SW6230401_Response To Comments_20230716

HILLIARD
PO Box 249,Sanford,NC 27331
[phone]
To: TRANSMITTAL
Division of Energy,Mineral&Land Resources
Stormwater Program
Att:Brianna Holland
1612 Mail Service Center
512 N.Salisbury Street
Raleigh,NC 27699-1612
Date: 07/16/23
Project: Phalanx Crossfit
HE#: HC2217
Please find enclosed the following:
One(1) Original hard copy of all revisions
Two(2) Copies hard copy of Signed and Sealed Affected Plan Sheets due to revisions
The enclosed are submitted for approval per comment letter received via email July 12,2023
Responses to comments are below:
1.The bottom elevation in the calcs was a typo and has been corrected. Supplement EZ has been updated to reflect this also.
2.The Main pond bottom was corrected and uploaded to the web link on July 7th. A copy of that revision is attached here.
3.The design volume is 3511 cf. This has been updated where required,however,the change was not signficant enough to change the orifice size.
4.Attached is the entire USDA soils report. The entire report will also be uploaded to the repository.
5.a Vegetated setback was revised to 30'
b.The depth of forebay was changed to match the supplement and the plans.
6.a.The discharge flow comes from the 100 year routing in the pond calculations and is larger than the actual outflow and larger than required by min.
design criteria of 10 years. However,the updated 100 year pond outflow is attached and that is where the disharge rate comes from.
b.The discharge in the 05-15 HDPE Outlet rip rap calcs is from the previously submitted pipe capacity calculations and represents the discharge into the
forebay where the apron is located.
c.The existing swale on site is an NCDOT swale and currently has no structural lining at all. The swale is simply lined with grass at this time.
The proposed project is actually reducing the amount of discharge lower than pre-development conditions and is designed for the 100-year storm.
However,we have provided a calculation for a 10 year storm and extended the rip rap lining all the way from the driveway
pipe to the existing 24"pipe. In addition,we have extended the rip rap apron from the SCM outflow all the way down to the ditch line for good measure.
Noted:
Due to the fact that this project's SCM mitigates the 100-year recurrence interval,an emergency spillway is not provided as these are typically provided
to allow for overflow of up to the 100-year storm for SCM's with a design much lower than what the SCM is designed for. In addition,much of the SCM is
in a cut condition and any overflow discharge greater than a 100-year storm would occur at grade rather than across a steep constructed embankment
per the grading plan.
The'provided surface area'discussed over mail on 7/11/23 is enclosed for consistency.
Please let me know if you have any questions or need any additional information.
Jarrod E.Hilliard,PE,CFM
Hilliard Engineering, PLLC