|
Tunnel and Reservoir Plan (Phase One)
Project of the Year: Environmental
One of the greatest assets of Chicago is its magnificent lakefront
where millions of people marvel at the city's beautiful third
coast.
|
Protecting Lake Michigan is one of the primary responsibilities
of the Metropolitan Water Reclamation District of Greater
Chicago.
In 1972, the district selected Tunnel and Reservoir Plan as
the Chicago area's plan to comply with federal and state water
quality standards in the 375-sq.-mi. combined sewer areas
of Chicago and 51 suburbs.
The first phase, which is also known as the "Deep Tunnel,"
is complete and is composed of four independent tunnel systems:
Upper Des Plaines, Mainstream, Des Plaines and Calumet.
The tunnel systems were put into service over the last 31
years, and phase one was completed in early 2006 with the
construction of the Little Calumet Leg tunnel.
The goals of TARP are ambitious, including protecting Lake
Michigan from river backflows, eliminating waterway pollution
from combined sewer overflow, providing an outlet for floodwaters
to reduce basement sewage backups and complying with federal
and state environmental laws.
Some History
Since its inception in 1889, the district has been working
to improve the quality of Lake Michigan.
An early lesson is that dilution is an insufficient solution
to water pollution.
Despite the reversal of the Chicago River and the construction
of the largest wastewater treatment plant in the world, contaminants
continued to accumulate in the rivers, canals and Lake Michigan.
The persistence of the problem was due mainly to the fact
that a large portion of the Chicago area is served by combined
sewers, and both sewage and storm flow are conveyed through
the same pipes.
As the area developed and more land was paved over, the amount
of rain water entering the sewer system dramatically increased.
During rain, the sewer system and treatment plants could not
accommodate the additional flow, and combined sewage would
overflow to local waterways.
There were 645 outfalls that release combined sewage overflows
into the waterways in combined sewer areas.
During particularly large storms, the rivers were forced to
reverse their natural direction, releasing raw sewage into
the lake.
The once majestic and serene Chicago River deteriorated into
a drab lifeless open drain. Beach closings on Lake Michigan
were frequent. Waterfront property became a liability, rather
than an asset. Fishermen and boaters fled to clearer waters.
Project of Superlatives
The Deep Tunnel is the first project of its kind built for
combined sewer overflow control.
Since the project's inception, other cities have used TARP as
a model, including Milwaukee and Atlanta, but no subsequent
project has reached the massive scale of the original. TARP
is the largest, longest and deepest of its kind.
The system consists of 109.4 mi. of deep tunnels, more than
250 drop shafts, three pumping stations and more than 600 surface
connecting and flow control structures.
Tunnel diameters range from 9 to 33 ft. and are constructed
in rock approximately 300 ft. below ground.
At the outset, the use of tunnel boring machines was mandated
for TARP, even though this technology was little used and not
well developed.
In fact, the economics favored drill and blast mining, but it
was thought that TBMs could reduce the amount of fracturing
in the rock and that the machines and their cost would improve
over time.
Mining records were set on some tunnel contracts. For example,
the TBM crew on the recently complete Little Calumet Leg broke
several world records for a machine of its size during the project,
including the best advance in a single eight-hour shift (150
ft.), best advanced in a day (383 ft.), best advance in a week
(1,557.4 ft.) and most rock excavated in 24 hours (3,708.9 cu.
yds.).
TARP has overcome significant engineering management challenges.
Twenty-six engineering firms and dozens of individual construction
contracts were awarded and overseen by the district, including
10 tunnel contracts, thee pump station contracts, 47 connecting
structure contracts, eight tunnel/connecting structure contracts,
one tunnel/pump station contract and nine miscellaneous contracts.
Although the total system was not completed until 2006, portions
of phase one have been in service for more than 20 years, resulting
in the capture and treatment of more than 830 billion gallons
of combined sewer overflow.
The Deep Tunnel system captures and enables treatment of an
estimate 85 percent of the combined sewer overflow pollution
from TARP's service area.
Prior to TARP, raw sewage and rainwater rushed into area waterways
during storms about 100 times a year. That has been reduced
by 75 to 80 percent and will become rarer when reservoirs are
completed in phase two.
Water quality improvements in rivers have led to a three-fold
increase in fish populations, with 68 species of fish, including
game fish, now inhabiting local urban waterways.
Jury Comments: "When you get to spend multiple billions
of dollars, it's going to have a huge impact. TARP is kind of
its own world. It's comparable to the Big Dig in Boston, but
there are no apparent cost overruns. The price with TARP could
have easily been twice as much. The scale of the project is
amazing. You have to give them credit for being at the forefront
of this kind of a project."
Click
here for more Best of 2006 Award Winners >>
|
print this page
e-mail this page
