What Pollutants are Found in Stormwater?
Characterizing Contaminants - the First Step Clean-up
Jul 9, 2009
Stormwater pollution is finding increasing importance in the work in environmental protection efforts. As non-point source, control of contamination in stormwater run-off is taking time to develop because of the difficulty of characterizing the nature and quantity of pollutants in the run-off. The first effort to make this characterization happened in the mid-1980s, yet more work is still needed.
First Attempt to Categorize Stormwater Pollutants: the NURP
Following amendments to the Clean Water Act enacted by Congress, amendments which mandated that the EPA address non-point sources of pollution to waters of the US, the EPA launched a large-scale program to sample stormwater and measure and categorize pollutants in it. Called the National Urban Runoff Program (NURP), this study sampled 2,300 rainfall events at eighty-one sites that were representative of urban conditions in the United States.
This gave a good, first look at just what kinds of contaminants might be in urban run-off that could be harmful to the environment. From this data, the EPA was able to issue Phase 1 stormwater regulations in 1991, establishing a system of permits under which the most likely polluters of stormwater would be allowed to discharge.
Additional Work on Stormwater Pollutant Measurements
Since the NURP gave America its first real data on what pollutants are in stormwater, additional work has been done to characterize pollutants in stormwater. EPA has been in the forefront of this, and their website contains much data and guidance for urban stormwater pollution.
EPA is not alone in the efforts to characterize the pollution potential of stormwater. Many universities have programs for sampling and analyzing stormwater. Most State highway departments also have such programs. In addition, many cities in the US are required to sample run-off and keep records as a condition of their stormwater discharge permit. All of this data is slowly building up into a database that will help civil engineers plan and design stormwater treatment.
Typical Pollutants in Stormwater
The Stormwater Authority web site includes a comprehensive listing of what pollutants might be found in stormwater. They break these down into natural pollutants, chemical pollutants, and litter. These might include any of the following.
- Nitrogen: promotes 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 are: decaying vegetation, organic matter, treated wastewater, biodegradable detergents, irrigated lawns, fertilizers, animal waste, and others.
- Oil/grease: Petroleum products form a film over water which spreads and makes oxygen transfer difficult and toxic for aquatic animals and plants. Sources of petroleum in stormwater include: vehicle and equipment areas, industrial plants, substandard drum storage, food preparation facilities (retail and commercial), and others.
- Sediment/solids: are the largest pollutant constituents in stormwater. They accumulate and have significant negative impacts on the environment, including: increase in turbidity, making it difficult for aquatic organisms to capture function normally; decrease in light for photosynthesis; contamination of gills in fish and aquatic species; reduction in spawning of fish and general survival; increase in the transportation of heavy metals, phosphorous and other pollutants through waterways as they attach to the sediment particles and harm water quality. The sources of sediment in urban run-off are many, including sand and gravel storage, construction sites, unpaved areas, agriculture/livestock uses, and wash-off of dirt from almost every manmade surface.
- Phosphorous chemicals: similar to nitrogen in terms of harmful effects and sources.
- Metals: toxic to aquatic plants and animals in certain concentrations, and can bioaccumulate in some species, such as mussels. 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. The sources are many, including transportation equipment, manufacturing, and pesticides.
- Bacteria: pose not only a serious threat to the environment, but also to public health, especially 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 are animal wastes, treated wastewater, industrial effluent, and fertilizers.
- pH: Anything that alters the chemical balance of our waterways may kill some aquatic plants and animals. Sources of this imbalance are metal plating, printing/graphic industries, cement/concrete production, cleaners, and others. Air conditioner bleed-off water may also contribute.
- Biochemical oxygen demand: An all encompassing pollutant that will develop due to other pollutants in the water.
This only a general listing of what contaminants (pollutants) might be found in stormwater—in neighborhood run-off, in roadside ditches, in streams, and in rivers. Clean-up efforts revolve around removing some one or more of these items from run-off.
The attempt to clean up storm water is truly in its infancy, and considerably more work is needed to improve the characterization of stormwater pollution and thus better target treatment methods and costs.
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