Attach. 10, 20160226 GHI Mayo Report Final

GEO-HYDRO, INC
Consulting in Geology and Hydrogeology
1928 E. 14th Avenue
Denver, Colorado 80206
[phone]
EXPERT REPORT OF
MARK A. HUTSON, PG
Mayo Steam Electric Plant
Roxboro, NC
Prepared for:
Southern Environmental Law Center
601 West Rosemary Street
Suite 220
Chapel Hill, NC 27516-2356
February 2016

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1. Summary of Opinions Formed
Based upon my review of the available information I have formed the following opinions on closure
of the coal ash basin at the Mayo Steam Electric Plant (Mayo).
Coal ash stored in the Mayo ash basin is the source of contamination detected in surface
water and groundwater resources.
2. Capping the waste within the footprint of the Mayo ash basin will not be protective of
groundwater and surface water quality downgradient of the basin.
3. Monitored Natural Attenuation (MNA) is not a viable remedial option for impacted
groundwater and surface water downgradient of the Mayo ash basin.
4. Capping coal ash located within the Mayo ash basin will not be protective of surface water
quality in Crutchfield Branch.
Removal of the coal ash will reduce the concentration and extent of groundwater and surface
water contaminants.
6. The coal combustion residual impoundment risk classification proposed by North Carolina
Department of Environmental Quality (NCDEQ) improperly minimizes protection of
environmental quality.
The background and rationale behind each of these opinions are described in this report.

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2. Introduction
Duke Energy currently stores approximately 6,900,000 tons of coal ash in an unlined, water -filled
lagoon at the Mayo facility in Persons County NC. Pollution caused by the coal ash at this site is
currently the subject of an enforcement action brought by the NCDEQ. Organizations represented
by the Southern Environmental Law Center are also parties to this litigation.
North Carolina General Assembly Session Law 2014-122, the Coal Ash Management Act (CAMA)
of 2014, required the owner of coal combustion waste surface impoundments to conduct
groundwater monitoring, assessment and remedial activities at coal ash basins across the state, as
necessary. The owner of coal ash surface impoundments were required to submit a Groundwater
Assessment Plan (GAP) to NCDEQ by December 31, 2014. Comprehensive Site Assessment (CSA)
reports that reported the results of site characterization activities were required to be submitted
within 180 days of approval of the GAP. Information developed under the CSA provided the data to
be used to prepare Corrective Action Plans (CAP) that were to be submitted to NCDEQ within 90
days of submittal of the CSA. An agreement between Duke Energy and NCDEQ resulted in
breaking the CAP into Parts 1 and 2. As of this date only the CAP Part 1 has been produced for the
Mayo site.
Further, CAMA specifies that any impoundments classified by NCDEQ as high-risk be closed no
later than December 31, 2019 by dewatering the waste and either, a) excavating the ash and
converting the impoundment to an industrial landfill, or b) excavating and transporting the waste off-
site for disposal in an appropriately licensed landfill. Intermediate -risk impoundments are required
to be closed similarly to high-risk impoundments, but under a relaxed closure deadline of December
31, 2024. Impoundments classified as low-risk by NCDEQ must be closed by December 31, 2029
either similarly to the high and intermediate -risk sites, or by dewatering to the extent practicable and
capping the waste in place.
In January 2016 the NCDEQ issued Draft Proposed Risk Classifications (NCDEQ, 2016) for 10 ash
impoundment sites, including Mayo. The draft proposed risk classification assigned to Mayo is low
risk, thus allowing for closure of the impoundment by capping waste in place. On behalf of the
Southern Environmental Law Center, I have reviewed the Groundwater Assessment Plan (SynTerra,
2015a), Comprehensive Site Assessment (SynTerra, 2015b), the Corrective Action Plan Part 1
(SynTerra, 2015c), the Draft Proposed Risk Classifications (NCDEQ, 2016), and the National
Pollutant Discharge Elimination System (NPDES) permit for Mayo (North Carolina Department of
Environment and Natural Resources (NCDENR, 2009).
