Point vs Non-Point Water Pollution

By Jacklyn Hockey

Point:

Definition:

Defined as “any single identifiable source of pollution from which pollutants are discharged, such as a pipe, ditch, ship or factory smokestack”.

Sources:

Factories and sewage treatment plants are two types of point sources. Factories, including oil refineries, pulp and paper mills, and chemical, electronics and automobile manufacturers, usually discharge one or more pollutants into discharged waters. Sewage treatment plants treat human wastes and send the treated effluent to a stream or river.

Effects:

When there is an excessive amount of rain, a combined sewer system may not be able handle the volume of the rainwater, and some of the combined runoff and raw sewage will overflow from the system, discharging directly into the nearest waterbody without being treated. This combined sewer overflow is considered point source pollution, and can cause severe damage to human health and the environment.

Prevention:

To control point source discharges, the Clean Water Act established the National Pollutant Discharge Elimination System (NPDES). Under the NPDES program, factories, sewage treatment plants, and other point sources must obtain a permit from the state and EPA before they can discharge their waste or effluents into any body of water. The point source must use the latest technologies available to treat its effluents and reduce the level of pollutants before the discharge occurs. A second, more stringent set of controls can be placed on a point source to protect a specific waterbody, if needed.

Nonpoint:

Definition:

Pollution discharged over a wide land area, not from one specific location.

Sources:

Generally results from land runoff, precipitation, atmospheric deposition, drainage, seepage or hydrologic modification. Nonpoint source pollution, unlike pollution from industrial and sewage treatment plants, comes from many diffuse sources. NPS pollution is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters and ground waters.

Effects:

Most nonpoint source pollution occurs as a result of runoff. When rain or melted snow moves over and through the ground, the water absorbs and assimilates any pollutants it comes into contact with.


Nonpoint source pollution can also have harmful effects on the economy. U.S. Coastal and marine waters support 28.3 million jobs, generate $54 billion in goods and services through activities like shipping, boating, and tourism, and contribute $30 billion to the U.S. economy through recreational fishing alone.

Prevention:

Remove obstructions from stream channels and revegetate stream banks. Don’t mow all the way to the edge of a lake or pond. Leave a buffer of tall grasses or shrubs to filter pollutants. Landscape yards to minimize rainwater runoff. Preserve neighborhood trees that help minimize the damage caused by surface runoff. Place retaining walls or diversions on steeply sloping ground to reduce the rate of water flow and erosion. Make sure septic tanks work properly. Dispose of litter in garbage cans or in recycling bins. Recycle glass, aluminum, plastic, paper, motor oil, and newspapers. Compost yard and garden waste. Pick up pet waste and bag it with regular household trash or flush it in the toilet.