What is a combined sewer overflow (CSO)?  A CSO is a discharge from a combined sewer system directly into a waterway.  A combined sewer system is designed to collect a mixture of rainfall runoff, domestic and industrial wastewater in the same pipe for conveyance to a wastewater treatment plant.  A CSO may occur during heavy rainfalls when the inflow of combined wastewater exceeds the capacity of the combined sewer system and the wastewater treatment plant.  The CSO outfalls to the waterway act as relief points for the excess flow in the sewers, thereby reducing the frequency and severity of sewer backups and flooding.

What are the impacts of CSOs?  Although CSOs may contain highly diluted sewage that could include bacteria which may cause illness, they may also cause temporary water quality degradation in the waterways.  Therefore, swimming, canoeing, or other activities where immersion in water is possible should be avoided and is not recommended, particularly during and immediately following rainfall.

Who's Identifying the Affected Public
The City of Metropolis has solicited comments and feedback from the affected public in the development of the CSO Public Notification Plan.  The City of Metropolis considers the affected public to include governmental organizations, civic groups, recreational groups or any public citizen with an interest in or responsibility for the condition of the Ohio River, the City of Metropolis identified the following organizations to be among the affected public:  the USEPA; the IEPA; ORSANCO; and other environmentally based organizations.  Other groups which are to be specifically identified include the recreational and commercial users of the Ohio River such as boaters, recreational and commercial fishing. 
The identified affected public was invited to the public meeting held on July 14, 2008.  Comments and feedback were solicited at that time.  Advisories about the planned public meeting were available through news media alerts to local print. 

The City of Metropolis is developing an electronic “Address Book” containing a list of email addresses of interested parties.  The Address Book will be updated on an as-needed basis as other members of the affected public are identified. Members of the public are encouraged to sign up to receive e-mail notification of CSO events by clicking HERE.  These parties will be sent an email alert in the event of a known CSO event. 
      
Why does Metropolis have a CSO?  Metropolis and the older cities have a combined sewer system, in which both sanitary waste and storm water are conveyed in the same pipe.  Cities built since 1950 have separate sanitary and storm sewer systems. 

Where do CSOs occur?  When CSOs occur, they impact the waters of the Ohio River on the north bank just east of the railroad bridge. 

What is being done to reduce the occurrence of CSOs?  The City of Metropolis has been tasked by IEPA to alleviate the polluting effects of CSOs and to provide relief from local flooding by following the Nine Minimum Controls for Combined Sewers and to create a Long Term Control Plan (LTCP).  An LTCP is a plan that the City is in the process of developing that will help control or eliminate discharges from the CSO.  The LTCP has nine key elements
Characterization, monitoring and modeling
Public participation
Consideration of sensitive areas
Evaluation of alternatives
Cost/performance considerations
Operational plan
Maximization of treatment at the existing wastewater treatment plant
Post-construction compliance monitoring program

How can the public reduce CSOs?  During periods of high flow, every gallon of wastewater and stormwater kept out of the sewer system is a gallon that will not add to a CSO discharge.  Examples of ways to reduce the wastewater load include avoiding unnecessary water usage, toilet flushing, dishwashing, clothes washing, and showering.  Additionally, individuals and businesses could install rain barrels/cisterns to collect rainwater runoff from their roofs.  This water would be used for garden/lawn watering and similar uses, thereby reducing both the impact of heavy rain events and the use for potable water for non-potable uses.