The precedent for
this degree of remediation is occurring currently in North Carolina among several sites. In
addition, care will need to be taken with the excavation process due to the site's proximity to the
Catawba River. This can be accomplished by means such as the construction of sheet piles and
coffer dams, or by the installation of temporary hydraulic control wells prior to excavation.
Excavation alone, however, will not prevent discharges of COIs to the Catawba River nor
migration of COIs westward into the adjacent residential areas. Because of the significant depth
of the bedrock unit and the rocky composition of the lower groundwater -bearing zones, barrier
walls on the site boundaries are probably not feasible. As a result, hydraulic containment would
need to be implemented for some time following coal ash removal to remove COI -impacted
groundwater at the western and eastern site boundaries so that COIs are maintained on the Duke
property.
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 10 Philip B. Bedient, Ph.D., P.E.

13 April 2016
A line of wells oriented north -south along the western site boundary would serve to pull
impacted groundwater eastward onto Duke property. Continued pumping of these wells at a
reduced rate would create a hydraulic barrier to prevent impacted groundwater from crossing the
compliance boundary and might eventually reduce COIs in groundwater to acceptable levels.
Likewise, even at the lower elevations on the eastern site boundary along the Catawba River, the
significant depth of the bedrock aquifer makes a barrier wall impractical. Because significant
groundwater flow occurs in the bedrock, a barrier wall that cuts off the shallow and deep zones,
but not the bedrock, would be ineffective. Thus, additional measures would need to be
implemented following coal ash removal, such as hydraulic containment along the Catawba
River; to both prevent COI discharges to the lake and to eventually reduce COIs in groundwater
to acceptable levels.
5.0 References
Bedient, 1997. Ground Water Contamination: Transport and Remediation. Second Addition.
Bedient, Philip B.; Rifai, Hanadi S.; Newell, Charles J. 1997.
HDR, 2015a. "Comprehensive Site Assessment Report, Allen Steam Station Ash Basin, HDR
Engineering," Inc. of the Carolinas, August 23, 2015.
HDR, 2015b. "Corrective Action Plan Part 1, Allen Steam Station Ash Basin," HDR
Engineering, Inc. of the Carolinas, November 20, 2015.
HDR, 2016. "Corrective Action Plan Part 2, Allen Steam Station Ash Basin," HDR Engineering,
Inc. of the Carolinas, February 19, 2016.
NRC, 1994. Alternatives for Ground Water Cleanup. National Research Council (NRC). 1994.
Remediation of Soil and Groundwater Expert Opinion of
Allen Steam Station, Belmont, NC 11 Philip B. Bedient, Ph.D., P.E.

1 .
1
,
1
_
1 ,
1
1
,
1
a
1
�
�
1
1
1
1
�
1
1
1
1
�
1
�
�
s
I
♦ I
,
1
♦
1
I�
I
1
1
1
♦1
-
1
1
I I
♦
1
I
♦
1
,, ♦ r
I �
�
1
1
1
1
f:
r1
1
�
hr
` �a 6Yir'9�o
I,
�c
j QL
c�¢a
N
0 0.25
I i I
Miles
I r
1
1
1
i
1
1
,
210 m
�1
2
Ohs
MD
wv
Ash Basin Waste Boundary
1 1 Duke Property Outline
KY
VA
TN
NC
SC
GA
P.B. Bedient Remediation of soil and groundwater at FIGURE 1
and Associates Inc. the Allen Steam Station, Belton, NC
I Site Location and Extent of Coal Ash
P.O. Box 1892 Date: 29 Feb 2016 Scale: As Shown Requiring Excavation and Proper
Houston, Texas 77251 _ Drafter: RH Checked by: PBB Disposal

P.B. Bedient Remediation of soil and groundwater at FIGURE 2
and Associates, Inc. the Allen Steam Station, Belton, NC
Date: 29 Feb 2016 Scale: As Shown Locations of Wells and Groundwater
P.O. Box 1892 Standard Exceedances for Any COI
Houston, Texas 77251 - Drafter: RH Checked by: PBB