20180682 Ver 1_Notification of Revisions to Culvert 1 Design_20180720

Carpenter,Kristi
From: Beasley, Troy <[e-mail]>
Sent: Friday, July 20, 2018 4:29 PM
To: Andy Williams; Norton, April R
Subject: [External] Northwood High School Access Road -
Pittsboro, Chatham County - Notification of Revisions
to Culvert 1 Design (AID #SAW-2018-01017)(DWR
Proj #20180682)
Attachments: Northwood HS Access Rd NCDWR 401 Permit
06.28.18.pdf; Northwood HS Access RD_USACE 404
Permit_06.29.18.pdf; Stream and Buffer Impact
Maps_Revised for Arch Span Culvert_07.16.18.pdf
Andy and April,
The 404 NWP 39 (AID #SAW-2018-01017) & 401 WQC (Proj #20180682) (attached) were
recently issued for the Northwood High School Access Road project, which authorized
152 If of permanent stream impacts and 142 If of temporary stream impacts associated
with two culverted stream crossings for the secondary access road into the school.
This road may be ultimately taken over by NCDOT for future maintenance, and was
submitted to NCDOT for review and comments. After the 404/401 permits were issued,
NCDOT provided comments requiring revisions to the design for Culvert 1(Impacts 1-
5). The permitted design for Culvert 1(dated 5-16-18) proposed a 72" RCP culvert to
carry base flow with two perched 48" RCP culverts to carry high flow. NCDOT specified
concerns that the proposed three culvert design posed future maintenance problems
and increased cost of maintenance and requested that the design be changed to a single
arch span flat bottom culvert (10'-3" span x 6'-9" rise), as shown in the attached
"Stream and Buffer Impact Maps_Revised for New Culvert_07.16.18". The arch span
flat bottom culvert will meet the hydraulic requirements for the same high flow capacity
as the previous three culvert design.
The revision of the culvert design for Culvert 1 will be the exact same as the previously
authorized permanent and temporary stream and buffer impacts which consist of:
• Impact 1A - Permanent Buffer Impacts (Road Crossing) —Zone 1: 8,116 sf; Zone
2: 3,709 sf
• Impact 1B —Temporary Buffer Impacts (Dewatering) — Zone 1— 644 sf; Zone 2:
N/A
• Impact 2A—Temporary Stream Impacts (Culvert Installation & Dewatering) —44
If
• Impact 2B —Temporary Stream Impacts (Culvert Installation) — 13 If
• Impact 3— Permanent Stream Impacts (Culvert) — 52 If
• Impact 4— Permanent Stream Impacts (Rip-rap dissipator) — 32 If
• Impact 5—Temporary Stream Impacts (Rip-rap installation) — 10 If

Additionally, the proposed arch span flat bottom culvert will be installed 12" below the
stream bed and will not result in a widening of the stream channel or decrease in base
flow depth as shown in the cross-section detail on the revised impact plans, and
therefore meets the aquatic life passage requirements.
Since the change in culvert design will not result in a change in the impacts as previously
permitted, can this email serve as notification of a modification of design to be included
in the file, and avoid the need for a modification of the 404/401 permits?
I apologize for the additional coordination on this project, but we didn't anticipate
NCDOT requiring a modification of the culvert design. Thanks for your help with this
project.
Troy Beasley
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