SW4230101_Response To Comments_20230510

To:
Project:
Type of Review:
Stormwater Permit
Project Contact:
Phone:
Email:
TIMMONS GROUP
iSION ACHIEVED GH OURS.
Brianna Holland
EM Holt Elementary School On -site Queuing Improvements
Administrative Review
SW4230101
Garrett Frank, PE
[phone]
[e-mail]
• Response to review comments have been added below comment and are in bold.
• Comments were provided by Brianna Holland, NCDEMLR (919-707-9218,
Brian [e-mail])
1. Per 15A NCAC 02H .1003 (d):
a. (i) The curb outlets shall be designed such that the swale or vegetated area can
carry the peak flow from the 10-year storm at a non -erosive velocity. Note that
the two curb cuts are classified as curb outlets. Please provide calculations in the
narrative exhibiting that this requirement is met for PDD2, PDD3, and the ditch
from the parking lot curb cut, and label the permanent diversion ditches on the
plans.
RESPONSE: Calculations for all permanent diversion ditches including PDD2,
PDD3, and PDD8 have been provided in the narrative exhibiting that they can
carry the peak flow from the 10-year storm at non -erosive velocities.
b. The longitudinal slope of the swale or vegetated area shall not exceed five
percent, except where not practical due to physical constraints. Per the
Supplement-EZ, Low Density, Line 7, the maximum longitudinal slope of curb
outlet swales is 6.7%
RESPONSE: The longitudinal slope of all swales do not exceed 5%. This has
been updated in the Supplement-EZ line 7.
c. (iii) The swale's cross-section shall be trapezoidal with a minimum bottom width
of two feet. Per the Temporary Diversion Ditch/Berm table on Detail 2 (Sheet
C5.4) and the Drainage Ditch Design calculations, the bottom width of the PDD2,
PDD3, and the ditch from the parking lot curb cut which appear to be curb outlet
swales, are 0 ft. Per the Supplement-EZ, Low Density, Line 8, the bottom width
of the curb outlet swales is 5 ft, this is acceptable, but does not correlate with the
plans and calculations.
RESPONSE: The cross-section of PDD2, PDD3 and PDD8 now reflects a 2-ft
bottom width. This has been updated in the plans (Detail 2 Sheet C5.4),
calculations, and Supplement-EZ line 8.
d. (v) The minimum length of the swale or vegetated area shall be 100 feet. Please
provide calculations in the narrative exhibiting that this requirement is met for
PDD2, PDD3, and the ditch from the parking lot curb cut. Note that the length of

the swale or vegetated area is allowed to start before a culvert and continue at
the outlet of the culvert. Per the Supplement-EZ, Low Density, Line 10, the minim
length of the curb swale is 3.5 ft, but it must be at least 100 ft per the rule.
RESPONSE: Calculations for all permanent diversion ditches including
PDD2, PDD3 and PDD8 have been provided in the narrative to show ditch
lengths. The length of PDD8 does not meet the required 100-ft minimum.
The location of PDD8 improves the existing drainage issues and directs
flow to the existing drop inlet'Al' to prevent sheet flow across the
proposed queue lanes to PDD2.
2. Please ensure consistency between the plans and calculations. Please also ensure that
the values used in the calculations are accurate.
a. In the plan view and Storm Structure Table (Sheet C3.0), Structure Al is a
concrete drop inlet, and in the narrative, it is a FES. If FES Al is the same as
Structure Al in the table, and correlates to Pipe G1-Al , the pipe diameter shown
on the plans is 6" but is 18" in the "Outlet Protection Design" calculations.
RESPONSE: The pipe network and narrative have been updated for structure &
pipe clarity. See sheet C3.0.
b. The pipe length for Pipe 132-131 is listed as 46.05 LF but listed as 54 ft in the
"Outlet Protection Design" calculations, resulting in a different slope. FES C1,
FES D1, FES El, have a similar issue.
RESPONSE: The pipe lengths have been updated in the calculations.
c. FES H1 has discrepancies with the naming on the storm structure table and plan
view, and the invert elevations between the plans and "Outlet Protection Design"
calculations.
RESPONSE: FES-11-111 has been renamed to EW-1 and has been updated on the
plans and calculations. See sheet C3.0
d. Riprap FES Al in the "Outlet Protection Design" calculation does not coordinate
with the grading sheet C3.0.
RESPONSE: Riprap FES Al was renamed to correlate with EW-1. See sheet C3.0.
e. The maximum side slopes in the Supplement-EZ is listed as 82.1, but is listed as
6.1 in the plans and calculations. If a flat receiving area is intended instead of a
curb outlet swale, please specify on the plans and narrative.
RESPONSE: The maximum side slope in the Supplement-EZ has been updated to
3:1 and the calculations have been updated to reflect each swale's maximum side
slope.
3. On the Site Details (Sheet C5.4), the energy dissipater schedule lists all energy
dissipaters as "RR -Al," please revise with the name of each riprap structure for clarity.
The schedule uses the same pipe sizes and dimensions as the second row for all
subsequent rows. This does not match the calculations.
RESPONSE: The energy dissipater schedule on sheet C5.4 has been updated to
match the plans and calculations.

