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

anadromous fish including American shad, alewife and blueback herring. These species also
serve as prey for a number of federally managed species and are considered a component of EFH
pursuant to the MSA. The Merrimack River also contains the federally endangered Shortnose
sturgeon and Section 7 consultation for the proposed activity has already been completed
pursuant to the Endangered Species Act. In addition to impacts associated with habitat loss
through temporary and permanent fill, we are concerned that the physical placement of
construction equipment and associated noise and turbidity could impact EFH and other trust
resources within the Merrimack River through the disruption of fish during the spawning and
migration seasons.
The proposed bridge replacement activities include the construction of the new northbound
structure, removal of the existing deteriorated bridge and construction of the new southbound
structure. The construction and removal of the bridge piers will be conducted within
cofferdams. The cofferdams surrounding the northernmost piers will be driven into the gravel
and sand substrate and the cofferdams surrounding the southern piers will be anchored and
pinned to the ledge outcrop present in this area. There are two main channels within the
Merrimack River at the project site, which are separated by a rock ledge outcrop that is partially
exposed during low water periods.
The installation of the piers and the driving ofthe cofferdam can generate intense underwater
sound pressure waves that may adversely affect EFH. Sound pressure waves have been shown
to injure and kill fish through rupturing of the swimbladder and internal hemorrhaging (CalTrans
2001). Temporary or permanent hearing loss may also result from loud underwater sounds
which can lead to reduced fitness, and therefore may increase vulnerability to predators and result
in reduced success in locating prey, inability to communicate or inability to sense their physical
environment (ICF Jones & Stokes and Illingworth and Rodkin, Inc. 2009). The use of best
management practices including the use of vibratory hammers and construction phasing may
minimize such impacts.
Sediment plumes may be produced around the cofferdams during installation; however, the
southern cofferdams will be installed by cutting to the shape of the rock substrate and grouting in
place. The sediments in the area ofthe northern cofferdams mostly consist ofgravel and sand,
although there is a layer of silty material in the vicinity of Pier 3. Silty sediments can lead to
greater turbidity impacts than coarser materials which tend to settle more rapidly. High turbidity
can impact fish species through greater expenditure of energy, gill tissue damage and mortality
(Johnson et al. 2008, Newcombe and Jensen 1996). Elevated suspended sediments have also
been shown to disrupt the schooling behavior of migratory fish (Wildish and Power 1985;
Chiasson 1993). Sub-lethal effects to estuarine fishes can include decreased feeding, impacts
from lowered oxygen levels, as well as impacts on gills and associated respiratory impacts
(Wilber and Clarke 2001). Due to the high flow and tidal currents present in the Merrimack
River, combined with the use of best management practices during the installation of the
cofferdams turbidity impacts may be minimized.