Lots of American hometowns have sewer pipes that drain stormwater from their streets and parking lots and deposit it in a stream, river or bay. And about 75 percent of Americans have municipal wastewater treatment facilities piping untreated sewage from our sinks and toilets. In order to dig once, not twice, many stormwater and wastewater pipes were laid together. Of course they were originally designed to keep the sewage and stormwater apart.
But climate change has made many of these designs obsolete. Extreme single-day precipitation events, with growing frequency and volume this century, are causing Combined Sewer Overflows (CSOs) which force the two sewers to mix their contents, right there under our feet, and deposit untreated sewage nearby. We may see and smell the filth flowing down our streets, or we may know nothing about it until the river starts poisoning our kids.
Ways to cope
Some climate protections at the surface can help, like diverting rainwater and snowmelt from town sewers onto green areas, or temporarily storing flows to be treated and released after the storm passes. But for the most part, extreme rain can’t be stopped from overflowing combined drainage systems, finding its way into wastewater sewers, and flushing out untreated sewage.
A few examples
Engineering and financial challenges have meant that correcting combined sewers often takes years. Here are a few examples; some data go back over decades.
Louisville, Kentucky has had 115 dangerous overflow points within its sewer service area, Initially the city spent about $25 million to start fixing them. Altogether sewer separation was estimated to cost $210 million - subject to the price of funding and the complexity of completing projects in fully urbanized areas.
Burlington, Iowa initially spent $16.2 million to fix their CSOs and faced $20.3 million to implement the rest of the plan. Many residents are on fixed incomes or earning low wages, and cannot afford increased sewer rates. Work will be paid for by a mix of Community Development Block Grants, federal grants, and municipal bonds.
Randolph, VT with fewer than 5,000 residents has worked on replacing sewer lines, upgrading collapsed and failing manholes, and separating their sewers. These projects are not always straightforward. After initial work it was found that they weren’t fully successful; bypasses still occurred during heavy rain. For a small town the costs have been huge. Funding has been provided through state grants and state revolving loans, with 25% coming out of Randolph’s town finances.
Costs
For decades, state and federal prohibitions on CSOs have forced around 860 cities and towns (with 40 million residents) to rebuild parts of their combined sewers to comply with the Clean Water Act. These communities are mostly located in the northeast and around the Great Lakes.
As climate change makes the problems worse, rising sewer rates, local taxes to service long-term municipal bonds, and other ways of paying to fix CSOs have slowly become permanent costs to residents in these areas. The Environmental Protection Agency estimates that altogether the outlays to control CSOs throughout the country have been approximately $56 billion - with more coming.
Watch this space
CSOs are just an early problem for municipal septic systems. Longer-term and more expensive damages are on their way. The effects of climate change on the land under our communities - flooding, erosion, saturation, subsidence and sea level rise - will eventually force many towns to dig up and rebuild their sanitary sewer systems at a higher elevation to keep them from remaining in wet soil or standing water all the time.
CSOs are just another long-term financial burden to us from climate change — far less obvious than the costs of wildfires, storms, floods and other headline-makers.
Here’s a map of CSOs across the United States.
More on CSO management.
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