4. Please revise the Supplement-EZ form
a. Cover, Line 7-8: Compliance with 02H .1003(4)- While there is no surface water,
and therefore no vegetated setbacks associated with this project please fill in.
Per 15A NCAC 02H .1017 (10), the vegetated setback shall be at least 30 feet in
width.
RESPONSE: Lines 7-8 have been updated on the Supplement-EZ.
b. Drainage Areas, Line 4: This should be answered as 1," not "7." This will result
in an updated Drainage Area Information Table. Note: Because this is a low
density project, the "Entire Site" and "LD 1" columns will match.
RESPONSE: The drainage areas have been updated to "1" on Line 4.
c. Drainage Area Information Table, Line 16: "Existing are that is already permitted"
is "237,838 SF," however, there is not an existing permit, so this line should
remain blank.
RESPONSE: Line 16 has been updated accordingly.
d. Low Density
i. Line 5: The maximum velocity conveyed during the 10 year storm must
align with the maximum velocity provided in the swale calculations.
RESPONSE: The maximum velocity conveyed during the 10-year storm has
been updated to match the calculations.
ii. Line 12: Compliance with 15A NCAC 02H .1003 (4) (e): Stormwater that
has not been treated in an SCM shall not be discharged through a
vegetated setback; instead it shall be released at the edge of the
vegetated setback and allowed to flow through the setback as dispersed
flow. This line is required to be answered as "Yes."
RESPONSE: Line 12 has been updated to answer "Yes."
iii. Line 15: Please specify which swales are "Curb Outlet Swales" here.
RESPONSE: The curb outlet swales have been listed in Line 15.
5. Please correct the following issue with the Operation & Maintenance Form and provide
1 original, signed & notarized hard copy of the O&M Agreement Form: NOTE: It is
recommended to get a second copy of this form signed & notarized for the Applicant's
records (it will be helpful for recording with the Register of Deeds).
RESPONSE: Updated O&M Agreement has been provided.
a. Curb outlet system should be selected in the "Low Density" row. This will
generate the necessary additional pages.
RESPONSE: Curb outlet system has been selected in the "Low Density" row.
6. Note, per 15A NCAC 02H .1003 (1) (b) A project with existing development may use the
calculation method in Sub -Item (1)(a) or shall have the option of calculating project
density as the difference of total built -upon area minus existing built -upon area divided
by the difference of total project area minus existing built -upon area. Using this
calculation method (excluding the existing impervious area) would result in a lower
percent impervious area (Application Section IV, 8 and 10).

RESPONSE: The percent impervious calculation has been updated to reflect this
method and has been updated on the application.
7. Note that electronic submittals are required and were not provided with the last
submission. 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
RESPONSE: Electronic submittal has been provided.
b. Hard copies must be mailed or delivered to the following address:
i. For FedEx/UPS:
Brianna Holland
512 N. Salisbury Street, Office 640E
Raleigh, NC 27604
For USPS-
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.
NOTE: Hard copies should not be sent to a Regional Office. Doing so will
delay the review process and the submission package may be lost while
being sent from the Regional Office to me in the Central Office.
RESPONSE: Noted, thank you.