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This report details my opinions regarding: the source of groundwater and surface water pollution at
Mayo, potential remedies for that pollution discussed in the Corrective Action Plan, and the
proposed risk classification for the Mayo site.

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3. Qualifications
The opinions expressed in this document have been formulated based upon my formal education in
geology and over thirty-five years of experience on a wide range of environmental characterization
and remediation sites. My education includes B.S. and M.S. degrees in geology from Northern
Illinois University and the University of Illinois at Chicago, respectively. I am a registered
Professional Geologist (PG) in Kansas, Nebraska, Indiana, and Wisconsin, a Certified Professional
Geologist by the American Institute of Professional Geologists, and am currently serving as Past
President of the Colorado Ground Water Association.
My entire professional career has been focused on regulatory, site characterization, and remediation
issues related to waste handling and disposal practices and facilities. I have worked on contaminated
sites in over 35 states and the Caribbean. My site characterization and remediation experience
includes activities at sites located in a full range of geologic conditions, involving soil and
groundwater contamination in both unconsolidated and consolidated geologic media, and a wide
range of contaminants. I have served in various technical and managerial roles in conducting all
aspects of site characterization and remediation including definition of the nature and extent of
contamination, directing human health and ecological risk assessments, conducting feasibility
studies for selection of appropriate remedies to meet remediation goals, and implementing remedial
strategies. For the last ten years much of my consulting activity has been related to groundwater
contamination and permitting issues at coal ash storage and disposal sites.
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4. Site Background
The Mayo plant is a coal-fired electricity -generating facility located in north -central North Carolina in
the northeastern corner of Person County, North Carolina, north of the City of Roxboro. The northern
Plant property line extends to the North Carolina/Virginia state line. Mayo Lake borders the entire
eastern portion of this part of the Site. The Mayo Plant began coal-fired power production in 1983.
The 144 acre Mayo ash basin was formed by construction of a dam across the upper reaches of
Crutchfield Branch, a perennial' stream that once flowed in the valley immediately northwest of the
Mayo Steam Power Plant (Figure 1). The basin is impounded by an earthen dam approximately 2,300
feet long, with a dam height of 110 feet, and a crest height elevation of 479.8 feet above mean sea level
(msl). The ash basin contains approximately 6,900,000 tons of Coal Combustion Residuals2. Coal ash
and ash -impacted water have buried Crutchfield Branch behind the dam. The ash basin acts as an
elongated bowl -like feature with groundwater flowing to the basin from all sides, except from the
northeast, which is the discharge side from the basin. Groundwater flows north-northeast from the ash
basin into the small valley formed by Crutchfield Branch. Crutchfield Branch flows north off of Mayo
Plant property into Virginia3.
Constituents leached from ash into ash basin pore water at concentrations greater than North Carolina
Groundwater Quality Standards (2L) or Interim Maximum Allowable Concentrations (IMAC) include
antimony, arsenic, barium, boron, cobalt, iron, manganese, pH, thallium, total dissolved solids (TDS),
and vanadium 4. Ash -impacted water exits the impoundment by seeping through and around the dam
and discharging to the surface to reform the buried Crutchfield Branch, by migrating downgradient
from the impoundment as groundwater, and through NPDES discharge 0025 that discharges water
from the coal ash impoundment directly to Mayo Lake. Two engineered toe drains are located on the
downstream side of the dam and flow either directly into or eventually into Crutchfield Branch. Some
of the ash -contaminated impoundment water that infiltrates through the dam discharges to the surface
through the toe drains and other unplanned seeps below the dam to reform Crutchfield Branch.
The CSA determined that leaching from waste impounded within the ash basins impacts groundwater
in the vicinity of the ash basin 6. That document describes three hydrogeologic units or zones of
groundwater flow at the Mayo Plant. The zone closest to the surface is the shallow or surficial flow
1 The USGS Cluster Springs, VA -NC 7.5 minute topographic map shows Crutchfield Branch as a perennial stream across
most of the impounded area with intermittent reaches in the upper arms of the impoundment.
