Two years since tunneling work completed on Chicago’s Tunnel and Reservoir Plan (TARP), the project pushes on. Phase I of the massive urban infrastructure project lasted better than 30 years with 109.4 miles of tunnels bored beneath the Chicagoland area. The second part of the project is under way, consisting of mining and construction of several reservoirs.
Situated for the most part on marsh land, Chicago has long had wastewater troubles. The City’s main waterway, the Chicago River, was ineffective in carrying sewage away from the city. When the river was effective, it dumped wastewater into Lake Michigan and clogged the first pumps set up to provide the City’s drinking water. Subsequently, several outbreaks of cholera and typhoid hit in the late 19th and early 20th centuries, causing the deaths of as much as 10 percent of the City’s population.
The most prominent of the early solutions occurred in 1900 when the flow of the river was reversed using a series of locks to divert flow to the newly-constructed Sanitary and Ship Canal. Additionally, several canals were constructed to further direct wastewater away from the lake and bring freshwater inland.
Flooding became an increasing problem with the development of the areas surrounding Chicago occupying what had previously been drainage areas for the City. In the 1960s, officials began researching regional solutions to its various water and drainage difficulties. The Federal Clean Water Act of 1972 led to TARP’s designation as the solution of choice and construction began in 1975.
TARP Phase I
TARP was initially conceived as a one-phase project with multiple features. An early split was made, however, to take advantage of grant funding opportunities offered by the federal government.
Primarily geared toward pollution control, Phase I is made up of deep tunnels, drop shafts, near-surface connection and control structures and dewatering pump stations. This portion of the project directly addresses roughly 85 percent of the CSO pollution load. As noted, the tunnel portion of work totaled 109.4 miles of tunnel construction and made up of four systems: Mainstream, Des Plaines, Calumet and O’Hare. Also included in this first phase are three dewatering stations of up to 35.4 cu m/s (1,250 cfs) capacity, more than 250 drop shafts 4- to 17-ft diameter and more than 600 near-surface connecting structures and appurtenances.
The Mainstream Tunnel System comprises 40.5 miles of tunnel ranging from 8- to 33-ft diameter bored through limestone. “The tunnels were bored through a dolomitic limestone layer that was chosen by design for its engineering properties,” notes Joseph Sobanski, Chief Engineer for the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC). “The limestone has proven quite favorable to the technique.”
The tunnel system was divided into 10 separate contracts with the first contract awarded in 1975 (to Kenny/Paschen/S&M JV) for the Addison to Willmette portion. The last contract for the Mainstream system was awarded in 1992 to Perini/ICA/O&G JV for portions of the North Branch system.
Reading a list of the contract awards is like looking at a tunneling yearbook and recalling old friends. No single JV won more than one of the remaining eight contracts for the Mainstream system, though individual contractors do pop up with involvement in more than one JV. The other contracts were to: MK/Healy/Paschen/S&M (3.36 miles), Paschen/MK/Kenny (4.68 miles) and Healy/Ball/Horn (4.80 miles) in 1977; Ball/Healy/Horn (4.15 miles) and Shea/Kiewit/Shea (8.19 miles) 1978; Healy/Ball/Grow (6.71 miles) and MK/Paschen (0.56 mile) in 1979; and Kenny Construction (3.38 miles) in 1985.
The Des Plaines System is made up of 25.6 miles of tunnel ranging between 10-and 33-ft diameter. Two of the three contracts were awarded in 1988 with one going to MK/Paschen JV and the other to Impreglio/Ebsco/Losinger JV. The final contract went to Kenny/Kiewit/Shea JV in 1995 for a 6.74-mile portion of the system.
The Calumet Tunnel system is 36.7 miles of 9- to 30-ft diameter tunnel. Construction started with the 1977 award of one contracts to Traylor/Ferrara/Resco JV for 9-mile drive from Crawford to the Calumet Plant. Overall, the Calumet system was separated into seven contracts: Kenny/Jay Dee (2.29 miles) in 1979; Healy/Vanessa (5.84 miles) in 1982; Kenny/Kiewit/Shea (11.38 miles) in 1990 and (7.99 miles) 1998; and Jay Dee/Affholder (7.43 miles) in 2002. Also included in the Calumet system was a contract to Jay Dee/Traylor for 2.02 miles of tunnel associated with the Thornton Transitional Reservoir.
