Joliet’s Collaborative Approach to CSOs

Firm:Strand Associates, Inc.

Other Consultants: V3 Companies, Ltd., Mott MacDonald, GZA GeoEnvironmental, Inc., RJN Group, Inc., Joseph J. Henderson & Son, Inc., Triad Engineering and Contracting Company, Midwest Mole, Austin Tyler Construction, Inc., Williams Brothers Construction, Inc.

Owner: City of Joliet

Description:The City of Joliet’s eastside sewer system is primarily a combined sewer system, spanning both sides of the Des Plaines River. Since 1985, the City has reduced its number of permitted Combined Sewer Overflow (CSO) outfalls from 32 to 8 through successful basin separation efforts. The City’s National Pollutant Discharge Elimination System (NPDES) permit requires reducing the overflow frequency from the remaining 8 CSOs per a compliance schedule. Strand Associates, Inc. ® (Strand) completed a Long-Term Control Plan (LTCP) to address these reduction requirements. This LTCP was approved by the United States Environmental Protection Agency (USEPA) and Illinois Environmental Protection Agency (IEPA) and included significant conveyance, storage, and wet-weather treatment infrastructure to serve the City’s eastside sewer system. The conveyance improvements included the Phase II West Side Interceptor and Des Plaines River Tunnel projects. These combined projects established the backbone to collect and convey both average-day and wet-weather flow from the west side of the Des Plaines River to the City’s Eastside Wastewater Treatment Plant (WWTP) and the Phase III Wet-Weather Treatment Plant on the east side of the river. This project also provided the City with a critical replacement for the aging single existing sewer crossing siphon of the river.

Phase II included construction of a wet-weather screening structure, siphon control structures, a circular drop shaft, an 865-foot long tunnel, a rectangular drop shaft configured for a future wet-weather pumping station, and the West Side Interceptor. Phase III included construction of a wet-weather treatment facility. Flow on the west side is screened via a deflection screen on the west side and flow on the east side is screened with multi-rake bar screens. Screened flows from both sides are conveyed to the 117 million gallons per day (MGD) capacity Wet-Weather Pump Station where it is pumped to the influent control structure and the first 4 million gallons of combined sewage is diverted to the first flush tanks for storage and treatment at the Eastside WWTP after the event. When the first flush tanks are full, flow is diverted to two, 180-foot diameter clarifiers and a chlorine contact tank, which have a treatment capacity of 90 MGD.

City of Joliet

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