SW5221102_Response To Comments_20230414

ENGINEERING
Designing the Future... Today!
April 7th, 2023
Jim Farkas
State Stormwater Engineer
DEMLR Post -Construction Stormwater Program
RE: Request for Additional Information Stormwater Permit No. SW5221102 Bryson's Ridge
Subdivision — Phase 2 Nash County
This letter is written in response to the red -lines and comments dated February 23rd, 2023,
regarding the stormwater application for Bryson's Ridge Subdivision — Phase 2 in Nash County, NC.
A reply or explanation for each comment issued by your office is provided below and follows the
original format of your memorandum.
1. Please reach out to the 401/Buffer Permitting Branch
(https:Hdeg.nc.gov/about/divisions/water-resources/water-quality-permitting/401-
buffer-permitting-branch) to see if a permit is needed for the proposed wetland crossing. If
required, please update Section II, 4a of the Application.
We have acquired the401 and 404 permits for the site. Copies have been provided in this
response package. In addition, Section II, 4a of the Application has been updated to reflect
the 404/401 proposed impacts as additional project requirements.
2. Please upload the electronic files for this project at the following link:
https:Hedocs.deg.nc.gov/Forms/SW-Supplemental-Upload. Electronic files are
required in accordance with 15A NCAC 02H .1042(2).
Understood, updated files will be uploaded to the link.

3. The following issues were noted with the general design of the proposed SCMs:
a. Please provide calculations showing that the inlets and outlets of the SCMs are
stable in accordance with General MDC 4.
All inlets will be discharged at the main pond elevation for both ponds. Meaning,
most of the energy from the discharge will be dissipated by the ponded water.
Additional permanent Rip Rap Aprons have been provided for the inlets on CE-28
am CE-29. Pond 2 will have its discharge over a concrete weir into #57 stone and
its 4" outlet will discharge into a 6' x 6' scour hole. Pond 3's Rip Rap Apron has
been sized and is shown on CE-17 and CE-24.
b. Please clearly show the stormwater maintenance access & easement on the plans
(General MDC 8 & 9).
Done, please see CE-01 and CE-02.
c. The drawdown calculations (Wet Pond MDC 7) should be based upon the design
volume of the SCM (typically the volume that can be stored above the
permanent pool surface elevation and below the lowest bypass elevation). For
example, for Wet Pond #2, the permanent pool surface elevation is at elevation
243.5' and the lowest bypass elevation is at elevation 245.5' (the weir outlet
structure). The provided calculations use the head value associated with these
two elevations (2.0') but they do not use the storage volume associated with
these two elevations (approximately 62,000 cf) when determining the drawdown
time. Please revise as needed.
Understood we have corrected the drawdown time for both ponds as described.
For Pond 2, the design volume is calculated from 243.5' (elevation @ outlet) to
245.5' (elevation @ the weir outlet). For Pond 3, the design volume was
calculated from 253.5' (elevation @ the outlet) and 255.5' (the elevation @ the
top of drop inlet). Please see updated drawdown times attached.
d. This project is located within a Nutrient Sensitive Watershed (NSW). Please
ensure that the SCM reduces nutrient loading in accordance with 15A NCAC
02H .1017(9)(c).
We have filled out the SNAP Tool for this site. According to the results, we meet
the nutrient loading targets for Nitrogen and Phosphorous. Please see attached.

4. The following issues were noted with the design of Wet Pond #2:
a. Please exclude the sediment storage zone from the forebay volume calculation
(Wet Pond MDC 5a). Per the plans, the top of the sediment storage zone in the
forebay is located at elevation 240.0'. Any storage volume provided below this
elevation does not count towards the volume of the forebay. Please revise as
needed.
We have adjusted the pond to have the bottom of the forebay be 238' on the plans
for Wet Pond #2. Please updated calculations and CE-23.
b. As designed, this pond appears to short-circuit (Wet Pond MDC 4). Please relocate
the drawdown orifice further away from the inlets/forebay (see attached for
possible alternative locations) to better maximize the flow path through the wet
pond.
Understood, we have moved the orifice to be in a location to avoid short
circuiting in the pond. Please see CE-23.
c. There appears to be a discrepancy between the vegetated shelf size as shown in
the calculations (5,232 sf with 1,308 plants) and as shown on the plans (4,506 sf
with 1,128 plants). Please revise as needed for consistency. NOTE: Both planting
plans meet the minimum required plant density requirement as outlined in Wet
Pond MDC 11b it is just unclear which one is actually being proposed.
Noted, the vegetated shelf has been updated to the correct value of 4,506 sf on
CE-23 and the calculations. Please see attached.
5. The following issues were noted with the design of Wet Pond #3:
a. There appears to be an issue with the provided stage -storage tables for the main
pool and forebay. The plans indicate that the permanent pool surface elevation is
at elevation 253.5' whereas the stage -storage tables for the forebay and main pool
only go up to elevation 253.0' and the incremental volume calculation between
elevations 252.0' & 253.0' appears to be incorrect. Please revise as needed.
We have added 253.5' to the calculations. In addition, we have changed the
storage for removal to be 250.5' instead of 250' for Pond 3. Please see calculations
and CE-24.

