SW4210601_Response To Comments_20230303

NNERLY
ENGIN EERINGG &DESIGN, INC.
March 2, 2023
Jim Farkas
Environmental Engineer
Dept. of Environmental Quality
Division of Energy, Mineral &
Land Resources Stormwater Program
512 N. Salisbury Street
1612 Mail Service Center
Raleigh, NC 27699-1612
RE: Comments and Responses - Stormwater Permit
Stormwater Permit No. SW 4210601
Third Request for Additional Information
Wynnfall Subdivision — Phase One, Davidson County
Mr. Farkas,
Attached are Kennerly Engineering & Design, Inc. (KED) responses to emailed comments from
your review on February 2nd, 2023.
The comments and responses are in the order of the letter received.
Should you have any questions, please do not hesitate to contact us at 336.775.2118.
Sincerely,
Timothy S. Kennerly, PE
Vice President/ Senior Engineer
Phone:[phone]
12133 N. HWY 150, Ste. F Winston-Salem, NC 27127 Fax: [phone]
www.kennerlyengineering.com

21 WYNNFALL SUBDIVISION PHASE ONE STORMWATER PERMIT MOD
PERMIT #SW4210601 - THIRD REQUEST FOR ADDITIONAL INFORMATION
ADDRESS: HINKLE LANE, LEXINGTON, NC / DAVIDSON COUNTY
Review Comments
1. "Original Comment 2 — "Please complete the drainage area table on Page 3 of the SWU101
Application... [15A NCAC 02H .1042(2)(a)]..." Please make the following corrections to the
Application, Section IV, 10:
a. 'Total Drainage Area Line — See "Off -Site Drainage Area Line" comment. Changing the
Off -Site Drainage Area Line value will change the Total Drainage Area from 1,616,114 sf
to 1,271,952 sf. Please revise."
Response: Have revised the Total Drainage Area to 1,271,952 SF.
b. "Off -Site Drainage Area Line — It is noted that some off -site areas drain onto the project
area/to the proposed vegetated conveyances, however, as noted in the prior request
for additional information letter, low -density projects do not typically have an off -site
component, even if neighboring areas drain onto the site (The reason for this is that the
"low -density drainage area" of this project corresponds to the project area and there
are no off -site components to the project area). Please revise this item to 0 sf."
Response: Have revised this item to 0 SF.
c. "Proposed Impervious Area Line — See "Total Line" comment. Changing the On -Site
Buildings/Lots Line value will change the Total (and the Proposed Impervious Area) from
305,268 sf to 305,229 sf. Please revise."
Response: Have revised to 305,229 SF.
d. "On -Site Buildings/Lots Line — Per the provided Deed Restriction Document, each of the
47 lots is allocated 4,965 sf of BUA. 47 lots at 4,965 sf/lot equals a total of 233,355 sf
(233,394 sf is shown). Please revise."
Response: Have revised to 233,355 SF.
e. 'Total Line —See "On -Site Buildings/Lots Line" comment. Changing the On -Site
Buildings/Lots Line value will change the Total from 305,268 sf to 305,229 sf. Please
revise."
Response: Have revised to 305,229 SF.
2. "Prior Comments 5b & 5c — "Please correct the following issues with the provided plan set:
a. "Please include the type of grass that will be used for the vegetated conveyances on the
vegetated conveyance detail. This item will be used to verify the maximum allowable
velocity for the vegetated conveyances (per 15A NCAC 02H .1003(2)(c)(ii)) and is
KEN N ERLY Phane:: 3667.2118
12133 N. NC HWY 156, Ste. F Fax: 33.
76.0797
Mr eNGMEEWNG a DESIGN, INC. Winston-Salem, NC27127 www.kennerlyengineering.corn

