Heavy rains and sewage add up to health risk

When it rains, or when snow melts, that water has to go somewhere. In New York City, a lot of that water goes down the drain. The storm water and runoff mixes in with household sewage, and it all goes off to a plant to get treated.

But when it rains a lot, the treatment plant can’t take the added volume. So all that extra water — raw, untreated sewage included — runs straight into the river. It’s called “combined sewage overflow” (CSO), and every year, an estimated 25 to 30 billion gallons of raw sewage pours into the rivers around New York City.

The northwest Bronx is home to more than 10 CSOs, including one of the largest discharge points in the city — the outflow for the Broadway sewer, which runs under Broadway and discharges into the Harlem River. It is designated as a “Tier 1” CSO, meaning it accounts for 50 percent of total CSO volume for the area covered by Ward’s Island water treatment center. It also has the most CSO incidents of any outflow in the city.

“CSOs are a major health issue. People are canoeing and kayaking in the Harlem River, and our community is polluting the Harlem River,” said Christina Taylor, executive director of Friends of Van Cortlandt Park.

The reason this particular CSO is the among the worst dates back centuries, to when the Van Cortlandts lived in what is now Van Cortlandt Park. The family dammed Tibbetts Brook, which used to run south from Yonkers all the way to the Harlem River, and created today’s Van Cortlandt Lake, Ms. Taylor explained. At some point — history is fuzzy on this, she says the best guess is a railroad company — forced Tibbetts Brook underground, into the sewer system. Park visitors can see this in action, at the waterfall by the golf house.

Expensive to treat

These days, that means even during dry weather, an average of 1.45 million gallons of water leaves Van Cortlandt Lake each day and goes into the Broadway sewer, mixes with the sewage and goes to Ward’s Island treatment plant. The water that used to be Tibbetts Brook costs the city more than $2 million a year to treat.