NC0004961_Application for Special Order by Consent_20160725

DUKE
ENERGY,
July 25, 2016
Mr. Jeffrey Poupart
North Carolina Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
Re: Application for Special Order by Consent
Duke Energy Carolinas, LLC.
Riverbend Steam Station
Permit #: NC0004961
Gaston County
Dear Mr. Poupart,
Henry K. Sidens
Senior Vice President
Environmental, Health 6 Safety
526 S. Church Street
Mail Code: EC3XP
Charlotte, NC28202
(704) 3a2-4=
RECEIVEDINCDEQ/DWR
JUL 2 6 2016
Water t]ual
Perrnftft n
Duke Energy Carolinas, LLC (Duke Energy) is submitting herewith three copies of the
independent consultant certification report to accompany the subject application as required by
15A NCAC 2H .1206(6)(1).
Should you have any questions regarding this letter or require additional information, please
contact Mr. Shannon Langley at (919) 5462439 or at shannon.langleyC&duke-energy.com.
"! certify, under penalty of law, that this document and all attachments were prepared under my
direction or supervision in accordance with a system designed to assure that qualified personnel
properly gather and evaluate the information submitted. Based on my inquiry of the person or
persons who manage the system, or those persons directly responsible for gathering the
information, the information submitted is, to the best of my knowledge and belief, true, accurate,
and complete. l am aware that there are significant penalties for submitting false information,
including the possibility offtnes and imprisonment for knowing violations. "
Sincerely,
Harry Sideris
SVP - Environmental, Health & Safety
Enclosures
Duke Energy cc: Richard Baker, Jim Wells, Matt Hanchey, Shannon Langley, Brad Loveland

a
161P
ynTena TECHNICAL MEMORANDUM
Date: July 25, 2016 File: 1026.15.02
To: Richard E. Baker (Duke Energy)
Shannon Langley (Duke Energy)
Cc: Kathy Webb (SynTerra)
Michael Spacil (SynTerra)
Kevin Campbell (SynTerra)
From: Matt Huddleston, PhD
Subject: Technical Memorandum — Supplemental information to support Duke
Energy's Application for Special Order by Consent related to existing
and/or unavoidable future violations of pH and total hardness permit
conditions or limits at the Riverbend Steam Station
This memorandum provides the deliverable as described in Proposal 12544 dated July 7, 2016.
The technical memorandum demonstrates that future non-compliance of current NPDES permit
conditions or effluent limits for pH, total hardness, and possibly total suspended solids ('TSS)
associated with Outfalls 101 through 112 would likely be attributed to natural geochemical
processes, regional groundwater conditions, and possibly sampling procedure (in the case of
TSS) rather than associated with operation and maintenance of the wastewater treatment
system (ash basins) at the Riverbend Steam Station. This document will supplement the
application for Special Order by Consent prepared by Duke Energy, July 2016.
BACKGROUND
Duke Energy anticipates future violations of limits on pH, total hardness, and possibly TSS in
Outfalls 101 through 112 at the Riverbend Steam Station (Riverbend). The outfalls are
designated in the NPDES permit as discharges of wastewater that has migrated from the
impoundment (ash basin) via seepage into groundwater. While migrating through the
subsurface, the wastewater interacts with soil, rock, biota, and stormwater in ways that cannot
be controlled by Duke Energy. The interactions can result in pH total hardness, and TSS ranges
that are consistent with naturally occurring conditions, with extremes that may fall outside of
the Riverbend Effluent Limitations. This technical memorandum examines natural
groundwater conditions of the region.
pH
Natural waters contain various salts, acids, and bases that contribute to the H' and OH- ions in
varying ways, depending on specific conditions. The pH of a solution is usually defined as the
logarithm of the reciprocal of the concentration of free hydrogen ions, and describes whether a
P:\Duke Energy Progress.1026\15. RIVERBEND\.02DEC Wastewater Treatment Tech Memo\Riverbend_Tedhnical
Memo_SOC Supp Info_07252016.doo

