In the late 1890s, the Sanitary District of Chicago sought to create a navigation link between the now-defunct West Fork of the South Branch of the Chicago River and the Chicago Sanitary & Ship Canal. The District’s solution was to build the Collateral Channel. With the filling of the West Fork in the 1930s, the Collateral Channel became a 1,600-foot dead-end slip used only to provide boat access to riparian properties and to receive local sewer and stormwater discharges. The Collateral Channel is typical of other areas on Chicago’s urban waterways. Contaminated sediment with large quantities of organic and inorganic pollutants from past municipal and industrial wastes in combined sewer overflows, stormwater and direct industrial discharges are more the norm than the exception. For example, other areas with contaminated sediments include Bubbly Creek and unused navigation slips along the South Branch east of Ashland Avenue.

Today, the Metropolitan Water Reclamation District of Greater Chicago (MWRD), which owns the channel, has partnered with the Wetlands Initiative and the University of Illinois at Chicago to address the dual problems of sediment contamination and impaired water quality in the Collateral Channel. The Collateral Channel Demonstration Project will use an innovative technology, called “active capping,” to stabilize the contaminated sediments in the channel, improve water quality, and control greenhouse and noxious gas emissions. In addition, a high quality wetland will be restored on top of the protective cap, providing habitat for wildlife and outdoor recreation space.

Active capping is a promising new treatment approach for sediment remediation that offers long-term immobilization and also has the potential to break down or destroy pollutants with the use of degradation agents in an applied, multi-layer cap. In the Collateral Channel, the sediments are highly contaminated with more than 100 chemical compounds. Samples taken in 1994 and 2005 suggest that natural processes are not breaking down these compounds and ecological damage will continue until remedial actions are taken. Unlike traditional capping or armoring techniques, active capping involves thin layers of different materials that actively sequester contaminants. Microbes underneath the cap materials break down or absorb the contaminants. Gases that are naturally produced in the process, such as methane and carbon dioxide, are transported underneath the cap to a gas vent, where they are slowly released.

To further improve water quality, a diverse wetland composed of deep and shallow marsh and wet prairie plant communities will be planted on top of the cap. Since water flow within the channel normally is stagnant, water will be pumped to the wetland from the Sanitary & Ship Canal. The water will flow slowly through the wetland and back into the channel. This project, though quite small, will help demonstrate the ability of a wetland to clean contaminated water in an urban setting, while also providing habitat for native and migrating wildlife. After construction, scientists will monitor the effectiveness of the capping technology and the ability of the plants and microbes within the wetland to naturally improve water quality. The knowledge gained from this demonstration project will be used to support other urban restoration projects both in Chicago and across the country. Patrick Engineering, Inc. has conducted the design/engineering work.