Difference Between Stormwater & Polluted Runoff

Point vs. Nonpoint Sources of Water Pollution

• Water pollution is classified as point or nonpoint, depending on the source of the pollutants. Point sources of pollution come from a single discrete source, such as a broken pipe, factory or confined animal feeding operation. They are relatively easy to identify and control. Nonpoint sources, or polluted runoff, cannot be linked to a single source of pollution. Nonpoint pollution comes from water running over the ground, picking up pollutants along the way and depositing them as it enters streams, rivers or lakes.

Nonpoint Pollution

• Nonpoint pollution is the technical name for polluted runoff. It comes from urban and rural sources, but the common thread is that they originate from places where humans have altered the land. Rural nonpoint water pollution can result from water washing herbicides, pesticides and fertilizers into water sources. Soil itself can also be a pollutant, adding sediment that plugs the gills of fish and invertebrates. Urban sources of nonpoint pollution include petroleum products and other toxic chemicals, herbicide and fertilizer runoff from lawns, road salt and fecal bacteria from pets.

Stormwater is a Type of Nonpoint Pollution

• Just like all squares are rectangles, but not all rectangles are squares, stormwater is a type of polluted runoff, but not all polluted runoff is stormwater. When rain falls on soil, it can be absorbed, making its way to the groundwater reservoir. When rain falls on roofs, sidewalks and roads in urban areas it simply runs off to be collected in storm sewers. This is important because it means that developed areas produce a greater volume of runoff than the same area of permeable ground. It also means that stormwater does not get filtered by the plants, bacteria and soil that could remove and even use some pollutants.

Specific Challenges of Stormwater Runoff

• There are several characteristics that set stormwater apart from other sources of nonpoint pollution. First, stormwater is generally collected in storm sewers by municipalities, moving large volumes of water into streams and lakes very quickly, causing erosion. Controlling the flow of stormwater does offer opportunities to divert it to holding ponds or otherwise mitigate the impacts of the water and the pollutants it carries. Another distinctive quality of stormwater is that agricultural runoff may contain large amounts of one pollutant, but stormwater runoff contains a wide range of pollutants.