NC0005088_Bedient_Exprt_Rpt_Final_20160229

REMEDIATION OF SOIL AND GROUNDWATER
AT THE
CLIFFSIDE STEAM STATION
OPERATED BY DUKE ENERGY CAROLINAS, LLC
MOORESBORO, 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
29 February 2016

29 February 2016
REMEDIATION OF SOIL AND GROUNDWATER
AT THE
CLIFFSIDE STEAM STATION
OPERATED BY DUKE ENERGY CAROLINAS, LLC
MOORESBORO, 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................................................................................................................... 2
2.2 Hydrogeology..................................................................................................................... 3
2.3 Cliffside Coal Ash Basins and Coal Combustion Products (CCP) Landfill ....................... 3
2.4 Contamination.....................................................................................................................4
3.0 Efficacy of Remedial Options for Coal Ash Contaminants Evaluated by HDR.......... 4
3.1 Excavation and Removal.................................................................................................... 5
3.2 Cap-In-place........................................................................................................................5
4.0 Opinions.............................................................................................................................. 5
4.1 The groundwater flow and transport model developed by HDR to evaluate
remediation scenarios at the site is fundamentally flawed .................................................. 5
4.2 The remediation scenarios evaluated by HDR will not prevent coal ash
contaminants from migrating across the compliance boundary and into the Broad
River for the foreseeable future.......................................................................................... 6
4.3 Successful remediation of groundwater will require excavation and removal
coupled with hydraulic groundwater containment.............................................................. 7
5.0 References........................................................................................................................... 7
Remediation of Soil and Groundwater Expert Opinion of
Cliffside Steam Station, Belmont, NC i Philip B. Bedient, Ph.D., P.E.

29 February 2016
REMEDIATION OF SOIL AND GROUNDWATER
AT THE
CLIFFSIDE 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) Cliffside 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 for measuring compliance with applicable water quality
standards by the North Carolina Department of Environmental Quality (NCDEQ). 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. In
particular, I have not yet reviewed the Corrective Action Plan Part 2 (HDR, 2016) issued by
Duke at the time of this report, and I reserve the right to alter my opinions based on my review of
that document.
1.1 Summary of Opinions
It is my opinion that:
• The groundwater flow and transport model developed by HDR to evaluate remediation
scenarios at the site is fundamentally flawed.
• The cap -in -place remediation scenario 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, prevent coal ash contaminants from migrating
across the compliance boundary, or prevent migration into Suck Creek and the Broad
River for the foreseeable future.
• Successful remediation of groundwater will require excavation and removal coupled with
additional measures, such as hydraulic groundwater containment.
' 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.
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29 February 2016
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.
2.1 Physical Setting
Duke Energy owns and operates the Cliffside Steam Station (CSS) which is located in
Moorseboro, North Carolina. Operation as a coal-fired generating station began at CSS in 1940
Remediation of Soil and Groundwater Expert Opinion of
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29 February 2016
(HDR, 2015). CSS was once a 6-unit operating station. In 2011, Units I through 4 were retired
while Units 5 and 6 continue to operate.
2.2 Hydrogeology
The CSS site is located in the Inner Piedmont within the Cat Square terrane, which is one of a
number of tectonostratigraphic terranes that have been defined in the southern and central
Appalachians (HDR, 2015). According to the Corrective Action Plan (CAP) Part I, the Cat
Square Terrane is bounded by the younger -over -older Brindle Creek fault to the west that places
the terrane over the Tugaloo terrane of the Inner Piedmont and the Central Piedmont suture to the
east. The terrane is characterized by gentle dipping structures and low -angle thrust faulting and
sillimanite and higher amphibolite grade metamorphism (HDR, 2015).
The fractured bedrock is overlain by a mantle of unconsolidated material known as regolith
(HDR, 2015). According to the CAP Part I, the regolith includes residual soil and saprolite
zones, and where present, alluvial deposits. Saprolite, the product of chemical weathering of the
underlying bedrock, is typically composed of clay and coarser granular materials (HDR, 2015).
