NC0004987_NOV-2019-SP-0008 Response_20191219

(s DUKE Paul Draovitch,P.E.
Senior Vice President
ENERGY® Environmental,Health&Safety
and Operations Support
526 S. Church Street
Mail Code:EC3XP
Charlotte,NC 28202
[phone]
December 19, 2019
Mr. Bob Sledge
North Carolina Department of Environmental Quality
1617 Mail Service center D
Raleigh NC 27699-1617 RECEIVE
RE: Response to NOV-2019-SP-0008 DEC 2 7 2019
Duke Energy Carolinas, LLC. WRINp0ES
Marshall Steam Station NCQEQIp
Special Order by Consent WQS17-009
Dear Mr. Sledge,
Duke Energy Carolinas, LLC (Duke Energy) appreciates the opportunity to provides this response
and supporting information to the subject Notice of Violation. Duke Energy continues to
progress with activities at the Marshall Station in efforts to safely close the station's ash basin.
This response provides supporting and background information to demonstrate Duke Energy's
position that the noted exceedence of water hardness was due to circumstances and events
beyond the reasonable control of Duke Energy and therefore further penalties and actions
should not be due in accordance with condition 5 of the subject order.
Background and claim
Duke Energy asserts that the water hardness levels were not related to any inappropriate
action or inaction on the part of Duke Energy and were a result of"an extraordinary event
beyond Duke Energy's control". A quarterly sample was taken as required from the location
identified as S-1 on September 25, 2019. This sample test result was reported as having a
"water hardness" of 316 mg/I. The subject Consent Order establishes an interim level for this
location of 200 mg/I.
Duke Energy contends that the levels of water hardness in the sample is primarily a function of
drought related conditions at the time of the sample and therefore beyond the control of Duke
Energy. As noted during the sampling event, the flow of the tributary was as low as has been
observed during the term of the Consent Order. Table 1 presents the data collected at location
S-1 since the effective date of the consent order. This data shows the general correlation
between concentration of water hardness and flow. Chlorides values are also presented as an
additional calibration point.
V V V,duke-Cncrp'.corn

Mr. Bob Sledge
Response to NOV SP 2019-0008
December 19, 2019
Table 1. Flow and Hardness comparison
Date Approximate Flow(gpm) Hardness (mg/I) Chloridel(mg/I)
6/7/2018' 13.46 159 66
9/11/2018 4.94 195 84
10/31/2018 15.71 137 50
3/27/2019 Not recorded 138 53
5/7/2019 No flow recorded 166 63
9/25/2019 4.75 316 170
11/22/2019 Not recorded 205 97
12/5/20194 13 169' 63
1 Chloride data presented as an additional reference
2 First sample event after the effective date of consent order EMC WQ S17-009
3The only difference in operating conditions between the 9/25/19 sample and the 12/5/19 sample is meteorological
conditions. 9/25/19 was taken during dry conditions and 12/5/19 was taken after a return to more normal rainfall levels.
4 Samples taken evaluating various treatment between September 25 and December 5 will be submitted under separate cover.
As demonstrated in Table 1, when flows are generally below 5 gpm, hardness levels are around 200 mg/I
or greater. When flows are higher, the hardness concentrations are generally lower. This supports the
position that the hardness concentration was primarily caused by lack of rainfall and therefore beyond
the control of Duke Energy. This reduction in flow volume during dry periods means that groundwater
impacted by the ash basin makes up a larger proportion of the base stream flow than at other times and
g
while the groundwater is likely carrying no more (and possibly even less) mass of pollutants than
historically, the concentration increased above the listed Interim Action Level (IAL). This was an event
that was not foreseen during the development of the IALs and was beyond the reasonable control of
Duke Energy. Duke Energy is undertaking an expedited schedule under the subject consent order to
lower the water levels in the ash basin to address this very type of situation in the long term. As of
December 8, 2019, the water level has been lowered by 10 feet. Because of the review of hardness
data, Duke Energy has submitted a request to modify the subject consent order to amend the interim
action level for hardness.
Duke Energy has previously submitted a report detailing specifics as to the influence of drought on the
sampling event. This report was required to be developed and submitted by condition 2.(c).(1) of the
Consent Order. Duke Energy includes the details and supporting information in that report by reference
and has attached a copy of that report as a part of this submittal. A second, independent evaluation of
the water hardness levels at location "S-1" in relation to rainfall was undertaken as a result of the Notice
of Violation and is also attached. This evaluation documents the inverse relationship using a 6-week
precipitation total and measured water hardness at location "S-1".
An additional potential minor factor that led to increased hardness concentrations in the ash basin is the
facility's requirement to cease all flows to the ash basin under the Federal CCR rule. Flows to the ash
basin were terminated in April 2019 in accordance with the Federal CCR rule. This led to the removal of
a service water flow necessary to protect the former wastewater wetland treatment plants but also
appears to have resulted in increased hardness levels in the ash basin itself. Table 2 illustrates the ash
basin hardness levels before and after the removal of wastewater flows as required by the Federal CCR
rule. It appears, based on sampling data,that the cessation of flows to the basin led to an increased
it

