Constructed Wetland for Excess Flow Storage

Rockford, IL

In an effort to meet their Compliance Commitment Agreement (CCA) with the Illinois Environmental Protection Agency (IEPA) to reduce sanitary sewer overflows (SSOs), the Rock River Water Reclamation District (RRWRD) retained Clark Dietz, Inc. to provide design engineering services for an excess flow facility. The CCA required the District to provide storage capacity for a 10-year, 24-hour storm event. Clark Dietz proposed a constructed wetland storage basin versus a conventional impervious bottom basin to detain the excess flows.

Approval by the IEPA required the submission of a preliminary design report. Clark Dietz and sub-consultant Orchard, Hiltz, & McCliment, Inc. (OHM), conducted detailed assessments and modeling studies to form the basis of the design report submitted to the IEPA. After a rigorous review process, the project received approval from the IEPA for the first constructed wetland in Illinois for overflow polishing and treatment.

Clark Dietz partnered with Huff & Huff, Inc. to design the constructed wetland. The project included a 25 MG wetland basin with naturalized plantings and a new excess flow pump station rated for up to 65.4 MGD of flow. The station provides pumping capacity for all flows in excess of the WWTPs hydraulic capacity of 80 MGD and operates in parallel with the existing main pump station at the WWTP. The constructed wetland will be used approximately one time per year for excess flow, therefore it will serve a dual purpose of providing polishing effluent from the secondary clarifiers during much of the year. This saves on energy use, chemical use, and minimizes nutrient loads to the river. The RRWRD plans to use the wetlands and other features of the WWTP as an educational facility to improve public awareness of water quality and its relationship to the ecosystem.


ACEC Wisconsin’s Best of State for Engineering Excellence – 2017