Buck Background Groundwater Dataset Evaluation - December 2016

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Technical Memorandum
Date: Tuesday, December 13, 2016
Project: Buck Steam Station Ash Basin System
To: Sean DeNeale
From: Chad Hearn
Subject: Additional Background Monitoring Well Determinations
The purpose of this memorandum is to provide justification for additional monitoring wells that should be
considered as background wells for the Buck Steam Station (Buck) ash basin system. Monitoring wells
BG -1 S/D/BR, BG-2S/D, BG-3S/BRU, and MW-6S/D were previously evaluated and chosen to represent
background groundwater quality as documented in Appendix B of the Buck Corrective Action Plan (CAP)
Part 1, dated November 20, 2015. Although BG-3S/BRU and MW-6S/D were considered as background
wells in the CAP Part 1, additional evaluation was suggested to confirm the well cluster can be
considered as background. Justification for why BG-3S/BRU and MW-6S/D should be considered
background wells is provided below.
The potential additional background monitoring wells at Buck include GWA-1S, MW-6BR, and MW-
8S/D/BR. These potential background wells are being proposed based on evaluation of the following
criteria: groundwater flow direction, groundwater elevation as compared to the nearest ash basin surface
water or porewater elevation, historical analytical results, and horizontal distance to the ash basin system.
Distances and elevations pertinent to the evaluation are provided in Table 1. Locations for each
monitoring well discussed below are shown on Figure 1. Additional details are provided for each
monitoring well cluster on the following pages of this memorandum.
Historical analytical data for previously evaluated background wells (CAP Part 1) and the potential
background wells listed above are provided in Table 2. The background wells and analytical data are
separated by groundwater flow layer (shallow, deep and bedrock) and a valid sample count is provided
for each constituent. Samples with field measured turbidity greater than 10 nephelometric turbidity units
(NTU) and/or pH greater than 8.5 standard units (SU) are denoted with red -colored text and were not
included in the valid sample counts.
BG -3S and BG-3BRU
Monitoring wells BG -3S and BG-3BRU were installed onsite as background monitoring wells during the
CSA and included in the Buck CAP Part 1 Appendix B evaluation described above. The well pair is
located in the southeastern area of the site, south of Cell 2 and southeast of Cell 1, along Buck's southern
property boundary. As mentioned in the CAP Part 1 Appendix B, additional evaluation would be
conducted to determine if BG-3S/BRU should be considered background wells. An additional well pair
(GWA-13S/D) was installed along a topographic ridge to the northeast of BG-3/BRU in February and
March 2016 to define groundwater flow direction and groundwater quality in this area of the site.

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Water levels measured during the May and September 2016 sampling events indicate that
groundwater flow follows the slope -aquifer concept in the southeastern area of the site (south of
Cell 2 and southeast of Cell 1), and that groundwater in this area of the site flows to the north and
northeast. Monitoring wells BG-3S/BRU are located sidegradient of Cell 1 and upgradient of Cell
2.
Analytical data included in Table 2 indicate that boron was not reported in the BG -3 wells at
concentrations which equal or exceed the laboratory method reporting limit. Chloride was
reported at concentrations less than two orders of magnitude less than the 2L Standard. Sulfate
was reported at approximately one to two orders of magnitude less than the 2L Standard.
Based on the justification provided above, groundwater passing through monitoring wells BG-3S/BRU
originates upgradient or sidegradient of the ash basin system, and is not impacted by the ash basin
system. Therefore, groundwater samples collected from BG-3S/BRU represent background water quality
relative to the Buck ash basin system and have been included in the valid background sample counts.
MW -6S and MW -6D
Monitoring wells MW -6S and MW -61D were installed onsite as voluntary ash basin monitoring wells in
June 2006, and were included in the Buck CAP Part 1 Appendix B evaluation described above. The well
pair is located in the southeastern area of the site, southeast of Cell 1, along Buck's southern property
boundary. As mentioned in the CAP Part 1 Appendix B, additional evaluation would be conducted to
determine if MW-6S/D should be considered background wells.
• Monitoring wells MW-6S/D have been considered background for the ash basin's NPDES
compliance monitoring program since 2011.
