ABOUT COMBINED SEWER OVERFLOWS (CSO)
What are CSOs?
Underneath our streets lies a network of pipes that carry sewage from homes and businesses, and stormwater runoff from our roofs and city streets. In many parts of City of Rock Island, sewage and stormwater flow together in pipes. This is called a Combined Sewer System.
 Most of the time, all of the combined sewage and stormwater goes to a sewage treatment plant, but some heavy rains, may cause the pipes to fill and induce overflows through outfalls into waters like the Mississippi River and Rock River. These overflows are called Combined Sewer Overflows (CSOs).
CSO outfalls act for protection when the combined sewer system gets overloaded. CSOs help prevent backups into homes and businesses, flooding in city streets, and bursting underground pipes.
Where are CSO's located?
The map shows all the CSO outfall locations in City of Rock Island.
How often do these sites overflow?
City of Rock Island Public Works Deparrtment measures and records CSO occurrences using overflow monitors. Discharge Monitoring Reports (DMR) recorded CSOs to Illinois Environmental Protection Agency.
How will you know if you live by a CSO outfall?
City CSO outfalls are posted with one of the signs below:
What’s the Problem?
CSOs directly discharge to Mississippi River and Rock River, and other "receiving waters" around City of Rock Island. CSOs by their nature contain untreated sewage, even though it is very diluted with rainwater. Untreated sewage contains bacteria such as fecal coliform. CSOs may also contain other contaminants that wash off streets, rooftops, and parking lots.
The purpose of reducing CSOs is to reduce any potential adverse effects on receiving water quality. Water quality standards are intended to protect human health (swimming, fishing, etc.) and the health of other aquatic life and shoreline habitats.
How do CSOs affect water quality?
Fecal coliform bacteria are usually present in elevated concentrations in receiving waters during and immediately after an overflow. However, there are many sources of fecal coliform besides CSOs, such as pets and wildlife, that contribute to fecal coliform contamination problems in local waters.
There might be some metals such as zinc and copper, which most likely come from storm runoff from streets and parking lots, to exceed ambient water quality criteria in receiving water bodies. However, it is unlikely for other chemical contaminants to exceed water quality criteria. Reducing overflows will improve water quality in the immediate overflow areas.
|
