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.

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"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 sewer lines.

"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 treatment.
The system consists of 109 mi. of underground tunnels, about 300 ft. below the city, the last 8 mi. of which is currently being lined.

"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 with it."

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.

Storm Concerns

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 and coordination.

"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 barrier.

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.