Aquitards (low-permeability rock formations) bear attractive features for waste isolation, as they are expected to act as natural hydrological barriers, segregating potential contamination at land surface from the underlying aquifers. However, the heterogeneous structure of these formations, which contain highly transmissive fractures, poses serious questions regarding the efficacy of aquitards as natural barriers. This meeting focuses on the critical, cutting-edge research theme of how water and contaminants migrate through fractured aquitards. The meeting covers a wide range of innovative research problems, including advanced geophysical and hydro geological characterization methods, theoretical models of flow, transport and dispersion, geochemical interactions among fluids, contaminants and the host rock, and microbiological aspects. Integration of these methods and approaches is essential to development of realistic, quantitative models for flow and transport. Such models are critical to sustainable management and protection of groundwater resources, and to evaluation of a variety of waste isolation scenarios.