Final Environmental Impact Report - Whittier Bridge/I-95 ...

Whittier Bridge/I-95 Improvement Project FEIR
Chapter 3.0: Mitigation and Commitments
Sections of the proposed and altered existing drainage systems will be connected as they are
completed.
Mitigation will be implemented in the following general sequence:
Install erosion and sedimentation controls – interchange and wetland mitigation site;
Establish equipment wash off areas at equipment and material lay down sites;
Construct wetland mitigation site, coordinated with the rate of wetland affected on-site and the
need for embankment material construction;
Construct stormwater sedimentation forebays and recharge basins to the extent feasible and
expand to final condition as soon as practicable; and
Construct embankment grading and noise walls as construction becomes feasible, by location.
To mitigate traffic impacts, work that requires lane closures that cause unacceptable travel delay will
be conducted at night. The goal will be to minimize nighttime construction as much as possible.
3.15.2 Erosion and Sedimentation Control
Erosion and sedimentation controls will be employed to minimize the transport of sediment into the
existing drainage system and adjacent resource areas during the initial earthwork and subsequent
construction phases of the project. All erosion and sedimentation control measures will be installed
prior to excavation or disturbance and will be maintained throughout construction. The work will be
sequenced to minimize the extent of land disturbed at any one time.
Erosion control techniques proposed could include compost filter tubes, catch basin filters and inlet
sediment traps, temporary diversion drainpipes and sandbags, and stone check dams. A detailed
description of each technique is discussed below. During the growing season, slope stabilization will
be achieved by applying topsoil followed by seeding and mulching as soon as final grades are
achieved. Organic mulching or jute netting could be used to stabilize slopes completed outside of the
growing season. Permanent drainage structures and treatments will be constructed as soon as
possible.
Controls during construction will be incorporated in a SWPPP that complies with the NPDES
requirements for construction. A SWPPP will be prepared for the project prior to initiating earthdisturbing
activities and provided to the conservation commissions in Newburyport, Amesbury, and
Salisbury through the wetlands permitting process. The plan will include consideration of the
following measures:
Compost Filter Tubes. Compost filter tubes (CFTs) will be placed to trap sediment transported
by runoff before it reaches the drainage system or leaves the construction site. Triple CFTs are
proposed in areas greater than 3:1 slope, and in areas warranting increased erosion control
based on site conditions as determined by the contractor and the environmental monitor.
Compost filter tubes may also be backed up by sedimentation fences in areas where high runoff
velocities or high sediment loads are expected, at the discretion of the contractor and the
environmental monitor. This semi-permeable barrier made of a synthetic porous fabric will
provide additional protection. The sedimentation fence and compost filter tube barrier will be
replaced as determined by periodic field inspection. Compost filter tubes will be staked into the
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