Stormwater Runoff

Stormwater Runoff is Not Clean Water

Stormwater runoff carries pollutants that can seriously harm our waters.

Cause

Land development projects typically replace existing natural ground features with new impervious surfaces such as driveways, rooftops, sidewalks, and streets. Stormwater runoff occurs when water from snowmelt and rain can no longer infiltrate into the ground. The runoff can carry toxic materials into our stormwater drainage systems, including:

• Bacteria
  • Microorganisms - Bacteria, viruses, and other disease-causing organisms make waterways unsafe for swimming, wading, and other types of recreation. Some of these organisms, notably Cryptosporidium, may endanger the health of people who come in contact with lakes and streams high in microorganisms. Sources of bacteria and viruses in urban runoff are pet wastes; bird droppings from pigeons and geese, other urban wildlife (squirrels, chipmunks); and sanitary sewer overflows.
• Soil Particles
  • Sediment - During construction projects, the soil is exposed and susceptible to erosion when vegetation is removed from the landscape. Rain falling on bare soils can cause erosion and create stormwater runoff that carries soil particles, known as sediment. Construction sites are one of the largest sources of sediment that can pollute a city's water resources.
    • Sediment deposited in a lake or stream makes the water cloudy or turbid. When sediment settles out of the water, it gradually fills in the stream, lake bed, or wetland and can destroy fish spawning areas and other aquatic habitats. Construction sites are not the only source of sediment. Freeways, industrial sites, commercial sites, institutional, and residential development can also contribute significant sources of sediment in stormwater runoff.
• Nutrients
  • Phosphorus and Nitrogen - Runoff from both urban and rural areas contains nutrients such as phosphorus and nitrogen. Phosphorus, often carried in with the sediment, fuels the growth of algae and aquatic weeds. Rapid and excessive growth of algae and aquatic plants can degrade water quality and interfere with swimming, fishing, and other recreation. When algae die, they sink to the bottom and decompose in a process that removes oxygen from the water. Fish and other aquatic organisms die when dissolved oxygen levels are lowered.
    • Phosphorus compounds attach to the soil particles in sediment, but phosphorus can also be in a soluble form. Urban sources of phosphorus include lawn fertilizers, pollen, leaves, grass, and orthophosphate in vehicle exhaust. One pound of phosphorus can produce 300-500 pounds of algae.
• Oil & Pesticides
  • Toxic Chemicals - Motor oil, gasoline, grease, automotive antifreeze, lead from gas and auto exhaust, zinc from roof drains and tires, and other toxic chemicals in stormwater runoff may kill aquatic organisms or impair their health, growth, or ability to reproduce. Road salt mixed with stormwater runoff can also be toxic to aquatic life.
    • Household hazardous wastes like insecticides, pesticides, paint and solvents can poison aquatic life. Land animals and people can become sick or die from eating diseased fish and shellfish or ingesting polluted water.
• Pet Waste, Debris & Trash
  • Oxygen Demanding Materials & Other Wastes - Organic materials such as pet waste, leaves, grass clippings, and litter in storm water runoff use up oxygen as they decay. After a storm sewer washes this type of organic waste into an urban waterway, it can deplete the oxygen in that waterbody. Fish kills can result when oxygen levels drop.
    • Debris such as plastic bags, six-pack rings, bottles and cigarette butts washed into water bodies can choke, suffocate, or disable aquatic life like ducks, fish, turtles and birds.
• Fertilizers

Wetlands, streams, lakes, and rivers ultimately receive the discharging waters from all city stormwater systems.

Dangers

Polluted runoff contributes to:

• Decline in recreational uses of lakes.
• Deceased fish
• Habitat destruction
• Reduction in drinking water quality.
• Stream siltation

Stormwater Runoff Can Cause Waterway Erosion

Development changes the natural flow of water across the landscape. Construction of new buildings and parking lots in areas that were fields or woods typically reduces infiltration and increases stormwater runoff, which leads to flashy flows in area streams during storm events and no flow during dry conditions. Higher flows in streams can create erosion, loss of aquatic habitat, and sediment deposition downstream.