HomeMy WebLinkAboutIn-Town TechMemo 1-10-07_201406021635428178TECHNICAL MEMORANDUM
Pref. Alt. Description and Potential Impacts, In-Town Bike Path & Sidewalk Imp. Proj. – Nantucket, Massachusetts
GPI Greenman-Pedersen, Inc.
105 CENTRAL STREET ♦ SUITE 4100 ♦ STONEHAM, MA 02180 ♦ TELEPHONE: (781) 279-5500 ♦ FACSIMILE: (781) 279-5501
REF: MAX-2005128.00
DATE: January 10, 2007
TO: Mr. T. Michael Burns
Nantucket Planning & Economic Development Commission
16 Broad Street
Nantucket, Massachusetts 02554
FROM: Ms. Rebecca S. Williamson, P.E., Project Manager
Mr. Joseph Johnson, P.E., Engineer
RE: Technical Memorandum
Preferred Alternative Description and Potential Impacts
In-Town Bike Path & Sidewalk Improvement Project
Nantucket, Massachusetts
Greenman-Pedersen, Inc. (GPI) has prepared this synopsis to accompany the Preferred
Alternative Design Concept for the In-Town Bike & Sidewalk Improvement Project in
Nantucket, Massachusetts. GPI has completed Phase I of this project which includes the field
survey for the project as well as the development of four conceptual alternatives for the bike
path. The concepts were provided to the County Commission and the Nantucket Planning Board
for comment and guidance in the selection of a preferred alternative. Based on input provided by
the Town, an initially Preferred Alternative was established. Phase II of this project will involve
the final design of the Preferred Alternative. This document describes the alternatives that were
considered and the preferred alternative. Discussion of the preferred alternative includes
potential project impacts in terms of right-of-way, private property and environmental
permitting. Design related concerns are also discussed.
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DESCRIPTION OF CONCEPTUAL ALTERNATIVES
In general, the intent of the project is to provide safe and convenient bicycle/pedestrian access
between the downtown core of Nantucket and the outlying bicycle paths. The project limits are
along Orange Street and Washington Street between the Milestone Rotary and the proposed
Transportation Center at the corner of Washington Street and Commercial Wharf in the
downtown core. Currently bicyclists are required to “Share the Road” with vehicles while
sidewalks for pedestrians are not continuous and are located sporadically throughout the project.
The concept alternatives that were developed consist of two basic alignments. One alignment
runs from the Milestone Rotary westerly along Orange Street to Union Street, Francis Street and
northerly along Washington Street to its intersection with Commercial Street.
The second alignment utilizes abandoned railroad right-of-way to connect Orange Street with
Washington Street thus avoiding work along Union Street and Francis Street as described in the
first alignment. The land adjacent to the abandoned railroad right-of-way consists of salt marsh
on one side and wetlands on the other.
Both alignments utilize variations of either a separate bicycle path facility or shared
vehicular/bicycle travel lanes. Following is a short description of each alternative and the
associated advantages and disadvantages of each.
Option 1A:
This concept consists of a 10’ shared-use recreational path that is independent of vehicular traffic
(i.e., separated from vehicle travel lanes via curbing). Adjacent roadways have minimum travel
lane widths of 11’. This concept utilizes the alignment that runs along Orange Street, the
abandoned railway and Washington Street. A concept plan is provided in the Appendix.
Following is the proposed cross section along Orange Street.
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As shown in the cross section, the 10’ shared use bike path is separated from vehicular traffic,
but is adjacent to the roadway. This is not always a desirable situation when bicycle traffic is
heading towards oncoming vehicular traffic. Ideally, when more right-of-way is available, a
grass strip (5’ to 7’ wide) or physical buffer would be provided between the path and vehicular
travel lane to prevent potential collisions and promote a level of comfort among drivers and trail
users alike. Unfortunately the right-of-way width along this project does not lend itself towards
the proper separation of the roadway and the path.
The proposed cross section along Orange Street requires the roadway alignment to shift to the
south to make room for the path on the northerly side. A concrete sidewalk is proposed along
the southerly side of Orange Street while its width varies depending on the remaining available
right-of-way.
Heading northwesterly along Orange Street, the path takes a turn onto Goose Pond Road for a
short distance before heading onto the abandoned railway through the salt marsh. Following is
the cross section proposed through the salt marsh.
