SW6231106_Response To Comments_20240228

STOCKS
ENGINEERING
Designing the Future,Today
Monday, February 26, 2024
Brianna Holland
512 N. Salisbury St.
Office 625Y
Raleigh, NC 27604
RE: Response — Request for Additional Information
Stormwater Permit No. SW6231106
High Density Subdivision — 3 Wet Ponds
Bryant Road Subdivision, Harnett County
To Whom it May Concern,
This letter is written in response to the comments, issued February 11, 2024, regarding the proposed
subdivision in Erwin that is currently known as Bryant Road Subdivision. A reply or explanation for
each comment issued by the Engineer is provided below and follows the original format of your
memorandum.
1. Per the latest USGS topographic map, it appears that surface water is immediately
adjacent to the site and a portion may be on-site. Ensure that the surface water is
excluded from the project area, and that vegetated setbacks are clearly shown on
the plans. A landscape buffer is currently shown on the plans, but per 15A NCAC
02H.1042(2)(g)(iii), vegetated setbacks from the surface water must be shown on
plans. Per 15A NCAC 02H .1017 (10), at least 30' is required. Note that vegetated
setbacks must remain vegetated.
The 30' vegetated setback are now shown. There is no proposed grading
activity within the 30' vegetated setbacks.
2. Per the Application, Section IV, 4, the total property area is 54.82 acres. The sum of
the total drainage areas provided in the drainage area table in Section IV, 10, is
(588,931 SF+ 1,228,828 SF + 814,572 SF)/(43,560 SF/acres)= 60.43 acres. This
indicates that there is off-site area draining to the SCMs.
There is almost no offsite area draining to the SCMs. The only exception being
a small portion of ROW along St. Matthews Road that drains into SCM#2. I
misunderstood the chart in the application and included all areas draining to
the offsite discharge point. Per comments and emails with Brianna, I have
revised this chart on the application.
J.Michael Stocks, PE 252.459.8196(voice)
801 E.Washington Street 252.459.8197(fax)
PO Box 1108 252.903.6891 (mobile)
Nashville, NC 27856 [e-mail]

a. Please revise the package to ensure that the off-site portions of the drainage
areas to the SCMs are correctly accounted for at their full build-out potential
(per 15A NCAC 02H .1003(3)(b)). Full build-out potential is determined by
either having the property owner and permittee enter into a legal agreement
limiting the amount of BUA and drainage area being directed from the off-site
area to the SCM or by assuming that the off-site area is 100% BUA, its full
build-out potential. It is recommended to bypass off-site drainage areas
around proposed SCMs as the permittee has no control over how off-site
areas are developed (which is why they are required to be accounted for at
their full build-out potential). Indicate which option is being pursued and revise
the package as necessary. See additional information on this item at the
conclusion of this letter.
The chart and package have been revised. The offsite area that drains
across our property is not directed to the SCMs except for a small area
of existing ROW that is directed through SCM#2.
3. Application, Section IV, 3 — Please revise. Stormwater runoff from this project drains
to the Cape Fear River Basin.
The Application has been revised to reflect the correct river basin.
4. Stormwater outlets shall be designed so that they do not cause erosion downslope
of the discharge point during the peak flow from the 10-year storm event as shown
by engineering calculations. If inlet and/or outlet protection being utilized to meet this
requirement, ensure that it is shown on the plans with sizing specifications that
correspond to the design calculations.
Outlet protection calculation worksheets for the pond outlets have been added
to the calculation packet and the sizing is shown on the plans.
J.Michael Stocks,PE 252.459.8196(voice)
801 E.Washington Street 252.459.8197(fax)
PO Box 1108 252.903.6891 (mobile)
Nashville, NC 27856 [e-mail]

5. All Wet Ponds
a. Per General MDC 4, The inlets SCMs shall be designed to protect the SCM
from erosion resulting from stormwater discharges. The outlets of SCMs shall
be designed so that they do not cause erosion immediately downslope of the
discharge point during the peak flow from the 10-year storm event as shown
by engineering calculations. If inlet and/or outlet protection being utilized to
meet this requirement, ensure that it is shown on the plans with sizing
specifications that correspond to the design calculations.
Outlet protection is now shown in the plan set and the calculation
worksheets have been added to the calculation packet.
b. Per the drainage area table provided in Section IV, 10, the total drainage area
to Wet Pond 1 is 588,931 SF, which is 13.52 acres. The provided calculations
sized Wet Pond 1 using a drainage area of 5.09 acres. Please revise for
consistency, as this results in an underestimation of the minimum treatment
volume if 13.52 acres is the correct drainage area to Wet Pond 1. Similar
issues appear in the calculations for Wet Pond 2 and 3.
The chart in section IV 10 of the application has been revised to only
reflect the area that is draining into the SCMs. The onsite bypass area
and the offsite areas that drain across our property have been excluded
from this table.
c. Per Wet Pond MDC 1, the volume of the main pools and the forebays should
not include the sediment storage zone since this portion of the pond is
intended to be filled up with sediment and can therefore not count towards
provided storage volume. Please revise the stage storage tables, associated
volumes, and calculations (such as average depth). Revise the Supplement-
EZ accordingly.
The sediment storage was lowered 1'so that the other
documents/calculations did not need to change. The stage storage
tables were revised per other comments.
J.Michael Stocks,PE 252.459.8196(voice)
801 E.Washington Street 252.459.8197(fax)
PO Box 1108 252.903.6891 (mobile)
Nashville, NC 27856 [e-mail]

