NCS000578_Supplemental Information Letter_20180119

q^ / DUKE
ENERGY®
1pEC
MAM
Suck Combined Cr.fe Plant
1385 Dukevflle Roao
Salisbury, NO 28146
[phone]
[phone] (fax)
January 10, 2018 1 19 2018
Mr. Rick Riddle
Environmental Engineer
NC Division of Water Resources
1617 Mail Service Center
Raleigh, NC 27699-1617
Re: NPDES Industrial Storm Water Permit Application Update
Duke Energy Carolinas, LLC.
Buck Combined Cycle and Buck Steam Station
Rowan County
Dear Mr. Riddle,
Duke Energy Carolinas, LLC (Duke) is submitting herewith two copies of supplemental information in
support of the NPDES Industrial Storm water permit update for the subject facility. This update is in
addition to the renewal application submitted September 29, 2014 and previous update submitted July 15,
2017(via email).
This submittal provides additional detail related to storm water outfalls and updated site information. We
do not anticipate the additions provided will result in any significant modifications of the future permit
but are providing these details so that the drainage areas and associated outfalls are clearly identified as
part of our application.
We appreciate your attention to these requests and look forward to finalizing the NPDES permit for Buck
in the near future. Should you have any questions regarding this letter or require additional information,
please contact Ms. Elizabeth Glenn at [phone] or at [e-mail].
"I certify, under penalty of law, that this document and all attachments were prepared under my
direction or supervision in accordance with a system designed to assure that qualified personnel
properly gather and evaluate the information submitted. Based on my inquiry of the person or
persons who manage the system, or those persons directly responsible for gathering the
information, the information submitted is, to the best of my knowledge and belief, true, accurate,
and complete. I am aware that there are significant penalties for submitting false information,
including the possibility of fines and imprisonment -for knowing violations. "

Sincerely .
Henry Botkins
General Manager Buck Combined Cycle
Enclosures
Certified Mail: 7017 0660 0000 6105 7857

Duke Energy cc:
Henry Botkins
Dale Wooten
Max Gardner
Tom Leap
Richard Baker via email
Elizabeth Glenn/Filenet

BUCK STEAM STATION
Stormwater Discharge Permit Application
Form 2F Supplemental Information
NPDES Permit #NC0004774
January 2018

GENERAL SITE INFORMATION
Buck Steam Station is a previously active fossil -fueled, electric generation plant located
in Rowan County approximately three miles east of Spencer, North Carolina. The
station has six retired coal-fired generation units that are in the process of being
decommissioned. The original two coal-fired units (Units 1 and 2) were put into service
in 1926. Units 3 and 4 were retired in mid -2011, and Units 5 and 6 were retired in April
2013. The station also had three active oil or gas-fired combustion turbine units (Units 7,
8, and 9) that were retired in October 2012. The Buck Steam Station property
encompasses 643 acres that border the southern shore of the Yadkin River in the upper
reaches of High Rock Lake. The station is accessed from Dukeville Road off of Long
Ferry Road. The facility includes the Powerhouse and the former coal storage yard
located south of the Powerhouse that encompass approximately 8.5 acres; the Units 3
and 4 Switchyard located immediately east of the Powerhouse that encompasses 1
acre; and the Units 5 and 6 Switchyard located immediately southwest of the
Powerhouse that encompasses 1.3 acres. The facility also contains non -operational
coal unloading and handling structures, two warehouses, paved parking areas, rail lines,
paved roadways, and gravel surfaced roadways. The former coal-fired and oil -fired
station generation area encompasses approximately 50 acres. The station is currently
being decommissioned and most structures formerly associated with coal-fired and oil-
fired generation will be or are in the process of being demolished. The empty fuel oil
storage tank and associated fuel oil unloading station have been removed as pari of
decommissioning activities.
The facility also includes three active and interconnected ash basins (Cell 1, Cell 2, and
Cell 3) located generally southeast of the station Powerhouse. An additional
approximately 60 acres of stormwater runoff from certain station yard areas is also
routed to the yard sump and subsequently pumped to this ash basin system. Discharge
structures conveying stormwater runoff at Buck Steam Station include various
corrugated metal pipes (CMP), reinforced concrete pipes (RCP), and steel pipes.
