Weatherspoon - Tech Memo FINAL 05262017_20170526

synTerra
TECHNICAL MEMORANDUM
Date: May 26, 2017 File: 1026.109.26
To: Ryan Czop (Duke Energy)
Cc: Kathy Webb (Syn era
From: Ted Volsk —/
Subject: Background Groundwater Data Update — W.H. Weatherspoon Plant
The North Carolina Department of Environmental Quality (NCDEQ) provided a response letter
(Zimmerman to Draovitch, April 28, 2017) to the technical memorandum titled Statistical
Methods for Developing Reference Background Concentrations for Groundwater and Soil at Coal Ash
Facilities (HDR Engineering, Inc. and Synterra Corporation, January 2017) requesting the following
technical issues be addressed in order to progress site assessments and corrective actions:
47 Collect a minimum of ten valid background groundwater samples, opposed to eight,
prior to the determination of background threshold values (BTVs) for constituents in
each flow zone; and
41, Provide updated spreadsheets of background groundwater data for each facility.
NCDEQ requests that the updated background data spreadsheets contain strike-throughs of
data that may be omitted from the background dataset due to one or more of the following
conditions:
41, Sample pH is greater than or equal to 8.5 standard units (S.U.);
4� Sample turbidity is greater than or equal to 10 Nephelometric Turbidity Units (NTUs);
,611 Result is a statistical outlier identified for background sample data collected through
March 2017;
41, Sample collection occurred less than a minimum 60 days between sampling events; and
,611 Non -detected results are greater than 2L/IMAC.
Table 1 provides a summary of existing background well data for each flow zone and indicates
which samples are considered for use in statistical calculations to determine concentrations of
naturally occurring (background) inorganic constituents in groundwater. Sample results
designated as statistical outliers or were collected less than 60 days between sampling events
are identified in Table 1. The following discussion quantifies the number of valid results
collected through January 2017 within each flow zone. Groundwater sampling was recently
completed in April 2017. The April 2017 results will augment the dataset provided herein, when
the data is received.
P:\Duke Energy Progress.1026\Statistics_CAMA\May 26 2017 - Updated Background Data
Spreadsheets for NCDEQ\Tech Memo - Response to NCDEQ 04282017 Letter\Final\Weatherspoon
Tech Memo 05262017.docx

Background Groundwater Data Update May 19, 2017
W. H. Weatherspoon Power Plant Page 2 of 3
BACKGROUND WELL NETWORK
The current background groundwater monitoring well network consists of wells installed
within three flow zones: surficial (upper unconfined), Lower Yorktown formation (lower
unconfined), and Pee Dee (first confined).
SURFICIAL GROUNDWATER
Five background monitoring wells (BW-2S, BW-3S, MW-1, and CCR-101-BG) are screened
within the surficial (upper unconfined) flow zone. The surficial background groundwater
dataset satisfies the requirements for the minimum number of ten samples to conduct statistical
analysis for each constituent.
LOWER YORKTOWN GROUNDWATER
Two background monitoring wells (BW-2I and BW-31) are screened within the Lower Yorktown
(lower unconfined) flow zone. Sampling of well BW-2I has yet to yield results associated with a
turbidity less than or equal to 10 NTUs; therefore, no valid samples have been collected from
this well.
Lower Yorktown background monitoring monitoring well BW-3I has been sampled 19 times
since March 2015. Seven of the sampling events satisfy criteria for dataset incusion except for
the 60 day minimum period between sampling events to address potential autocorrelation. Five
sampling events satisfy criteria for dataset incusion and the 60 day minimum between sampling
events. An analysis of the two potentially autocorrelated datasets is recommended to
determine if they are sufficient to perform statistical calculations.
Outlier analysis identified one of the five analytical results for arsenic and one of the five
analytical results for nitrate/nitrite to be outliers. Consequently, six additional sampling events
are needed to meet the minimum of 10 valid samples for each constituent to conduct statistical
analysis. The projected timeframe to collect ten valid samples for every constituent is third
quarter, 2018. Subsequent outlier screening of the Yorktown Formation background dataset
may warrant additional sample collection.
PEE DEE GROUNDWATER
Two background monitoring wells (BW-2D and BW-3D) are screened within the Pee Dee zone.
Sampling of BW-2D was ceased June 3, 2015 due to apparent grout contamination (pH >8.5
S.U.) and is not viable for sample collection. No valid were previously collected prior to
ceasation of BW-2D sampling.
Pee Dee background monitoring monitoring well BW-3D has been sampled 12 times since
March 2015. Ten of the sampling events satisfy criteria for dataset incusion except for the 60
day minimum period between sampling events to address potential autocorrelation. Eight
sampling events satisfy criteria for dataset incusion and the 60 day minimum between sampling
events. An analysis of the two potentially autocorrelated datasets is recommended to
determine if they are sufficient to perform statistical calculations.
P:\Duke Energy Progress.1026\Statistics_CAMA\May 26 2017 - Updated Background Data
Spreadsheets for NCDEQ\Tech Memo - Response to NCDEQ 04282017 Letter\Final\Weatherspoon -
Tech Memo 05262017.docx

Background Groundwater Data Update May 19, 2017
W. H. Weatherspoon Power Plant Page 3 of 3
Analysis for radiological parameters was not initiated until March 2016 and outlier analysis
identified one of the five analytical results for radium-228 to be an outlier. Conseequently, six
additional sampling events are needed to meet the minimum of 10 valid samples for each
constituent to conduct statistical analysis. The projected timeframe to collect ten valid samples
for every constituent is third quarter, 2018. Subsequent outlier screening of the Pee Dee
background dataset may warrant additional sample collection.
ATTACHMENTS: Table 1: Background Analytical Results through March 2017
P:\Duke Energy Progress.1026\Statistics_CAMA\May 26 2017 - Updated Background Data
Spreadsheets for NCDEQ\Tech Memo - Response to NCDEQ 04282017 Letter\Final\Weatherspoon -
Tech Memo 05262017.docx