20210622_Letter Supporting Permit Modification_with figures

Page 1

4700 Falls of Neuse, Suite #300
Raleigh, NC 27609

[phone]Fax: [phone]
www.moffattnichol.com
June 22, 2021
Mr. Greg Currey
Regulatory Field Office
U.S. Army Corps of Engineers, Wilmington District
69 Darlington Ave.
Wilmington, NC 28403

RE: 2021/2022 Oak Island Beach Renourishment Project: Additional Information to
Support the General Permit 291 Application (Action ID# SAW 2018-02230)

Dear Mr. Currey,
Per the request of Mr. Mickey Sugg of your office, please accept this letter as supplemental information
in support of the Town of Oak Island’s 2021/2022 Oak Island Beach Renourishment Project permit
application (Action ID# SAW 2018-02230). Based on an on-site agency meeting, held June 15, 2021,
it was requested by the USACE to provide additional measures/actions that will be taken during the
planned 2021/2022 Oak Island Renourishment Project including: 1) avoidance of areas of the Jay Bird
Shoal borrow area with a high carbonate percentage to the maximum extent practicable; 2) review of
the current sediment analyses to provide expectations of material and safeguard that the material
placed on the beach is in compliance with N.C. Technical Standards for Beach Fill Projects (15A
NCAC 07H.0312) and, 3) Improve communication and transparency during all aspects of the
construction process to all for mitigative and adaptive decision making. The Town is committed to
comply with all State and federal conditions to provide viable habitat for nesting sea turtles on its
beaches.

The recently constructed 2020/2021 Oak Island Renourishment Project resulted in concerns of 1)
placement of material slightly above the allowable threshold for carbonate content percentage in
specific locations along the profiles in areas the Dredge Dodge Island worked and 2) the color of the
material. Avoidance and minimization measure the Town is agreeable to implement both in the short
term and during the construction process to adhere to the State’s technical standards and to reduce
adverse impacts to nesting sea turtles are described below.

Monitor Sand Temperature
To monitor the effect of the color of material placed on the beach during the 2020/2021 Oak Island
Renourishment Project, Moffatt & Nichol (M&N) will coordinate with State and federal agencies,
including the N.C. Wildlife Resources Commission (NCWRC) and the U.S. Fish and Wildlife Service
(USFWS), to deploy six (6) temperature loggers on the face of the dune to monitor sand temperatures
and document visual observations of color (see Figure 1). Two control sites will be located
approximately 1,000 - 1,500’ outside of the 2020/2021 project boundary including one site east of the
project within Caswell Beach, and one site west of the project in the emergency dune constructed

Page 2
June 22, 2021
from overwash sand after Hurricane Isaias. Four temperature monitoring stations will be located
within the 2020/2021 project limits; two will be located in areas where the hydraulic dredge Ohio
placed material that originated from Zone 1 and Zone 3 of the borrow area and two will be placed in
areas where the hopper dredge Dodge Island placed material that primarily originated from Zone 2.
Dune sand temperatures will be monitored throughout the end of August and data will be provided
to the agencies on a biweekly basis. Temperature and color monitoring methodology will be consistent
with the 2018 monitoring conducted by the Town.
Dredging Limitations within the Borrow Area
Based on the proximity of the beach fill placement areas to the borrow area(s) it is anticipated the
2021/2022 project will be performed by a hopper dredge. As a means of improving sediment quality
from Jay Bird Shoals, the Town proposes to limit the Contractor from dredging in certain locations
of the borrow area. Although the area(s) to be limited are within the N.C. State Technical Standards
for Beach Fill Projects, the contractor will be penalized for removing material from the areas by
deduction of an equal quantity of beach fill removed from these designated areas. To determine the
areas within the borrow area to be limited, M&N evaluated two approaches; 1) re-analyze material
that was deemed to be of questionable quality during the 2020/2021 project and, 2) further evaluate
existing vibracores in the area(s) of the Jay Bird Shoals Borrow Area likely to be excavated for the
2021/2022 project.
For the initial determination of avoidance area(s) deemed to be questionable quality, there were several
instances, primarily in Zone 1, where the hydraulic dredge Ohio moved the dredge when encountering
questionable material (locations shown in red on Figure 2). The entire area shaded in yellow in Figure 2
will not be made available to the Contractor for dredging during the 2021/2022 project to avoid
questionable material.
To provide detail on the expected carbonate content for the 2021/2022 Oak Island Renourishment
Project, an analysis was performed of the material that was dredged and placed on the beach as beach
fill during the 2020/2021 project. The material removed from Jay Bird Shoals for the 2021/2022
project will be removed from Zone 2 (as well as Zones 1 & 3) as it provides allowable depths for a
hopper dredge. The work the hopper dredge Dodge Island performed on the 2020/2021 project
removed material from Zone 2, with the resulting material placed on the beach from Station 430+00
to 470+00. The results of the sediment samples placed on the beach were evaluated to determine an
overall average carbonate level. The material placed on the beach yielded a carbonate content of
22.12% from 11 samples collected during construction from Station 430+00 to 470+00. This is within
the required standard of 25% but some areas of the beach profile exceeded the 25% standard resulting
in concerns of compaction.
Vibracore data from the borrow area was then evaluated including any surrounding vibracores not in
the permitted borrow area that may have influenced the material being dredged. Based on the
evaluation, it is probable that vibracores JB-02 and JB-05 had an influence on the material removed
from Zone 2 in the vicinity of vibracores JB-01 and JB-06 (see Figure 3). Using the after-dredge survey
performed by the contractor, the amount of material removed from Zone 2 was calculated at
corresponding elevations/locations influenced by nearby vibracores. Based on this calculation the
estimated composite carbonate content of the material removed from the Zone 2 was 21.46% which
is a close relation to the carbonate content of the sediment placed on the beach. Since vibracores JB-

