Overview of the study design for the SMC’s street sweeping effectiveness study

The SMC launched an investigation in 2022 into whether routine street sweeping is effective in reducing contaminants in runoff that can enter storm drains and contribute to impaired water quality.

A portion of street segments from a selected site will be swept, while another portion that will be the control group will not be swept. A custom-built rainfall generator will be used to create controlled rainfall patterns for all street segments.

Each street segment will be isolated in a way that prevents runoff from nearby buildings, parking lots and other surfaces from mixing with the runoff generated by the street segments.

Researchers expect to simulate three storm events along each isolated street segment. By controlling for rainfall volume and intensity, the rainfall generator will help ensure results are not confounded by the unpredictable timing, intensity and duration of real-life wet-weather events.

If researchers are able to measure a difference, the study could be scaled up to additional sites and include monitoring for other contaminants. A later phase of the study also calls for repeating the study during natural wet-weather events – a way to help validate the results of the simulated rainfall events.

This study represents the first known field-scale effort to isolate and study just the portion of street pollution that is removed during routine street sweeping. Past studies have not sufficiently controlled for real-world environmental conditions and other confounding factors, stymieing researchers’ ability to quantify the effectiveness of street sweeping with statistical confidence.