Located just south of the Foss Park Golf Course in North Chicago, the ComEd substation lies almost entirely within the 100-year floodplain and the regulatory floodway. The site was naturally prone to frequent flooding events, exacerbated by approximately 0.25 miles of failing 30-inch storm sewer, originally used as an agricultural drain tile, which conveyed the Skokie River underground.

To reduce flooding, the East Skokie Drainage District (ESDD) initially proposed replacement of the failing storm sewer with an upsized sewer and new alignment. However, Gewalt Hamilton Associates, Inc. (GHA) proposed abandoning the sewer and excavating a naturalized drainage channel, a process known as “daylighting”. After an exhaustive meeting and negotiation process, all sides came to recognize the environmental and flood-control benefits of restoring above-ground conveyance to the Skokie River. The 12,000 cubic yards of earth excavation required would also serve as compensatory storage for an additional flood-proofing effort for the substation.

The innovative design included replacing the underground piping with an engineered, open-channel trench with floodplain benches, planted with native vegetation. The design reduces stormwater velocity, allowing sediment to settle and reducing erosion, as well as filtering pollutants. At the north project limit, the 30-inch pipe was replaced with a 60-inch pipe, directing the flow into an adjacent unused irrigation pond, which was converted to a wet detention basin. The overall design provides stable conveyance of small, frequent nuisance rainfall events as well as additional flood storage within the watershed for more severe storms.

GHA services included surveying, wetland delineation, hydraulic analysis/modeling, design and construction documents, stakeholder meetings/coordination, permitting assistance, and a successful application for an Illinois Environmental Protection Agency (IEPA) Section 319 Grant. This $800,000 improvement was made possible through a cooperative effort between the ESDD, City of North Chicago, Lake County Stormwater Management Commission, IEPA, and the United States Army Corps of Engineers. Construction concluded in July of 2015.

This non-traditional approach to storm sewer replacement took advantage of unused property to incorporate multiple water quality treatment benefits. Not only did daylighting help attenuate flows in the watershed, filter pollutants, and provide habitat for native plants and animals, but the resulting floodplain storage allows for the protection of critical power infrastructure. The project’s success earned that year’s Lake County Stormwater Management Commission’s Best Management Practice of the Year award.