b. There appears to be a discrepancy between the drawdown orifice size as shown in
the calculations (1.5" diameter) and the plans (1.75" diameter). Please revise as
needed.
1.5" is the correct orifice size. The plans and calculations now match. Please see
CE-24 and calculations.
6. Please ensure that the area downstream of FES 205 meets the curb outlet system
requirements outlined in 15A NCAC 02H .1003(2)(d)). Please also revise the portions of
the Low -Density Page of the Supplement-EZ Form related to the curb outlet system. NOTE:
Curb outlet systems can either be swales (as indicated in the Supplement-EZ Form) or
vegetated areas. If using a vegetated area, fill out as much of the Supplement-EZ Form as
possible.
We have added a swale downstream of FES to be in compliance with the code mentioned
in this comment. The new swale is 5-47. The modeling Results have been included along W/
an updated Low Density EZ page. Please see CE-17 for the updated swale location.
7. The following issues were noted with the Supplement-EZ Form:
a. Wet Pond Page:
i. Line 25 —The temporary pool surface elevation is typically determined by the
lowest bypass elevation (245.5' for Wet Pond #2)
Understood, line 25 is now fixed.
ii. Lines 26-28, Wet Pond #3 Column — See earlier comment with regard to the
stage -storage tables, please revise as needed.
Lines 26-28 have been updated to match the changes made.
iii. Line 32 —See earlier comments.
Line 32 has now been updated to match.
iv. Line 34 —The cleanout depth of the forebay is the distance from the permanent
pool surface elevation (243.5' for Wet Pond #2 & 253.5' for Wet Pond #3) to the
top of the sediment storage zone for the forebay (240.0' for Wet Pond #2 & 250.0'
for Wet Pond #3), expressed in inches.
We changed the sediment removal to 239' for Pond 2, making the depth 54in.
Pond 3's removal is now 250.5' making the depth 36".

v. Line 35 — See earlier comment. The design volume is typically the volume that
can be stored above the permanent pool surface elevation and below the lowest
bypass elevation.
Understood, this value has been updated.
vi. Lines 37 & 55 — See earlier comment with regard to the drawdown orifice size.
Please revise as needed.
The orifices now match, please see calculations and EZ-form.
vii. Line 40 — See earlier comment with regard to the drawdown calculation.
Understood, this value has been updated.
b. Low -Density Page:
Lines 4 & 15 — Since multiple different cross slopes for the vegetated
conveyances are proposed, please indicate this in the additional
information section.
Understood, additional information has been updated w/ the range of the side
slopes for the swales.

8. 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:Hedocs.deg.nc.gov/Forms/SW-Supplemental-Upload
b. Hard copies must be mailed or delivered to the following address:
i. For Fed Ex/UPS:
Jim Farkas
512 N. Salisbury Street, Office 640M
Raleigh, NC 27604
ii. For USPS:
Jim Farkas
1612 Mail Service Center
Raleigh, NC 27699-1612
iii. Hand Delivery:
Please reach out to me prior to hand delivering a submission to make sure
that I (or someone else in my group) will be able to receive the submission.
Do not leave the package in the foyer with the security guard.
Understood, we will submit the response package through the appropriate channels.
If there are any further questions or concerns, please contact Stocks Engineering at
252.459.8196. Thanks!
Sincerely,
Stocks Engineering, P.A.
Isaac Hardison