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What is Stormwater?

What Is Stormwater?

Stormwater is water resulting from rain or snowmelt that runs off surfaces such as rooftops, paved streets, highways and parking lots. Along the way, the water may pick up and transport contaminants including motor oils, gasoline, antifreeze, and brake dust (commonly found on pavements), fertilizers and pesticides (found on landscaped areas), and soil sediments (from farms and construction sites). The water eventually flows into a local stream, river or lake, or into a storm drain and continues through storm pipes until it is released untreated into a local waterbody.

Stormwater results in significant pollution to surface water affecting primary contact recreation such as swimming and aquatic life use support.  Pollutant sources related to stormwater runoff are discussed below.

  • Impervious surfaces such as roads, driveways, decks, and even compacted soils, change the way the water flows over and through the land. They prevent stormwater from soaking into the ground, which increases the volume of stormwater runoff that needs to be managed by the City. Unmanaged stormwater runoff contributes to flooding, erosion, reduced water quality, and reduced groundwater recharge.
  • Erosion is the gradual wearing away of land by water, wind, or ice. During construction, land can be disturbed by excavation, filling, and paving. This can increase erosion by exposing the soil to stormwater. Nutrients such as phosphorus have the ability to “stick” to soil and can be transported to lakes and rivers.
  • Fertilizer, pet waste, and septic systems can contribute excess nutrients that speed up plant and algae growth, including cyanobacteria, which can harm humans and animals and can be a nuisance for swimming and boating. They can also contribute bacteria that can make swimmers sick and lead to beach closures.
  • Other pollutant sources that may contaminate stormwater runoff include salt and deicing materials, lawn and agricultural pesticides, and automobile chemicals among others. Many of the chemicals in these products may be toxic to aquatic organisms, humans, and other animals.