31 WYNNFALL SUBDIVISION PHASE ONE STORMWATER PERMIT MOD
PERMIT #SW4210601 - THIRD REQUEST FOR ADDITIONAL INFORMATION
ADDRESS: HINKLE LANE, LEXINGTON, NC / DAVIDSON COUNTY
required per Section V1, 81 of the Application." The grass specification (Tall Fescue) does
not appear to be provided on the plans. Please revise to include this item on the plans."
Response: Have added Kentucky 31 Tall Fescue Specification to the detail sheets.
b. "Please clearly delineate any on -site wetlands... Please also include a note on the plans
stating the name and qualification of the individual that made this determination." This
item, the name and qualification of the individual that made the determination, was not
provided and is required to be included on the plans per Section V1, 8m of the
Application. Please revise to include this item on the plans."
Response: Have revised plans. No wetlands are present on the project.
c. "Prior Comments 6a, 6b, & 6c — "Please correct the following issues with the design:
a. "As designed, vegetated conveyances 5, 9, 10, 12, 13, 15, 19, and 21 may have
erosive velocities..." Updated calculations were not provided in the latest
submission so this item could not be reviewed. Please provide these calculations.
Based on the information provided in the Supplement-EZ Form, none of the
vegetated conveyances appear to have velocities in excess of their maximum
allowable velocities."
Response: Have provided the updated calculations.
b. "Please provide calculation showing that the natural channel downstream of
vegetated conveyance 21 will remain stable during the 10-year design storm
(Required per 15A NCAC 02H .1003(2)(c)(ii)." As noted above, updated calculations
were not provided in the latest submission so this item could not be reviewed.
Please provide these calculations"
Response: Have provided the calculation for Conveyance 22 which is the down stream
channel of Conveyance 21.
c. "The calculations show vegetated conveyance 21 as having a drainage area of 6.26
ac (back -calculated from the provided flowrate, Q = 23.22 cfs, C = 0.54, & I = 6.87
in/hr), however, the sum of the contributing drainage areas (DAs 5-8 and DA 21) is
7.4 ac. Please revise as needed." As noted above, updated calculations were not
provided in the latest submission so this item could not be reviewed. Please provide
these calculations. Per the information shown on the Supplement-EZ Form, the
drainage area to swale 21 is shown as 7.10 ac while the information shown on the
drainage area plan sheet still indicates a total drainage area (sum of the drainage
areas to swales 5-8 & 21) of 7.4 ac."
Response: Have revised the calculation and provided the calculations.
KENNERLY P"onx:3677.2118
12133 N. NC HWY 156, Ste. F Fax: [phone]
ENGINEERrN6 a DESIGN, MC. Winston-Salem, NC 27127 www.kenneriVengineering.com

4 1 P a g e WYNNFALL SUBDIVISION PHASE ONE STORMWATER PERMIT MOD
PERMIT #SW4210601 — THIRD REQUEST FOR ADDITIONAL INFORMATION
ADDRESS: HINKLE LANE, LEXINGTON, NC / DAVIDSON COUNTY
4. "Please correct the following issues with the Supplement-EZ Form:
a. "Drainage Areas Page:
"Line 4 —This project contains 1 low -density drainage area (the entire project
area). Please revise. NOTE: The drainage area information for the individual
vegetated conveyances is included on the Low -density page.
Response: Have revised the Low -Density Drainage Area to 1 drainage area.
ii. "Drainage Area Table — Please include the Drainage Area Table (click on the
"click to load forms" link, similar to the one on the cover page used to generate
the low -density page). This table should have 2 columns, one for the entire site
and one for the low -density drainage area. Since, for this project, the low -
density drainage area is the same as the project area, the information in each
column will be identical and will correspond to the information shown in Section
IV, 10 of the Application."
Response: Have Revised to add this information.
b. "Low -Density Page:
Line 5 — The maximum shown velocity in the design table is 4.84 fps while 4 is
shown for this item. Please revise."
Response: Have revised to 4.84 FPS
"Line 11—This item should only be selected as "yes" if the vegetated
conveyances are designed in accordance with the design requirements outlined
in 15A NCAC 02H .1061"
Response: Have revised this box to "No".
iii. "Drainage area size for vegetated conveyances 12, 21, & 22 — These values (1.23
ac, 7.10 ac, & 6.01 ac respectively) do not appear to correspond to the
information shown on the ditch drainage area map plan sheet. Vegetated
conveyance 12 is shown with a drainage area of 0.54 ac, vegetated conveyance
21 is shown with a drainage area of 7.40 ac (sum of drainage areas 5-8 & 21),
and vegetated conveyance 22 is shown with a drainage area of 6.43 ac (sum of
drainage areas 1-4 & 22). Please revise either the plans or Supplement-EZ Form
as needed."
Response: Have revised the Supplement-EZ form to correct the drainage areas.
KEN N ERLY Phone: [phone]
16n12133 N. NC HWY 150, Ste. F Fax: [phone]
ENGINEERING. A DESIGN, INC. Winston--Salem, NC 27127 www.kennerlyengineering.com