Also located within the Buck Steam Station property boundary is the Buck Tie Station
and the Buck Combined Cycle (CC) Station. The Buck Tie Station is a large 230 kV and
110 kV regional substation facility located within the Buck Steam Station property
boundaries approximately 1,500 feet south and upgradient of the Powerhouse. This tie
station is a separate facility unassociated with any Buck Steam Station activities. The
Buck Combined Cycle (CC) station is a generation facility located south of the Buck Tie
Station that came online in late 2011. Similar to the tie station, the Buck CC is located
upgradient and is unassociated with any Buck Steam Station activities associated with
stormwater permitting. These areas have been included in the comprehensive site plan,
however, the associated basin outfalls are not part of this stormwater discharge permit
application narrative.
The Buck Steam Station maintains an up-to-date Spill Prevention Control and
Countermeasure (SPCC) Plan in place in accordance with the U.S. Environmental
Protection Agency (USEPA) Oil Pollution Prevention Regulation 40 CFR Part 112..
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STORMWATER OUTFALLS AND DRAINAGE AREA DESCRIPTIONS
Buck Steam Station has three NPDES process water outfalls summarized as follows:
• NPDES Outfall 001 — Once -Through Cooling Water
This discharge is a once -through non -contact cooling water (CCW) system which
condensed steam from the plant condensers when the station was active (This is
no longer generated). This discharge occurs directly to the Yadkin River.
• NPDES Outfall 002 - Ash Basin
This is the outflow from the ash settling basin system. The ash settling basins
are the repositories for waste ash sluiced from the station. Stormwater runoff
from the coal storage pile and from industrial use areas surrounding the
Powerhouse is routed into the station yard sump that subsequently pumps to the
ash basins. The ash basin system is also the repository for various wastewater
streams from the Buck CC.
• NPDES Outfall 002A --Yard Sump Overflow
Should the pumps in the Yard Sump lose power, experience a mec-lanical
failure, or become inundated during a large storm event, the sump would
overflow through a pipe into the Yadkin River. Overflow from this sump is not a
normal occurrence.
Buck Steam Station has 37 identified active stormwater outfalls (21 of which are
Powerhouse roof drains) that discharge to surface waters as part of this stormwater
discharge permit application narrative update. The outfall locations and contributing
drainage area delineations are shown on the accompanying site plan drawing. All
identified stormwater outfalls either discharge directly into the Yadkin River, or discharge
onto the ground in close proximity to the river.
A description of the contributing drainage area for each outfall is provided below.
Included with the description is the approximate location coordinates of the outfalls, the
approximate amount of impervious surface area within the drainage areas, a description
of any significant materials and activities located within the drainage areas, the type of
discharge conveyances, and a description of any discharge control measures.
In addition to any significant materials particular to each drainage basin, herbicides are
applied to selected areas at the Buck Steam Station to eliminate undesirable vegetation.
Herbicides are generally used along railways, pipelines, and the perimeter fence.
Herbicides are also applied, as needed, in the gravel parking lots, switchya-d, laydown
areas, yard sumps, transformers, trailers, and the intake structure. The discharge of
herbicides is covered under the NPDES general permit NCG560000. Reccrds are
retained at the facility documenting the areas treated, and the type and amount of
herbicides used.
Outfall SWO01 (Drainage Area 1)
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Discharge Structure: 12 -inch -diameter CMP
Location: West of Units 5 and 6 Switchyard, outside of station fence.
