Understanding Stormwater And Its Sources Of Pollution

Stormwater is water that comes from precipitation events such as heavy rain, hail, and snowmelt. It can either soak into the soil, be stored on land surfaces in ponds and puddles, or contribute to surface runoff. Stormwater runoff is when stormwater flows over the land and into nearby streams, rivers, or other large water bodies. This runoff can pick up and carry pollutants such as trash, sediment, nutrients, bacteria, pesticides, metals, and petroleum byproducts, which can contaminate these water bodies and harm fish and wildlife populations. Urban areas with a high proportion of impervious surfaces, such as pavement and buildings, are particularly susceptible to generating stormwater runoff and the associated pollution.

What is Stormwater and How Does it Become Polluted?

Stormwater is water from precipitation, including rain and snowmelt

In undeveloped areas, precipitation typically soaks into the ground. However, in urban and suburban areas with extensive paved surfaces and hard landscapes, the ground cannot absorb water effectively. This leads to the generation of stormwater, which can cause flooding and infrastructure issues. During heavy rainfall or snowmelt, wastewater systems may overflow, discharging untreated sewage into nearby water bodies.

Stormwater becomes polluted as it flows over these impervious surfaces, collecting pollutants such as bacteria, oil, chemicals, trash, debris, and excess nutrients. These pollutants are picked up from streets, parking lots, lawns, and other contaminated areas. The polluted stormwater then enters storm drains and is discharged into lakes, rivers, streams, or coastal waters without treatment. This polluted runoff is the leading cause of water pollution in the United States.

The impact of polluted stormwater on the environment and public health is significant. It contaminates drinking water sources and swimming areas, posing risks of various diseases, including diarrhea, vomiting, respiratory infections, hepatitis, and dysentery. Additionally, the pollutants harm aquatic life, leading to the destruction of aquatic habitats and the suffocation of fisheries.

To address stormwater pollution, it is essential to implement green infrastructure and natural stormwater management techniques. These approaches aim to slow down and disperse stormwater, allowing it to infiltrate the ground and be filtered by plants. Examples include rain gardens, pervious pavement, rain barrels, and green roofs. Individual actions, such as proper waste disposal, reducing trash, and participating in waterway cleanups, are also crucial in mitigating stormwater pollution.

Stormwater can infiltrate the soil or contribute to surface runoff

Stormwater is water from rain or snow storms that cannot soak into the ground due to the presence of buildings, parking lots, roads, and other hard, impervious surfaces. This water, instead of being absorbed into the soil, flows over these surfaces and into a storm drain or body of water. This is known as stormwater runoff.

Stormwater runoff can become polluted as it flows over streets, parking lots, and roofs, collecting excess nutrients and pollutants. These pollutants include bacteria, oil, road salt, toxic chemicals, motor oil, gasoline, grease, automotive antifreeze, and more. These pollutants are often deadly to aquatic life, such as salmon and orcas, and can harm or kill fish and other wildlife.

Stormwater can infiltrate the soil through stormwater infiltration practices. This is the process by which stormwater flows into and through the subsurface soil. Stormwater infiltration occurs when rainfall lands on pervious surfaces, when runoff flows across these surfaces, or when runoff is collected and directed to a stormwater infiltration Best Management Practice (BMP). Infiltration BMPs capture, retain, and infiltrate stormwater, and they can be installed as offline treatment systems.

In urban areas, stormwater infiltration can be enhanced by disconnecting impervious surfaces and improving pervious surfaces. For example, routing discharge from a roof drain onto a lawn promotes infiltration and reduces overall site runoff. Infiltration practices can remove some types of physical and chemical pollutants, but careful consideration is needed when implementing these practices in potential stormwater hotspots or contaminated sites. Contaminated sites require management options to ensure that infiltration does not mobilize contaminants in the soil or groundwater.

Stormwater runoff is worsened by human activities and can contain many pollutants

Stormwater runoff is a significant issue, especially in urban and suburban areas with extensive paved surfaces. When rain or snowmelt, known as stormwater, flows over impervious surfaces like streets, parking lots, and roofs, it collects various pollutants before entering storm drains or water bodies. This problem is often exacerbated by human activities, leading to contaminated runoff that poses environmental and public health risks.

Human activities play a significant role in worsening stormwater runoff. Urbanization has altered the natural water flow patterns by introducing hard surfaces that prevent water from soaking into the ground. As a result, stormwater flows over streets, parking lots, and other paved areas, picking up pollutants such as oil, chemicals, trash, and debris. This polluted runoff then enters storm drains, leading to water bodies like rivers and streams.

