§ 2.2. Stormwater Runoff Constituents and Sources

Urban runoff contains many types and forms of constituents; some occurring in higher concentrations than found in runoff before development and some that are not naturally present in surface runoff from undeveloped land. Runoff from undeveloped watersheds contains sediment particles, oxygen-demanding compounds, nutrients, metals, and other constituents. Once developed, constituent loads increase because surface runoff volumes increase and the sources of many of these pollutants also increase. Also, additional sources of constituents may exist in a catchment and find their way into runoff. They may include the following:

• Metals, lubricating compounds, solvents, and other constituents originating from vehicles, machinery, and industrial and commercial activities.

• Pesticides, herbicides, and fertilizers.

• Household solvents, paints, roofing materials, and other such materials.

• Pet litter, garbage, and other debris.

• Suspended solids washed off impermeable surfaces.

• Increased soil erosion during construction activities.

Table SQ-1 lists the common constituents in stormwater runoff and their impacts.

TABLE SQ-1 URBAN RUNOFF POLLUTANTS

Constituents	Sources	Effects
Sediments - TSS, Turbidity, Dissolved Solids	Construction sites urban/agricultural runoff landfills, septic fields	Habitat changes, stream turbidity, recreation and aesthetic loss, contaminant transport, bank erosion
Nutrients - Nitrate, Nitrite, Ammonia, Organic Nitrogen, Phosphate, Total Phosphorus	Lawn/agricultural runoff, landfills, septic fields, atmospheric deposition, erosion	Algae blooms, ammonia toxicity, nitrate toxicity
Pathogens - Total and Fecal Coliforms, Fecal Streptococci Viruses, E.Coli, Enteroccus	Urban/agricultural runoff, septic systems, illicit sanitary connections, domestic/wild animals	Ear/intestinal infections, shellfish bed closure, recreation/aesthetic loss
Organic Enrichment - BOD, COD, TOC and DO	Urban/agricultural runoff, landfills, septic systems	Dissolved oxygen depletion, odors, fish kills
Toxic Pollutants - Metals, Organics	Urban/agricultural runoff, pesticides/herbicides, underground storage tanks, hazardous waste sites, landfills, illegal disposals, industrial discharges	Toxicity to humans and aquatic life, bioaccumulation in the food chain
Salts - Sodium Chloride	Urban runoff snowmelt	Contamination of drinking water, harmful to salt intolerant plants
Source: Handbook: Urban Runoff Pollution Prevention and Control Planning, 1993.