Constructed Wetlands: A New Solution to Excess Flow Storage

Clark Dietz was awarded ACEC-WI 2017 Best of State for Engineering Excellence for the Constructed Wetlands: A New Solution to Excess Flow Storage. The award recognizes the highest degree of technical innovation, client satisfaction, and contributions to the engineering industry.

The Rock River Water Reclamation District (RRWRD) needed to provide excess storage capacity at the wastewater treatment facility to reduce SSOs during major storm events. Clark Dietz’ provided an innovative solution that achieved both the engineering and environmental stewardship goals of the RRWRD.

Clark Dietz facilitated IEPA approvals and led the project’s design. The RRWRD received IEPA approval for the first constructed wetland in Illinois for overflow polishing and treatment. The project consisted of two primary components: an excess flow basin and an excess flow pump station. Hydraulic modeling and historical data assessments, determined that the excess flow basin needed capacity for 25 MG to handle flows beyond the plant’s rated capacity. The system also needed to operate in parallel with the existing main pump station at the WWTP and allow for continuous operation during construction.

In addition to providing excess flow storage, the constructed wetland serves the dual purpose of providing effluent polishing during much of the year. An estimated 56,000 gallons per day will be diverted from the secondary clarifiers to the wetland, providing treatment to a portion of the effluent which would normally discharge into the Rock River. Intelligent use of plants and sandy soils provides natural filtration, minimizing nutrient loads to the river. The RRWRD will also benefit from energy savings and reduced chemical use.

The constructed wetland now serves as a thriving ecosystem supporting both insects and wildlife. The RRWRD plans to use the wetlands and other features of the WWTP to improve public awareness of water quality and its relationship to the ecosystem. As the first constructed wetland in Illinois for wastewater polishing and treatment, the success of this pioneering project will help pave the way for future endeavors that protect public health and nurture the natural environment.

Awards judge Dan Talarczyk praised the project, saying “This project exemplified an innovative green solution to an engineering problem. It combined interesting design nuances with natural process to create an aesthetically pleasing storage and treatment facility.”