At the northerly terminus of the abandoned railway/salt marsh, the path enters a section of
Washington Street that carries a very low volume of vehicles. Along this portion of Washington
Street (from railway to Francis Street) the bicyclists/pedestrians are required to share the
roadway with motor vehicles. From Francis Street to the northerly project limit at Commercial
Street, the following cross section is proposed along Washington Street.
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The 10’ shared path is located along the southerly side of Washington Street adjacent to the
vehicular travel lane. The existing right-of-way width will not accommodate a sidewalk on the
northerly side of Washington Street.
Of all the concepts, Option 1A has the least encroachment on private property and has the lowest
construction cost. It is also anticipated that wetland impacts will be minimal depending on the
type of construction used for the path along the abandoned railway. This concept does shift the
roadway alignment of Orange Street closer to abutting properties on one side of the roadway and
does not provide the ideal separation of the path and vehicular traffic.
Option 1B:
This concept consists of a shared-use recreational path that is independent of vehicular traffic
(i.e., separated from vehicle travel lanes via curbing). The path is 10’ wide along Orange Street
and Washington Street. The proposed path is 8’ wide along Union Street and Francis Street.
Adjacent roadways have minimum travel lane widths of 11’. This concept does not utilize the
abandoned railway alignment. A concept plan is provided in the Appendix. The proposed cross
sections along Orange Street and Washington Street are identical to those presented previously
under Option 1A. Following are the proposed cross sections for Union Street and Francis Street.
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Along Francis Street the path is located along the westerly curbline while the path is located
along the northeasterly curbline of Union Street. No pedestrian/bicycle accommodations are
proposed on the opposite curblines along Francis Street and Union Street.
Similarly to Option 1A, it is less than desirable to have bicycle traffic heading towards oncoming
vehicular traffic without a grass strip or a physical barrier of some sort. Unfortunately the right-
of-way width along this project does not lend itself towards the proper separation of the roadway
and the path.
Similarly to Option 1A, the Orange Street roadway alignment is shifted to the south to make
room for the path on the northerly side. A concrete sidewalk is proposed along the southerly side
of Orange Street while its width varies depending on the remaining available right-of-way.
The 10’ shared path is located along the southerly side of Washington Street adjacent to the
vehicular travel lane. The existing right-of-way width will not accommodate a sidewalk on the
northerly side of Washington Street.
Option 1B provides a continuous path along the project adjacent to the roadways and does not
utilize the abandoned railway alignment. It is anticipated that wetland alteration will be required
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in two locations with this Option. This Option also has severe widening impacts on private
property along Union Street, Francis Street and a narrow section of Orange Street. This concept
does shift the roadway alignment of Orange Street closer to abutting properties on one side of the
roadway and does not provide the ideal separation of the path and vehicular traffic.
Option 2A:
This concept consists of striped bicycle lanes along Orange Street and Washington Street while
also using the abandoned railway alignment through the salt marsh. A concept plan is provided
in the Appendix. Following is the proposed cross section along Orange Street.
As shown in the cross section, 10’ motor vehicle lanes are proposed with 4’ bicycle lanes. A
sidewalk is proposed along the northerly side of Orange Street. The existing right-of-way width
along Orange Street does not allow for a sidewalk on the southerly side of Orange Street. The
proposed cross section along Orange Street requires the roadway alignment to shift to the south
to make room for the sidewalk on the northerly side.
Heading northwesterly along Orange Street, bicyclists and pedestrians will turn onto Goose Pond
Road for a short distance before heading onto the abandoned railway through the salt marsh.
The cross section proposed through the salt marsh is identical to that shown for Option 1A.
At the northerly terminus of the abandoned railway/salt marsh, the path enters a section of
Washington Street that carries a very low volume of vehicles. Along this portion of Washington
Street (from railway to Francis Street) the bicyclists/pedestrians are required to share the
roadway with motor vehicles. Following is the proposed cross section along Washington Street
from Francis Street to the northerly project limit at Commercial Street.
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The concrete sidewalk is proposed along the southerly side of Washington Street. The existing
right-of-way width will not accommodate a sidewalk on the northerly side of Washington Street.
The alignment of Washington Street is shifted to the north to make room for the increased
roadway width as well as the proposed sidewalk.
