Have you ever noticed how often the words we use in day-to-day conversations have confusing or contradictory meanings? For example, you drive on a parkway but park on a driveway. A football is thrown or passed from hand to hand, and the phrases “fat chance” and “slim chance” somehow mean the same thing.
In the fall, many communities deploy street sweepers to clean-up city streets. Though the phrase “street sweeping” may conjure up images of a people with brooms, industriously sweeping our roadways, many modern street sweepers actually suck, like vacuums. Street suckers to the rescue?
Cities use street sweepers to maintain a tidy appearance, but these machines can also be an important and cost-effective tool for reducing stormwater pollution. Street sweepers remove dirt and leaves on city streets that would otherwise get washed into storm drains and contribute to algae growth and water pollution in downstream lakes, rivers, streams, and wetlands.
There are three main types of street sweepers. Mechanical broom sweepers do, in fact, operate pretty much like a giant broom and dustpan. A broom spins around and brushes debris off the street and onto a giant conveyor belt that carries the debris into a hopper inside the truck. Mechanical sweepers are good at picking up litter and wet, matted leaves but usually leave behind a thin layer of sand and silt, which often contains heavy metals, nutrients and hydrocarbons. For this reason, many communities have switched to regenerative air sweepers and vacuum sweepers that are able to better collect those “fines.”
In 2017, the Comfort Lake – Forest Lake Watershed District received a $36,000 Minnesota Clean Water Fund grant to develop an enhanced street sweeping plan for the City of Forest Lake. Analysis conducted by EOR Inc. showed that the city could keep an additional 137 pounds of phosphorus and 169,793 pounds of solids out of local lakes if it began sweeping twice a month with a regenerative air sweeper and focused on streets with heavy tree cover. For perspective, one pound of phosphorus can grow 500 pounds of algae!
Now, as part of the Lower St. Croix Comprehensive Watershed Management Plan, local partners are looking to establish similar street sweeping programs in more than a dozen small communities within the St. Croix watershed, including Rush City, Harris, North Branch, Stacy, Wyoming, Taylors Falls, Marine on St. Croix, Scandia, Stillwater, Bayport, Lakeland, Lake St. Croix Beach, and Afton. Roughly $140,000 in new funding from the Minnesota Board of Water and Soil Resources is available to evaluate the highest priority locations for enhanced street sweeping, and help communities develop and implement new street sweeping programs.
Even though street sweepers can take a large bite out of stormwater pollution, there is still a need for residents to help protect local waterways this fall. There is a limit to how much, and how often, street sweepers can be deployed. The machines are expensive and driving every city street at five miles an hour is a time consuming process. Even if you live on a street that gets swept in the fall, you should still rake the leaves out of the street in front of your own house so that sweepers are better able to suck up the dirt and sand underneath. Individual action is also important in smaller communities and rural areas where street sweepers aren’t used.
To learn more about stormwater pollution and what to do with the litter, leaves and sediment you collect from in front of your home, head to www.Adopt-a-Drain.org.