20181527 Ver 2_More Info Received_20200908

Strickland, Bev
From: Greer, Emily C CIV USARMY CESAW (USA) < [e-mail] >
Sent: Tuesday, September 8, 2020 2:22 PM
To: Snider, Holley; Steenhuis, Joanne
Subject: [External] FW: [Non-DoD Source] Re: 2018-01501 Salter's
Follow Up Flag: Follow up
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From: Williams, Kim <[e-mail]>
Sent: Friday, August 21, 2020 10:20 AM
To: Greer, Emily C CIV USARMY CESAW (USA) <[e-mail]>; Dan Fisk <dfisk@paramounte-
eng.com>; Allison Engebretson <[e-mail]>; Greg Finch <[e-mail]>; Steve
Morrison <[e-mail]>
Subject: [Non-DoD Source] Re: 2018-01501 Salter's
Hi Emily
I wanted to follow back up with you on the culvert replacement at Factory Road. I've been trading emails with
Paramounte Engineering regarding the proposed culverts and their discussions with NCDOT. Here is some information
from the engineer regarding existing conditions and what is proposed.
• The existing culvert is a dual pipe system, a 30" and a 24" with the upstream invert of the 24" pipe being roughly
0.4' higher than the 30", but still within what would appear to be the stream's cross-section elevation. This
condition in itself appears to be wider than the 4' upstream width mentioned.
• Existing drainage swales —the upstream side of the culvert crossing has a contributing roadside swale from the
north. The downstream side of the culvert crossing has contributing roadside swales from both the north and
the south.
• The existing 30" and 24" culvert crossing does not meet hydraulic requirements for the existing 25-year storm,
which is the reason for replacement/upsizing. Therefore, larger culverts are needed.
• Based on recent discussions with DOT, the engineer has revised the culvert layout slightly. Two 48" culverts are
still proposed. The 48" culvert located to the south will still be buried 12" for the main stream conveyance.
However, the opening for the northern pipe will be around 9" higher. This pipe will include the same 12" fill as
the other pipe, so you would maintain 9" of embankment between the two pipes (see below for schematic).
DOT appears to be satisfied with this adjustment.
• Since one of the culverts will be buried, the design satisfies the USACE's regional condition to maintain water
flow. But since one of the pipes will be raised, this minimizes disturbance to the stream bed (regional
condition). Additionally, the embankment between the two pipes will help to maintain stream width (regional
condition).

Let me know if you have any questions or require additional information. Once we get your feedback, we can provide a
more detailed cross section.
Thanks,
Kim
Kim Williams I Environmental Scientist
Land Management Group I Environmental Consultants
Direct: 910-452-0001 x 1908 1 Cell: 910.471.5035 1 Fax: [phone]
3805 Wrightsville Ave., Suite 15 I Wilmington, NC 28403
Email: kwilliams(a lmgroup.net I Website: Blockedwww.lmgroup.net
On Tue, Jul 21, 2020 at 11:56 AM Greer, Emily C CIV USARMY CESAW (USA) <[e-mail]> wrote:
Kim -
I have an inquiry from DOT RE: the Factory Road crossing for Salter's that I can't definitively answer because
the drawings are not adequate and I don't recall anything in the PCN write-up that addresses the concerns. I
measured the upstream stream width at 4' and the downstream width as 8' right at the culvert inlet/outlet.
The concern regards stream widening in relation to compliance w our regional conditions and DOT standards.
Our regs state:
N

3.6.1 For all NWPs that involve the construction/installation of culverts, measures will be included in the
construction/installation that will promote the safe passage of fish and other aquatic organisms. The dimension,
pattern, and profile of the stream above and below a pipe or culvert should not be modified by altering the width or
depth of the stream profile in connection with the construction activity. The width, height, and gradient of a
proposed culvert should be sufficient to pass the average historical low flow and spring flow without adversely
altering flow velocity. Spring flow is the seasonal sustained high flow that typically occurs in the spring. Spring
flows should be determined from gage data, if available. In the absence of such data, bank -full flow can be used as a
comparable indicator.
3.6.3 Where adjacent floodplain is available, flows exceeding bank -full should be accommodated by installing
culverts at the floodplain elevation. Additional culverts or culvert barrels at such crossings should not be buried, or
if buried, must have sills at the inlets to ensure that they only receive flows exceeding bank -full.
3.6.4 Excavation of existing stream channels shall be limited to the minimum necessary to construct or install the
proposed culvert. The final width of the impacted stream at the culvert inlet and outlet should be no greater than the
original stream width. A waiver from this condition may be requested in writing; this request must be specific as to
the reason(s) for the request. The waiver will be issued if the proposed design would result in less impacts to the
aquatic environment and/or if it can be demonstrated that it is not practicable to restore the final width of the
impacted stream at the culvert inlet and outlet to the width of the original stream channel.
3.6.5 The width of the culvert shall be comparable to the width of the stream channel. If the width of the culvert is
wider than the stream channel, the culvert shall include baffles, benches and/or sills to maintain the width of the
stream channel. A waiver from this condition may be requested in writing; this request must be specific as to the
reason(s) for the request. The waiver will be issued if it can be demonstrated that it is not practicable or necessary
to include baffles, benches or sills and the design would result in less impacts to the aquatic environment.
4.1.6 If riprap stabilization is needed, it should be placed only on the stream banks, or, if it is necessary to be
placed in the stream bed, the finished top elevation of the riprap should not exceed that of the original stream
bed.
DOT standards are:
S. Stream pattem, dimension and profile shall be maintained
by pipel ulvert installation.
• A 4-foot diameter pipelcul'vert installed in a Moot
wide stream may require baffles in order to
maintain aquatic organism passage (AOP) during
low flog conditions.
• Pipe size should at least match stream ► idth
wherever possible, but a -foot wide culvert
installed in a 4-foot wide stream may also creed
baffles to reduce velocities.

• Two 48 inch pipes lrrstaMed In a 10-foot wide
BMPs 1w Consimetkm and Maintenance Actewties
Page 2-,
4.2 - Pipel elver# Installation
stream would require that one pipe be installed at
a lower elevation, and in alignment with the tow
flow stream channel elevation, so that A OP is
maintained during low flow conditions.
the low flow pipe should be aligned with the
deepest part of the stream channel, so that flog is
maintained during low flav+w+ conditions.
Please provide a written response addressing how the project meets each of the above requirements with any
supplemental drawings that better depict the crossing and demonstrates that the project is in compliance. Please let
me know if you discover the crossing is not in compliance so we can get that taken care of asap. Let me know if you
have questions.
Thank you -
Emily Greer, Regulatory Specialist
Wilmington District - Wilmington Regulatory Field Office
69 Darlington Avenue, Wilmington, NC 28403
910.251.4567 (o)
4