HomeMy WebLinkAboutNHC SW_Comment Reponse Letter_Round 1
GE Aerospace North Gate Improvements
WSP Project No. 6260-23-0100
Page 1
April 4, 2025
Galen Jamison, PE
Chief Project Engineer
New Hanover County
230 Government Center Drive, Suite 160
Wilmington, NC 28403
Re: GE Aerospace – North Gate Improvements – Request for Additional Information
Mr. Jamison,
In response to the Comment Letter dated March 17, 2025, regarding review of the above referenced project
(stormwater permit application and application package), we offer the following responses in italicized text.
1. Onslow loamy fine sand is classified as a B hydrologic soil type but the narrative with calculations
indicated an A soil type. Please clarify.
- Response: Email correspondence on 3/17/2025 said to disregard this comment.
2. Per Section 2.3.2.1 and Table 2-4 of the New Hanover County Stormwater Design Manual, items 5 and
16, please indicate on the plans the (non) presence of 404 wetlands and delineation of offsite and onsite
drainage contributing to the open channel.
- Response: Plans have been updated to reflect the jurisdictional information as shown on SAW-2024-
01272 (GE) and delineation of offsite and onsite drainage. File has been attached to this response for
your records.
3. Per Section 3.6.3, please use a Type III rainfall distribution in lieu of the type II used in the hydrology
calculations.
- Response: Hydrology calculations revised to reflect Type III rainfall distribution instead of Type II.
4. The energy dissipator calculation indicates a slope of 1.38% but the plans indicate 0.5%, please clarify.
- Response: Energy Dissipator calculation revised for 0.50%.
5. Per Section 2.3.2.2 and Table 2-5, items 5, 6, 11 and 12, please include in the narrative the required
calculations as an appendix for the open channel and culvert/pipe system; NOAA Atlas 14 rainfall data; a
list with discussion of coordinating permits; and a discussion on easement requirements.
- Response: Please see revised Narrative and Calculations appendix.
6. Per Section 2.3.2.3 and Table 2-7, please provide the pipe calculations for the 12” pipe extension starting
at the proposed ditch.
- Response: The 12” pipe extension has been removed. 18” RCP’s are now proposed in place of the
existing 12” and 15” RCP’s. Calculations are provided with this resubmittal.
7. Per Section 2.3.2.3 and Table 2-9, please include the open channels calculations as indicated in chapter
4 as an appendix to the narrative
- Response: Calculations for the proposed open channel has been included with this resubmittal.
5710 Oleander Drive
Suite 110
Wilmington, NC 28403
(910) 452-1185
wsp.com
GE Aerospace North Gate Improvements
WSP Project No. 6260-23-0100
Page 2
8. Per Section 7.8 of New Hanover County Stormwater Ordinance, please provide 2, 10 and 25-year storm
attenuation for the site. Should there be adequate capacity for the increase in post development flow
rates in the existing SCM, documentation will need to be provided.
- Response: Please see revised narrative and calculations showing attenuation in the 2-, 10-, 25- year
storm events.
9. Per Section 2.3.2.5, please submit the executed operation and maintenance (O&M) plan and agreement.
The form can be downloaded at https://www.nhcgov.com/DocumentCenter/View/465/Stormwater-
Maintenance-Form-PDF
- Response: Executed O&M plan and agreement form included with this resubmittal.
10. Per Section 3.5, please use the frequency factor with the revised calculations that rely on the rational
method.
- Response: Frequency factors have been utilized in rational method calculations with this resubmittal.
11. Per Section 4.4.2, the minimum pipe diameter is 15”. Therefore, please provide a design variance
requested signed and sealed by a professional engineer on company letterhead per Section 7.12 of the
NHC Stormwater Ordinance. The letter should indicate why and indicate whether the 25-year hydraulic
grade line remains within the piped system.
- Response: The existing 12” pipe and proposed pipe extension have been removed. System to be
replaced with 18” RCP’s. Design variance not required due to system replacement and upsizing.
12. Please send, as individual PDF files, the comment responses, consolidated plans and narrative report
from native PDF digitally with the resubmission.
- Response: PDF’s have been digitally resubmitted as individual files.
Separately noted, a state stormwater permit package is being prepared to obtain a state stormwater permit.
Thank you again for your assistance in review of this project. If you have any questions, please do not hesitate to
contact me by email (ryan.spiker@wsp.com) or by phone at (910) 279-9000.
Sincerely,
Ryan Spiker, PE
Senior Civil Engineer