WQ0000020_ARO Permit Renewal Comments_20200812

August 12, 2020

Ranveer Katyal
Division of Water Resources
Non-Discharge Branch
1617 Mail Service Center
Raleigh, North Carolina 27699-1617

Subject: Asheville Regional Office Staff Report for the Duke Energy Progress Ash
Distribution Program Renewal Application (WQ0000020)

Dear Mr. Katyal,

The Asheville Regional Office (ARO) is providing the following staff report in support of the
Duke Energy Progress (Duke) Ash Distribution Permit renewal (WQ0000020). Due to the
complexities associated with this permit, a more detailed staff report is being submitted in lieu
of the traditional staff report form.

As you may be aware, the passage of the North Carolina Coal Ash Management Act in 2014
affected this permit and subsequently was rewritten in 2015 with a focus on the operation,
maintenance, and monitoring of the Asheville Regional Airport (Airport) coal combustion
products (CCP) structural fill project. Please note that the ARO has issued two Notices-of
Violation (NOV) to Duke and one NOV to the Greater Asheville Regional Airport Authority
(GARAA) with regards to ongoing compliance issues at a CCP structural fill referred to as Area 1.
In addition, Duke and GARRA are currently in negotiations with the Department in regards to
permitting, fiscal responsibility, long-term care, and resolution of compliance issues. This staff
report contains a brief site history, summary of violations, corrective action issues, and permit
renewal recommendations.

Asheville Regional Airport Coal Combustion Products Structural Fill Project
The Airport CCP structural fill project began in 2008 as a partnership between then Progress
Energy Carolina, Inc. (Duke) and GARAA. The goal was to utilize wet-sluiced coal ash or CCP fill
from Duke’s Asheville Steam generating plant (located 2 miles away) to expand buildable land
around the airport. The Asheville Regional Airport CCP structural fill project was completed in
2015. The Airport is utilizing the CCP fill project to support runway expansion and future
development.

DocuSign Envelope ID: 8E8AE8C9-6228-43C5-BF45-6192482D2A92

Ranveer Katyal
August 12, 2020
Page 2 of 9

The project consists of three separate CCP structural fills referred to as Area 1, Area 3, and Area
4 (see attached map 1). Area 1 is 18-acres in size and contains approximately 732,408 tons of
CCP fill. Area 3 is 31-acres in size and contains approximately 2.2 million tons of coal ash. Area 4
is 45-acres in size and contains approximately 1.1 million tons of coal ash.

In September 2017, there was a shallow slope failure and subsequent exposure of CCP fill at
Area 1. The ARO issued Duke a Notice of Violation (NOV-2017-PC-0616) for failure to properly
maintain and operate the structural fill. An additional Notice of Violation (NOV-2018-DV-0101)
was issued to Duke and GARAA in April 2018 for discharging CCP leachate to surface waters at
Area 1.

Area 1 CCP Structural Fill Comprehensive Site Assessment
It is important to note that the Area 1 CCP fill is constructed differently than the other two CCP
structural fill projects. Area 1 is underlain by a geosynthetic clay liner (GCL) and capped with
soils ranging from 2 – 6 feet in depth. A proposed impervious layer consisting of buildings,
roads, parking lots, and traditional stormwater conveyances was never constructed. The other
two projects (i.e., Areas 3 & 4) are underlain by a GCL and a 60 ml HDPE liner, internal leachate
collection system, and capped by a 30 ml HDPE liner and soils ranging from 2 – 6 feet in depth.
The top and bottom HDPE liners are heat sealed to encapsulate the CCP fill.

