Rainfall runoff from stormwater often contains significant quantities of organic chemicals and metal elements. These constituents can adversely affect surface water and groundwater resources. Infiltration basins are best management practices (BMPs) that are designed for passive treatment and are increasingly used to control runoff and reduce stormwater contaminants in surface waters. The large amount of percolation in such BMPs over an extended duration may adversely affect groundwater quality, however, by eventual delivery of stormwater contaminants to the water table. Moreover, the existence of naturally occurring colloids and the deposition of air-borne colloids in stormwater can enhance the transport of highly sorbing constituents to the groundwater. Due to the large surface area of fine colloids, contaminants with high affinity to the solid phase can bind to colloidal particles and therefore the colloids can act as a vehicle for transport of contaminants in the porous media. In this research, a previously developed colloid-facilitated transport model was used to predict the effect of such colloids on the fate and transport of multiple metal contaminants in infiltration basins. The model was used to predict the transport of several metals in an infiltration basin in Fresno, CA, and a sensitivity analysis was performed to investigate the effect of various parameters on the fate and transport of metals. It was found that colloid-facilitated transport can explain the fast movement of highly sorbing metals in a porous medium while the two-phase model was not able to produce the observed movement in the soil.

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