Removing Pollutants from Stormwater

Stormwater Pollution can be divided into three categories:
Natural — organic material such as leaves, grass clippings and sediment
Chemical — such as detergents, coolant, oil, grease, fertilizer and paint
Litter — such as plastic bags and cigarette

Stormwater is vehicle for transporting pollutants into our waterways, rivers, lakes and streams.  During a rainstorm or snowmelt, chemicals and sediments are conveyed into our waterways.  These discharges cause significant damage to our environment and aquatic life.  This is otherwise known as nonpoint pollution (unlike pollution that originates directly from industrial and sewage treatment plants).

The effects of nonpoint source pollutants on specific waters vary and may not always be fully assessed. However, we know that these pollutants have harmful effects on drinking water supplies, recreation, fisheries, and wildlife.

Some pollutants are toxic, and in small concentrations, can greatly impact an entire ecosystem.   Nutrients produced in great quantities can overwhelm a natural system, causing toxic algae blooms, changes in oxygen levels, along with other problems in our waterways.

Effective removal of these stormwater pollutants is accomplished through choosing the most applicable Best Management Practice (BMP).  BMP maintenance is equally important to the “system” effectiveness. 

We will walk you through each of the pollutant types commonly found in stormwater when run-off is not treated properly.  Here you will find a list of common sources of pollutants and the impacts on the environment.

Selecting the Right Treatment

A variety of treatment technologies are available to manage stormwater, and the effectiveness of each on specific pollutant removal is quite diverse.  Some treatment technologies are very effective at removing pollutants or nutrients than others, often causing the decision to select a technology based on a prioritization of pollutant removal. 

Treating a variety of pollutants may require multiple structural and non-structural BMPs, known as a treatment train.   Understanding the pollutant removal effectiveness and various levels of performance (ex: 80% removal efficiency) can assist you in achieving your stormwater goals.

Nitrogen

Harmful Effects:
Nitrogen promotes toxic and non-toxic algae blooms which harm aquatic life by depleting the amount of oxygen in the water and by decreasing light penetration for photosynthetic organisms   This pollutant also promotes unwanted weeds.

Sources
Decaying vegetation
Organic matter
Treated wastewater
Biodegradable detergents
Irrigated lawns
Fertilizers
Animal wastes

Oil/Grease

Sources
Vehicle & Equipment areas
Industrial areas
Poor Storage of oil drums
Food preparation

Harmful Effects:
High amounts of petroleum products enter stormwater run-off from parking lots, roads, and gas stations, and where cares and automobiles are congested.  An accumulation of oil and grease forms a film over water which spreads and makes oxygen transfer difficult and toxic for aquatic animals and plants.  One gallon of oil can contaminate one million gallons of drinking water.

Sediments/Solids

Harmful Effects
The accumulation of sediments and solids in water have significant negative impact on the environment.  These negative effects include:

• A decrease in visibility and increase in turbidity for aquatic organisms, making it difficult for these organisms to capture prey
• A decrease in light availability for photosynthetic organisms
• Closing of gills in fish and aquatic species
• Reduction in spawning of fish and general surviva
• Increase in the transportation of heavy metals, phospherous and other pollutants through waterways as they attach to the sediment particles and harm water quality

Sources
Sand/gravel storage
Construction sites
Unpaved areas
Agriculture/livestock uses

Phosphorous Compounds

Harmful Effects
Phospherous compounds promote toxic and non-toxic algal blooms which harm aquatic life by depleting the amount of oxygen in the water and by decreasing light penetration for photosynthetic organisms promotes unwanted weed growth.

Sources
Decaying vegetation
Organic matter
Treated wastewater
Biodegradable detergents
Animal faeces
Irrigated lawns
Fertilizers
Animal wastes

Metals

Harmful Effects
Metals have toxic effects on aquatic plants and animals and can bioaccumulate in aquatic species, such as mussels, which can then have a dangerous impact all the way through the food chain. Trace metals, such as arsenic, copper, cyanide, mercury, nickel, and lead come from and even air emissions from far away factories. These metals are toxic to aquatic life and accumulate in the sediments of streams, lakes, and estuaries as well as in fish tissue. These metals may come from pesticides, industrial waste discharges, solid waste landfill leachate, agricultural waste, or corroding metal pipes and storage tanks.  

Sources

Cadmium: burning of fossil fuels, paint, batteries and electroplating

Chromium: air-conditioning coolants, timber treating works, leather tanning works and electroplating

Copper: vehicle brake pads, natural minerals, copper plumbing, irrigation water and pesticides

Zinc: vehicle tires, motor oils, galvanizing works, corrosion from galvanized iron

Lead: mainly car exhausts and engines

Arsenic: brake linings, fluid leaks, vehicle emissions

Bacteria (Fecal Coliform)

Harmful Effects
The accumulation of bacteria from wastes pose not only a serious threat to the environment, but also to public health standards, especially for waterways where recreational activities take place.   Fecal bacteria increases nutrient levels in stormwater which can cause imbalances in the chemistry and lead to toxic algal blooms.  From stormwater, these bacteria make their way into streams and lakes, which can lead to closure of shellfish beds and swimming beaches.

Sources
Animal Wastes
Fertilizers

pH

Harmful Effects
Alters the chemical balance of our waterways, which may kill some aquatic plants and animals.

Sources
Metal plating
Printing/Graphic industries
Cement/concrete production
Cleaners
Groundwater. Possibly also from air-conditioner bleed off water.

Biological Oxygen Demand (BOD) & Trace Organics

Harmful Effects
When organic matter breaks down from bacteria, it exerts oxygen demand. Organic matter, such as leaves, grass, and tree branches, affect water quality because as they decompose, they deplete the level of oxygen in the water. Reduced oxygen has a detrimental affect on aquatic life, including fish, bugs and plants.

Litter

Harmful Effects
Litter produces an obvious visual pollution which can physically damage aquatic animals and fish and can release substances poisonous to natural systems as it breaks down.

Sources
Litter and packaging, general garbage, tree litter and vegetation