Allen Background GW Dataset Evaluation - December 2016

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Technical Memorandum
Date: Tuesday, December 13, 2016
Project: Allen 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 Allen Steam Station (Allen) ash basin system. Monitoring wells
BG -1 S/D and BG-3S/D were previously evaluated and chosen to represent background groundwater
quality as documented in Appendix B of the Allen Corrective Action Plan (CAP) Part 1, dated November
20, 2015. Although BG-1S/D were considered as background wells, additional evaluation was suggested
in the CAP Part 1 to confirm the well cluster can be considered as background. Monitoring wells BG-
2S/D/BR were evaluated in the CAP Part 1, but it was determined that additional evaluation was
warranted before considering these as background wells. Following submittal of the CAP Part 1,
additional monitoring wells were installed to further evaluate the viability of including BG-2S/D/BR as
background wells for the Allen ash basin system. Justification for why BG -1 SO and BG-2S/D/BR should
be considered as background wells is provided below.
The potential additional background monitoring wells at Allen include AB-4S/D/BR, BG-2S/D/BR, BG-
4S/D/BR, GWA-19S, GWA-21S/D/BR, GWA-23S, and GWA-26S/D. 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 -1 S and BG -1 D
Monitoring wells BG -1S and BG -1D were installed onsite as background monitoring wells during the CSA
and included in the Allen CAP Part 1 Appendix B evaluation described above. The well pair is located in
the southwestern extent of the site near Reese Wilson Road. As mentioned in the CAP Part 1 Appendix
B, additional wells were planned for installation between the BG -1 well pair and the ash basin to refine
groundwater flow direction and groundwater quality in this area of the site. Monitoring wells GWA-26S/D

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were installed north of BG -1 S/D along a topographic ridge between BG -1 S/D and the ash basin and
compliance monitoring well AB-12S/D.
• Water levels measured during the September 2016 sampling event indicate that groundwater flow
follows the slope -aquifer concept in the area between BG -1 S/D and the ash basin, and the
topographic high in the vicinity of monitoring wells GWA-26S/D acts as a groundwater divide.
o For the shallow flow layer, water elevations calculated for AB -12S, GWA-26S, and BG -1S
were 634.65, 644.45, and 635.24 feet, respectively.
o For the deep flow layer, water elevations calculated for AB -12D, GWA-26D, and BG -1 D
were 636.61, 636.88, and 635.37 feet, respectively.
• The historical water elevation in the southwest portion of the active ash basin is approximately
636.5 feet.
• For BG -1 S, 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 approximately two orders of magnitude less than the 2L
Standard.
• Note that background monitoring well BG -1 D is scheduled for reinstallation due to potential grout
contamination from when it was installed during the CSA. pH values have continued to stay
elevated (above 8.5 SU).
• For BG -1 D, analytical data included in Table 2 indicate that boron was not reported at
concentrations which equal or exceed the laboratory reporting limit, except for one sample in May
2016 where it was reported at 51.5 pg/L (laboratory reporting limit = 50 pg/L). Chloride was
reported at concentrations nearly two orders of magnitude less than the 2L Standard, except for
one sample in September 2016 that was near the 2L Standard. Sulfate was reported at
concentrations of one or less than one order of magnitude less than the 2L Standard. TDS was
reported at concentrations less than one order of magnitude less than the 2L Standard, which is
elevated compared to other deep flow layer background wells that are not impacted by grout. The
elevated concentrations of chloride, sulfate, and TDS compared to other deep flow layer
background wells is likely due to grout contamination.
Based on the justification provided above, groundwater passing through monitoring wells BG-1S/D
originates upgradient or side -gradient of the active ash basin, and is not impacted by the ash basin
system. Groundwater samples collected from BG -1 S represent background water quality relative to the
Allen ash basin system and have been included in the valid background sample counts. Following
reinstallation of BG -1 D and sampling, analytical results will be evaluated before considering BG -1 D as a
background well.
BG -2S, BG -2D, and BG-2BR
Monitoring wells BG -2S, BG -2D, and BG-2BR were installed onsite as background monitoring wells
during the CSA and included in the Allen CAP Part 1 Appendix B evaluation described above. The well
cluster is located approximately 1,825 linear feet west of the inactive ash basin across a topographic high
and groundwater divide located approximately along South Point Road. As mentioned in the CAP Part 1
Appendix B, additional wells were planned for installation between the BG -2 well cluster and old ash fills
located approximately 1,000 feet to the south-southwest to define groundwater flow direction and
groundwater quality. Monitoring wells GWA-16S/D were installed along the southernmost extent of Duke
Energy property between BG-2S/D/BR and the old ash fills to the south. Also, monitoring wells GWA-
2

