Environmental Information for Sweeping Professionals

Sweeping as a Best Management Practice

Street sweeping should be an important part of the management strategy for any stormwater pollution runoff program.

In its June 2006 issue, Better Roads magazine included an excellent story that provided an overview of current and projected stormwater regulations, including how they may affect all of us in the years to come.

Although filled with excellent information, in the recent Better Roads magazine article, "Stormwater Regulations -- Now and in the Future," the potential benefits of street sweeping were glaringly omitted. The only mention was the listing of street sweeping in the #9 spot of the Minnesota Pollution Control Agency's "Top 12 Stormwater Practices Needing Further Assessment."

Here's why the value of street sweeping is an omission that cannot be overlooked: CalTrans recently completed an assessment of the cost of structural BMPs, concluding that those various types of 'fixes' cost, on average, $10 to $60 for each pound of pollutant removed. This cost was minus the added expense of land procurement.

As a contrast, our industry studies show that today's air sweepers do the same job for between $2 and $5 per pound, with the latest crop of mechanical broom machines weighing in at between $5 and $10 per pound of pollutant removed. And, with sweepers, no real estate needs to be purchased.

Does this make street sweeping the new 'silver bullet' for stormwater pollutant runoff? Unfortunately, by no means is sweeping ready for that label. However, it does mean that jurisdictions should be evaluating the overall costs and benefits of street sweeping in an empirical fashion prior to investing in any of the considerably more costly, end-of-the-pipe infrastructures.

The fact is, many municipalities and other agencies are still sweeping for 'cosmetic' reasons, sweeping at whatever frequency they've determined will keep citizen complaints at bay. Instead, they should utilizing pavement sweeping as the vanguard of their fight against stormwater runoff pollution. Every city impacted by the Clean Water Act needs to engage in a cost analysis of its sweeping program, one designed to weigh the effectiveness of an increase in sweeping frequency, especially in runoff sensitive areas.

A component of this process should be an evaluation of the sweeper type best suited for the job. In some cases, for example, a shift from mechanical broom to air sweepers may make sense. In other areas, the least cost per pound of pollutant removed may actually be achieved via tandem sweeping (typically mechanical broom sweepers followed by an air machine). Where indicated, the tandem sweeping process is still likely to be much less costly than a structural retrofit.

Another plus of street sweeping, since it picks up polluted material prior to dilution into the runoff stream, is that it can handle the water soluble pollutants that thwart catch basin filtration systems. About half of the pollutants targeted by the EPA are water soluble.

In May of 2006, WorldSweeper.com sponsored seminars on sweeping as a stormwater management BMP in the L.A. and San Francisco areas of California. I attended these as both participant and speaker. To my surprise I discovered that even in those areas, the region of the country where non-point source pollution requirements are probably at the forefront, about half of the agencies we surveyed indicated they are still not even requiring vehicle removal on sweeping days!

Although somewhat of a political hot potato, mandated vehicle removal can more than pay for a city's sweeping program. Because of maneuverability issues, when cars are left on the street the sweeper misses about three car lengths of sweeping area for each car it has to swerve around. When it comes to sweeping for pollution abatement, that's an important factor.

Several program managers also told us that their sweeping program had actually been reduced due to budget concerns, even though large sums of money aimed at reducing runoff pollution were being expended elsewhere, often funded by stormwater assessment fees. In order to address this problem in a more wholistic fashion, I believe it makes sense to combine sweeping budgets with those of other programs designed to reduce runoff pollution, from catchbasin filters to building of grassy swales.

Then, do the best possible cost analysis of all competing solutions, including sweeping, and follow through by implementation of each according to its relative cost of pollutant removal. When they do so, I think most municipalities will find they are only sweeping at about 25% of the frequency that would actually maximize their pollutant reduction budget.

Although the National Urban Runoff Program studies of the early 1980s showed street sweeping to be largely ineffective at removing pollutants, for many reasons this does not appear to be the case today. I urge those making decisions in this regard to evaluate the newest crop of sweepers. When they do, they'll discover that today's sweepers -- both mechanical broom and air machines -- are far more efficient in picking up the small-micron materials that tend to foster pollutant attachment. At the same time, they remove the larger gross material that contributes to waterway siltation as well as the plugging of stormwater filters.

Given proper route evaluation, machine choice and sweeping frequency analysis, my belief is that today's street sweepers deserve a position at the forefront of compliance with the Clean Water Act. Sweeping certainly should be evaluated as to what it can actually do as a BMP in this regard. The mindset of considering just the cosmetic value of pavement sweeping must be discontinued. It's time for recognition that pavement sweeping, in many areas, represents the first, best and lowest cost opportunity to remove pollutants prior to their entering the runoff stream.

As a result of reading both the Better Roads article and this one, Mark Kinter, Technical Consultant for Elgin Sweeper Company, wrote a Letter to the Editor outlining some other factors to consider.

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