SW6220202_Response To Comments_20221213 (2)

underfoot
ENGINEERING
NCDEQ - Stormwater
Planning, Zoning and Inspections
512 N. Salisbury Street
Raleigh, NC 27604
Dear Mr. Farkas,
1149 Executive Circle - Suite C-1, Cary, NC 27511
919.576.9733 1 NCBELS C-3847
November 15, 2022
Re: Messer Parcels (SW6220202)
Construction Plan Review #2
Response Letter
Please find comment responses to the review dated November 3, 2022 via email for the
above referenced project. Staff comments from the staff review have been transcribed
for ease of review. Comment responses are in green below.
Prior Comment l.c. -The provided receiving stream, Thorton's Creek (18-19, WS-
IV), does not appear to be correct. Thorton's Creek is classified as part of a water
supply watershed (WS-IV) and areas that drain to water supply watersheds are
reviewed by local jurisdictions, not the State. Please take another look at this as it
appears that this site may actually drain to Black River (18-68-12-1, C;Sw). If you
believe that the project site actually drains to Thorton's Creek, please provide a
map showing the drainage from the site to Thorton's Creek.
Comment noted. The stormwater permit application has been updated to
accurately reflect Black River as the receiving stream.
Prior Comment 3.b.v. (Wet Pond Page of the Supplement-EZ Form, Line 28) -
Using Equation 3 [Davg = (Vperm.pool - Vshelf) / Abottomshelf] and [Vshelf = 0.5
* (Dshelfmax * Pperm.pool * Wsub.shelf)] with the following values, based on the
provided information [Vperm.pool = 53,262 cf, Abottomshelf = 12,447 sf,
Dshelfmax = 0.5 ft, Pperm.pool = 542 ft, & Wsub.shelf = 3.0 ft] results in an average
depth of approximately 4.2 ft [Vshelf = 0.5 * (0.5 ft * 542 ft * 3.0 ft) = 406.5 cf, Davg
_ (53,262 cf - 406.5 cf) / 12,447 sf = 4.2 ft]. Please revise as needed.
The Supplemental E-Z form has been updated to reflect 4.00 ft as the average
depth used (rounding down from 4.20 ft to be conservative).
Prior Comment 3.b.viii. (Wet Pond Page of the Supplement-EZ Form, Line 35) - Per
the provided stage -storage table and design information, the permanent pool
surface elevation is located at elevation 266.5' and the invert of the lowest
bypass orifice/weir is located at elevation 267.75' (the "Design Storm Orifice").
The stage -storage table/calculations indicates that approximately 23,088 cf of
storage can be provided between these elevations. Please revise as needed.
Please also revise the SCM design volume on the Drainage Areas Page, Line 20.
Forward Thinking. Grounded Design.
www.underfootengineering.com

underfoot
ENGINEERING
1149 Executive Circle - Suite C-1, Cary, NC 27511
919.576.9733 1 NCBELS C-3847
The wet pond design volume has been updated in both locations of the
supplemental E-Z form as required.
Prior Comment 3.b.ix. (Wet Pond Page of the Supplement-EZ Form, Lines 43 & 44)
- Please ensure that these depths are from the permanent pool surface
elevation to the excavated bottom of the forebay entrance and exit, not the
top of the sediment storage zone for the forebay entrance and exit. NOTE: Line
34 and the calculations indicate that the forebay cleanout depth (distance from
the permanent pool surface elevation to the top of the sediment storage zone) is
66 in. Since the permanent pool surface elevation is at elevation 266.5' this
would put the top of the sediment storage zone in the forebay at elevation
261.0'. The excavated bottom of the forebay entrance and exit must be at least
6 in. lower than the top of the sediment storage zone and the entrance must be
at a lower elevation than the exit. Please revise as needed.
Comment noted. The forebay depths have been revised as needed to meet
these requirements. These depths have been added to the SCM sheet for clarity.
Prior Comment 5 - Please upload the electronic files from the 8/9/2022 hard
copy submission at the following link: https://edocs.deg.nc.gov/Forms/SW-
Su12plemental-Upload
Please ensure that the off -site component of the drainage area is accounted for
at its full build -out potential (15A NCAC 02H .1003(3)(b)). It is recommended to
bypass this off -site component of the drainage area around the SCM since the
permittee has no control over what happens on property that they do not own
or have a right to. If the off -site area cannot or will not be bypassed, the off -site
area can be accounted for by either assuming that this area is 100% BUA (its full
build -out potential) or by having the property owners enter into a legal
agreement limiting the drainage area and BUA being directed from the off -site
area to the SCM. (You may want to just assume that the off -site area is 100% BUA
since it is such a small area and the SCM appears to be sufficiently sized to
handle the "extra" BUA).
Comment noted. Since the only offsite area being taken to the SCM is within the
right of way it has already been accounted for at its full build out potential.
Supplement-EZ Form, Cover Page, Line 7 - Please include the width of the
vegetated setback (it is noted that there are no surface waters located on -site,
however we ask that the setback width still be included. It is 30' in this part of the
State).
This section has been updated as required.
Supplement-EZ Form, Wet Pond Page, Line 53 - Please answer this item (The
pond embankments must be vegetated with non -clumping turfgrass per Wet
Pond MDC 1 1 a).
Forward Thinking. Grounded Design.
www.underfootengineering.com

underfoot
ENGINEERING
1149 Executive Circle - Suite C-1, Cary, NC 27511
919.576.9733 1 NCBELS C-3847
The species of non -clumping turf grass has been filled out as Bermuda and
added to the SCM sheet notes as well.
Respectfully:
Landon M. Lovelace, PE
Principal
Forward Thinking. Grounded Design.
www.underfootengineering.com