The pollutants in stormwater runoff can come from various human activities and sources. For example, household hazardous wastes, such as insecticides, pesticides, paint, solvents, and used motor oil, can be accidentally or intentionally washed into nearby waterways. Fertilizers, pet waste, and yard waste also contribute to the pollution, adding excess nutrients like nitrogen and phosphorus to the water.

In addition to the direct pollution of stormwater, human activities can also worsen runoff by altering the surrounding lands, known as the watershed. This alteration changes the way stormwater soaks into the ground or flows to local rivers, affecting the consistent supply of clean water that rivers depend on. When stormwater is mismanaged and treated like waste, it exacerbates flooding and becomes further contaminated with pollutants.

The consequences of polluted stormwater runoff are far-reaching. It affects aquatic life, with pollutants like oil, bacteria, and excess nutrients proving deadly to species like salmon and orcas. Polluted runoff also impacts water quality, with sewage overflows carrying pathogens that can end up in drinking water supplies and swimming areas, posing health risks to humans.

To mitigate the issue of stormwater runoff, various measures can be implemented. Green infrastructure, such as rain gardens, pervious pavement, rain barrels, and green roofs, can help slow down and infiltrate stormwater while providing natural filtration through plants. Additionally, proper waste disposal, reducing trash, and responsible chemical use can help prevent pollutants from entering stormwater in the first place.

Stormwater sewers collect runoff from impervious surfaces and transport it to nearby water bodies

Stormwater is rainwater or snowmelt that flows over the ground. In undeveloped areas, this precipitation soaks into the ground. However, in urban areas, the ground is often covered with impervious surfaces such as roads, parking lots, and roofs, which prevent the water from being absorbed. This results in increased runoff, which is collected by stormwater sewers and transported to nearby water bodies.

Stormwater sewers are designed to quickly transport runoff away from commercial and residential areas to prevent localized flooding. While this is important for flood control, it also means that the water is not filtered or treated before being released into natural water bodies. This can lead to pollution as the stormwater picks up various pollutants as it flows over impervious surfaces.

Pollutants commonly found in stormwater include trash, sediment, nutrients, bacteria, pesticides, metals, petroleum byproducts, and fertilizers. These pollutants can have harmful effects on the environment, including endangering soil integrity, reducing water quality, and killing aquatic life.

To address the issue of stormwater pollution, individuals and municipalities can take several measures. Redirecting downspouts towards planted areas instead of impervious surfaces can help reduce the amount of stormwater runoff and allow for some natural filtration. On a larger scale, implementing green infrastructure, such as rain gardens, pervious pavement, and green roofs, can help slow down and filter stormwater before it enters sewers or natural water bodies.

In the United States, the Clean Water Act requires towns and cities with populations greater than 10,000 to reduce the amount of pollution in stormwater runoff. This includes implementing measures to reduce pollutant loading and manage runoff volumes.

Stormwater pollution can be prevented with green infrastructure and other techniques

Stormwater is water from rain or snow that flows over the ground and into a body of water or a storm drain. In undeveloped areas, precipitation soaks into the ground. However, in urban and suburban areas, stormwater runs over pavement and parking lots, picking up oil and other pollutants before flowing into a nearby river or stream. This process, known as stormwater runoff, is often worsened by human activities, collecting excess nutrients and pollutants such as nitrogen and phosphorus from fertilizers, pet and yard waste, bacteria, and other toxins.

Examples of green infrastructure techniques include rain gardens, pervious pavement, rain barrels, and green roofs. Rain gardens are garden beds or street tree pits designed to treat stormwater runoff. They use special soil filter media to remove pollutants from road runoff. Pervious pavement, also known as permeable pavement, allows rainfall to move through the pavement to the soil beneath, providing water to nearby landscape areas. Permeable pavement can take the form of block pavers with infiltration gaps between them or porous material with infiltration gaps within it. Green roofs capture and slowly release rainwater, reducing the amount of runoff that rushes into a watershed, which helps curb flooding and erosion. The vegetation found on green roofs also captures carbon dioxide, which gets stored in plants and soil.

In addition to green infrastructure, other techniques can be used to prevent stormwater pollution. These include properly disposing of paint, cooking oil, grease, and trash, as well as avoiding the spread of chemicals, fertilizers, and insecticides outdoors. Reporting spills promptly can also help prevent stormwater pollution, as the sooner a spill is reported, the quicker it can be addressed.

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