Combined Sewer Overflow

Some towns, such as Brownsburg, collect rainwater runoff and sanitary wastewater in the same sewer pipes. These are called “combined sewers.” Sometimes, when it rains, combined sewers do not have enough capacity to carry all the rainwater and wastewater (sewage) to the Water Pollution Control Plant, and the Plant cannot accept all of the combined flow. In this situation, the combined wastewater overflows from the collection system into the nearest body of water — in Brownsburg’s case, into White Lick Creek — creating a combined sewer overflow (CSO).

Combined Sewer Overflows

During heavy rainstorms and rapid snowmelt, extra flow from stormwater runoff goes into these combined sewers which can overwhelm the main pumping station to the wastewater treatment plant. As the pump station becomes overwhelmed, the combined sewage and stormwater flows into a 1 million gallon storage tank. For extreme weather events, the tank does fill up and overflows to White Lick Creek to prevent flooded basements and streets. These Combined Sewer Overflows are referred to as CSOs. Brownsburg has one discharge point which is the overflow from the tank.

When CSOs occur, they discharge untreated sanitary/industrial wastewater and runoff from rainfall and snowmelt into White Lick Creek. The combination of raw sewage and stormwater can carry a variety of human bacteria and viruses. In addition, combined sewer overflows contain a variety of chemicals, oils and other wastes. Although the untreated overflow is typically diluted by rain and river water, it still poses a potential health and environmental hazard.

CSO Reduction Efforts

In the 1990s, the Town of Brownsburg Brownsburg installed process units called swirl concentrators to partially treat the overflows.

The Environmental Protection Agency (EPA) and Indiana Department of Environmental Management (IDEM) require communities to develop Long Term Control Plans for either treating discharges to a higher level of standards or totally eliminating the discharges. A million-gallon tank designed to meet the requirements as established by IDEM has been constructed to catch the overflow discharges.

Once a rain event is over, the tank is emptied by pumps and the flows are treated at the existing wastewater treatment plant. Brownsburg personnel collects data including flow monitoring, daily rainfall totals, and visual observations to verify the tank is operating as required by IDEM.

The CSO tank is designed to allow overflows to the creek in the event of intense heavy rain or snowmelt events. During these overflows, additional monitoring, sampling, and testing are required to determine the level of treatment the tank provides and whether or not additional control measures will be required in the future. With continued stormwater pipe and sanitary sewer pipe separations planned for the future, flows to the tank should continue to be reduced.

CSO Public Notification

The Town of Brownsburg hereby states that the potential for a combined sewer overflow into White Lick Creek during and immediately following any rain event or snow melt exists throughout the year. People who swim, wade in, or ingest the water contained in White Lick Creek at any time may become ill.  

Wastewater discharges are disinfected during the months of April through October. All individuals should remain clear of White Lick Creek during the winter months regardless of the weather. The overflow discharges are located downstream of Arbuckle Acres Park, but upstream of Williams Park. 

Individuals with property along White Lick Creek between Brownsburg and Plainfield may request a warning sign be posted along the creek bank of their property. For additional information or warning signs call (317) 852-1114.

CSO Overflow Graph

Brownsburg continues to make improvements to the existing infrastructure in an effort to decrease the number and volume of combined sewer overflow events. The next street/utility improvement project is the northside drainage downtown project.  These improvements include removing a portion of the catch basin drain connections from the sanitary sewer main and connecting them into a new storm line. Town personnel will continue to monitor the frequency and number of CSO events to determine if additional steps are needed to achieve compliance.