Coordinates: 350 42'44" N 800 22'46" W
Drainage Area: 3.3 acres
Impervious Area: 15 percent
Area Description
Drainage Area 1 is not associated with any industrial activity and includes most of the
vendor paved parking lot, part of the Units 5 and 6 Switchyard, and the grassed yard
areas southwest of the Units 5 and 6 Switchyard. The drainage area is mostly flat with
slight grading of paved surfaces towards the drop inlets and curbing containing grassed
islands. The Switchyard has a gravel surface. Circuit breakers are located within
concrete containments with open drains that discharge to an 8,000 -gallon -capacity oil
trap tank. Transformers are provided containment by nearby yard drains that discharge
into the oil trap tank. The ground cover is approximately 0.5 acre of paved parking lot,
approximately 0.3 acre of gravel area, and 2.5 acre of grassed yard areas.
Significant Materials/Activities
Oil: Mineral oil is stored in various transformers and circuit breakers located in the
Units 5 and 6 Switchyard. Stormwater runoff is conveyed via open drains and
yard drains into an 8,000 -gallon -capacity oil trap tank. The largest transformer
contains 5,250 gallons of mineral oil, with the total mineral oil contained in all the
electrical equipment being approximately 55,700 gallons. An 8,000 gallon
capacity oil trap tank is available for the oil -filled electrical equipment located in
Drainage Area 1.
Outfall SWO02 (Drainage Area 2)
Discharge Structure: 21 -inch -diameter CMP
Location: West of Units 5 and 6 Switchyard, outside of station tence.
Coordinates: 35" 42'47" N 80" 22' 45" W
Drainage Area: 3.1 acres
Impervious Area: 25 percent
Area Description
Drainage Area 2 is not associated with any industrial activity and is comprised of
approximately 1 acre of the gravel -surfaced Units 5 and 6 Switchyard, a small paved
area beneath the Units 8 and 9 Precipitators located north of the Switchyard, and
approximately 0.3 acre of paved parking located west of the Switchyard. The remainder
of the drainage area is grassed yard.
Most electrical equipment containing mineral oil located in the Units 5 and 6 Switchyard
is situated within curbed concrete containment pads with open drains to a 15,000 -gallon -
capacity oil trap tank. The tank is located west of the station access road.
Significant Materials/Activities
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Oil: Mineral oil is stored in various transformers and circuit breakers located in the
Units 5 and 6 Switchyard. Stormwater runoff is conveyed via open drains into a
15,000 -gallon -capacity oil trap tank. The largest transformer contains 5,250
gallons of mineral oil, and six small transformers located on the Units 8 and 9
Precipitators structure have a total capacity of 1,776 gallons of mineral oil. The
total quantity of mineral oil contained in all the electrical equipment is
approximately 55,700 gallons. A 15,000 -gallon -capacity oil trap tank is available
for the oil -filled electrical equipment located in Drainage Area 2.
Outfall SW003 (Drainage Area 3)
Discharge Structure: 10 -inch -diameter CMP
Location: Western End of Powerhouse.
Coordinates: 350 42'50" N 800 22'40" W
Drainage Area: 0.4 acres
Impervious Area: 72 percent
Area Description
The drainage area for SW003 encompasses the Service Building roof, a small storage
shed roof, a covered compressed gas storage pad, a vapor extraction tank, paved
driveways, and landscaped areas on the west side of the Service Building.
Significant Materials/Activities
Oil: Used oil is captured and stored in the 150—gallon-capacity vapor extraction tank.
The tank is located within a concrete containment basin with a closed and locked
manually operated drain valve. The containment contents are inspected prior to
draining.
Outfall SWO48 (Drainage Area 48)
Discharge Structure: 15 -inch -diameter steel pipe
Location: North of Units 3 and 4 Switchyard, outside of station fence.
Coordinates: 35" 42'50" N 80" 22'29" W
Drainage Area: 0.73 acres
Impervious Area: 0 percent
Area Description
Drainage Area 48 is not associated with any industrial activity and is comprised entirely
of the western half of the Units 3 and 4 Switchyard. The drainage area is gravel -
surfaced. Electrical equipment including transformers and circuit breakers is located
within curbed concrete containment pads with manually operated drain valves.
Significant Materials/Activities
Oil: Mineral oil is stored inside various transformers and circuit breakers within the
Unit 3 and 4 Switchyard. This includes four large transformers containing a total
of 18,081 gallons of mineral oil, and nine circuit breakers containing a total of 765
gallons of mineral oil. All electrical equipment is located within concrete
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containments with closed and locked, manually operated drain valves.