• Water levels measured during the May and September 2016 sampling events indicate that
groundwater flow follows the slope -aquifer concept in the southeastern area of the site (south of
Cell 2 and southeast of Cell 1), and that groundwater in this area of the site predominantly flows
to the north and northeast. Monitoring wells MW-6S/D are located side -gradient of Cell 1 and
upgradient of Cell 2.
• Analytical data included in Table 2 indicate that boron was not reported in the MW -6 wells at
concentrations which equal or exceed the laboratory method reporting limit. Chloride and sulfate
were generally reported at concentrations two orders of magnitude less than the 2L Standard.
Based on the justification provided above, groundwater passing through monitoring wells MW-6S/D
originates upgradient or sidegradient of the ash basin system, and is not impacted by the ash basin
system. Therefore, groundwater samples collected from MW-6S/D represent background water quality
relative to the Buck ash basin system and have been included in the valid background sample counts.
GWA-1 S
Monitoring well GWA-1 S was installed onsite as an upgradient well during the CSA. The well is located
south of Cell 1 along the southern property boundary. This well has been sampled five times between
June 2015 and September 2016. Water level measurements and calculated groundwater elevations from
April, June, and September 2016 have been considered for determining groundwater flow direction in this
area of the site.
Monitoring well GWA-1 S is located approximately 90 feet south of Cell 1 along the southern
property boundary. The ground surface elevation at the monitoring well is approximately 707 feet.
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• The closest ash basin surface water elevation was measured to be 701.94 feet in June 2016, in
the southern portion of Cell1.
GWA-1S is screened from approximately 5 to 20 ft bgs in the shallow flow layer (approximately
702 to 687 feet elevation). The average groundwater elevation calculated from the April, June,
and September 2016 gauging events was 702.68 feet (approximately 1 foot higher than the
nearest ash basin surface water elevation measured in June 2016). The lowest groundwater
elevation calculated for these sampling events was 698.59 feet (September 2016).
Analytical data included in Table 2 indicate that boron was not reported at concentrations which
equal or exceed the laboratory method reporting limit. Chloride and sulfate were reported at
concentrations between one and two orders of magnitude less than the 2L Standard.
Based on the justification provided above, groundwater passing through monitoring well GWA-1 S
originates upgradient and south of Cell 1, and is not impacted by the ash basin system. Therefore,
groundwater samples collected from GWA-1S represent background water quality relative to the Buck
ash basin system and have been included in the valid background sample counts.
MW-6BR
Monitoring well MW-6BR was installed adjacent to existing compliance monitoring wells MW-6S/D in
February 2016 to further evaluate groundwater quality and flow characteristics southeast of Cell 1. This
well was first sampled in February 2016 and then again during site -wide sampling events in June and
September 2016.
• As described above, groundwater in this area of the site predominantly flows to the north and
northeast and monitoring wells MW-6S/D are considered side -gradient of Cell 1 and upgradient of
Cell 2. Monitoring wells MW-6S/D, located adjacent to MW-6BR, have been considered
background for the ash basin's NPDES compliance monitoring program since 2011.
• Monitoring well MW-6BR is located approximately 450 feet southeast of the southeastern extent
of the ash basin waste boundary (Cell 1). The ground surface elevation at the monitoring well
cluster is approximately 719 feet.
• The closest ash basin surface water elevation (in the southern portion of Cell 1) was measured to
be 701.94 feet in June 2016.
• MW-6BR is screened from approximately 147 to 152 ft bgs in the bedrock flow layer
(approximately 571.5 to 566.5 feet elevation). The average groundwater elevation calculated from
the June and September 2016 gauging events was 697.17 feet (approximately 4 feet lower than
the nearest ash basin surface water elevation measured in June 2016). The lowest water
elevation calculated for these sampling events was 696.15 feet (September 2016).
• Analytical data included in Table 2 indicate that boron was not reported in MW-6BR at
concentrations which equal or exceed the laboratory method reporting limit. Chloride and sulfate
were generally reported at concentrations two orders of magnitude less than the 2L Standard.
Based on the justification provided above, groundwater passing through monitoring well MW-6BR
originates upgradient and south of Cell 1, and is not impacted by the ash basin system. Therefore,
groundwater samples collected from MW-6BR represent background water quality relative to the Buck
ash basin system and have been included in the valid background sample counts.

