Cape Fear BG GW FINAL Dec 2016 Part 1

TECHNICAL MEMORANDUM
Date: December 15, 2016 File: 1026.103.19
To: John Toepfer (Duke Energy)
Cc: Kathy Webb (SynTe a)
From: Chris Suttell
Subject: Quantification of �ialid Background Groundwater Data and Recommendation
of Additional Background Wells - Cape Fear Steam Electric Plant
Proposed Preliminary Background Threshold Values (PPBTVs) for groundwater will be
calculated for CAMA assessment constituents identified with concentrations greater than the 2L
or IMAC at the Cape Fear Steam Electric Plant (Site). A summary of background well analytical
results was originally presented in the Cape Fear Corrective Action Plant Part 1 submitted on
December 1, 2015 and updated in the CSA Supplement 1, submitted September 15, 2016. The
attached tables discussed below summarize existing background well data through August
2016 for each flow system and indicates which samples are considered for use in statistical
calculations to determine concentrations of naturally occurring (background) inorganic
constituents in groundwater. One additional sampling event was conducted in the fourth
quarter of 2016 that can be used to augment the dataset provided herein. The following
discussion quantifies the number of valid results to date within each flow zone and provides
justification for including monitoring wells BGMW-4, BGTMW-4, and MW-15SU and adding
the MW -20 well cluster as a background location within the evaluation of PPBTVs at the Site.
BACKGROUND WELL DATA ANALYSIS
The current background monitoring well network consists of wells installed within two flow
zones; surficial and bedrock, as shown on the attached Figure 1. Unconsolidated alluvium
comprises most of the surficial monitoring zone above the bedrock monitoring zone. Fine
grained alluvial deposits (typically clay & silt) comprise the "upper surficial" subgroup which
overlies coarser grained alluvial deposits (typically sands and gravels) that consist of the 'lower
surficial" subgroup. Bedrock consists of mudstone and sandstone. Wells BGMW-4 and
BGTMW-4 are the National Pollution Discharge Elimination System compliance background
wells. Wells considered to represent background for CAMA are installed in the upper and
lower surficial zone and within mudstone and sandstone bedrock as follows:
0 SURFICIAL - BGMW-4 (upper), MW-15SU (upper), MW-15SL (lower), MW -16S (lower),
and MW -20S (lower)
y BEDROCK - BGTMW-4 (mudstone), MW -9 (mudstone), MW-9BR (sandstone), MW-
15BR (mudstone), MW -16 (sandstone), and MW-20BR (mudstone)
P: \ Duke Energy Progress.1026 \ 103. Cape Fear Ash Basin GW Assessment \ 19.EG_CSASUP \ Background \ GW \ Cape
Fear TM BG GW Thru 2016-08.docx

Quantification of Valid Background Groundwater Data December 15, 2016
Cape Fear Steam Electric Plant Page 2 of 5
Samples from these wells must meet the following criteria to be considered valid for
determining PPBTVs:
y Sample pH is less than or equal to (<) 8.5 standard units (S.U.);
�7 Sample turbidity is less than or equal to (<) 10.0 Nephelometric Turbidity Units (NTUs);
and
10 Result is not a statistical outlier identified for background sample data collected through
April 2016 (SynTerra, September 15, 2016; CSA Supplement 1).
Professional judgement can be used to retain data that does not meet these criteria (such as pH);
however, the decision to retain data that does not satisfy these criteria must be documented.
For Cape Fear background locations, only an evaluation with pH <8.5 S.U. was conducted due
to the limited occurrence of groundwater with pH between 8.5 and 9.0 S.U.
RECOMMENDATION OF ADDITIONAL BACKGROUND WELLS
NCDEQ has indicated that wells BGMW-4/BGTMW-4 be excluded from use in determining
background groundwater quality due to potential offsite influence on groundwater quality.
This well cluster is located in an area likely downgradient of at least one manufacturing facility,
so there is potential for these wells to be impacted by offsite sources. However, analytical
results indicate that constituent concentrations at this well cluster are generally and routinely
within the range of background concentrations observed in other background wells located
elsewhere at the Site with potential exceptions for hexavalent chromium and iron. Therefore,
these wells should be re-evaluated for use as background wells and future statistical analyses
will consider the potential for anthropogenic influence. If the evaluation finds that the wells are
influenced by anthropogenic sources, the data will not be used to calculate PPBTVs.
NCDEQ has also indicated that MW-15SU be excluded for use in determining background
groundwater quality due to elevated turbidity. Turbidity has been elevated during at least one
sampling event and those results will not be, and have not been, used in statistical evaluations.
Turbidity has been less than 10 NTUs in this well during several other sampling events.
Therefore, data from this well should be re-evaluated and used to determine background
groundwater quality as long as results meet the criteria discussed above. If the evaluation finds
that the well is influenced by anthropogenic sources, the data will not be used to calculate
PPBTVs.
While evaluating the background data set, sample results from wells within the MW -20 cluster
were found to exhibit background water quality characteristics and are recommended for
inclusion within the determination of PPBTVs. Figures 1-65 and 1-66 (attached) from the CSA
Supplement 1 indicate the MW -20 cluster is side -gradient of the 1970 ash basin. Analytical
results indicate the ash basins have not affected groundwater quality in either well MW -20S or
MW-20BR as coal combustion residual indicator parameters have not been detected (boron) or
detected at levels much less than the 2L (sulfate) and other constituents concentrations, if
detected, are similar to those detected at other background locations. Furthermore, a sentinel
P: \ Duke Energy Progress.1026 \ 103. Cape Fear Ash Basin GW Assessment \ 19.EG_CSASUP \ Background \ GW \ Cape
Fear TM BG GW Thru 2016-08.docx

