Municipal water treatment plants deal with the raw sewage of roughly 80 percent of America’s households. Almost all of these facilities treat the waste and release the treated waste into a nearby body of water.
However, often, if the plant is handling more than its capacity, untreated waste is also leaked into lakes, rivers, and oceans.
According to the EPA, an estimated 23,000-75,000 sanitary-sewer overflows happen every year. Contaminants can get into the system due to flooding and agriculture etc. but the biggest culprit is the combined sewer system.
The EPA calls these systems, “the largest category of our Nation’s wastewater infrastructure that still needs to be addressed”, affecting Americans in 32 states.
The Atlantic reports:
“What is being done? Combined sewers have been an EPA priority for many years and, after decades of significant effort, the numbers are starting to move in the right direction, but this is not a problem that can be turned around quickly or cheaply. New York City’s combined sewers are still the single largest source of pathogens to the New York Harbor system, according to the New York Department of Environmental Protection. A single 2014 storm triggered a release into Lake Erie from Detroit, Michigan, of more than 44 million gallons of raw sewage from sanitary sewers and almost 3 billion gallons from combined sewers, and such releases from Detroit and the other cities with sewer outfalls on Lake Erie contribute to the fact that it blooms with algae every summer. Last summer, one of those algal blooms cost Toledo its drinking water for two days, and this year’s harmful algal blooms were projected to be even worse than last year’s.
As with any engineering project, the benefits of reducing overflows to zero—an effort estimated by the EPA in 2004 to cost $88.8 billion—must be weighed against its cost.
“We mustn’t forget the hugely successful effort in the 1970s and 1980s to provide secondary treatment at virtually every sewage-treatment plant in the country,” said Wayne Huber, a professor emeritus of Civil and Construction Engineering at Oregon State University. As an example, he describes what happened in Portland, Oregon, where a system of tunnels now contains 90 percent of the city’s stormwater surges. “Portland spent about $500 million on its deep tunnels and pumping system,” Huber said. “This has reduced the number of releases into the Willamette River from maybe 50 to 100 per year to five to ten per year.”
From the Atlantic article, it can be observed that there is still a lot of wastewater and stormwater network rehabilitation, upgrading and capacity improvement to be completed in the USA.
Inframanage.com note that applying the tools and techniques of infrastructure asset management will help in the planning of this required work.
By analyzing the required levels of service (often set by permit or EPA agreement for wastewater systems), the expected network capacity/growth, and the risks from overflows, old pipes, changing treatment requirements, and network resilience considerations – then integrated lifecycle management planning can be completed, and the long-term investment program calculated.