SW1210901_Add Info_20211021

ROY COOPER
Governor
ELIZABETH S. BISER
Secretary
BRIAN WRENN
Director
Dave Skurky, PE
4364 S. Alston Avenue, Suite 300
Durham, NC 27713
AND
NORTH CAROLINA
Environmental Quality
October 21, 2021
Greater Asheville Regional Airport Authority
Attn: Lew Bleiweis
61 Terminal Drive, Suite 1
Fletcher, NC 28732
Subject: Request for Additional Information
Stormwater Permit No. SW1210901
Asheville Regional Airport — Parking Lot D
Henderson County
Dear Mr. Skurky and Mr. Bleiweis:
The Division of Energy, Mineral and Land Resources (DEMLR), received a Stormwater
Management Permit Application for the subject project on September 14, 2021. A review of that
information has determined that the application is not complete. The following information is
needed to continue the stormwater review:
Please clarify the directions to the project site as there are many parking areas that are
located along Aviation Way (Section I, 3). The directions should allow an individual,
such as a field inspector, to locate the project area. You may wish to included directions
of travel and distances in these directions.
2. Since the permittee is also the property owner, Section IIl, 2 and Section IX of the
Application are not required. With your permission, I can cross out the provided original,
hard copy signature in Section IX of the Application. If this is not satisfactory, please
provide a revised original hard copy of the Application. Please revise and resubmit the
electronic version of this form with Section III, 2 and Section IX revised.
3. The stream index number for the French Broad River appears to be incorrect (Section IV,
10). The indicated value, "6-54.5" does not match the value as shown on the water
surface classification map
North Carolina Department of Environmental Quality I Division of Energy, Mineral and Land Resources
512 North Salisbury Street 1 1612 Mail Service Center I Raleigh, North Carolina 27699-1612
NORTH CAROLINA _
oepm nt of EnvimnmwUl uwl ry 919.707.9200

(https://ncdenr.maps.arcgis.com/appslwebgppviewerlindex.html?id=6e l25ad7628f49469
4e259c80dd64265)
4. Please provide an original signature and seal on the Supplement-EZ Form (Section V &
Section VI,3).
5. Please clearly dimension the project boundary in the main set of plans with bearings and
distances (Section IV, 8i).
6. Please clearly identify and dimension all BUA in the main set of plans (Section VI, 8j).
7. Please clarify where it is the overflow from the bioretention cells goes (Section VI, 8k).
Is there some sort of a ditch that directs overflow towards existing drop inlet D-0 or does
the overflow just flow into the street/sidewalk?
8. Please clearly indicate the bottom of the media layer, top of the media layer, IWS
elevation, design volume ponding elevation, peak attenuation ponding elevation, and
emergency bypass elevation on the cross -sectional view of the bioretention cells (Section
VI, 81). If you prefer, you can show this information in a table next to the typical section
on plan sheet SW-03.
9. Please delineate the wetlands in the main set of plans or provide a note in the main set of
plans stating that no wetlands are present on -site. Please also include a note in the main
set of plans indicating the identity and qualifications of the individual that made the
determination (Section VI, 8m).
10. Please show the existing drainage features (such as the pipe or pipes that connected
manhole D-3 to drop inlet D-0) in the main set of plans (Section VI, 8n). It is
recommended to include an "existing conditions" plan as part of the plan set.
11. Please delineate the drainage area to each bioretention cell (A-E) in the main set of plans
(Section VI, 8o).
12. As designed, this project contains 5 bioretention cells, not 1 bioretention cell. Adjacent
bioretention cells can only be considered as part of the same SCM if stormwater can
freely flow between them in either direction (this is typically accomplished by connecting
the ponding areas via a zero percent slope pipe and in this situation would require the
cells to be at roughly the same elevation since the design volume ponding depth is limited
to 12 inches). Please either revise the submission to show 5 bioretention cells or provide a
method for the individual cells to freely transfer stormwater between themselves.
13. As designed, bioretention cell C is undersized, the provided design volume is less than
the required design volume and any overflow does not flow into another bioretention cell,
but rather the piped collection system. Please revise. This under -sizing issue may also
apply to bioretention cell E if bioretention cell E does not overflow into bioretention cell
D (if bioretention cell E does overflow into bioretention cell D, it would be acceptable

