2019_07_31 Riverbend Station Response to July 25 2019 Letter

�•� DUKE
ENERGY®
CAROLINAS
July 31, 2019
Jon Risgaard, Chief
Animal Feeding Operations and Groundwater Section
North Carolina Department of Environmental Quality
512 North Salisbury Street
Office 640Y
Raleigh, NC 27604
Subject: Response to DEQ Comments on CCR Visual Removal Verification Report
Riverbend Steam Station
Dear Mr. Risgaard:
526 South Church Street
Mail Code EC3XP
Charlotte, NC 28202
Duke Energy is in receipt of your letter dated July 25, 2019 regarding Confirmation of
Excavation Requirements for the Riverbend Ash Basins. The letter requests clarification
regarding certain documents contained in the CCR Visual Removal Verification Report
Riverbend Steam Station, Gaston County, North Carolina Duke Energy submitted on April 18,
2019. Based upon discussion with personnel from the Division of Water Resources, Brandy
Costner and Joanna Harbison, and the Division of Waste Management, Elizabeth Werner, it is
Duke Energy's understanding that notwithstanding the clarification request, the North Carolina
Department of Environmental Quality (DEQ) confirmed that excavation requirements at the
Riverbend Steam Station Ash Basins under the Coal Ash Management Act (CAMA) have been
met and closure under NCGS 130A-309.214(a)(1) of these basins is complete.
The attached technical memorandum addresses the questions raised by DEQ in the July 25,
2019 letter. If you have questions on the enclosed information, please contact Bristol Grohol at
317-838-2719.
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Pau
Senior Vice President
Environmental, Health & Safety
cc (via email): Ed Mussler (NCDEQ)
Joanna Harbison (NCDEQ)
Brandy Costner (NCDEQ)
Elizabeth Werner (NCDEQ)
Ed Sullivan (Duke Energy)
John Toepfer (Duke Energy)

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Technical Memorandum
Date: July 30, 2019
To: Bristol Grohol, Duke Energy
From: Thomas Maier, Wood
Re: Responses to NCDEQ Comments on CCR Visual Removal Verification Report,
Riverbend Steam Station
The July 25, 2019 comments from the North Carolina Department of Environmental Quality
(NCDEQ) are repeated below followed by brief responses. Some of the responses reference
specific sampling locations. If NCDEQ has questions regarding additional locations, we can
address those in future correspondence or meetings.
Comment 1: The Polarized Light Microscopy sample number in the Verification Report data table
does not necessarily correspond to the sample results reported.
Response: The following needed corrections to PLM sample numbers in Table 2 are noted.
• The PLM sample numbers for grid location Z9 were mistakenly repeated from Q32 in
Table 2. The correct PLM sample numbers for Z9 are 2018031888 and 2018031889. The
PLM results for these samples are ND and ND (the same as reported on Table 2).
• The correct PLM sample numbers for grid location Z11 are 2018032022 and 2018032023
and the correct PLM results for these samples are 7% and 1%, respectively.
• The correct PLM sample number for the grid location BB29 deep sample is 2018039836.
The PLM result for this sample is ND (the same as reported on Table 2). Both BB29
samples (shallow and deep) were composite samples taken from material dumped from
an excavator bucket.
• For grid location BB31, only one sample (a composite sample from material dumped
from an excavator bucket) was obtained. The correct PLM sample number and result are
reported in the respective "Shallow" columns. However, values were also entered in the
respective "Deep" columns, which should be blank since there was only one sample
obtained.
Wood Environment & Infrastructure Solutions Inc.
2801 Yorkmont Road, Suite 100 Registered in North Carolina
Charlotte, North Carolina 28208 Engineering License No. F-1253
704-357-8600 Geology License No. C-247
woodplc.com

Response to NCDEQ Comments
Wood Project No. 7812190265
July 30, 2019
Additional discussion of samples obtained by excavator bucket rather than hand auger are
presented after Comment 5.
Comment 2: The rationale for resampling certain locations was not documented.
Response: Locations where additional material was excavated after sampling was performed
were resampled to document final post -excavation conditions, with the following three
exceptions. Locations J32 and J33 were sampled (shallow and deep) on 10/8/2018 and were
unnecessarily resampled (one composite sample each) on 10/31/2018 so there was ambiguity
regarding which round of sampling should be reported in Table 2. The four initial results were all
ND and the two composite resampling results were 1% and 8% respectively. After location CC11
was sampled on 10/4/2018, additional material was excavated in the vicinity so on 10/8/2018
samples were collected from 30 ft east and 42 ft east offset locations. One of these fourjars
broke on the way to the lab and was replaced by a sample collected on 10/15/2018. The result
from all six of the tested samples was ND.
Comment 3: Not all the sample results were reported for locations that were resampled.
Response: The purpose of the report is to document completion of CCR visual removal
verification (i.e., final post -excavation conditions). The photolog and report of visual
observations accomplish this purpose. The laboratory PLM testing results are supplementary
information. PLM test results not representative of final post -excavation conditions were not
included in Table 2 but were included in Attachment 3 of the Verification Report.
Comment 4: Samples were not consistently collected and/or documented above borehole refusal
as directed by the Surface Impoundment Closure Guidelines for Protection of Groundwater. In this
case, no rationale was provided to explain why there was deviation from the sampling strategy
outlined in the guidance.
Response: Section 3.1.3 of the Excavation Soil Sampling Plan states "deeper samples will be
collected... unless bedrock, refusal, or the water table are encountered." This guideline was
followed without deviation. If three hand auger offsets within a 10-foot radius from the original
point experienced shallow refusal then either "refusal" or "refusal due to rock" was noted (with
some variation in terminology and one occurrence of "refusal due to roots"). The guidelines do
not require that the object causing refusal be identified so the cause of refusal was not
investigated. Therefore, "refusal" should have been used consistently since "rock" was not
verified.
Comment 5: How discrete depth intervals (0 to 6-inches and 24 to 30-inches) were assigned to
composite samples that were collected by a 2-foot excavator bucket was not documented.
Response: Locations that were underwater or too soft to access on foot for hand augering were
sampled by obtaining a scoop of material approximately 2-feet deep using an excavator bucket.
The material was dropped by the excavator such that the deepest material was on top of the pile
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Response to NCDEQ Comments
Wood Project No. 7812190265
July 30, 2019
and the surficial material was on the bottom, so material obtained from the pile bottom was the
shallow sample and material from the pile top was the deep sample. If dark colored material was
present anywhere in the pile it was sampled and identified as a composite sample, since the
overarching goal is to identify if there is remaining CCR anywhere in the profile not just at
discrete intervals identified in the procedures document. If visually different dark materials were
present, this would be a reason to collect more than one composite sample.
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