2 SynTerra, 2015a, p.6.
3 SynTerra, 2015 b, 1-7.
4 SynTerra, 2015a, p.129.
s NCDENR, 2009
6 SynTerra, 2015b,p. 1-7.
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zone encompassing saturated conditions, where present, in the residual soil, saprolite, or alluvium
beneath the Site. A transition zone is encountered below the surficial zone and the bedrock is
characterized primarily by partially weathered rock of variable thickness. The bedrock flow zone
occurs below the transition zone and is characterized by the storage and transmission of groundwater
in water -bearing fractures.
Available potentiometric data generally confirm that groundwater flow in the vicinity of the
impoundment is toward the north-northeast towards the reformed Crutchfield Branch. An exception to
this statement exists in the area of the Flue Gas Desulfurization (FGD) ponds located on the southeast
side of the impoundment where geology and groundwater flow direction are inadequately defined.
Site Layout and Water Level Mapss included with the CSA Report each show the FGD ponds located
inside the waste boundary, apparently indicating that the FGD ponds were constructed over disposed
ash. Review of the USGS topographic map (Figure 1) corroborates this interpretation. Contradicting
this information are cross-sections9 included with the CSA that each show the FGD ponds located
above soil/fill. The location of the waste boundary must be confirmed in order to determine the extent
of waste that must be remediated, either by excavation or capping.
The direction of groundwater flow is also poorly defined in the area of the FGD ponds. The CSA
report describes Mayo Lake as acting as a groundwater discharge area on the east side of the Plant.
Each of the C -C' cross-sections (see footnote) show the water table declining to the east between the
ash basin and wells CW -1/1D with flow toward the east beneath the area of the FGD ponds. The
Water Level Map shows the hydraulic gradient flowing toward the north from a high beneath the
electric plant toward the ash basin in this same location. An additional well cluster located between
the FGD ponds and discharge canal is needed to provide additional control on geology and
groundwater flow direction, velocity and chemistry in the area of the FGD ponds.
The groundwater flow and transport model of the site was constructed and used in the CAP to evaluate
groundwater flow and investigate three remedial scenarios. The scenarios investigated included the
No Action scenario, a Capping Ash in Place scenario, and a Complete Ash Removal scenario. The
model was used to predict contaminant distributions for the next 5, 15 and 30 years, under each
scenario.
The Existing Conditions scenario 10 relies on natural attenuation processes to reduce contaminant
concentrations over time. The ash basin remains in place without modification and "the assumption is
made that current recharge and contaminant loading rates from the ash to the underlying formations are
7 Figure 2-1
8 Figure 6-9
9 C -C' Sections included presented in Figures 6-3, 6-6, 8-3, 11-1b, 11-2b. 11-3b, 11-4b, 11-5b, 11-6b, 11-7b, 11-8b, 11-9b,
and 11-10b
10 The entire description of this scenario is presented in the CAP, Appendix E, Section 6.1.
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held constant". "The flow system is assumed to be at steady state with respect to the conditions in
2015." "Concentrations in the ash were held constant at the measured concentrations." Using these
assumptions the model predicts that the boron and arsenic plumes will continue to expand and the
leading edge of the boron plume is predicted to move north of the compliance boundary over the next
30 years.
The Capping Ash Basin scenario' 1 involves placing a low permeability liner over the ash basin to
prevent infiltration. The description of this scenario assumes that there is no recharge within the basin,
that the dam was removed and that contaminant concentrations in the ash were allowed to vary
(concentrations were fixed in the Existing Conditions scenario). Other changes to the model included
modified boundary conditions to remove constant head conditions representing the impoundment and
the grid was modified to represent grading of the ash. Results of this modified model predict that the
leading edge of the boron plume would recede by 100 to 200 feet in the vicinity of the compliance
boundary. Arsenic concentrations are predicted to increase in the saprolite, but the increase is smaller
than that predicted under the Existing Conditions scenario.
