Helena Joyce
Stormwater runoff is one of the greatest threats to clean water in the US. As rainwater and snowmelt run off streets, parking lots, lawns, and other surfaces, they pick up and carry pollutants such as pet waste, pesticides, fertilizers, oils, and other contaminants into nearby lakes, rivers, and oceans. Urban and suburban areas with a high proportion of impervious surfaces such as pavement and buildings increase the risk of polluted runoff, as the water has no place to go but into local waterways.
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What You'll Learn
Urbanisation and loss of natural filters
Urbanisation, the process of transforming rural areas into urban environments, has had a significant impact on the environment and water quality. As cities expand, natural green spaces are replaced by concrete jungles, increasing impervious surfaces such as roads, rooftops, and parking lots. This disruption of the natural water cycle means that rainwater no longer soaks into the ground but instead rushes across these hard surfaces as stormwater runoff, picking up and carrying various pollutants.
This polluted runoff is a significant source of harmful nitrogen pollution, which continues to grow in watersheds. As rainwater and snowmelt run off streets, parking lots, and other surfaces, they collect a toxic mix of contaminants, including pet waste, pesticides, fertilizers, oil, heavy metals, microplastics, and other chemicals. These pollutants are then carried into local rivers, streams, and oceans through storm drains and ditches, untreated, posing risks to both the environment and human health.
The increase in impervious surfaces due to urbanisation has led to a higher volume of stormwater runoff. This, coupled with the loss of natural filters like forests, meadows, and wetlands, has resulted in increased stream power and flashier stormwater runoff response, causing erosive flows that reshape waterways and endanger aquatic life. The complex dynamics of urban areas, with a mix of impervious and pervious surfaces, also make it challenging to predict and manage stormwater runoff effectively.
To mitigate the impact of urbanisation on water quality, implementing "green infrastructure" solutions is essential. This involves strategic greening efforts, such as planting rain gardens and other natural spaces, using green roofs, and replacing old pavement with permeable pavements. These measures help slow down and absorb polluted runoff, reducing the risk of flooding and improving water quality. Additionally, proactive community actions, such as regular street sweeping and raising awareness about water pollution, can further safeguard water resources for future generations.
While urbanisation brings about advancements and economic growth, it is crucial to address the environmental challenges it poses, especially regarding water quality. By understanding the impact of impervious surfaces and the loss of natural filters, we can take steps towards more sustainable urban planning and water management practices.
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Impervious surfaces, like roads and pavements
Impervious surfaces, such as roads and pavements, are a significant contributor to polluted runoff. When rain falls on these surfaces, instead of being absorbed into the ground, it quickly flows into storm sewers and local waterways, a process known as stormwater runoff. This runoff water picks up various pollutants, including fertilizers, oils, pesticides, road salts, metals, and bacteria, which can have detrimental effects on the environment and human health.
The increase in impervious surfaces is a direct consequence of urbanization and development. As cities expand, natural landscapes are replaced by roads, pavements, buildings, and parking lots. This transformation reduces the area where water can infiltrate the ground, leading to increased volumes of stormwater runoff. The impact of this is twofold: firstly, it overburdens drainage systems, increasing the likelihood of localized flooding; and secondly, it introduces a multitude of pollutants into nearby creeks, rivers, and oceans.
The materials that comprise impervious surfaces, such as concrete, asphalt, and brick, are designed to be durable and water-resistant. While these characteristics are advantageous for withstanding vehicular traffic and pedestrian use, they inadvertently contribute to the volume of stormwater runoff. The smooth and impenetrable nature of these surfaces allows water to flow swiftly, picking up pollutants along the way and carrying them directly into nearby water bodies.
The accumulation of pollutants in stormwater runoff has severe ecological consequences. High concentrations of inorganic nitrogen and phosphorus, derived from fertilizers, lead to the creation of "dead zones" in water bodies like the Chesapeake Bay and the Gulf of Mexico. Additionally, the presence of road salts and metals in the runoff can elevate chloride levels beyond the tolerance limits of aquatic life, degrading entire aquatic ecosystems.
To mitigate the adverse effects of impervious surfaces on polluted runoff, several strategies can be employed. One approach is to implement green infrastructure solutions. This includes the use of permeable pavements, such as porous asphalt or concrete, which allow water to percolate below the surface, reducing the volume of runoff. Another strategy is the creation of rain gardens, which are designed to hold, filter, and slowly release stormwater, reducing the stress on drainage systems and improving the health of receiving streams.
