Blueprint Columbus: Comprehensive Public and Private I/I Reduction Program Exceeds Target

This paper provides an overview of the planning analysis, implementation steps, and the Inflow/Infiltration (I/I) reductions achieved by the City of Columbus at the conclusion of its pilot public and private I/I reduction program. The City's integrated plan, "Blueprint Columbus," targets the reduction of Sanitary Sewer Overflow (SSO), manhole flooding, and water-inbasement (WIB) incidents, aiming at a 10-year Level of Service (LOS). The City adopted the "Model at the Source" hydrologic and hydraulic (H&H) modeling approach to identify and quantify I/I sources, and to plan for the required I/I reduction to meet the LOS. The modeling approach quantified the contributions from the various I/I sources such as house foundations, lateral sewers, and sewer mains, and was used to plan the extend of the required I/I reduction technologies. The actual reduction needed to mitigate the SSO and basement backup conditions up to 10-year flow recurrence storm event condition was determined to be 28%. The integrated plan report projects a 40% reduction in I/I during a 10-year historical storm flow level, assuming the City of Columbus lines 90% of the main sewers and lateral house connections, redirects 50% of the house roofs' drainage away from house perimeters, and installs sump pumps in 25% of the residences. In 2015, the Clintonville Main 1 (CV1) basin was selected as the pilot area for the I/I reduction program. In the CV1 area, 95% of the main sewers were lined between 2007 and 2014, and 91% of the lateral sewers were lined between 2018 and 2021. Based on the implementation plan, 95% of the lateral sewer lining was extended into private properties up to the 4"x6" house connections. From 2018 to 2021, roof drainage was redirected to the street for 55% of the roof drainage area that were previously causing water accumulation around houses. Additionally, storm sump pumps were installed in 22.5% of the houses between 2016 and 2021. Post-monitoring analysis for the CV1 pilot study area confirmed the effectiveness of the Blueprint Columbus program. Post-rehabilitation condition models were calibrated using postrehabilitation monitoring data. The 10-year flow recurrence historical storm revealed a median peak flow reduction of 41%, surpassing the planned I/I reduction target outlined in the 2015 Integrated Plan report. The most impactful technology was the lining of the laterals between the sewer mains and house connections. The installation of sump pumps demonstrated limited effectiveness due to the lack of foundation drains and restrictions on installation locations within basements. The redirection of roof drainage proved beneficial, although its effectiveness was compromised in a few basins due to the poor condition of house gutters.