After the September 2017 slope failure at Area 1, Duke Energy was issued an NOV and required
to take immediate action to stabilize and monitor the weakened CCP fill slope and to conduct a
comprehensive site assessment (CSA) in support of a corrective action plan. The CSA was
conducted between 2017 – 2019 and includes the following action items required by the ARO:

• Temporary stabilization of the CCP fill slope;
• Monthly and quarterly site inspections;
• Hydrogeologic conceptual model development;
• Piezometric surface investigation (i.e., groundwater beneath CCP fill);
• Phreatic surface investigation (i.e., water inside CCP fill);
• Construction of additional monitoring wells and piezometers;
• Installation of a geopin array and inclinometer to monitor slope movement;
• Monthly and quarterly slope monitoring;
• Geotechnical slope stability analysis;
• Assessment of soil cap, GCL, and the 60-inch RCP beneath the structural fill;
• Surface water monitoring including the sampling criteria for hardness-dependent
metals; and
• Development of remedial strategy.

Inadequate stormwater management along the crown of the CCP fill and an underperforming
soil cap is allowing precipitation/runoff to infiltrate the Area 1 CCP fill. The infiltrating water is
pooling inside the CCP fill and above the GCL at depths ranging from 10 ft. to 13 ft. (phreatic
surface). Water in contact with coal ash, or CCP leachate, is moving downslope along the top of
DocuSign Envelope ID: 8E8AE8C9-6228-43C5-BF45-6192482D2A92

Ranveer Katyal
August 12, 2020
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the GCL and is presently discharging to an unclassified stream and tributary to the French Broad
River known locally as Hidden Creek. It important to note that this section of the French Broad
River [6-(54.75)] is listed as a Class B stream. This phreatic surface is also responsible for
saturating portions of the CCP fill slope and contributed to the shallow sliding failure in
September 2017. The Area 1 CCP fill slope remains in a weakened state, which necessitated
temporary emergency measures such as installation of a rock buttress, installation of an
inclinometer, a slope monitoring system, and the installation of piezometers and monitoring
wells (see attached map 2)

A pre-construction hydrogeologic assessment of the Area 1 CCP fill was conducted in 2008 and
concluded that local groundwater elevations fluctuate in a narrow range and estimated 7 ft. of
separation between the seasonal high-water table (SHWT) and the base elevation of the Area 1
CCP fill. The assessment failed to account for the extreme drought conditions affecting
Buncombe County during the period of investigation and consequently underestimated the
elevation of the SHWT relative to the proposed base elevation of the CCP fill. Two piezometers
that penetrate the GCL indicate current groundwater surface elevations range between 4 - 11
feet above the base elevation of the CCP fill. In other terms, hydraulic pressures beneath the
structural fill are increasing and is putting strains on the i nfrastructure such as the CCP fill slope,
RCP corridor, and the GCL. It is important to note the Area 1 CCP fill no longer meets the 2 feet
of separation from the SHWT as required by 15A NCAC 02T .1206.

The ARO also believes that the placement of a low-conductivity liner (GCL) across pre-existing
groundwater pathways and within an active groundwater discharge area has altered the
movement of groundwater locally resulting in groundwater mounding on the east -side of the
Area 1 CP fill. Over the last decade, groundwater surface elevations have risen an estimated 10
– 40 feet on the east side of the structural fill. Furthermore, groundwater elevations on the
east-side of the CCP fill are near or exceeding the GCL termination elevations signifying the
potential for an inward hydraulic gradient of groundwater into the CCP fill.

A Notice of Violation (NOV-2018-DV-0101) was issued to Duke and GARRA in April 2018 for the
discharge of CCP leachate at an active seep (SW8-A1) located at the toe of the Area 1 CCP fill
slope. Analytical results indicate elevated concentrations of arsenic, barium, boron, calcium,
iron, magnesium, manganese, molybdenum, and strontium. Duke conducted a surface water
quality monitoring event in July 2018 to determine exceedances of 2B surfa ce water standards
using the criteria for hardness-dependent freshwater metals outlined in 15A NCAC 02B .0211
(11). The arsenic concentration at SW8-A1 is exceeding the chronic freshwater aquatic life
standard (150 ug/l) and the human health standard (10 u g/l) for a Class B stream. Duke is
currently monitoring 7 surface water sites downgradient of the Area 1 CCP fill on a quarterly
basis.

