Editorial: The real problem with cleaning public waterways

Paris’s Austerlitz basin is a giant stormwater overflow tank the size of 20 Olympic swimming pools. It is the centerpiece of a $1.5 billion public works project that aims to make the Seine River, which flows through the middle of Paris, swimmable.

The tank—deep beneath Square Marie Curie, next door to the Austerlitz train station—will hold overflow on rainy days and then gradually pump it back into the city’s wastewater system at a rate the pipes and treatment plants can handle.

The project also connects boats moored along the riverbank to the sewer and added a supplementary treatment plant upstream from the city. Previously, most boats had flushed their waste into the river.

Paris needs such a massive effort because it uses one network of pipes for both sewage and stormwater. In heavy rain, the volume of water is more than what those pipes can move, and the overflow dumps into the Seine.

A swimmable Seine has been a goal and campaign promise of French politicians since the late 1980s. Paris mayor Anne Hidalgo upped the ante when Paris was selected to host the 2024 Summer Olympics. Under her leadership, the city decided to hold open-water aquatic events and the opening ceremonies in the Seine with no backup plan. The clock is ticking.

If Paris can make the Seine safe for swimming in time for the Olympics, it will provide a shining example of what engineering solutions can do.

Similar efforts are underway in cities around the world. London completed construction on its own giant underground tank in March and is in the process of connecting it to the existing sewer. The “super sewer” is a 25 km tunnel that will be able to hold the equivalent of 600 Olympic swimming pools when fully operational.

Environmental activists are eager to see action; a March report by the nonprofit River Action UK found that the city was dumping sewage into the Thames most days.

Baltimore spent $430 million on an aboveground stormwater overflow tank in 2020 and is now sending crews underground to scrape out and reline pipes clogged with sediment.

Like in Paris, the Baltimore project is happening only for external reasons—in its case, a 2017 consent decree imposed by the US Environmental Protection Agency to stop the millions of liters of sewage that Baltimore was sending into the Chesapeake Bay every time it rained. Local environmental groups had to sue multiple times to secure enforcement of the consent decree.

Paris and Baltimore are both making progress. When the sun is shining and it’s been several days since any rain fell, fecal bacteria counts in the Seine and Baltimore’s Inner Harbor are usually low enough that people with healthy immune systems can safely get into the water.

Mayor Hidalgo and French president Emmanuel Macron are promising to jump into the river sometime before the Olympics. They had committed to June 23 but backed out, citing expected rainfall.

Also on June 23, at least 150 of Baltimore’s dignitaries, residents, and press scheduled a swim in the Inner Harbor to celebrate the city’s progress.

It’s great to see tangible results. But cities should invest in cleaning up their waterways without waiting for external pressure to force them into action. New wastewater technologies, such as the peracetic acid disinfection that the US city of Memphis, Tennessee, has been using for 4 years, give utilities a bigger toolbox. Pipes can be rapidly relined using epoxy-impregnated felt tubes. And within the next few years, we’ll have reams of data about how well storm surge overflow tanks improve pathogen counts in Paris, London, Baltimore, and several other major cities.

We know too much, and have too much chemistry and engineering capability, to keep treating public waterways as trash dumps.

This editorial is the result of collective deliberation in C&EN. For this week’s editorial, lead contributor is Craig Bettenhausen.

Views expressed on this page not necessarily those of ACS.