In the framework of the "Fifth workshop Harmonisation within atmospheric dispersion modelling for regulatory purposes", a model intercomparison exercise was performed which aimed to assess (i) the environmental impact, and (ii) the compatibility of the performance of similar dispersion models under severe weather and topography conditions. The contributors were asked to use the same meteorological input data and perform dispersion calculations in the surroundings of the As Pontes power plant in northwest Spain for four individual days. The predicted concentrations are compared with observed near ground concentrations measured at 17 receptors located around the source. The models are also compared with one another to examine the degree of similarity of their predictions. A statistical analysis, based on the bootstrap re-sampling method, is employed to yield the bounds of a compatible result.