What is a (CSO) combined sewer overflow?

A lot of communities have sewer systems that combine sanitary sewage and stormwater runoff from streets and other areas into one sewer system. Our plant currently owns and maintains four combined sewer overflows.

With dry weather, our treatment plant has the capacity to treat all the wastewater that comes into it. With heavy rain or snowstorms, however, we get overloaded and unable to treat all of the wastewater and stormwater that’s coming in.

The wastewater and stormwater that is untreated from CSOs can be a huge source of water pollution.

The over flow has diluted untreated human waste; commercial and industrial wastes; trash, oil, and grease washed from streets and parking lots when we have rain.

Our next issue will have more with how the community controls pollution from CSOs.  

Difference between Sanitary and Storm Sewers

In order to help prevent environmental damage it’s important to know the difference between a sanitary and storm

sewer drain.


The storm sewer is designed to receive rainfall and other drainage. The runoff carries into underground pipes and discharges untreated drainage into local streams, rivers and other bodies of water. Storm drain inlets are normally found in curbs and low outdoor areas.  Motor oil, common household cleaners and paints that get into the storm drain will poison fish birds and other wildlife.  Remember, only rain down the drain.

The sanitary sewer has underground pipes that carry sewage from bathrooms, kitchens, sinks and other plumbing in the home to a wastewater treatment plant where it filters, treats and discharges.

Pollution from Pet Waste affects Water Quality by going into the stormwater drains, or directly into local waterways.  Which can be very harmful to other animals, adults and children.

Some ways to easily prevent this from happening:

How to reduce Stormwater Runoff for your home