Measuring Runoff Water Quality Improvement from Street Sweeping in Southern California

Abstract Submission: Street sweeping is considered a non-structural stormwater best management practice (BMP) credited with 5-10% pollutant load reduction in many California stormwater MS4 NPDES permits. Literature 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. Sweepers accumulate tons of sediment and debris; however, these types of data are difficult to translate into improvements in runoff pollutant concentrations.
We developed a custom rainfall generator (RFG) and implemented it in controlled field-scale experiments to determine whether differences in runoff water quality can be measured between unswept and swept street segments. The RFG creates repeatable environmental conditions for conducting runoff monitoring, eliminating the high storm-to-storm variability limiting the ability to draw conclusions in previous street sweeping field studies. The RFG delivers a constant, uniform rainfall intensity of 1.25 in/hr, approximating a 2-yr, 15-min rainfall intensity typical of Southern California. 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. Whole-of-event composite samples were collected of the runoff from each pavement condition. Street sweeping resulted in measurable improvements in the concentrations of total suspended solids, total phosphorus, total nitrogen, total PAHs, total coliforms, and 6 heavy metals. Data to date suggests that %-reductions are greater than the assumed 10% for many parameters at this testing location. The mobile configuration of the RFG enables similar experiments to be conducted at a wide range of locations. Its components are commercially available and can be constructed for approximately $5,000 (not including labor). A parts list, assembly, and operation instructions are available on an open-source repository.

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