HomeMy WebLinkAboutNCS000549_Supplemental Information_20140618Strickland, Bev
From: Bennett, Bradley
Sent: Wednesday, June 18, 2014 9:57 AM
To: Strickland, Bev
Subject: FW: Supplemental Stormwater Outfall Information for Duke Energy Riverbend Site
Attachments: Duke Energy Riverbend SW Outfall Information.pdf
M.
M..*
Bradley Bennett
Stormwater Permitting Program Phone: (919) 807 -6378
NC Division of Energy, Mineral and Land Resources Fax: (919) 807 -6494
1612 Mail Service Center Email: brad ley. bennett(a.ncdenr.pov
Raleigh, NC 27699 -1612 Web: http: / /Portal.ncdenr.org /web /ir /stormwater
Email correspondence to and from this address may be subject to public records laws
From: Velte, John S [ mai Ito: John.VelteCa)duke- energy.com]
Sent: Wednesday, June 18, 2014 9:45 AM
To: Bennett, Bradley
Cc: Davis, Tracy; Reeder, Tom; Vandervaart, Donald
Subject: Supplemental Stormwater Outfall Information for Duke Energy Riverbend Site
Dear Mr. Bennett,
The attached letter provides supplemental information pertaining to Duke Energy's Riverbend Steam Station
stormwater outfall SW007, SW008, and SW014. This information was requested of us by you during the Duke
Energy /North Carolina Department of Environment and Natural Resources video conference held Wednesday June 11,
2014 . A hard copy of this letter addressed to you will be placed in the mail today. Thank you.
John Velte
Manager, NPDES Compliance
Duke Energy, Environmental Services
Office Phone: 980 - 373 -7308
Cell Phone: 704 -572 -6119
Email: John.Velte @duke- ener.gy.com
June 17, 2014
Mr. Bradley Bennett, Supervisor
North Carolina Department of Environment and Natural Resources
Division of Energy, Mineral, and Land Resources
Stormwater Permitting Program
1612 Mail Service Center
Raleigh, North Carolina 27699 -1612
Environmental Services
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Subject: Duke Energy Carolinas LLC — Stormwater Supplemental Information
Riverbend Steam Station — Individual NPDES Stormwater Permit #NCS000549
(pending)
Dear Mr. Bennett:
A request has been made of Duke Energy (DE) by the North Carolina Department of
Environment and Natural Resources (NCDENR) to provide details relative to three stormwater
(SW) outfalls (SW007, SW008, and SW014) at the Riverbend Steam Station site for which DE
has been unable to collect valid samples. The following outfall- specific sections describe outfall
circumstances, current status, and anticipated likelihood of sample collection.
Outfall SW007 (Drainage Area 7)
Discharge Structure: 24 inch diameter steel pipe
Location: Mountain Island Lake
Coordinates: 35 021'80" N 80058'29'W
Drainage Area: 0.9 acres
Impervious Area: 0%
Description:.
The drainage area for SW007 is comprised of a small portion of a grassed embankment on the
northern side of the coal storage pile and a small section of gravel- surfaced roadway and
laydown yard for inert materials (i.e., structural steel, cable, truck trailers, etc.) located between
the coal storage pile and Mountain Island Lake. There are no discharge controls.