SOC Supplemental Information July 2016
Duke Energy Carolinas, LLC - Riverbend Steam Station Page 2 of 4
solution is acidic (pH < 7), neutral (pH = 7), or basic (pH > 7). pH is governed to a large extent
by the interaction of H' ions arising from the dissociation of carbonic acid (HaCO3)and from OH -
ions produced during hydrolysis of bicarbonate. The pH of natural waters can range between
the extremes of < 2 to 12.
A compilation of groundwater -quality data collected as part of a United States Geological
Survey (USGS) study in cooperation with North Carolina Department of Environmental Quality
(NCDEQ) provides a basis for understanding the ambient geochemistry related to the
geological setting of the Piedmont and Blue Ridge Physiographic Provinces of North Carolina
(Harden et al., 2009). All geozones in the study, including those that comprise the Riverbend
geology, had multiple wells with groundwater sample results outside the pH range of 6.5 to 8.5,
most of which were less than 6.5, indicating that natural groundwater conditions are acidic and
PH values of 6.0 or less are not uncommon.
It is our understanding that the pH of wastewater in and leaving the ash basin at Riverbend
falls within the permit requirements of 6.0 to 9.0. Chemical adjustment of pH is usually
required because the basin can exhibit pH above 9.0, which is not uncommon for ponded
waters in the region, such as those used to settle coal and wood ash. During the day, algae
present in water consume carbon dioxide during photosynthesis. The removal of carbon
dioxide from water increases pH. Depletion of inorganic carbon from water by algae results in
high pH levels in natural waters as well, which can increase to 10 or greater in the presence of
algae.
Thus, the possibility for pH of Outfalls 101 through 112 to fall below 6.0 would not be
associated with the higher observed pH values of the ash basin, but rather natural groundwater
conditions of the region, as cited in the USGS study (Harden et al. 2009).
HARDNESS
Water hardness is frequently used as an assessment of the quality of water supplies. The
hardness of a water is governed by the content of calcium and magnesium salts, largely
combined with bicarbonate and carbonate and with sulfate, chloride, and other anions of
mineral acids (Wetzel 1983). As water moves through soil and rock, it dissolves naturally -
occurring calcium and magnesium, thereby increasing groundwater hardness under the
appropriate conditions.
The basic ionic compositions of bedrock groundwater in the Riverbend region are generally
classified as a calcium-sodium/bicarbonate or calcium-magnesium/bicarbonate water type
(Harden et al., 2009). Review of background monitoring wells at Riverbend indicates that
calcium and magnesium ion concentrations ranged up to approximately 83 mg/L and 3 mg/L,
respectively (HDR, 2015). Using these ion concentrations, total hardness can be calculated as:
P:\Duke Energy Progress.1026\ 15. RIVERBEND\.02DEC Wastewater Treatment Tech Memo\Riverbend—Technical
Memo_SOC Supp Info_07252016.docc

SOC Supplemental Information July 2016
Duke Energy Carolinas, LLC — Riverbend Steam Station Page 3 of 4
Total Hardness (mg/L as CaCO3) _
Calcium Hardness (mg/L as CaCO3) + Magnesium Hardness (mg/L as CaCOa) _
2.497 x Calcium Conc. (mg/L as Ca2') + 4.116 x Magnesium Conc. (mg/L as Mgt*)
(Ref: http://www.water.ncsu.edu/watershedss/info/hardness.html, accessed on July 12, 2016)
Thus, total hardness of background groundwater conditions at Riverbend (unaffected by the
ash basins) can exceed the Effluent Limitation of 100 mg/L (e.g., 185-233 mg/L as CaCO3). Total
hardness of the outfalls in excess of 100 mg/L could represent natural groundwater conditions.
The geology of the Riverbend site is known as the Charlotte terrane (HDR 2015), which is
comprised of mafic gneisses, amphibolites, and metagabbros among other metamorphic rock
types. Mafic (dark colored) rock, especially gabbro, tends to be low in silica content relative to
most rocks. The low silica content limits or, in the case of gabbro, prevents the formation of
quartz (SiO2). Silicate minerals would include olivine, pyroxene, amphibole, and feldspars
(Carmichael et al., 1974). Each of these minerals can incorporate substantial calcium and
magnesium into the crystal structure.
The Comprehensive Site Assessment Report for Riverbend (HRD, 2015) stresses that the
transition zone between overlying saprolite and bedrock beneath is likely the most transmissive
groundwater flow unit in the subsurface. The combination of relatively high groundwater flow
rates and relatively fresh rock in the transition zone yields a chemically active environment
prone to liberation of calcium and magnesium to solution as the primary minerals are altered to
oxides and clay minerals. This hydrogeologic setting, with or without anthropogenic features
like ash basins, is well suited for generation of groundwater with elevated hardness during the
natural chemical weathering processes that convert rock to soil. Finally, the highly transmissive
transition zone is the most likely source of surface seeps. All these factors combine to produce
conditions conducive to elevated hardness and TSS in goundwater.
T55
Total Suspended Solids (TSS) are those solids (minerals and organic material) that remain
trapped on a filter when the sample is analyzed in the laboratory. Suspended solids can enter
groundwater naturally in areas of highly transmissive flow (as stated above) and through
runoff from industrial, urban, or agricultural areas after storm events. Practices associated with
activities such as construction tillage can strip vegetation and allow the quick influx of sediment
into groundwater via overland flow. Thus, construction activities associated with ash basin
closure could influence TSS in the outfalls from time to time, but these occurrances would be
transient. Further, although extreme care is exercised when collecting samples, there is
potential for increased TSS levels due to the sampling procedure itself. Suspension of sediment,
flocculent, and/or organic materials in surface water channels when collecting samples for
analysis can artificially elevate TSS levels, as well as falsely increase other parameters (e.g., total
P:\Duke Energy Progress.1026\ 15. RIVERBEND\.02DEC Wastewater Treatment Tech Memo\Riverbend_Teduucal
Memo_SOC Supp Info_07252016.dooc