Containment contents are inspected prior to draining.
Outfall SW073 (Drainage Area 73)
Discharge Structure: 36—inch-diameter CMP
Location: Approximately 400 feet east of yard sump, outside of station
fence.
Coordinates: 35" 42' 50" N 800 22' 17" W
Drainage Area: 10.1 acres
Impervious Area: 0 percent
Area Description
Drainage Area 73 is comprised of a large, primarily vegetated area located east of
Drainage Area 56. The drainage area contains approximately 500 feet of rail lines and
approximately 1,100 linear feet of gravel roadway.
Significant Materials,
/Activities
Coal: Coal fines remain in the rail corridor from past operation: however, since the
steam station no longer operates, rail cars loaded with coal no longer travel to
Buck. This area will have the remaining rail lines removed by the end of January
2018.
Outfall SW075 (Drainage Area 75)
Discharge Structure: 30 -inch -diameter CMP
Location: Approximately 150 feet east of yard sump, outside of station
fence.
Coordinates: 350 42'49" N 80" 22'22" W
Drainage Area: 8.7 acres
Impervious Area: 1 percent
Area Description
The drainage area for SW075 is comprised of a gravel roadway, gravel -surfaced areas
surrounding rail lines near the yard sump, part of a paved roadway, and grassed areas
including the former fuel storage tank area. The drainage area contains approximately
250 feet of rail lines and approximately 250 linear feet of gravel roadway.
Significant Materials/Activities
Coal: Coal fines remain in the rail corridor from past operation: however, since the
steam station no longer operates, rail cars loaded with coal no longer travel to
Buck. This area will have the remaining rail lines removed by the end of January
2018.
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Outfall SW077 (Drainage Area 77)
Discharge Structure: 30 -inch -diameter CMP
Location: Between Units 3 and 4 Switchyard and the yard sump, outside of
station fence.
Coordinates: 350 42'50" N 80" 22'25" W
Drainage Area: 20.6 acres
Impervious Area: 8.9 percent
Area Description
The drainage area for SW077 is comprised of the former coal yard, the Un is 5 through 7
Precipitators, approximately 400 feet of rail lines south of the Units 3 and 4 Switchyard,
and the paved- and gravel -surfaced areas surrounding rail lines near the yard sump.
The drainage area also includes portions of a grassed embankment north of the former
combustion turbine area. Rail lines, ties, and ballast south of the Powerhouse and west
of the combustion turbine access road have been removed.
Significant Materials/Activities
Coal: Coal fines remain in the rail corridor from past operation: however, since the
steam station no longer operates, rail cars loaded with coal no longer travel to
Buck. This area will have the remaining rail lines removed by the end of January
2018.
Eastern half of Units 3 and 4 Switchyard Outfalls
(Outfalls SW051, SW052, SW053, and SW057)
Discharge Structure: 4 -inch -diameter steel pipe
Location: Eastern half of Units 3 and 4 Switchyard.
Coordinates: 35" 42'50" N 800 22' 28" W (general area)
Drainage Area: 0.5 acres
Impervious Area: 100 percent
Area Description
The eastern half of Units 3 and 4 Switchyard is has 4 additional outfalls that are not
currently functional. Outfalls SW051, SW052, and SW053 are have been grouted
closed. Outfall SW057 is a 4 -inch drain pipe that has a removable plug. The oil
contained within this drainage area has been removed.
Powerhouse Roof Drain Outfalls
(Outfalls SWOOS, SWO07, SW011, SW015, SWO16, SW023, SW025, SW027, SW032,
SW034, SW035, SW038, SW039, SW058, SW065, SW066, SW067, SW069, SW070,
SW071 and SWO72)
Discharge Structure: Small diameter steel pipes.
Location: North face of Powerhouse; discharge directly into the station
intake area.
