As part of its environmental management efforts, the City of Rock Island has taken strides to respond to issues related to storm water management and Combined Sewer Overflow.

Underneath the streets lies a network of pipes that carry sewage from homes and businesses, and storm water runoff from roofs and city streets. In many parts of the City, sewage and storm water flow together in pipes. This is called a Combined Sewer System.

Most of the time, all of the combined sewage and storm water goes to a sewage treatment plant. However, heavy rain may cause the pipes to fill and induce overflows through outfalls into waters like the Mississippi and Rock Rivers. These overflows are called Combined Sewer Overflows (CSOs).

CSOs directly discharge to the Mississippi River, Rock River, and other "receiving waters” around the City. Although diluted with rainwater, CSOs contain untreated sewage. Untreated sewage contains bacteria such as fecal coliform. CSOs may also contain other contaminants that wash off streets, rooftops, and parking lots.

Although CSOs protect against backups in homes and businesses, flooding in City streets, and bursting underground pipes, reducing CSOs is important in order to prevent any potential adverse effects on receiving water quality.

The CSO Outfall Map shows all the CSO outfall locations in the City of Rock Island. Outfall Map 1, Map 2, Map 3, and Map 4 show more detailed outflow locations.

The City is required to monitor all CSO outfalls and submit an annual CSO report to the Illinois Environmental Protection Agency documenting discharge location and date for each combined sewer overflow. The 2018, 2019, 2020, 2021 and 2022 CSO Annual Reports are available.