SOC Suuvlemental Information
Duke Energy Carolinas, LLC - Riverbend Steam Station
July 2016
Page 4 of 4
metals). Review of Area of Wetness (AOW) monitoring data indicate that TSS concentrations
above the 30 mg/L Effluent Limitation at Riverbend are episodic, which supports the influence
of fluctuating groundwater flow (e.g., storm events) and possibly occasional construction
activities on observed TSS levels.
Duke Energy anticipates future violations of limits on pH, total hardness, and possibly TSS in
Outfalls 101 through 112 at Riverbend. The outfalls are designated in the NPDES permit as
discharges of wastewater that has migrated from the impoundment (ash basin) via seepage into
groundwater. As documented above, natural geochemical process and typical conditions of the
region support that such permit violations may occur irrespective of operation and maintenance
of the wastewater treatment system (ash basin). Groundwater pH values below 6.5 are normal
for the region, and total hardness of groundwater in excess of 100 mg/L can occur based on
review of the facility's background monitoring well data. Suspended solids values, while
episodic in nature, may be affected by various environmental conditions and therefore are, in
most cases, outside of Duke Energy's control. There is no evidence that possible future permit
violations of these parameters would be linked to operation and maintenance of the wastewater
treatment system (ash basin). This technical memorandum supports Duke Energy's request for
Water Quality Special Order by Consent for the Riverbend Steam Station.
Harden, S.L., Chapman, M.J., and Hamed, D.A. 2009. Characterization of groundwater quality
based on regional geologic setting in the Piedmont and Blue Ridge Physiographic Provinces,
North Carolina. U.S. Geological Survey Scientific Investigations Report 2009-51409.
Carmichael, I.S., Turner, F.J., and Verhoogen, J. 1974. Igneous Petrology. McGraw-Hill
International Series in the Earth and Planetary Sciences.
HDR. 2015. Comprehensive Site Assessment Report, Riverbend Steam Station Ash Basin,
August 18, 2015.
Wetzel, R.G. 1983. Limnology, Second Edition. Saunders College Publishing, Harcourt Brace
Jovanovisch, Inc., Orlando, Florida.
P:\Duke Energy Progress.1026\ 15. RIVERBEND\.02DEC Wastewater Treatment Tech Memo\Riverbend_Tedurical
Memo_SOC Supp Info_07252016.dooc

161P
nTerra
Date: July 25, 2016
To: Richard E. Baker (Duke Energy)
Shannon Langley (Duke Energy)
Cc: Kathy Webb (SynTerra)
Michael Spacil (SynTerra)
Kevin Campbell (SynTerra)
From: Matt Huddleston, PhD
TECHNICAL MEMORANDUM
File: 1026.15.02
RECEIVED/NCDEQ/DWR
JUL 2 6 2016
Water Duality
PenT ting Setstbn
Subject: Technical Memorandum — Supplemental information to support Duke
Energy's Application for Special Order by Consent related to existing
and/or unavoidable future violations of pH and total hardness permit
conditions or limits at the Riverbend Steam Station
This memorandum provides the deliverable as described in Proposal 12544 dated July 7, 2016.
The technical memorandum demonstrates that future non-compliance of current NPDES permit
conditions or effluent limits for pH, total hardness, and possibly total suspended solids (rSS)
associated with Outfalls 101 through 112 would likely be attributed to natural geochemical
processes, regional groundwater conditions, and possibly sampling procedure (in the case of
TSS) rather than associated with operation and maintenance of the wastewater treatment
system (ash basins) at the Riverbend Steam Station. This document will supplement the
application for Special Order by Consent prepared by Duke Energy, July 2016.
Duke Energy anticipates future violations of limits on pH, total hardness, and possibly TSS in
Outfalls 101 through 112 at the Riverbend Steam Station (Riverbend). The outfalls are
designated in the NPDES permit as discharges of wastewater that has migrated from the
impoundment (ash basin) via seepage into groundwater. While migrating through the
subsurface, the wastewater interacts with soil, rock, biota, and stormwater in ways that cannot
be controlled by Duke Energy. The interactions can result in pH, total hardness, and TSS ranges
that are consistent with naturally occurring conditions, with extremes that may fall outside of
the Riverbend Effluent Limitations. This technical memorandum examines natural
groundwater conditions of the region.
pH
Natural waters contain various salts, acids, and bases that contribute to the H' and OH- ions in
varying ways, depending on specific conditions. The pH of a solution is usually defined as the
logarithm of the reciprocal of the concentration of free hydrogen ions, and describes whether a
P:\Duke Energy Progress.1026\ 15. RIVERBEND\.02DEC Wastewater Treatment Tech Memo\ Riverbend_Tedudcal
Memo -SOC Supp Info_07252016.do«

