When It Rains, Sewage Often Pours Into Harbor

The below describes a problem which plagues a substantial number of cities around the U.S. The cost to modify the design of these systems needed to prevent the backwashing of the raw sewage into waterways is prohibitively expensive for most cities. And if you think this problem is restricted to big cities such as New York City or Seattle, think again. Even Burlington, Vermont dumps sewage into Lake Champlain whenever there are extremely heavy rains.

NY Times
August 11, 2007
By ANTHONY DePALMA

Besides flooding subways, the wild downpour this week provided a disconcerting glimpse into one of New York’s dirtiest environmental secrets: heavy rain regularly overwhelms the city’s vast sewage system and pushes polluted water into places it is not supposed to go.

New York has a storm water drainage system that was linked many years ago to the same pipes that carry wastes from homes and businesses. That, combined with the ever-expanding layer of asphalt and concrete that keeps rain from soaking into the ground, means that whenever it storms, some of the storm water and sewage in the 6,000 miles of sewer pipe in the city start to back up.

When that happens, millions of gallons of rainwater mixed with raw sewage are routed away from the city’s 14 sewage plants and toward a web of underground pipes that empty directly into the East River, the Hudson River and New York Harbor.

The backups could also prevent water from being drained from subway tunnels.

These events — called combined sewer overflows — have been recognized as a major environmental problem for decades. The city has been dealing with the issue in response to orders from the state and the federal government, but still has a long way to go.

This week’s subway snarl-up may increase the pressure for something more to be done.

A special task force will try to sort out exactly what happened in the subways and why. But when he was trying to explain why the transit system shut down Wednesday morning, Elliot G. Sander, the chief executive of the Metropolitan Transportation Authority, laid some of the blame on the city’s overloaded sewer system.

About half of the city’s subway stations have their storm water runoffs hooked up to the municipal system, environmental officials said. The other half use their own drains.

Mr. Sander said that crews trying to pump water out of the subways were sometimes stymied because the city’s sewers were already overflowing.

Transit officials had offered much the same explanation in 2004 when a similar early morning storm hobbled the subways.

But a subsequent investigation by the Inspector General’s office concluded that limitations in the capacity of the sewers that year may have hampered drainage for a time while it was raining, but “those limits were not the sole cause of delays.” Rather, debris on the tracks and poorly maintained valves were the principal causes.

New York City’s combined storm water and sanitary lines are not unique. About 800 American cities use the same system, although New York’s is by far the largest. In a typical year, about 27 billion gallons of raw sewage and polluted storm water are discharged into the harbor.

On a dry day, the Department of Environmental Protection, which runs the system, normally treats about 1.4 billion gallons of sewage at 14 plants spread throughout the city. But because storm water runoff flows through the same pipes, each plant has been equipped with enough capacity to handle double its ordinary load on rainy days.

But as little as a tenth of an inch of rain coming very quickly can overload that system. A series of devices called regulators that are buried deep in the ground automatically respond to pressure from the extra water by diverting the flow away from the treatment plants to nearly 460 registered sewage outflows that empty directly into the city’s rivers and waterways.

New York has a long history of using its waterways as dumps. Until the late 1980s, the city routinely poured untreated sewage into the harbor; in 1992, it became the last city in the country to halt the practice of dumping sewage sludge at sea.

As the harbor began to cleanse itself, attention was focused on the combined sewer overflows. Since the early 1990s, federal and state regulators have forced New York City to improve the way its handles storm water or face heavy fines. The city is now required to provide treatment for 75.5 percent of storm water flows. That is still below the 85 percent required by federal law but far above the 30 percent of storm water that the city used to treat before the regulators got tough.

Recently though another factor has added urgency to the way the city handles storm water — climate change.

“This is a problem that is getting a lot worse very fast,” said Emily Lloyd, commissioner of the Department of Environmental Protection. Very intense storms, like the one that whipped through the area this week, are becoming more common, Ms. Lloyd said, and the city’s aging sewers are increasingly overtaxed.

At the same time, the few remaining open areas in the city continue to be buried under concrete. From 1984 to 2002, 9,000 acres of trees, bushes and vegetative cover were paved over. That land, according to government analysts, could have absorbed 243 million gallons of water for each inch of rain that fell on the city.

New York is pursuing two different tacks in trying to control combined sewer overflows. One approach, a direct response to the regulators, is to build four giant holding tanks where storm water can be collected and held until the rain stops and the sewers become unclogged. Two of the four have already been completed and are in use, and work is proceeding on the other two.

But such big construction projects are expensive and disruptive. Environmentalists, including Basil B. Seggos, chief investigator at the Hudson River Riverkeeper, an environmental organization, want the city to take a less intrusive approach that could actually reduce the amount of runoff that ends up in the combined sewers.

“Green roofs, parks systems, more trees — these kinds of things will, at a minimum, offset the impact of a big storm like we saw this week,” Mr. Seggos said.

Many of these ideas were included in Mayor Michael R. Bloomberg’s recently released sustainability plan.

But Mr. Seggos said the city should have incorporated such ideas as roofs that can be planted with trees into a plan it submitted to state regulators in June for handling combined sewer overflows.

That plan focused primarily on completing the gigantic holding tanks, he said.

“We could be talking about billions of gallons a year being put to use as nature intended, as opposed to creating a hard engineering solution for responding to an impossible situation,” Mr. Seggos said.

And a side benefit of capturing the water on roofs, in parks, and around planted trees, he said, would be keeping it out of the subways.