It is believed water entering and interacting with the CCP fill is leaching divalent and polyvalent
cations such a calcium and magnesium ions. These polyvalent cations will chemically interact
(i.e., cation exchange) with the sodium bentonite in the GCL resulting in the alteration of its
DocuSign Envelope ID: 8E8AE8C9-6228-43C5-BF45-6192482D2A92

Ranveer Katyal
August 12, 2020
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physical properties namely reduced osmotic swelling and higher hydraulic conductivities. There
is a potential that increasing hydraulic pressures beneath the fill and a chemically -altered GCL
could create pathways for groundwater to enter the CCP fill. However, there is no indication
that this occurring presently. It is important to note that a compatibility test with CCP
constituents was never completed per the recommendation of the GCL manufacturer.

The 60-inch RCP was constructed beneath the Area 1 CCP fill as a federal/state requirement
(i.e., 404/401 permit) to maintain the continuity of stream flow from upgradient areas. The
conceptual design proposed creating a drainage layer for baseflow within the former stream
channel and beneath the RCP. Both drainage layers were backfilled with soil without the use of
filter fabric or other means of protecting against the migration of fines into the drainage voids.
Rising groundwater elevations beneath the CCP fill have inundated the RCP resulting in the
development of a potentially destabilizing seepage face on the CCP fill slope. Recent review
comments by the Division of Energy, Mineral and Land Resources expressed concern that the
saturated conditions surrounding the RCP could weaken the pipe bedding and potentially allow
the pipe joints to shift and leak. GARRA recently assessed and repaired a total of 46 pipe joints
along the RCP corridor, which included 9 high priority joint repairs, 3 junction box repairs, and
19 medium priority joint repairs.

Asheville Airport CCP Structural Fill Corrective Action Plan
On March 6, 2020, the ARO received an engineering design report from Duke detailing a
proposed cap system for the Area 1 CCP structural fill. The proposed cap system is a corrective
action requirement designed to abate or control seepage from Area 1 by eliminating infiltration
and providing long-term slope stability equal to above a factory of safety of 1.5.
The permanent cap system design was developed separately for the top deck and side slope
conditions and consists of the following layers:

• 0.5-ft thick vegetative layer;
• 1.5-ft to 5.5-ft thick soil layer;
• A drainage geocomposite layer
• 40-ml thick linear-low density polyethylene (LLDPE) geomembrane; and
• 2-ft thick prepared subgrade layer above CCP fill.

The ARO has reviewed the proposed cap design and is critical of a key component in that
design, which includes an intentional gap in the LLDPE geomembrane coverage at the toe of the
CCP fill slope (see attached diagram 1). This gap is designed to facilitate the dewatering of the
CCP fill by creating a permanent drainage outlet. Furthermore, any wastewater passing through
this drainage outlet will discharge to waters of the State in violation of Sections II.1 and III.1 of
the subject permit, which requires the structural fill to operate as a non -discharging system. It is
important to note that immediately downstream of this discharge feature is a residential
community served by private water supply wells.

DocuSign Envelope ID: 8E8AE8C9-6228-43C5-BF45-6192482D2A92

Ranveer Katyal
August 12, 2020
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Asheville Regional Office Permit Renewal Recommendations
The ARO currently recommends the following changes and additions to the renewed permit if
the permit is renewed under NCAC 2T:

• In August 2018, Duke was required to install four additional monitoring wells located
on the review boundary for the Area 1 CCP fill. The ARO recommends adding
monitoring wells MW6-A1, MW7-A1, MW8-A1, and MW9-A1 to the groundwater
monitoring requirements in the new permit. The list of monitoring analytes should
remain the same. The monitoring frequency should continue on a semi-annual basis
in the months of April and November.

• In November 2017, Duke was required to begin surface water monitoring
downgradient of the Area 1 CCP fill and is currently monitoring 7 sites on a quarterly
basis. The ARO recommends adding surface water monitoring sites SW2-A1, SW3-
A1, SW4C-A1, SW5-A1, SW6-A1, SW8-A1, SW9-A1, SW12-A1 to the new permit. The
ARO also recommends removing SW1-A1, which will be replaced by SW9-A1. The
monitoring frequency should continue on a quarterly basis in the months of January,
April, July, and December. The list of monitoring analytes should be consistent with
groundwater monitoring requirements.

