NC0003433_App D Update Fate and Transport_20160229

UPDATED SIMULATIONS FOR GROUNDWATER FLOW AND
TRANSPORT FOR CAPE FEAR STEAM ELECTRIC PLANT,
MONCURE, NC
February 9, 2016
Prepared for
SynTerra
148 River Street
Greenville, SC 29601
Investigators
Regina Graziano, M.S.
Ronald W. Falta, Ph.D.
Scott E. Brame, M.S.
Lawrence C. Murdoch, Ph.D.

This report is a continuation of the Groundwater Flow and Transport Modeling Report
for Cape Fear Steam Electric Plant (Graziano et. al., 2015) [Attachment E in CAP 1 report]. The
purpose of this report is to increase the time projection from 30 to 100 years for the scenarios No
Action, Cap -in -Place, and Excavation for boron and sulfate transport in groundwater. In
addition, a groundwater interceptor trench (trench), west of the 1985 Ash Basin, along with a
Cap -in -Place scenario for each of the five ash basins were simulated. Boron and sulfate were the
chosen constituents for each of the simulations listed above.
Extended Time Simulation-100 years
A 100 year projection for the No Action, Cap -in -Place, and Excavation scenarios for
boron and sulfate transport in groundwater were simulated. Originally, the groundwater
modeling report (Graziano et. al., 2015) projected 5, 15, and 30 years. The dates for those
simulations are referred to in the groundwater modeling report (Graziano et. al., 2015) as 2020,
2030, and 2045 respectively. In this report, the boron and sulfate simulations are projected 100
years after the corrective action plans take place. The date for the simulations is 2115. Details of
the No Action, Cap -in -Place, and Excavation modeling methods can be found in the
Groundwater Flow and Transport Modeling Report for Cape Fear Steam Electric Plant
(Graziano et. al., 2015).
It is critical to note that since many of the ash basin cells were dry during the simulation,
the specified concentration condition was placed in the upper surficial (model layer 2), which is
directly beneath the ash basins. As a result, this method places the source of constituents several
feet deeper than the modeled ash layer, which is considered a conservative approach. It is
possible simulating ash pore water concentrations within the upper surficial layer overestimates
constituent concentrations in the soils beneath the ash in some locations (Graziano et. al., 2015).
No Action
The results of the 2115 simulation to the 2045 conditions for the No Action scenario are
similar and predict that the simulated boron plume increases in concentration and horizontal
extent (Figures 1 and 2). The simulated boron plume within the lower surficial layer under the
1956, 1963, 1970, and 1978 ash basins and mill reject area stabilize in size from 2045 to 2115,
however the boron concentration increases within the 1970 Ash Basin. Within the lower surficial
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aquifer under the 1985 Ash Basin, the boron plume expands from the western boarder of the
1985 berm toward the cooling water effluent channel. The simulation also predicts boron
migration vertically downward and infiltrates into the upper bedrock (layer 5) under the mill
reject pile, the 1963 Ash Basin, the 1978 Ash Basin, and the northern section of the 1985 Ash
Basin. However, the simulation does not predict boron migrating downward within the middle
bedrock layer (Figure 3).
The 2115 model predicts the simulated sulfate plume is slightly shrinking within the
lower surficial and top bedrock layers (Figures 4 and 5) and is very similar in size and shape
from the 2045 simulations. However, in the vicinity of the 1978 ash basin, the plume is slightly
migrating towards the southeast. In addition, the simulated sulfate plume is slightly expanding
within the middle bedrock layer which depicts some migration vertically downward under the
1963, 1970, 1978, and 1985 ash basins (Figure 6). However, the simulated sulfate plume recedes
on the southern side of the 1956 Ash Basin within the middle bedrock layer.
