20230780 Ver 2_20230531-Sandbag Island Permit Supplement_Attachments_20230627

Project Name: Sandbag Island Bird Nesting Island Restoration
The U.S. Army Corps of Engineers (Corps) is seeking an Individual Water Quality
Certificate (WQC) from the North Carolina Department of Environmental Quality
(NCDEQ), Division of Water Resources (DWR), for placement of dredged material to
restore Sandbag Island, which is a nesting bird island managed by the North Carolina
Wildlife Resources Commission (NCWRC). This document is intended to address the
relevant project components in relation to the State's Section 401 program.
Pre -Filing Notification: A teleconference meeting was held with NCDWR personnel
(Sue Homewood, Stephanie Goss, Holley Snider, and Robert Tankard) on April 19,
2023, to discuss the reissuance of General WQC for control -of -effluent (4152). During
this meeting, it was noted that General WQC 4152 may not be reissued, which was
confirmed by Sue Homewood in a May 4, 2023, follow-up phone conversation. During
the April meeting, the Corps was informed that the call could be utilized as our pre -filing
notification meeting.
Activity Location: The project is located within waters of the United States, associated
with Back Sound, in Carteret County, North Carolina (Latitude: 34.6745140; Longitude:
-76.528441 °) (Figure 1).
Project Purpose: The project purpose is to enhance nesting bird habitat, by restoring
the existing Sandbag Island bird island to its previous extent, through the placement of
dredged material from the Back Sound federal navigation channel.
Proposed Project: The proposed project is the restoration of Sandbag Island, a nesting
bird island that is currently only about 1 acre in size, via hydraulic pipeline maintenance
dredging of the Back Sound navigation channel, to the authorized depth of -7.0 feet
mean lower low water (MLLW), with an allowable overdepth dredge to -9.0 feet MLLW.
Based on sediment analyses, the material contains less than 10% fine-grained
sediments; therefore, it is acceptable for bird island placement. Placement of dredged
material on Sandbag Island would be via control -of -effluent utilizing bulldozers to create
berms, proper slopes, and shape the island. An environmental window has been
established for the protection of nesting birds, from September 1 to March 31;
placement of dredged material would be conducted within this window. For the
upcoming maintenance dredging, approximately 160,000 cubic yards (CY) of material
would be placed to restore a portion of Sandbag Island. This initial placement effort is
expected to expand the island by about 5 acres. Subsequent placements would
gradually increase the island footprint; however, the island would never exceed the
limits of bird island construction established by the NCWRC of 25 acres in size and a
height of +15 feet (NAVD 88). Attached for further detail is the Channels from Back
Sound to Lookout Bight Maintenance Dredging Project, Proposed Plan for Sandbag
Island Placement Area supplement.
Project History: The Channel from Back Sound to Lookout Bight navigation project
was authorized under authority of the Rivers and Harbors Acts of August 26, 1937, and
March 2, 1945. The original project provided a channel 5 feet deep and 50 feet wide. A

channel 7 feet deep and 100 feet wide was authorized in 1945 by House Document
746/77/2, and construction was completed in 1956. The channel has been maintained
in approximately the same location since it was constructed. The Original
Environmental Assessment (EA) and Finding of No Significant Impact (FONSI) was
signed in November 1975 and assessed impacts associated with pipeline dredging the
federal navigation channel and placing material onto two bird islands (Morgan Island
and Sandbag Island) and on the oceanfront beach of Cape Lookout National Seashore.
Sandbag Island, which is managed by NCWRC, was created on top of a 1.66-acre
island in 1976. Sandbags were placed to contain the material dredged from the federal
navigation channel.
The last navigation contract for maintenance dredging of the Back Sound to Lookout
Bight channel was in the winter of 1997 via pipeline dredge, which removed 78,350
CY of dredged material. The Corps has no records regarding the placement location for
this material; however, 1998 aerial imagery shows a considerable increase in the size of
Sandbag Island (Figure 2), which was the placement area identified in the 1975
Environmental Impact Statement (EIS). Prior to that, dredging was completed by
hydraulic pipeline in 1992 (no additional information is available) and, in 1988, the
Corps removed 47,078 CY of material and placed it on Sandbag Island, which included
filling and placing the sandbags.
Figure 2 shows a time lapse of Sandbag Island and the six placement events that
occurred between 1976 and 1997. The island appears to have eroded steadily since
1998 after the last placement event. At the current size of 1.18 acres, the island has
lost 15.81 acres over the last 34 years. Sandbag Island appears to have been most
stable between years 2004 — 2016.
Avoidance and Minimization: Placement onto Sandbag Island via control -of -effluent
would utilize various methodologies designed to avoid impacts to submerged aquatic
vegetation (SAV) to the maximum extent practicable. Currently, the island is
approximately 1.18-acres in size, and was last used for dredged material placement in
1997. Control -of -effluent of dredged material from the Back Sound navigation channel
will require a suite of methods to restore the island with a minimal footprint of 25 acres
and a height of 15 feet and to protect the SAV beds located behind Sandbag Island to
the south-southwest. To protect these SAV beds, the Corps proposes several
measures, including geo-tubes, berm construction, and turbidity curtains. These
measures, alone or in combination, would be used to keep material from moving
towards the SAV beds while constructing the island towards the north and east. The
Corps would work closely with the contractor to ensure SAV beds, to the maximum
extent practicable, are not affected. The Sandbag Island placement plan is included as
an attachment to the Corps' submission. Placement on Sandbag Island would occur
from September 1 through March 31, to protect nesting shore birds.
Mitigation: There will be no loss of wetlands, submerged aquatic vegetation, or other
special aquatic sites, either physically or in functions and values; therefore,
compensatory mitigation is not proposed.

