Storm drains effectively prevent floods after storms by giving rainwater a place to go. However, these drains don’t just deal with rain. As water flows down the streets, it picks up chemicals, dirt, debris, bacteria, and other pollutants. It can even pick up other types of urban runoff, such as trash, metal, and gasoline. And it carries these contaminants through the drain and out to the local environment.
These pollutants harm wildlife-and even humans-when they enter our water sources or litter our street gutters.
According to a recent study, one of the best ways to eliminate this runoff from our cities is through street sweeping. The Massachusetts study, “Potential Reductions of Street Solids and Phosphorus in Urban Watersheds from Street Cleaning, Cambridge, Massachusetts, 2009-2011” was conducted by Jason R. Sorenson of the New England Water Science Center.
The study evaluated street sweeping in 4 different time periods: monthly, bimonthly, weekly, and three times weekly. Let’s take a look at the study’s background, method, and results to find out what street sweeping methods best reduced polluted runoff.
The study was conducted over a two-year period with support from the Massachusetts Department of Environmental Protection, the U.S. Environmental Protection Agency, and the City of Cambridge.
Researchers felt particularly concerned about the amount of phosphorus in the City of Cambridge. Excess phosphorus can lead to increased algae growth, which reduces the water’s overall oxygen. This condition can harm fish and other species and even affect drinking water.
For the study, researchers were curious to determine the amount of street solids and trace elements in Cambridge’s water runoff. In addition, they wanted to determine the most productive street cleaning methods and evaluate how street cleaning reduced the city’s phosphorus levels.
Water Quality Results
Researchers collected samples and evaluated the water quality. They determined that the amount of solids in the runoff was similar to other U.S. cities, including Baltimore, MD and Seattle, WA.
Researchers also found the most solids at the end of winter. Interestingly, they found a greater mass of phosphorus in water on residential streets than on commercial streets-probably due to grass clippings, tree leaves, fertilizer, and other substances.
Street Sweeping Results
Now, how did street cleaning reduce phosphorus and other substances? Good news: street sweeping in Cambridge reduced phosphorus up to 9.3% and solids up to 19%. Here are the results:
- Monthly: 16% solid reduction; 8% phosphorus reduction
- Bimonthly: 18% solid reduction; 8.3% phosphorus reduction
- Weekly: 18% solid reduction; 8.7% phosphorus reduction
- Three times a week: 19% solid reduction; 9.3% phosphorus reduction
Researchers stated that street sweeping was about 81% efficient at removing phosphorus.
What Cities Should Do
The study shows that regular street sweeping is important to reduce urban and stormwater runoff. For more information on how street sweeping can reduce pollution, see this post.
Now that you know the importance of street sweeping for your community, consider forming a street sweeping plan. Some of the decisions you’ll need to make include:
- Decide how often to send out the street sweepers. Generally, the more street sweeping, the better. Street sweeping three times a week was the most effective at reducing phosphorus and other solids. However, you need to consider this method’s practicality. Could you expect residents to move their cars this frequently? Can your city afford to send out street sweepers this often?
- Make sure you choose a reliable street sweeping company. This company should hire fully trained employees who practice proper street sweeping safety. Effective street sweeping relies on experience and training.
- Plan effective street sweeping routes. Street sweeping equipment is most effective when it doesn’t have to backtrack or make a lot of right turns. In addition, the street sweeping route should end at a dumping location.
- Spread the word to the locals. They’ll need to know when street sweepers will come through so they can move their vehicles. You can also tell citizens what they can do to reduce stormwater pollution in their city and neighborhood. Have them follow these tips.
Keep the results of the Cambridge study in mind as you determine the most cost-effective methods for cleaning your streets.