According to the CAP Part I, the groundwater system is a two medium system generally
restricted to the local drainage basin. The groundwater occurs in a system composed of two
interconnected layers: residual soil/saprolite and weather rock overlying fractured metamorphic
rock separated by a transition zone (TZ). Typically, the residual soil/saprolite is partially
saturated and the water table fluctuates within it; water movement is generally preferential
through the weathered/fractured bedrock of the TZ (i.e., zone of higher horizontal permeability)
(HDR, 2015). According to HDR, the character of the system results from the combined effects
of the rock type, fracture system, topography, and weathering. Topography exerts an influence
on both weathering and the opening of fractures, while the weathering of the crystalline rock
modifies both transmissive and storage characteristics (HDR, 2015).
The geologic and hydrogeological features influencing the migration, chemical, and physical
characteristics of contaminants are related to the Piedmont hydrogeologic system present at the
site (HDR, 2015). According to the CSA, the direction of the migration of the contaminants is
towards Suck Creek and the Broad River.
According to HDR, groundwater under CSS site flows horizontally generally toward the north
and discharges to the Broad River. Groundwater flow that is to the west of the active ash basin
and east of Unit 6 flows toward Suck Creek which discharges to the Broad River (HDR, 2015).
2.3 Cliffside Coal Ash Basins and Coal Combustion Products (CCP) Landfill
According to HDR, coal ash residue and other liquid discharges from CSS's coal combustion
process have been disposed of in the ash basin system located both west and east-southeast from
the station and adjacent to the Broad River.
As referenced in the CAP Part I, coal ash residue is conveyed to the active ash basin system at
the plant and is used to settle and retain ash generated from coal combustion at CSS. The ash
basin system is located adjacent to the Broad River and consists of the active ash basin, the Units
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29 February 2016
1-4 inactive ash basin, and the Unit 5 inactive ash basin, all of which are unlined (HDR, 2015).
According to HDR, the Units 1-4 inactive ash basin was converted into holding cells for storm
and plant process water. Two unlined ash storage areas are also located north and adjacent to the
active ash basin (HDR, 2015). During operation of the coal-fired units, the active ash basin
receives variable inflows from the ash removal system and other permitted discharges. Currently,
the active ash basin is permitted to receive variable inflows from the Unit 5 fly ash handling
system, Unit 5 bottom ash handling system, cooling tower blowdown, stormwater runoff from
yard drainage, coal pile runoff, gypsum pile runoff, limestone pile runoff, landfill leachate, and
wastewater streams generated from emission monitoring equipment (HDR, 2015).
Duke Energy also owns and operates the Cliffside Steam Station Coal Combustion Products
(CCP) Landfill (HDR, 2015). The CCP landfill is located nearly a mile southwest of the CSS on
Duke Energy property entirely within Rutherford County (HDR, 2015). According to the CAP
Part I, the CCP landfill is permitted to receive fly ash, bottom ash, boiler slag, mill rejects, flue
gas desulfurization sludge, gypsum, leachate basin sludge, nob -hazardous sandblast material,
limestone, ball mill rejects, coal, carbon, sulfur pellets, cation and anion resins, sediment from
sumps, and cooling tower sludge generated by Duke Energy North Carolina coal-fired facilities,
including from CSS.
2.4 Contamination
The CAP Part I assembled by HDR uses the term COI to describe any parameter that exceeded
its applicable regulatory standard or criteria. Review of laboratory analytical results within the
CAP Part I identified eight COIs including arsenic, barium, boron, cobalt, iron, manganese,
selenium, and vanadium. COIs identified in pore water in the ash basins and ash storage area
included antimony, arsenic, boron, cobalt, iron manganese, pH, sulfate, thallium, vanadium, and
TDS (HDR, 2015).
According to the CAP Part I, upgradient, background monitoring wells contain naturally
occurring metals and other constituents at concentrations that exceeded their respective 2L
Standards or Interim Maximum Allowable Concentration (IMACs). The CAP Part I explains the
that some naturally occurring metals and constituents, including antimony, chromium, cobalt,
iron, manganese, and vanadium were all detected in background groundwater samples at
concentrations greater than 2L Standards or IMACs however, groundwater monitoring data
shows concentrations of several other constituents exceeding their respective 2L Standards or
IMACS in groundwater across the site (HDR, 2015). These specific constituents with
exceedances include arsenic, barium, beryllium, boron, chromium, cobalt, lead, manganese,
nickel, sulfate, TDS, thallium, and vanadium (HDR, 2015).
