Piedmont Natural Gas Major Site Plan TRC Response 5.21.21RESPONSE TO COMMENTS >PNG-20000
2905 Meridian Parkway, Durham, NC 27713 / 919.361. 5000creatingexperiencesthrough experience
April 15, 2021
New Hanover County
Engineering
230 Government Center Drive,Suite 160
Wilmington, North Carolina 28403
Wilmington CNG Station
Response for Additional Information Comments
PNG-20000
The following are the response comments for the above-mentioned project. Our response comments are in bold.
ENGINEERING:
Galen M Jamison 910. 798. 7072
1.Per Section 30.2.1.1 & 2 of the New Hanover County Stormwater Design Manual, please provide all existing
site data and proposed site improvements information on the site plan. A statement on wetlands,
floodplain, soil types, regulated trees, summary of impervious areas, and profiles were not found in the
drawings.
McAdams Response:Site data table added to cover sheet.
2.Per Section 30.2.3, please provide drainage area for each inlet, culvert and ditch/swale and their associated
design calculations. Culverts and ditch/swales shall be designed for the 25-year storm event. See sections
50.3 and 60.1
McAdams Response:A section has been added to the SIA covering the proposed swales, including land
cover breakdowns, hydrologic calculations, and an exhibit of their respective drainage areas. Please
refer to the Erosion Control Report for culvert and swale calculations for this project.The culvert and
swales were designed to handle the 25-year event. The hydrologic calculation for the swales has been
added to the Erosion Control Report.
3.Per Section 30.3, please include executed Designer’s and Owner’s Certifications with original signatures on
at least one plan drawing sheet for the final submittal.
McAdams Response:Certifications have been added to the cover sheet.
4.Per Section 50.4, please provide energy dissipater (ED) calculations and necessary data on the drawing /
details for construction.Specifications for the filter blanket or filter fabric is missing from the detail on sheet
10.
RESPONSE TO COMMENTS >PNG-20000
creating experiencesthrough experience 2of2
McAdams Response:Calculations provided in Erosion Control Report and data provided on the
drawings.Note added to detail for filter fabric specification.
5.Per Section 70.1, please provide a pond analyzing the 100-year storm event with the primary outlet blocked
(no infiltration). Please indicate in the updated design narrative that this project is requesting a waiver to
the top of bank (or top of dam) having a minimum of 0.5’ of freeboard from the peak water surface
elevation resulting from the 100-year primary outlet blocked scenario.
McAdams Response:No pond or other SCM is proposed as part of this project. The site is a low-density
development, with swales and diffuse flow utilized to the maximum extent practicable.We are
modeling the hydrology and runoff in the SIA to demonstrate that infiltration is occurring onsite at a
sufficient rate, but we are not designing a detention facility; merely analyzing where water will go to
ensure no adverse impacts to downstream infrastructure.
6.The proposed contours for the 200’ long grass swale at 1.95% doesn’t provide for a 1.25’ of depth. Please
ensure contours are drawn accurately and/or consider adding a simple swale detail.
McAdams Response:Contours have been adjusted and swale detail added on sheet 10.
7.Per Section 20, please provide the pre and post hydrologic calculations for the 2 and 10 year storm events.
McAdams Response:The pre-and post-hydrologic calculations have been provided for the 2-, 10-, 25-,
and 100-year storm events. See the respective sections of the SIA for more information.
8.These items must be addressed before the review and approval of the project can be completed. Please be
advised, the area of disturbance appears large enough that you will need a separate Sedimentation &
Erosion Control Permit from NC Department of the Environment. Due to the nature of the owner, a New
Hanover County Sedimentation & Erosion Control Permit will not be required.
McAdams Response:Noted -NCDEQ land disturbing permit has been applied for.
Consideration of this response is greatly appreciated. If you should have any questions or require additional
information, please do not hesitate to contact me at 919. 361.5000.
Sincerely,
MCADAMS
Daniel Wiebke, PE
Project Engineer, Water Resources
DW/ms