The focus of the current paper is the Mock Urban Setting Test (MUST) carried out at Dugway Proving Ground. The MUST experiment was designed to represent an urban complex of about 120 buildings with symmetric characteristics. Throughout the 19 day MUST experiment, 63 pu and continuous releases were carried out using propylene as a tracer gas. In order to understand the importance of capturing these spatial variations and unsteadiness, the multipurpose nite element code FEFLO-URBAN was used to perform a Very Large Eddy Simulation (VLES) of MUST. One of the continuous release trials (2682353) was selected for a detailed study. The terrain surface was modeled with geometric roughness in order to circumvent the problem of lack of turbulence production in the vertical direction. The FEFLO-URBAN simulations of the concentrations of the passive tracer were compared with the experimental measurements, resulting in agreement within an order of magnitude about 76% of the time. A study of the sensitivity of the model results with respect to resolution was made with four different mesh resolutions (500K, 4M, 8.1M and 32M elements). A sensitivity study with the wind direction inow boundary condition was carried out. 2682353) was selected for a detailed study. The terrain surface was modeled with geometric roughness in order to circumvent the problem of lack of turbulence production in the vertical direction. The FEFLO-URBAN simulations of the concentrations of the passive tracer were compared with the experimental measurements, resulting in agreement within an order of magnitude about 76% of the time. A study of the sensitivity of the model results with respect to resolution was made with four different mesh resolutions (500K, 4M, 8.1M and 32M elements). A sensitivity study with the wind direction inow boundary condition was carried out.