Cumulative/Secondary Effects: The cumulative and secondary effects from the
proposed project takes into consideration the direct and indirect effects of dredging the
Back Sound navigation channel and placement of dredged material onto Sandbag
Island. Maintenance dredging, where needed, with placement on Sandbag Island, is
expected to occur every 3-5 years using a contracted pipeline dredge. Frequency of
dredging is an estimation since shoaling rates are unknown and may be determined by
the initial dredging event. Also, large storms may move significant quantities of material
into the channels in a short period of time. The action does not include an increase in
the footprint of areas to be dredged, as authorized channel dimensions would remain
the same as previously maintained. Effects on Sandbag Island placement would also
remain the same as previously authorized and recommended by NCWRC for bird island
construction.
Direct effects of dredging and placement of material would occur within the Back Sound
channel limits and Sandbag Island, and resources present within these limits that
cannot evade the impacts may be impacted by entrainment, burial, changes in water
quality, increased noise levels and changes to habitat, although only minor and
temporary. Resources that may be impacted include benthic invertebrates (sessile and
mobile), nektonic species that feed and dwell on the seafloor, and marine reptiles and
mammals such as sea turtles and manatee. However, direct effects to manatees and
sea turtles would be minimized by the contractor following the U.S. Fish and Wildlife
Service's Guidelines for Avoiding Impacts to the West Indian Manatee (2017) and the
National Marine Fisheries Service's 2020 South Atlantic Regional Biological Opinion for
dredging activities, respectively.
Secondary effects of dredging occur outside of the channel limits and, depending on
currents, tides, and weather, can have varying impacts on resources within an
approximately 1-mile distance from the dredge. Resources include species and habitat
in the estuary environment that can be impacted by changes in water quality and
increases in noise levels produced by the dredge and the equipment used on Sandbag
Island. Overall, due to the infrequency and short-term duration of maintenance events,
increases in indirect impacts are not expected to result in significant cumulative effects
on habitat and species present.
Effects from changes in water quality to other species are expected to be minor due to
dredged material consisting of sand and its propensity to settle quickly, short duration of
projects (2-3 months annually), and localized effects (within the dredging footprint and
immediate placement area) that would leave the surrounding areas unaffected. Mobile
species are expected to avoid adverse interactions with changes in water quality.
Benthic invertebrate populations impacted within the channels are expected to recover
quickly and have a minimal effect on predators that depend on them, although there will
be burial at the Sandbag Island placement site. Entrainment would only occur within
the dredging footprint and mostly on the channel bottom and is therefore a small area of
impact when compared to the greater size of the surrounding habitat.
Beneficial direct and indirect impacts to the human environment include improved
navigation for ferry services to Shackleford Banks and Lighthouse beach, and safer

recreation for boaters and other activities. Recreational and commercial fishing would
also improve in the area, thus having a boost on the local economy. In addition, the
restoration of Sandbag Island would provide additional bird nesting habitat for the region
as these areas are lost due to coastal development.
Conclusion: The Corps has concluded that the proposed restoration of Sandbag Island
bird island via hydraulic pipeline dredging would not adversely affect water quality of
Back Sound and surrounding waters, wetlands, SAV, or other special aquatic sites, nor
would it adversely affect endangered species, so long as all mitigative measures are
followed. No mitigation would be required for the proposed project, as there would be
no loss to wetlands, SAV, or other special aquatic sites. Based on this determination,
the Corps believes the proposed project meets the criteria of North Carolina's Section
401 of the Clean Water Act program.