Quantification of Valid Background Groundwater Data December 15, 2016
Cape Fear Steam Electric Plant Page 3 of 5
well (MW -13) exists between the 1970 basin and the MW -20 cluster. Analytical results from
MW -13 indicate minimal to no significant influence from the ash basin on groundwater quality
at that well as only hexavalent chromium, manganese, and vanadium have been detected more
than one time at concentrations slightly greater than applicable regulatory levels. This indicates
any potential influence the 1970 ash basin may have on groundwater quality is limited to an
area that may not extend beyond MW -13. Therefore, groundwater at the MW -20 cluster may
represent naturally occurring conditions south of the 1963/1970/1978 ash basins and along the
Cape Fear River and the location is recommended for use as a background well location.
Additional review of the use of the MW -20 cluster as background will be performed. If the
evaluation finds that the wells are influenced by the 1970 ash basin or other anthropogenic
sources, the data will not be used to calculate PPBTVs.
SURFICIAL BACKGROUND DATASET SUMMARY
Table 1a presents analytical results from surficial zone background wells MW-15SL and MW -
16S and excludes wells BGMW-4 and MW-15SU called into question by NCDEQ and well MW -
205, not previously considered a background location. This limited surficial background
groundwater dataset satisfies the requirements for the minimum number of samples to conduct
statistical analysis by the end of 2016 for each constituent with the exception radium and
uranium radionuclides (6 samples for each). Sufficient samples to bring the total to a minimum
of eight for radionuclides have already been collected as an additional sampling event has
already occurred in the fourth quarter of 2016 which is not accounted for on the attached tables.
Table 1b presents analytical results from additional wells (BGMW-4, MW-15SU, and MW -20S)
which may represent surficial zone background groundwater quality. This expanded dataset
satisfies the requirements for the minimum number of samples to conduct statistical analysis by
the end of 2016 for each constituent.
Using the expanded surficial groundwater dataset which incorporates the additional
background wells (BGMW-4, MW-15SU and MW -20S), data from the surficial zone can be
divided into subgroups. As discussed in the CSA Supplement 1 (SynTerra, September 2016),
preliminary analysis of available data indicates there may be a notable difference in naturally
occurring groundwater chemistry between the upper and lower surficial zone but results have
been inconclusive as no clear trends have been established. Future evaluations will include
analysis of these subgroups as divided on Table 1c and Table 1d to determine if there is a
significant difference in groundwater quality between the two zones.
Table 1c presents data from each well that may represent background groundwater quality in
the upper surficial zone. This upper surficial groundwater data set satisfies the requirements
for the minimum number of samples to conduct statistical analysis by the end of 2016 for each
constituent with the exception of hexavalent chromium (7 samples), and radium and uranium
radionuclides (5 samples for each). For hexavalent chromium, sufficient samples have already
been collected as a result of recently completed fourth quarter 2016 sampling. For
P: \ Duke Energy Progress.1026 \ 103. Cape Fear Ash Basin GW Assessment \ 19.EG_CSASUP \ Background \ GW \ Cape
Fear TM BG GW Thru 2016-08.docx