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19S/D were installed between BG-2S/D/BR and the inactive ash basin to confirm if there is a groundwater
divide along South Point Road.
• Water levels measured during the September 2016 sampling event indicates there is a
groundwater divide between BG-2S/D/BR and the inactive ash basin in the vicinity of the
topographic high and monitoring wells GWA-19S/D. In addition, groundwater appears to be
consistent with the slope -aquifer concept and should flow toward the west from the old ash fills.
o For the shallow flow layer, water elevations calculated for BG -2S, GWA-19S, and AB -37S
(the closest monitoring well located in the westernmost extent of the inactive ash basin)
were 590.01, 629.47, and 620.94 feet, respectively.
o For the deep flow layer, water elevations calculated for BG -2D, GWA-19D, and AB -37D
(the closest monitoring well located in the westernmost extent of the inactive ash basin)
were 588.01, 627.39, and 621.78 feet, respectively.
• For BG -2S, analytical data included in Table 2 indicate that boron was not reported at
concentrations which equal or exceed the laboratory method reporting limit. Chloride was
reported at concentrations between one and two orders of magnitude less than the 2L Standard.
Sulfate was reported at concentrations more than two orders of magnitude less than the 2L
Standard.
• For BG -2D, 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 approximately two orders of magnitude less than the 2L
Standard.
• Note that background monitoring well BG-2BR is scheduled for reinstallation due to potential
grout contamination from when it was installed during the CSA. pH values have continued to
exceed 12 SU, except for one sampling event where it was reported as 5.9 SU.
• For BG-2BR, 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 generally reported at concentrations just less than two orders of magnitude less than the 2L
Standard. TDS was reported at concentrations that exceeded the 2L Standard for each sampling
event since June 2015, which is elevated compared to other bedrock flow layer background wells
that are not impacted by grout, and is likely due to the grout contamination.
• In addition, analytical data for samples collected from GWA-16S/D in February, May and
September 2016 indicate that boron was not reported at concentrations which equal or exceed
the laboratory method reporting limit. Chloride and sulfate were generally reported at
concentrations approximately two orders of magnitude less than the 2L Standard. There's no
indication that groundwater impacted by the old ash fills is migrating toward BG-2/D/BR.
Based on the justification provided above, groundwater passing through monitoring wells BG-2S/D/BR
originates upgradient or side -gradient of the ash basin system, and is not impacted by the old ash fills
located to the south-southwest of BG-2S/D/BR. Groundwater samples collected from BG -2S and BG -2D
represent background water quality relative to the Allen ash basin system and have been included in the
valid background sample counts. Following reinstallation of BG-2BR and sampling, field parameters and
analytical results will be evaluated before considering BG-2BR as a background well.
AB -4S, AB -4D, and AB-4BR
Monitoring wells AB -4S and AB -4D are existing upgradient NPDES compliance monitoring wells for the
ash basin. AB-4BR was installed in December 2015 to further evaluate groundwater quality and flow