Coordinates: 350 42'50" N 80" 22'32" W (general area)
Drainage Area: 2.2 acres (total)
Impervious Area: 100 percent

Area Description
The drainage areas for these outfalls are comprised entirely of various sections of the
Powerhouse roof. These outfalls are mounted on the north face of the Powerhouse wall
and discharge directly into the river in the station intake area. Only Outfall SWO05 is
accessible. All of these outfalls will be eliminated during the upcoming demolition of the
Powerhouse and should be excluded from permitting considerations.
Significant Materials/Activities
No significant materials are located n this drainage area.
REMAINING DRAINAGE AREA DESCRIPTIONS
This section describes drainage areas at the station that:
a. Convey stormwater runoff into the station yard sump system that is subsequently
pumped to the ash basin,
b. Convey stormwater runoff from non -industrial use areas of the site,
c. Convey stormwater runoff as sheet flow (non -point source).
The Buck Steam Station has one ya,d sump that receives stormwater runoff from
approximately 60 acres of the station and subsequently pumps this runoff to the ash
basin system. Rarely occurring emergency sump overflows discharge directly to the
Yadkin River as NPDES Outfall 002A — Yard Sump Overflow. The yard sump will
eventually be decommissioned (circa March 2018).
Located within the yard sump stormwater drainage area are the following:
• The approximately 32 -acre drainage area of Outfall SW056 ;
• Paved- and gravel -surfaced areas located generally southeast of the
Powerhouse;
• All coal handling buildings, maintenance sheds, conveyors and equipment; and
• Two warehouses, the Office/Shop Building, and the Units 5 through 7
Precipitators,
Outfall SW056 (Drainage Area 56)
Discharge Structure: 36 -inch -diameter RCP
Location: Between Units 3 and 4 Switchyard and the yard sump, outside of
station fence
Coordinates: 350 42'50" N 800 22'27" W
Drainage Area: 32.1 acres
Impervious Area: 7 percent
Area Description
Drainage Area 56 is comprised of a large, partially vegetated area located southeast of
the Powerhouse with approximately 3,200 linear feet of paved roadway and
approximately 2,000 linear feet of gravel roadway. The north end of the drainage area
was formerly the location of the CT plant which is currently grassed and not used for
industrial activity. The area at the south end of the drainage area includes the
maintenance yard and facility for the Buck site and is primarily a gravel lot.

Stormwater runoff from Drainage Area 56 is grassed and graded to drain by
underground piping to the yard sump. The sump subsequently pumps this discharge to
the ash basin system. A diversion structure is currently in place to bypass the yard sump
and was designed to allow runoff in excess of a 2 -year design storm even_ to discharge
through Outfall 56. The outfall was fitted with a rubber flapper outlet to prevent any
backflow from occurring to the sump during high river levels. The outlet is typically
partially submerged. The yard sump will eventually be decommissioned (arca March
2018).
Stormwater discharges currently do not normally occur through Outfall 56. Most
stormwater runoff from Drainage Area 56 will discharge to the yard sump and be
pumped to the ash basin system until the storm water re-routing is completed by the end
of March 2018. Considering the submerged conditions of the outlet during such events,
no stormwater sample collection is currently possible at the outlet. Sample collection is
only possible at the upstream manway in the concrete diversion structure and only
possible during the extreme storm event. Consequently, Outfall SWO56 should be
excluded from permitting considerations until the modifications to the stormwater system
which will allow sampling in the upstream manway prior to the submerged discharge
point during normal storm events.
Significant Materials/Activities
No significant materials are located in this drainage area.
Non -Point Runoff Area East of Units 3 and 4 Switchyard:
This approximately 1 -acre area is located east of the Units 3 and 4 Switchyard and is
primarily gravel -surfaced. The area contains the yard sump and the yard sump service
transformer. The transformer contains 188 gallons of mineral oil, and is located inside a
concrete containment pit with an open drain to the yard sump. Stormwater runoff flows
northerly overland to the Yadkin River. This drainage area should be excluded from
permitting considerations.