Quantification of Valid Background Groundwater Data December 15, 2016
Cape Fear Steam Electric Plant Page 4 of 5
radionuclides, sufficient samples are projected to be collected by the end of the first quarter of
2017.
Table 1d presents data from each well that may represent background groundwater quality in
the lower surficial zone. This lower surficial groundwater data set satisfies the requirements for
the minimum number of samples to conduct statistical analysis by the end of 2016 for each
constituent with the exception of radium and uranium radionuclides (6 samples for each).
Sufficient samples to bring the total to a minimum of eight for radionuclides have already been
collected as an additional sampling event has already occurred in the fourth quarter of 2016.
Surficial groundwater samples eliminated from all background datasets include:
411 Elevated turbidity in one sample at BGMW-4, MW-15SL, and MW-15SU.
BEDROCK BACKGROUND DATASET SUMMARY
Table 2a presents analytical results from bedrock background wells MW -9, MW-9BR, MW-
15BR and MW-16BR and excludes well BGTMW-4 called into question by NCDEQ, and well
MW-20BR, not previously considered as a background location. This limited bedrock
background groundwater dataset satisfies the requirements for the minimum number of
samples to conduct statistical analysis by the end of 2016 for each constituent.
Table 2b presents groundwater analytical results from additional wells (BGTMW-4 and MW-
20BR) that may represent bedrock background groundwater quality. This expanded dataset
satisfies the requirements for the minimum number of samples to conduct statistical analysis by
the end of 2016 for each constituent.
Using the expanded surficial groundwater dataset which includes wells BGTMW-4 and MW-
20BR, data from the surficial zone can be divided into subgroups. As discussed in the CSA
Supplement 1 (SynTerra, September 2016), preliminary analysis indicates there may be a
statistically significant difference in naturally occurring mudstone and sandstone groundwater
chemistry. Future evaluations will include an analysis of these subgroups as divided on Table
2c and Table 2d to determine if there is a significant difference is maintained in groundwater
quality within the two bedrock types.
Table 2c presents data from each well that may represent background groundwater quality in
mudstone bedrock. This mudstone bedrock groundwater data set satisfies the requirements for
the minimum number of samples to conduct statistical analysis by the end of 2016 for each
constituent.
Table 2d presents data from each well that may represent background groundwater quality in
sandstone bedrock. This sandstone bedrock groundwater data set satisfies the requirements for
the minimum number of samples to conduct statistical analysis by the end of 2016 for each
constituent with the exception of radium and uranium radionuclides (7 samples). Sufficient
samples to bring the total to a minimum of eight for radionuclides have already been collected
P: \ Duke Energy Progress.1026 \ 103. Cape Fear Ash Basin GW Assessment \ 19.EG_CSASUP \ Background \ GW \ Cape
Fear TM BG GW Thru 2016-08.docx

Quantification of Valid Background Groundwater Data December 15, 2016
Cape Fear Steam Electric Plant Page 5 of 5
as an additional sampling event has already occurred in the fourth quarter of 2016 which is not
accounted for on the attached tables.
Bedrock groundwater samples eliminated from all background datasets include:
y Elevated turbidity in one sample at MW -9.
0 Elevated pH, observed during the first three sampling events at BGTMW-4.
ATTACHMENTS:
Figure 1: Well Location Map
Figure 1-65: Bedrock Water Level Map - July 2016
Figure 1-66: Surficial Water Level Map - July 2016
Table 1a: Surficial Groundwater Background Analytical Results Through August 2016 -
Excluding Wells BGMW-4, MW-15SU, and MW -20S
Table 1b: Surficial Groundwater Background Analytical Results Through August 2016 -
Including Wells BGMW-4, MW-15SU, and MW -20S
Table 1c: Upper Surficial Groundwater Background Analytical Results Through August
2016
Table 1d: Lower Surficial Groundwater Background Analytical Results Through August
2016
Table 2a: Bedrock Groundwater Background Analytical Results Through August 2016 -
Excluding Wells BGTMW-4 and MW-20BR
Table 2b: Bedrock Groundwater Background Analytical Results Through August 2016 -
Including Wells BGTMW-4 and MW-20BR
Table 2c: Mudstone Bedrock Groundwater Background Analytical Results Through August
2016
Table 2d: Sandstone Bedrock Groundwater Background Analytical Results Through August
2016
P: \ Duke Energy Progress.1026 \ 103. Cape Fear Ash Basin GW Assessment \ 19.EG_CSASUP \ Background \ GW \ Cape
Fear TM BG GW Thru 2016-08.docx