How CSOs (combined sewer/water systems) work, why they’re bad

USEPA and New Jersey Future
CSOs are Combined Sewer Overflow systems put in place centuries ago when stormwater was considered to be as much a public inconvenience as sewage is – instead of being regarded as the asset it really is. After all, nobody can live without water and for various reasons, we have less clean water today than any other time in history, so there’s a growing awareness of how much we need to treasure and protect our water resources.

In the CSO model, both clean street stormwater and sewage waste are channeled through municipal pipes into the municipal sewage waste treatment facility. That’s a waste of taxpayer funds right out of the box, because there’s no need to treat street water that’s already, just about clean. And even worse, the CSO system becomes a huge public health hazard when there’s a big weather event and CSO-connected sewage plants close off their incoming pipes to avoid becoming overwhelmed and flooding. When this happens, both effluent and water in the municipal pipes are pushed out into nearby natural bodies of water.

This is not only a truly icky phenomenon. It’s also damaging to the waterways’ ecosystems and obviously makes using them for recreation while sewage is present, entirely out of the question.

In a NJ Spotlight Opinion Piece, Daniel J. Van Abs offers a synopsis of the CSO problem:

The Romans developed a technology, now called combined sewers, to move sewage and stormwater off the streets and out of the city. London revived the use of combined sewers in the 1800s. Many cities in this country also built combined sewers from roughly 1860 to the 1920s, including 21 New Jersey municipalities, where they still exist. Initially, the combined sewage and stormwater were discharged directly to rivers, lakes, and bays, getting it out of the city as quickly as possible. Only later was treatment added – sometimes.

H2 Oh No! is a short video about CSOs from the Center for Urban Pedagogy.

Both Rutger’s Water Resources Department in New Jersey and New York’s Riverkeeper recommend on-site treatments to contain stormwater where it falls by sequestering it in the leaves of plants and trees at street height or in green roofs, getting it to percolate into the ground or capturing it in cisterns and rainbarrels for later use.

Here’s a CSO factsheet from Riverkeeper showing on-site treatments effectively provide for stormwater management. This keeps stormwater away from sewage lines and consequently, reduces the incidents of CSO pollution.

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