d. Per Wet Pond MDC 3, the forebay and main pool shall have a minimum
sediment storage depth of six inches. Per MDC 5 (b), the forebay entrance
shall be deeper than the forebay exit. Revise the plans accordingly. For
example, the plans indicate that the exit of the Wet Pond 1 forebay is at
elevation 191.00, but the storage elevation is at elevation 189.00. Revise
Ponds 1-3.
The SCM detail sheets have been revised to list the forebay exit that still
provides 6 inches of sediment storage above the bottom of the forebay.
e. Per Wet Pond MDC 2, the average depth shall be between 3-8 ft.
i. For example, per the provided Wet Pond 1 calculations, the average
depth for the pond is 1.5 ft. Please revise to meet this minimum design
criteria.
1. Please revise the SA/DA ratio calculation to utilize the
calculated average depth. The calculations used an average
depth of "3" which does not correspond to the provided
calculations or the average depth provided in the Supplement-
EZ.
There was a formula error in the excel where the average
depth calculated to be 1.5' was reading the wrong cells.
That has been corrected. All of the SA/DA ratio calculations
have been revised to include the increased average depth
which ultimately reduced the surface area of the ponds.
The required volume and the size of the actual designs
were not changed.
f. Per Wet Pond MDC 7, the design volume shall draw down to the permanent
pool level between two and five days. The design volume for a wet pond is
equivalent to the volume that is retained between the temporary pool
elevation and the permanent pool elevation. Per the Supplement-EZ, using
Wet Pond 1 as an example, the temporary pool elevation is 195.35 and the
permanent pool elevation is 193.08. This is not consistent with the 1 ft driving
head from water surface to centroid orifice provided in the calculations.
Please revise for consistency.
J.Michael Stocks, PE 252.459.8196(voice)
801 E.Washington Street 252.459.8197(fax)
PO Box 1108 252.903.6891 (mobile)
Nashville, NC 27856 [e-mail]

i. Please revise the design volume listed in the Supplement-EZ, Wet
Pond Page, Line 35 to correspond to the volume stored between the
temporary and permanent pools.
The calculations for the drawdown times have been revised. This
caused minor changes to the orifice sizes and very minor
changes to the hydra flow reports. The new reports are included
in the calculation package.
g. Please specify the species of turf to be installed on the dams and
embankments to ensure compliance with Wet Pond MDC 11 (a).
Each detail sheet specifies that the pond side slopes should be seeded
with centipede seed at a rate of 60 lbs./ac.
h. O&M Agreement
i. Per the plans, the proposed wet ponds do not appear to incorporate a
vegetated filter strip (a vegetated filter strip is typically located
downstream of the outlet structure and is different than the vegetated
shelf). Please provide a revised table.
ii. The O&M Agreement is inconsistent with the package. The following
uses Wet Pond 1 as an example, but the principles can be applied to
Ponds 1-3.
1. The O&M Agreement lists a temporary pool elevation of 195.5.
The temporary pool of a wet pond is set by the lowest bypass.
Per the details provided on Sheet D-17 and the Supplement-EZ,
this is the top of the drop inlet at 195.35. Please revise for
consistency.
2. The O&M Agreement lists the forebay sediment removal
elevation as 188 and the bottom elevation as 187, but this does
not correspond to the rest of the package.
3. The O&M Agreement lists the main pool sediment removal
elevation as 188 and the bottom elevation as 187, but this does
not correspond to the rest of the package.
The O&M agreement has been revised per the above
comments.
J.Michael Stocks, PE 252.459.8196(voice)
801 E.Washington Street 252.459.8197(fax)
PO Box 1108 252.903.6891 (mobile)
Nashville, NC 27856 [e-mail]

6. Wet Pond 1
a. The Supplement-EZ, Wet Pond Page, Wet Pond 1 Column, Line 37 lists an
orifice diameter of 2 inches, but the plans show 1.5". Please revise for
consistency. You may need to overwrite the cell or list it in Line 55 as
"Additional information." A similar issue is present for Wet Pond 3.
The form was pre-set to round to nearest whole number. This has been
revised to accurately represent the proposed orifice size.
b. In the Supplement-EZ, Wet Pond Page, Line 24, the elevation of the top of
the vegetated shelf is stated to be 293.08. This appears to be an error.
You are correct, the top should have been 193.08. This has been
corrected.
7. Wet Ponds 1-2 Only: Please revise the stage storage tables to include the
permanent pool elevation and the temporary pool elevations so that volumes,
surface area, and related calculations can be confirmed.
The stage storage tables have been revised to include these specific
elevations, areas, and volumes.
8. When uploading the response, ensure that the electronic repository is complete. The
narrative, calculations, Supplement-EZ, O&M Agreement, NRCS Soils Map, USGS
topographic map, and necessary plan sheets were noted to be missing.
Ok, Thanks.
9. Provide PDFs of all revisions, 2 hardcopies of revised plan sheets, Application, and
Supplement-EZ, 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:
Brianna Holland
512 N. Salisbury Street, Office 625Y
Raleigh, NC 27604
ii. For USPS:
J.Michael Stocks,PE 252.459.8196(voice)
801 E.Washington Street 252.459.8197(fax)
PO Box 1108 252.903.6891 (mobile)
Nashville, NC 27856 [e-mail]

Brianna Holland
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.
The digital copies have been uploaded and the hard copies have been mailed
via FedEx.
Included you will find all the requested plans with the comments addressed and any additional
information that was needed to show the modifications to the plans as described above. If you have
any further questions regarding the above response to the comments issued, please contact us.
Thank you.
Sincerely,
Stocks Engineering, P.A.
J . Andrews Stocks
J. Andrew Stocks, PE
J.Michael Stocks,PE 252.459.8196(voice)
801 E.Washington Street 252.459.8197(fax)
PO Box 1108 252.903.6891 (mobile)
Nashville, NC 27856 [e-mail]