Civil Engineering Reference
In-Depth Information
cataloging this single project's environmental effects and finding ways of
remedying them.
CATALOGING THE EFFECTS, FINDING REMEDIES
Looking at the maps for the proposed Harbor Bridge (at the alternative 1
site) in Great Lake City, investigators immediately observe that the bridge
pier at the outer landing disturbs a freshwater wetland. Through field investi-
gations to examine soil, vegetation, and hydrology, a wetlands expert should
now report on the extent of the interference and propose ways to remedy, or
in the standard language,
mitigate
it. In EIS practice, the preferred sequence
of activities to mitigate environmental harm is (in simplified form) as fol-
lows:
avoid
the effect if at all possible, but otherwise sequentially favor
each of the preceding over the subsequent options:
minimize
,
rectify, reduce,
compensate,
and
monitor.
If the bridge structure at the selected site must have a pier in the
wetland (if project managers cannot
avoid
it), it may yet be possible to
minimize
effect by reducing the pier's and ramps' footprints or positioning
them in the least sensitive part of the wetland. Even so, disruptions will
be larger during the construction than afterward. Some projects
reduce
the
construction impacts by installing temporary raised platforms and board-
walks on which construction equipment is positioned. The project team
may afterward
rectify
the disturbance by removing those platforms to restore
the wetland habitat and
monitor
the affected area to assure that vegetation
regrows and wildlife returns. If the effect on the wetland is permanent and
unavoidable, the project managers can
compensate
: project investors pay for
the expansion or preservation of a wetland located elsewhere.
The EIS investigators also predict that the bridge, its ramps, new
accessory roadwork, and nearby soils compacted to restrain earth move-
ment near these structures will all release additional rain and snow into
the harbor. This rain and snow is usually known as
stormwater.
Instead
of soaking into the ground (as it does on open soil before the structure is
built), the stormwater washes over these paved surfaces, carrying dirt, debris,
road de-icing salt, motor oil, and other pollutants into the water. Sediment
makes the water cloudier, possibly harming aquatic plants; debris can choke
wildlife and simply litter the water surface; and paint and oil, among other
substances, can poison fish and degrade drinking water.
Sedimentation is likely to be most intense during construction, when
excavation and cutting and filling release silt into the waterway. Also, con-
struction equipment can leak fuels. In keeping with “best management prac-
tices,” the project team can make sure that construction contractors
reduce
these impacts by installing fences or
curtains
in the water to trap silt. The
