Venice Island, which officially opened this month in Philadelphia, has all the amenities you might expect from a nice city park—gardens, basketball court, amphitheater—but also something unexpected: a 4 million gallon sewage overflow tank. And you know what? A park built on top of the sewer is a very good thing.

Like many old cities, Philadelphia has a combined sewer system, where stormwater and wastewater flow through the same set of pipes. This usually works okay, but it can get nasty during heavy rain. When rainfall overwhelms the sewer system, stormwater and raw sewage alike flow directly into the river untreated. One solution is massive sewage overflow tanks, which temporary hold water until the storm is over. Usually, however, these tanks are just buried somewhere underground.

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Philadelphia has taken a more integrated tank to its water infrastructure, writes Sarah Goodyear in Next City Daily. When the city needed a new sewage overflow tank, it decided to also rebuild the aging park on top of the tank. Venice Island is now a community center and part of the city's sewage infrastructure.

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Aerial rendering of Venice Island

The overflow tank itself is below ground, but a concrete pump house marks its presence. Air filters prevent the smell from coming up. The landscaping above ground is also designed to deal with heavy rainfall. "Tree trenches" channel stormwater away, and walls of caged rocks are designed to prevent erosion on the island's banks during floods.

Venice Island is only one part of Philadelphia's 25-year, $2.5 billion Green City, Clean Waters program, which aims to be a national model for green water infrastructure. It also, for example, now charges commercial property owners for runoff from their properties, so parking lots that create a lot of stormwater runoff also pay more in sewer fees.

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It's too easy to take our sewers for granted. But considering how they make our clean, comfortable lives possible, we should celebrate—rather than hide—our sewage system. [Next City Daily, Hidden City Philadelphia]

Images via Philadelphia Water Department