'Second River Thames' Built Below London

The River Thames is a cleaner river than it was a few decades ago—and far cleaner than it was in Victorian times, when survivors of a shipwreck on the outskirts of London died from ingesting polluted water—but there's still plenty of room for improvement. That's the purpose of a huge project dubbed the "Super Sewer," Popular Science reports. The Thames Tideway Tunnel project, which includes a 15.5-mile tunnel mostly built beneath the Thames, is designed to take the pressure off the sewer system built by chief engineer Joseph Bazalgette in the 1860s. London is three times bigger than it was in Bazalgette's day and much more of it is paved, meaning even small amounts of rain can cause sewers to overflow.

Taylor Geall, spokesman for construction company Tideway, tells Popular Science that London's combined sewer system—in which stormwater and sewage go through the same pipes—causes an estimated 44 million tons of rainwater and untreated sewage to flow into the Thames every year at overflow points. This kills wildlife and creates what Deborah Leach, CEO of the environmental group Thames 21, calls "disgusting" mounds of wet wipes in places like Hammersmith Bridge. "We are still seeing these stinking foreshores that you last saw back in Victorian times," she says.

The tunnel—which Geall calls "ridiculously big," with a diameter of almost 24 feet—is now complete. At its deepest, it is 217 feet below the ground. The entire project, including new sewage treatment facilities, is due to be finished in 2025, with a budget of more than $5 billion. Tideway estimates that it will reduce sewage spillage into the Thames by 95%. In a look at the project earlier this year, the Times of London described it as a "second River Thames." The newspaper noted that when construction began six years ago, archaeological finds were made as an access shaft was dug for tunnel-boring machines. The most notable one was a 16th-century skeleton of a man, who was wearing only leather boots and had been beaten to death. (More London stories.)