October 30th, 2024

Nonpoint Source (NPS) Pollution

What is it?

Point source (PS) pollution comes from a specific source, such as industrial or sewage treatment plants. Nonpoint source pollution differs in that there is no specific source. It is an accumulation of both natural and manmade occurrences that are picked up by runoff. These can include fertilizer, oil and grease, sediment, bacteria and nutrients from livestock, and many others.

NPS pollutants are a leading cause of water quality problems and they cannot be monitored and managed the way PS pollutants are through the Clean Water Act. Another layer of difficulty in managing NPS is the nature of urban (and suburban) areas.

Nonpoint source figure that shows the difference between nature ground cover and impervious cover.
Relationship between impervious cover and surface runoff. Impervious cover in a watershed results in increased surface runoff. As little as 10% of impervious cover in a watershed can result in stream degradation (EPA, February 2003)

Why the added difficulty?

Large, uninterrupted coverage of pavement in these areas does not allow recharging of groundwater sources and leaves runoff as the only option for rainfall and snowmelt. This runoff inevitably leads to the accumulation of pollutants and carries them to surface level water sources.

The route of storm sewage systems builds and concentrates the volume and energy of the runoff. As it leaves the sewage system, that power and volume are dumped into a stream and damage streambanks and their ecosystems. In addition to pollutants, these waters often carry higher temperatures that adversely affect aquatic life.

Another, counterintuitive, effect of this runoff surge is the increase of drought to these stream areas. This is because the groundwater source has been neglected and is not suitable for sustaining the streams and rivers during dry months. Instead of nature maintaining a rhythmic homeostasis throughout the seasons, the disruption causes extreme flooding in wet months and drought in dry months.

What can we do?

Unironically, the solution to Nonpoint Source Pollution is to start at the source. This includes, but is not limited to, infrastructure design, litter maintenance, responsible gardening and lawn care, appropriate chemical disposal, septic system maintenance, etc.

Low Impact Developments (LID) utilize natural structure in designing infrastructure and allow stormwater flows to function as they would without the obstruction of human development. A common term for areas employing this is “Green Spaces”. These areas contain natural landscaping and encourage productive waterflow. Ultimately, utilizing LID methods preserves nature and lowers infrastructure and maintenance costs.