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characteristics west of the ash basin. To confirm groundwater elevations compared to the ash basin,
groundwater elevations from November 2004 through September 2016 were reviewed for AB-4S/D and
from February, May and September 2016 for AB-4BR. Site -wide gauging events from June 2015, May
2016, and September 2016 have been considered for determining groundwater flow direction in this area
of the site.
Monitoring wells AB-4S/D/BR are located approximately 80 feet north-northwest of the
southwestern extent of the active ash basin waste boundary. The ground surface elevation at the
monitoring well cluster is approximately 647 feet, approximately one foot above the edge of the
active ash basin waste boundary (646 feet).
The closest ash basin surface water elevation from June 2016 is 636.5 feet, in the southwest
portion of the active ash basin. Historically, this closest ash basin surface water elevation has
remained at approximately 636.5 feet.
AB -4S is screened from approximately 12.5 to 27.5 feet below ground surface (ft bgs) in the
shallow flow layer (approximately 638 to 623 feet elevation). The average groundwater elevation
calculated from November 2004 through September 2016 gauging events is 638.6 feet
(approximately 2 feet higher than the nearest historical ash basin surface water elevation). Note
there were five sampling events where the groundwater elevation was less than the historical ash
basin surface water elevation of 636.5 feet (November 2007, November 2008, November 2011,
July 2012 and November 2012), with the lowest groundwater elevation of 633.83 feet occurring in
November 2012.
AB -41D is screened from approximately 49.5 to 54.5 ft bgs in the deep flow layer (approximately
600 to 595 feet elevation). The average groundwater elevation calculated from November 2004
through September 2016 gauging events was 637.30 feet (approximately 2 feet higher than the
nearest historical ash basin surface water elevation). Note there were five sampling events where
the groundwater elevation was less than 636.5 feet (November 2007, November 2008, November
2011, July 2012 and November 2012), with the lowest groundwater elevation of 633.86 feet
occurring in November 2012.
• AB-4BR is screened from approximately 83 to 88 ft bgs in the bedrock flow layer (approximately
565.5 to 560.5 feet elevation). The average groundwater elevation calculated from the February,
May and September 2016 gauging events was 640.51 feet (approximately 4 feet higher than the
nearest historical ash basin surface water elevation). The lowest water elevation calculated for
these sampling events was 638.4 feet (September 2016), approximately 2 feet higher than the
historical ash basin surface water elevation.
• Although there were five events when the water elevations in AB -4S and AB -41D were lower than
the historical elevation of the nearest ash basin surface water, groundwater flow at the site
follows the slope -aquifer concept and has historically been from the west toward the active ash
basin and ultimately the Catawba River.
• Analytical data included in Table 2 indicate that boron was not reported in any of the AB -4 wells
at concentrations which equal or exceed the laboratory method reporting limit. Chloride was
reported at concentrations approximately one to two orders of magnitude less than the 2L
Standard. Sulfate was reported at one to two orders of magnitude less than the 2L Standard.
Based on the justification provided above, groundwater passing through monitoring wells AB-4S/D/BR
originates upgradient and west of the active ash basin, and is not impacted by the ash basin system.
Therefore, groundwater samples collected from AB-4S/D/BR represent background water quality relative
to the Allen ash basin system and have been included in the valid background sample counts.
4

