Mayo_CoverLetterToSheliaHolman_20181115

KE
ENERGY.
November 15, 2018
Ms. Sheila Holman
Assistant Secretary for Environment
North Carolina Department of Environmental Quality
1611 Mail Service Center
Raleigh, North Carolina 27699-1611
Paul Draovitch
Senior Vice Presidsnt
Environmental, HaaJth & Safety
526 S. Church Street
Mail Code: ECUP
Charlotte, NC282d2
[phone]
Subject: Mayo Steam Electric Plant ash basin closure options, groundwater modeling and
community impact analysis
Dear Ms. Holman:
Duke Energy is providing information in response to the North Carolina Department of
Environmental Quality's requests on September 13 and October 8, 2018, to submit preliminary
updates to the closure options analysis, groundwater modeling and community impact analysis
for the Mayo Steam Electric Plant. These studies represent a key portion of the work the
company has performed to develop closure plans that balance a variety of considerations,
Duke Energy is committed to closing ash basins in ways that are safe, timely, environmentally
sound, and based on thorough science and engineering. In addition, effective closure plans are
site -specific and must ensure ash is managed in ways that continue to protect public health,
safety and the environment. Importantly, the planning process also considers how closure
choices may affect neighbors and communities.
After considering a number of potential closure options at Mayo, three options were advanced
for detailed analysis: closure -in -place, closure -by -removal and closure -in -place hybrid.
Based on a comprehensive assessment, Duke Energy will recommend at a later date either
closure -in -place or a hybrid closure plan to safely close the Mayo ash basin. We look forward to
input from regulators and interested stakeholders as we continue to evaluate safe closure
methods in a manner that protect people and the environment, while also minimizing disruption
to communities and managing cost.
North Carolina As a National Leader
To help ensure that the work done in North Carolina balances various considerations and
incorporates interdisciplinary perspectives, the company created the National Ash Management
Advisory Board (NAMAB) in 2014. This group of well -recognized experts in environmental
engineering, waste remediation, toxicology and other fields continues to provide ongoing
technical input and vet the various choices and tradeoffs inherent to any closure plan.
As previously stated, the enclosed documents represent key elements among the extensive
science and engineering being conducted by dedicated teams at Duke Energy and outside
experts, with ongoing input from NAMAB, to identify safe and smart basin closure plans for
remaining sites in North Carolina.

Groundwater Modeling
As multiple sources have validated, the ash basin has not affected neighbors' drinking water
wells near Mayo. For communities concerned that nearby well water could be affected in the
future, state lawmakers in 2016 passed legislation requiring the company to proactively provide
permanent drinking water sources. The company has completed the installation of advanced,
whole -home filtration systems for neighbors within a half -mile of the Mayo basin, even though
evidence demonstrates the ash basin is not impacting them, and most neighbors' well water
already met the appropriate performance standards for the filter systems.
In addition to advanced planning for safe drinking water, the N.C. Coal Ash Management Act
(CAMA) outlines an elaborate process to monitor and study groundwater near ash basins. This
involves thousands of monitoring wells across the state and using those real -world data points
to develop site -specific models that seek to predict how groundwater will respond to various
closure scenarios. This process also involves several iterations of extensive groundwater
studies and developing proposed corrective action steps that will work in tandem with basin
closure as necessary to address groundwater impacts.
Based on extensive study, the company understands that groundwater at Mayo moves slowly
and that coal ash impacts are very localized near the ash basin and generally on plant property.
In any closure scenario, the most effective step the company can take to improve groundwater
is to safely remove the free water from the ash basin. When predicting future groundwater
response at Mayo, the models demonstrate that:
• The patterns of decreasing boron concentration in the three closure scenarios are
generally similar for decades. Beyond 2125, the groundwater impact appears to resolve
slightly more quickly in the closure -by -removal and closure -in -place hybrid scenarios for
the deep zone and the area just upstream of the dam.
• The simulations indicate there will continue to be no impact to drinking water wells.
Groundwater impacts will continue to be evaluated as the updated modeling expands to other
parameters.
The models do not include the effects of any additional groundwater remediation steps the
company may take in the future. As part of a separate state -directed process, the company will
submit corrective action plans that propose steps that can be taken where groundwater
necessitates additional or more timely improvement. In particular, the company will pursue
groundwater remedial actions where needed with a focus on any surface water or offsite
property impacts.
Community Impact Analysis
In addition to relying on strong science and engineering, the company felt it was important to
consider various stakeholder interests and community impacts when developing its
recommended ash basin closure plans. In addition to its own research, which is included in the
comprehensive options analysis, the company relied on an outside consulting firm, Exponent, to
study the potential community impacts of various closure scenarios. Key take-aways include:
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• All closure options evaluated would be protective of human and ecological health. .
• All closure options evaluated would create similar levels of local community disturbance,
but the disruption in closure -by -removal and closure -in -place hybrid scenarios (noise
and traffic) would be extended because of the time necessary to complete construction.
• Closure -in -place would cause a net loss in ecological services (protection of biodiversity
and natural beauty), because a grass cap is less valuable habitat than open fields,
wetlands or forested areas. Any net loss in ecological services resulting from closure -in -
place can be offset by reforestation of land parcels.
The community impact analysis does not compare greenhouse gas emissions from onsite and
offsite trucking activity; therefore, a supplemental analysis will be provided comparing the
impact of various closure options on greenhouse gases and other air emissions.
The results of the community impact analysis vary by site, but in all cases cap -in -place closure
may be performed without adversely impacting the community. In some cases, reforestation of
land parcels may be advisable to offset any net habitat losses.
The conclusions in the community impact analysis are subject to revision if new landfill space
must be created to accommodate production ash. In such circumstances, excavation options
would score lower, in the community impact analysis.
Options Analysis
The company's options analysis considers the many aspects and tradeoffs related to basin
closure including environmental protection, schedule and the company's own analysis of
community impacts. In addition, as a regulated utility, Duke Energy is obligated to evaluate the
cost-effectiveness of the closure options. The company developed a relative weighting and
scoring system with input from the NAMAB that was used to evaluate and score various closure
alternatives.
For Mayo, key take-aways from the options analysis include:
• The closure -in -place option has the lowest estimated capital construction cost, while
excavation would cost more than double that amount.
• No ash transportation occurs on public roads for the closure -in -place and closure -in -
place hybrid options. Under Option 3 for closure -by -removal, trucks would cross Boston
Road/Highway 501 to the existing landfill numerous times a day for nearly seven years.
• The closure -in -place option can be completed in the shortest time frame and meet the
CAMA deadline of 2029. The closure -in -place hybrid and closure -by -removal options
would take longer, and excavation would not be completed by the 2029 deadline.

The company's recommended closure approach across its North Carolina sites reflects a
science -based combination of excavating, capping in place and recycling ash for concrete and
other beneficial purposes. Duke Energy remains committed to safely closing ash basins and
welcomes input from DEQ and the public to best balance these various tradeoffs.
Sincerel ,
Pa Draovitch
Senior Vice President
Environmental, Health & Safety
cc: Jim Wells, Duke Energy
Dave Renner, Duke Energy
Randy Hart, Duke Energy
Ed Mussler, DWM
Jon Risgaard, DW R
Andrew Brooks, DEMLR
Bill Lane, NCDEQ General Counsel
M