SW5210603_Response to Comments_20211004

ENGINEERING Mh6'
Designing the Future... Today!
Wednesday October 4th, 2021
Jim Farkas
Environmental Engineer
NCDEQ Stormwater Program
512 N. Salisbury Street, Office 640 K
Raleigh, NC 27604
RE: Second Request for Additional Information
Stormwater Permit No. SW5210603
Duck Thru at Spring Hope, NC
Nash County
This letter is written in response to the comments and recommendations from Jim Farkas
dated September 23rd, 2021. A reply or explanation for each comment issued by your
office is provided below and follows the original format of your memorandum.
NCDEQ Stormwater Program
Jim Farkas Jim. Farkas(a)ncdenr.gov [phone]
Based on the provided information, it appears as though the Bojangles at Spring
Hope (SW5200701) will need to perform a minor modification on their permit,
indicating that the drainage area and BUA draining to their SCM are being
reduced (we can add language into their modified permit so that they get the
credit for this reduction in BUA) and that part of their project area is being sold
off. This minor modification should be applied for concurrently with this permit
(ideally, I would like to issue them together since they are intertwined). Since
BUA that will exist within this (SW5210603) project area will be treated by the
Bojangles (SW5200701) SCM, the Bojangles permit (SW5200701) will be set up
as the master permit and this project (SW5210603) will utilize an off -site SCM.
For this project (SW5210603), you will need to do the following:
From our phone conversation with you on 10/11/21 we will be submitting a
modification to the Bojangles at Spring Hope Stormwater Permit
(SW5200801) for its change in drainage area caused by the Duck Thru site.
We will make the changes below to the Duck Thru Stormwater Permit
(SW5210603) as you have requested.

A. Section II, 2 of the Application — Please indicate that this project also drains to an
offsite stormwater system (do not uncheck the high -density box).
Done, the application has been updated. The updated section is included in
this response.
B. Section IV, 9 of the Application — Please update this value to "2", one for the
proposed, on -site wet pond and one for the off -site SCM.
Done, the application has been updated. The updated section is included in
this response.
C. Section IV, 10 of the Application — Please add a second drainage area column
for the portion of the project area that drains to the off -site SCM. For this
drainage area to the off -site SCM, only include the portion of the drainage area
that is located within this project's project area, not the entire drainage area to
the offsite SCM. Any proposed BUA added to the access road (outside of this
project area, but within the project area of SW5200701) can be handled by the
SW5200701 minor modification.
Done, the application has been updated to show the drainage area that
drains to the off -site SCM permitted in SW5200701. The updated section is
included in this response.
D. Similar to the prior point, the Supplement-EZ form should be revised to include
the use of the off -site SCM. In addition to including the off -site drainage area on
the Drainage Area Page of this form, there is an item on the Cover Page (Line 6)
that should be marked as "Yes" and doing so will allow an Off -Site SCM Page to
be generated (similar to the Wet Pond Page).
The EZ form has been updated per your requests.
2. Prior Comments 2 & 3 — Laserfiche is currently down so I can't verify that these
comments have been addressed (I have no reason to doubt that they were
addressed, but I just can't verify at this time). Once Laserfiche is back online, I
will verify that these items have been addressed and let you know if they have
not been. If you plan on resubmitting the electronic files within the next couple of
business days, please email me the PDFs since you will not be able to upload
them through the usual portal.
I will email you the comment response, updated plan sheets and
associated documents to ensure they get to you.

3. Prior Comment 5 — "Per 15A NCAC 02H .1003(3)(b), any off -site areas that
drain to the proposed SCM must be accounted for at their full build -out potential.
This can either be handled by having the Applicant and the Off -site Property
Owner enter into a legal agreement limiting the amount of BUA that can be built
on this off -site area (there's more information on this following the comments) or
by assuming that the off -site area is at its maximum build -out potential (typically
100% BUA). For this reason, it is recommended to bypass all off -site areas
around the proposed SCM."The off -site drainage area must either be bypassed
or accounted for at its full build -out potential, either through a legal agreement
limiting future BUA placement in this area (which NCDOT will most likely not
enter into with the Applicant) or by assuming this area is at its full build -out
potential (100% BUA). While not likely, it is possible that, at some point in the
future, NCDOT could add a sidewalk, a bike path, or re -grade this area to
increase the amount of BUA being directed to the proposed SCM without the
owner's consent (and by extension bring the SCM out of compliance with the
permit). It is for this reason that we require any off -site drainage areas that are
not bypassed or limited by a legal agreement to be accounted for at their full
build -out potential. Taking a quick look at the calculations, the proposed wet
pond appears to be able to accommodate this extra storage volume without the
need for a redesign. You can place a note in the "Additional Information" section
of the Wet Pond Page of the Supplement-EZ Form indicating that this wet pond
is oversized and has "x" cubic feet of additional water quality storage volume
available to account for this off -site drainage area.
Considering the total water quality storage for this pond is 31,063 cf and
the current water quality storage design volume is 12,549. There is an
additional 18,514 (31,063 — 12,549) cf available to treat increases in
impervious area. A note stating "Should the 5,764 sf of offsite drainage
area become built upon the Duck Thru Pond has an additional 18,514 cf of
storage available to treat the increase in impervious area" has been added
to the Wet Pond page of the EZ form.

