Combined Sewer Overflow (CSO)
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 is then treated by the city’s Water Pollution Control Department and discharged to the receiving stream, which in Lafayette is the Wabash River.
To best manage CSO, Lafayette developed a CSO Long Term Control Plan (CSO LTCP), including the development and implementation of a CSO Operational Plan. The LTCP also requires preparation of a Stream Reach Characterization and Evaluation Report (SRCER) to characterize the collection system and Wabash River. The SRCER involves flow monitoring, along with preparation and calibration of a computer model of the collection system and Wabash River. It also incorporates CSO and river sampling. In addition, the city is developing CSO control alternatives and conducting a financial capability analysis for the LTCP.
In 2017, Lafayette will begin work on a massive CSO project involving the Brown Street sewer and Greenbush CSO storage tank.
The proposed sewer, which is required under the approved CSO LTCP is needed to store and convey wet weather flows to the Pearl River Lift Station. The proposed Phase II of the Brown Street Sewer project is located on the northwest side of Lafayette approximately 1,000 feet north of Main Street. It will extend from a point just south of the intersection of Erie Street and Union Street and continue southwest along Erie Street, then northwesterly to a point near the intersection of Brown Street and 13th Street, then along Brown Street to a point just west of the intersection of Brown Street and 3rd Street.
Phase II of the Brown Street Sewer project includes approximately 4,230 linear feet of 72 inch diameter gravity sewer, approximately 390 linear feet of 84 inch gravity sewer, and approximately 25 linear feet of 96 inch gravity sewer. The design will include green infrastructure features to reduce the potential for sewer surcharging and reduce the overall stormwater loading to the City's CSO system. Additionally, a new backflow preventer will be installed at the existing CSO 002 outfall structure to prevent backflow from the Wabash River entering the City's sewer collection system. The construction will also include modifications to the existing CSO 002 headwall structure to accommodate the backflow preventer.
Greenbush CSO Storage Tank
The City of Lafayette's approved Combined Sewer Overflow Long Term Control Plan requires full treatment of wastewater flows and a level of control of no more than four (4) CSO overflows during a typical year. To achieve this level of control, the recommended plan was divided into four sub-phases (Phase II-A, II-B, II-C, II-D). As a component of Phase II-B, the City is required to plan, design, construct, and place into operation a 4.2 million gallon (MG) CSO storage tank in the area near the existing CSO 001 diversion structure by the year 2020. The Greenbush CSO Storage Tank is required to store and convey wet weather flow to the Lafayette Waste Water Treatment Plant (WWTP) when the WWTP has capacity thereby improving the water quality in the Wabash River.
The Greenbush CSO Storage Tank project includes a 4.2 MG covered below grade storage tank, a building to house electrical and SCADA components, pumps and related equipment for tank dewatering in compliance with IDEM standards, a screening, and backflow prevention at a newly constructed CSO 001 outfall from the proposed 4.2 MG storage tank, Additional project components include yard piping, site work (including grading), and SCADA integration.