SOC Supplemental Information July 2016
Duke Energy Carolinas, LLC — Riverbend Steam Station Page 2 of 4
solution is acidic (pH < 7), neutral (pH - 7), or basic (pH > 7). pH is governed to a large extent
by the interaction of H' ions arising from the dissociation of carbonic acid (1-hCO3)and from OH -
ions produced during hydrolysis of bicarbonate. The pH of natural waters can range between
the extremes of <2 to 12.
A compilation of groundwater -quality data collected as part of a United States Geological
Survey (USGS) study in cooperation with North Carolina Department of Environmental Quality
(NCDEQ) provides a basis for understanding the ambient geochemistry related to the
geological setting of the Piedmont and Blue Ridge Physiographic Provinces of North Carolina
(Harden et al., 2009). All geozones in the study, including those that comprise the Riverbend
geology, had multiple wells with groundwater sample results outside the pH range of 6.5 to 8.5,
most of which were less than 6.5, indicating that natural groundwater conditions are acidic and
pH values of 6.0 or less are not uncommon.
It is our understanding that the pH of wastewater in and leaving the ash basin at Riverbend
falls within the permit requirements of 6.0 to 9.0. Chemical adjustment of pH is usually
required because the basin can exhibit pH above 9.0, which is not uncommon for ponded
waters in the region, such as those used to settle coal and wood ash. During the day, algae
present in water consume carbon dioxide during photosynthesis. The removal of carbon
dioxide from water increases pH. Depletion of inorganic carbon from water by algae results in
high pH levels in natural waters as well, which can increase to 10 or greater in the presence of
algae.
Thus, the possibility for pH of Outfalls 101 through 112 to fall below 6.0 would not be
associated with the higher observed pH values of the ash basin, but rather natural groundwater
conditions of the region, as cited in the USGS study (Harden et al. 2009).
HARDNESS
Water hardness is frequently used as an assessment of the quality of water supplies. The
hardness of a water is governed by the content of calcium and magnesium salts, largely
combined with bicarbonate and carbonate and with sulfate, chloride, and other anions of
mineral acids (Wetzel 1983). As water moves through soil and rock, it dissolves naturally -
occurring calcium and magnesium, thereby increasing groundwater hardness under the
appropriate conditions.
The basic ionic compositions of bedrock groundwater in the Riverbend region are generally
classified as a calcium-sodium/bicarbonate or calcium-magnesium/bicarbonate water type
(Harden et al., 2009). Review of background monitoring wells at Riverbend indicates that
calcium and magnesium ion concentrations ranged up to approximately 83 mg/L and 3 mg/L,
respectively (HDR, 2015). Using these ion concentrations, total hardness can be calculated as:
P:\Duke Energy Progress.1026\15. RIVERBEND\.02DEC Wastewater Treatment Tech Memo\ Riverbend—Tedmical
Memo—SOC Supp Info_07252016.docc

