Description of the development of a comprehensive plan called the Tunnel and Reservoir Plan (TARP) to alleviate water pollution and provide an outlet for flood waters. Principle features of the project include 209 km (130 miles) of tunnel in rock 3.0–10.7 m (10 - 35 feet) in diameter and 45.7–91.4 m (150 - 300 feet) below ground, 320 drop shafts to divert wet weather flows from 640 existing combined sewer overflow outlets to the tunnels, a quarried reservoir of 33,589 hectare/.30 meter (83,000 acre-foot) capacity, and a 2000 barrel/day (710 mgd) underground pumping plant to pump the contaminated water to an existing sewage treatment plant. Included is a summary of contracts, financing and a description of mining equipment used for boring in rock.

BACKGROUND OF TARP

The first settlement in Chicago in the 1830's was only 0.61 m (2 ft) above the level of Lake Michigan. The area was flat and swampy with local streams and rivers generally flowing to Lake Michigan. Repeated outbreaks of cholera and typhoid fever in the middle and late 1800's led to the reversal of the river system (away from Lake Michigan to the Mississippi River). As a result of this reversal, the Chicago land area has had to restrict water withdrawals from Lake Michigan and has had to develop and implement water management programs in compliance with orders set down by the Supreme Court of the United States. In order to comply with restricted lake diversion requirements and to compensate for a natural setting which was essentially hostile to human habitation, it has been necessary to embark on the construction of massive public works which include the world's largest water filtration plants, the world's largest wastewater treatment plants and finally the construction of TI\RP. The rivers and streams in the Chicago area are the headwaters of the Illinois Waterway system. These headwaters are heavily polluted from combined sewer overflows of the area. Present.pollution control laws require that combined sewer overflows be eliminated so that the rivers and streams can be used by the citizens of Cook, Du Page and Will Counties and other downstream communities. Fifty-three of the older most densely populated communities including the City of Chicago, covering an area of 971 sq km (375 sq miles), are served by combined sewers. Combined sewers carry both raw sewage and stormwater. Because porous ground surfaces have been covered over by buildings, streets and parking lots, stormwater runoff into sewers frequently exceeds the capacity of the sewers. When this happens, flows from the combined sewers bypass treatment plants and discharge rainwater mixed with raw sewage directly into the area's waterways at 645 overflow points. The result is severe pollution of the waterways and flooding in many communities. During particularly heavy rains, overloaded rivers may have to be relieved by opening the locks and allowing the polluted waterways to flow into Lake Michigan, the region's water source. TARP is designed to intercept the flow of combined sewers, and store their mixture of rainwater and sewage until it can be pumped to treatment plants, purified, and released into the waterways as clean water.

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