Concerns with the Capping Ash Basin scenario include the assumption of no recharge within the basin
and changing the way that contaminant concentrations in the source material are handled. The
hydrogeologic setting of the impoundment 12 describes groundwater discharges into the impoundment
form the east, west and south sides. Capping of the ash in the basin will not control discharging
groundwater. The discharges of groundwater into the ash are likely significant as groundwater
discharges into the basin were sufficient to support a perennial reach of Crutchfield Branch prior to
burying the stream with coal waste.
The concentration of contaminants in the ash were held constant in the Existing Conditions simulation
but were allowed to vary in the Capping Ash Basin scenario. This change in assumptions allowed the
concentration in the ash to decrease more rapidly in the Capping Ash Basin scenario than in the
Existing Conditions simulation. The rationale for changing the method of handling source
concentrations between simulations was not discussed. Comparison of the No Action scenario and
Capping Ash Basin scenario simulations show the leading edge of the boron plume receding by 100 to
200 feet by 2045. It is unclear if this reduction is a result of cap installation, or if it is an artifact of the
change in assumptions.
The Removal of Ash 13 scenario represents complete removal of the ash by applying zero concentration
levels and regional recharge within the ash basin. Even if one ignores the defects with the first two
simulations, the Removal of Ash scenario predicts, by far, the largest reduction in ash -related
11 The entire description of this scenario is presented in the CAP, Appendix E, Section 6.2
12 SynTerra 2015b, p. 1-7 and 1-11.
13 The entire description of this scenario is presented in the CAP, Appendix E, Section 6.3
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contaminant concentrations. Figures 2, 3 and 4 show predicted 2045 boron concentrations within the
saprolite layer (Layer 5) for all three of the simulated options.
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5. Opinion 1: Coal Ash Stored in the Mayo Ash Basin is the Source
of Contamination Detected in Surface Water and Groundwater
Coal ash is the source of contaminants detected in surface water and groundwater at concentrations
above applicable standards in the vicinity and downgradient of the ash basin. Data collected during
the CSA show that that ash basin pore water contains antimony, arsenic, barium, boron, cobalt, iron,
manganese, pH thallium, TDS and vanadium at concentrations greater than 2L or IMAC standards 14
The contaminated pore water migrates into groundwater and is discharged into impoundment water,
each of which subsequently discharge to Crutchfield Branch. This interpretation is consistent with
the conclusions of the CSA which states that "The CSA found that leaching of CCR accumulated in
the ash basin is a source of COIs detected in groundwater and surface water downgradient of the
basin"ls
14 SynTerra 2015b, p. 1-7
15 Synterra 2015a, p.127, Constituent of Interest (COI)
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6. Opinion 2: Capping Coal Ash Located Within the Mayo Ash
Basin Will Not Protect Groundwater Quality Downgradient of the
Basin
Capping the waste within the footprint of the ash basin will not be protective of groundwater quality
downgradient of the basin. Further, the CAMA process proposed designation of the Mayo Site as
low-risk creates the possibility that Duke Energy (Duke) could pursue closure of the Mayo
impoundment by capping the disposed ash in place.
Environmental contaminants contained in coal ash are leached into groundwater when precipitation
infiltrates through the waste or, when groundwater flows through waste that has been placed below
the water table. In the case of the Mayo ash basin, both of these processes are currently acting to
create the contaminated ash porewater, groundwater, and surface water that discharge into
Crutchfield Branch and contaminate surface water downstream of the impoundment. The cap -in-
place remedy would likely reduce the amount of water that enters the waste from precipitation. This
remedy would however do nothing to reduce the amount of water that flows laterally into the basin
from surrounding geologic materials, through the capped waste, and eventually into Crutchfield
Branch.