Page 3
June 22, 2021
02 and JB-05 had an influence along the “slanted” portion of the borrow area, it was considered to
remove this portion of the borrow area for the 2021/2022 project. However, considering vibracores
JB-02 and JB-05 have lower carbonate content below 3.0 feet and the contractor removed the top
approximately 2.0 feet of material in this area, the high carbonate content material should have
essentially been exhausted. Since this material has already been removed, the remaining material is
expected to be of lower carbonate content for the 2021/2022 project.
For the expectation of the sediment quality for the 2021/2022 project, the remaining material available
in Zone 2 was investigated utilizing the same techniques used for calculating the carbonate content of
the material removed during the 2020/2021 project. The calculation again used the vibracores within
Zone 2 and those outside of Zone 2 (JB-02 & JB-05) that have an influence on the material within the
permitted borrow area. Based on after-dredge survey of Zone 2 the material remaining in the borrow
area was calculated at the corresponding location/elevation of the vibracores to determine a weighted
composition of the carbonate content of 16.57% remaining in Zone 2 which is approximately a 5%
reduction of carbonate from the 2021/2022 project or almost 25% reduction in carbonate content.
Finally, areas were investigated to eliminate from the borrow area to further reduce the level of
carbonate while still meeting the project quantity needs. The bottom of JB-18 was identified to have
elevated levels of calcium carbonate. Reducing the allowable dredging elevation by three feet in the
quadrant controlled by JB-18 (see Figure 4), would remove approximately 120,000 cy of elevated
carbonate content material and further reduce the expected carbonate content on the beach for the
2021/2022 project to 15.87%.
To ensure the contractor avoids the lower 3 feet of JB-18 and portions of Zone 1, a 50% non-pay
penalty will be instituted for any material removed from those areas as set forth in the plan set.
Require Tilling in Potential Nesting Footprint
The upcoming 2021/2022 project will require tilling on the berm and berm slope as well as 10 feet up
the slope of the seaward face of the primary dune prior to the start of sea turtle nesting season of May
1. Generally, when tilling occurs on a beach nourishment project, it is performed on the flat surface
of the berm and the gently sloping beach that leads into the water. However, due to the difficulty with
tilling on a steeper slope (dune face) due to material possibly sloughing out of the required payment
section, the contractor will typically stay 2 to 5 feet from the dune toe to not damage the dune section.
To alleviate potential concerns by the contractor in regards to the effects on the payment section,
beach profiles will be surveyed for payment and acceptance prior to the tilling of the dune face. If
necessary, the contractor may be required to have a modified tiller that is narrower in width to allow
easier access to the dune face.
Require Additional Sand Samples with Expedited Lab Results
To provide more real-time sediment monitoring in the 2021/2022 project, daily visual monitoring will
be requested of the contractor and a sediment sample will be taken for full lab analysis every third day
or placement of each 50,000 cubic yards of beach fill whichever is sooner. The full lab analysis will be
provided to the Engineer by the close of business no later than the third day after the sample is taken
and then transmitted to the agencies. During the 2020/2021 project, the project specifications required
