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Bioretention has emerged as a promising and viable solution for mitigation of the adverse impacts of urban stormwater runoff. A bioretention structure is a water treatment feature that retains water for a period of time for storage, infiltration, and treatment through biological processes. It has become one of the most commonly used Low Impact Development (LID) practices to reduce or eliminate several significant pollutants collected by stormwater. The overall objective of this research was to evaluate and model bioretention performance in the mitigation of impacts of stormwater runoff over three phases: a field scale phase, a lab scale phase, and a modeling phase. The project assessed field scale bioretention LID site performance in reducing the stormwater runoff volume and improving water quality by comparing the pollutant load reduction of stormwater for two field sites, a bioretention cell located at South Texas College, McAllen, TX and a permeable pavement parking lot at a Recreation Center in La Feria, TX. The bioretention system at STC effectively reduced not only runoff volume (82±20%) but also provided a substantial improvement in the water quality of the effluent by reducing total pollutant loadings for TSS, BOD5, TKN and TP average removal is 96±1.8, 51±23, 65±44, and 83±16%; respectively, especially for indicator bacteria 49%. This research evaluated various mechanisms of bioretention features primarily bacterial mitigation through the development of a simplified LID laboratory study using a biofilter column and fecal indicator bacteria for complex bacterial removal processes. The removal of bacteria through bioretention columns were investigated by fitting effluent microbial concentrations to a one-dimensional advection-dispersion model with attachment providing insight into the potential mechanisms of straining and attachment.