What is a Combined Sewer Overflow (CSO)?
During dry weather and small wet weather events (i.e., rainfall and snowmelt), combined sewers are designed to transport all flows to the 30 MGD Water Pollution Control Facility (WPC) and the 4 MG storage tank. During larger wet weather events, the volume of storm water entering the combined sewer system may exceed the capacity of the WPC. When this happens, combined sewers are designed to allow a portion of the untreated combined wastewater to overflow into the E. Poe Rd ditch. This prevents the backing up of sewage into basements, and/or flooding of streets. The locations where these discharges of untreated combined wastewater occur, as well as the discharge events themselves, are known as Combined Sewer Overflows (CSOs). The City has one CSO located near the E. Poe Rd / Mercer Rd intersection.
Why are CSO’s a concern?
CSO’s contain not only storm water but also untreated human and industrial waste, toxic materials, and debris. This is a major water pollution concern. CSO’s are among the sources responsible for beach closings, shellfishing restrictions, aesthetic impairments and other water body impairments. Additionally, contact with discharges from CSO’s can have adverse effects on human health.
What is the City doing to reduce the number of CSO events?
The City of Bowling Green has spent millions of dollars to reduce Inflow and Infilltration into the combined and sanitary sewer system, as well as increasing the treatment capacity at the WWTP. As a result, the duration of over flows and the concentration of pollutants has been reduced.
The City is working with the Ohio EPA to reduce our CSO events to 4 or less per year. A Long Term Control Plan (LTCP) was created that addresses the necessary steps to reduce the number of CSO events to NPDES permit limits. The current LTCP is on hold for further review until modifications are made to the WPC, and the E. Poe Rd / Mercer Rd Pump Station.
In addition, the City has developed a Comprehensive Waste Water Strategy (CWWS) to help reduce CSO’s. Click here to view the CWWS document.
The following list are just a few examples to achieve these goals:
- Increase the treatment capacity of the WPC to 30 Million Gallons per Day.
- Alter treatment process at the WPC to increase treatment capacity earlier during wet weather conditions and still meet NPDES permit limits.
- Installing flow restrictors on storm catch basins in the combined sewer area.
- Reducing impervious surfaces in the combined sewer area.
- Installing underground detention on City owned parking lots.
- Flow monitor and televise separated sanitary sewer system for clean water inflow / infiltration.
- Replacing or relining Combined and Sanitary sewers that have large sources of infiltration.
- Educating the public about CSO’s, wet basements, and removing clean water connections from the combined or sanitary sewer.
What can citizens do to help minimize CSO’s?
There are multiple ways in which citizens can help reduce the impacts of CSO’s. Please contact the Utilities Department or the Water & Sewer Division for more information. Click here to view the Clean Water Removal page.
The City also distributed a Wet Basement brochure in the utility bills in September 2009. This brochure explained how removing clean water from the sewer can help reduce wet basements and CSO’s. Click below to view the Wet Basement brochure.