Combined Sewer Overflows

Prior to the Clean Water Act, it was common practice to construct combined sewer systems, designed to collect rainwater runoff, domestic sewage and industrial wastewater in the same pipe. In dry weather or during small storms, combined sewer systems transport all of the wastewater to the wastewater treatment plant, where it was then treated and discharged to the receiving stream, which in Lafayette is the Wabash River.


During periods of heavy rainfall or snow-melt, however, the wastewater and stormwater runoff volume in a combined sewer system can exceed the capacity of the sewer system or the treatment plant. In these cases, the system was designed to over-flow occasionally and discharge excess wastewater and stormwater directly into nearby streams, rivers or other water bodies.

Combined sewer overflows (CSOs) are a major water pollution concern for the approximately 900 cities in the United States that have combined sewer systems. This includes our very own City of Lafayette, which currently has 10 overflow points permitted by the Indiana Department of Environmental Management.


Taking Action for a Better Environment

The City of Lafayette submitted a Combined Sewer Overflow (CSO) Long Term Control Plan (LTCP) report to the Indiana Department of Environmental Management (IDEM) in September 2009 in accordance with the State Judicial Agreement requirements.  The LTCP was approved in September 2009 and incorporated into Lafayette's National Pollution Discharge Elimination System (NPDES) permit.

 

Current Approved CSO LTCP

The list of LTCP-mandated projects is split into two phases.  All Phase I projects, listed below, consist of early action projects that were initiated prior to the approval of the LTCP in 2009.  These projects involved reduction in CSO volumes, frequencies, and durations and helped maximize flows to the WWTP:

•             Elimination of Shamrock Park CSO (CSO 008)

•             Elimination of Romney Road CSO (CSO 017)

•             Ross Road Lift Station

•             Prairie Oaks Lift Station

•             Pearl River Lift Station

•             Backflow prevention at CSOs 006 and 007

•             Elliott Ditch Interceptor Improvements

•             WWTP Upgrade and Expansion

•             Pearl River Storage and Conveyance Tunnel

•             Parking Lot Lift Station Elimination (Elimination of CSO 004)

 The recommended plan for Phase II, as approved during the most recent update to the LTCP in November 2016, was selected based on feasibility and capital cost.  Phase II is divided into four sub-phases, Phases II-A, II-B, II-C, and II-D, to include the implementation of the integrated CSO control alternatives.  Table 2-1 reflects all changes to Phase II during the various updates to the LTCP between 2012 and 2016.

Table 2-1 Updates to the Original CSO LTCP

After implementation of Phase II-D of the recommended alternative, a two-year post-construction compliance monitoring program will be conducted.


Water Quality Impacts

The implementation of the CSO LTCP has contributed to substantial improvement in water quality of Lafayette waterways, most notable the Wabash River.  Since the construction of LTCP projects began, the annual CSO volume based on a typical year storm has decreased by 61%.  See Figure 5-1 and Figure 5-2 for the total CSO event and volume reduction, with the latest available data from the XPSWMM collection system model following completion of the Greenbush CSO Storage Tank in 2019.

Figure 5-1 and 5-2 for CSO


You Can Help

The Wabash River provides enjoyment through fishing, boating and nature watching, and the City of Lafayette is committed to enhancing the quality of the river to support these recreational uses. You can be part of the solution. By understanding the system and staying informed along the way, you can help your government make the best decisions on this serious and complex issue. Your participation is vital to ensure that future generations will be able to enjoy clean waterways too.

 

Keeping You Informed

Lafayette Renew is in full compliance with all federal and state regulations regarding the treatment of our City's wastewater. The Department's aim is to educate about the most important water process issues affecting your environment.


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