Accelerated Remediation DEQ Draft_20151204

Asheville Steam Electric Plant - Accelerated Remediation — For Offsite Groundwater Impacts
December 4, 2015 - Draft
Background
Groundwater sampling performed for the Asheville Steam Electric Plant CSA found exceedances of 2L
Standards or IMACs for boron, chloride, cobalt, iron, manganese, sulfate, total dissolved solids (TDS),
and vanadium in monitoring wells located west of the 1964 ash basin and west of Interstate 26. The
concentrations in this area are influenced by the flue gas desulfurization (FGD) wastewater treatment
wetlands as evident by chemical analysis and hydraulic conditions in the area. Groundwater flow in this
area is from the 1964 basin to the west, towards the French Broad River.
The monitoring wells of note are located on Duke Energy property; however there is a 12 acre parcel of
property within the 1-26 corridor not owned by Duke Energy. Groundwater beneath this parcel is likely
similar to the groundwater up and downgradient. Seep and surface water data in the same area indicate
exceedances of 2L Standards or IMACs for boron, chloride, cobalt, iron, manganese, mercury, selenium,
sulfate, TDS, and vanadium.
The receptor survey (included in the CSA) indicates there are no public or private water supply wells
located in the area with groundwater impacts mentioned above. The French Broad River is located
approximately 150 feet west of this area.
Proposed Accelerated Remediation Actions
To address the requirement for accelerated remediation in the recent NCDEQ and Duke Energy
agreement, the following steps are recommended.
• Discontinue use and remove the FGD wastewater treatment wetlands. Removal of the wetlands
is currently underway. All flow to the wetlands has been diverted to the municipal sewer with
complete removal of the wetlands anticipated early in 2016.
Initiate preliminary siting and design for a hydraulic capture system to be installed to the east of I-
26, between the interstate and the former FGD wetlands. The system would consist of
groundwater extraction wells installed to mitigate groundwater impacts near the source area and
minimize migration toward the 12 acre parcel. Low permeability zones within the bedrock flow
system may reduce the efficacy of this remedial option. Additional groundwater modeling is
recommended to predict the potential benefit of groundwater extraction. Extracted groundwater
could be pumped through the existing NPDES system.
Predictive numerical groundwater modeling has demonstrated that source area removal will
reduce contaminant transport to the 12 acre parcel. The Mountain Energy Act of 2015 requires
closure of the coal combustion residual surface impoundments no later than August 1, 2022. A
November 13, 2015 update to the Coal Ash Excavation Plan indicates excavation of the 1964
basin is currently planned to begin in 2020 (https://www.duke-energy.com/pdfs/asheville-
excavation-plan.pdf).
Additional monitoring wells may be required to monitor performance of the hydraulic capture system.
Permits required for this remediation system would include: NCDEQ recovery well permits, erosion &
sediment control permit, and modification of the NPDES permit.
The conceptual hydraulic control system for the area is shown on the figure attached.