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Chicago Approves Stormwater Ordinance

Last fall the Chicago City Council passed a new stormwater management ordinance designed to promote programs that minimize the negative stormwater impacts of new development and redevelopment in the city. The first half-inch of rainwater often funnels the most pollutants into the sewer system, explains Environment Commissioner Sadhu Johnston. This new ordinance (download it here), which takes effect on January 1, 2008, requires new developments or redevelopments of a certain size to capture the first half-inch of runoff from all impervious surfaces (roofs, driveways, sidewalks, and so forth) onsite, instead of allowing it to run into the sewers or nearby waterways. Developers can adopt a variety of techniques—such as green roofs, permeable pavement, rain barrels and cisterns, bioswales or rain gardens—to capture this initial rainfall so that the water will infiltrate and recharge the underground aquifer. For developments that do not directly discharge to waterways or to a separate municipal storm sewer system, the ordinance seeks to achieve a 15 percent reduction in impervious surfaces from existing conditions.

For a 2,000-square-foot rooftop, for instance, this would mean an average reduction in the amount of stormwater flowing into the sewers of approximately 44,900 gallons a year.

Since roughly 60 percent of the rainfall in the Chicago region is in low intensity events—a quarter-inch to a half-inch of rain—this ordinance could result in significantly less polluted water entering rivers, streams, and sewers over time.

“Under Mayor Richard M. Daley’s leadership, the City of Chicago is demonstrating that we can and should also focus on the ‘inputs’ to the sewer system,” says Margaret Frisbie, executive director of Friends of the Chicago River.

“Projects like green roofs on City Hall, the Cultural Center, and the Chicago Center for Green Technology, as well as the use of permeable pavement and the McCormick Place stormwater tunnel, show that there is a valuable opportunity to manage stormwater before it ever gets to our sewer system, and begin to treat this water as a desired commodity.”

—Debra Shore