Street sweeping is often considered a non-structural stormwater best management practice (BMP) capable of reducing pollutant concentrations from streets during wet weather runoff. Many stormwater MS4 NPDES permits “credit” non-structural BMPs, including street sweeping, with 5-10% pollutant   load reduction. Contrary to the important role of street sweeping in water quality planning, a literature review reveals that actual water quality of runoff post-sweeping has not been measured with statistical confidence, nor has a robust comparison to runoff quality from non-swept streets been verified. Our study developed and implemented a controlled field-scale experiment whereby a custom-built rainfall generator was used to measure whether differences in runoff water quality can be measured between unswept and swept street segments. Testing of unswept and swept pavements occurred in   a parking lot in Long Beach after 2 weeks of antecedent dry weather on three occasions. A regenerative air sweeper swept one side of the parking lot on   the morning of each test day. Street sweeping resulted in measurable improvements in the concentrations and loads of total suspended solids, total phosphorus, total nitrogen, total PAHs, total coliforms, and total heavy metals including arsenic, cadmium, copper, nickel and zinc. Data to date suggests that percent reductions in runoff are greater than the assumed 10% for many parameters at this testing location.

Workshop Host: Southern California Coastal Water Research Project