Water Online

May 2017

Water Innovations gives Water and Wastewater Engineers and end-users a venue to find project solutions and source valuable product information. We aim to educate the engineering and operations community on important issues and trends.

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By Daniel Buonadonna and Tammy Cleys A ging infrastructure and infrastructure spending are two hot topics in the news today. Given that much of the United States' infrastructure is aging and reaching the end of its useful life, many municipalities and water/wastewater utilities recognize the cash infusion needed to update, repair, or replace their water infrastructure. In the U.S. alone, an estimated 240,000 water main breaks occur every year; addressing this issue is estimated to cost in the hundreds of billions. Wastewater and stormwater systems need attention, too, with an estimated cost of nearly $200 billion over the next 20 years. For centuries, centralized large- diameter wastewater interceptors and large-diameter drinking water transmission lines have frequently been the backbone of a municipal system. Today, we are seeing many large-diameter pipelines that have been in service well past their design life fail, which is why sinkholes, pipe collapses, and overflows are making the local headlines frequently. The consequences of pipe failures to the communities, including fines cities must pay, are significant. Portland Trailblazing To prevent these types of problems from occurring in wastewater collection systems, many cities and utilities are taking proactive steps. By implementing asset management programs to assess the condition of their large-diameter pipelines, they are addressing problem areas before they become worse. The City of Portland, OR, 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-linear- foot (LF), 66 to 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. 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 life cycle costs and risk mitigation for each rehabilitation strategy. The outcomes of the NBCR calculation and evaluation method were sufficient for the City of Portland to make an informed 12 wateronline.com n Water Innovations Lessons On Rightsizing Water And Sewer Infrastructure Projects Two case studies prove that the key to cost-effective condition assessment is choosing the right approach for your system. 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.

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