GW Modeling Request for CAP Planning 10-16-19

ROY COOPER
Governor
NCHAEL S. REGAN
Secretary
LINDA CULPEPPER
Director
Paul Draovitch
Senior Vice President
Environmental, Health, & Safety
Duke Energy
526 South Church Street
Mail Code EC3XP
Charlotte, North Carolina 28202
NORTH CAROLINA
EnvbvnmmntolQua ty
October 16, 2019
Subject: Groundwater Modeling Requests for Corrective Action Planning
Dear Mr. Draovitch:
Updated flow and transport (F-T) models simulating "excavation" and "excavation plus
corrective actions" are being prepared by Duke Energy in support of Corrective Action Plans
(CAPS). To enhance the models and assist DEQ review efforts, the following information should
be provided in any updates and documentation:
1. Provide a shapefile of the excavation footprint depicted in closure plan engineering design
drawings.
2. Simulate "max_2D" boron results showing the maximum boron in any layer for each 2D grid
cell. For purposes of documentation, these results should be shown for times corresponding to
current conditions, excavation completion, 100 years after excavation, and 1000 years after
excavation. For consistency across models and CAPS, include boron ranges of 75-700 ug/L
(light green), 701-4000 (tan), 4001-10,000 (red), and >10,000 (dark blue).
3. Include cross -sections showing the four boron ranges listed in item 2 above and groundwater
velocity vectors in areas of interest identified by DEQ. Cross sections should be oriented along
(parallel to) and across (perpendicular to) plume(s) and (or) the compliance boundary.
4. Include boron concentration -time curves at points of interest identified by DEQ. The curves
should be provided for the following: a) a representative shallow unit (saprolite or transition
zone) layer, b) a representative bedrock layer, and c) "max_2D" at the identified point(s).
5. For each time interval simulated, provide the following: a) the mass flux and the total annual
mass of boron leaving the model domain through drain segments of interest identified by DEQ;
b) the maximum concentration of boron (and its location) leaving the model domain through
each of the identified drain segments; and c) the mass flux 'of boron (from any and all layers)
crossing selected vertical planes of interest identified by DEQ.
6. To the extent that updated models incorporate groundwater extraction, state (a) whether the
simulated extraction rates are sustainable over the modeled period within the pumped flow units
North Carolina Department of Environmental Quality I Division of Water Resources
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and any field evidence (e.g. aquifer testing) that is available to support this conclusion, and (b)
whether a long-term operation, maintenance, and treatment plan will be submitted that is
operative throughout the duration of the modeled extraction period.
7. Move Allen's eastern model boundary eastward to prevent boundary -induced artifacts to the
three-dimensional flow and transport field.
8. For any saturated ash that remains at a facility for any reason, model source depletion using
rate limited sorption in ash layers and equilibrium sorption in all other layers. For ash layers, use
the sorption constant (Kd) that was applied to the 2018 models times a multiplier of between 5
and 30, a 2nd order rate limited constant of 0.000024 d-', and an initial concentration of solid ash
boron corresponding to the geomean of solid ash measurements at the facility. For all other
layers, use the Kd that was applied to the 2018 models times a multiplier of between 5 and 30, a
2nd order rate limited constant of 1 V, and an initial concentration of solid ash boron
corresponding to the sorbed concentration remaining at the end of the interim model.
9. For each model submitted provide a comparison of the Kd used in the model's ash layers with
the Kd that would result from samples collected in ash layer monitor wells and borings across the
facility (i.e. solid ash boron divided by corresponding porewater boron).
If you have any questions, please feel free to contact Ted Campbell (Asheville Regional Office)
at (828)-296-4683.
Sincerely,
Linda Culpepper, Director
Division of Water Resources
cc: WQROS Regional Offices (electronic copy)
GWRS Central File Copy