the contractor to visually monitor the sediment quality daily, provide a visual assessment with
Page 4
June 22, 2021
descriptive analysis on the third day each week and a lab analysis of sediment quality on the seventh
day each week. In some instances, during the 2020/2021 project, it took over one week to receive the
full lab analysis (including carbonate content).
Provide a Required Completion Date One Month Before Permit Window
During the 2020/2021 project there was concern that it became more difficult for the contractor to
maintain standard quality control in efforts to finish the project. For the 2021/2022 project, the
required completion date before the onset of liquidated damages will be set to March 31 for beach fill
activities rather than the authorized date of April 30. To further enforce this requirement, the penalties
for liquidated damages will be increased from $4,000 per calendar day to $10,000 per calendar day of
delay past the completion date of March 31.
In closing, it is our belief that the measures outlined herein will significantly reduce the likelihood of
similar issues taking place during our 2021/2020 project. If you have any questions about any of
these measures, please do not hesitate to contact us at your convenience.
Sincerely,
MOFFATT & NICHOL
Johnny Martin, PE
Senior Coastal Engineer
cc: Maria T. Dunn, NCWRC
Kathy Matthews, FWS
Heather Coats, NCDCM
Mickey Sugg, USACE
Temperature Gage Location #2SE 58th St. Beach AccessOhio Placement #1~ Elev 12' NAVD88(~20' up dune face)
Temperature Gage Location #329th Pl E Vehicle AccessOhio Placement #2~ Elev 12' NAVD88(~20' up dune face)
Temperature Gage Location #411th PL E Beach AccesDodge Placement #1~ Elev 12' NAVD88(~20' up dune face)
Temperature Gage Location #56th PL E Beach AccessDodge Placement #2~ Elev 12' NAVD88(~20' up dune face)
Temperature Gage Location #1SE 67th St Beach AccessEast of Placement Area~ Elev 12' NAVD88Based on March 2021 Survey
Temperature Gage Location #65th PL West Beach AccessWest of Placement AreaNearest High Ground
27
0
+
0
0
28
0
+
0
0
31
0
+
0
0
34
0
+
0
0
33
0
+
0
0
32
0
+
0
0
35
0
+
0
0
39
0
+
0
0
37
0
+
0
0
26
0
+
0
0
36
0
+
0
0
38
0
+
0
0
40
0
+
0
0
41
0
+
0
0
4
5
0
+
0
0
4
6
0
+
0
0
4
8
0
+
0
0
4
7
0
+
0
0
4
4
0
+
0
0
5
0
0
+
0
0
5
2
0
+
0
0
5
3
0
+
0
0
4
9
0
+
0
0
5
1
0
+
0
0
5
4
0
+
0
0
Ohio PlacementDodge IslandPlacement
Legend
OKI Survey Transects
AD Survey Boundary ¹0 2,000 4,0001,000 Feet Figure 1: Temperature Logger Placement
2284000
2284000
2286000
2286000
2288000
2288000
2290000
2290000
2292000
2292000
44
0
0
0
44
0
0
0
46
0
0
0
46
0
0
0
48
0
0
0
48
0
0
0
Legend
JB-20
Zone 1
Zone 2
Zone 3
-16 - -15
-17 - -16
-18 - -17
-19 - -18
-20 - -19
-21 - -20
-22 - -21
-23 - -22
-24 - -23
-25 - -24
-26 - -25
-27 - -26
-28 - -27
-29 - -28
-29.99 - -29
0 1,000 2,000500Feet .
Elevation (ft, NAVD88)
JB-20
Figure 2: JBS Zone 1 Areas of Avoidance
JB-02
JB-05
2284000
2284000
2286000
2286000
2288000
2288000
2290000
2290000
2292000
2292000
44
0
0
0
44
0
0
0
46
0
0
0
46
0
0
0
48
0
0
0
48
0
0
0
Legend
Vibracore Influence Areas
Zone 1
Zone 2
Zone 3
-16 - -15
-17 - -16
-18 - -17
-19 - -18
-20 - -19
-21 - -20
-22 - -21
-23 - -22
-24 - -23
-25 - -24
-26 - -25
-27 - -26
-28 - -27
-29 - -28
-29.99 - -29
0 1,000 2,000500Feet .
Elevation (ft, NAVD88)
Figure 3: JBS Zone 2 Area of Influence
2284000
2284000
2286000
2286000
2288000
2288000
2290000
2290000
2292000
2292000
44
0
0
0
44
0
0
0
46
0
0
0
46
0
0
0
48
0
0
0
48
0
0
0
Legend
JB-18
Zone 1
Zone 2
Zone 3
-16 - -15
-17 - -16
-18 - -17
-19 - -18
-20 - -19
-21 - -20
-22 - -21
-23 - -22
-24 - -23
-25 - -24
-26 - -25
-27 - -26
-28 - -27
-29 - -28
-29.99 - -29
0 1,000 2,000500Feet .
Elevation (ft, NAVD88)
JB-18
Figure 4: JBS Zone 2 Area of Avoidance