Impact of model structure on radionuclide transport in urban stormwater

This paper compared simulation results from different SWMM model constructions after radiological contamination from a hypothetical dirty bomb. The model constructions included a utility-provided combined sewer model, a high-resolution mesh surface flow model, and a hybrid of the two. The models were run under three different rainfall configurations including a 3-h event, a 24-h event, and a 24-h event with 48 h of drainage to investigate the influence that model structure had on transport of ¹³⁷Cs. Model structure was found to impact the contaminant loading of the stormwater model from the air modeling. It was also found to impact the amount of contaminant washoff (high resolution modeling produced more washoff), flow of contamination through outfalls (more contamination through outfalls connected to underground pipes), and ¹³⁷Cs levels per pipe. The implications of these findings are that few stormwater models are considered ready to aid in response and recovery as originally designed.