4. Prior Comment 9 — "Since there are off -site components to the proposed SCM
drainage area, please explain how the off -site impervious area was determined
(Section IV, 11)."Similar to above, you can add a note here stating that the wet
pond has additional water quality storage volume and can treat this off -site area if
it ever becomes BUA.
Same response as comment #3. Considering the total water quality storage
for this pond is 31,063 cf and the current water quality storage design
volume is 12,549. There is an additional 18,514 (31,063 — 12,549) cf available
to treat increases in impervious area. A note stating "Should the 5,764 sf of
offsite drainage area become built upon the Duck Thru Pond has an
additional 18,514 cf of storage available to treat the increase in impervious
area" has been added to the Wet Pond page of the EZ form.
5. Prior Comment 13 — "...Please also clearly show the sediment storage elevation
(in both the forebay and main pool) on the wet pond cross-section." Please do
this as it is currently ambiguous as to how deep the wet pond should be
excavated (the plan view indicates one thing and the cross-section another).
Please provide some clarification on the cross-section view that indicates that the
forebay and main pool need to be excavated to 255 ft and 251 ft respectively.
This could be accomplished with a note under the detail or by making the detail
more detailed.
Done, more detail has been added to the cross section outlining the
sediment storage elevations.
6. Prior Comment 17 — "The incremental storage shown at elevation 262.0 on plan
sheet CE-04 (10,015 co appears to be incorrect (the incremental storage shown
might be the provided storage between elevation 261.0 & 262.0 however, a
cross-section for elevation 261.47 is included in the stage -storage table and
should be accounted for)."There appears to be an issue with the stage -storage
table near the permanent pool elevation. The cross -sectional area of pool at the
temporary ponding elevation (261.4 ft) does not appear to be correct. The cross -
sectional area at elevation 261.4 ft (11,566 sf) is larger than the cross -sectional
area at elevation 262.0 ft (11,333 sf), which isn't possible, the cross -sectional
areas of the pond should increase as the elevation increases (otherwise the pond
would have an hourglass figure). Interpolating the cross -sectional area at
elevation 261.4 ft from the cross -sections above and below it results in a cross -
sectional area at elevation 261.4 ft closer to 10,000 sf (and a cumulative storage
volume at this elevation of a couple hundred cubic feet less than the design
volume). Please revise as needed.
I have changed the table to its correct depth and area. The correct WQV is
at stage 1.43, or 261.43' in elevation. The correct contour area is 10,110.
The remaining values on the table have been updated. Please see CE-04 for
these changes.

7. Drainage area 1 e (plan sheet CE-08) appears to have more BUA (9,939.7 sf)
than drainage area (9,929.7 sf). Please revise as needed.
The correct value for drainage area 1e is 9,939.7 sf. The drainage sheet has
been corrected.
8. Please provide calculations and outlet protection (if applicable) for the 4 ft wide
concrete flume that flows into the forebay of the proposed wet pond (General
MDC 4).
The flume should be dispersing into the pond at the permanent pond level
(260'). Therefore, the water should be dispersing the energy of the
discharge and outlet protection calculations should not be applicable.
However, we will add an 8'x8' pad of Class B Rip Rap for outlet protection.
9. 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.gov/Forms/SW-Supplemental-Upload
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
c. For USPS:
Suzanne McCoy
1612 Mail Service Center Raleigh, NC 27699-1612
The documents will be provided as you have requested.
If there are any further questions, please contact Stocks Engineering at 252.459.8196.
Thanks!
Sincerely,
Engineering, P.A.
Isaac Hardison