Storm Water is water from precipitation (such as rain or snowmelt), over-irrigation from sprinklers, wash water from hoses or hydrants, any other water that flows over the ground surface and enters a drainage way. This water picks up debris, sediment, nutrients, bacteria, and other pollutants that eventually flow, untreated, into creeks, streams and rivers. Impervious surfaces such as sidewalks, driveways, rooftops, and streets prevent storm water from soaking into the ground and therefore produce runoff.
As a result of federal regulations, referred to as the Phase II Storm Water Rule, storm water discharges from small Municipal Separate Storm Sewer Systems (MS4s) are required to obtain a storm water permit for their system. Pennington County was issued such a permit.