2015-12-29 Mayo CAP I Comments

SOUTHERN ENVIRONMENTAL
VIRON ENTAL A ENTER
Telephone [phone] WEST ROSEMARY STREET, SUITE 220 Facsimile 919-929-9421
CHAPEL HILL, NC 27516-2356
December 29, 2015
Mr. Donald R. van der Vaart, Secretary
North Carolina Department of Environmental Quality
1601 Mail Service Center
Raleigh, North Carolina 27699-1601
K r Corrective Action Plan Part.L
Dear Mr. van der Vaart:
On behalf of the Roanoke River Basin Association, the Southern Environmental Law
Center submits the following first set of comments on Duke Energy's Corrective Action Plan
Part I for its Mayo Steam Station facility in Roxboro, N.C.
The Mayo Corrective Action Plan Part I (the "CAP") suffers from at least two
fundamental flaws. First, it demonstrates that much of the Mayo coal ash will remain submerged
in the groundwater if it is capped in place, yet does not discuss this fundamental problem in the
report or provide clear information on the extent of the problem. Second, the CAP improperly
relies on a nonexistent option for groundwater remediation, which in effect would adopt a "Flush
It to Virginia" approach by allowing the groundwater contamination to be flushed over the state
line into Virginia. Needless to say, this is not a recognized or valid option for groundwater
remediation. Our comments on these key issues and other specific problems with the CAP are
set out below.
The Coal Ash Will Remain Submerged In Groundwater If Capped In Place
The CAP and its modeling results show that much of the coal ash in the Mayo ash basin
will remain submerged in the groundwater under the Cap in Place scenario. Comparison of the
hydraulic head map for the Cap in Place option (Appendix E, Figure 17a) with the Closure in
Place Profile (Appendix E, Figure 16) reveals that much of the disposed ash would remain
saturated after capping. The data presented in these figures are consistent with the hydrogeology
of the site. A significant amount of groundwater will continue to flow into the ash basin from
adjacent areas, and some infiltration through the cap would also 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, where they will be flushed across the
state line to Virginia.
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Conspicuously, Duke Energy has failed to provide any discussion of this fundamental
problem in the text of the CAP, and has omitted any figures illustrating the extent of the
groundwater saturation of the coal ash in the basin under the Cap in Place scenario.
The volume and thickness of ash that will remain saturated under the Cap In Place
closure option as well as the expected volume of contaminated groundwater that will continue to
discharge to Crutchfield Branch under this option must be clearly discussed in the CAP. DEQ
should not approve any closure plan that will result in significant amounts of coal ash remaining
submerged in groundwater and continuing to discharge pollutants beyond the compliance
boundary.
1 '# D I r
The CAP goes to great lengths to make it appear that monitored natural attenuation is a
viable remedial option for the Mayo ash basin. In the effort to justify monitored natural
attenuation, Duke Energy has gone so far as to invent a nonexistent form of purported
contaminant attenuation, which the CAP calls "attenuation by dilution." However, this proposal
- - is not attenuation at all. Instead, it amounts to flushing the contamination from the Mayo ash
basin downstream into Virginia. This is not an acceptable form of groundwater remediation.
There is no such thing as "attenuation by dilution." Attenuation and dilution are two
different processes. Attenuation occurs when contaminants interact with the soil or rock through
which the water is flowing and contaminants are removed from the groundwater. 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 CAP
document provides no support for attenuation to treat the groundwater contamination at Mayo or
the spread of the ash contaminated boron plume.
Instead, what the Duke Energy document proposes is to leave the coal ash pollution in the
groundwater, mix it with the waters of Crutchfield Branch, and send it downstream into Virginia.
Duke Energy's Mayo site does not qualify for valid natural attenuation under the North
Carolina groundwater rules, as discussed in more detail below, because the groundwater
pollution and pollution of North Carolina and Virginia waters will continue if the coal ash is left
in place. Perhaps recognizing this, Duke Energy and its consultants have invented a nonexistent
remediation option of letting the pollution flush out of the Mayo ash basin into Virginia. This
approach must be rejected.
Specific Comments
Page 2-, Section, 1.2, Provisional Background Groundwater Concentrations - The second
paragraph of this section indicates that historic data sets were evaluated to exclude results with
elevated sample turbidity above 10 NTUs but provides no indication that the data were evaluated
for the presence of outliers unrelated to turbidity, such as laboratory errors, sampling problems,
etc. The data set must also be tested for additional outliers that may not be related to,saple
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turbidity, because including such outliers could artificially raise the purported background
concentration levels.
In addition, there is no discussion about how the 10 NTU level was selected. Please
justify selection of the 10 NTU criteria for modifying the data set.
Page 4-10, Section 4.3.2.1, Existing Conditions — This section of the document describes the
results of groundwater flow and contaminant transport modeling under existing conditions. The
model predicts that between the years 2015 and 2045, the boron plume would continue to expand
beyond the site boundary at Mayo Lake Road. Thus, Duke Energy's own model indicates that
reliance on natural attenuation to control the spread of groundwater contaminants would not be
effective.
