In most cities, storm sewers convey runoff from impervious surfaces (parking lots, roads, roof tops) to area rivers and lakes. Sanitary sewers convey waste water from sinks and other drains to a water reclamation plant. Conversely, in some cities, storm sewers and sanitary sewers are combined. They both convey water to the water reclamation plant. When a large rain event occurs, the volume of water entering the sewers can exceed the system's capacity. Therefore, these systems have permitted overflow outlets, which allow excess water to be discharged to area water bodies. This allows both stormwater and sanitary waste water to be released, which can contaminate surface water bodies (and sometimes beaches) with enteric (from the intestines) microorganisms. The above map illustrates the number of combined sewer overflow outlets, as permitted through the NPDES Program, in the St. Joe River Watershed. The height of each bar and the red numeral represent the number of outlets in each labeled city.
Click on Niles or St. Joseph, Michigan for more information about those permittees.

LINKS

IDEM CSO Workgroup

MDEQ CSO information