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MW -8S, MW -8D, and MW-8BR
Monitoring wells MW -8S and MW -8D were installed onsite as ash basin NPDES compliance monitoring
wells in December 2010. Monitoring well MW-8BR was installed adjacent to MW-8S/D in October 2016 to
further evaluate groundwater quality in the bedrock flow layer. Monitoring wells MW-8S/D/BR are located
onsite and south of Cell 1. Monitoring wells MW-8S/D have been sampled since March 2011. Due to
there being no sample results available from MW-8BR, justification for these wells are based on data from
MW-8S/D. To confirm groundwater elevations compared to the ash basin, groundwater elevations from
March 2011 through September 2016 were reviewed for MW-8S/D. Water level measurements and
calculated groundwater elevations from June 2015 and September 2016 have been considered for
determining groundwater flow direction in this area of the site.
• Monitoring wells MW-8S/D are located approximately 500 feet south of Cell 1 along the southern
property boundary. The ground surface elevation at the monitoring well is approximately 711 feet.
• The closest ash basin surface water elevation was measured to be 701.94 feet in June 2016, in
the southern portion of Cell1.
• MW -8S is screened from approximately 6 to 21 ft bgs in the shallow flow layer (approximately
704.5 to 689.5 feet elevation). The average groundwater elevation calculated from the March
2011 through September 2016 gauging events was 706.96 feet (approximately 5 feet higher than
the nearest ash basin surface water elevation measured in June 2016). The lowest groundwater
elevation calculated for these sampling events was 704.38 feet (July 2015).
• MW -8D is screened from approximately 56 to 61 ft bgs in the deep flow layer (approximately
654.5 to 649.5 feet elevation). The average groundwater elevation calculated from the March
2011 through September 2016 gauging events was 707.41 feet (approximately 5.5 feet higher
than the nearest ash basin surface water elevation measured in June 2016). The lowest
groundwater elevation calculated for these sampling events was 705.18 feet (September 2016).
• MW-8BR is screened from approximately 108.5 to 113.5 ft bgs in the bedrock flow layer
(approximately 602 to 597 feet elevation).
• Analytical data included in Table 2 indicate that boron was not reported in MW-8S/D at
concentrations which equal or exceed the laboratory method reporting limit. Chloride and sulfate
were generally reported at concentrations two orders of magnitude less than the 2L Standard.
Based on the justification provided above, groundwater passing through monitoring wells MW-8S/D
originates upgradient of Cell 1, and is not impacted by the ash basin system. Therefore, groundwater
samples collected from MW-8S/D represent background water quality relative to the ash basin system
and results have been included in the valid background sample counts. Following receipt of analytical
results for MW-8BR samples, field parameters and analytical results will be evaluated before considering
MW-8BR as a background well.
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Table 1. Background Monitoring Well Information
Buck Steam Station Ash Basin System
Notes:
1. Elevations presented in North American Vertical Datum (NAVD) 88.
2. The groundwater elevations presented are the averaged based on available groundwater elevation measurements from sampling/gauging events at the site.
