Ultraviolet (UV) treatment of water is known to be an effective means for reducing bacterial concentrations. While previous research has typically focused on UV treatment efficiency for disinfection of drinking water, the utility of this technology in treating more turbid samples is less clear. This study investigates the use of UV treatment for the disinfection of stormwater from combined sewer overflow (CSO) events and specifically focuses on how suspended solids influence treatment efficiency for Escherichia coli. Stormwater containing different size fractions of suspended solids was exposed to UV treatments and the rate of disinfection was determined. After approximately 3-orders of magnitude reductions in E. coli survival, significant tailing in the rate of disinfection was observed for unfiltered stormwater and stormwater containing particles less than 20μm. A particle-associated bacteria (PAB) model which directly utilizes the concentration of suspended solids to estimate the effect of shielding is proposed and evaluated as well as a biphasic model, with two first-order rate constants. Experimental results confirm that suspended particles are important and need to be accounted for when determining UV treatment efficiency of CSO stormwater. However, tailing observed may not be accurately described by current models and particle size suggests a mechanism other than shielding is responsible for tailing.