Since the 1990s, SCK CEN, EIG EURIDICE and ONDRAF/NIRAS have been investigating the impact of gas generation on the Boom Clay and the engineered barriers. Several experiments have been performed to study gas transport in Boom Clay at laboratory scale and in the HADES URL. This paper gives an overview of these experiments. The transition from the laboratory to the in-situ scale is still a challenging task. It is our ambition to address these issues for Boom Clay, starting with the diffusive transport of dissolved gas. A large set of gas diffusion coefficients in Boom Clay from small-scale lab experiments (centimetre scale) is already available, and in order to validate these for use on a larger (metre) scale, an in-situ diffusion experiment with dissolved gas will be performed in the HADES URL, using the existing boreholes. In this new experiment, called NEMESIS, dissolved neon gas will be injected in one filter, and its diffusion will be monitored by three other filters. By re-using existing boreholes dating from the 1990s, the NEMESIS experiment will continue to provide new diffusion data for the next five years.