SW6191002_AddInfoRequest_20191203

ROY COOPER
Governor
MICHAEL S. REGAN
Secretary
S. DANIEL SMITH
Director
Jerry Oberholtzer, PE
Lowe Engineers
990 Hammond Drive, Suite 900
Atlanta, GA 30328
NORTH CAROLINA
Environmental Quality
December 3, 2019
Subject: Request for Additional Information
Stormwater Permit No. SW6191002
Fort Bragg Special Operations Facility — PN92594
Cumberland County
Dear Mr. Oberholtzer:
The Division of Energy, Mineral and Land Resources (DEMLR), received a Stormwater
Management Permit Application for the subject project on October 18, 2019. A review of that
information has determined that the application is not complete. The following information is
needed to continue the stormwater review:
1. The proposed media mix does not meet the specifications required by Bioretention MDC
6 [15A NCAC 02H .1052(6)].
2. Please provide calculations to show that the inlets and outlets from the SCMs have
sufficient outlet protection to prevent erosion during the 10-year storm event in
accordance with General MDC 4 [15A NCAC 02H .1050(4)].
3. How was the seasonal high water table determined for the bioretention cell and detention
pond? The Boring Location Plan (Sheet B-101) does not show any borings in the area of
the proposed SCMs.
4. Please provide a detail of the bioretention cell outlet structure.
5. Please provide calculations to show that the bioretention cell underdrain is sufficient to
convey runoff from the bioretention cell. Guidance on these calculations can be found in
Part B of the Stormwater Design Manual.
6. When calculating runoff volumes, the Discrete NRCS Method must be used. This method
calculates the runoff separately for pervious and impervious areas rather than use a
weighted curve number. Using a weighted curve number often underestimates the runoff
volumes generated on site.
D EQ �� North Carolina Department of Environmental Quality Division of Energy, Mineral and Land Resources
512 North Salisbury Street 1 1612 Mail Service Center Raleigh, North Carolina 27699-1612
NORTH CAROLINA
Depadm.mofEnmmnm.maaualfty /� 919.707.9200

7. Please provide stage storage data for the bioretention cell and detention pond to verify the
storage volumes.
8. Please provide a table for each drainage area showing the areas of built upon area and
pervious area and their respective curve numbers.
9. Volume reductions from the bioretention cell should be calculated using the credits
provided in the North Carolina Stormwater Control Measure Credit Document.
10. Runoff volume match must be based on the annual runoff volume rather than the runoff
volume from individual storm events. This can be calculated using the Simple Method
and the average annual rainfall to calculate an average annual runoff before and after
development.
11. Provide pdfs of all revisions, 2 hardcopies of revised plan sheets, and 1 hardcopy of other
documents. Pdfs must be uploaded using the form at:
hltps:Hedocs.deq.nc.gov/Forms/SW ProjectSubmittal
Please note that this request for additional information is in response to a preliminary review.
The requested information should be received by this Office prior to January 2, 2020, or
the application will be returned as incomplete. The return of a project will necessitate
resubmittal of all required items, including the application fee. Please reference the State
assigned project number SW6191002 on all correspondence.
If you need additional time to submit the information, please submit your request for a time
extension to the Division at the contact below. The request must indicate the date by which you
expect to submit the required information. The Division is allowed 90 days from the receipt of
a completed application to issue the permit.
The construction of any impervious surfaces, other than a construction entrance under an
approved Sedimentation Erosion Control Plan, is a violation of NCGS 143-215.1 and is subject
to enforcement action pursuant to NCGS 143-215.6A.
If you have any questions concerning this matter please feel free to contact me at
Corey.Anen(d),ncdenr.gov or [phone].
Sincerely,
6&u'� &I ---
Corey Anen
Environmental Engineer
Stormwater Program
cc: Fayetteville Regional Office