Page 4-11, Section 4.3.2.2 Capping Ash Basin — The description of this scenario says that it
assumes the same conditions as the "Existing Conditions" scenario, with the exception of placing
an impermeable liner over the ash basin. However, that is not the case. The groundwater
modeling report (Appendix E) clearly states that assumptions on the concentrations of
contaminants in the ash (source material) were "relaxed" by being allowed to vary in the
"Capping Ash Basin" scenario but were held constant in the "Existing Conditions" simulation
(Appendix E at § 6.2). As Appendix E of the CAP states, "This change allows the concentration
in the ash and at shallow depths to decrease more rapidly [for Cap In Place] than in the No
Action scenario." Id. The report provides no rationale for changing this source concentration
variable between simulations, and RRBA is not aware of any justification for this approach. By
changing two parameters at once (adding the cap while simultaneously allowing the
concentrations of contaminants in the ash basin to decrease), the CAP makes it impossible to
meaningfully compare the Capping Ash Basin simulation with the Existing Conditions
simulation. Also, it may thereby overstate the supposed benefits of Capping in Place.
Page 4-11, Section 4.3.2.2 Capping Ash Basin — This section describes a scenario that includes
placement of an "impermeable liner" over the regraded ash basin as indicated on Figure 4-2.
The assumption of an impermeable cap was included in modeling of this option by assuming no
recharge within the ash basin (Appendix E, Section 6.2). However, the description of Option 2
provided in Figure 4-2 of the CAP report describes closure as capping of the graded ash only
with reclaimed soil from the dam and off-site borrow material. A soil cap constructed of
excavated dam soils and borrow material will not be impermeable. If the description in Figure 4-
2 is accurate, infiltration of precipitation through a soil cap must be realistically estimated and
the groundwater model must be revised to reflect more appropriate assumptions.
In addition, it is not clear whether the "no recharge" assumption described in Section 6.2
of Appendix E refers only to rainfall permeating through the cap or whether the model also
assumed no groundwater recharge from the sides of the basin valley. If the latter, this
assumption is incorrect and must be revised.
Page -11, Section 4.3.2.2 Capping Ash Basin — Comparison of the hydraulic head map for the
Cap in Place option (Appendix E, Figure 17a) with the Closure in Place Profile (Appendix E,
Figure 16) shows that much of the disposed ash will remain saturated after capping.

Groundwater will continue to flow into the ash basin from adjacent areas and some infiltration
through the cap will occur even if the basin is capped. Groundwater that flows through the ash
will continue to leach metals from the ash and transport those metals down -gradient, discharging
into Crutchfield Branch. However, no discussion of this issue is provided in the text. The
discussion in this section provides no indication of the thickness or volume of the accumulated
ash in the Ash Basin that will remain saturated. The CAP must clearly set out the volume and
thickness of ash remaining saturated after closure as well as the volume of contaminated
groundwater that will continue to discharge to Crutchfield Branch.
Page 4-11, Section 4.3.2.2, Capping Ash Basin — The CAP contains inconsistent descriptions of
how much of the ash basin dam would be removed under the Cap in Place scenario. The
preliminary concept for capping the ash basin referenced in this section (Figure 4-2) depicts
partial removal of the existing dam. The description provided in the text of this section simply
says that the dam would be removed, with no detail about how much of the dam structure would
be removed. Partial dam removal is also consistent with the closure in place profile provided in
Figure 16 of the groundwater modeling report (Appendix E). However, the description of the
capping in place scenario provided in the text of the groundwater modeling report describes
modeling based on removal of the entire dam, including removing low conductivity materials
from below grade. These inconsistent descriptions make it unclear how much of the ash basin
dam would be removed with the Cap in Place option. The details of what actions the Cap in
Place scenario would include needs to be consistent between the various documents, figures, and
modeling scenarios. Otherwise, the results of the modeling are invalid.
Page 4-11, Section 4.3.2.3, Removal of Ash — Despite the fact that groundwater modeling
results 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
entire discussion of this option consists of only one paragraph in the CAP report. Buried in an
Appendix, (Appendix E), is the conclusion of the groundwater modeling report that removing the
ash significantly reduces the size and concentration of the boron plume in the saprolite and
transition zones. Evaluation of remedial alternatives must not be pre -determined by Duke prior
to being fully evaluated and discussed in the CAP.
Page 4-14, Section 4.4.2, Surface Water Quality —The third full paragraph on this page
indicates that concentrations of ash -related constituents in Crutchfield Branch decrease with
distance downstream from the ash basin due to "attenuation by dilution." There is no such thing
as "attenuation by dilution." This is simply consultant -speak for allowing the Mayo coal ash
contamination to be flushed downstream into Virginia.
