Chicago and 51 other municipalities in Cook County have combined sewer systems. This means when rain falls, storm runoff drains into a combined sewer where it mixes with the sewerage flow from homes and industry. The net result is one massive quantity of dirty water. A system which was designed to treat 2 billion gallons of wastewater per day may be inundated with more than 5 billion gallons of rainwater runoff (about 1" of rain) during a single rainstorm. In the 1970s, a team of engineers from the District, the City of Chicago, Cook County and State agencies considered various plans to solve the problem of flooding and water pollution. The hybrid plan selected as best and most cost-effective was the Tunnel and Reservoir Plan (TARP). Under this plan, 109 miles of huge underground tunnels would be burrowed under the city to intercept combined sewer overflow and convey it to large storage reservoirs. After the storm had subsided, the overflow could then be conveyed to treatment plants for cleaning before going to a waterway. The McCook Reservoir forms a portion of the overall TARP system and will serve as one of the overflow reservoirs.

ACT was awarded the contract through a Best Value Selection process (RFP) by the US Army Corps of Engineers Chicago District. The project initiative was to complete 2 separate test sections, utilizing 2 separate drilling methods. Borehole washing data, water testing data, grouting data, borehole imaging results, and borehole deviation surveys were utilized by the Corps to analyze the drilling methods.

Work included: overburden drilling and overburden casing installation, water hammer percussion rock drilling, rotary rock drilling, initial exploratory drilling, borehole washing, water testing, pressure grouting, and final exploratory verification hole drilling. Other activities included: daily quality control testing of grout mixes, real time computer monitoring of grouting operations, borehole deviation surveys, and borehole imaging. Full scale real time computer monitoring was performed utilizing ACT’s state of the art IntelliGrout® system allowing Engineering of the grouting program “on the fly”. This project is one of the deepest (400 feet deep) grout curtains in North America.