A giant boring machine plunged through a wall of rock 180 feet underground Wednesday, completing 26 years of burrowing beneath the Chicago area to make the 109-mile Deep Tunnel system.
The underground network is part of the $3 billion Tunnel and Reservoir Plan (TARP) aimed at protecting the area from flooding and water pollution caused by storm-water runoff. About 101 miles of tunnels making up about 1.6 billion gallons in volume already are operating.
The tunnels, which will feed into storage reservoirs, won’t be complete until 2006, but the digging wrapped up Wednesday near Interstate Highway 57 in Dixmoor.
About 25 people gathered in a dank cavern at the bottom of a long shaft to see the 3,300 horsepower machine rip through the dolomite limestone that runs beneath Cook County. The group watched as the last major tunnel in an epic engineering project was completed.
The tunnels are civil engineering’s answer to basement floods, fish kills, closed beaches and reeking rivers.
Before the tunnels, storms easily overwhelmed area sewer systems, forcing water reclamation plants to dump the excess, sewage and all, into local waterways, namely the Chicago River.
When the excess deluge becomes large enough to raise the level of the river above that of Lake Michigan, the locks are opened and the untreated water is released into the lake.
That still can happen, but the tunnels now capture the excess runoff first and have greatly reduced the odds that local waterways will turn into local “open sewers,” said John Farnan, general superintendent for the Metropolitan Water Reclamation District of Greater Chicago.
The tunnels “take the top off the storms,” he said.
Excess runoff is channeled into the tunnels until it can be purified by water treatment plants and released into waterways.
Deep Tunnel will hold a total of about 1.8 billion gallons when the last leg is lined with concrete and brought into service. That is only about 10 percent of the total TARP project, which, when all reservoirs are finished in 2014, will have a total capacity of about 18 billion gallons.
Storm and sewage water hasn’t been funneled to the lake since August 2002, according to Reclamation District spokeswoman Peggy Bradley. Before a large section of the tunnels came on line in 1985, discharges to the lake happened about five times a year, officials said.
Most of TARP’s storage capacity will be in two future reservoirs. The McCook reservoir, which will be about a half-mile west of Illinois Highway 171 on the south side of Interstate Highway 55 in Bedford Park, will hold about 10 billion gallons. The Thornton reservoir, at Interstate Highway 294 and Vincennes Road in Thornton, will hold almost 8 billion gallons.
The Thornton reservoir will replace a temporary reservoir completed in June at Halsted Street and I-294 in Thornton that holds about 3 billion gallons. There also is a 350 million-gallon reservoir just northwest of O’Hare in Des Plaines. It was completed in 1998.
Water from Deep Tunnel flows into the reservoirs, leaving enough capacity in the tunnels to handle sewer overflows. There will be about 250 drop-shafts strategically located across Cook County that can direct runoff into the tunnels.
The monumental scope of the TARP project drew ridicule when it first was dreamed up in the 1960s. Now, cities across the world are copying the system, which is designed to handle all but the most catastrophic storm events.
“We were the leaders,” said Joseph Zurad, chief engineer for the Reclamation District. “Now they are following in droves.”
Milwaukee, Cleveland, Detroit and Atlanta are among the cities developing similar plans.
“It’s really a symbol of our commitment to live in high-density communities,” said Charles Dowding, a civil engineering professor at Northwestern University.
Even the Chunnel, the celebrated passageway beneath the English Channel, took its lead from Deep Tunnel.
Chunnel engineers visited Deep Tunnel in the late 1970s to get a handle on using the rock-boring process.
“Boring machines really came into their own here,” Dowding said. “What we’ve learned here has enabled so many other projects.”
About 1 inch of rain fell Tuesday night in the Chicago area, according to the National Weather Service–that amount would have kept some low-dwelling homeowners up worrying 20 years ago. Now, they can sleep soundly.
