Combined Sewer Outflows (CSOs)

CSOs are points permitted by the Department of Environmental Protection (DEP), where the sanitary and stormwater systems combine and occasionally discharge. During dry weather the CSOs have no impact on our local waterways. However, during significant wet weather events when the capacity of the system is exceeded, CSOs are designed to discharge excess flows directly to nearby streams, rivers, or other water bodies. During such discharges, the baseline flow (set by the conveyance capacity of the pipeline) continues to flow to the wastewater plant for treatment.

CSO discharges may contain stormwater and untreated human and animal waste, toxic materials and debris. Deckers Creek has 22 CSOs located along its banks and the Monongahela River has 16. One CSO is located along Popenoe Run near Brewer St, with another being at the entrance to the wastewater plant.

Unfortunately, CSOs are part of a legacy system and are common in systems such as ours. Prior to the construction of our wastewater treatment plant in Star City in 1965, all sewage was sent to the river or local creeks untreated. As the system was developed in 1965, CSOs were necessary given the limited capacity of the wastewater treatment plant and pipelines because constructing a plant large enough to manage all stormwater flows and sanitary flows was prohibitively expensive. It's important to remember that before that time untreated sewage was discharged so the use of CSOs was not a concern.

While MUB would love to eliminate CSOs from the local system, doing so is not financially realistic. The cost of eliminating CSOs themselves would easily run into the hundreds of millions of dollars. Of course, this would require borrowing money which would increase sewer rates incomprehensibly.

It's important to note that CSO discharge rates vary significantly by location. In 2018, some have not discharged at all while some have discharged as many as 65 times. CSOs are individually inspected each time it rains in accordance with specific rainfall thresholds.

A multi-year, quarter of a million dollar, comprehensive study on the effects of local CSOs upon water chemistry and aquatic life was conducted to assess the impacts of these wet weather discharges. These studies demonstrated that 72-hours following a significant wet weather event, there remained no impact of CSO discharge in local waterways.

To help educate the public about this issue, MUB recently installed new signs along the river and Deckers Creek both at public access points and downstream of CSO outfalls. The best advice is simple: Avoid the water for 72-hours following a rain event.

To aid in public awareness, MUB has developed a Google map listing CSO locations, with CSOs that most frequently discharge highlighted in red. The map can be found online here. Also, while a list of CSOs and their discharges have always been publicly available, this information can now be found online here..