Environmental Engineering Reference
In-Depth Information
and relieve congestion in the two tunnels under Boston Harbor that serviced
Logan Airport. The need was to relieve traffic on the major artery entering
the city from the north, mitigate the division of the city by the elevated high-
way, and create open space in downtown Boston.
The environmental analysis, which was an EIS under NEPA because of the
large percentage of U.S. Department of Transportation funding, took several
years and was forced to address a largely conceptual project description.
The description lacked detail because much of the engineering and con-
struction was cutting edge and the exact implementation methods, and in
some cases, exact location could not be determined until well into engineer-
ing design. The analysis considered a full suite of alternatives, including
mass transit, various alignments, and conceptual construction techniques
but was short on details, such as traffic management during construction
and specific description of excavated material handling and disposal.
The proposed action resulting from the analysis and comparison of alter-
natives consisted of two primary components. The first and largest was
the destruction and replacement of approximately three kilometers of ele-
vated highway that divided the city and isolated the neighborhoods. The
replacement was to be a depressed central artery constructed by an open
cut trench through the center of the city, hence the affectionate name Big
Dig. The second component was a new, Third Harbor Tunnel connecting the
Massachusetts Turnpike directly to Logan Airport. The proposed action also
included significant mitigation:
r Expanded mass transit
r A linear park over the depressed artery with an in-perpetuity guar-
antee of no structures over the artery
r Connections to walking/biking trails in the city
r Very specific constraints addressing disruption of surface traffic
during construction
Not unusual for an endeavor of this scope and magnitude, several dozen
environmental permits were required to implement the Big Dig and these
were identified in the EIS. However, in many cases the permitability of many
of the individual elements of the project could not be specifically evaluated
due to the lack of engineering detail at the environmental analysis phase.
To compensate for this lack of detail and permissibility analysis, the EIS
included commitment to a permitting plan and approach which was sup-
ported by the state, local, and federal permitting agencies. Part of the plan
was to have a dedicated permitting staff as part of the Big Dig engineering/
construction team and an assigned staff at the permitting agencies to work
closely with the project proponent. The approach worked well and eventu-
ally the project was issued all the necessary environmental permits. There
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