Option 2A provides a more desirable configuration of a striped bicycle lane as opposed to the off
road facilities proposed in Options 1A and 1B. Generally off road paths are preferred as long as
a buffer from the adjacent roadway can be provided. Unfortunately the right-of-way width along
this project does not allow for a buffer in Options 1A and 1B. It is anticipated that wetland
impacts will be minimal depending on the type of construction used for the path along the
abandoned railway. This concept does shift the roadway alignment of Orange Street and
Washington Street closer to abutting properties on one side of the roadway.
Option 2B:
This concept consists of striped bicycle lanes along Orange Street, Union Street, Francis Street
and Washington Street. This concept does not utilize the abandoned railway alignment. A
concept plan is provided in the Appendix. The proposed cross sections along Orange Street and
Washington Street are identical to those presented previously under Option 2A (10’ motor
vehicle lanes with 4’ bicycle lanes). Following are the proposed cross sections for Union Street
and Francis Street.
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As shown in the cross sections, 10’ motor vehicle lanes are proposed with 4’ bicycle lanes.
Along Francis Street the proposed sidewalk is located along the westerly curbline. The proposed
sidewalk is located along the northeasterly curbline of Union Street. No pedestrian/bicycle
accommodations are proposed on the opposite curblines along Francis Street and Union Street.
Similarly to Option 2A, the Orange Street and Washington Street roadway alignments are shifted
to make room for the proposed sidewalks. This places the roadways closer to abutting properties
and reduces the existing buffer.
Option 2B provides continuous bike lanes along the project and does not utilize the abandoned
railway alignment. Proposed is a more desirable configuration of a striped bicycle lane as
opposed to the off road facilities as shown in Options 1A and 1B. It is anticipated that there will
be wetland alteration in two locations with this Option. This Option also has widening impacts
on private property along Union Street, Francis Street and a narrow section of Orange Street.
This concept does shift the roadway alignment of Orange Street and Washington Street closer to
abutting properties on one side of the roadway.
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PREFERRED ALTERNATIVE
Based on input from the Town, Option 2A was chosen as the preferred alternative for the project.
Advantages and disadvantages of each option are provided in the Appendix. It appears that use
of the abandoned railway alignment and proposing striped bicycle lanes provides the least impact
to wetlands and abutters while providing the safest bicycle/pedestrian accommodations. The
Preferred Alternative is provided in the Appendix.
Right-of-Way Impacts – Given the narrow width of right-of-way through the project area, Option
2A does have impacts to adjacent private property. Based on the conceptual design, it is
estimated that 60% of the properties (42 properties) abutting the project will require a fee taking
of some degree (approximately 9,500 sf of property taking project wide). Approximately 15% of
the abutting properties (26 properties) will only require a temporary easement for construction
while approximately 25% of the abutting properties (16 properties) will have no right-of-way
impacts. Impacts to properties include driveway and slope grading, removal and resetting of
fence and the removal and resetting of walls.
Environmental Permitting – With the implementation of Option 2A, wetland alteration may be
necessary along the abandoned railway alignment. Depending on how the path is designed
through the wetlands, different degrees of impacts result. An environmental assessment of
Option 2A has been completed and is included in the Appendix.
Utility Concerns – The construction of Option 2A will require the relocation of approximately 16
utility poles along the project. Hydrants and drainage catch basins will also require relocation as
a result of the proposed curbline locations. All manholes, water meters, water gates and any
other surface installed utilities will require adjustment as well.
Design Concerns – The design of the path through the wetlands will need to be finalized as part
of Phase II of the project. This may require the narrowing of this portion of the trail or other
alternative treatments as discussed in the environmental assessment. Following are other design
concerns along the project:
• Design should minimize impacts to abutting properties. Design may require resetting
existing fences and walls, the replacement of existing landscaping features and rebuilding
existing access points to building (i.e., stairs, walkways).
• Design of Washington Street from railway to Francis Street should incorporate signing
and striping to have pedestrians/bicyclists share the road.
• There are pinch points along the project where abutting properties have existing
immovable features that will encroach on the sidewalk. These encroachments will need
to be minimized and the design will have to be advanced in accordance with guidelines
compliant with the Americans with Disabilities Act regulation.