SOC Supplemental Information July 2016
Duke Energy Carolinas, LLC - Riverbend Steam Station Page 3 of 4
Total Hardness (mg/L as CaCO3) _
Calcium Hardness (mg/L as CaCO3) + Magnesium Hardness (mg/L as CaCa) _
2.497 x Calcium Conc. (mg/L as Ce) + 4.116 x Magnesium Conc. (mg/L as Me)
(Ref: http://www.water.ncsu.edu/watershedss/info/hardness.html, accessed on July 12, 2016)
Thus, total hardness of background groundwater conditions at Riverbend (unaffected by the
ash basins) can exceed the Effluent Limitation of 100 mg/L (e 8.,185-233 mg/L as CaCO3). Total
hardness of the outfalls in excess of 100 mg/L could represent natural groundwater conditions.
The geology of the Riverbend site is known as the Charlotte terrane (HDR 2015), which is
comprised of mafic gneisses, amphibolites, and metagabbros among other metamorphic rock
types. Mafic (dark colored) rock, especially gabbro, tends to be low in silica content relative to
most rocks. The low silica content limits or, in the case of gabbro, prevents the formation of
quartz (SiO2). Silicate minerals would include olivine, pyroxene, amphibole, and feldspars
(Carmichael of al, 1974). Each of these minerals can incorporate substantial calcium and
magnesium into the crystal structure.
The Comprehensive Site Assessment Report for Riverbend (HRD, 2015) stresses that the
transition zone between overlying saprolite and bedrock beneath is likely the most transmissive
groundwater flow unit in the subsurface. The combination of relatively high groundwater flow
rates and relatively fresh rock in the transition zone yields a chemically active environment
prone to liberation of calcium and magnesium to solution as the primary minerals are altered to
oxides and clay minerals. This hydrogeologic setting, with or without anthropogenic features
like ash basins, is well suited for generation of groundwater with elevated hardness during the
natural chemical weathering processes that convert rock to soil. Finally, the highly transmissive
transition zone is the most likely source of surface seeps. All these factors combine to produce
conditions conducive to elevated hardness and TSS in goundwater.
TSS
Total Suspended Solids (17SS) are those solids (minerals and organic material) that remain
trapped on a filter when the sample is analyzed in the laboratory. Suspended solids can enter
groundwater naturally in areas of highly transmissive flow (as stated above) and through
runoff from industrial, urban, or agricultural areas after storm events. Practices associated with
activities such as construction tillage can strip vegetation and allow the quick influx of sediment
into groundwater via overland flow. Thus, construction activities associated with ash basin
closure could influence TSS in the outfalls from time to time, but these occurrances would be
transient. Further, although extreme care is exercised when collecting samples, there is
potential for increased TSS levels due to the sampling procedure itself. Suspension of sediment,
flocculent, and/or organic materials in surface water channels when collecting samples for
analysis can artificially elevate TSS levels, as well as falsely increase other parameters (e.g., total
P:\Duke Energy Progress.1026\ 15. RIVERBEND\.02DEC Wastewater Treatment Tech Memo\ Riverbend—Technical
Memo SOC Supp Inf6_07252016.dooc

SOC Supplemental Information July 2016
Duke Energy Carolinas, LLC - Riverbend Steam Station Page 4 of 4
metals). Review of Area of Wetness (AOW) monitoring data indicate that TSS concentrations
above the 30 mg/L Effluent Limitation at Riverbend are episodic, which supports the influence
of fluctuating groundwater flow (e.g, storm events) and possibly occasional construction
activities on observed TSS levels.
CONCLUSION
Duke Energy anticipates future violations of limits on pH, total hardness, and possibly TSS in
Outfalls 101 through 112 at Riverbend. The outfalls are designated in the NPDES permit as
discharges of wastewater that has migrated from the impoundment (ash basin) via seepage into
groundwater. As documented above, natural geochemical process and typical conditions of the
region support that such permit violations may occur irrespective of operation and maintenance
of the wastewater treatment system (ash basin). Groundwater pH values below 6.5 are normal
for the region, and total hardness of groundwater in excess of 100 mg/L can occur based on
review of the facility's background monitoring well data. Suspended solids values, while
episodic in nature, may be affected by various environmental conditions and therefore are, in
most cases, outside of Duke Energy's control. There is no evidence that possible future permit
violations of these parameters would be linked to operation and maintenance of the wastewater
treatment system (ash basin). This technical memorandum supports Duke Energy's request for
Water Quality Special Order by Consent for the Riverbend Steam Station.
REFERENCES
Harden, S.L, Chapman, M.J., and Hamed, D.A. 2009. Characterization of groundwater quality
based on regional geologic setting in the Piedmont and Blue Ridge Physiographic Provinces,
North Carolina. U.S. Geological Survey Scientific Investigations Report 2009-51409.
Carmichael, I.S., Turner, F.J., and Verhoogen, J. 1974. Igneous Petrology. McGraw-Hill
International Series in the Earth and Planetary Sciences.
HDR. 2015. Comprehensive Site Assessment Report, Riverbend Steam Station Ash Basin,
August 18, 2015.
Wetzel, R.G. 1983. Limnology, Second Edition. Saunders College Publishing, Harcourt Brace
Jovanovisch, Inc., Orlando, Florida.
P:\Duke Energy Progress.1026\ 15. RIVERBEND \.02DEC Wastewater Treatment Tech Memo\ RiveIbend_Tedmical
Memo3OC Supp Info_07252016.docc