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BG -4S, BG -4D, and BG-4BR
Monitoring wells BG-4S/D/BR were installed in December 2015 and January 2016, and sampled for the
first time in February 2016. To improve understanding of background groundwater quality at the Allen
site, this background monitoring well cluster is located north of the Station Discharge Canal in an area
where there are no known CCR -related operations upgradient that would potentially impact groundwater.
To confirm groundwater elevations compared to the Station Discharge Canal, groundwater elevations
from May and September 2016 were reviewed.
• Monitoring wells BG-4S/D/BR are located approximately 480 feet north of the Station Discharge
Canal (closest surface water), and approximately 1,900 feet north of the inactive ash basin waste
boundary.
• The ground surface elevation at the monitoring well cluster is approximately 659 feet.
• The surface water elevation in the Station Discharge Canal has historically been similar to the
elevation of the Catawba River located east of the Allen site (approximately 565.5 feet).
• BG -4S is screened from approximately 78 to 93 ft bgs in the shallow flow layer (approximately
581 to 566 feet elevation). The average groundwater elevation calculated from March, May, and
September 2016 gauging events is 638.08 feet (approximately 73 feet higher than the Station
Discharge Canal elevation).
• BG -4D is screened from approximately 106 to 111 ft bgs in the deep flow layer (approximately
553 to 548 feet elevation). The average groundwater elevation calculated from March, May, and
September 2016 gauging events is 637.30 feet (approximately 72 feet higher than the Station
Discharge Canal elevation).
• BG-4BR is screened from approximately 160 to 165 ft bgs in the bedrock flow layer
(approximately 499 to 494 feet elevation). The average groundwater elevation calculated from
March, May, and September 2016 gauging events is 640.51 feet (approximately 75feet higher
than the Station Discharge Canal elevation).
• Analytical data included in Table 2 indicate that boron was not reported in any of the BG -4 wells
at concentrations which equal or exceed the laboratory method reporting limit. Chloride was
reported at concentrations approximately two orders of magnitude less than the 2L Standard.
Sulfate was reported at concentrations approximately one to two orders of magnitude less than
the 2L Standard.
Based on the justification provided above, groundwater passing through monitoring wells BG-4S/D/BR is
originates upgradient of the Station Discharge Canal and is not impacted by the ash basin system.
Therefore, groundwater samples collected from BG-4S/D/BR represent background water quality relative
to the Allen ash basin system and have been included in the valid background sample counts.
GWA-19S
Monitoring well GWA-19S was installed offsite and west of the Allen ash basin in March 2016 to further
evaluate groundwater quality and flow characteristics between the ash basin and background monitoring
wells BG-2S/D/BR. This well was first sampled in April 2016. To confirm groundwater elevations
compared to the ash basin, groundwater elevations from April, May and September 2016 were reviewed.
Monitoring well GWA-19S is located approximately 700 feet west of the inactive ash basin waste
boundary in the vicinity of a topographic high and groundwater divide located approximately along
South Point Road. The old ash fills (mentioned above) are located topographically downgradient

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and southwest and south of GWA-19S. Based on the slope -aquifer concept, the old ash fills can
be considered downgradient of GWA-19S.
• The ground surface elevation at GWA-19S is approximately 671 feet, approximately 46 feet
higher than the western extent of the inactive ash basin (625 feet).
• The closest monitoring well located in the westernmost extent of the inactive ash basin (AB -37S)
had an average groundwater elevation of 623.17 during the February, May and September 2016
sampling events.
• GWA-19S is screened from approximately 42 to 57 ft bgs in the shallow flow layer (approximately
628 to 613 feet elevation). The average groundwater elevation calculated from the April, May,
and September 2016 gauging events was 629.94 feet.
• 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 approximately two orders of magnitude less than the 2L Standard.
Based on the justification provided above, groundwater passing through monitoring well GWA-19S
originates upgradient and west of the ash basin system, and is not impacted by the ash basin system.
Therefore, groundwater samples collected from GWA-19S represent background water quality relative to
the Allen ash basin system and have been included in the valid background sample counts.
GWA-21 S, GWA-21 D, and GWA-21 BR
Monitoring wells GWA-21 S and GWA-21 D were installed in the January and February 2016, and GWA-
21 BR was installed in June 2016. These monitoring wells were installed offsite to further evaluate
groundwater quality and flow characteristics west of the ash basin. GWA-21 S and GWA-21 D were first
sampled in March 2016 and then again during site -wide sampling events in May and September 2016. To
confirm groundwater elevations compared to the ash basin, groundwater elevations from May and
September 2016 were reviewed for GWA-21 S/D and from September 2016 for GWA-21 BR. Site -wide
gauging events from May 2016 and September 2016 have been considered for determining groundwater
flow direction.
• Monitoring well GWA-21 S/D/BR are located approximately 640 feet northwest of the active ash
basin waste boundary.
• The ground surface elevation at the GWA-21 well cluster is approximately 672 feet,
approximately 26 feet higher than the closest portion and southwestern extent of the active ash
basin (646 feet).
• The closest ash basin surface water elevation has historically been approximately 636.5 feet, in
the southwest portion of the active ash basin.
• GWA-21 S is screened from approximately 23 to 38 ft bgs in the shallow flow layer (approximately
648 to 633 feet elevation). The average groundwater elevation calculated from the May and
September 2016 gauging events was 644.86 feet.
• GWA-21 D is screened from approximately 177.5 to 182.5 ft bgs in the deep flow layer
(approximately 494 to 489 feet elevation). The average groundwater elevation calculated from the
May and September 2016 gauging events was 637.29 feet.
• GWA-21 BR is screened from approximately 202 to 207 ft bgs in the bedrock flow layer
(approximately 470 to 465 feet elevation). The groundwater elevation calculated from the
September 2016 gauging event was 635.47 feet.
6

