Sources of Contamination in Urban Runoff

Sediment-loaded stream

Street Pavement: The components of road surfaces, including breakup and degradation of asphalt, tar, and other oil-based substances are sources of contamination in urban runoff.
Motor Vehicles: Fuels and lubricants spill or leak, particles are worn off from tires or brake linings, exhaust emissions collect on the road surface, and corrosion products or broken parts fall from vehicles. While the quantity of material deposited from individual vehicles may be small, the combined impact from numerous vehicles is significant. Automotive service stations tend to have high concentrations of the above contaminants.
Atmospheric Fallout: Air pollutants include dust, contaminants and particles from stacks and vents, from automobiles and planes, and from exposed land. The airborne matter will settle on the land surface and wash off as contaminated runoff.
Vegetation: Leaves, grass clippings, and other plant materials that fall or are deposited on urban land may become part of the runoff problem. Quantities depend on the geographic location, season, landscaping practices, and disposal methods.
Spills: Producers and manufacturers must store and use large quantities of hazardous substances to supply the goods we demand. Sometimes - through mismanagement, neglect, or accidents - leaks or spills of these substances introduce them into the air, land and water. Consumer products such as paint thinner, lacquers, wax resins, detergents, etc., also find their way into storm drainage systems.
Litter: This consists of various kinds of discarded refuse items, packaging materials, and animal droppings. Although the quantities may be small, the pollutant sources can be significant and may be the most visible form of urban runoff.
Anti Skid Compounds and Chemicals: In the northeast, urban areas employ large amounts of substances designed to melt ice in the winter. Salts, sand, and ash are the commonly used agents. A variety of other chemicals may be used as fertilizers, pesticides and herbicides. Many of these substances will become part of the urban runoff when improperly stored or applied.
Construction Sites: Soil erosion from land disturbed by construction is a highly visible source of solids in urban runoff. Important sites include large-scale projects such as highway construction and urban renewal. Construction methods and control measures will influence stormwater quantity and quality. Storm Sewers: These tend to accumulate deposits of materials that will eventually be dislodged and transported by storm flows.
Combined Sewer Overflow: Wet-weather loading from combined storm/sewage overflows may be many times larger than loads discharged from sewage treatment plants during storms, and equal or exceed total annual discharges from sewage treatment plants. (This will only occur in areas of existing development having combined sanitary and storm sewers.)
Home Septic Systems: Failing or poorly designed and/or located systems are more likely to overflow during wet weather periods. Sewage may then be carried with runoff into receiving waters.