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Figure 2. Sandbag Island Dredged Material Placement History

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Soil Map —Carteret County, North Carolina
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Page 1 of 3

Soil Map —Carteret County, North Carolina
Map Unit Legend
Map Unit Symbol
Map Unit Name
Acres in AOI
Percent of AOI
CL
Carteret sand, low, frequently
flooded
68.9
3.4%
Du
Duckston fine sand, frequently
flooded
2.8
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0.3%
Mn
Mandarin sand
0.0
0.0%
Nc
Newhan-Corolla complex, 0 to
30 percent slopes
3.2
0.2%
Nd
Newhan fine sand, dredged, 2
to 30 percent slopes
31.1
1.5%
W
Water
1,913.7
94.5%
Totals for Area of Interest
2,026.2
100.0%
USDA Natural Resources Web Soil Survey 5/19/2023
Conservation Service National Cooperative Soil Survey Page 3 of 3

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Channels from Back Sound to Lookout Bight
Maintenance Dredging Project
Proposed Plan for Sandbag Island Placement Area
Project Background: The proposed area being considered for dredged material
placement from maintenance of the Back Sound federal navigation channel is a
previously authorized bird nesting island managed by the State of North Carolina,
locally known as Sandbag Island. At present, the island is less than 2 acres in size, and
was last used for dredged material placement in 1997 when it was built to it maximum
size of 18 acres. The island has eroded considerably over the last 25 years and is
subject to seasonal heavy winds from the northeast and boat wakes from the nearby
navigation channel.
Dredged material from the Back Sound navigation channel contains very fine-grained
sand, with the average grain size ranging from 0.13-0.18 mm (just above the grain size
of silt which is 0.075 mm). Behaviors of fine-grained sand make it challenging to
contain and stack up, requiring a suite of methods to build the island with a minimal
footprint. Past methods of successful placement include control -of effluent measures
that used sandbags to contain the material released from the dredge pipe, allowing
material to build above mean high water (MHW) level. Once the material stacked high
enough for ground moving equipment to safely maneuver, berms were constructed to
manipulate material, controlling the direction of flow.
Control -of -effluent measures have been used on various placement areas that serve as
bird nesting habitat managed by the State. This proposed plan for reestablishing
Sandbag Island is to provide a placement area for the material removed from the
navigation channel over the lifetime of the project. The USACE estimates the need for a
25-acre island that would receive material approximately every 3-5 years depending on
funding and need. Final elevations of the island would not exceed 15 feet (NAVD).
The backside of Sandbag Island (southwest side, Figure 1) contains a dense bed of
submerged aquatic vegetation (SAV). The USACE will attempt to avoid impacts to SAV
during island construction to the maximum extent practicable. Efforts using sandbags,

geotubes, berm construction and turbidity curtains will be made to direct effluent away
from the direction of SAV and build the island to the north and east.
Alternatives Considered:
1. Sandbags —Sandbags are created by filling bags onsite using dredged material
and are generally inexpensive to construct. These were previously used during the 1997
construction to assist in controlling the effluent. A sandbag barrier would be constructed
to the size needed to contain the quantity of material and built to an elevation to
withstand overwash.
Remnant sandbags are visible from two previous construction events (Figure 1). These
sandbags are not effective today for island construction and removal would require an
extensive effort. Likewise, new sandbags would be difficult to remove once buried with
new material. Regular placement activities (every 3 years) could attempt to cover over
any exposed sandbags so they do not pose a threat to wildlife.
2. Geotubes — Geotubes are created by filling tubes onsite using dredged material.
They are large, single structures as opposed to numerous individual sandbags and thus
more effective in controlling effluent and providing a barrier between the placement
limits and SAV. They are more resistant to incoming tides and wind -driven waves,
requiring less maintenance than sandbags. Costs can range from $200-$300 afoot,
which could add substantial construction costs overall ($300k - $500k).
Following construction, geotubes may be cut open but their casings would be very
difficult to remove completely. USACE has limited knowledge and experience using
geotubes for coastal projects.
3. Berm Construction — Berm construction is the least expensive containment
method and the most environmentally friendly method since they are moveable and do
not pose a threat to wildlife. However, existing material on the island is insufficient to
construct berms needed to control effluent successfully. Also, due to the fine to very
fine-grained nature of the dredge material, using berms alone will be difficult to contain
the placement material. Berms can be easily eroded during incoming tides, and can
require persistent maintenance during dredging.
4. Turbidity Curtains —Turbidity curtains are effective in trapping sediments
suspended in water (clays, silts, and very fine to fine grained sand). Installation and
removal are relatively straight forward and costs are generally inexpensive, $16-$20 ft.
However, use of curtains are constrained by shallow water depths; water depth must be

