Dissolved krypton gas (Kr) has been used as a novel, applied and "environmentally-friendly" groundwater tracer in the fissured Sherwood Sandstone aquifer at Queen's University Belfast, Northern Ireland. The tracer test involved a single-well slug injection and withdrawal (so-called "push-pull") technique, to study the dual-permeability nature of the aquifer. Analytical modelling of the tracer transport demonstrates that the shape of the Kr breakthrough curve is a result of two processes: relatively rapid dispersion of the tracer through rock fissures and slower diffusion into the sandstone pore spaces. Characterisation of this dual-permeability nature is important in assessing movement and fate of groundwater contaminants in the aquifer