Station Paved Parking Lot and Landscaped Areas Northwest of Units 5 and 6
Switchyard:
This non -industrial use areas containing portions of the station paved parking lot,
grassed lawn areas, and landscaped areas located northwest of the Units 5 and 6
Switchyard. Some stormwater runoff from these areas enters catch basins that
discharge through either outfall SW078 (12 -inch diameter CMP) or outfall SW079 (4 -inch
diameter plastic pipe) into the Yadkin River northwest of the areas. Other stormwater
runoff discharges to northwest into the Yadkin River as non -point source runoff. No
significant materials or activities are located within these areas. This drainage area
should be excluded from permitting considerations.
Station Access Road:
Several culverts beneath the station access road direct stormwater toward the Yadkin
River from the CTCC, Buck Tie Station, and non -industrial use yard areas located east
of the road. The contributing drainage areas for SW099, SW102, and SW103 do not
have industrial activity within their boundaries. The Buck Tie Station discharges through
SW101 on the updated stormwater outfall figure. Mineral oil within the transformers is
the only significant material present; two oil/water separators are used to process the
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water draining from the Buck Tie Station. The Buck CC station collects all runoff in a
detention basin and discharges through a single outfall (SW001 from Buck CTCC
NPDES Permit NCS000554).
Outfall SW099 (Drainage Area 99)
Discharge Structure: 48 -inch -diameter CMP
Location: South of driveway for CTCC.
Coordinates: 350 42'20" N 80° 22'32" W
Drainage Area: 15.8 acres
Impervious Area: 72 percent
Area Description
The drainage area for SW099 is not associated with any industrial activity and
encompasses the exterior vegetated embankment slopes of the primary ash basin
located east of the station access road and south of the CTCC driveway access. The
area also includes the eastern half of the station access roadway.
Outfall SW102 (Drainage Area 102)
Discharge Structure: 24 -inch -diameter CMP
Location: West and northwest of Buck Tie Station.
Coordinates: 350 42'32" N 80" 22'43" W
Drainage Area: 10.7 acres
Impervious Area: 0 percent
Area Description
Drainage Area 102 is not associated with any industrial activity contains gravel parking
lots and roadways; grassed areas with transmission towers and a water tower; and a
single building.
Outfall SW103 (Drainage Area 103)
Discharge Structure: 24 -inch -diameter CMP
Location: South of station fence and northwest of the Buck Tie Station.
Coordinates: 35" 42'39" N 800 22'47" W
Drainage Area: 4.3 acres
Impervious Area: 0 percent
Area Description
Drainage Area 103 is not associated with any industrial activity and comprised of a
grassed area with transmission towers and trees. The drainage area is has one small
building at the edge of the drainage area. Electrical equipment does not include any oil.
Buck CC and Substation Drainage Areas
The Buck CC station area has its own NPDES permit with one outfall which is described
below as Outfall SW100 in the Buck SS NPDES permit. The Buck Tie Station does not
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have an NPDES permit because no industrial activity occurs within the drainage area,
These areas are described to provide additional information for the surrounding facilities.
Outfall SW100 (Drainage Area 100)
Discharge Structure: 24 -inch -diameter CMP
Location: West of CTCC.
Coordinates: 35" 42'30" N 800 22'41" W
Drainage Area: 29.8 acres
Impervious Area: 0 percent
Area Descriptio
Drainage Area 100 is comprised of the Buck CC station plus the cooling tower, a
clarifier, office buildings, and a detention pond. The drainage area is mostly paved
roadways and building area but the runoff is delayed by using a detention pond.
Electrical equipment including transformers and circuit breakers is located within curbed
concrete containment pads with manually operated drain valves. Natural gas pipelines
run underground to provide fuel to the station.
Significant Materials/Activities
Natural Gas: Pipelines supplying the CTCC station run under the station access road
and through the drainage area to the plant.
Oil: Mineral oil is stored inside various transformers and circuit breakers
within the Unit 3 and 4 Switchyard. This includes four large transformers
containing a total of 18,081 gallons of mineral oil, and nine circuit
breakers containing a total of 765 gallons of mineral oil. All electrical
equipment is located within concrete containments with closed and
locked, manually operated drain valves. Containment contents are
inspected prior to draining.
