The Chapaton Retention Treatment Basin in Macomb County, Michigan.
Stormwater and sewer overflows are collected before releasing them to Lake St. Clair.
Automated Total Residual Chlorine monitoring at the Chapaton Retention Basin.
A SWAN sensor measures Total Residual Chlorine levels in real-time.
Macomb County is the first wastewater system manager in Michigan to use a SWAN sensor.

Chapaton Retention Treatment Basin Automated TRC Monitoring


Macomb County Public Works Department


Macomb County, MI

The Macomb County Public Works Commissioner retained OHM Advisors to study automating water quality monitoring at the Chapaton Retention Treatment Basin (RTB). The RTB collects controlled stormwater and sewer overflows to provide chlorination and settling before release to nearby Lake St. Clair. Historically, the RTB team has manually sampled Total Residual Chlorine (TRC) levels to meet effluent fecal coliform limits described in the basin’s permit and protect water quality. Since this has always been a labor and staff intensive process, the objective of this study was to automate TRC monitoring to optimize chlorine dosing.

Our team of experts analyzed the RTB’s sampling process and explored options for automation, then made the innovative recommendation to implement a SWAN sensor, not typically used for this purpose, to measure TRC levels in real-time. The unit fully integrates into the existing SCADA systems and gives live TRC readings every ten minutes, enabling operators to make more precise chlorine dosing decisions and minimize manual sampling efforts.

After the sensor’s installation, our team conducted vertical profile sampling in the basin, collecting samples at 4-foot intervals at five locations within the basin while the basin was filling and then again when filled to help the RTB team understand how the disinfection solution (sodium hypochlorite) was distributed throughout the basin over time. We analyzed those results, and with them were able to identify treatment area “hotspots” and recommend the number of additional SWAN sensors that would be needed to scale the automation and achieve continuous real-time monitoring throughout the basin.

Implementation of the SWAN sensor is an innovative approach to TRC monitoring. With this pilot at the Chapaton RTB, our team demonstrated that automating TRC monitoring was possible even under the challenging conditions of high turbidity and suspended solids loading. Macomb County became the first wastewater system manager in the state to use this system to optimize its decision-making process. With OHM Advisors’ forward-thinking solution, the Chapaton RTB team has met its treatment targets in real-time, reduced staff stress and staffing costs previously linked to manual testing, and streamlined and optimized treatment processes while continuing to improve the public health and safety of their local communities.

Project Highlights: wastewater system analysis, smart water quality initiative, TRC monitoring, SCADA, smart water technology