Work is about to begin on the last leg of tunnels in Chicagos massive, award-winning flood and pollution control program. Started in the October of 1975, the Tunnel and Reservoir Plan is a long-term effort to increase the storage capacity of the Chicago wastewater system during severe storm events.
The effort should also improve water quality by capturing combined sewer overflows and storing the polluted wastewater until it can be treated.
The city is currently boring a 30-foot-wide tunnel to store combined stormwater and wastewater until it can be treated. The tunnel will connect to reservoirs which are being built as part of the Chicago Underflow Plan (CUP), an element of TARP phase two, in cooperation with the Army Corps of Engineers.
CUP is a network of reservoirs linked to the TARP tunnels to increase storage capacity. The plan will cost Chicago an estimated $10 million in the 1999-2000 fiscal year.
As part of the CUP, construction will begin July 28 on the 350 million gallon McCook Reservoir. A 10.5 billion gallon reservoir is already under construction and a seven billion gallon reservoir is being planned.
The tunnel phase of TARP will cost Chicago an estimated $2.4 billion in total expenses. The first tunnel, Addison Street to Willamette, was 9.8 miles long. It was started in October 1975 and completed in April 1993. Out of the total plan for 109.2 miles of tunnel, 93.4 miles have been completed. Another 8.1 miles are under construction, and the contract for the last stretch (7.7 miles) will be awarded in late 2000-early 2001.
The tunnel under construction is 200 to 350 feet deep and runs through dolomite rock. Drop shafts will be needed, plus construction shafts for workers to be lowered in. After the tunnel is bored, workers will grout the inside with a 1-foot-thick concrete mixture to prevent infiltration from the surrounding rock. The tunnel is mostly following the path of the Chicago river, thus minimizing the need to purchase right-of-ways for the project. In some cases, the city had to get subterranean easements.
