Nonpoint source (NPS) pollution occurs when rain runs off farmland, city streets, construction sites, suburban lawns, roofs and driveways, and enters our waterways. The 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" in 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 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.

States are required to assess their waters and identify those adversely affected by nonpoint sources of pollution. They must also assist local governments, soil and water conservation districts and individuals in restoring, protecting and improving water quality through grants provided by the Virginia Water Quality Improvement Fund. 

Steps to Help Control NPS 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.
• Participate in one of Virginia's Watershed Roundtables.
• Participate in restoration and planning opportunities in Virginia's Nonpoint Source Implementation program.