20200812 Ver 1_PCN Application Form Section D Edits_20200722

D. Impact Justification and Mitigation
1. Avoidance and Minimization
1 a. Specifically describe measures taken to avoid or minimize the proposed impacts in designing project.
A scoping meeting for this project was held on December 10, 2018. The proposed roadway design at that time would have
resulted in 800 linear feet of impact to Stream C. Discussions with Brad Shaver (US Army Corps of Engineers), Robb Mairs
(NC Division of Water Quality), and Tim Lowe (Roadway Engineer at DAVENPORT) resulted in a change in roadway design
that brought the proposed impacts to Stream C to their current level of 335 linear feet. In order to accommodate this new
roadway design, engineers incorporated retaining walls and guardrails to help minimize impacts to the stream. Project
managers also coordinated with Marine Corps Base Camp Lejeune Public Works concerning the future relocation of a Sub -
Station just north of the project area as well as the existing overhead power lines under which the new access road would
cross. This coordination with Public Works permitted the current design in which the new access road is placed on the
northern side of Stream C, minimizing impacts.
Fill slope ratios at most sites were designed at a 3:1 ratio in order to minimize disturbances to streams and wetlands. At Site
3, the fill slope ratios were designed at a 2:1 ratio to avoid fill impacts to Stream B.
The culvert outlet protection designed for Sites 3, 4, and 5, and the culvert inlet protection designed for Site 2 involve the
placement of riprap in the stream channel. To install the riprap, the streambed will be overexcavated, and riprap will be
installed to a depth that is even with the natural streambed elevation. Installation depths of riprap at the different impact Sites
as well as full construction specification for the culvert outlet protection can be found in the attached Plan Sheet CC503. This
sheet also contains details for culvert inlet protection; however, this detail will only be used for non -jurisdictional ditches and
not for any jurisdictional feature.
For Impact Numbers S1 through S3, note that the current stream channel (Stream A) is not aligned with the proposed 60"
RCP and the proposed culvert opening is approximately 5 feet east of the current stream channel. The reason for this
misalignment is that the proposed 60" RCP is an extension of an existing 60" RCP that continues under Birch Street. A
complete replacement of the existing 60" RCP is unfeasible due to the cost of replacement and the need to completely close
down Birch Street, a major thoroughfare in the Marine Base, in order to replace the existing RCP. The impacts to Stream A
include channel alignment to direct the stream to the proposed headwall, riprap placed in the stream channel for inlet
protection, and the extension of the 60" RCP. The riprap is necessary to stabilize any sediment that may be received from the
proposed ditch before water enters the proposed 60" RCP extension. This riprap will be installed by overexcavating the
stream channel and placing riprap to a depth that is consistent with the natural streambed elevation.
The demolition plans call for the removal of a sluice gate that was installed within Stream C. The installation of this sluice gate
effectively and functionally divided Stream C into two different stream segments and likely acted as a barrier to the
movements of aquatic organisms. Removing the sluice gate will restore the stream back to more natural conditions.
At Site 4, the proposed access road crosses the stream at an angle less than 75 degrees. A crossing at a higher degree was
not possible due to the presence of the overhead electric power lines and supporting poles in this area. The road was
designed to parallel these power lines.
There are two road crossing proposed for Stream C (see both Site 4 and Site 5). One purpose of this project is to improve the
safety of the Birch Street and Holcomb Boulevard. Currently, this intersection has many curb -cuts and conflict points that can
be reduced by the construction of the new access road behind the commercial buildings. This new access road is designed to
ease circulation among the existing businesses, but this can only be accomplished if there are two crossings of Stream C.
These crossings were designed to be as far apart as possible from each other in order to minimize the cumulative impact on
the stream.
The outlet protection riprap for Sites 4 and 5 will impact 48 and 39 linear feet of stream, respectively. Calculations for the
amount of riprap needed are provided in Plan Sheet CC503 included in the Impact Figures. This large amount of riprap was
needed because of the high maximum flow velocities estimated for this stream. To reduce impacts, the riprap will be buried in
the stream channel and set flush with the stream bottom.
In Site 1, there is an existing non -jurisdictional ditch located parallel to the north side of Birch Street that flows into Wetland B.
The proposed design will use a supraelevated roadway design to eliminate this ditch and direct water to stormwater inlets in
the middle of Birch Street. The water will then be redirected into Wetland B through a proposed 36" pipe.

b. Specifically describe measures taken to avoid or minimize the proposed impacts through construction techniques.
Sediment and erosion control Best Management Practices (BMPs) have been developed specifically for this project. Silt
fences will be used on stream banks in order to prevent sedimentation into the stream. In addition, a silt fence will be installed
around the entire project area to further minimize sedimentation. Silt fences and other sediment and erosion control devices
will be removed after completion of each phase.
The construction of the project will be phased in order to limit the amount of time that streams and wetlands will undergo
temporary impacts.
Construction of the culverts will be done 'in the dry' when feasible in order to minimize impacts. Construction of the culverts
will conform to "The 2018 North Carolina Department of Transportation's Standard Drawings and Specification for Roads and
Structures."
Tree and vegetation clearing will be minimized to the greatest extent possible. Precautions will be taken not to disturb root
mats outside the project area. Construction equipment will not be staged on wetlands or near streams.
3. Complete if Using a Mitigation Bank
3a. Name of Mitigation Bank: Bachelor's Delight Mitigation Bank
3b. Credits Purchased (attach receipt and letter)
Type Stream
Quantity 294
3c. Comments: Total wetland impacts are less than 0.1 acres and do not require mitigation.
For stream impacts, there will be a total loss of 23 linear feet in Stream A, and a total loss of 248 feet in Stream C. These
impacts result from the installation of new pipes. Impacts from the installation of riprap are not mitigatable since the riprap will
be buried in the stream channel or will be placed in the stream channel to a depth that will not exceed the natural streambed
elevation. We are proposing to mitigate Stream A at a 2:1 ratio (46 credits) and Stream C at a 1:1 ratio (248 credits) for a total
of 294 credits. A credit reservation letter for 428 credits has been attached to this application. We have reserved more credits
than requested in the case that our mitigation strategy is not approved.
Stream A is a perennial stream rated as Medium using the NC Stream Assessment Method (NCSAM). Please see attached
NCSAM forms and photos. Stream C is also a perennial stream, but was rated as Low using the NCSAM. Stream C is located
in a heavily commercial area of the Base and has been impacted by historic and current land use. These impacts include the
installation of a sluice gate and riprap within the stream in order to control flow. Upstream of the sluice gate, Stream C is very
sluggish and flow rates are minimal, resulting in a more of a lentic environment with emergent vegetation such as cattails.
Downstream of the gate, Stream C is very incised, likely a result of high storm events released with the opening of the sluice
gate. In the impact area, the top of stream bank is extremely narrow and ranges from 0.5 feet to 1.5 feet. This area also lies
under two electrical power lines. The maintenance of vegetation under these lines has resulted in a lack of shade. These
factors contributed to the rating of 'Low' in all three functional classes of the NCSAM rating: hydrology, water quality, and
habitat.
The proposed project will remove the sluice gate in Stream C, which would help restore the stream's natural flow regime. The
sluice gate and riprap that is immediately northwest of the gate have effectively provided a barrier to the movement of aquatic
organisms and has altered the flow regime of Stream C. Removal of this gate should help mitigate some of the other impacts
of the proposed project.