Irene's gone, but what's in the water?

With significant rainfall comes significant runoff, carrying with it pesticides, sewage and oil. And it also disturbs sediment.

What you don’t see in flooding footage and destruction photos…

Hurricane Irene is likely to have caused less visible environmental damage by dumping sewage, pesticides and other contaminants into waterways along the east coast. New York Times’ Green blog reports.

With significant rainfall comes significant runoff.

The condition of 7 rivers, including New York’s Hudson River, are just beginning to be assessed. On Sunday, the US Geological Survey sent crews out to follow Irene’s path between Washington D.C. and Massachusetts – testing for pesticides, bacteria and nutrients flushed in by heavy rains.

Pesticides (such as those used against termites) are carried in from farms, gardens and lawns, while bacteria and nutrients (such as nitrogen and phosphorus) flow from sewer discharges.

Excess nutrients can cause algae blooms that threaten aquatic life and fisheries; sewage can lead to higher E. coli concentrations in areas that use surface water for drinking.

In New York City – with a combined sewer system that carries both storm runoff and sewage – high bacteria counts are normal in the Hudson after rainfall. With this storm, higher counts than normal aren’t expected, since the amount of sewage we produce remains the same no matter how heavy the rain.

“As you dump more rain, you’re actually diluting the sewage,” says John Lipscomb, who samples water for the environmental group Riverkeeper. However, he adds: “The river is brown like hot chocolate and absolutely full of debris.”

High flows of water can also disturb sediment and make it settle out in new deposits, where they might clog oyster beds or require new dredging in shipping channels.

Flooding from Irene also caused hundreds of oil spills in New York, mostly from overturned heating oil tanks in basements. Almost all of them were under 100 gallons and minor, though 300 people were evacuated from a building in Rye when 2,000 gallons were spilled on Sunday. They were told to leave because of fumes and damage to electrical systems.

Most spills involving tanks in typical home basements may ruin furniture and walls, but much of it is transitory, according to Dennis Farrar, chief of emergency response for the Department of Environmental Conservation.

“A lot of the oil is carried off by the floodwater,” he says. It ends up in rivers and the ocean.

Via NYT’s Green blog.

Image: Hurricane Irene approaching NYC by joshbateman via Flickr

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