Slush meets sewage

To the many miseries of this winter’s relentless snowfall, ice and slush, add one more: all that wet stuff has been testing the limits of the city’s sewer system.

On at least three occasions so far this fall and winter, state records show, untreated sewage has found its way into New York City waterways after melting snow and ice challenged the capacity of wastewater equipment.

Last Friday night, Feb. 7, rain and melting ice caused sewage to flow into the Harlem River in the South Bronx for about 25 minutes.

Snow may be beautiful on tree branches, but melted in the sewer system it can have ugly consequences. Photo: Matt Yeager/Flickr

Snow may be beautiful on tree branches, but melted in the sewer system it can have ugly consequences. Photo: Matt Yeager/Flickr

On Dec. 15, Flushing Bay in Queens received untreated sewage for seven hours, while in Brooklyn, the Gowanus Canal experienced a three-hour influx of untreated sewage. The city Department of Environmental Protection (DEP) attributed the incidents to “weather conditions.”

While reports are not yet in for this week’s storm, water-safety experts say it’s likely the city sewers are feeling the pressure of 9.5 inches of snow followed by nearly two inches of rain and then more snow.

According to DEP, between 60 and 70 percent of New York’s sewers are “combined,” mixing wastewater from homes, businesses and storm drains and transporting it to treatment facilities. If these plants reach twice their normal dry-weather capacity, excess sewage needs somewhere to go.

Since 2005, DEP has been coordinating with the state on long-term efforts to curb so-called combined sewer overflows. Currently, special retention tanks and other projects allow the city to capture about 80 percent of overflows. But when it’s wet outside, things can get difficult.

“In dry weather, the system works,” said John Lipscomb, the Patrol Boat Captain for Riverkeeper, a clean-water watchdog group. He tests the water quality of the New York harbor on a weekly basis.

He notes that rain, not snow, accounts for most combined sewer overflows. But, on a day like Thursday, where a lot of snow fell and then melted quickly, there may be cause for concern.

One foot of snow has the same impact as about an inch of rain, Lipscomb explained. “In some parts of the city,” he said, “one-tenth of an inch is enough to double the flow.”

Following particularly heavy snow storms, the city Department of Sanitation calls on three dozen snow melting machines, which send about 240 gallons a minute into the sewers.

“We use snow melters when we have pretty significant snowfalls,” said Sanitation spokesperson Belinda Mager, who said the machines weren’t used in this week’s storm. “When it does happen, DSNY only uses storm drains identified as appropriate by the City DEP.”

DEP did not respond to questions about the impact of Thursday’s storm on the sewer system. The state last updated its inventory of reported sewage discharges on Tuesday.

Under New York’s Sewage Pollution Right to Know Act, discharges of untreated or partially treated sewage from public treatment facilities or sewer systems must be reported to the state within two hours. Since the law went into effect in May 2013, government agencies have reported about 1,200 discharge incidents across the state attributed to wet weather, blockages in sewer systems or other factors. Forty-eight of the instances occurred in New York City.

Roland Lewis, the President and CEO of the Metropolitan Waterfront Alliance, said that water-absorbing surfaces, rooftop gardens and the city’s MillionTreesNYC initiative, begun under former Mayor Michael Bloomberg, all help keep water out of sewers in the first place.

“We’re hopeful that Mayor de Blasio will take that baton and keep it going and maybe even go further to further our green environment and soak up the stormwater,” Lewis said.

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