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When an SSO occurs, raw sewage may be released into basements, city streets, properties, rivers and streams. Such overflows are illegal, but they may occur during wet weather conditions when sanitary systems receive storm water in-flow or infiltrating ground water. When they do occur, it's obvious that the system has malfunctioned.
In addition to sanitary sewer systems, many older communities, like Birmingham, operate on a combined sewer system, meaning that the sewers carry both raw sewage and storm water in one pipe. Such combined systems are designed with overflow points because the sewer system can't handle all the volume of water that is associated with some larger storm water events.
Combined sewer systems are designed to collect snowmelt, rainwater runoff, domestic sewage and industrial wastewater in the same pipe. Most of the time, combined systems transport all the wastewater to a sewage treatment plant where it is treated and then discharged into a body of water. During heavy rainfall or massive snowmelt, however, the wastewater flow rate in a combined sewer system can exceed the capacity of the sewer system or treatment plant. Because the combined systems were designed to overflow into local water bodies during significant wet weather events, combined sewer systems have historically been among the major sources for beach closings and other water quality issues.
"A sanitary sewer overflow is raw sewage," Verona said. "A combined sewage overflow is a combined system, so you have both. It's diluted sewage, but (it's) an untreated discharge."
Both Combined Sewer Overflows (CSOs) and Sanitary Sewer Overflows (SSOs) can result in the release of untreated human and industrial waste, toxic materials, debris, and disease-causing organisms onto the ground or into area rivers, lakes and streams.
About 13.74 million gallons of combined wastewater was released into surface water in Oakland County due to rainfall in 2014, according to records available from the MDEQ.
"An untreated CSO is when the system capacity is exceeded and you have a discharge, or it will back up into people's basements," Verona said. "With the retention treatment facilities, the water is treated. It goes to these retention basins and it is treated before it is discharged."
Prior to 2004, only releases from municipalities were required to be reported to the MDEQ. However, the National Resources Protection Act was amended to include the reporting of treated and partially-treated sewage releases from private systems that serve more than a duplex. When raw or partially-treated sewage is released, the responsible party is required to notify the local health department and other entities specified under the law....continued on page 4