• Surface water samples should include both total and dissolved samples and one out
of every four monitoring events must be conducted using the criteria for hardness -
dependent freshwater metals outlined in 15A NCAC 02B .0211 (11). When practical,
sampling should be conducted at base flow conditions to the maximum extent
possible and at least 5 days after a rain event of any magnitude.

• It is important to designate a representative upgradient or background site(s) for
evaluating surface water quality downgradient of the Area 1 CCP fill. Because the
headwaters for Hidden Creek have been eliminated by development, the current
background site (i.e., SW2-A1) is a 54-inch RCP used to convey industrial stormwater
from the Airport. Surface water quality downstream of the CCP fill is a mix of
industrial stormwater, CCP leachate, and baseflow. Therefore, the ARO recommends
designating SW2-A1 and current upgradient monitoring well MW4A-A1 as the
designated background sites for purposes of evaluating and regulating unpermitted
wastewater discharges at the toe of the Area 1 CCP fill.

• The ARO is recommending that Duke implement a program to monitor groundwater
elevations near the Area 1 CCP fill waste boundary as well as internal water
elevations inside the CCP fill. This can largely be accomplished using existing
monitoring wells and piezometers. Although, the installation of two new
piezometers near the southern waste boundary is recommended. Groundwater
elevations should be recorded on a quarterly basis at piezometers PZ-2 and PZ-3D
and monitoring wells MW7-A1 and MW8-A1. Internal water elevations should be
DocuSign Envelope ID: 8E8AE8C9-6228-43C5-BF45-6192482D2A92

Ranveer Katyal
August 12, 2020
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recorded on a quarterly basis at piezometers PZ1-A1, PZ2S-A1, PZ3-A1, PZ4-A1, PZ5-
A1, PZ6-A1, and PZ7-A1. Water elevations should be reported to the ARO on a
quarterly basis.

• The ARO recommends updating the operation and maintenance (O&M) p lan to
reflect the changing conditions at the Area 1 CCP fill and to better define the shared
responsibilities between Duke and GARRA. An important addition to the O&M plan
will be to conduct an annual video inspection and assessment of the 1,100 foot 60-
inch RCP that runs underneath the Area 1 CCP fill. The ARO is recomme nding that a
sealed annual inspection/assessment report, for the entire CCP structural fill project,
be submitted to the ARO annually in the month of December.

• The ARO recommends updating the site map for the Area 1 CCP fill to reflect
changes in the piezometer and monitoring well networks as well as the addition of
surface water monitoring sites.

The ARO is available to discuss these matters further and can assist with updating the permit
tables in the appendix. Feel free to contact Brett Laverty if you have any questions or concerns.
He can be reached at [phone] or [phone] or [e-mail].

Sincerely,

G. Landon Davidson, P.G., Regional Supervisor
Water Quality Regional Operations
Asheville Regional Office

Brett Laverty
Water Quality Regional Operations
Asheville Regional Office

ec: ARO file
DocuSign Envelope ID: 8E8AE8C9-6228-43C5-BF45-6192482D2A92

Map1: Aerial view of the Asheville Regional Airport CCP structural fill project.
DocuSign Envelope ID: 8E8AE8C9-6228-43C5-BF45-6192482D2A92

Map 2: Aerial view of the Area 1 CCP fill slope showing slope monitoring program (geopin survey) and temporary slope repairs.
DocuSign Envelope ID: 8E8AE8C9-6228-43C5-BF45-6192482D2A92

Diagram 1: Area 1 CCP Fill proposed cap design showing permanent drainage outlet at the toe of the fill slope.
Permanent drainage outlet
Drainage layers
DocuSign Envelope ID: 8E8AE8C9-6228-43C5-BF45-6192482D2A92