England The pore-water signal left behind by a glacier overriding a porous medium is considered. Important processes are infiltration, tracer diffusion, radio-active decay, penetration of freezing fronts and erosion and deposition. Infiltration could be negligible or affect the whole depth of the aquifer.
Diffusion is limited by the tortuosity parameter, which as yet is poorly explained by theory.
Diffusion over twenty thousand years may only only affect a depth of ten metres, which means that the relevant areas are readily accessible by cores but are likely to have been disturbed by surface effects. The influence of sedimentation and unstable tracers is discernible but sometimes difficult to distinguish from the effects of the glaciation history. First steps in an observation programme should be the establishment of the typical depth to which marine sediments are affected. This will constrain the basal hydrology, and reduce the number of possible scenarios.