This is FRONTLINE's old website. The content here may be outdated or no longer functioning.

Browse over 300 documentaries
on our current website.

Watch Now
poisoned waters

Primer: Stormwater Runoff Pollution

It's a massive problem. But it's poorly understood. And that's because it's largely invisible...

What is runoff pollution?

While we're used to associating water pollution with heavy industry, the EPA [Environmental Protection Agency] now calls runoff -- also called nonpoint source or stormwater pollution -- "the leading remaining cause of water-quality problems" in the United States. And unlike those industrial discharges, runoff is produced by every one of us.

When rain falls or snow starts to melt, the water moves over the ground, picking up the chemicals we leave behind: oil from our cars; fertilizers, herbicides and insecticides from our lawns, gardens and farmland; pet and livestock wastes laden with bacteria and nutrients; contamination from faulty septic systems; and countless other byproducts of human activity.

Bit by bit, running water carries those chemicals into a creek or a storm drain, eventually joining our rivers, lakes and larger water bodies, where the drops start to add up. As Jay Manning of the Washington state Department of Ecology told FRONTLINE, stormwater in his state "picks up on an annual basis a volume of oil that is equivalent to half of the Prince William [Sound] spill from Exxon Valdez."

Why is it so hard to regulate?

The EPA's term for runoff, "nonpoint source pollution," itself points toward the problem. Point sources were the original targets of the Clean Water Act -- they are both "stationary" and "discrete," such as a drainpipe coming from a factory. In a point source situation, the regulator can clearly link a polluting discharge to its origin, which allows the EPA to apply a permit to control emissions from that source.

Nonpoint source pollution, by definition, has an uncertain or unknown origin, making it difficult to regulate under the Clean Water Act. In 1987, the EPA added an amendment to the act to fund runoff management, which has had some success.

What does development have to do with it?

While runoff occurs in rural and agricultural settings, urban settings exacerbate the problem because of the large amount of impervious surface, such as asphalt or concrete.

As Jay Manning explained the problem to FRONTLINE, when rain lands on a forested area, it filters down through the forest canopy, through the soil and moves slowly through the groundwater to emerge clean in streams and rivers. If that forested area is developed, the rainwater lands instead on pavement, rooftop or other impervious surface. It moves across that surface more quickly and at a higher volume, which can result in flooding, damage to habitat in waterways and property damage for people downstream.

According to the EPA, "urbanization also increases the variety and amount of pollutants transported to receiving waters."

What can we do?

The EPA offers a list of household dos and don'ts to reduce your personal contribution, as well as fact sheets about different sources of runoff pollution, and a collection of sites and readings on related issues such as low-impact development.

The National Resources Defense Council offers a report looking at mitigation strategies in different regions.

Additionally, community groups in your area and your state's department of environmental protection or natural resources may offer information about runoff and mitigation strategies in your region.

posted april 21, 2009

poisoned waters home page · watch online · dvd/transcript · credits · site map
FRONTLINE series home · privacy policy · journalistic guidelines

FRONTLINE is a registered trademark of WGBH Educational Foundation.
Web Site Copyright ©1995-2014 WGBH Educational Foundation
main photograph © corbis, all rights reserved