• Proper signing should be utilized along Orange Street to direct bicyclists/pedestrians
along the Goose Pond Road/marsh path.
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• Striping should be utilized at Goose Pond Road to separate bicyclist/pedestrian traffic
from motor vehicles.
• Portions of the proposed sidewalk along the north side of Orange Street are not
continuous. These sections should either be justified or eliminated from the project.
Consideration could also be given to midblock crossings where sidewalks are terminated.
• Guide signing at the project limits should be considered to direct bicyclists to existing
nearby bicyclist routes/paths.
CONCLUSIONS AND RECOMMENDATIONS
The existing roadway widths throughout the project limits are very narrow and are unsuitable to
safely accommodate pedestrians and bicyclists. It is recommended that Option 2A (the preferred
alternative) be presented publicly for comment and be advanced to final design and eventual
construction. The proposed project will have impacts to abutting properties and wetlands but
will enhance public safety and positively contribute to the already existing network of shared-use
recreational paths in Town.
TECHNICAL MEMORANDUM
Pref. Alt. Description and Potential Impacts, In-Town Bike Path & Sidewalk Imp. Proj. – Nantucket, Massachusetts
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APPENDIX
CONCEPTUAL ALTERNATIVE - OPTION 1A
CONCEPTUAL ALTERNATIVE - OPTION 1B
CONCEPTUAL ALTERNATIVE - OPTION 2A
CONCEPTUAL ALTERNATIVE - OPTION 2B
CONCEPT COMPARISON/ANALYSIS
PREFERRED ALTERNATIVE
ENVIRONMENTAL ASSESMENT
TECHNICAL MEMORANDUM
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CONCEPTUAL ALTERNATIVE - OPTION 1A
TECHNICAL MEMORANDUM
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CONCEPTUAL ALTERNATIVE - OPTION 1B
TECHNICAL MEMORANDUM
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CONCEPTUAL ALTERNATIVE - OPTION 2A
TECHNICAL MEMORANDUM
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CONCEPTUAL ALTERNATIVE - OPTION 2B
TECHNICAL MEMORANDUM
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CONCEPT COMPARISON/ANALYSIS
12345
More Desirable Average Less Desirable
Option 1A Option 1B Option 2A Option 2B
Bicycle 2134
Safety
Notes:
Options 1A and 1B consist of a shared use bicycle/pedestrian path off the roadway which makes them safer than
Options 2A and 2B which consist of bicycle lanes on the roadway.
Construction 1425
Cost
Notes:
Options 1A and 2A would cost significantly less than options 1B and 2B because part of the bicycle route would be
directed through the salt marsh as opposed to reconstructing and widening Union St., Francis St. and an additional
section of Orange St. through town.
ROW 2435
Impacts
Notes:
All of the options would have significant right of way impacts, however routing the bicycle route through the salt marsh
as in Options 1A and 2A would yield much less impacts than in Options 1B and 2B.
Environmental 1415
Impacts
Notes:
2 Wetland Alterations would be required with Options 1B and 2B while no alterations are anticipated with
Options 1A and 2A.
Concepts
Nantucket In-Town Bike Path
Rating Scale
TECHNICAL MEMORANDUM
Pref. Alt. Description and Potential Impacts, In-Town Bike Path & Sidewalk Imp. Proj. – Nantucket, Massachusetts
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PREFERRED ALTERNATIVE
TECHNICAL MEMORANDUM
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ENVIRONMENTAL ASSESMENT
Page 1 of 4
Preferred Bike Path Option
The preferred option for the proposed bike path, previously identified as Options 1/1A and 2/2A, route the
10-foot wide pathway along the abandoned railroad bed from Goose Pond Road to Washington Street.
The elevated railroad bed traverses wetlands: Freshwater Wetlands are located on the leeward or interior
side, and salt marsh is located on the seaward facing side. Additionally, the top of the seaward facing
embankment constitutes the top of the Coastal Bank.
This routing option was selected in part because direct alteration to wetland resource areas can be avoided
and/or minimized to the greatest extent practicable; other alignment options have both physical and
environmental constraints. In accordance with the regulations at 310 CMR 10.55(4), the various design
alternatives to the preferred option are discussed below.
