20210751 Ver 1_Interagency_Letter_Figure3_White_Oak_Topo_20200924

Carpenter,Kristi
From:Burhans, Terry <[e-mail]>
Sent:Thursday, September 24, 2020 10:03 PM
To:Steenhuis, Joanne; [e-mail]
Cc:Baker CIV Jessi O
Subject:\[External\] RE: MCB Camp Lejeune Bridge Replacements - White Oak River Trestle
Bridge - Deck Stormwater Drainage
Attachments:Interagency_Letter_Figure3_White_Oak_Topo.pdf; Camp Lejeune - BJB sketches -
scuppers.pdf
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Good Evening Joanne and Brad,

I hope all is well. I am reaching out because Michael Baker International is working with the USMC and NAVFAC on a
couple projects on and near MCB Camp Lejeune that involve bridge replacements. One project is the Onslow Beach
Bridge Replacement Project at Camp Lejeune and the other involves the replacement of Railroad Trestle Bridges over
Queens Creek and the White Oak River near Stella, NC. I have been coordinating with Jessi Baker (copied) on setting up
an Interagency Scoping Meeting through Cameron Weaver so you should receive a request with more in-depth
reference material on both projects in the near future. However, the reason that I am reaching out before the
Interagency Meeting is to hopefully get some advice on an issue related to bridge deck stormwater drainage that we see
as being critical early on in our design process.

- We are proposing to replace the existing Trestle Railroad Bridge that crosses the White Oak River and its an
associated adjacent wetland complex. (See attached Project Location map)

- Our scope of work involves removing the existing open deck timber tie system trestle bridge and replacing the
structure on the same location with a new bridge that will be constructed with a concrete closed ballasted deck
with ballast curbs, which is industry standard and allows for better load distribution and better structure
longevity.

- The proposed bridge deck is 20’ wide with 10’ draining to each side (normal crown). Scuppers (slots in the
ballast curb) will be spaced approximately 6’ apart along the length of the trestle (actual spacing will depend on
the final location of bridge support beams and expansion joints). \[I have attached an example typical that is
Norfolk Southern Railroad standard for their deck drains / scuppers. The final spacing on our bridge will be a
little different than what is shown on the typical\]

- At this 6’ spacing, the flow from each drain has been calculated to be 0.005 cubic feet per second (cfs), so a very
low amount of stormwater will discharge from each scupper.

- The proposed bridge grade across the wetland and White Oak River is 0% (flat) at approximate elevation 14.3’.
Mean High Water is at elevation 1.1’, so deck drains will be approximately 13.2 feet above MHW. In our
experience on previous NCDOT bridge projects, it has been agreed upon that drains
discharging greater than 12’ above MHW were considered diffuse flow.

- Also Per NCDOT Guidelines,
“For bridges over sounds or the Intracoastal Waterway, the volume of stormwater runoff from bridge
deck drains is miniscule relative to these immense water bodies, and there typically are no practical
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locations in which to provide effective treatment. Bridges in these areas may be allowed to discharge
directly into the surface waters, unless otherwise advised by the regulatory agencies. Most of these
bridges also provide navigational clearance for boating and shipping traffic, so the effects of the high rise
and coastal winds would help to diffuse and diminish any detrimental impact of stormwater from bridge
decks.” - NCDOT Guidelines for Drainage Studies and Hydraulic Design (Nov. 21, 2016), Section 8.5.2.10
Bridge Deck Drainage – Bridges in CAMA Counties

If direct discharge from scuppers is not allowed, the bridge grade across open water of White Oak River will have to be
sloped in order to allow for a closed drainage system that would be approximately 800 feet in length. This system would
outlet into the wetlands on each end of the bridge (pending agency approval).

We are aware that the White Oak River has a Water Quality Classification of SA-HQW and that the wetlands along the
White Oak River are tidally influenced Coastal Wetlands.

Do you think that there would be an issue utilizing scuppers along the deck for drainage for this trestle bridge? Do you
know the process for obtaining a waiver or variance if needed?

I appreciate any guidance you can provide an look forward to talking with you.

Please let me know if you have any questions or concerns.

Cheers

Terry Burhans PWS, CPSS| Environmental Scientist
Michael Baker International
8000 Regency Parkway, Suite 600 | Cary, NC 27518
\[O\] 919-481-5775 | \[M\] 858-243-9900
[e-mail] | www.MBakerintl.com

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I RECOVERY BRIDGES
DESIGN-BUILD AT
MCB CAMP LEJEUNE, NC
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Q Bridge
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Figure 3.
White Oak River
Railroad Trestle Replacement
N Topographic Map
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