Cap -in -Place
The 100 year Cap -in -Place modeling scenario predicts that the simulated boron plumes
recede from 100 to 400 feet in the lower surficial layer under the 1956, 1970, 1978, and 1985 ash
basins (Figure 7). Simulated boron concentrations within the lower surficial layer reduce under
the 1970 and 1985 ash basins. The model predicts that boron concentrations within the top
bedrock layer in the vicinity of the 1985 ash basin increases and boron continues to migrate
toward the cooling water effluent channel (Figure 8). The boron horizontal extent within the top
bedrock layer slightly migrates to the northeast in the vicinity of the 1970 Ash Basin, however
the concentration reduces in comparison to the 2045 simulation. Vertical migration into the
middle bedrock layer was not indicated (Figure 9).
The 100 year model predicts that the distribution of the simulated sulfate plumes recede
significantly within all three layers under all five ash basins (Figures 10 through 12). The plume
within the 1970 ash basin is below the 2L standard after 100 years. The simulated sulfate plume
within the 1963 and 1978 ash basins recedes about 500 to 2,000 ft. The 1985 Ash Basin
simulated sulfate plume recedes about 50 to 900 feet and the 1956 Ash Basin recedes about 20 to
500 feet.
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Excavation
The model predicts that after the excavation closure scenario is implemented and
completed after 100 years. Within the lower surficial layer, simulated boron plumes in the
vicinity of the 1956, 1970, 1978, and 1985 ash basins and mill reject pile reduce in size (Figure
13). As the simulated boron plume recedes in the lower surficial layer on the eastern side of the
1985 ash basin, the simulated boron plume migrates toward the cooling water effluent channel.
The simulated 2115 boron plumes within the top bedrock layer starts to become present in the
1978 Ash Basin and expands in size in the 1970 and 1985 ash basins (Figure 14). Similar to the
No Action and Cap -in -Place scenarios, simulated boron plume within the top bedrock layer
migrates from the 1985 Ash Basin to the cooling water effluent channel. The model does not
predict any 2L detections for boron within the middle bedrock layer (Figure 15).
Figures 16 through 18 show the simulated sulfate concentrations in the lower surficial,
top bedrock, and middle bedrock layers at 100 years. Sulfate plumes within all three layers
under the 1956, 1963, 1970, 1978, 1985 ash basins, and the mill reject pile, have reduced in
horizontal extent. However, the simulated sulfate plume under the 1963 Ash Basin is slightly
migrating towards the Cape Fear River within the top and middle bedrock layers. In addition, the
sulfate plume in the middle bedrock layer under the 1985 Ash Basin is slowly migrating to the
cooling water effluent channel.
Trench & Cap -in -Place
The combined scenario of Cap -In -Place and interceptor trench assumes that a trench will
be installed and all five ash basins will be capped. The trench is simulated approximately 25 to
40 feet in depth and extends between the western and southern border of the 1985 Ash Basin and
the railroad right-of-way (ROW), currently owned by Norfolk Southern Corporation. A trench is
being considered as a contingent groundwater remedy and would be used to change the hydraulic
regime on the west-southwest of the 1985 Ash Basin to prevent plume migration into the railroad
ROW. The bottom of the trench is simulated at the surface of the bedrock contact and was
simulated in the flow model as a MODFLOW DRAIN feature (Figure 18). The capping of all
five ash basins is the same as the Cap -in -Place scenario and the modeling method can be found
in the Groundwater Flow and Transport Modeling Report for Cape Fear Steam Electric Plant
(Graziano et. al., 2015).
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For this scenario, the results for boron and sulfate simulations are within the lower
surficial aquifer (layer 3), the top bedrock layer (layer 5), and middle bedrock layer (layer 6).
Figures 19 through 42 display the results of the Trench & Cap -in -Place scenarios for the years
2020, 2030, 2045, and 2115 respectively.
Figures 19 through 30 show the simulated boron concentrations in the lower surficial, top
bedrock layer, and middle bedrock layer. Modeling predicts the use of a trench reduces boron
concentrations in the upper surficial aquifer and prevents migration from the 1985 Ash Basin
onto the railroad ROW (Figures 19 and 28) over the course of the 100 year scenario. The model
also predicts the distribution of boron in the top bedrock layer under the 1956 Ash Basin, 1963
Ash Basin, 1970 Ash Basin, and mill reject pile area are similar to the Cap -in -Place scenario.
