Marshall Pumping Test Work Plan Response to Comments_05 24 18

TECHNICAL MEMORANDUM

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Work Plan Response to Comments TM.docx
Date: 5/24/2018 File: 1026.18
To: John Toepfer
Cc: Tyler Hardin, Courney Murphy, Kathy Webb, Chris Bruce
From: Brian Wilker, NC L.G.
Subject: Response to NCDEQ MRO Comments to the Marshall Steam Station
Pumping Test Work Plan
This Technical Memorandum summarizes SynTerra’s responses to NCDEQ MRO’s
comments to the Pumping Test Work Plan (Work Plan). This memorandum is
accompanied by a revised work plan reflecting the changes discussed in SynTerra’s
responses below.
NCDEQ Comment 1 - Can Duke use the same naming convention that was used for Allen so
that there is no confusion due to wells having the same nomenclature?
SynTerra’s Response – Yes. The Work Plan text, tables, and figures have been
updated to accommodate this request.
NCDEQ Comment 2 - Why were observation wells installed 30 ft. away at the AB-12 and AB-
18 well clusters, but not at the AB-15 well cluster? Why is there not a consistent approach to
each well cluster?
SynTerra’s Response - At the AB-12, AB-15 and AB-18 locations, a combination
of newly installed and existing wells will be used for the 30-ft observation points
(Table 1). The Work Plan text has been modified to help clarify this.
NCDEQ Comment 3 - Figure 3 shows extracted groundwater being discharged to the
south/southeast of the AB-12 well cluster which is downgradient; however, MRO requests
groundwater extracted from the AB-12 well cluster be discharged in the canal to the
east/northeast which is about the same distance as what was proposed and would greatly reduce
the potential for test interference during the pumping tests.
SynTerra’s Response - Figure 3 of the Work Plan has been modified to show the
planned discharge line extending towards the requested area. An attempt will be
made to meet this request, however, it should be noted the area between AB-12
wells and the canal to the east/northeast is inundated and typically contains
Response to NCDEQ’s Comments to the Pumping Test Work Plan May 24, 2018
Duke Energy Carolinas, LLC, Marshall Steam Station SynTerra
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Work Plan Response to Comments TM.docx
ponded water and tall grasses. It may not be physically feasible or safe to
traverse these areas.
NCDEQ Comment 4 - Figure 4 shows extracted groundwater being discharged to the
north/northeast of the AB-15 well cluster; however, MRO requests that a holding tank be
utilized at the AB-15 well cluster to eliminate the potential for test interference during the
pumping tests.
o Please provide information regarding handling/disposal plan for groundwater
extracted at AB-15 well cluster.
SynTerra’s Response – The Work Plan text and Figure 4 have been modified to
reflect the use of three frac tanks (21,000 gallons per tank) for containment of
pumping test discharge at the AB-15 location. At the completion of the test, the
water will be discharged to the ground surface.
NCDEQ Comment 5 - Please ensure any extracted groundwater that is proposed to be
discharged to the ash basin is done so in compliance with the existing NPDES permit (please
coordinate as appropriate with the NPDES permitting group).
SynTerra’s Response – A Duke Energy letter dated May 3, 2018 (Baker to
Poupart) notified NCDEQ of the planned pumping tests. NCDEQ responded to
the letter on May 4, 2018 with an email from Poupart to Baker, et al., that stated
“We concur with your letter of May 3 that water from well tests can be pumped to the
ash basins as described as the volumes are minor in comparison to overall system flow
and the water is originating from under or groundwater directly adjacent to the ash basin
and not expected to cause exceedance of NPDES permit limits or water quality standards
in receiving stream.”
NCDEQ Comment 6 - It was stated in the work plan that water-quality samples would be
collected daily. MRO requests pre-pump test sampling be conducted at each pumping well prior
to commencement of the pump testing.
SynTerra’s Response – The Work Plan text has been modified to include the
collection of a groundwater sample from each of the pumping wells prior to the
start of the step test at each location.
NCDEQ Comment 7 - Why was it not proposed to monitor the all deep and bedrock flow layers
within the observation area (AB-12BR, AB-15BR, and AB-18D)? This could provide valuable
information regarding interconnectivity of flow layers, etc.
Response to NCDEQ’s Comments to the Pumping Test Work Plan May 24, 2018
Duke Energy Carolinas, LLC, Marshall Steam Station SynTerra
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Work Plan Response to Comments TM.docx
SynTerra’s Response - Based on the planned duration of pumping tests and
anticipated conductivity/transmissivity of the ash and saprolite (less than 15 gpm
in the ash and less than 5 gpm in the saprolite, as indicated by well
development), it is not anticipated that drawdown will extend vertically to
depths monitored by the transition zone or bedrock. However, SynTerra will
manually measure water levels in the transition zone and bedrock at pumping
test locations every 2 hours during the constant rate pumping test. The Work
Plan text and tables have been modified accordingly.
NCDEQ Comment 8 - Also, why was it not proposed to monitor other wells in the
shallow/deep/bedrock flow layers near the observation area (AB-10D/BR, AB-9S/D/BR, AB-
8S/D, AB-13D, AB-16S/D)?
SynTerra’s Response - Similarly as discussed above, based on duration of aquifer
test and anticipated conductivity/transmissivity of the ash and flow rates (less
than 15 gpm in the ash and less than 5 gpm in the saprolite as indicated by well
development), it is not anticipated that drawdown will extend laterally to the
wells mentioned in the comment. However, SynTerra will manually measure
water levels every 2 hours during certain pumping tests as indicated in Table 2.
The Work Plan text and tables have been modified accordingly.
NCDEQ Comment 9 - Please ensure during the pump test that manual readings are collected as
indicated in the work plan at 2 hour intervals during active pumping.
SynTerra’s Response - Water levels at the pumping test well cluster location will
be recorded every 2 hours for the duration of the aquifer test (Table 2).
NCDEQ Comment 10 - What is the estimated amount of groundwater to be extracted during the
pump tests?
o Per 15A NCAC 02C .0105, any water-well or well system with a design capacity
of 100,000 gpd or greater requires issuance of a permit.
SynTerra’s Response - Based on well development records for AB-12, AB-15 and
AB-18 the ash pumping wells will produce sustained yields of less than 15 gpm
(less than 21,600 gallons per day from each well each). Well AB-18 saprolite
pumping well will produce a sustained yield of less than 5.0 gpm (less than 7,200
gallons per day). Since the anticipated yields do not encroach upon the capacity
threshold triggering a permit requirement, a request for permit is not planned.