The CAP and its included modeling results show that much of the coal ash in the Mayo ash basin
will remain submerged below the water table under a cap -in-place remedy. The thickness of
saturated waste that would remain saturated can be estimated by comparing the pre -impoundment
topographic map of the basin (Figure 1) with the calculated hydraulic head map for the cap in place
option (Figure 5). The topographic map of the buried valley shows that natural land surface below
the impoundment is located at approximately 400 feet above mean sea level (msl) near the center of
the basin. The calculated hydraulic head in the basin after ash is capped in place is predicted by the
model to be approximately 460 to 470 feet msl near the center of the basin. Therefore, the model of
the cap -in-place scenario predicts 60 to 70 feet of saturated ash would remain in portions of the
basin. The data presented in these figures is consistent with the known hydrogeology of the site.
Groundwater will continue to flow into the ash basin from adjacent areas and some infiltration
through the cap would continue to occur. Groundwater that flows through the ash will continue to
leach metals from the ash and transport those metals down -gradient before discharging into
Crutchfield Branch.
Further, the results of the groundwater modeling exercise undertaken as part of this program indicate
that removal of the Mayo coal ash is by far the most effective option for improving groundwater
quality and preventing future discharges to Crutchfield Branch. The modeling results indicate that
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removal of the ash significantly reduces the size and concentration of the boron plume in the
saprolite and transition zones, something that capping -in-place does not achieve.
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7. Opinion 3: Monitored Natural Attenuation Is Not An Acceptable
Groundwater Remediation Strategy at Mayo
The CAP 16 indicates that Duke may evaluate Monitored Natural attenuation as a potential
groundwater remedy for certain area of the Mayo site. The CAP attempts to make it appear that
Monitored Natural Attenuation (MNA) is a viable remedial option for impacted groundwater and
surface water downgradient of the Mayo ash basin. However, MNA is not a viable closure option
for this site for several reasons including the following North Carolina requirements for
implementing MNA:
1.0 NCAC 02L.0106 (1)(1) requires a demonstration that all sources of
contamination have been removed or controlled. So far, Duke Energy has not proposed
removal of the waste for disposal in a secure location. Modeling presented in this
document shows that most of the ash would remain saturated after capping. Saturated
ash will continue to leach metals into groundwater that will flow toward and eventually
discharge into Crutchfield Branch. As a practical matter, in the absence of removal all
sources of contamination cannot be controlled
2.0 NCAC 02L .0106 (1)(2) requires a demonstration that the contaminant has the
capacity to degrade or attenuate under site-specific conditions. Many of the ash -related
constituents in groundwater at this site neither degrade nor attenuate. The Geochemical
Site Conceptual Modell? states that boron best represents the extent of impact to
groundwater because it "does not sorb or precipitate within the ash or on aquifer
materials." Because of this, the Mayo site would not be eligible for NINA.
3.0 NCAC 02L.0106 (1)(6) requires a demonstration that groundwater discharge
will not possess contaminant concentrations that would result in violations of surface
water standards. Crutchfield Branch, which receives the contaminated groundwater
discharge at Mayo, currently exceeds surface water standards for several parameters.
Sampling has detected ash -related metals at concentrations above background and
relevant NCAC 2B and/or 2L standards, including boron, cobalt, copper, iron,
manganese, thallium, vanadium, and zinc 18. These surface water exceedances are likely
to continue since the majority of flow in Crutchfield Branch is associated with drainage
from the ash basin19 and the groundwater model shows that a substantial amount of ash
will continue to be saturated with groundwater that eventually flows to Crutchfield
Branch, even if the basin is capped.