Mr. Bob Sledge
Response to NOV SP 2019-0008
December 19, 2019
hardness concentration level in the ash basin after the April 11, 2019 wastewater cessation date. Duke
Energy was required by Federal law to remove these flows in order to comply with the Federal CCR rule.
However, based on review of well data near S-01 it is concluded that the ash basin increase in hardness
would have a minor effect on the increase in hardness at S-1, with the drought still being the main cause
of this issue.
Table 2. Measured ash basin hardness levels
Date Ash basin discharge
hardness(mg/I)
1/7/2019 404
2/4/2019 625
3/4/2019 493
4/1/2019 683
6/3/2019 851
5/8/19 889
7/1/2019 767
8/5/2019 827
9/3/2019 858
10/7/2019 900
•
Ash basin discharge
hardness (mg/I)
889 851 767 827 858 900
625 683
404 493
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Mr. Bob Sledge
Response to NOV SP 2019-0008
December 19, 2019
Additional support and mitigating factors
1. There was no harm associated with the water hardness level measured on September 25, 2019.
Water hardness itself is not an environmental concern. The North Carolina Environmental
Management Commission has not established a criterion for water hardness in Class "C" waters
but only in waters classified as "water supply". The criteria in "water supply" waters is intended
to protect against the scale buildup in pipes and appurtenances and in aesthetic conditions that
can be exacerbated by hardness of water(e.g. difficulty in lathering of soap, etc).
Water hardness can also reduce the bio-availability of certain metals and thereby reduce toxicity
from metals. The following excerpt is taken from the DEQ document Summary of North Carolina
surface water quality standards dated April 2015.
The calcium and magnesium ions that contribute to water hardness are
known to lower the toxicity of some metals by competing with the
dissolved metal ions for binding sites on an aquatic organism. Toxic
impacts to aquatic organisms occur when the metal ions bind to these
sites on the organism (such as on the gills of a fish). The higher the
water hardness (indicating more hardness related ions are present) the
• lower the toxicity of some metals. The hardness ions are able to out-
compete the metal ions for binding sites on the aquatic organisms;
therefore, the organisms are ultimately exposed to less metal.
2. While the hardness of the small tributary to Lake Norman did have a sample result above the IAL
in September 2019,the water hardness in Lake Norman has remained consistently low and
unimpacted. Table 3 lists the measured water hardness in Lake Norman below the S-1 location
and above any drinking water intake.
Table 3. Measured water hardness in Lake Norman
Date Upstream Water hardness(mg/I) Downstream Water hardness (mg/I)
6/7/2018 13.5 13
9/11/2018 14.6 14.3
10/31/2018 14 14.4
3/27/19 12.8 12.7
5/7/19 14.8 15
8/8/19 15.9 16.4
12/5/19 19.2 19.3
3. Duke Energy will soon be submitting a groundwater corrective action plan for the site. In this
plan Duke Energy will provide more details as to proposed measures to address impacted
groundwater influences at the location termed "S-1" in the consent order. Duke Energy
requests that the Department review those proposed long-term measures prior to forming a
decision as to whether or not to demand a stipulated penalty for the exceedence of water
hardness IAL at sampling location "S-1".

Mr. Bob Sledge
Response to NOV SP 2019-0008
December 19, 2019
If you have any questions regarding this letter, please contact Mr. Robert Wylie at (704) 382-
4669 or [e-mail].
I 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. lam aware that there are significant penalties for submitting false
information, including the possibility of fines and imprisonment for knowing violations.
Since ely,
aul Draovitch,
Senior Vice President
Attachments •
cc: MRO DEQ WQ Supervisor w/enclosure
610 East Center Avenue, Suite 301
Mooresville, NC 28115
Robert Wylie -via email
Shannon Langley—via email
Chris Hallman—via email
Richard Baker—via email
Rick Roper—Marshall Station Manager

FINDINGS OF RE-ASSESSMENT
D EVALUATION OF REMEDIAL ACTIONS
UNDER SPECIAL ORDER BY CONSENT -
EMC SOC WQ S17-009
AT
MARSHALL STEAM STATION
8320 NC HIGHWAY 150
TERRELL, NORTH CAROLINA 28682
NOVEMBER 2019
PREPARED FOR:
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FINDINGS OF RE-ASSESSMENT AND
EVALUATION OF REMEDIAL ACTIONS UNDER
SPECIAL ORDER BY CONSENT -
EMC SOC WQ S17-009
AT
MARSHALL STEAM STATION
8320 NC HIGHWAY 150
TERRELL, NORTH CAROLINA 28682
NOVEMBER 2019
PREPARED FOR
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas, LLC,Marshall Steam Station SynTerra
TABLE OF CONTENTS
SECTION PAGE
1.0 INTRODUCTION 1-1
2.0 RE-ASSESSMENT APPROACH 2-1
3.0 RE-ASSESSMENT ACTIVITIES AND FINDINGS 3-1
3.1 Stream Conditions 3-1
3.2 Surface Water Sampling and Data Evaluation 3-1
3.3 Groundwater Sampling and Data Evaluation 3-4
3.4 Ash Basin Conditions and Decanting 3-5
3.� Local Precipitation Data 3-5
3.6 Ion Exchange Resin Evaluation and Deployment 3-6
4.0 PRELIMINARY CONCLUSIONS 4-1
5.0 PROPOSED REMEDIAL OPTIONS 5-1
5.1 Short-Term 5-1
5.1.1 Normal Streamflow Capture, Pump and Treat- Impoundment 5-2
5.1.2 Normal Streamflow Capture, Pump and Treat -Trench 5-2
5.1.3 Stream Channel Dewatering, Pump and Treat - Extraction Wells 5-2
5.1.4 Stream Channel Dewatering, Pump and Treat Extraction Wells with
Clean Water Injection 5-2
5.2 Long-Term 5-3
5.2.1 Ash Basin Decanting and Dewatering 5-3
5.2.2 Ash Basin Closure and Groundwater Corrective Action 5-3
6.0 REMEDIAL EFFECTIVENESS MONITORING AND REPORTING 6-1
rage

