Stormwater Best Management Practices in an Ultra-Urban Setting: Selection and Monitoring
3.8.1 Description and Purpose
Streetsweeping entails regular street cleaning using mechanical vehicles to reduce pollutants in stormwater runoff from street surfaces. Streetsweeping vehicles physically remove solids from impervious surfaces, by mechanical means (which can be vacuum-assisted), thus reducing the availability of solids and associated pollutants for pickup by subsequent runoff-generating rainfall.
Under certain circumstances street cleaning may include "street flushing," in which water transported by tanker trucks is used to wash accumulated solids from the street into gutters and stormwater inlets. The primary utility of street flushing is in areas served by combined sewers, where runoff generated by flushing would be conveyed to a municipal wastewater treatment plant. Most NPDES permits for separate storm drains do not allow street flushing.
While earlier results of the Nationwide Urban Runoff Program (USEPA, 1983) suggested that conventional streetsweeping had a relatively low impact on the improvement of water quality in the Midwest and eastern United States, more recent studies have found vacuum-assisted streetsweeping to be more effective. Streetsweeping using equipment based on new vacuum-assisted technologies can significantly reduce pollutant washoff from urban streets. Weekly to bimonthly sweeping programs can achieve reductions of up to 80 percent in annual total suspended solids and associated pollutants (Sutherland and Jelen, 1996).
3.8.2 Design Alternatives
There are three basic types of conventional street sweepers—mechanical, vacuum-assisted, and regenerative. Mechanical and vacuum-assisted sweepers use gutter brooms to loosen particles and remove them from the street. For both types, a fine water spray is used to limit dust generation. Mechanical sweepers carry the particles removed to a storage hopper using a conveyor belt, whereas the vacuum-assisted sweepers place the particles in the path of a vacuum intake leading to a hopper. Sweeping operations may be performed in tandem, with a first pass conducted by a mechanical sweeper followed immediately by a vacuum-assisted sweeper. Regenerative air sweepers alternately blast air onto the pavement and vacuum it back to entrain and capture accumulated sediment.
A new type of vacuum-assisted dry sweeper has been developed, an example is that produced by Enviro Whirl Technologies, Inc. The sweeper provides the important components of tandem sweeping in a single unit, with a specialized, water-free rotating brush used for the mechanical sweeping component. Tests indicate that the vacuum-assisted dry sweeper has greatly enhanced capabilities for fine sediment pickup and containment compared to conventional street sweepers.
Sutherland, R.C., and S.L. Jelen. 1996. Studies Show Sweeping has Beneficial Impact on Stormwater Quality. APWA Reporter (November):8-23.
USEPA. 1983. Final Report of the Nationwide Urban Runoff Program. U.S. Environmental Protection Agency (USEPA), Water Planning Division, Washington, DC.