Alternative Design Options
Proposed wetland alteration is necessary to widen the existing, nearly level surface, requiring placement
of fill on the side slopes. Due to the steepness of these slopes, any fill on these slopes would unavoidably
result in alteration to the wetland resource areas. Within the proposed bike path alignment along the
abandoned railroad bed, various options on path widths were considered. The first option involves a path
width of 10 feet with 2-foot shoulders on both sides, giving a total right of way width of 14 feet. The
second option involves a path width of 8 feet with 2-foot shoulders on both sides, giving a total right of
way width of 12 feet. The third option is a 10-foot wide wooden boardwalk with safety barriers on each
side. Based on these options the impact areas to the adjacent wetlands were determined (see Table 1).
Table 1. Summary of different options for path widths along the preferred bike path route and associated
wetland impacts.
Design Options Wetland Impact Area
(s.f.)
Coastal Bank Impact
(s.f.)
1 10-ft. wide, 2-ft. shoulder 1,600 1,400
2 8-ft. wide, 2-ft. shoulder 800 1,200
3 14-ft. wide boardwalk 0 0
Several assumptions were made in the determination of the impact areas. The proposed centerline grade
of the bike path would mimic the existing footpath elevation. Any cutting or filling would have a side
slope of 2 (horizontal) to 1 (vertical) feet (i.e., 2:1 slopes). Due to the sensitive nature of the seaward side
of the abandoned railroad bed, all estimated wetland impacts would occur on the leeward (interior) side of
the footpath, resulting in unavoidable alteration to the freshwater Bordering Vegetated Wetland (BVW)
surrounding Consue Springs. Alterations on the seaward side are limited to the Coastal Bank. For the
first two design options, the wetland resource impacts are due to the side slopes required to maintain the
stability of the proposed width of the pathway and not the actual pathway or shoulder. The boardwalk
option would not result in impacts to wetland resource areas because the width between the wetland
boundaries is at least 10 feet over the existing footpath. Although the boardwalk option does not have
any wetland impact areas, the cost to build and maintain a wooden boardwalk that is up to 560 linear feet
in length, as well as the safety concerns of an elevated section of the bike way, should be considered
when selecting this design option.
Regulatory Implications
Any alteration to these wetland resource areas or within the 100-foot jurisdictional buffer zone will
require review and permitting under the Massachusetts Wetlands Protection Act (M.G.L. Ch. 131 § 40),
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its implementing Regulations (310 CMR 10.00), and the Town of Nantucket Wetlands By-law (Chapter
136) and any associated local regulations.
No work is proposed in any portion of salt marsh, as any proposed salt marsh alteration would require
additional permitting, requiring a 401 Water Quality Certification from the Massachusetts Department of
Environmental Protection (DEP), as well as review through the Massachusetts Environmental Policy Act,
M.G.L. c. 30 §§ 61 through 62H, inclusive (MEPA). However, alteration of a Coastal Bank is one of the
review thresholds requiring submittal of an Environmental Notification Form in accordance with MEPA;
see 301 CMR 11.03(3)(b)(a)] should State funding is used to implement the proposed project or if
additional State or federal permitting is required. A list of the potential wetland-related permits required
for construction of the preferred bike path option follows.
Massachusetts Wetlands Protection Act
As the proposed project will result in the unavoidable alteration of BVW and Coastal Bank, as well as
within the coastal flood zone (Land Subject to Coastal Storm Flowage or LSCSF), the Town will be
required to obtain a permit (Order of Conditions or OOC) from DEP, as implemented through the
Nantucket Conservation Commission. In addition, the Nantucket Conservation Commission must issue an
OOC under the local Nantucket Wetlands Bylaw. This may be done concurrently with the OOC issued
under the Massachusetts Wetlands Protection Act.
Massachusetts Environmental Policy Act
Should the project require the use of State funds, the project will require submittal of an Environmental
Notification Form (ENF) through the Massachusetts Environmental Policy Act (MEPA) under regulation
310 CMR 11.03(3)(b)f. for “alteration of coastal dune, barrier beach or coastal bank.”
Mitigation Measures
Erosion and Sedimentation Control
The applicant proposes to protect the downgradient wetland resource areas by implementing a
sedimentation and erosion control program during and immediately following construction. A sediment
and erosion control barrier consisting of siltation fencing will be placed at the limit of proposed site
grading and along the seaward facing slope. Erosion control barriers will remain in place and will be
maintained in good condition until all soils have been stabilized.
