NC0004987_Response to Notice_20220128

DUKE
E ER Y.
UPS GROUND DELIVERY
January 28, 2022
Mr. Corey Basinger, Supervisor
Mooresville Regional Office
Division of Water Resources
NC Department of Environmental Quality
610 East Center Avenue, Suite 301
Mooresville, NC 28115
Marshall Steam Station
8320 East NC hway 50
fECEIVED/NCDE IW , rOc 28682
JAN 3 1 1K
WORDS
MOORESVILLE REGIONAL OFFICE
Subject: Marshall Steam Station
Inadvertent Release of Submerged Flight Conveyor (SFC) Bottom Ash Transport Water
Analytical Results from Sampling Activities
NPDES Permit No. NC0004987
Catawba County
Dear Mr. Basinger:
In accordance with our letter dated January 7, 2022, Duke Energy committed to collecting and analyzing
samples for Outfall 002, the Ash Basin (Evoqua Treatment System Influent) and the transport water
associated with the Bottom Ash Recycle System Sump. Analytical results have been received and are
provided in Table 1 below.
Table 1 - Analytical Results from Sampling Activities
Parame`
Flow, MGD
0.62
ash Basin
Evoqua
nfluent)
NA
NA
pH
Turbidity, NTU
Total Hardness, mg/L
Calcium, mg/I
7.8
< 0.5
321
80.3
7.8
9.90
7.5
520
333 69.6
82.5 22.5
Magnesium, mg/I
Oil and Grease, mg/I
Total Suspended Solids, mg/I
Arsenic, ug/I
Boron, mg/I
29.3
< 5
< 2.5
4.28
2.88
30.9 3.26
< 5 <5
7.8 760
13.6 22.6
3.27 0.314
Bromide, mg/L
Chromium, ug/l
Copper, ug/l
Iron, mg/I
2.8
< 1
<2
0.039
2.7 < 1
< 1 19.1
< 2 19.9
0.502 10.0
Lead, ug/I
< 1
< 1 7.91

Mr. Corey Basinger, Supervisor
NC DEQ DWR MRO
Page 2
Table 1 (Continued) - Analytical Results from Sampling Activities
Mercury, ng/I
< 0.5
< 0.5
5.68
Nickel, ug/I
1.43
9.84
20.0
Selenium, ug/I
5.84
8.54
7.37
Zinc, ug/I
< 5
13.7
50.8
Nitrate/nitrite as N, mg/L
0.076
0.11
0.28
Nitrogen, Kjeldahl, Total (TKN) mg/I
< 0.50
0.57
< 0.5
Total Nitrogen (NO2+NO3+TKN), mg/L
< 0.50
0.68
< 0.5
Total Phosphorus, mg/L
< 0.050
< 0.05
0.22
Chronic Toxicity
PASS
NA
NA
The transport water characteristics of the SFC Sump are not substantially different from characteristics
observed in the Ash Basin. It should be noted that the sump samples were taken following the storm event
(during normal operations) which contributed to the sump overflow event and would have contributed to a
substantial amount of stormwater to the release. The Ash Basin's significant hydraulic capacity provided
ample buffering capacity for this inadvertent release. Effluent produced by the Ash Basin's treatment
system (Evoqua Advanced Treatment System) clearly shows the effectiveness of producing a high quality
effluent which meets the effluent limitations associated with Outfall 002 of NPDES Permit No. NC0004987.
Upon further review of our January 7, 2022 response to this inadvertent release, we wanted to provide
more detail to the question regarding reliability aspects and the Bottom Ash Recycle System Sump:
Please explain details of the sump / pump arrangement as well as high water alarms or
other system reliability aspects.
The SFC receives bottom ash from all four unit boilers at Marshall Steam Station via a wet sluice
conveyance process. The bottom ash is separated from the conveyance water inside three drag chain
conveyor systems (or trains). The water is then transferred from the train to a surge tank before it is
returned to the boilers for reuse. Both the surge tank and conveyor trains are inside a concrete
containment with a central sump (with duplicate pumps) that is used to pump collected ash contact water
and storm water to the surge tank. The sump level is monitored electronically, and a high-level alarm
would be received by the operations control room monitor for notification. As a contingency, a large
maintenance tank was also installed during SFC construction that would allow surplus accumulated
stormwater to be stored for equalization back into the bottom ash water system. A high -high alarm was
programmed to notify the control room of the increased water level and to electronically reroute the sump
water to the maintenance tank. Prior to the inadvertent release on January 3, the control room had
confirmed receipt of the high -high alarm and notification that the sump water was directed to the
maintenance tank as designed. It was later determined that sediment internal to the maintenance tank
pipe was plugging the discharge of the inlet piping preventing the sump pumps from removing the water
from the containment resulting in the overflow and inadvertent release.
We trust you find this information sufficient to address any concerns which may have been associated with
this inadvertent release. Duke Energy continues to believe appropriate actions have been taken to properly
manage this release and Duke Energy has not observed any adverse environmental impacts within the
affected area. We believe the SFC Sump and Ash Basin characteristics are similar in nature and
compliance with the effluent requirements associated with NC0004987 Outfall 002 demonstrate the Evoqua
treatment system is functioning well to protect the receiving stream (Catawba River; Lake Norman).

Mr. Corey Basinger, Supervisor
NC DEQ DWR MRO
Page 3
If you have any questions or wish to discuss in further detail, please contact Mr. Scott LaSala, Marshall Site
Environmental Professional or Mr. Don Safrit, P.E., Lead Environmental Specialist at [phone].
Sincerely,
Jeff Pahagan, Plant Manager
Marshall Steam Station
cc: Mr. Wes Bell, NC DEQ DWR MRO
Mr. Scott LaSala, Marshall Site Environmental Professional
Mr. Don Safrit, P.E., Duke Energy Permitting & Compliance