since bioretention cell D is sized to handle the treatment volume from its drainage area in
addition to the overflow from bioretention cell E).
14. General MDC 3 — The maximum allowable side slope of vegetated SCMs is 3:1. Please
revise. Steeper slopes can be considered on a case -by -case basis if it can be demonstrated
that the soil and vegetation will remain stable.
15. General MDC 4 — Please provide calculations showing that the inlets and outlets of the
bioretention cells are protected from erosion.
16. General MDCs 8 & 9 — Please clearly show the proposed maintenance accesses and
easements for these SCMs in plan view. It is noted that a typical detail with maintenance
access and easement is shown on plan sheet SW-03, however, the precise location of the
maintenance accesses and easements should be shown on the plans.
17. Bioretention MDC 1 — Please provide site -specific SHWT borings so that the separation
can be determined. It is recommended to get at least 1 SHWT boring per SCM and 1
SHWT boring per 10,000 sf of surface area for larger SCMs. NOTE: The minimum 2 ft
separation is from the lowest excavated portion of the bioretention cell (the bottom of the
media) not the lowest portion of the finished grade (top of the media).
18. Bioretention MDC 2 — Please clearly show the locations of the emergency spillways in
plan view. It is noted that the typical cross-section of the bioretention cell contains the
emergency spillway, however the plan view (plan sheet SW-01) does not appear to show
these emergency spillways as part of the proposed grading. Please also indicate the
elevation of these emergency spillways so that Bioretention MDC 3 can be verified.
19. Bioretention MDC 3 — See prior comment.
20. Bioretention MDC 4 — As currently set up, there is insufficient IWS in most of the
bioretention cells. The planting surface for bioretention cell A is located at elevation
2,157 ft. Bioretention MDC 4 requires the IWS elevation to be set a minimum of 18 in
below the planting surface (at elevation 2,155.5 ft) which is higher than the bypass
elevation of bioretention cell C and about a foot and a half above the top of existing drop
inlet D-0. This issue arises since, as designed, the bioretention cells share an underdrain
line and the upturned IWS elbow is shared. This configuration would work if all of the
bioretention cells had planting surfaces at approximately the same elevation, but that is
not the case here. It is recommended to give bioretention cells that have planting surface
elevations that differ by more than a couple of inches their own underdrain line/IWS
elbow.
21. Bioretention MDC 10 — Please provide two hard copies and one electronic copy of a full-
sized, signed, sealed, and dated planting plan (per 15A NCAC 02H .1042(2)(i)).
22. The drainage area information entered into the Application (Section IV, 10) and the
drainage area information on plan sheet SW-03 do not match. The Application indicates
that the on -site drainage area to the bioretention cells is equal to 31,849 sf or 0.73 ac

(which is larger than the entire project area) and the plan sheet indicates that the
combined drainage area to the bioretention cells is 0.64 ac. Please revise as needed for
correctness and consistency.
23. Please correct the following issues with the Supplement-EZ Form:
a. Cover Page — Please provide an original, signed & sealed cover page.
b. Drainage Areas Page:
i. Line 2 — As previously mentioned, this project contains multiple SCMs.
Please update this item and complete a drainage area column for each
SCM.
ii. The entire site column should be an accounting of all BUA located within
the project area (whether or not it drains to the proposed bioretention cells)
and the drainage area columns should be an accounting of all of the BUA
located within the drainage area to each SCM (similar to the information
shown on plan sheet SW-03). NOTE: Lines 17-19 are not required for the
entire site column
iii. Line 18 — The design volume shown on this line should be the design
volume required, not the design volume provided (I believe that newer
versions of this form differentiate the required design volume and
provided design volume on the SCM specific pages, but you can add this
information in the additional information section if you like).
c. Bioretention Cell Page:
i. Please complete one column per SCM.
ii. Lines 2 & 22 — See earlier comment.
iii. Line 5 — See earlier comment.
iv. Line 9 — Please elaborate in the additional information section what
dewatering method will be used.
v. Line 19 — See earlier comment. The bottom of the bioretention cell is the
bottom of the media layer, not the top of the media layer.
vi. Lines 23-25 — The detail on plan sheet SW-03 indicates that the
bioretention cell has peak attenuation storage. Please revise as needed for
correctness & consistency.
vii. Line 29 — See earlier comment.
viii. Line 31 — This information does not correspond to the planting plan.
Please revise as needed for correctness & consistency.
24. Provide pdfs of all revisions, 2 hardcopies of revised plan sheets, 1 hardcopy of other
documents, and a response to comments letter briefly describing how the comments have
been addressed.
a. Pdfs must be uploaded using the form at:
https://edocs.deq.nc.gov/Forms/SW-Supplemental-Upload
b. Hard copies must be mailed or delivered to the following address:

i. For FedEx/UPS:
Jim Farkas
512 N. Salisbury Street, Office 640E
Raleigh, NC 27604
ii. For USPS:
Jim Farkas
1612 Mail Service Center
Raleigh, NC 27699-1612
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 November 20, 2021, 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 SW1210901 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
[e-mail] or [phone].
Sincerely,
Jim Farkas
Environmental Engineer
Stormwater Program
cc: Asheville Regional Office