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Fertilisers, pesticides, and other contaminants
Fertilisers, when not managed properly, can negatively impact plant and animal life. They can cause algae blooms, leading to oxygen depletion in surface waters, and introduce pathogens and nitrates into drinking water. Excessive fertiliser use results in high levels of dissolved nutrients in runoff water, increasing the risk of contaminating streams, wetlands, and lakes.
Pesticides, designed to kill or control pests, are often soluble in water to facilitate their application. However, this solubility increases the risk of leaching into water sources. The stability and half-life of pesticides also contribute to their persistence in the environment. Irrigation practices further increase the likelihood of pesticide migration into groundwater and surface water.
Other contaminants, such as copper from brake linings, zinc from car tires and road salt, and toxic metals like lead, chromium, and cadmium, are also present in runoff. These contaminants can have detrimental effects on aquatic life and the environment.
To address this issue, it is crucial to implement regenerative agriculture practices and adopt "green infrastructure" solutions. These strategies aim to reduce the use of fertilisers and pesticides, improve water filtration, and mitigate the harmful effects of polluted runoff on the environment and human health.
By taking proactive measures, we can minimise the impact of fertilisers, pesticides, and other contaminants on polluted runoff and work towards protecting our valuable water resources.
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Brake linings and toxic metals
Brake linings and tyres are major sources of toxic metal emissions in urban areas. These toxic metals are released into the environment as particles that wear away from the brake linings and tyres. Despite new regulations and efforts from the auto industry to reduce the use of these metals, they continue to be a significant source of pollution.
Brake linings are known to contain toxic metals such as copper, zinc, antimony, lead, and cadmium. These metals are released into the environment as brake linings wear down during use. Copper, in particular, has been detected in high levels, with the Maryland Department of the Environment finding it in 92% of runoff samples from urban areas. Additionally, 53% of the copper levels detected were acutely toxic to aquatic life.
Zinc and copper are the most common toxic metals emitted from brake linings, and their levels have remained relatively unchanged over the years. Lead and cadmium emissions, on the other hand, have decreased by one-tenth during the same period. While manufacturers have reduced metal concentrations in tyre treads, tyres remain a significant source of zinc and cadmium emissions.
The presence of these toxic metals in the environment poses risks to both ecosystems and human health. For example, toxic metals have been linked to an increased risk of atherosclerosis, a dangerous buildup of plaque in arteries that can obstruct blood and oxygen flow to vital organs.
To address this issue, researchers have suggested the use of regenerative braking systems, which can help reduce the emission of toxic metals from brake linings.
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Septic system failures
Septic systems are designed to treat household wastewater before it filters into the soil. However, if a septic system fails, untreated sewage is released, causing a health risk to humans and animals and polluting the environment. Septic system failures can be caused by a variety of factors, including:
Inlet baffle clogging
This occurs when the inlet pipe from the house to the tank is blocked by toilet paper and other debris. This can be prevented by only flushing human waste and toilet paper and having the system inspected annually.
Outlet baffle or effluent filter clogging
This may result in sewage backing up into the house or surfacing near the septic tank. This issue may indicate that the tank is receiving too much water and can be addressed by cleaning or replacing the effluent filter.
Drainfield failure
When the drainfield fails or becomes saturated with water, sewage may back up into the house, causing wet and soggy areas to develop above or near the drainfield. This could be due to improper operation, with too much solid material reaching the drainfield, or simply because the drainfield has reached the end of its lifespan.
Lack of routine maintenance
Most septic systems malfunction due to poor maintenance. Routine maintenance includes inspecting the system annually and pumping the tank every 3 to 5 years, depending on various factors such as tank size, the number of people in the household, and water usage habits.
Improper design or installation
Some soil-based systems are installed at sites with inadequate soil or excessive slopes, which can lead to hydraulic failures and contamination of nearby water sources.
Excess water use
Excessive water use can overload the septic system, leading to failures. It is important to be mindful of water usage and spread out activities such as laundry throughout the week.
Solid migration into the drainfield
Over time, solids in the tank can migrate into the drainfield, clogging the system. Regular pumping of the tank can help prevent this issue.
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Frequently asked questions
Polluted runoff is stormwater that has picked up pollutants from the ground and carried them into nearby waterways.
Sources of polluted runoff include streets, parking lots, roofs, farms, construction sites, and automotive facilities.
Polluted runoff can have harmful effects on the environment and human health. It can contaminate drinking water supplies, close swimming beaches, and harm or kill fish and other wildlife.
