| Chicago's Tunnel, Reservoir Plan
Two Basins to Help Filter City Water
Out of sight and earshot of the public, Chicago's Deep Tunnel
is expanding via the project's tunnel and reservoir plan.
The plan adds three reservoirs and tunnels to serve them,
providing Chicago and Cook County residents with greater protection
from basement flooding and reducing pollution from stormwater
and sewage spills in waterways and lakes.
The 350-million-gallon O'Hare reservoir went online in 1999.
The 7-billion-gallon McCook reservoir, in the southwest suburbs,
will follow in two stages in 2013 and 2019. The Thornton Transitional
Reservoir, currently online in a quarry in the south suburbs,
will be replaced in 2014 by a permanent, 7.9-billion-gallon
reservoir a short distance away.
"These reservoirs are the terminus for some of the Deep
Tunnel system," said Scott Vowinkel, project manager
for the Chicago division of the U.S. Army Corps of Engineers,
the project's federal sponsor.
Vowinkel added that Chicago, like most cities its age, was
constructed with a system that combined storm sewers and sanitary
"You have sewer pipes coming from people's homes going
out to the street and connecting into a bigger lateral drain
system," he added. "Rainfall runoff flows into little
catch basins and then flows into the same system. Every bit
of rainfall and sewage in Chicago has to be treated."
The Deep Tunnel project began in the mid-1970s. Currently,
in periods of heavy rainfall, a series of drop shafts allows
the combined storm runoff and sewage to flow into the Deep
Tunnel system, where it is held and gradually released for
The system consists of 109 mi. of underground tunnels, about
300 ft. below the city, the last 8 mi. of which is currently
"Before the Deep Tunnel capacity was there, sewage would
spill into the local waterways," Vowinkel said. "If
it was a severe enough storm, the city would open some gates
into Lake Michigan. And where do you think the city's drinking
water comes from?"
In times of heaviest rainfall, the system needs greater capacity
than the billion-gallon-deep tunnel provides. The three reservoirs
will fill that gap.
Early McCook Work
Bob Rautenberg, project manager on the McCook project for
Wheeling, Ill.-based Kenny Construction Co., said work is
under way on four distribution tunnels that will eventually
serve the McCook reservoir.
The tunneling project, which began in February 2003, is slated
for completion in August 2005. The $60 million tunnel work
is part of a $532 million overall budget.
All four are "horseshoe" tunnels, round on top and
flat on the bottom. Two of the tunnels, with lengths of 1,500
ft. and 971 ft., are 13.5 ft. at their highest and widest
points. The other two, at lengths of 500 ft. and 160 ft.,
are 10.5 ft. at their highest and widest points.
Vowinkel said the Corps of Engineers wrote the specifications
to allow either use of a tunnel boring machine or traditional
drill and blast methods. Rautenberg said the short length
of the tunnels and the rather tight curves in some of them
made drilling and blasting a more economical alternative.
Safety is a paramount concern in this type of operation.
"After you blast, you check the air to make sure the
oxygen levels are OK and there is no residue from the explosives,"
Rautenberg said. "Then you have to get in and scale the
rock to make sure it is safe enough for the guys to get in
there and work."
After the scaling, which has to be done by hand, is complete,
rock bolts are installed to support the rock. Crews then go
in to drill out the face of the rock, load it with explosives
and the process begins again. Crews progress at a rate of
8 to 9 ft. per day.
Muck from the blasting and scaling is removed from the tunnels
and trucked to the Vulcan quarry in McCook where is will be
used as road bases and fill on the quarry site.
Rautenberg said the composition of the rock being found in
the tunnel is not optimal for underground work.
"This is fine-layered shale, not dolomite," he added.
"When you keep running equipment on it, it turns to mud."
Joseph Sobanski, chief engineer for the Metropolitan Water
Reclamation District of Greater Chicago, the local project
sponsor, said that there are few surprises left underground
for the agency.
"This project has been going on since 1976," he
said. "Everything you could have seen out there we have
already seen at least once or twice by now, and we have dealt
Although these tunnels are approximately 300 ft. below ground,
surface vibration from the blasting is a concern. Rautenberg
said that three seismographs are set at different locations
for each blast.
The other concern while working on the McCook tunnel is the
possibility that a bad storm might mean the tunnel has to
go into short service on short notice.
"We have to install a watertight bulkhead in the tunnel,"
Rautenberg said. "If they have too much flow we will
get eight hours notice to close up and get out."
When the tunnels are completed, they will be tied into existing
tunnels, in what Rautenberg described as a "live connection."
Vowinkel said the McCook reservoir is being constructed in
two stages, each with a capacity of 3.5 billion gallons.
Terrence J. O'Brien, president of the board of commissioners
of the Metropolitan Water Reclamation District of Greater
Chicago, said the first stage of the McCook reservoir will
go online in 2013, followed by the second in 2019.
"We could actually construct this in a quicker period
of time, but we are impacted by the ability to get the stone
out of the ground," Vowinkel said.
If Congress gives authorization, a third phase of 3.5 billion
gallons will also be added in the future.
"One (issue) is that no one has built a seven-billion-gallon
reservoir for combined sewer overflows before and no one has
had to deal with aeration and odor issues on such a massive
volume," Vowinkel said.
In addition, having commercial mining activities going at
the same time as construction activities and adding pumps
to a working sewage facility have demanded careful planning
"We are also working sandwiched between two big rivers,"
Vowinkel added. "We have to make sure that we don't empty
the rivers into our hole in the ground." A grouted slurry
wall was created to prevent seepage along the river. A shale
layer at the bottom of the reservoir will serve as a natural
The biggest challenge may be money.
"This project takes a lot of federal money each year,
and we have to compete with everybody else while all the budgets
keep getting cut," Vowinkel said.
O'Brian said the budget for 2005 is $25 million, "and
we really use upwards of $45 million. We are even looking
at funding the Thornton ourselves."
The Thornton Transitional Reservoir is part of an ongoing
project known as the Thornton Composite Reservoir. It uses
a borrowed quarry as a temporary reservoir until another nearby
lobe of that quarry is mined to an appropriate depth for use
as a permanent reservoir. At that point the temporary quarry
will be turned back over to its owner for further mining and
the new one put into use.
Work began on the Thornton Transitional Reservoir in 1998.
It went online last March.
The new quarry, scheduled to become operational in 2014, has
an overall budget of $255 million.