Under the 1985 Ash Basin, the 2115 simulated boron plume within the top bedrock layer reduces
in size and concentration in comparison to the 2045 simulation; however the simulated boron
plume slightly migrates northwest along the modeled trench. Vertical migration into the middle
bedrock layer was not indicated (Figures 21, 24, 27 and 30).
Figures 31 through 42 show the simulated sulfate concentrations in the lower surficial,
top bedrock layer, and middle bedrock layer at year 2020, 2030, 2045, and 2115. Sulfate
concentrations within the upper and lower surficial aquifers are almost identical with regard to
sulfate concentrations and distribution in the Cap -in -Place scenario, however sulfate distribution
adjacent to the 1985 ash basin reduces to a greater extent (compare Figure 12 with Figure 42).
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References
Langley, W.G., J. Daniels, and S. Oza, 2015, Sorption Evaluation of the. Cape Fear Steam
Electric Plant. Charlotte Department of Civil and Environmental Engineering, report
prepared for SynTerra,
McDonald, M.G. and A.W. Harbaugh, 1988, A Modular Three -Dimensional Finite -Difference
Ground -Water Flow Model, U.S. Geological Survey Techniques of Water Resources
Investigations, book 6, 586 p.
Graziano, R. A., R. W. Falta, S. E. Brame, and Murdoch, L.C., November 2015. Groundwater
Flow and Transport Modeling Report for Cape Fear Steam Electric Plant, Semora, NC.
Niswonger, R.G.,S. Panday, and L Motomu, 2011, MODFLOW-NWT, A Newton formulation
for MODFLOW-2005, U.S. Geological Survey Techniques and Methods 6-A37, 44-.
SynTerra, 2015, Comprehensive Site Assessment Report, Cape Fear Steam Electric Plant,
Semora, NC. September 2, 2015.
Zheng, C. and P.P. Wang, 1999, MT3DMS: A Modular Three -Dimensional Multi -Species
Model for Simulation of Advection, Dispersion and Chemical Reactions of Contaminants
in Groundwater Systems: Documentation and User's Guide, SERDP-99-1, U.S. Army
Engineer Research and Development Center, Vicksburg, MS.
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Figure 1. Simulated 2115 boron concentrations (µg/L) in the model layer of the lower surficial
aquifer (layer 3) for No Action.
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Figure 2. Simulated 2115 boron concentrations (µg/L) in the top model layer of the bedrock
aquifer (layer 5) for No Action.
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Figure 3. Simulated 2115 boron concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for No Action.
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Figure 4. Simulated 2115 sulfate concentrations (mg/L) within the lower surficial aquifer (layer
3) for No Action.
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Figure 5. Simulated 2115 sulfate concentrations (mg/L) in the top bedrock layer (layer 5) for
No Action.
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Figure 6. Simulated 2115 sulfate concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for No Action.
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Figure 7. Simulated 2115 boron concentrations (µg/L) in the model layer of the lower surficial
aquifer (layer 3) for Cap -in -Place.
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Figure 8. Simulated 2115 boron concentrations (µg/L) in the top model layer of the bedrock
aquifer (layer 5) for Cap -in -Place.
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Figure 9. Simulated 2115 boron concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Cap -in -Place.
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Figure 10. Simulated 2115 sulfate concentrations (mg/L) within the lower surficial aquifer
(layer 3) for Cap -in -Place.
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Figure 11. Simulated 2115 sulfate concentrations (mg/L) in the top bedrock layer (layer 5) for
Cap -in -Place.
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Figure 12. Simulated 2115 sulfate concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Cap -in -Place.
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Figure 13. Simulated 2115 boron concentrations (µg/L) in the model layer of the lower surficial
aquifer (layer 3) for Excavation.
