Washington Street Combined Sewer Overflow

American Structurepoint has commenced with designing the next phase of the city of Norwalk, Ohio Combined Sewer Overflow (CSO) Program. This is in response to the City addressing the most significant element in their final projects defined in their EPA- approved Long Term Control Plan (LTCP), which is the elimination of CSO #1 on the city’s west side and CSO #2 on the city’s east side. The recommended improvements will include installation of approximately 8,500 lft of 48-inch-diameter relief sewer to transport the peak wet weather flow to the city of Norwalk’s Wastewater Treatment Plant (WWTP). This project included a cost/benefit analysis in the preliminary design phase to determine which construction method (tunneling vs. open cut) for the interceptor sewer would be the more beneficial to the City. The resulting decision had the least impact on the area residents while also controlling costs.

The WWTP is currently rated for 8 MGD peak treatment capacity. The preliminary and primary treatment processes were recently upgraded for a peak treatment capacity of 15 MGD, but the remaining processes (secondary biological treatment, tertiary filtration, and post treatment disinfection) remain in need of upgrades. American Structurepoint performed a study of the WWTP to determine the improvements needed to expand the secondary, tertiary, and post-treatment capacity from 8 MGD to 15 MGD. The study included evaluations for each unit process, including treatment performance, hydraulic analysis, capital costs, and operations and maintenance life cycle costs. Additionally, an expansion of the existing equalization basin at the WWTP will be needed to attenuate the peak flow that is in excess of the existing treatment capacity of the WWTP.