3. Ash basin surface water elevations closest to monitoring wells were measured during the June 2016 gauging event.
4. NA = not available
5. Monitoring well MW -6D is screened in the fractured bedrock flow layer.
Distance and DirectionClosest
Ground
Elevation of
Ash Basin
from Source Area
Groundwater
Surface
Screened
Elevation of
Surface Water
Groundwater Elevation
Well ID
Flow
Elevation
Interval
Groundwater
Elevation to Well
Monitoring Events
Ash Basin
Direction
(feet)
(feet)
(feet)
(feet)
(Cell 1, Cell 2)
CAP Part 1 Established Background Monitoring Wells
BG -1 S
2,050 ft SW
NW
723
707.5-692.5
705.04
701.94
2016 - March, June, September
Cell 1
BG -1 D
2,050 ft SW
NW
723
624-619
705.02
701.94
2016 - March, June, September
(Cell 1
BG -1 BR
2,050 ft SW
NW
723
587-582
606.81
701.94
2016 - March, June, September
Cell 1
BG -2S
2,050 ft SW
NW
727
710-695
707.19
701.94
2016 - March, June, September
Cell 1
BG -2D
2,050 ft SW
NW
727
628-623
708.00
701.94
2016 - March, June, September
(Cell 1)
BG -3S
590 ft S
NE
719
694-679
689.78
683
2016 - March and June
Cell 2
BG-3BRU
590 ft S
NE
719
649.5-644.5
691.96
683
2016 - March, June, September
Cell 2
MW -6S
450 ft SE
NE
720
700.5-690.5
700.65
701.94
2016 - March, June, September
Cell 1
MW -6D5
450 ft SE
NE
719
615-610
700.13
701.94
2016 - March, June, September
(Cell 1
Proposed Additional Background Monitoring Wells
GWA-1 S
90 ft S
Cell 1
N
707
702-687
702.68
701.94
2016 - April, June, September
MW-6BR
450 ft SE
NE
719
571-566
697.17
701.94
2016 - June, September
Cell 1
MW -8S
500 ft S
N
711
704.5-689.5
704.62
701.94
2015 - June
Cell 1
2016 - September
MW -8D
500 ft S
N
711
654.5-649.5
705.29
701.94
2015 - June
Cell 1
2016 - September
MW-8BR
500 ft S
N
711
602-597
NA
701.94
NA
Cell 1
Notes:
1. Elevations presented in North American Vertical Datum (NAVD) 88.
2. The groundwater elevations presented are the averaged based on available groundwater elevation measurements from sampling/gauging events at the site.
3. Ash basin surface water elevations closest to monitoring wells were measured during the June 2016 gauging event.
4. NA = not available
5. Monitoring well MW -6D is screened in the fractured bedrock flow layer.

Table 2. Buck Steam Station Ash Basin System Background Groundwater Baseline Analytical Results
POTENTIAL WELLS TO INCLUDE IN BACKGROUND DATASET - IUSTIFICATION ATTACHED
Notes:
Red text indicates samples that will not be used in determining proposed provisional background threshold values (PPBTVs) due to pH > 8.5 orturbidity>10 NTL
0 - Bold highlighted concentration indicates exceedance of the 15A NCAC 02L Standard or LMAC, Appendix 2, Apnl 1, 2013.
urn = micron
pg/L = micrograms per lifter
= microsiemens per centimeter
ft = feet
url = milligrams per liter
Eh values were wlwlated by adding 200 mV to the field -measured ORP value. Depending on the field meter used, Eh vaWes calculated using this formula can vary by 1/- 5 m,
MV=
millivolts
NTU - nephelometric turbidity units
pG/L = picacunes per liter
SU =standard unit
I = laboratory estimated concentration
I- = estimated concentration, biased low
3+ = es, mated concentration, biased high
U = results not detected at concentrations which equal the laboratorys method reporting firm
02L = North Carolina groundwater standards as specified in T15A NCAC 02L
D = dissolved
Deg C = degree Celsius
DHHS = North Carolina Department of Health and Human Service
DO = dissolved oxygen
GW- groundwater
GWQS = groundwater quality stand—
IMC = Interim Maximum Allow Concentrator,
N = normal
NS = no standard
PPBC = Proposed Provisional Background Concentration,
T = total
TDS = total disxalved solids
TOC = total organic carbon
* BG -10 and BG -IBR are scheduled for replacement due W potential grout contaminam
Page 2 of 2

NOTES:
1. WASTE BOUNDARY AND ASH STORAGE AREA BOUNDARIES ARE APPROXIMATE SCALE (FEET)
2. THE COMPLIANCE BOUNDARY IS ESTABLISHED ACCORDING TO THE DEFINITION FOUND IN
15A NCAC 02L.0107 (a) 500 0 500 1,000
3. AERIAL IMAGERY IS A COMBINATION OF A WSP AERIAL SURVEY (2014) AND NC ONEMAP (2010)
4. HYDROGRAPHY WAS DIGITIZED FROM USGS 1:24,000 SCALE TOPOGRAPHICAL MAPS
5. AS -BUILT CAMA ASSESMENT AND NPDES SERIES WELLS HAVE BEEN PROVIDED BY WSP AND
DUKE ENERGY
FEZ
WELL LOCATION MAP
DUKE ENERGY CAROLINAS, LLC
BUCK STEAM STATION ASH BASIN
ROWAN COUNTY, NORTH CAROLINA
DATE
DECEMBER 2016
FIGURE