Wednesday, July 26, 2006

The new watersheds

Every day that I ride my bike to work from Brooklyn, the Hudson River greenway bike path takes me past the huge North River sewage treatment plant in Harlem. There's a number of interesting things about this place - the state park on its roof, for instance, with picnic areas, playing fields and swimming pools - but today I fancied to think of it as the mouth of New York City's man-made wastewater river. Or one of the mouths, anyhow.

A little bit of background - we've been doing a lot of bald eagle programs at Inwood now that the birds are flying around the park, and I've been asking participants for ways they might be able to help these new New Yorkers. I try to get them to name ways they can improve water quality, since the eagles rely on healthy fish for food, and the Hudson River's pollution was the main factor that drove the bald eagles away from the city a hundred years ago. But it's been surprising how little people know about where their water goes beyond the drain or the gutter.

Eventually, it all goes into the river. But first, wastewater from Inwood, Washington Heights, and the rest of the western half of Manhattan above Greenwich Village drains to the treatment plant beneath Riverbank State Park. During dry weather, the plant treats 125 million gallons of wastewater a day, and the plant is designed to handle up to 340 million gallons during storms, according to the DEP. New York City's entire system of treatment plants are designed to handle 1.8 billion gallons of wastewater a day from the five boroughs. To put that into context, the Delaware River carries about 5.3 billion gallons of water past Trenton, New Jersey on a typical June day. So New York's sewers are a respectably-sized watershed, with a delta of fourteen mouths spread out across the harbor, and millions of tributaries in households, streets, and businesses all over the city.

Unfortunately, this is a very polluted watershed, and it floods into the rivers and bays of the region with alarming frequency. Because stormwater from the streets mixes with sewage from homes and businesses, every big rainstorm strains the city's treatment capacity. An inch of rain falling on the city's 120,000 acres produces 3.14 billion gallons of water. Some of that gets absorbed into the ground (the rain that falls on parks and street trees, for instance), but much of it ends up going down gutters and into the sewers. Thus, all the nasty stuff on the city's streets, from gasoline to household chemicals to dog crap, washes away with every storm, mixes with our raw sewage, overwhelms treatment plants, and ends up untreated in the region's waterways. Riverkeeper estimates that an average of half a billion gallons of sewage get discharged from overflowing sewers every week.

Everyone who sends water down a drain is culpable, to some degree, for creating wastewater. Individuals can make a huge difference by minimizing water use during storms and by being vigilant against dumping nasty stuff on the streets and down the gutters. For information on what the city government might do to fix this problem, take a look at Riverkeeper's website.

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