Quantifiable Risk Management for Large Diameter Sewers, Portland's Approach to Rehabilitation of a 100-yr-old Brick Outfall

The Taggart Outfall 30 is 7,600 LF, 66-120” brick sewer constructed in 1906 and is one of the longest-serving, large diameter, sewer pipes in the City of Portland. Over the past century, the City's Bureau of Environmental Services has utilized this asset with multiple retrofits that allow the tunnel to function today as a critical piece of the combined sewer infrastructure and in 2012 had identified it as a candidate for structural rehabilitation. As part of their proactive approach to asset management for critical conveyance assets such as this, the City developed a quantifiable, risk-based approach to prioritizing rehabilitation of large diameter wastewater pipelines known as the net Benefit-Cost Ratio (nBCR) method. This paper will review the background, preliminary design & alternatives analysis with a description of the nBCR lifecycle cost method.