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Storm water overflow


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"Southeast Oakland County was some of the first land developed, and because of that, a lot of that is a combined system," said Gary Nigro, assistant chief engineer at the Oakland County Water Resources Commissioner's Office. "A lot of the northeast portion of the county, and other areas, they have separated sewers for storm and sanitary. Things are being looked at in southeast Oakland County, like Birmingham, Troy, Madison Heights, Royal Oak and those areas."

Raw and inadequately treated sewage that is discharged from municipal systems has been a problem in Michigan for decades. But according to the MDEQ, the state took a more aggressive approach to address discharges in the late 1980s and subsequent years. However, to better understand the issues that lead to overflows, it's first necessary to understand how sanitary and storm water sewer systems work.

Sanitary sewers are designed to carry only sanitary sewage to a wastewater treatment plant, while storm water is designed to be directed to nearby rivers, lakes or streams through a system of storm sewers.

Sanitary wastewater is treated in several stages, involving primary and secondary treatment states, and a final disinfecting stage. During the primary stage, nearly half of the solids in the wastewater is removed. This removal is often done through screens and grit chambers that utilize sand, grit and other materials.

The secondary stage removes about 85 to 90 percent of the remaining pollutants. One method used includes the use of an aeration tank, followed by a secondary sedimentation tank. In the aeration process, air is mixed in the tank and microorganism concentrations are kept high to speed the consumption of the organic matter. The microorganisms and other solids settle to the bottom of the tank during the sedimentation process and are removed. After that, a disinfectant such as chlorine is often used to kill disease-causing organisms before the wastewater leaves the treatment plant.

When sanitary sewers become clogged or malfunction, a sanitary sewer overflow (SSO) may occur, resulting in the discharge of raw, untreated sewage

"Sanitary sewer overflows are illegal. That's a discharge of raw sewage," said Laura Verona, southeast Michigan district supervisor with the MDEQ Water Resources Division. "If you look at communities that have issues with that, they are under an administrative order with us. Typically, they have a problem and they go in and fix it. A corrective action doesn't necessarily mean enforcement."

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