Outfall SW101 (Drainage Area 101)
Discharge Structure: 30 -inch -diameter CMP
Location: West of the Buck Tie Station.
Coordinates: 350 42'31" N 800 22'43" W
Drainage Area: 14.3 acres
Impervious Area: 0 percent
Area Description
Drainage Area 101 is not associated with any industrial activity and includes the Buck
Tie Station, a road, and parking lot. The drainage area is mostly gravel-suraced with
the exception of a single building in the tie station. Electrical equipment inc uding
transformers and circuit breakers is located within the tie station and isolated from the
drainage piping by two oil -water separator tanks.
Significant Materials/Activities
10

Oil: Mineral oil is stored inside various transformers and circuit breakers within the
Buck Tie Station. The two substations with the Tie Station includes several large
transformers containing a total of 18,081 gallons of mineral oil, and nine circuit
breakers containing a total of 765 gallons of mineral oil. All electrical equipment is
located within the gravel drainage area that drains to a sump with two oil -water
separator tanks before discharging through SW101.
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DESCRIPTION OF FUTURE WORK
Elimination of flows of wastewater and stormwater streams to the ash basins is required
to facilitate closure. As such, modifications to Drainage Areas SWO02, SW073, SW075,
SW077, and the powerhouse will occur in conjunction with demolition and restoration
activities. In particular, the powerhouse and Drainage Area SWO02 structures
associated with generation will be demolished and removed. Drainage Area SWO02 will
have the Units 8 and 9 precipitators removed, but the Unit 5 and 6 switchyard will
remain.
Drainage Areas SW073, SW075, and SW077 will have the remaining rail corridor
restored. The restoration activities include removal of rail, railroad ties, ballast stone, and
remnant coal from former operation, grading, and seeding. The rail corridor will be
converted into a primary drainage swale with headwall inlets at each of the outfall
locations. In addition, the existing outfall pipes will remain in order to discharge
stormwater runoff to the Yadkin River. However, the capacity of these existing outfalls
do not meet Duke Energy's design requirement for carrying runoff from a 25 -year, 24-
hour storm event. These currently have capacity for the 2 -year, 24-hour storm event.
Therefore, a series of overflow spillways have been designed to safely discharge
stormwater runoff from larger storm events than the existing outfall pipes. Essentially, in
the event the outlet pipe for SW077 gets overwhelmed by a larger storm event,
stormwater flow will overtop the spillway and continue down the rail corridor Swale to the
next outfall, SW075. In the event the outlet pipe for SW075 also becomes overwhelmed,
stormwater flow will overtop its spillway and continue down the rail corridor swale to the
next outfall, SW073. The outlet pipe for SW073 is the low point of the rail corridor Swale.
In the event it becomes overwhelmed, stormwater flow will overtop its spillway into a
wide and shallow overflow channel which discharges into the Yadkin River.
IDENTIFICATION OF NON-STORMWATER DISCHARGES
A visual assessment for non-stormwater discharge was conducted on September 22,
2014. Each accessible outfall was observed for outflow after a period of at least 72 hours
of dry weather. Outfalls SW001, SWO02, SW048, SW073, and SW077 were dry at the
time of observation. Outfall SWO03 had a fast drip that appeared to originate from
stormwater runoff within a drop inlet located in the circle driveway.
MONITORING AND SAMPLING DATA
There are 37 stormwater outfalls at Buck Steam Station. Many of these outfalls convey
stormwater from areas of substantially identical activities and materials. Stormwater
Outfalls SW001, SWO02, SW003, SW005, SW048, SW073, SW075, and SW077 are
accessible for sampling. After the future work on the stormwater system is completed,
SW056 will be accessible for sampled. Stormwater Outfalls 007, 011, 015, 016, 023,
025, 027, 032, 034, 035, 038, 039, 058, 065, 066, 067, 069, 070, 071, and 072 are
inaccessible. All Powerhouse roof drains (including SW005) will be eliminated during
demolition of the Powerhouse and should be excluded from any permitting requirements.
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