SW6220601_Response to Comments_20221103

KEN BRIGHT ASSOCIATES, PLLC
Consulting Engineers
October 24, 2022
Jim Farkas
Environmental Engineer
North Carolina Department of Environmental Quality
Division of Energy, Mineral, & Land Resources — Stormwater Program
512 N. Salisbury Street, Office 640M
Raleigh, NC 27699-1612
Re: SW6220601 Magnolia Ridge Subdivision
Dear Mr. Farkas,
In response to your comments of September 13, 2022, the following changes were made:
Swales flow calculations:
■ Swale 5 — The drainage area value used to calculate the flow in this swale is shown
as 0.13 ac in the plans and in the calculations (resulting in a Q of 0.56 cfs), but is
shown as 0.32 ac in the Supplement-EZ Form (resulting in a Q of 1.38 cfs). Please
revise as needed. Supplement-EZ form was corrected
■ Swale 12 — The runoff coefficient, C, value used to calculate the flow in this swale is
shown as 0.49 in the calculations (resulting in a Q of 11.4 cfs), but is shown as 0.59 in
the Supplement-EZ Form (resulting in a Q of 13.8 cfs). Please revise as needed.
Supplement-EZ form was corrected
■ Swale 21 — The flow in this swale is shown as 25.5 cfs in the calculations, but is
shown as 2.47 cfs in the Supplement-EZ Form. Please revise as needed.
Supplement-EZ form was corrected
Outlet protection:
■ Please provide the riprap sizing calculations to show that the outlets will remain stable
in accordance with 15A NCAC 02H .1003(5). Calculations provided. Revised sheet
C12.1 is included with the apron information for pipes at Sta 0+20 & Sta 6+85
Blossom.
BUA information:
■ Adding up the BUA (as shown in the Application & Supplement-EZ Form) equals
521,575 sf (410,000 sf + 103,075 sf + 5,500 sf + 500 sf + 2,500 sf = 521,575 sf)
whereas the total BUA is shown as 521,075 sf in the Application & Supplement-EZ
Form. Please revise as needed. The BUA calculations were modified as indicated
in the revised application.
■ The percent BUA for the low -density project area is shown as 23.18% in Section IV,
10 and is shown as 22.76% in Section IV, 8 (for this project, these values should be
the same). Please revise as needed. Project density calculation information is shown
in 15A NCAC 02H .1003(1). The correct value is 22.76% and both places match.
Supplement-EZ Form:
Drainage Area Page:
■ Please revise in accordance with earlier comment. Corrections made
Low -Density Page:
P.O Box 553 Phone: [phone]
2305 Carthage Street
Sanford, NC 27330 e-mail: [e-mail]

Line 4 — Swale 9 appears to have side slopes of 3:1 (whereas the other swales have
side slopes of 4:1) please make a note of this in the Additional Information Section
(Line 15) Note was added
Line 5 — Please provide this value. There may be a formatting issue with this cell that
may prevent you from being able to enter this information in correctly, if that is the
case, please either manually enter it in or add this information in the Additional
Information Section (Line 15). Note was added to line 15.
Line 15 — Please add a note in this section indicating that the swale information is on
an attached page. swale information is on an attached page Note was added
NOTE: The dry ponds were not reviewed for compliance with the MDCs since they are not
required in order to meet the treatment requirements for this project. Special permitting
language will be added to the permit indicating that these are non -enforceable SCMs
(essentially stating that they are only included as part of the permit documents for reference,
they were not reviewed for the MDCs, and they are not a part of the permitted treatment
system). Okay.
NOTE: Can you please provide a source for the Manning n value chart used in the calculations?
(This isn't a required item, I'm just personally curious as I haven't seen that chart before) It is
Figure 8.05C from the NC Erosion and Sediment Control Planning and Design Manual
The following attachments are included
- 1x hard copy & 1x electronic copy of the revised calculations.
- 1x hard copy & 1x electronic copy of the revised pages of the Application Form.
- 1x hard copy & 1x electronic copy of the revised pages of the Supplement-EZ Form.
- 2x hard copies & 1x electronic copy of the revised plan sheets (if needed), NOTE: The
swale design summary table that was provided in the Supplement-EZ Form is also
located on plan sheet C12.5. Revised sheets C12.1 & 12.5 are included
- 1x hard copy (2x hard copies for plan sheets) & 1x electronic copy of anything else
needed to address the above comments.
If you have any questions, please feel free to contact me.
Sincerely,
) V. )
Ken W. Bright, PE
File.project2021/Letter Response to Comments from Stormwater 10-24-2022
P.O Box 553
2305 Carthage Street
Sanford, NC 27330
Phone: [phone]
e-mail: [e-mail]