Pollutant removal associated with street sweeping
In development
Pollutant removal of traditional structural stormwater best management practices, such as bioretention and permeable pavement, can be determined by determining pollutant concentrations entering and leaving the practice and knowing the volume of runoff being treated. For example, constructed Design Level 2 stormwater ponds are assumed to remove 84 percent of total suspended solids, 50 or 68 percent of total phosphorus depending on absence or presence of an iron amendment, and 30 percent of total nitrogen (see Information on pollutant removal by BMPs).
Unlike stormwater practices such as bioretention and constructed ponds, direct measurement of water quality performance for street sweeping cannot be performed. Pollutant removal is a function of the amount of material removed and the chemical composition of the material removed. This simplified approach also assumes all material and pollutants on impervious surfaces would reach a receiving water. Another complicating factor is that concentrations of some pollutants, such as nutrients, varies considerably during the year, with the result that sweeping effectiveness also varies with timing. This differs from a traditional practice, such as bioretention, which treats runoff throughout the year, thus allowing calculation of annual average removal.
The following discussion summarizes general conclusions on the effectiveness of street sweeping in removing pollutants.
Phosphorus
Hobbie et al. determined phosphorus concentrations in street sweepings from six municipalities. Results indicate significantly greater concentrations of phosphorus during fall when leaf drop occurs. Combined with the much greater mass of material generated at this time of year, targeted sweeping during fall leaf drop provides by far the most effective way of reducing phosphorus concentrations in stormwater runoff.