The former wastewater treatment facility serving the community of Mount Carroll, Illinois, was constructed in 1959 and last upgraded in 1979. The integrity of the facility had become questionable due to general age and structural deterioration, with equipment and infrastructure nearing the point of experiencing major failure. These issues were compounded by the fact that the treatment plant is located in close proximity to the Wakarusa River—a river which has experienced numerous and significant 100-year flooding events over the years. The City knew they needed to act, and act soon.

MSA was hired in 2017 to design a new treatment plant, and preparations began in earnest for the development of a new activated sludge (Aero-Mod) plant, to be constructed above the 500-year flood elevation. This adjusted location would greatly help reduce any potential flooding of the facility and would help protect plant operations as well as the greater Wakarusa River watershed. The new treatment facility consists of preliminary treatment systems including influent pumping, vertical and manual screens and grit removal. Secondary and final treatment processes include aeration tanks, clarifiers and UV disinfection. A new flow equalization tank was added to allow for temporary storage of wastewater if the system were to experience high flows. Sludge produced as byproduct from the treatment process is stored in aerobic digesters and storage tanks, before being dewatered and treated to be applied to local and regional farm fields as fertilizer.

MSA, City leaders and project partners broke ground on the new wastewater treatment facility in August of 2019 and operations officially switched over to the new system in November, 2020. The project has significantly improved wastewater treatment capabilities in the community and has provided for a safer, more resilient and reliable system.

The City of Mount Carroll celebrated with an open house and tours of the new facility in June 2021, and the project was selected by the American Council of Engineering Companies (ACEC) of Illinois to receive a 2022 Engineering Excellence Honor Award — a designation given to projects of exemplary engineering and benefit to public welfare in the state of Illinois.