HE-0001 Responses to DWR

Responses to Kevin Mitchell, NCDWR Comments Received Monday, May 1, 2023
NCDOT HE-0001 Section 404/401 Permit Application
1. The stormwater drainage system from 1126+50— 1131+50 WBL is currently being built for I-
4700 and should be shown in green. Please correct this on the plans and any other stormwater
drainage that is part of the 1-4700 protect. [15A NCAC 02H .0502(c)]
New plan sheets created with correct line colors.
2. Plans at CP 4c showed outlet protection on culverts at Site 5. 6. and 7. The submitted plans in
the application did not show outlet protection on the culverts at Site 5, 6, and 7. Please explain
why the protection was removed and demonstrate that the stream can handle the increased
velocitv at the outlet. (15A NCAC 02H .05061.
The submitted plans include protection at the outlets. The CP 4c plans included rip rap in the
stream bed at these outlet locations. The protection included in the submitted plans does not
impact the stream beds and is depicted in the details on the sheet (see details 9F & 10K).
3. Detail 5A stationine 24+50 RPC (Sheet 5) should read LT and not RT. Please correct on
plans. [15A NCAC 02H .0502(c)]
New plan sheets created with correct description.
4. (A) On the pre/post stormwater analysis table the applicant references a 55"RCP in the
interchange. Is that referrine to the 66" RCP (Station 35+00 RPC) on the plans?
No, It is referring to the existing 54" pipe that crosses 1-26 WBL at Sta 1133+00. This location was
selected to address the increase in discharge from Ramp A and upstream (Stream SA). Because
Stream SDX is being relocated in a new 66" pipe under the proposed interchange there is no
existing stream at the outlet of the proposed 66" pipe, a pre/post comparison for the proposed
66" pipe is not possible.
(B) Also, the velocity table that was submitted in the 4C meeting minutes (table 1 page 5) is
significantly different from the pre/post numbers in the application table. For example Post 10-
year velocities for Stream SA below the proposed 36 inch RCP are 11.2 f/s; however, the table in
the application indicates that the velocity is 3.7 f/s post construction.
The calculation presented in the 4C meeting summary erroneously used the pipe slope and the
drainage retained in the energy dissipator. The current velocity calculations appropriately use
the stream grade.
(C) Please clarify any differences in these tables and indicate an approximate location on the
table. Are the velocities on the table in the application below the proposed outlets? I have
attached the meeting minutes from 4c for reference. [15A NCAC 02H .0502(c)]
The table has been revised as requested, a note about energy dissipaters was also added, as
appropriate.

Responses to Kevin Mitchell, NCDWR Comments Received Monday, May 1, 2023
NCDOT HE-0001 Section 404/401 Permit Application
5. On page 4 of 5 of the Stormwater Management Plan (SMP), under additional notes, please
reference the additional swales that did not meet the criteria but were added into the
design. [15A NCAC 02H .0502(c)]
This has been addressed.
6. Please note on page 5 of 5 of the SMP whether the Pre -Formed Scour Holes meet the design
criteria for the NCDOT BMP toolbox. 115A NCAC 02H .0502(c)l
This has been addressed.
7. Please include a narrative in the SMP that demonstrates that the applicant evaluated BMPs to
meet the NC SELDM Catalog recommendation. Documentation of the recommendations,
measures taken to meet the treatment goals, or restrictions to implementation were to be
included in the final SMP per CP 4A. f15A NCAC 02H .05061
The SMP has been updated and additional documentation is included in the supplemental
document (PDF) "Comparison of SELDM Vs. Design Stormwater Control Devices".