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

Whittier Bridge/I-95 Improvement Project FEIR
Chapter 3.0: Mitigation and Commitments
side casting of dredged material is proposed. The barge will be surrounded with silt curtains
suspended from a floating boom to minimize the spread of any sediment runoff from the barge.
Mitigation Measures
Mitigation measures will be performed during demolition and construction activities to minimize the
impacts to water quality during the in-water portion of the work associated with the construction of
new bridge piers and removal of the existing piers. Cofferdams will be installed to enclose existing
and new bridge piers to eliminate impacts from resuspended sediments in the water column.
Locations for the disposal of dredged material will be the responsibility of the of the design/build
contractor to be selected for project construction. MassDOT will include special provisions in the
contract documents to ensure proper handling and disposal of the dredged material
The cost of the cofferdams is estimated at $7.5 million.
Summary of Discharge of Fill Material (BRPWW10)
The project will result in the discharge of approximately 22,300 square feet of fill material to LUO and
vegetated wetlands. Approximately 17,100 square feet of fill will be discharged within LUO of the
Merrimack River for the placement of the six new piers.
The remaining 5,200 square feet of fill within vegetated wetlands north of the Merrimack River is
associated with highway widening and drain line installation. Of the 5,200 square feet, approximately
1,640 square feet will be temporary alterations associated with a work zone/construction access to
build a retaining wall at Wetland H and drain line crossings at Wetland M. The remaining 3,560
square feet of permanent alterations will result from the highway widening at Wetlands H and I.
Temporary alterations to LUO in the Merrimack River will be approximately 28,520 square feet
(excluding the footprint of the existing and proposed piers) from the installation of cofferdams around
the six new permanent piers during construction, around each of the four existing Whittier Bridge
piers during demolition and from construction of two (2) temporary support piers during construction
of the I-95 northbound bridge.
Avoidance and Minimization
Where possible, the introduction of retaining walls was used to minimize the extent of fill.
Mitigation
Temporary impacts to Bordering Vegetated Wetland H (Amesbury), as well as to Isolated Vegetated
Wetland M (Salisbury), will be mitigated on site at each wetland location by in-situ restoration. To
mitigate for permanent impacts to vegetated wetlands H and I (3,560 square feet), the replication
concept in Amesbury will consist of expanding Wetland H by excavating approximately 4,960 square
feet of upland at its northern end within the right of way.
The removal of the existing piers within the Merrimack River will restore approximately 10,130
square feet of LUO.
For work occurring in upland areas, erosion and sediment controls will be employed to minimize the
transport of sediment into the existing drainage system and adjacent resource areas during
construction. The BMPs to manage storm water and control the discharge of pollutants will be
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