The O’Hare Tunnel system accounts for 6.6 miles of 9- to 20-ft diameter tunnel. The two contracts were awarded to Healy/Ball/Greenfield (4.18 miles) in 1975 and McHugh (2.02 miles) in 1976.
As each tunnel segment was completed, it was immediately placed into service and benefits have been increasingly noticeable as each new portion went online. “The dramatic improvement in the water quality of the inland waterways and greatly reduced frequency of polluted backflows into Lake Michigan have enabled the public to see first-hand how TARP has made a positive impact,” says Sobanski. “The Chicago River is now a desirable place to recreate and residential and commercial development along the river has skyrocketed.”
Given the 31-year construction schedule, crews on later contracts were able to take advantage of lessons from earlier tunnel segments. “Some of the tunnels in the later stages were redesigned to incorporate improvements identified on earlier contracts,” Sobanski says. “There was a learning curve and by the last contract some record-breaking bore rates were achieved, including 452 ft in one day.” That last contract was to Jay Dee/Affholder for the West heading of the Little Calumet Leg of the Calumet system. A Robbins TBM was used for the 3.62-mile, 18.3-ft diameter drive.
Chicago Underflow Plan (CUP, or “TARP Phase II”)
“We are currently working on the reservoir portion of the project,” Sobanski says, referring to the second phase of TARP. Formally known as TARP Phase II, this second phase has been renamed the Chicago Underflow Plan. In 1986, the U.S. Army Corps of Engineers (COE) reevaluated the original plan and concluded, based on its own economic evaluation criteria, that the total reservoir volume should be reduced by 62 percent and that 21 miles of supplemental conveyance tunnels be eliminated. This dramatic change in the overall scope of the project led to the second phase being renamed with the COE’s name for the project.
The COE commenced construction of the first of the three planned reservoirs in 1990 and completed work in 1998. The O’Hare CUP has a capacity of 342 million gallons and is online. To date, the reservoir has yielded $116 million in flood damage reduction benefits to the three communities it serves.
The CUP reservoirs provide flood relief and enhance Phase I’s pollution control capability. In the case of a wet weather event, Phase I facilities and tunnels capture and store combined sewer overflow until it can be treated at one of the area’s seven water reclamation plants. Once the remaining CUP-phase reservoirs are online, the storage capacity of the system is greatly enhanced (by 15.15 billion gallons), which then optimizes the capacity of the existing sewer system. By alleviating the pressure on the existing sewers, pollution control is enhanced by minimizing backups into local sewer systems.
The Thornton Reservoir is under way in a two-stage construction schedule. Completed in 2003, a 3.1 billion gallon Natural Resources Conservation Service (NRCS) reservoir called the Thornton Transitional Reservoir has captured 10.9 billion gallons of flood water to date. This transitional reservoir provides over-bank flood relief for nine communities.
The second stage of the Thornton Reservoir is a permanent 7.9 billion gallon combined NRCS/CUP reservoir. When complete, it will provide 3.1 billion gallons of NRCS storage and 4.8 billion gallons of storage for CUP. Scheduled for mining completion in 2012 and in service in 2014, the Thornton Reservoir will provide an anticipated $40 million annually in benefits to 15 communities.
The McCook Reservoir will also complete in a two-stage scheduled build. The first stage will provide 3.5 billion gallons of storage is scheduled for completion in 2015. The second stage will provide an additional 6.5 billion gallons of storage.
Through completion it is estimated that TARP will cost roughly $3.5 billion, with over 50 percent of that funding coming from the federal government. The program has won an array of awards from both the local and federal EPA, as well as several organizations. Public sentiment has remained positive as notable benefits of TARP and CUP have reached residents across the region. Fewer basement floods will go a long way toward improving quality of life. The project has benefitted people, especially, by its effect on the environment.
“People that have lived here a long time have watched the inland waterways improve dramatically, supporting ever-increasing numbers of fish species and other wildlife,” says Sobanski. “None of this would have happened before the implementation of TARP.”
Greg Thompson is assistant editor of Tunnel Business Magazine.
