Sewer & Your Home

Sanitary Sewer vs. Storm Sewer – What’s the Difference?

It is important to understand the difference between sanitary sewage and stormwater flow.  The City of Oregon sewer network consists of sanitary sewers that are separated from storm sewers.  A sanitary sewer system is meant to convey wastes from bathrooms, sinks, industrial and commercial processes, and other sources to the City’s wastewater treatment plant where the sewage can be treated before being discharged into Lake Erie.  This treatment has to meet criteria established within the aforementioned NPDES permit.

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It is necessary to keep these two systems of sewers separated.  Sewage from sewer overflows can cause major environmental concerns for nearby creeks, rivers, and lakes.  Rain or groundwater flowing into the sanitary sewer can cause sanitary sewer back-ups as well as a large amount of unnecessary treatment costs.  Keeping these sewer systems separated is a win-win situation for the environment and all entities involved.

The following diagram shows the correct plumbing system for a home.  Roof downspouts are allowed to discharge onto the ground where the water can fall away to the public right-of-way, swale, ditch, or storm sewer.  The sump pump may also discharge onto the ground or discharge to a storm sewer, but it cannot discharge to the sanitary sewer.  The only legal discharges to the sanitary sewer are from washer appliances or plumbing fixtures such as sinks, tubs, showers, and toilets. 

SSOs are an example of an OEPA water quality violation and are not permitted under the City’s NPDES wastewater treatment plant permit.  SSOs can cause significant environmental and public health problems. They can pollute surface waters, endanger aquatic life, interfere with recreational uses and industry resources, and contaminate drinking water supplies.  SSOs often contain high levels of suspended solids, pathogenic organisms, toxic pollutants, nutrients, oil, and grease. Typical consequences of SSOs include the closure of beaches and other recreational areas, inundated properties, and polluted waterways.

SSOs within the City of Oregon typically occur during extreme wet weather events due to the amount of stormwater I/I entering the sanitary sewer system.  One goal of the I/I Reduction Program is to eliminate these overflows by reducing the amount of stormwater I/I the sanitary sewer is subject to.