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• Note that monitoring well GWA-21 D is scheduled for reinstallation due to potential grout
contamination from when it was installed. pH values have exceeded 11 SU during the March,
May, and September 2016 sampling events.
• For GWA-21S and GWA-21 BR, 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 approximately two orders of magnitude less than the
2L Standard.
• For GWA-21 D, 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. TDS was reported at concentrations that are elevated compared to other deep flow
layer background wells that are not impacted by grout, and is likely due to the grout
contamination.
• Monitoring wells AB-4S/D/BR are located between the GWA-21 well cluster and the closest ash
basin surface water. As described above, there are no indications of impacts from the ash basin
at AB -4 and the well cluster should be considered upgradient and a background monitoring well
location relative to the ash basin.
Based on the justification provided above, groundwater passing through monitoring well GWA-21 S/D/BR
originates upgradient and west of the ash basin system, and is not impacted by the ash basin system.
Therefore, groundwater samples collected from GWA-21 S and GWA-21 BR represent background water
quality relative to the Allen ash basin system and have been included in the valid background sample
counts. Following reinstallation of GWA-21 D and sampling, field parameters and analytical results will be
evaluated before considering GWA-21 D as a background well.
GWA-23S
Monitoring well GWA-23S was installed onsite and west of the active ash basin in January 2016 to further
evaluate groundwater quality and flow characteristics between the ash basin and offsite properties to the
west. This well was first sampled in February 2016 and then again during site -wide sampling events in
May and September 2016. To confirm groundwater elevations compared to the ash basin, groundwater
elevations from May and September 2016 were reviewed.
• Monitoring well GWA-23S is located in the vicinity of a topographic high and approximately 430
feet north of the southwestern portion of the active ash basin.
• The ground surface elevation at GWA-23S is approximately 667 feet, approximately 22 feet
higher than the closest point of the ash basin waste boundary (645 feet).
• The closest ash basin surface water elevation has historically been approximately 636.5 feet, in
the southwest portion of the active ash basin.
• GWA-23S is screened from approximately 20 to 35 ft bgs in the shallow flow layer (approximately
647 to 632 feet elevation). The average groundwater elevation calculated from the May and
September 2016 gauging events was 639.10 feet.
• 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 approximately two orders of magnitude less than the 2L Standard.
Based on the justification provided above, groundwater passing through monitoring well GWA-23S
originates upgradient of the active ash basin and is not impacted by the ash basin system. Therefore,
7

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groundwater samples collected from GWA-23S represent background water quality relative to the Allen
ash basin system and have been included in the valid background sample counts.
GWA-26S and GWA-26D
Monitoring wells GWA-26S and GWA-26D were installed onsite between the BG -1 well pair and the
active ash basin in January 2016 to define groundwater flow direction and groundwater quality. These
wells were first sampled in February 2016 and then again during site -wide sampling events in May and
September 2016. To confirm groundwater elevations compared to the ash basin, groundwater elevations
from May and September 2016 were reviewed.
• Monitoring wells GWA-26S/D are located onsite along a topographic ridge approximately 700 feet
south of the active ash basin. In addition, GWA-26S/D are located between background wells
BG -1 S/D and the ash basin and compliance monitoring wells AB-12S/D.
• The ground surface elevation at GWA-26S/D is approximately 680 feet, approximately 38 feet
higher than the closest point of the ash basin waste boundary (642 feet).
• The closest ash basin surface water elevation has historically been approximately 636.5 feet, in
the southwest portion of the active ash basin.
• GWA-26S is screened from approximately 52 to 67 ft bgs in the shallow flow layer (approximately
627.5 to 612.5 feet elevation). The average groundwater elevation calculated from the May and
September 2016 gauging events was 641.17 feet.
• GWA-26D is screened from approximately 112 to 117 ft bgs in the deep flow layer (approximately
568 to 563 feet elevation). The average groundwater elevation calculated from the May and
September 2016 gauging events was 637.38 feet.
• 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 approximately two orders of magnitude less than the 2L Standard.
Based on the justification provided above, groundwater passing through monitoring wells GWA-26S/D
originates upgradient or side -gradient of the active ash basin, and is not impacted by the ash basin
system. Therefore, groundwater samples collected from GWA-26S/D represent background water quality
relative to the Allen ash basin system and have been included in the valid background sample counts.
8