Dilution of a contaminant plume occurs when contaminated water is mixed with cleaner
water, thus diluting the plume but not removing any pollution. Attenuation occurs when
contaminants interact with the soil or rock through which the water is flowing and contaminants
are removed from the groundwater. Dilution of contaminants is not a form of attenuation; in
fact, it is a form of non -attenuation. The best description of the approach put forward by Duke
Energy and its consultant is Non -Attenuation by Dilution — something that North Carolina law
does not allow.
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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 attenuation as a remedy demonstrate that the contaminant has the capacity to degrade or
attenuate under site-specific conditions. Here, no data supporting attenuation as a mechanism
controlling the spread of the ash contaminant (boron) plume were provided. Thus, Duke Energy
has not made the required demonstration that the Mayo site is eligible for monitored natural
attenuation.
Page 5-1, Section 5.0, Corrective Action Plan Part 2 — Item 92 at the bottom of this page
indicates that monitored natural attenuation may be evaluated as a potential groundwater remedy
for certain areas of the site. However, monitored natural attenuation is not a viable closure
option for this site because:
• NCAC 02L.0106 (1)(1) requires a demonstration that all sources of contamination
and free product have been removed or controlled. So far, Duke Energy has not proposed
removal of the waste for disposal in a secure location. Controlling the waste will likely
require active operation of remedial systems for many decades if impacts to Crutchfield
Branch are to be controlled. 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.
• 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 Model (Section 3.2) 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 boron contamination at Mayo would not be eligible for
monitored natural attenuation. As discussed above, and contrary to what is stated in this
report, "attenuation by dilution" does not exist.
• 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 (see Table 2-14). These surface water exceedances are likely to
continue since the majority of flow in Crutchfield Branch is associated with drainage
from the ash basin (Page 4-13, Section 4.4. 1) and the groundwater model shows that a
substantial amount of ash will continue to be saturated with groundwater that flows to
Crutchfield Branch, even if the basin is capped.
Appendix E, Section 4.8, Transport Model Sources and Sinks — The 4t' paragraph of this
section indicates that modeling results show that the outflow channel on the east side of the
Mayo ash basin gains groundwater. Groundwater that discharges into the outflow channel likely
transports coal ash pollution into the channel that is not reflected in discharge monitoring
conducted at NPDES Outfall 002. The contaminated groundwater is then channeled directly into
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Mayo Lake. The magnitude and extent of groundwater contamination in the area of the outflow
channel must be determined.
Appendix E, Section 6.2, CAP2 — Capping Ash in Place — Comparison of the hydraulic head
map for the Cap in Place option (Figure 17a) with the Closure in Place Profile (Figure 16) shows
that much of the disposed ash is expected to remain saturated after capping. However, this report
discusses neither the thickness nor volume of ash that will remain saturated after the cap is
installed. The Corrective Action Plan and Groundwater Modeling Report (Appendix E) must
each identify and discuss the amount of ash that would remain saturated after closure by capping
and clearly set out the impacts to Crutchfield Branch as well as groundwater in the vicinity and
downgradient of the ash basin.
Appendix E, Section 6.2, CAP2 — Capping Ash in Place — This section clearly states that
assumptions on the concentration of contaminants in the ash (source material) were held constant
in the Existing Conditions simulation and allowed to vary in the Capping Ash Basin scenario.
This change allowed the concentration in the ash and at shallow depths to decrease more rapidly
than in the Existing Conditions simulation. No rationale is given for changing the method of
handling source concentrations between the two simulations.. While comparison of the Existing
Conditions and Capping Ash in Place simulations show the leading edge of the boron plum
receding by 100 to 200 feet by 2045, this change may be only a result of the change in
assumptions. In other words, by using different assumptions for the two simulations, the Duke
Energy report may have overstated the effect of the Cap In Place approach. DEQ cannot rely on
modeling results that are based on changes in multiple variables at once, because it is impossible
to determine whether the results are based on the addition of a cap or the changed assumption
about contaminant concentrations in the basin.
Cnnehminn
The Mayo CAP shows that the coal ash will remain submerged in the groundwater under
a cap -in-place scenario. That is an unacceptable result that will leave the source of the
groundwater pollution — the coal ash — in contact with groundwater, where it will continue to
leach out dangerous pollutants into public groundwater supplies. In addition, the CAP proposes
to simply flush the contaminated groundwater to Virginia. It attempts to avoid acknowledging
this unacceptable approach by giving it the invented name "attenuation by dilution" — a
regulatory and scientific contradiction in terms - but flushing pollution to a neighboring state is
not a valid form of remediation. As Duke Energy's own flawed report shows, there is no
evidence to support capping in place or attenuation of groundwater at the Mayo site.
Thank you for your consideration of these comments.
KSinSin erely,
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Fran S. Holleman III
Nicholas S. Torrey

cc: Stanley (Jay) Zimmerman, Director, Division of Water Resources, Central Office
Rick Bolich, DEQ Raleigh Regional Office
Harry Sideris, Senior Vice President of Environmental, Health & Safety, Duke Energy
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