16 SynTerra, 2015b, p.5-1
17 SynTerra, 2015b, Section 3.2
18 SynTerra, 2015b, Table 2-14
19 SynTerra, 2015b, Page 4-13, Section 4.4.1
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8. Opinion 4: Capping Coal Ash Located Within the Mayo Ash
Basin Will Not Be Protective of Surface Water Quality in
Crutchfield Branch
Prior to construction of the Mayo plant Crutchfield Branch was a free-flowing perennial stream that
occupied the valley through which it flowed. The coal ash basin was constructed by damming the
stream and used to segregate and store coal combustion wastes that were allowed to settle in the
basin. If coal ash located within the Mayo ash basin is capped in place, the surface water in
Crutchfield Branch will continue to be polluted and a significant portion of Crutchfield Branch will
remain buried by waste.
Crutchfield Branch, which receives the contaminated groundwater discharge at Mayo, currently
exceeds surface water standards for several parameters. Sampling has detected ash -related metals at
concentrations above background and relevant NCAC 2B and/or 2L standards, including boron,
cobalt, copper, iron, manganese, thallium, vanadium, and zinc 20. These surface water exceedances
will continue since the majority of flow in Crutchfield Branch is associated with drainage from the
ash basin 21 and the groundwater model shows that a substantial amount of ash will continue to be
saturated with groundwater that eventually flows to Crutchfield Branch, even if the basin is capped
(See Opinion #2). Coal ash must be separated from the groundwater and surface water flow
systems if further contamination of these resources is to be avoided
The surface water quality discussion in the CAP 22 indicates that concentrations of ash -related
constituents in Crutchfield Branch decrease with distance downstream from the ash basin due to
"attenuation by dilution." This is problematic because, of course, there is so such process as
attenuation by dilution. Attenuation and dilution are two different processes. Attenuation occurs
when contaminants interact with the soil or sediments, and contaminants are removed from the
water. Dilution does not remove or treat any contaminants; instead, the concentration, but not the
amount, of a pollutant is reduced by diluting the polluted plume with water containing a lower
concentration of the contaminant. Thus, dilution and attenuation are distinctly different processes.
The made-up process referred to as "Attenuation by Dilution" appears to have been invented in an
effort to make discharges of contaminated groundwater and subsequent exceedances of surface water
quality standards appear acceptable.
North Carolina regulations covering corrective action plans based on natural processes (NCAC 02L
.0106 (1)(2)) require that a corrective action plan that proposes to utilize monitored natural
20 SynTerra, 2015b, Table 2-14
21 SynTerra, 2015b, Page 4-13, Section 4.4.1
22 SynTerra, 2015b, Section 4.4.2
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attenuation as a remedy demonstrate that the contaminant has the capacity to degrade or attenuate
under site-specific conditions. The Geochemical Site Conceptual Mode123 states that boron best
represents the extent of impact to groundwater because it "does not sorb or precipitate within the ash
or on aquifer materials." The properties of the contaminants at Mayo would therefore render the site
ineligible for remediation by MNA, even if attenuation by dilution were a real process. In addition,
capping the coal ash in the in place would leave a significant portion of Crutchfield Branch buried in
waste. Now that the Mayo waste handling system is no longer going to be used there is no
justification for leaving the existing stream covered in coal ash.
13 SynTerra, 2015b, Section 3.2
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9. Opinion 5: Removal of the Coal Ash Will Remove the Source and
Reduce the Concentration and Extent of Groundwater and
Surface Water Contaminants
Removal (excavation) of the coal ash from the Mayo ash basin will remove the source, and reduce
the concentration and extent of groundwater and surface water contaminants. The groundwater flow
and transport model of the site was used in the CAP to evaluate groundwater flow and investigate
three remedial scenarios. The scenarios investigated included the No Action scenario, a Capping
Ash in Place scenario, and a Complete Ash Removal scenario. The model was used to predict
contaminant distributions for the next 5, 15 and 30 years, under each scenario.
The extent of boron in groundwater for each scenario at the end of 30 years are shown in Figures 2,
3 and 4. The model shows that the Removal of Ash scenario results in, by far, the largest reduction
in ash -related contaminant concentrations.