Findings of Re
-Assessment e Assessment and Evaluation of Remedial Actions Under
Special Order by Consent-EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas,LLC, Marshall Steam Station SynTerra
LIST OF TABLES
Table 1 Historic and Recent Hardness Results Comparison
Table 2 Historical Hardness Levels and Average
Table 3 Groundwater Quality Data
Table 4 Drought Condition Summary
LIST OF FIGURES
Figure 1 S-1 Re-Assessment Area of Investigation
Figure 2 S-1 Re-Assessment Background Sample Locations
•
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent—EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas,LLC,Marshall Steam Station SynTerra
1.0 INTRODUCTION
Duke Energy Carolinas, LLC (Duke Energy) and the North Carolina Environmental
Management Commission entered into Special Order By Consent SOC No. S17 009, which
was approved on April 18, 2018.
Monitoring of classified waters of the State receiving flow from non-constructed seeps,
found in Attachment B of the SOC, and reporting of analytical results have been
completed as required.
Certain interim action levels (IALs) were established in the agreement, including, at
Seep ID Number S-1: pH 5-10 standard units (S.U.) and hardness 200 mg/L. An
exceedance of any interim action level by 20% in a single sampling event or for two
consecutive monitoring events requires Duke Energy to take specific actions, involving
increased monitoring and seep re-assessment.
Samples collected at S-1 on September 25, 2019 for the third quarter 2019, indicated
hardness at 316 mg/L, exceeding the hardness interim action level by approximately 55
percent.
This document fulfills the reporting requirement described in section 2. c. Additional
Compliance Measures 1)of the SOC:
If the monitoring of any classified water of the State receiving f ow from
seeps regulated by this Special Order indicates exceedance of any interim
action level established by the Special Order, Duke Energy shall increase
monitoring at that location from quarterly to monthly until concentrations
of monitored characteri.stics return to those observed at the initiation of the
Special Order. If any interim action level established by the Special Order
is exceeded by more than 20% in a single sampling event, or exceeded for
two (2) consecutive monitoring events, in addition to paying the
associated stipulated penalty, Duke Energy shall conduct a re-assessment
of the contributing seep(s), including, but not limited to, evaluation of
proposed remedial actions for treatment and or control of the seep such
that impacts to the receiving waters are quickly mitigated. A report
compiling the findings of the re-assessment, including proposed remedial
actions, shall be provided to the Director of DWR within 60 days of any
applicable exceedance. Following its review, DWR shall notify Duke
Energy of its concurrence or disapproval of Duke Energy's proposed
remedial actions.
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas,LLC,Marshall Steam Station SynTerra
Activities for the re-assessment of S-1, evaluation of interim remedial actions and
proposed short- and long-term corrective actions in pursuit of exceedance mitigation
are compiled in the remainder of this document.
•
•
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
e
Special Order by Consent- EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas, LLC,Marshall Steam Station SynTerra
2.0 RE-ASSESSMENT APPROACH
Planning for the re-assessment of the S-1 seep began on September 27, 2019, upon
receipt of the laboratory report containing the third quarter SOC sample data from the
September 25, 2019 sampling event.
The following activities were outlined to evaluate current S-1 seep conditions and
develop preliminary remedial options to quickly mitigate affects to receiving waters, as
required by the SOC.
• Evaluate conditions upstream and downstream of the S-1 location
• Collect surface water samples upstream of the S-1 location and analyze for the
SOC quarterly parameter list
• Collect surface water samples at previously-sampled background locations SW-7
and SW-8 and analyze for the quarterly SOC parameter list
• Collect groundwater samples in the vicinity of S-1 (19 monitoring wells: BG-
2S/BR, GWA-7S/D, MW-14S/D/BR/BRL, GWA-10S/D, AL-1S/D/BR/BRL, GWA-
11S/DBR, GWA-15S/D) and analyze for Interim Monitoring Plan (IMP)
parameters
• Collect information regarding ash basin decanting
• Review and evaluate historical and current surface water data
• Review and evaluate historical and current groundwater data
• Review and evaluate historical, local precipitation data
• Develop preliminary conclusions
• Develop conceptual remedial actions
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent- EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas, LLC,Marshall Steam Station SynTerra
3.0 RE-ASSESSMENT ACTIVITIES AND FINDINGS
Re-assessment field activities began on October 10, 2019. Duke Energy and SynTerra
staff performed multiple tasks to quickly evaluate current conditions affecting the water
quality at S-1 and remedial options for mitigating the hardness levels at the sample
location. Surface water and groundwater samples were collected, visual reconnaissance
of the stream reach, including adjacent wetlands and upland drainage was conducted,
bench- and field-testing of an ion exchange resin was performed and information on
site conditions was gathered.
3.1 Stream Conditions
Visual assessment of upstream and downstream conditions from S-1, adjacent wetlands
and upland drainage area was conducted on October 15, 2019:
• Stream flow at the location of S-1 was estimated at 1-2 pe
r gallons minute
• Stream flow was not contiguous throughout the reach
- For approximately 200 feet upstream of the S-1 location, the stream was
P Y P
characterized by alternating flowing and ponded conditions from natural
grade control structures and dams from historic beaver activity
Beyond approximately 200 feet upstream of S-1, the reach, was
characterized by disappearing stream conditions and pools
• The stream water was visibly clear, which indicated that the turbidity was low
throughout the stream reach where water was present
• Iron floc and other evidence of filamentous bacteria was noted, primarily in the
lower two-thirds of the stream reach above the S-1 location
• Apparent wetlands adjacent to the stream were characterized by varied
hydrologic conditions ranging from inundated to dry
• Visual inspection of the immediate drainage area of the stream did not indicate
any discharges of materials considered to impact downstream water quality
3.2 Surface Water Sampling and Data Evaluation
Surface water sampling was co
nducted ducted on October 10, 2019 toprovide
P gdata as part of
the re-assessment work, which included process control and evaluation samples aimed
at assessing the effectiveness of certain potential remedial options.
Samples were collected at 2 locations upstream of the S-1 seep and 3 locations
considered background (i.e., beyond the influence of groundwater containing coal ash
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent-EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas,LLC, Marshall Steam Station SynTerra
constituents). The sample locations upstream of S-1 were 'S-1 In Process' and 'S-1
Springhead'. The background locations were the previously sampled SW-7 and SW-8
(which are located on small streams to the northwest of the ash basin) and a new
location BG-200. Figure 1 illustrates the sampling locations along the tributary to Lake
Norman. Monitoring wells in the vicinity of S-1 that were sampled as part of this re-
assessment are also shown on Figure 1. Figure 2 illustrates the three background
surface water locations that were sampled.
Water quality data collected during the re-assessment sampling, indicate an increase of
historical hardness levels at all locations.
Data provided through monthly and later quarterly samples at S-1 collected under
NPDES permit NC0004987(Outfall 101) from October 2016 to April 2018 and quarterly
S-1 samples collected under the SOC since June 2018 indicated an average hardness of
203 mg/L.
As shown in Tables 1 and 2, the September 25, 2019 sample result for hardness of 316
mg/L represents a 55°% increase compared to the average hardness analytical results of
203 mg/L and a 12% increase from the highest sample result (281 mg/L on 10/6/2016 and
8/2/2017) found in the NPDES and SOC dataset.
It should be noted that during the period of coverage of S-1 (Outfall 101), discharges by
the NPDES permit,a pH limit between 6.0 S.U. and 9.0 S.U. was required. To maintain
compliance, the seep S-1 flow was actively treated using limestone. The use of
limestone in the unnamed tributary above S-1 apparently increased the hardness
concentrations for those sample events. Therefore, the elevated hardness values during
the period of NPDES coverage were not considered when determining the SOC IALs
for S-1. Any increases and averages noted in this report were derived using the
hardness data collected during the NPDES coverage period discussed above.
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent _ EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas, LLC, Marshall Steam Station SynTerra
TABLE 1
HISTORIC AND RECENT HARDNESS RESULTS COMPARISON
Hardness (mg/L)
Re-Assessment NPDES and
Sample ID September Sampling SOC Average 2018 Increase
25, 2019 October 10, (October 2016 Average Over
2019 to May 2019) Earlier
Data
S-1 (Outfall 101) 316 203 55
S-01 In Process 305
S-1 Springhead 92.6
SW-7 18 13 38
SW-8 28.2 18 57
8G-200 38.4
Prepared by: CBC Checked by: WCG
Mote:
Any increases and averages noted in this report were derived using the hardness data collected during the NPDES coverage period
discussed above.
TABLE 2
HISTORICAL HARDNESS LEVELS AND AVERAGE
Sample ID Sample Collection Date Hardness (mg/L)
OUTFALL 101 10/06/2016 281
OUTFALL 101 11/07/2016 244
OUTFALL 101 12/09/2016 241
OUTFALL 101 01/09/2017 209
OUTFALL 101 02/02/2017 153
OUTFALL 101 03/06/2017 201
OUTFALL 101 04/11/2017 142
OUTFALL 101 05/04/2017 163
OUTFALL 101 06/09/2017 190
OUTFALL 101 07/12/2017 222
OUTFALL 101 08/02/2017 281
OUTFALL 101 09/05/2017 278
OUTFALL 101 10/02/2017 268
OUTFALL 101 11/15/2017 220
OUTFALL 101 12/05/2017 226
OUTFALL 101 01/04/2018 216
OUTFALL 101 04/02/2018 139
S-01 06/07/2018 159
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent-EMC SOC WQ SI7-009 November 2019
Duke Energy Carolinas, LLC,Marshall Steam Station SynTerra
TABLE 2
HISTORICAL HARDNESS LEVELS AND AVERAGE
Sample ID Sample Collection Date Hardness (mg/L)
S-01 09/11/2018 195
S-01 10/31/2018 137
5-01 03/27/2019 138
S-01 05/07/2019 166
S-01 AVERAGE 203
Prepared by: CBC Checked by: WCG,
Five samples had been collected at background location SW-7 during the month of
August 2018. As shown in Table 1, the October 10, 2019 sample resulted in a hardness
level of 18 mg/L, a 38°,increase when compared to the average 2018 hardness analytical
results of 13 mg/L.
Five samples had been collected at background location SW-8 during the month of
August 2018. As shown in Table 1, the October 10, 2019 sample resulted in a hardness
level of 28.2 mg/L, a 57% increase when compared to the average 2018 hardness
analytical results of 18 mg/L.
Hardness data variations in surface water appear to be seasonal (Table 2), with the
highest levels of hardness recorded during August through November. This is likely
attributable to decreased precipitation during the last summer and fall months.
According to the U.S. Drought Monitor, the MarshaII Steam Station area was considered
to be in moderate to severe drought conditions during September and October 2019.
Additional information on precipitation can be found in Section 3.5 below.
3.3 Groundwater Sampling and Data Evaluation
Groundwater samples were collected on October 14, 2019 from monitoring wells
considered to be proximal to the S-1 location. The following wells were sampled to
assess water quality conditions in the area: BG-2S/BR, GWA-7S/D, MW-14S/D/BR/BRL,
GWA-10S/D, AL-1S/D/BR/BRL, GWA-11S/D/BR, GWA-15S/D. The groundwater
samples were analyzed for IMP parameters, including calcium and magnesium.The
monitoring well locations are shown on Figure 1.
Data review and comparison with the historical dataset indicate stable groundwater
quality conditions in the S-1 vicinity. No increases in constituent concentrations that
might affect hardness at S-1 were noted. The groundwater quality data are summarized
on Table 3.
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent- EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas,LLC,Marshall Steam Station SynTerra
3.4 Ash Basin Conditions and Decanting
To accommodate closure of the ash basin, decanting of free water from the basin via
gravity flow commenced on July 16, 2019 from a pond elevation of 787.94 feet.
Mechanical decanting commenced on September 13, 2019 from a pond elevation of
786.44 feet. On October 15, 2019, the date of the initial re-assessment site visit, the pond
level was 783.10 feet and decanting operations had removed 83.61 million gallons of
water from the ash basin for discharge.
Visual conditions of the ash basin during the re-assessment sampling reflected the
decrease in pond elevation - pond surface area appeared diminished and additional
coal ash was exposed compared to previous site observations.
At nearby monitoring well (AL-15), the water elevation decreased more than 3 feet
since gravity-flow decanting began.
3.5 Local Precipitation Data
Approximately 2 years of regional and local precipitation data was reviewed as part of
this re-assessment.
According to data available from the U.S. Drought Monitor
(https://droughtmonitor.unl.edu/Maps/MapArchive.aspx), a product produced by the
National Drought Mitigation Center, National Oceanic and Atmospheric
Administration and United States Department of Agriculture, the Marshall Steam
Station area, during the following time periods shown in Table 4, was characterized by
the indicated drought conditions:
TABLE 4
DROUGHT CONDITION SUMMARY
Marshall Steam Station Area
Time Period Drought Condition
October 2016 Abnormally Dry
November 2016 - December 2016 Moderate
January 2017 (First 3 weeks)_ Abnormally Dry
Februa - A ril 2017 Moderate
Mid-November to December 2017 Abnormally Dry
January to February (First Week) 2018 Moderate
Februa Second Week to March First Week 2018 Abnormal) D
September(Weeks 2 and 3) 2019 Abnormally Dry
September (Week 4) to October(Week 1) 2019 Moderate
October (Weeks 2 - 4) 2019 Severe
October (Week 5) 2019 Moderate
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas,LLC, Marshall Steam Station SynTerra
Data collected by a Duke Energy automated weather station located at the Marshall
Steam Station indicated decreased precipitation totals when compared to average
historical, regional rainfall records and generally aligned with the drought conditions
published by the Drought Monitor.
3.6 Ion Exchange Resin Evaluation and Deployment
Preliminary evaluation of remedial options was performed as part of the subject re-
assessment effort. A cation exchange resin, widely utilized in water-softening and
demineralization treatment, was selected for bench-testing to determine the
effectiveness in addressing the hardness levels in the S-1 waters. Test results indicated
promising treatment. Authorization was received from the North Carolina Department
of Environmental Quality, Division of Water Resources and United States Army Corps
of Engineers to place cation exchange resin socks and related materials in the stream
above the S-1 location.
On October 16, 2019, 1 sock was deployed at each of 2 locations upstream of the S-1
sample point; 1 sock approximately 5 feet upstream of S-1 and 1 sock approximately 20
feet upstream of S-1. Deployment of the socks was perpendicular to streamflow.
After approximately 24 hours, on October 17, 2019, a total hardness field screen was
utilized to evaluate treatment effectiveness at the S-1 location. Upstream of the
treatment socks, hardness tested as 320 mg/L and at S-1 hardness was tested as 280
mg/L. One additional treatment sock was deployed at the 5-foot upstream Iocation and
2 additional treatment socks were deployed at the 20-foot upstream location to increase
treatment effectiveness.
On October 18, 2019, a total hardness field screen test was utilized to evaluate treatment
effectiveness at the S-1 location. Two separate hardness tests indicated 160 and 200
mg/L at S-1. A sample was collected at S-1 and analyzed per quarterly SOC parameters.
An additional sample, 'S-1 Above' (upstream of the treatment socks), was analyzed for
hardness. Analytical results indicated hardness of 297 mg/L at S-1 and 310 mg/L at'S-1
Above'. Reliability of the field hardness screening information was reconsidered after
receipt of the October 18 sample dataset.
After conferring with the cation exchange resin vendor, it was decided to deploy new
socks in an alignment parallel with streamflow, rather than perpendicular to flow as
initially deployed. On October 25, 2019, 5 new socks were deployed just above the S-1
location parallel with streamflow and the previously-deployed socks were repositioned
parallel with the stream channel, as well. Once stream conditions were suitable for
sampling (e.g., flow and turbidity normalized), approximately 1 hour after sock
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas,LLC, Marshall Steam Station SynTerra
installation, samples were collected at S-1 and analyzed per quarterly SOC parameters
and 'S-1 Above' for hardness. Analytical results indicated hardness at S-1 at 122 mg/L
and 'S-1 Above' at 272 mg/L.
In addition to the SOC parameter sampling described above, 4 hourly hardness samples
were collected at S-1 on October 25, 2019, to assess the effectiveness of the ion exchange
socks over time. Sample results are listed below:
• Time 12:10 Result: 121 mg/L
• Time 13:10 Result: 145 mg/L
• Time 14:10 Result: 149 mg/L
• Time 15:10 Result: 155 mg/L
The resin socks remained in-place to allow for continued treatment of seep waters.
Upon determining the effectiveness of the resin to reduce hardness to levels below the
established SOC interim action levels, Duke Energy ordered additional supplies to
maintain the treatment materials, while more sustainable remedial options are
evaluated, designed and implemented.
Page 3-7

Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent- EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas, LLC,Marshall Steam Station SynTerra
4.0 PRELIMINARY CONCLUSIONS
Recent and historical data evaluated for the re-assessment of seep S-1, indicate the
reported exceedance of hardness from Q3 SOC (9/25/19) sample at S-1 (316 mg/L)
exceeds historical hardness concentrations at this location.
Groundwater data collected on October 14, 2019 indicated generally stable conditions
across all well locations and did not reveal any increases in constituents that might have
affected the hardness levels at S-1 (Table 3)
Ash basin mechanical decanting operations, which began on September 13, 2019,
decreased the ash basin free water elevation by 4.84 feet as of October 15, 2019 by the
removal of over 83 million gallons of water. Decanting of the ash basin (the assumed
source of the elevated hardness concentrations) is part of the long-term corrective action
to reduce groundwater migration from the basin toward S-1.
Correlation between hardness levels at S-1 (Outfall 101) and seasonal effects due to
precipitation variation is evident, as shown in Table 2. Severe drought conditions
reduce natural infiltration to groundwater and are likely a contributory factor in the
recent increase in hardness at S-1.
Based on historical trends, hardness levels at S-1 would be expected to decrease during
the late winter, early spring months when precipitation increases.
Immediate actions were taken by Duke Energy to reduce hardness levels at S-1 and to
mitigate affects to receiving waters. Further remedial action development and
implementation will be required to develop a more permanent remedy.
The exceedance of the IAL for hardness in the small low-flow tributary, has no known
detrimental effect on the environment. There is no human health or aquatic life concern
with increased hardness. Water quality standards (WQS) for hardness have only been
established in waters classified as Water Supply where hardness is considered
undesirable for economic or aesthetic reasons.
Hardness levels recorded in Lake Norman as part of SOC sampling requirements
indicate hardness levels well below WQS. Hardness concentrations recorded at the SOC
Lake Norman sample locations have been 20.7 mg/L or less.
Page 4-1

Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent-EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas,LLC,Marshall Steam Station SynTerra
5.0 PROPOSED REMEDIAL OPTIONS
Re-assessment actions conducted per the SOC requirements included evaluation of
remedial options for treatment and/or control of the S-1 seep to quickly mitigate
possible affects to receiving waters.
After receiving the data from the September 25, 2019 sampling event, Duke Energy
immediately pursued mitigation options to reduce hardness levels at the S-1 seep
location. Duke Energy staff identified the option to utilize the cation exchange resin
socks and began procurement of the materials to conduct bench-scale and field-scale
testing. As described in Section 3.6, use of treatment socks did prove acceptable to
decrease hardness levels; however only for short durations. Operation and
maintenance requirements are very high due to frequent replacement needs and their
use can increase TDS levels in the treated area. Thus, treatment using resin socks is not
considered a viable solution.
Evaluation of short-term and long-term proposed remedial actions is underway with
the alternatives being considered described below. •
All options under consideration require further analysis of local hydrology and
hydrogeology, planning and engineering, which will be completed in the upcoming
phase of the response, before selection of the most effective and implementable
remedial option.
Once approval of the selected remediation system has been received, permitting, final
designs and planning will begin, followed by implementation of the remedial selection.
5.1 Short-Term
Ash basin decanting, a part of ash basin closure, is currently underway and will reduce
the hydraulic head near the topographic divide, located to the west of S-1, that
separates the basin from the stream. The reduction in hydraulic head in the ash basin
will reduce the hydraulic driving force for potential constituents of interest(COI)
migration in groundwater from the basin toward S-1, supporting short-term remedial
efforts.
Currently, development of long-term
corrective actionplans for theMarshall
p Steam
Station are underway. The short-term remediation approaches below are expected to
address the hardness levels in excess of the SOC interim action levels until alternate
remediation efforts are implemented.
Page 5-1

Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent—EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas, LLC,Marshall Steam Station SynTerra
Capture of stream channel flow or control of groundwater discharge to the stream
channel in the vicinity of S-1 were considered the two most reliable and effective
methods to remediate the hardness. Under both approaches, the collected water would
be conveyed to the Marshall Steam Station wastewater treatment system.
5.1.1 Normal Streamflow Capture, Pump and Treat —
Impoundment
This approach utilizes an impounding structure to capture normal stream base
flow upstream of the S-1 location and eliminate (or significantly reduce) the
discharge to receiving waters below. Impounded water would be collected via a
mechanical pump and delivered to the Marshall Steam Station wastewater
treatment system.
Dam design would include a mechanism to bypass storm water flow during
elevated precipitation events.
5.1.2 Normal r a Streamflow Capture, Pump and Treat — Trench
This approach utilizes a subsurface trench to capture normal stream base flow
upstream/upgradient of the S-1 location and eliminate(or reduce) discharge to
receiving waters below. The trench would be constructed perpendicular to the
stream channel and contain porous material (e.g., washed stone). Captured
water would be collected via a mechanical pump and delivered to the Marshall
Steam Station wastewater treatment system.
Trench design would include a mechanism to bypass storm water flow during
elevated precipitation events.
5.1.3 Stream Channel Dewatering, Pump and Treat —
Extraction Wells
This conceptual approach utilizes a line of 6 groundwater extraction wells
installed in the stream valley adjacent to the run of the tributary to capture
groundwater in the vicinity of the S-1 location. These wells would reduce the
groundwater base flow discharge to the stream channel and to receiving waters
below. Extracted groundwater would be collected via a mechanical means and
delivered to the Marshall Steam Station wastewater treatment system.
5.1.4 Stream Channel Dewatering, Pump and Treat —
Extraction Wells with Clean Water Injection
As of the date of this report, the basin closure plan and groundwater corrective
action plan have not been submitted to NCDEQ. Therefore, groundwater
Page 5-2

Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas,LLC,Marshall Steam Station SynTerra
remediation alternatives have not been finalized. However, a robust
groundwater remedial design is being prepared as part of the Corrective Action
Plan Update to control migration of dissolved phase constituents of interest
beyond the ash basin compliance boundary at concentrations above the
respective 02L standards. The eastern portion of the Marshall Steam Station site,
between the Phase I Dry Ash Landfill and the unnamed tributary, is included in
the remedial design. The groundwater remedy in this portion of the site is
comprised of a network of vertical groundwater extraction wells and clean water
infiltration/recharge wells, associated pumps, piping and control systems.
It is recommended that any groundwater remedy installed to address IAL
exceedance in the tributary be compatible with the Remedial Alternative design
in the CAP Update(in progress).
Accelerated implementation of portions of the site-wide groundwater remedial
design along the eastern side of ash basin, between the unnamed tributary and
the Dry Ash Landfill (Phase I) could also help address the discharge of
groundwater to the tributary with elevated concentrations of hardness. Based on
the groundwater remedial alternative being proposed in the CAP Update, it is
estimated that 10 extraction wells and 10 clean water infiltration/recharge wells
would be installed. Installation of an active groundwater extraction and
infiltration system should result in short-term affects to surface water quality in
the tributary.
Before implementation of a groundwater remedy, additional field investigations
(e.g., aquifer pumping tests and groundwater/surface water interactions from
both banks of the stream)should be performed to inform the design.
5.2 Long-Term
5.2.1 Ash Basin Decanting and Dewatering
Ash basin decanting, a part of ash basin closure, is currently underway and will
reduce the hydraulic head near the topographic divide, located to the west of S-1,
that separates the basin from the stream. The reduction in hydraulic head in the
ash basin will reduce the hydraulic driving force for potential COI migration in
groundwater from the basin toward S-1.
5.2.2 Ash Basin Closure and Groundwater Corrective Action
As presented in Section 5.1.4,above, as of the date of this report, the basin
closure plan and groundwater corrective action plan have not been submitted to
Page 5 3

Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent -EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas, LLC,Marshall Steam Station SynTerra
NCDEQ. Therefore, groundwater remediation alternatives have not been
finalized. However, a robust groundwater remedial design is being prepared as
part of the Corrective Action Plan Update to control migration of dissolved
phase constituents of interest beyond the ash basin compliance boundary at
concentrations above the respective 02L standards. The eastern portion of the
Marshall Steam Station site, between the Phase I Dry Ash Landfill and the
unnamed tributary, is included in the remedial design. The groundwater
remedy in this portion of the site is comprised of a network of vertical
groundwater extraction wells and clean water infiltration/recharge wells,
associated pumps, piping and control systems.
It is recommended that any groundwater remedy installed to address IAL
exceedance in the tributary be compatible with the Remedial Alternative design
in the CAP Update (in progress).
Accelerated implementation of portions of the site-wide groundwater remedial
design along the eastern side of ash basin, between the unnamed tributary and
the Dry Ash Landfill (Phase I) could also help address the discharge of
groundwater to the tributary with elevated concentrations of hardness. Based on
the groundwater remedial alternative being proposed in the CAP Update, it is
estimated that 10 extraction wells and 10 clean water infiltration/recharge wells
would be installed. Installation of an active groundwater extraction and
infiltration system should result in short-term affects to surface water quality in
the tributary. Ongoing operation and maintenance of the remedial system
would have a long-term effect in reducing the discharge of site-related
constituents to the unnamed tributary as ash basin closure is implemented.
Before implementation of a groundwater remedy, additional field investigations
(e.g., aquifer pumping tests and groundwater/surface water interactions from
both banks of the stream)should be performed to inform the design.
Page 5-4

Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas, LLC, Marshall Steam Station SynTerra
6.0 REMEDIAL EFFECTIVENESS MONITORING AND REPORTING
Following remedy selection and system startup, monthly system effectiveness updates
will be provided to NCDEQ.
Monitoring for effectiveness would begin after system startup and would potentially
include the volume of water collected and conveyed for treatment, groundwater
elevation monitoring data and stream water quality data.
If system performance is not adequate, optimization of existing components and
utilization of additional methods would be considered. Modifications or additions to
treatment would be implemented and reported in a timely manner.
Page 6-1

1
Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order byConsent- EMC SOC WQS17-009
P November 2019
Duke Energy Carolinas, LLC, Marshall Steam Station SynTerra
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Findings of Re-Assessment and Evaluation of Remedial Actions Under
Special Order by Consent-EMC SOC WQ S17-009 November 2019
Duke Energy Carolinas, LLC, Marshall Steam Station SynTerra
FIGURES

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REVISED BY:C.NEWELL DATE 11/19/2019
CHECKED BY;E,WEBSTER DATE:11✓19/2019 AREA OF INVESTIGATION
APPROVED BY:W.GERALD DATE:11/19/2019 MARSHALL STEAM STATION
PROJECT MANAGER:B.WILKER TERRELL, NORTH CAROLINA
Syr1L www.synterracorp.com

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Anchor QEA of North Carolina, PLLC ANCHOR
231 Haywood Street
Asheville,North Carolina 28801 QEA c
828 281 3350
Technical Memorandum December 17, 2019
To: Richard E. Baker,Jr., Duke Energy
From: Michael Gefell, PG, Anchor QEA, LLC
cc: Scott Davies and Matt Hanchey, Duke Energy
Re: Marshall Steam Station S-1 Hardness and Hydrologic Evaluation
At the request of Duke Energy,Anchor QEA, LLC, reviewed information pertaining to hydrology and
water hardness concentrations at Seep ID Number S-1 (S-1) at the Marshall Steam Station (MSS) in
Terrell, North Carolina and evaluated the potential influence of hydrologic conditions on measured
hardness at S-1. The S-1 sampling location is along a small intermittent stream that has measured
flow rates up to approximately 15 gallons per minute.
This memorandum summarizes the results of Anchor QEA's evaluation, specifically focused on three
questions that Duke Energy posed in an email dated November 22, 2019 (Baker 2019).
Did MSS Enter a Drought?
Anchor QEA downloaded drought severity data from the National Drought Mitigation Center's
U.S. Drought Monitor for the period coinciding with available S-1 hardness data. The Drought Monitor
synthesizes data including precipitation, soil moisture, streamflow, and other drought indices and
classifies drought conditions in weekly intervals (NDMC et al. 2019). The Drought Monitor's drought
severity index includes the following classifications, with increasing drought intensity: No Drought
Conditions;Abnormally Dry; Moderate Drought; Severe Drought; Extreme Drought; and Exceptional
Drought. During the periods shown in bright red and dark red in Figure 1,the Drought Monitor
classified the conditions in the MSS area as moderate and severe drought, respectively.
Figure 1
Hardness(S-1)and Drought Severity Index
350 Hardness Interim
own 300 Action Level /
E 250 1 / i
200 _ �— — +�
c 150 A•
-a
s_ 100
(13
I 50
0 ..
b
OREM No Drought mom Abnormally Dry Mod.Drought Severe Drought — * —Hardness(mg/L)
\\ashevillel\asheville\Projects\Duke Energy\Marshall\S-1 Evaluation\Seep S-1 FINAL Technical Memorandum_2019_12 17.docx

