SW1210901_Response To Comments_20220127

ULICK ENGINEERING, LLC
I
January 27, 2022
Jim Farkas
North Carolina Department Environmental Quality
512 North Salisbury Street
Raleigh, NC 27699
Office: [phone]
Subject: Asheville Regional Airport— Parking Lot D
Review Comments dated October 21, 2021 (via email)
Stormwater Permit No. SW1210901
Dear Mr. Farkas,
Thank you for providing comments on the Asheville Regional Airport Parking Lot D project. Please see
our responses to your comments below.
Initial Plans Dated: July 2021
Initial Comments Dated: October 21, 2021 (NCDEMLR)
Revised Plans Dated: January 27, 2022
1. 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.
Correction: Section 1.3 is now updated with more detailed instructions on how to access the
project site.
2. Since the permittee is also the property owner, Section III, 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.
Correction: since we are already revising this application, Section 111.2 is removed. Section IX
is no longer signed.
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
(https://ncdenr.maps.arcgis.com/apps/webappviewer/index.html?id=6el25ad7628f4946
9 4e259c80dd64265)
Correction: The stream index number for the French Broad River has been updated to "6-
54.75", as shown on the provided map.
ASHEVILLE REGIONALAIRPORT PARKING LOT D- NCDEMLR COMMENTS AND RESPONSES

ULICK ENGINEERING, LLC
V
4. Please provide an original signature and seal on the Supplement-EZ Form (Section V &
Section VI,3).
Correction: The original seal is now included on the Supplemental-EZ Form
5. Please clearly dimension the project boundary in the main set of plans with bearings and
distances (Section IV, 8i).
Correction: Project boundary with bearings and distances is shown on the BUA Exhibit, now
provided in Appendix F of the Stormwater Report.
6. Please clearly identify and dimension all BUA in the main set of plans (Section VI, 8j).
Correction: The BUA is shown on the BUA Exhibit, now provided in Appendix F of the
Stormwater Report.
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?
Correction N/A: A bioretention cell is no longer a part of the design for this project due to
the presence of bedrock. A Dry Detention Pond is now proposed. There is an overflow
designed for the dry pond though.
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.
Correction N/A: A bioretention cell is no longer a part of the design for this project due to
the presence of bedrock. A Dry Detention Pond is now proposed.
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).
Correction: A note is now provided on sheet SW-01 that no wetlands are present on -site. A
note is also included on the same sheet indicating the identity and qualifications of the
individual that made this determination.
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.
Clarification: The existing D-3 manhole is not connected to D-0 until the proposed
conditions. The previously submitted plans reflect this. SW-00 is now included as "Existing
Conditions".
ASHEVILLE REGIONALAIRPORT PARKING LOT D- NCDEMLR COMMENTS AND RESPONSES

ULICK ENGINEERING, LLC
V
11. Please delineate the drainage area to each bioretention cell (A-E) in the main set of plans
(Section VI, 8o).
Correction N/A: A bioretention cell is no longer a part of the design for this project due to
the presence of bedrock. A Dry Detention Pond is now proposed and the entire parking lot
drains to it.
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.
Correction N/A: A bioretention cell is no longer a part of the design for this project due to
the presence of bedrock. A Dry Detention Pond is now proposed and is updated in the
SuppEZ forms as a single SCM.
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).
Correction N/A: A bioretention cell is no longer a part of the design for this project due to
the presence of bedrock. A Dry Detention Pond is now proposed.
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.
Correction: The side slopes of the proposed dry detention pond are 3:1.
15. General MDC 4 — Please provide calculations showing that the inlets and outlets of the
bioretention cells are protected from erosion.
Correction N/A: A bioretention cell is no longer a part of the design for this project due to
the presence of bedrock. A Dry Detention Pond is now proposed but the inlets and outlets
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.
Correction: 10' maintenance easement is now called out on sheet SW-01.
ASHEVILLE REGIONALAIRPORT PARKING LOT D- NCDEMLR COMMENTS AND RESPONSES

ULICK ENGINEERING, LLC
I
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).
Correction: A bioretention cell is no longer a part of the design for this project due to the
presence of bedrock. A Dry Detention Pond is now proposed, which allows 6" of separation
from the SHWT per the NCDEQ Stormwater Design Manual. Bedrock was found at
approximately 3ft deep and no SHWT was found between. The Dry Detention Pond is only
1ft in depth, so this 6" of separation has been achieved.
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.
Correction N/A: A bioretention cell is no longer a part of the design for this project due to
the presence of bedrock. A Dry Detention Pond is now proposed and does have an
emergency spillway.
19. Bioretention MDC 3 — See prior comment.
Correction N/A: A bioretention cell is no longer a part of the design for this project due to
the presence of bedrock. A Dry Detention Pond is now proposed.
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.
Correction N/A: A bioretention cell is no longer a part of the design for this project due to
the presence of bedrock. A Dry Detention Pond is now proposed and does not need IWS.
21. Bioretention MDC 10 — Please provide two hard copies and one electronic copy of a
fullsized, signed, sealed, and dated planting plan (per 15A NCAC 02H .1042(2)(i)).
Correction: Two hard copies and one electronic copy is provided.
ASHEVILLE REGIONALAIRPORT PARKING LOT D- NCDEMLR COMMENTS AND RESPONSES

ULICK ENGINEERING, LLC
V
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.
Correction N/A: A bioretention cell is no longer a part of the design for this project due to
the presence of bedrock. A Dry Detention Pond is now proposed and the drainage area
information matches.
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.
Corrections:
ASHEVILLE REGIONALAIRPORT PARKING LOT D- NCDEMLR COMMENTS AND RESPONSES

AULICK ENGINEERING, LLC
a. An original, signed & sealed cover page has been provided.
b. i. One SCM is now designed for this project, this form has been updated accordingly
ii. All of this projects' BUA is located within the drainage area to the one SCM, so the
"entire site" column has been filled out rather than splitting the BUA up into individual
drainage areas.
iii. This volume now lists the required design volume of the SCM.
c. A bioretention cell is no longer a part of the design for this project due to the presence
of bedrock. A Dry Detention Pond is now proposed and all comments in c are not
applicable.
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.deg.nc.eov/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
Correction: The requested documents will be provided with this submittal and uploaded.
ASHEVILLE REGIONALAIRPORT PARKING LOT D- NCDEMLR COMMENTS AND RESPONSES