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10. Opinion 6: The Coal Combustion Residual Impoundment Risk
Classification Proposed by NCDEQ Improperly Minimizes
Protection of Environmental Quality
A risk ranking process was specified in CAMA to determine the type of closure permitted at each
facility. The law specifically requires NCDEQ to classify each impoundment as either high-risk,
intermediate -risk, or low-risk, based on consideration, at a minimum, of all of the following criteria.
(1) Any hazards to public health, safety, or welfare resulting from the impoundment.
(2) The structural condition and hazard potential of the impoundment.
(3) The proximity of surface waters to the impoundment and whether any surface waters are
contaminated or threatened by contamination as a result of the impoundment.
(4) 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.
(5) The location and nature of all receptors and significant exposure pathways.
(6) The geological and hydrogeological features influencing the movement and chemical and
physical character of the contaminants.
(7) The amount and characteristics of coal combustion residuals in the impoundment.
(8) Whether the impoundment is located within an area subject to a 100 -year flood.
(9) Any other factor the Department deems relevant to establishment of risk.
In order to evaluate each impoundment on the nine criteria the NCDEW established a risk
classification group24. The Risk Classification Group was broken into three sub -groups of people
based on areas of expertise (Groundwater, Surface Water, and Dam Safety) to develop a set of risk
factors to address each of the nine required criteria. Each subgroup reportedly placed a primary
emphasis on risk as it relates to the public from a groundwater, surface water, and dam safety
perspective and established one key factor that "plays a significant role in assigning an overall
classification" for that group. Other factors not identified as Key Factors were supposedly used to
"refine the risk classification and address the actual or potential risk to the environment and natural
resources."
The result of the risk classification methodology utilized by NCDEQ is that environmental and
ecologic risks posed by the Mayo site were not fully considered by NCDEQ when establishing the
overall site risk and clean-up priority. This resulted in an overall Low Risk rating, a rating that
essentially ignores the known environmental impacts of the Mayo Ash Basin. For example, Table
24 NDEQ, 2016, p. 13, Classification Methodology
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provides a listing of the groundwater risk classification factors and associated ratings for Mayo. Ten
groundwater risk factors were established and received ratings by NDEQ. Of the 10 rated factors, 6
received High or Intermediate Ratings, one factor was rated as Low/Intermediate, and only 3
received ratings of Low Risk. Only 30% of the rated groundwater risk classification factors were
rated Low Risk, yet NCDEQ gave Mayo an overall Low Risk Rating for Groundwater.
Table 1
Groundwater Risk Classification
Groundwater Factors
Mayo Rating
Number of downgradient receptors within 1500 feet of compliance boundary that
are potentially or currently known to be exposed to impacted water. (Key Factor)
Low Risk
Amount of stored CCR reported in an impoundment
Intermediate Risk
Depth of CCR with respect to the water table
High Risk
Exceedance of 2L or IMAC standards at or beyond the established CCR
compliance boundary
High Risk
Population served by water supply wells within 1,500 feet upgradient or side
gradient of the compliance boundary
Low /Intermediate Risk
Population served by water supply wells within 1,500 feet downgradient of the
compliance boundary
Low Risk
Proximity of 2L or IMAC exceedances beyond the compliance boundary with
respect to water supply wells
High Risk
Groundwater emanating from the impoundment exceeds 2L or IMAC and that
discharges to a surface water body
High Risk
Ingestion of contaminated soil or fugitive emissions
Low Risk
Data Gaps and Uncertainty
Intermediate Risk
Table 2 provides a listing of the surface water risk classification factors and associated ratings for
Mayo. A total of eight surface water risk factors were rated by NCDEQ. Of the 8 rated factors, 3
were High or Intermediate Risk, and additional 3 factors were rated as Low/Intermediate Risk, and
only 2 of 8 factors are rated Low Risk. Only 25% of the rated surface water risk classification
factors were rated Low Risk, yet NCDEQ gave Mayo an overall Low Risk Rating for Surface Water.
