HomeMy WebLinkAbout2013_8_15 SBPF Submission_201405230855447710BAXTER ROAD AND SCONSET BLUFF STORM DAMAGE PREVENTION PROJECT
NOTICE OF INTENT (DEP FILE NO. SE 048-2581)
RESPONSES TO QUESTIONS FROM NANTUCKET CONSERVATION COMMISSION ASKED AT
PUBLIC HEARING ON AUGUST 8, 2013
August 15, 2013
To assist the Commission and the public with the review of the NOI, SBPF is presenting specific
responses to the topics that were covered at the public hearing on August 8, 2013. The format of
this document is to present a brief summary of each comment or question in bold followed by a
response in regular text.
QUESTIONS/COMMENTS FROM CONSERVATION COMMISSION MEMBERS
I. DESIGN
Provide updated plans based on the 2013 LIDAR, including the new toe design and additional
section views.
See the revised plans included with this submission, which are based on the recent (2013) LIDAR
survey and include the new toe design and additional section views.
What is the southern extent of the Project Area?
The southern extent of the Project area has been moved to 63 Baxter Road so as to include only
those areas where the coastal bank is actively eroding. The revised Project area is 63-119 Baxter
Road, as shown on the attached plans.
What is the grain size data for the Project area?
The Applicant previously performed a thorough sediment sampling effort for an approximately
three-mile section of the eastern shore of Nantucket extending from Sesachacha Pond to just south
of the Town sewer beds. A total of 248 sediment samples were collected at various cross-shore
positions along thirty-six defined transects spaced approximately every 500-feet, and included the
coastal bank (where present), coastal dune (where present), coastal beach, wave breaking zone, and
offshore area.
When these data were reviewed for the current revetment Project, it was determined that Transects
L12 through L19 fell within the current Project area from 119 to 63 Baxter Road. Along each
transect, bank samples were taken from the upper bank, middle bank, and lower bank. Transects
L19 and L20 were located along a well-vegetated portion of the bank where no sediment was
exposed; no Coastal Bank samples were collected along these transects. When grain size summary
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Responses to August 8, 2013 Hearing
characteristics were calculated just for those samples falling within the current Project area, the
mean size for the coastal bank samples was 0.45 mm with an average silt content of 13.4%. Table
1 contains a summary of grain size results for the coastal bank within the Project area.
Table 1 Coastal Bank Grain Size Summary for the Project Area
Coastal Bank
Mean grain size
(mm)
Silt
(%)
Minimum 0.18 0.4
Maximum 0.67 44.4
Mean 0.42 10.0
The results for the revetment Project area are very similar to both the summary statistics for the
entire coastal bank and the summary statistics for the area from 99-55 previously considered for the
marine mattress and gabion project. The mean grain size for the entire dataset of coastal bank
samples was 0.42 mm with an average silt content of 12%. The mean grain size for the area from
99-55 Baxter Road previously considered for the marine mattress and gabion project is 0.45 mm
with an average silt content of 13%.
II. CONSTRUCTION
Provide more details on the Construction Protocol.
Stone Delivery: All stone, including the filter layer will be delivered via barge directly to
the beach. Initially, a landing (or “pier”) barge will beach itself at high tide, setting its spuds
(temporary pilings) at its seaward end, and dropping a ramp onto the beach. The location
of the landing barge will be determined by the Contractor and is expected to be within or
adjacent to the high priority area located seaward of 99-105 Baxter Road.
Delivery barges will tie off to the pier barge while the tug boat and/or anchor (crown) buoys
keep the stern of the pier barge in place. All-terrain dump trucks will back onto the pier
barge from the beach, and get loaded by an excavator aboard the barges. The excavator
and the dumps will continue to work their way back until the delivery barge has been
emptied.
The all-terrain dumps will deliver the stone to either the active work area, or designated
staging areas within the bounds of the project. The staging areas will be temporary and will
change, so are not specifically mapped, and will be determined by the contractor.
Equipment Delivery: The equipment will mostly be delivered by barge, including: front
end loaders, all terrain dumps, excavators and possibly a small crane. There will also be a
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small all-terrain transport vehicle used for getting workers to and from Hoicks Hollow,
where they will park their vehicles.
Equipment Fueling: All construction equipment will be fueled at Hoicks Hollow by a
local fuel truck, as far landward of resource areas as feasible.
Revetment Installation: The toe of the revetment will be excavated in approximately 20'
lengths at a time. There will be will be some minor cutting and filling required in order to
achieve a relatively straight revetment, as shown on the section views. As the toe stones are
being excavated, any excavated material in excess of what will be used for backfill will be
used for filling behind the revetment in areas and smoothing the face of the bluff as
required.
Once the toe is excavated, the geofabric will be laid in place, followed by the filter layer
stone and toe stones prior to backfilling. Driving steel sheathing will be used at the sections
where material will need to be held back relative to the excavation. The sheathing will be
removed after the toe is installed and the revetment area has been smoothed out and
prepped. A second crew will lag behind by a section or two, and will install the above
grade section of the revetment. The placement of the stone can be done with either a long
reach excavator or a small crane. This will be variable based on the contractor selection
and their preferred or available equipment.
