By: Daniel Buonadonna, CH2M Global Technology Lead
Daniel presented his paper, “Quantifiable Risk Management for Large Diameter Sewers, Portland’s Approach to Rehabilitation of a 100-yr-old Brick Outfall,” co-authored by the City of Portland’s Tammy Cleys and CH2M’s Mark Johnson, on Wednesday, September 28, at 10:30 a.m., during WEFTEC.
Centralized collection—using large diameter interceptors, trunk lines and transfer sewers—has frequently been the backbone of a wastewater collection system for centuries. In the United States, many large diameter sewers have been in service well past their design life, and consequently, we’re seeing more headlines in the local newspapers of sinkholes, pipe collapses and overflows taking place when these aging sewer systems fail. The consequences of pipe failures to the communities, including fines cities must pay, are significant when billions of gallons of raw sewage are discharged into natural waters.
To prevent these types of problems from occurring in their wastewater collection systems, many utilities are taking proactive steps and implementing asset management programs to assess the condition of their large diameter sewers, with the intent of addressing problem areas before they become worse. The City of Portland is one utility that has established an asset management team and invested in a strategy to identify the pipes with the highest risk exposure and prioritize between urgent projects by determining which rehabilitation approach provides the greatest value.
The City put its strategy to the test on one of its aging brick sewers, the Taggart Outfall 30. Constructed in 1906, the 7,600 LF, 66-120” brick sewer was used to replace cesspools, helping reduce the death rate from typhoid fever and other infectious diseases in Portland’s densely settled neighborhoods. At the time, with an initial budget of $250,000, it was the largest diameter and most expensive sewer Portland had constructed. Over the past century, the City’s Bureau of Environmental Services has continued to utilize this asset with multiple retrofits that allow the tunnel to function today as a critical piece of the combined sewer infrastructure, rerouting wet weather flows through different diversion structures and relief sewers.
However, in 2014, the City engaged CH2M to perform a condition assessment to evaluate rehabilitation alternatives that could provide a long-term solution to the historic pipeline. The unique characteristics and large dimensions of the outfall allowed a broad range of trenchless technologies to be considered, including tunnel rehabilitation technologies. To address the City’s challenges and find the “right size rehabilitation” plan, a net benefit cost ratio (nBCR) approach, which took into consideration the consequence of failure, likelihood of failure and cost of alternatives, was used to evaluate the lifecycle costs and risk mitigated for each rehabilitation strategy.
The outcomes of the nBCR calculation and evaluation method were sufficient for the City of Portland to make an informed and valid alternative selection. By quantifying the likelihood of failure (in time), and reducing all the consequences of failure as well as the potential alternatives down to triple bottom line costs (in dollars), much of the subjectivity of other alternative analysis methods is avoided. While the Taggart Outfall 30 project team moves forward into design, the Portland Bureau of Environmental Services is continuing to refine and improve their powerful nBCR asset management tool.
Daniel Buonadonna joined CH2M in 2008 and currently serves as the Global Technology Lead for CH2M’s Condition Assessment and Rehabilitation Services (CARS) team and the Deputy Regional Service Leader for CH2M’s Conveyance Community of Practice in the Northwest United States. Daniel is dedicated to helping communities face the challenges associated with aging infrastructure and asset management. He has expertise in consulting, engineering design, operations and maintenance and project management. Daniel received his bachelor’s degree in civil engineering from the University of Notre Dame and holds a Master of Science in Environmental Engineering from the University of California. He is a member of the North American Society for Trenchless Technologies, Water Environment Federation and Engineers Without Borders.