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Figure 14. Simulated 2115 boron concentrations (µg/L) in the top model layer of the bedrock
aquifer (layer 5) for Excavation.
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Figure 15. Simulated 2115 boron concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Excavation.
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Figure 16. Simulated 2115 sulfate concentrations (mg/L) within the lower surficial aquifer
(layer 3) for Excavation.
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Figure 17. Simulated 2115 sulfate concentrations (mg/L) in the top bedrock layer (layer 5) for
Excavation.
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Figure 18. Simulated 2115 sulfate concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Excavation.
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Figure 18. Location of trench (green line), west-southwest of the 1985 Ash Basin.
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Figure 19. Simulated 2020 boron concentrations (µg/L) in the model layer of the lower surficial
aquifer (layer 3) for Trench and Cap -in -Place.
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Figure 20. Simulated 2020 boron concentrations (µg/L) in the top model layer of the bedrock
aquifer (layer 5) for Trench and Cap -in -Place.
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Figure 21. Simulated 2020 boron concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Trench and Cap -in -Place.
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Figure 22. Simulated 2030 boron concentrations (µg/L) in the model layer of the lower surficial
aquifer (layer 3) for Trench and Cap -in -Place.
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Figure 23. Simulated 2030 boron concentrations (µg/L) in the top model layer of the bedrock
aquifer (layer 5) for Trench and Cap -in -Place.
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Figure 24. Simulated 2030 boron concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Trench and Cap -in -Place.
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Figure 25. Simulated 2045 boron concentrations (µg/L) in the model layer of the lower surficial
aquifer (layer 3) for Trench and Cap -in -Place.
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Figure 26. Simulated 2045 boron concentrations (µg/L) in the top model layer of the bedrock
aquifer (layer 5) for Trench and Cap -in -Place.
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Figure 27. Simulated 2045 boron concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Trench and Cap -in -Place.
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Figure 28. Simulated 2115 boron concentrations (µg/L) in the model layer of the lower surficial
aquifer (layer 3) for Trench and Cap -in -Place.
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Figure 29. Simulated 2115 boron concentrations (µg/L) in the top model layer of the bedrock
aquifer (layer 5) for Trench and Cap -in -Place.
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Figure 30. Simulated 2115 boron concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Trench and Cap -in -Place.
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Figure 31. Simulated 2020 sulfate concentrations (mg/L) within the lower surficial aquifer
(layer 3) for Trench and Cap -in -Place.
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Figure 32. Simulated 2020 sulfate concentrations (mg/L) in the top bedrock layer (layer 5) for
Trench and Cap -in -Place.
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Figure 33. Simulated 2020 sulfate concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Trench and Cap -in -Place.
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Figure 34. Simulated 2030 sulfate concentrations (mg/L) within the lower surficial aquifer
(layer 3) for Trench and Cap -in -Place.
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Figure 35. Simulated 2030 sulfate concentrations (mg/L) in the top bedrock layer (layer 5) for
Trench and Cap -in -Place.
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Figure 36. Simulated 2030 sulfate concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Trench and Cap -in -Place.
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Figure 37. Simulated 2045 sulfate concentrations (mg/L) within the lower surficial aquifer
(layer 3) for Trench and Cap -in -Place.
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Figure 38. Simulated 2045 sulfate concentrations (mg/L) in the top bedrock layer (layer 5) for
Trench and Cap -in -Place.
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Figure 39. Simulated 2045 sulfate concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Trench and Cap -in -Place.
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Figure 40. Simulated 2115 sulfate concentrations (mg/L) within the lower surficial aquifer
(layer 3) for Trench and Cap -in -Place.
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Figure 41. Simulated 2115 sulfate concentrations (mg/L) in the top bedrock layer (layer 5) for
Trench and Cap -in -Place.
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Figure 42. Simulated 2115 sulfate concentrations (µg/L) in the middle layer of the bedrock
aquifer (layer 6) for Trench and Cap -in -Place.
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