Physical Characteristics of Particulate Matter Recovered from Urban Drainage Systems

Abstract

Particulate matter (PM) accumulates on urban interfaces, including pavement, as source areas. This PM can be recovered with street sweeping (SS) before transport by stormwater. Without SS recovery, PM is transported/deposited in a series of drainage components from a stormwater inlet/catch basin without a sump (CB), a conveyance system, a best management practice (BMP), and to receiving waters. PM separated in a CB and BMP can be recovered by maintenance. This study quantifies PM recovered from SS, CB, and BMP maintenance across Florida. Moisture content (MC) and particle size distribution (PSD) were measured for all samples. PM dry bulk density (ρb) as a function of MC was only examined for SS. With a cumulative gamma model, shape factor (γ, an index of size heterodispersivity), scale factor (k, an index of size central tendency) and gravimetric size (diameter) indices are generated from PSD data. Study results indicate a statistically significant increase in the MC of PM in BMPs as compared to SS. The median MC values are 34%, 27%, and 6% for BMPs, CB, and SS. The median dry ρb of the heterodisperse PM recovered by SS is 1.36 g/cm3, approximately log-normally distributed and a non-linear function of MC. In this study, SS is less effective in recovering finer PM. Coarse PM is deposited during conveyance/treatment, therefore PSDs recovered from BMPs are relatively monodisperse compared to SS. Results inform the design of maintenance for PM load recovery. Extensibility to nutrient/metal load credits can be based on PM-partitioned data. Such extensibility can target PM recovery and used in a basin management action plan for a total maximum daily load.