Nonpoint source pollution occurs when rain runs off farmland, city streets, construction sites, and suburban lawns, roofs and driveways and enters our waterways. This runoff often contains harmful substances such as toxics, pathogens, excess nutrients and sediments. It is called nonpoint source pollution because it does not come from a single source, or point, such as a sewage treatment plant or an industrial discharge pipe. Therefore nonpoint source pollution does not meet the legal definition of "point source" from Section 502(14) of the Clean Water Act.
There are four main forms of nonpoint source pollution: sediments, nutrients, toxic substances and pathogens.
- Sediments are soil particles carried by rainwater into streams, lakes, rivers and bays. By volume, sediment is the greatest pollutant of all. It is caused mainly by erosion resulting from bare land, some farming practices, and construction and development.
- Nutrients are substances that help plants and animals live and grow. The main concern is excessive amounts of two nutrients: nitrogen and phosphorus.
- Toxic substances are chemicals that may cause human and wildlife health concerns. They include organic and inorganic chemicals, metals, pesticides, household chemicals, gasoline, motor oil, battery acid, roadway salt and other pollutants.
- Pathogens are disease-causing microorganisms present in human and animal waste. Most pathogens are bacteria.
Virginia's nonpoint source pollution prevention efforts focus strongly on managing nutrients and sediments because they pose the most significant threat to the health of our waterways, especially the Chesapeake Bay and its tributaries.
Impacts of nonpoint source pollution
Nonpoint source pollution from farms yields sediment, toxic substances and excess nutrients. Statewide, farmland loses several tons of soil per acre per year. While this soil is productive on land, in the water it reduces light needed by aquatic plants, obstructs waterways and covers aquatic habitat with sediment. Soil from farmland sometimes takes with it pesticides and nutrients. An estimated 50 percent of the nitrogen and 29 percent of the phosphorus entering surface waters come from farmland.
In addition, urban and suburban areas contribute significant levels of nutrients as well as toxic substances, pathogens and sediment. City streets and other impervious surfaces yield pollutants such as motor oil, gasoline, antifreeze and other toxic chemicals. Because these surfaces do not absorb rainwater, runoff from urban areas is nine times greater than runoff from forest land.
Life in Virginia’s rivers, streams, lakes and bays could not exist without nutrients. But excess nutrients over-enrich our waterways, causing algal blooms that deplete oxygen. This makes the oxygen unavailable to fish and shellfish, so they suffocate and die. The algae also cloud the water and coat underwater vegetation, reducing much-needed sunlight.
Sediment clouds water too, and it obstructs waterways, clogs sewers, interferes with navigation, and smothers fish and shellfish spawning grounds. Natural erosion and sedimentation occur at a lower rate than that resulting from human land use activities. Underwater plants and aquatic animals are particularly threatened by nonpoint source pollution.
Steps to help control nonpoint source pollution
- Fertilize lawns and gardens according to soil test results. Contact a local extension agent for instructions.
- Apply pesticides according to instructions on the label.
- Collect litter and animal waste before they wash into storm drains.
- Recycle grass clippings and leaves by mulching or composting.
- When changing engine oil, take the used oil to a recycling station. Never dump oil into a storm drain.
- Home septic tanks should be located, constructed and installed according to regulations. Maintenance and prompt correction of problems are important.
- Direct roof runoff onto a grassed area or into a rain barrel.
- Watch for soil erosion. Seed, install sod or plant ground cover to protect an eroded site.
- Use porous surfaces such as flagstone, gravel, stone and interlocking pavers rather than concrete or asphalt.
- If there are concerns about the effects of runoff leaving a construction site, contact the local governing body responsible for erosion and sediment control. Most land disturbance is regulated by local ordinances under the Virginia Erosion and Sediment Control Law.
- Join a civic or environmental group and participate in stream cleanup activities, such as the Department of Conservation and Recreation's Adopt-a-Stream.
- Participate in one of Virginia's Watershed Roundtables.
- Participate in restoration opportunities in Virginia's Nonpoint Source TMDL Implementation Projects.