Street Sweeping: The Grit that Keeps on Giving

The only time most people think about clean streets is when they get stuck behind a sweeper as it goes about its business of collecting grit, dirt, bits of paper, and the ubiquitous cigarette butt.
Street sweeping, however, is an important part of keeping both busy streets and quiet, leaf-strewn residential ones clean. Cities and towns throughout the country spend millions of dollars and untold hours on their street maintenance. Keeping road salt, sand, and other small particles out of surrounding roadways and wastewater treatment plants makes sense; proper sweeping protects the environment, ultimately saves money for the folks over at the sewer department, and gives a tidy look to the cityscape.
Yet, disposing of all that sweeper debris is not only cumbersome but can also be extremely costly. That is why a network of environmentally minded agencies and communities has worked on ways to keep street debris out of landfills—or at least to keep the waste from becoming part of the trash that is dumped there.
Some cities have been recycling or reusing their street waste for years, enacting complicated and, in many respects, very expensive facilities for screening, composting, or otherwise cleaning the debris.
Out in Oregon—the West Coast seems to be the leader in this sort of thing—the City of Portland is working with the nearby Sunderland Recycling Facility to re-use street waste. The city collects about 25,000 cubic yards of street sweeping waste each year, and until recently, most of it ended up in landfills. The cost to the city for transporting and disposing of the material costs about $1 million a year.
The Southern California city of Long Beach sweeps about 170,000 miles of streets each year, removing about 13,000 tons of dirt, garbage, and grit in the process. About 96 percent of the sweeper debris ends up in a composting facility where it is run through a set of screens that separate trash from sand, dirt, and grit. Paper and any other materials that can be composted go back into the composting facility, where the resulting compost is sold to farmers in the agricultural-rich area.

So why don’t more cities have the same commitment to recycling street waste? For one, it is expensive. California communities have been under strict state requirements to reduce the amount of waste that goes into landfills, and the law can be a powerful motivator. Another reason is that as other cities work desperately to make up for lagging tax dollars because of the economy, venturing into new programs—even ones that can eventually save money—seems like a luxury that many simply cannot afford right now.

While most street sweeper waste unintentionally ends up in landfills, a small amount is intentionally put there to serve a specific reason. Under the proper circumstances, states will allow the grit and dirt from sweeper hoppers to be used as a top cover on landfills. The Minnesota Pollution Control Agency offers specific guidelines for using the material as a daily cover on sanitary and construction landfills. The agency recommends that the refuse should only be used as a top cover in landfills that have groundwater monitoring mechanisms in place.

Studies have been done elsewhere to show the economic value of finding alternative disposal methods for street-sweeping debris—methods that do not involve landfills. In fact, last year, researchers at the University of Massachusetts Boston detailed the experience of the town of Natick, MA and its street sweeping trash.

Natick, just outside of Boston, has about 32,000 residents. Dirt, sand, and organic material from street sweeping and catch basins are regulated by the state’s Department of Environmental Protection. The study, conducted through the John J. Collins, Jr. Center for Public Management, noted that the debris is considered a solid waste and, therefore, has to be taken to a landfill for disposal. The only way that the material can be used as a landfill cover or for other purposes is if chemical tests can prove it is safe for reuse in such a manner. The study noted that the cost of dumping sweeping waste in a landfill was up to $100 per ton for the town, but could easily climb even higher if the waste were categorized as hazardous. The waste was substantial. Natick’s 195 miles of roadways generate between 700 and 1,000 cubic yards of street sweepings each year, according to the study.

For that reason, several years ago, Natick asked the state for permission to conduct a pilot project to find new uses for the dirt and grit that the town’s street sweepers collected. Actually, most of what Natick collected was sand—valuable in Massachusetts’ cold and snowy winter climate. The town had two uses for the sweeping debris: reusing the sand on its roads during the wintertime and mixing it with already-collected composted yard waste so that it could spread on a closed gravel pit.

The pilot program showed that Natick’s start-up costs were about $25,000, which covered the initial preparation of the application to gain state permission for the project. That, of course, was a one-time expense. Annual costs are estimated at about $8,000—almost all of it related to testing the material for contaminants. The rest, about $1,000, covers staff expenses. The payback for the pilot program came within the first year.

“Making this change leads to a net savings of about $25,300 annually after the first year, during which the one-time start up expense reduces the net savings to $300,” the study concluded. “This program pays for itself within the first year.”

While the University of Massachusetts Boston study focuses solely on Natick, its findings can be applied to communities elsewhere, with a few stipulations. Municipal leaders need to ask themselves five questions to help determine if alternative disposal of street-sweeping debris is right for their cities.

  1. How many cubic yards of sweeping does the municipality collect annually?
  2. How likely is it that the municipality’s sweepings will meet the standards for use as a soil additive?
  3. Does the municipality have a use for extra soil additive?
  4. How much is the municipality currently paying to transport and dispose of the sweepings?
  5. Can the municipality find the money to pay for the upfront cost of preparing the Beneficial Use Determination application?

 

        Environmental regulators are quick to acknowledge that street-sweeping debris needs to be handled with care. After all, it routinely contains pieces of glass, metal, salt, and all types of other materials. All bets are off if street sweepings and catch basins have been the unwelcome repository of gasoline or similar hazardous wastes. Connecticut’s Department of Environmental Protection has published a guideline for managing street sweepings and catch basin debris and encourages municipalities to develop a plan for collecting the material, safely storing it, and reusing it locally “in a manner that does not pose a risk to public health or a risk to wetland and water quality.”

        Among the reuse options for screened street sweepings—minus costly analytical testing—is to mix it with new salt and sand mixtures to treat roads, parking lots, and sidewalks in the winter; to cover landfills; to fill potholes and then cover them with asphalt; to fill in the median strips or along road shoulders on city-owned public right of ways; or to use as an aggregate in concrete or asphalt. With chemical testing, the options increase even more. The debris can be used as fill on industrial or commercial properties, or it can help absorb hazardous materials in an emergency, the Connecticut DEP noted.

        One thing is certain when it comes to street sweeping debris: as landfill dumping prices and transportation expenses continue to rise, cities will be looking harder at and more favorably for ways to reuse the material. Compost, pothole filler, traction for winter-slick roads—many recycling options have the potential to be far cheaper than hauling the waste to a landfill.

As the University of Massachusetts Boston study authors pointed out, “Because the costs of dealing with street sweepings are now lower (and partially de-linked from the actual amount of sweepings collected), there is greater incentive to do more street sweeping. More sweeping can lower the amount of debris that goes into the catch basins, which may in turn have additional financial and environmental effects, both positive and negative, that are more difficult to quantify.”

Story by Marie Elium

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