The preceding analysis uses the risk ratings applied by NCDEQ with no evaluation or judgment
about whether they were or were not appropriately applied. The risk ratings given to the Mayo ash
basin point out that protection of environmental and natural resources are not being treated as
priority issues by the North Carolina agency entrusted with the responsibility to do just that. The
approach utilized by NCDEQ effectively ignores impacts to the natural environmental and natural
resources, and even ignores future human users of the groundwater and surface water resources. It
appears that in the view of NCDEQ the only way that a site can be rated as Intermediate or High
Risk is if a facility is located within a 100 -year floodplain or if 11 or more people within 1,500 feet
of the compliance boundary are potentially or currently known to be exposed to ash -impacted
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groundwater25. It is hard to imagine that exposed persons 1 through 10 would agree with this rating
scheme.
Table 2
Surface Water Risk Factors
Surface Water Factors
Mayo Rating
Landscape Position and Floodplain (Key Factor)
Low Risk
NPDES Wastewater and Ash Disposal Methods
Low/ Intermediate Risk
Impoundments Footprint Siting in Natural Drainage Way or
Stream
Low/ Intermediate Risk
Potential to Impact Surface Water Based on Total Ash Amount at
Facility
High Risk
Potential to Impact Surface Water Based on Dilution
High Risk
Development Density of Single -Family Residences along
Lake/Reservoir Shoreline
Low Risk
Classification of the Receiving Waters
Low/ Intermediate Risk
Proximity to Water Supply Intake
Intermediate Risk
15 NCDEQ, 2016, page 15, Key Factors

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References
NCDEQ, 2016, Coal Combustion Residual Impoundment Risk Classifications, January 2016.
NCDENR, 2009, Permit to Discharge Wastewater Under the National Pollutant Discharge
Elimination System, Permit NC0038377, October, 2009
SynTerra, 2014, Groundwater Assessment Work Plan for Mayo Steam Electric Plant, September
2014
SynTerra, 2015a, Comprehensive Site Assessment Report, Mayo Steam Electric Plant, Roxboro,
NC, September 2015.
SynTerra , 2015b, Corrective Action Plan, Part 1, Mayo Steam Electric Plant, Roxboro, NC,
December 2015.
United States Geological Survey, Cluster Springs VA. — N.C., 7.5 Minute Topographic Map, 1968,
photorevised 1987.
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Figures

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Figure 1
GEO-HYDRO INC Image taken from
� USGS Cluster Springs VA —NC
Ash Pond Topography
Consulting in Geology and Hydrogeology 1968
Mayo Steam Electric Plant
Photorevised 1987

Figure 32. Simulated October, 2045 boron concentrations (pg -I) in the model laver of the
saprolite (layer 5) for CAP I,
Images from Mayo CAP Part 1,
Appendix E
Figure 2
GEO-HYDRO, INC Predicted 2045 Layer 5
Consulting in Geology and Hydrogeology Boron Concentration
No Action Scenario
Mayo Steam Electric Plant

E=igurc 50. Simulated October, 2045 boron concentrations (jigFL.) in the mode) layer of the
saprolite (layer 5) ror CAP2.
Images from Mayo CAP Part 1,
Appendix E
Figure 3
GEO-HYDRO, INC Predicted 2045 Layer 5
Consulting in Geology and Hydrogeology Boron Concentrations
Capping Ash Basin Scenario
Mayo Steam Electric Plant

Figure Vii . Simulated October, 2045 Moron concentrations; (pg/L) in the model layer of tete
:iproliw (layer 5) ruT CAPS.
Images from Mayo CAP Part 1,
Appendix E
Figure 4
GEO-HYDRO, INC Predicted 2045 Layer 5
Consulting in Geology and Hydrogeology Boron Concentration
Removal of Ash Scenario
Mayo Steam Electric Plant

Images from Mayo CAP Part 1,
Appendix E
GEO-HYDRO, INC
Consulting in Geology and Hydrogeology
f4�
Remove ash
Figure 5
Calculated Head Maps
Mayo Steam Electric Plant