Table 1. Background Monitoring Well Information
Allen Steam Station Ash Basin System
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Distance and Direction
Closest Ash
from Source Area
Ground
Elevation of
Basin
Groundwater
Elevation of
Surface
Surface
Screened
Well ID
Flow
Groundwater
Water
Groundwater Elevation Monitoring Events
Active
Elevation
Interval
Inactive
Direction
(feet BGS)
Elevation to
Ash
(feet)
(feet BGS)
Ash Basin
Well
Basin
(feet)
CAP Part 1 Established Background Monitoring Wells
1,275 feet
635.15
2015 - June, September, November December
BG -1 S
---
SE
692
643-628
636.5
SE
2016 - March, May, September
1,275 feet
2015 - June, September, November December
BG -1 D*
---
SE
692
578-573
635.22
636.5
SE
2016 - March, May, September
2,700 feet
2015 - June, September, November December
BG -3S
---
SE
672
602.5 - 587.5
606.48
636.5
NW
2016 - March, May, September
2,700 feet
2015 - June, September, November December
BG -3D
---
SE
672
574-579
606.53
636.5
NW
2016 - March, May, September
Proposed Additional Background
Monitoring Wells
AB -4S
80 feet N
---
E
648
638-623
638.08
636.5
2016 - May, September
2015 - September
AB -4D
80 feet N
---
E
647
600-595
637.30
636.5
2016 - May, September
AB-4BR
80 feet N
---
E
646
565.5-560.5
640.06
636.5
2016 - May, September
2015 - June, September
BG -2S
---
1,825 feet W
NW
641
588.5 - 573.5
589.58
636.5
2016 - May, September
2015 - June, September
BG -2D
---
1,825 feet W
NW
641
534-529
587.30
636.5
2016 - May, September
2015 - June, September
BG-2BR"
---
1,825 feet W
NW
641
506.5 - 501.5
573.06
636.5
2016 - May, September
BG -4S
---
1,900 feet N
S
659
581-566
638.08
641
2016 - March, May, September
BG -4D
---
1,900 feet N
S
659
553-548
637.3
641
2016 - March, May, September
BG-4BR
---
1,900 feet N
S
659
499-494
640.51
641
2016 - March, May, September
GWA-19S
---
700 feet W
NW
670
628-613
629.94
636.5
2016 - April, May, September
640 feet
GWA-21S
---
E
672
648-633
644.86
636.5
2016 May and September

Table 1. Background Monitoring Well Information
Allen Steam Station Ash Basin System
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Notes:
Elevations presented in North American Vertical Datum (NAVD) 88.
Groundwater elevations included are averaged from available groundwater elevation measurements from sampling/gauging events at the site.
Ash basin surface water elevations were provided by Duke Energy.
" indicates monitoring well is scheduled for replacement due to potential grout contamination.
10
Distance and Direction
Closest Ash
from Source Area
Basin
Ground
Elevation of
Groundwater
Elevation of
Surface
Surface
Screened
Well ID
Flow
Groundwater
Water
Groundwater Elevation Monitoring Events
Active
Elevation
Interval
Inactive
Direction
(feet BGS)
Elevation to
Ash
(feet)
(feet BGS)
Ash Basin
Well
Basin
(feet)
640 fleet
GWA-21 D*
---
E
672
494-489
637.29
636.5
2016 — May and September
NW
640 feet
GWA-21 BR
---
E
672
470-465
635.47
636.5
2016 - September
NW
GWA-23S
430 feet N
---
E
667
647-632
639.10
636.5
2016 — May and September
GWA-26S
700 feet S
---
NE
680
627.5 - 612.5
641.17
636.5
2016 — May and September
GWA-26D
700 feet S
---
NE
680
568-563
637.38
636.5
2016 —May and September
Notes:
Elevations presented in North American Vertical Datum (NAVD) 88.
Groundwater elevations included are averaged from available groundwater elevation measurements from sampling/gauging events at the site.
Ash basin surface water elevations were provided by Duke Energy.
" indicates monitoring well is scheduled for replacement due to potential grout contamination.
10