Sediment Delivery: Sediment will be transported via dump truck from one or more local
contractor’s pit(s) off Milestone Road to the delivery location on Baxter Road (see following
paragraph), where it will be dumped into a hopper, then transported via conveyor belts to
the edge of the coastal bank. The conveyor belts at the top of the bank will dump into a
chute (made of 3-foot diameter ADS drainage pipe) for transport down to the lower bank
(see Figure 1). The chutes will be positioned a foot or two above the face of the coastal
bank using bracing made of pressure-treated wood to protect bank vegetation. These
chutes are light enough to be quickly installed and removed during seasonal sediment
delivery. Sediment will then be positioned by a front-end loader or skid steer.
Five sediment delivery locations will be established along the side of Baxter Road, as shown
on Figure 1. Temporary structural turf pull-over areas will be installed at four of these
locations; no structural turf is required at the northernmost delivery location near 119
Baxter Road due to the large paved area already present.
In the instance of successive storms, sand will be delivered via ADS pipe from above until
there is sufficient material at the northern end of the structure for a skid steer to ramp up to
the platform at the top of the revetment. This way the skid steers can access other areas of
the revetment to disperse sand as required.
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Demobilization: Upon completion of phase one and two, the landing barge will be
removed from the nearshore by tugs pulling it off at high tide. The equipment used for the
construction will be aboard the landing barge upon departure.
PUBLIC QUESTIONS/COMMENTS
MEPA should be asked if they have jurisdiction over the Project.
MEPA jurisdiction over projects is defined in the MEPA regulations review thresholds at 301 CMR
11.03. For projects subject to wetlands review, the project trigger is the requirement for a state
permit (Superseding Order of Conditions) and that certain thresholds are exceeded. Any alteration
of coastal bank triggers MEPA review if a Superseding Order of Conditions is required. Thus, if a
local Order of Conditions is appealed to DEP, the applicant would be required to file an
Environmental Notification Form (ENF) with MEPA.
The other potential MEPA trigger is for the category of State-listed Species under MGL 131A
(Massachusetts Endangered Species Act). Since the project has decided to not include work on lots
south of 63 Baxter Road, there will be no work in either Priority Habitats for State-Protected Species
or Estimated Habitats for Rare Wildlife (see Figure 9 in Attachment B of the NOI).
Owners need to sign the NOI application.
All participating property owners from 63-119 Baxter Road have signed the NOI application, other
than the property owner at 71 Baxter Road who has elected not to participate in the project. The
revetment at 71 Baxter Road will be installed on Town property; that part of the proposed
vegetation on the upper bank which is on private property will not be installed.
The Third Party consultant is not looking at the effects of the rocks on littoral drift. What happens if
you lose the barrier beach in front of Sesachacha Pond? This area is Piping plover habitat. If you
cause erosion, it affects their habitat.
Sand will be added in front of the revetment and downdrift of the revetment to mitigate for the sand
that would otherwise have been supplied by the coastal bank without the revetment. This sand will
be carried by littoral drift to the north at a rate that will be similar to the current rate. Shoreline
monitoring transects which extend in front of Sesachacha Pond and northward to Quidnet, Squam
and Wauwinet (see Figure 10, Attachment B in the NOI) will be monitored and compared to
control locations to determine if the project is causing accelerated erosion; if necessary, mitigation
will be provided. If the revetment is causing acceleration of shoreline erosion downdrift of the
structure, immediately adjacent areas would experience that erosion first before it would be
experienced much farther downdrift at Sesachacha Pond or even farther north at Quidnet, Squam
or Wauwinet. Densely-spaced shoreline monitoring transects immediately downdrift and adjacent
to the revetment would measure any accelerated erosion due to the revetment, allowing mitigation
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Responses to August 8, 2013 Hearing
to be provided before any acceleration of shoreline erosion would be apparent as far north as
Sesachahca Pond, Quidnet, Squam, or Wauwinet.
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!.BAXTER ROADSANKATY ROADI
SABEL
L
E'S WAYISOBELS WAYSANKATY HEAD ROADPOLPIS ROAD
BAYBERRY LANE
85
99
97
87
73
83
101
105
109
81
79
93
91
77
117
75
115
113
119
107
107A
53
63
51B
59
69
61
55
51A
71
67
65
Source: Esri, DigitalGlobe, GeoEye, i-cubed, USDA, USGS, AEX, Getmapping, Aerogrid, IGN, IGP,swisstopo, and the GIS User Community
G:\Projects\Lighthouse\2013\NOI\sediment_delivery\locations.mxd
Figure 1Sediment Delivery Locations
Baxter Road and Sconset Bluff Storm Damage Prevention Project Nantucket, MA
LEGEND
Basemap: 2011 Aerial Imagery, ESRI
Participating Property
Parcel Boundary
!.Hopper Location
Structural Turf Location
Conveyor Belt for Sediment Delivery
Chute for Sediment Delivery
Coastal Bank
Coastal Dune
°0 150 30075Feet1 inch = 300 feetScale1:3,600
top of coastal bank toe of coastal bank