greater than 3 ft for turbidity curtains to be installed. The project area is very shallow <2
ft. NAVD88, therefore these curtains may not be effective. Until new survey information
is obtained placement of turbidity curtains remains unknown
Sandbag Island Conceptual Design:
In FY23-24, USACE proposes to place approximately 130,000 CYs onto Sandbag
Island using a cutter suction pipeline dredge. The placed material will be managed by
means of control -of -effluent using a combination of sandbags, geotubes, berm
construction and turbidity curtains. There is no other placement area available for this
material that is economically and environmentally feasible.
The conceptual design requires topographic and bathymetric surveys to better
conceptualize the proposed design.
Prior to placing material on the island, filling and placement of geotubes and/or
sandbags on the west and east side of Sandbag Island would occur to establish a
barrier between the placement area and SAV (Figure 1). The total length of geotubes
and/or sandbags would be approximately 1400 ft with the west side containing 610 ft. of
geotubes and/or sandbags and the east side containing 790 ft. of geotubes and/or
sandbags. The height and location of the geotubes and/or sandbags will be determined
at later date once a survey of the island is complete. If surrounding waters are 3 feet or
greater in depth, turbidity curtains could be installed to prevent the fine-grained dredged
material from migrating over the SAV. Using the dredged material in the federal
navigation channel, the dredge pipe would be directly connected to the geotubes to fill
them to their maximum capacity. Once the geotubes and/or sandbags are filled and
placed on the west and east extents of the placement area, the center of the island
would then be reworked through earth moving equipment. Material would be pushed
away from the center of the island toward the placed geotubes and/or sandbags and to
the northern and southern placement extents to create a basin at the center of the
island. The dredge pipe would then be oriented toward the north or south (not directed
toward SAV) and initial placement would begin in the center of the island. As the
dredged material piles up in the center of the island, between the geotubes and/or
sandbags, the placed material will be reworked again and pushed away from the center
of the island toward the north and south building out berms to further contain the placed
material. Placing material in this manner would require around the clock attention to
ensure the center of the island does not overfill with material and to ensure berms
constructed from placed material do not blow out. Depending on the orientation of the
pipe, the effluent would need to be controlled to ensure water velocities are slow
enough to allow dredged material to settle out while water continues to flow away from
the placed area. After the federal navigation channel is dredged the placed geotubes
and/or sandbags will need to be cut and removed from the island. The material trapped

in the geotubes and/or sandbags will then need to be reworked and tie into the existing
grade.
Avoidance and Minimization Measures:
• Survey the existing island and proposed placement area to determine the
existing topography and capacity for dredged material. Surrounding waters are very
shallow (1-2 feet).
• At early stages of pumping/island construction, geotubes or sandbags will be
necessary to contain the dredged material. Once construction is complete
geotubes/sandbags should be removed.
• Keeping the discharge end of the pipe below the water level can decrease
sediment runoff/suspended sediments and help material to stay within the desired area.
• Once there is enough material on the island, construction of berms will be
necessary to help reduce suspended sediments in the surrounding waters and control
and direct material away from SAV.
• Turbidity curtains may be useful if water depths are adequate (3ft or greater).
• Continuous bulldozing/manipulation of material will be necessary to construct the
island to design. Once placement begins, it is recommended that there should be no
planned breaks during pumping until placement of all material is complete (per Erica
Janocha, USACE, SAS).
• To reduce future erosion, suggest planting marsh grass (Spartina sp) sprigs
along the eastern perimeter of the island. This would also qualify for EFH mitigation if
required by agencies. Oyster bags and cultch could also be an option for
stabilization/m itigation.
• Work will be conducted during fall/winter (September — March) to minimize
impacts on nesting birds and their young.
Figure 1. Proposed island footprint adjacent to the ground-truthed SAV bed
(in blue). A combination of geotubes and/or sandbags, constructed berms, and
turbidity curtains are being considered to assist with the containment of placed
dredged material.

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