3.0 Efficacy of Remedial Options for Coal Ash Contaminants Evaluated by
HDR
In its CAP Part I, 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 reduce leaching of contaminants to groundwater. The efficacy of these two
Remediation of Soil and Groundwater Expert Opinion of
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29 February 2016
remediation options for the COIs present in groundwater at the Cliffside 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 disposing of in a
secure landfill that is equipped with a proper liner and leachate collection system. 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 Broad 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 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 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 has been constructed so that only one pattern
of groundwater flow is possible; flow from the south site boundary northward to the Broad
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29 February 2016
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.
No flow boundaries to the west and east are not realistic and pre -define the groundwater flow
direction. The flow model developed for Duke allows groundwater to flow only generally
northward, from the coal ash basins into the Broad River. The no -flow boundaries to the west
channel this flow and pre -establish the flow direction. This a priori dictation of flow direction
limits the utility of the model for investigating COI transport, and inaccurate flow paths also lead
to erroneous expectations of contaminant migration pathways and mass loading to the Broad
River.
The southern boundary condition in the flow model is not technically supported. The no -flow
boundary to the south presumes that there is a groundwater divide that follows the east -west
trending ridge south of the site. There is not enough evidence to support this assumption of a
distinct groundwater divide south of the site.
The Duke model does not account for the significant pumping from wells in the vicinity of the
coal ash ponds, which would serve to divert groundwater from the direction calculated by the
flow model. Many groundwater wells near the boundaries of the flow model could affect
groundwater flow patterns, and these are not included in the CAP I model.
4.2 The remediation scenarios evaluated by HDR are inadequate.
The cap -in -place remediation scenario 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, prevent coal ash contaminants from migrating across the compliance
boundary, or prevent migration into Suck Creek and the Broad River for the foreseeable future.
The CAP I 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 Cliffside Station. In Appendix C of the CAP (HDR,
2015b), Duke acknowledges that under the cap -in -place scenario, many COIs will remain above
groundwater cleanup standards at the Broad 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 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. Of course, remediation measures that fail to meet groundwater
standards beyond the compliance boundary will also fail to restore groundwater to the required
standards within the compliance boundary.
The excavation and removal option would perform better than the cap -in -place option, as
acknowledge by HDR in the CAP (HDR, 2015b). However, even under the excavation and
removal scenario, several COIs are all projected to remain above cleanup standards at the Broad
River compliance boundary after many decades. With a more appropriate value of Kd, it is likely
that other constituents would also exceed groundwater cleanup levels at the Broad River
compliance boundary.
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29 February 2016
4.3 Successful remediation of groundwater will require excavation and removal coupled
with hydraulic groundwater containment.
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 Broad River. This can be accomplished by means such as the construction
of sheet piles and coffer dams, or by the installation of hydraulic control wells prior to
excavation.
Excavation alone, however, will not prevent discharges of COIs to the Broad River. 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. Thus, the
implementation of additional measures will be needed in order to meet groundwater standards
under the excavation and removal approach. As a result, additional measures would need to be
implemented following coal ash removal, such as hydraulic containment to remove COI -
impacted groundwater so that COIs are maintained on Duke property. Ultimately, full excavation
and removal of the ash coupled with the suggested additional measures is the most effective
remedial approach. It is important to note that pairing such additional measures with lesser
source control strategies, such as the cap -in -place option, will still not be sufficient to meet the
groundwater standards.
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, Cliffside Steam Station Ash Basin, HDR
Engineering," Inc. of the Carolinas, August 23, 2015.
HDR, 2015b. "Corrective Action Plan Part 1, Cliffside Steam Station Ash Basin," HDR
Engineering, Inc. of the Carolinas, November 20, 2015.
HDR, 2016. "Corrective Action Plan Part 2, Cliffside Steam Station Ash Basin," HDR
Engineering, Inc. of the Carolinas, February 19, 2016.
Remediation of Soil and Groundwater Expert Opinion of
Cliffside Steam Station, Mooresboro, NC 7 Philip B. Bedient, Ph.D., P.E.