Current Status:
During a June 5, 2014 USC Plan review site visit by the NCDENR Mooresville Regional Office
of the Division of Energy, Mineral, and Land Resources ( DEMLR), discussions took place about
SW007 which is located in the area where the coal pile remediation work is to begin. During this
conversation, DEMLR indicated that DE could remove this outfall and stabilize the area. The
affirmed abandonment of this outfall as demolition activities progress was provided in an email
from Ryan Korrnanik to Donna Burrell dated June 12, 2014. Duke Energy intends to remove
Outfall SW007, therefore we do not believe that sampling is warranted or would prove
beneficial
Outfall SW008 (Drainage Area 8)
Discharge Structure: 36 inch diameter corrugated metal pipe (CMP)
Location: Mountain Island Lake
Coordinates: 35 021'51" N 80 058'16" W
Drainage Area: 70 acres
Impervious Area: 2%
Area Description:
Drainage Area 8 is located in the central area of the station property and includes the closed dry
ash stack occupying approximately 35 acres, and the cinder pit encompassing approximately 9
acres. Drainage Area 8 extends into undeveloped woodland areas on the south side of
Horseshoe Bend Beach Road. Located within the drainage area is approximately 7 acres of
woodlands, approximately 1,600 linear feet of ash sluice piping, approximately 6,150 linear feet
of rail lines, approximately 2,425 linear feet of gravel - surfaced roadways, and approximately
3,500 linear feet of the paved Horseshoe Bend Beach Road. All coal deliveries and ash sluicing
activities have been terminated. Two service transformers for the yard sump pumps are located
within the drainage area at the north end of the coal storage pile. These transformers are
surrounded by a containment dike with a chemical polymer oil containment barrier. Stormwater
runoff from the ash stack and all areas south of the rail lines within Drainage Area 8 enters a
stormwater collection basin located west of the ash stack. This basin discharges into the cinder
pit through a pipe beneath the rail lines. All stormwater runoff from within Drainage Area 8
eventually enters the cinder pit which functions as a large dry detention pond. The pit is fitted
with a 3 -foot high vertical riser constructed of CMP leading to the 36 -inch diameter CMP
discharge outlet. Noteworthy materials in this area include mineral oil present in the two yard
sump pump service transformers located within a containment berm and various inert sources
associated with the scrap yard within the drainage area. Discharge control is provided by the
cinder pit dry detention pond.
Current Status:
Stormwater entering the cinder pit typically evaporates and/or infiltrates before reaching a level
high enough to crest the 3 -foot riser pipe and constitute an outfall discharge. Discharges from
the 36 -inch diameter CMP rarely occur, and it is unclear when a discharge from this outfall last
occurred. It is highly unlikely that a rainfall event will be of sufficient magnitude to crest the riser
pipe. Duke Energy believes that sampling opportunities will be rare, and that proper selection of
representative stormwater outfails at Riverbend can eliminate the need to sample Outfall
SW008.
Outfall SW014 (Drainage Area 14)
Discharge Structure; 12 inch diameter CMP
Location: East side of station intake canal
Coordinates: 35 021'42" N 80 058'30" W
Drainage Area: 0.02 acres
Impervious Area: 0%
Area Description:
The drainage area for SW014 is comprised wholly of a grassed bermed area surrounding the
station septic tank. Stormwater runoff from within this small bermed area enters a catch basin
that discharges into the intake canal from the steep eastern side of the canal embankment.
Access to the discharge end of this pipe is difficult due to thick vegetation and the steepness of
the bank. There are no significant materials stored or activities occurring in this area, and no
discharge controls are present.
Current Status:
Potential impact associated with this outfall has historically been the existence of the septic tank
overflow pipe. That overflow pipe has been sealed and capped and the septic system receives
minimal inflow (only a few employees now report to the Riverbend site). Given the extremely
small drainage area (--870 square feet) and lack of industrial activities associated with SW014,
Duke Energy believes that sampling entails considerable challenges for no benefit.
The following observations apply to all three outfalls described above:
• None of these outfalls were previously designated as representative by DE or NCDENR.
The inability to safely collect valid SW samples at these locations is supportive of the
concept of representative SW outfalls and our original designations.
• DE has collected and evaluated rainfall totals from Mt. Island Hydro near the Riverbend
Steam Station from May 2014 through present. A rainfall event on May 15th (when the
second set of Riverbend samples was collected) had the highest rainfall total (- 1.4
inches) of any storm since the seep /stormwater sampling began, yet no flow was
observed from the three outfalls of interest. DE now understands that rainfall events
exceeding 1.4 inches (and potentially considerably more) will be necessary to produce
flow from these outfalls.
If additional information is needed, please advise. Should you have questions regarding these
outfalls, please contact Allen Stowe at (704) 382 - 4309.
Sincerely,
n Velte, Manager
NPDES Compliance
Environmental Services, Water & Natural Resources
cc (via email): Tracy Davis
Tom Reeder
Donald Vandervaart