Success of the Rain-Derived Inflow and Infiltration Program in Portland, OR: Fid-Bau Portal

Success of the Rain-Derived Inflow and Infiltration Program in Portland, OR

Cleys, Tammy / Besaw, Ian / Collins, David / Young, Henry

The city of Portland, Oregon, Bureau of Environmental Services (BES) initiated a rain-derived inflow and infiltration (RDII) Program as an element of an overall system plan. The system plan recommended conveyance improvements and prioritized RDII reduction projects to address capacity deficiencies, provide for community growth, and the rehabilitation of an aging collection system. Repeated sanitary sewer overflows (SSOs) from a manhole located near a middle school and upstream of a small creek resulted in a mandate and schedule from the state to eliminate the SSOs at this location. High inflow and infiltration (I/I) rates into a sanitary sewer system that serves this hillside residential area of Portland caused the repeated sewer overflows. To address this, the city embarked on a comprehensive, multiple year program to identify sources of I/I, reduce sources through pipe rehabilitation projects, and then quantify the effectiveness of the rehabilitation efforts at lowering I/I rates. The city conducted source detection and flow monitoring to establish baseline conditions. Hydraulic and hydrologic models of the system were created and calibrated to the flow monitoring data. The models were used to evaluate RDII reduction and conveyance alternatives. RDII reduction projects in three sub-basins were selected for ‘early action’. These projects included rehabilitation of mainlines, public laterals, and private laterals. Post-project flow monitoring and modeling were conducted to evaluate the effectiveness of the projects. The program had set 40% and 60% reduction goals and has achieved 56% and 73% reduction effectiveness. This paper will set out the program, the hydraulic analysis, the capital improvement program (CIP) implementation, the measurable RDII reduction, and the ongoing verification of these results.