Wetland Mitigation
As stated above, proposed alterations within the interior BVW will require review and permitting through
the Conservation Commission. Minimal, unavoidable alterations would occur with at least two of the
three practicable design options, and the preferred design option would result in the loss of up to 1,600
s.f. of BVW. It should be noted that the vegetative community within the BVW is dominated by common
reed (Phragmites australis) and Japanese knotweed (Polygonum cuspidatum), two aggressively
colonizing, non-native species, identified by the Massachusetts Invasive Plant Advisory Group (MIPAG)
as invasive (see Photos 1 and 2). Wetland replacement in close proximity to this wetland wouldn’t be
advisable as a viable mitigation option.
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Photo 1. View of the Consue Springs vegetative community dominated by common reed (Phragmites
australis).
Photo 2. View of existing trail along abandoned railroad bed (southern aspect). Consue Springs is to the
right. The vegetative community dominated along the side slopes of the embankment between Consue
Springs and the salt marsh associated with Nantucket Harbor is dominated by Phragmites and Japanese
knotweed (Polygonum cuspidatum).
Page 4 of 4
Concurrent Project
The Nantucket Land Council in cooperation with the Town of Nantucket is currently advocating a
separate project in the same vicinity through the Massachusetts Wetlands Restoration Program (MWRP).
A study concluded in June 2006 examined the hydrologic and hydraulic characteristics of the tidal
culverts that connects Nantucket Harbor with Consue Springs, examining the culvert replacement options
that may improve tidal flushing and mixing between Consue Springs and Nantucket Harbor. Currently,
the existing twin 18-inch culverts within the abandoned railroad bed that connect Consue Springs with
Nantucket Harbor appear to restrict tidal exchange between these two water bodies. This study
considered two potential restoration scenarios to improve tidal fluctuations within Consue Springs that
involve lowering the culvert. Both scenarios involve replacing the existing 18-inch pipes with a box
culvert having a two-foot high by three-foot wide opening and a flat slope.
Due to the nature of the existing BVW, it is our professional option that improved tidal exchange will
provide better mitigation than the more traditional 1:1 physical wetland replacement. The culvert
replacement project will result in a vast improvement to the wetland areas, both the impacted,
Phragmites-dominated BVW, and within the salt marsh, and will improve the ability of these resource
areas to protect the interests under the Massachusetts Wetlands Protection Act and the Nantucket
Wetlands Bylaw. We suggest that the culvert replacement project will provide ample mitigation for the
loss of up to 1,600 s.f. of highly degraded BVW. However, should the issuing authority require wetland
replacement, the applicant will propose a wetland replacement area in accordance with the performance
standards at 310 CMR 10.55(4)(b)(1 through 7).
Coastal Bank Impacts
The abandoned railroad embankment, while physically meeting the regulatory definition of a Coastal
Bank, does not represent a naturally occurring physical feature in the traditional sense. The Coastal Bank
is densely vegetated with non-native species, such that it is unlikely that the Coastal Bank provides a
sediment source to downgradient coastal beaches, coastal dunes, or barrier beaches. Alterations to the
Coastal Bank will involve placement of fill along approximately 225 l.f. (up to 1,400 s.f.), due to existing
contours and the need to provide a safe passage along this segment of the proposed bike path. These
alterations are not anticipated to adversely affect the ability of the Coastal Bank to provide storm damage
prevention and flood control.
The existing vegetative community provides limited wildlife habitat value. Suggested mitigation for
alterations to the Coastal Bank include revegetation with a native seed mix to stabilize the disturbed slope
and enhancement plantings with native shrubs and grasses to provide increased habitat value.
Recommended species include beach plum (Prunus maritima), bayberry (Myrica pensylvanica), and
switchgrass (Panicum virgatum), among other species.
The tidal restriction removal project will serve the wetland interests and values, as specified in the
Massachusetts Wetlands Protection Act and the local bylaw pertaining to wetland resource area
protection, by contributing at a minimum to the prevention of pollution, protection of land containing
shellfish, protection of marine fisheries, the protection of wildlife habitat, recreation, and aesthetics. The
project will also serve these interests and values by meeting the performance standards for the protected
wetland resource areas in or near the project location.