December 17,2019
Page 2
The yellow periods were also abnormally dry but not classified as drought.
Did the Drought Cause or Contribute to the Increase in Hardness at S-1?
Figure 1 compares S-1 hardness values to drought severity index. S-1 hardness data show seasonal
fluctuations with relative peaks in late summer to autumn, and relative lows in the late winter to
spring. During the period from October 2016 to April 2018, the S-1 seep was treated with limestone
to adjust pH, which may have increased S-1 sample hardness values during the same period.
Four seasonal hardness data peaks have exceeded the S-1 hardness Interim Action Level of
200 milligrams per liter(mg/L): 1) in 2014 during a period with no drought; 2) in 2016 during abnormally
dry conditions; 3) in 2017 with no drought; and 4) in 2019 during moderate drought.The abnormally dry
period in 2016 and drought conditions in late 2019 may have contributed to the S-1 hardness peaks in
October 2016 and September 2019. However,the 2014 and 2017 data indicate that increases in
hardness at S-1 can also occur without drought conditions,as classified by the drought severity index.
The drought severity index accounts for a large amount of data that may be important for agronomic
purposes but may not be hydrologically relevant to surface water quality in the S-1 stream.
Anchor QEA also evaluated historical daily precipitation data recorded at the MSS weather station.
Precipitation data for a range of periods were graphically compared to S-1 hardness trends.A
general inverse relationship was identified using a 6-week moving total precipitation, where each
precipitation data point indicates the total precipitation of the preceding 6-week period. All four
hardness peaks above the Interim Action Level occurred during or near times preceded by 6 weeks
of relatively low precipitation. The 6-week period is somewhat arbitrary, but suggests that sustained
periods of low precipitation likely cause elevated S-1 hardness, as expected based on fundamental
hydrologic principles.
Figure 2
Q Hardness(S-1)and Observed Precipitation
v
12 350 Hardness Interim 300
cB 10 A Action Level A /#464 1
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6-wk Precipitation — f —Hardness(mg/L)

December 17,2019
Page 3
During dry periods, stream hardness is dominated by minerals dissolved in discharging groundwater.
However, stream hardness can decrease significantly due to direct runoff from precipitation, which
has low hardness. Direct runoff includes overland flow and subsurface stormflow, and has relatively
low mineral content compared to groundwater (Freeze and Cherry 1979).The S-1 stream setting
should promote significant subsurface stormflow because of the following characteristics: 1) steep,
convex surrounding slopes; 2) a narrow valley bottom; 3) permeable soil; and 4) forested slopes with
leaf litter(Freeze and Cherry 1979). We interpret that direct runoff from precipitation would
significantly decrease S-1 stream hardness levels during extended rainy periods. However, the
converse would also apply; in extended periods with little or no precipitation, subsurface stormflow
would abate and stream concentrations would increase to those that are dominated by discharging
groundwater concentrations. This relationship would produce an inverse relationship between
precipitation and S-1 hardness, as generally observed in Figure 2. The inverse relationship between
S-1 hardness and 6-week running total precipitation also suggests the influence of another
mechanism with longer duration than direct runoff from individual storms.
Changes in relative groundwater recharge and discharge from either side of the stream could also
influence hardness at S-1. Based on October 2019 groundwater analytical results, the average
groundwater hardness measurement southwest of the stream (approximately 270 mg/L at well
clusters AL-01 and MW-14) was higher than that measured northeast of the stream (approximately
150 mg/L at well cluster GWA-10). Using only the shallow monitoring well data, the hardness
contrast is more significant: approximately 340 mg/L southwest of the stream versus 40 mg/L to the
northeast. Therefore, during periods of relatively high groundwater elevation on the southwest side
of the stream and relatively low groundwater elevation on the northeast side, as may occur in the
late summer or fall, the total groundwater contribution of hardness to S-1 would increase. A detailed
groundwater flow and transport evaluation could help clarify the relationship between relative
groundwater flow contributions from both sides of the stream to S-1 hardness.
Has MSS Recovered from the Drought?
U.S. Drought Monitor data indicate the following recent drought conditions at MSS (dates in 2019):
• October 15-22: severe drought
• October 29-November 12: moderate drought
• November 19: abnormally dry
• November 26: none
• December 3: none
• December 10: none
Based on these data, MSS had recovered from the late 2019 drought as of November 19 or 26, 2019.
As shown in Figure 2, when the 6-week running total precipitation increased in late 2019, the S-1
hardness concentration dropped to below the Interim Action Level.

December 17,2019
Page 4
References
Baker, Richard E., Jr. (Duke Energy), 2019. Email regarding: Marshall S-1 — Request for Technical
Evaluation. November 22, 2019.
Freeze, R.A., and J.A. Cherry, 1979. Groundwater. Englewood Cliffs, New Jersey: Prentice-Hall.
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