Table 2. Allen Steam Station Ash Basin System Background Groundwater Baseline Analytical Results

Table 2. Allen Steam Station Ash Basin System Background Groundwater Baseline Analytical Results
Red text'md,re samples that will not be used in datermining proposed provisional background threshold values (PPMs) due to pH > 8.5 or turbidity, 10 NM
Q - Bold highlighted c,nc,nVabon indict s mmd,nm of the lSA NaC 02L Sta,dard or IMAC, Appendix 2, April 1, 2013.
P
m -
pg/L =mmiaograms per liter
p5/cm = microsieens per centimeter
I- ee m
mgIL =milligrams per liter
Eh values were calculated by adding 200 mV W the field -measured ORP value. Depending on the feld meter used, Eh values calculated using this formula can vary by +/- 5 V.
mV =millivolts
NTU - nephelometric turbidity units
pCiVL = picocuries per liter
SU - standard unit
= laboratory esfimated concentration
]- = estimated concentuabon, biased low
)+ = estimated concentration, biased high
U = results not deteced at concentrafions which equal the laboratory's method reporting limit
02L = North Carolina groundwater standards as specifetl in TISA NCAC 02L
D = dissolved
Deg C = degree Celsius
DHHS = North Carolina Department of Health and Human Services
DO = dissolved oxygen
GW = groundwater
GWQS = groundwater quality standard
IMAC = Interim Maximum Allow Concentration
N = normal
NS = no standard
PPBC = Proposed Provisional Ba&ground Concentrations
T = total
TDS = total dissolve0 solids
TOC = total organic carbon
-BG-ID, 35-2BR, and GWA-21D are scheduled for replacement due to potential grout contamination
ISR. roil
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Red text'md,re samples that will not be used in datermining proposed provisional background threshold values (PPMs) due to pH > 8.5 or turbidity, 10 NM
Q - Bold highlighted c,nc,nVabon indict s mmd,nm of the lSA NaC 02L Sta,dard or IMAC, Appendix 2, April 1, 2013.
P
m -
pg/L =mmiaograms per liter
p5/cm = microsieens per centimeter
I- ee m
mgIL =milligrams per liter
Eh values were calculated by adding 200 mV W the field -measured ORP value. Depending on the feld meter used, Eh values calculated using this formula can vary by +/- 5 V.
mV =millivolts
NTU - nephelometric turbidity units
pCiVL = picocuries per liter
SU - standard unit
= laboratory esfimated concentration
]- = estimated concentuabon, biased low
)+ = estimated concentration, biased high
U = results not deteced at concentrafions which equal the laboratory's method reporting limit
02L = North Carolina groundwater standards as specifetl in TISA NCAC 02L
D = dissolved
Deg C = degree Celsius
DHHS = North Carolina Department of Health and Human Services
DO = dissolved oxygen
GW = groundwater
GWQS = groundwater quality standard
IMAC = Interim Maximum Allow Concentration
N = normal
NS = no standard
PPBC = Proposed Provisional Ba&ground Concentrations
T = total
TDS = total dissolve0 solids
TOC = total organic carbon
-BG-ID, 35-2BR, and GWA-21D are scheduled for replacement due to potential grout contamination
ISR. roil

NOTES:
1. WASTE BOUNDARY AND ASH STORAGE AREA BOUNDARIES ARE APPROXIMATE
2. THE COMPLIANCE BOUNDARY IS ESTABLISHED ACCORDING TO THE DEFINITION FOUND IN SCALE (FEET)
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
ALLEN STEAM STATION ASH BASIN
GASTON COUNTY, NORTH CAROLINA
DATE
DECEMBER 2016
FIGURE