SW3210803_Response To Comments_20210915

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September 10, 2021
Mr. Jim Farkas
Environmental Engineer
North Carolina Department of Environmental Quality
512 N. Salisbury Street
1612 Mail Service Center
Raleigh, NC 27699-1612
RE: Stormwater Permit No. SW3210803
Belle Mar Subdivision
Union County
Dear Mr. Farkas:
Thank you for the timely review and response to our plans submitted for the
subject project. We are in receipt of the below listed review comments from the
letter dated September 2, 2021 based on the submitted construction drawings
dated August 4, 2021 consisting of the development of a 10 lot residential
subdivision on parcel #06153009. The original comments below are followed by
the actions taken and/or clarifications to address the comments.
1) Since this project is a low -density project, the "drainage area" listed in
Section VI, 10 of the Application is the total project area (as shown in Section
IV, 7). This is explained in Section IV, 9 of the Application. Please revise the
total, on -site, and off -site drainage areas (since the drainage area is the project
area, there is typically no off -site component to the "drainage area"). It is also
recommended to further breakdown the "On -site streets" BUA into "On -site
P ;„t o , , , r Parking" (the portions of the driveways that are located within the common
area/public right-of-way) and "On -site streets" (the private roadway within
the common area/public right-of-way). If there are other types of on -site BUA
that were lumped into the "On -site streets" BUA, please report them under
their appropriate BUA type.
The drainage areas listed on the Application have been revised such that the total and
x '"4 84 `' ° on -site drainage areas match. The on -site streets BUA has been broken down into on -
site streets and on -site parking.

September 10, 2021
Page 2 of 5
2) There appears to be a discrepancy between the total BUA allocated to the lots
as shown in the Application and plans (84,500 so, and the sum of the
individual lot allocations as shown in the deed restriction document and
calculation booklet (adds up to 84,450 sf). Please revise as needed for
consistency.
The total lot BUA has been updated on the plans and application to match the
stormwater report.
3) Please indicate the project site location on the USGS topographic map
(Section VI, 6).
Project site location is indicated on the attached USGS Quad Map in the bottom
right corner. This was provided with the last submittal.
4) Please ensure that the on -site surface water surface area is excluded from the
"total area" of the "total project" section of the "impervious area"
calculations shown on page 8 of the calculation booklet (Section VI, 7).
The impervious calculations on page 8 of the stormwater report have been updated to
exclude the on -site sui face water area from the total project area.
5) Please list the identity and qualification of the individual that made the on -
site wetland determination in the main set of plans (Section VI, 8m).
The existing wetlands callout on the plans has been modified to include the
qualification and name of the individual that made the on -site wetland
determination.
6) Please delineate the drainage areas to the proposed permanent vegetated
conveyances in the main set of plans (Section VI, 8o). It is noted that the
drainage areas to the proposed permanent vegetated conveyances are
included in the calculation booklet, however, the submittal items outlined in
Section VI, 8 are required to be included in the main set of plans.
The permanent ditch drainage area delineation lines are shown on Sheet C6.0. The
drainage area for each permanent ditch is shown on the permanent ditch design table
in the detail on Sheet C8.1.
7) Please clearly show the required vegetated setbacks from surface waters in
the main set of plans (Section VI, 8p). More information about the vegetated
setback requirements can be found in 15A NCAC 02H .1003(4) & 15A NCAC
02H .1017(10).
The required 30' vegetative setback has been shown on the plans. (See sheets C3.0
and C6.0.) There is no proposed BUA within the 30' vegetative setback.
MCKIM&CREED

September 10, 2021
Page 3 of 5
8) Please either remove culvert 4 or provide a justification for its inclusion in a
low -density project. 15A NCAC 02H .1003(2)(c) allows for a minimal amount
of non -vegetated conveyances when it cannot be avoided (such as the
road/easement crossings that culverts 1-3 are needed for), however, it
appears as though culvert 4 could be replaced with a vegetated conveyance
that captures the runoff from swale 8 and from culvert 3 and is therefore
avoidable.
This drop inlet and culvert outlet were required by the Town of Weddington to
prevent erosion on the relatively steep slope down to the pond. Without the
structure, the whole ditch would require riprap to prevent erosion. We added a
structure to drop and discharge the water into a ditch with only 0.6% slope to
minimize erosive flows and allow for vegetative conveyance.
9) Please clarify if the short segment of swale connecting culvert 3 to culvert 4 is
part of one of the labeled swales or if it is its own separate swale. If it is a
separate swale, please label it as such on the plans and include the design
information for the swale in the calculations and Supplement-EZ Form.
The short segment of Swale connecting Culvert 3 to Culvert 4 is included in the
calculation for Permanent Ditch #4. This calculation was revised to include the
additional drainage area from Permanent Ditch #10. All ditch calculations were
updated as well to include the 1' wide ditch bottom as shown on the plans.
(Previously, the calculations were based on V-bottom ditches).
10) Please correct the following issues with the Supplement-EZ Form:
a) Cover Page:
i) Line 2 — Please list the project area (as shown in Section IV, 7 of the
Application) for this item, not the "property" area (as shown in
Section IV, 4 of the Application).
The total project area was updated to match the Application.
b) Drainage Area Page:
i) Similar to the earlier comment about the BUA table in Section IV, 10
of the Application, the "drainage area" that should be reported on
Lines 5-7 of the entire site column should match the information in
Section IV, 10 of the Application and should refer to the total project
area.
These values have been updated to match the Application.
MCKIM&CREED

September 10, 2021
Page 4 of 5
ii) Similar to the earlier comment about the BUA table in Section IV, 10
of the Application, it is recommended to further breakdown the BUA
shown in the "Roadway' portion of Line 12 as appropriate.
These values have been updated to match the Application.
c) Low -Density Page:
i) Line 12 —This item is required per 15A NCAC 02H .1003(4)(e).
This has been changed to "yes" as required.
ii) Vallow Column — Typically, we determine the maximum allowable
velocity in a vegetated conveyance based on the type of grass to be
used and the type of underlying soils (A table in Part C-11 of the
Stormwater Design Manual summarizes this information). Please
provide some form of technical justification (i.e., a spec or some other
information from the manufacturer) showing the maximum allowable
velocities and/or sheer stress for the proposed netting and matting
linings so that we may verify that the conveyances will remain stable
for the 10-year storm event.
The maximum allowable velocity in the table has been changed to 5.5 fps,
which is taken from Table 1 in Part C-11 of the Stormwater Design Manual
for Tall Fescue grass in Erosion Resistant Plastic (Clay Mixes) soil.
11) 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:
ittl)s: j./edgcs.deg.nc.govJFot-nis/SW-Supplemental-Upload
NOTE: When uploading plan sheets, please break the plan set up into
its respective sheet types. The form used to upload the submittal
items automatically renames the files based on the file type. Currently,
there are 19 pages worth of "cover sheet" in the electronic file for this
project since that was the selected file type for the entire plan set
(which is something that will need to manually corrected). We've also
had issues in the past with large files, particularly plan sets, not
uploading through the form properly.
V� MCK1M&CREED

September 10, 2021
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b) Hard copies must be mailed or delivered to the following address:
i) For FedEx/UPS:
Suzanne McCoy
512 N. Salisbury Street, Office 640K
Raleigh, NC 27604
ii) For USPS:
Suzanne McCoy
1612 Mail Service Center
Raleigh, NC 27699-1612
If additional clarification is needed to ensure your comments have been
addressed, please contact me at 704-841-2588, ext. 1360.
Respectfully,
Patrick Needham, PE
Project Engineer
Cc: Project File
MCI< M&CREED