What is polluted runoff?

As water flows over yards, farmland parking lots, roads, open spaces and other surfaces, it can pick up pollutants from the ground and carry them, through both natural and man-made drainages, to our local streams and rivers and eventually to the Pacific Ocean. Some of these pollutants can be very harmful to the environment.

Do you know the difference between the sanitary sewer system and the storm drain system?


Illustration by John Finger courtesy of the City of Palo Alto

The water that goes down a sink, toilet or floor drain in a home or business travels through the sanitary sewer system and ends up at a wastewater treatment plant, where most pollutants are removed with filters and treatment. The water is then discharged, under a permit, to a waterway or used as recycled water.

storm drainOn the other hand, the water that flows down the storm drain from parking lots, roads, agricultural fields or other surfaces is not treated. It flows directly to a local creek, then to the San Joaquin River, the Delta and eventually the San Francisco Bay and the Pacific Ocean.

Common pollutants that end up in runoff include motor oil, pesticides and herbicides, brake dust, pet waste, household chemicals and more. The 2005 California Water Plan reports that In the San Joaquin River watershed, it is believed that the main water quality problems are the result of many factors, including:

  • reduced freshwater flows into the river;
  • permitted and unpermitted municipal and industrial wastewater discharges;
  • runoff from urban areas such as parking lots and roads;
  • natural and imported salt loads from higher up in the watershed agricultural drainage; and
  • runoff and other pollutants associated with long-term agricultural irrigation and production, including nutrients, selenium, boron and organophosphate pesticides.

These pollutants can have harmful effects on wildlife, recreation and on our drinking water supplies. Runoff in California is regulated by the State Water Resources Control Board and, in our area, by its Central Valley Regional Water Quality Control Board.

What Can You Do to Keep the River Clean?

Find out more about polluted runoff at the federal Environmental Protection Agency and the California Environmental Protection Agency Web sites.

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