What is a sanitary sewer overflow?
Sanitary sewer overflows, SSOs, are a release of untreated or partially treated waste from a city sewer. Sanitary sewer overflows are illegal. But when normal systems become overloaded through heavy rain or a larger load from an increasing population, SSOs occur. When they occur, they must be reported to the Illinois EPA. SSOs can be caused by blockages, line breaks, sewer defects, power failures, improper sewer design, vandalism, or groundwater overloading the system, as is often the case during heavy rainfall.
Sanitary sewer systems use a single dedicated pipe to carry wastewater from homes and businesses to the treatment plant, and another separate pipe to handle runoff.
In a combined sewer system, one pipe carries wastewater and stormwater together. Combined sewer systems, found in big cities such as St. Louis and Chicago, also have overflows. In those systems, wastewater and rainwater collect in a single pipe, often with a dam or other type of filtering system that water flows through before discharging into a body of water. These overflows are not strictly prohibited, like sanitary sewer overflows are, but they’re regulated.
How are sanitary sewer overflows regulated?
Some cities and sewer districts that report overflows to the U.S. Environmental Protection Agency and the Illinois EPA are regulated under the National Pollutant Discharge Elimination System (NPDES) — such as Carterville and East St. Louis. Reports submitted by NPDES permitted facilities, which are those that discharge to waters of the U.S., are entered into the U.S. EPA’s Integrated Compliance Information System (ICIS) database. That database is public.
NPDES permittees are required to notify Illinois EPA regional wastewater staff within 24 hours of the overflow. This can be done via email or over the phone. Then, the permitted agency must submit a written report describing the overflow to Illinois EPA within five days of the overflow.
The National Pollutant Discharge Elimination System regulates discharges. The type and amount of discharge determines whether a permit is needed. Discharges can include any of the following:
- Treated municipal and industrial effluent (liquid waste or sewage discharged into a river or sea)
- Coal and non-coal mining discharges
- Concentrated Animal Feeding Operations
- Public water supply treatment plant discharges
- Pesticide discharges
- Stormwater
The discharges permitted by NPDES permits must keep pathogenic organisms below certain levels. Under state law, the Illinois EPA is required to issue a permit unless based on the contents of the permit application doing so would violate state law.
NPDES permits can also require permitted entities to develop a plan to reduce overflows after they’re recorded. Overflows “occur occasionally” in nearly every system, according to the U.S. EPA, but if “SSOs happen frequently, it means something is wrong with the system.”
Other entities that submit overflow reports to the Illinois EPA are not NPDES permittees, like Cahokia Heights. Facilities without an NPDES permit do not have the same overflow reporting requirements as NPDES-permitted facilities, according to Illinois EPA spokeswoman Kim Biggs.
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