Best practice methods for the chemical and isotopic characterisation of porewater in low-permeability bedrock

Sedimentary and crystalline rock formations are currently being intensely investigated in several countries as potential host rocks for deep geological repositories for radioactive wastes. An important aspect of investigations is to characterise and understand the movement and compositions of water in these rocks—both mobile groundwater in aquifers and faults/fractures, and immobile porewater in the matrix of intact rock. Non-reactive solutes, primarily Cl and Br, water isotope ratios, and dissolved helium are ‘natural tracers’ of diffusive transport and exchange between groundwater and porewater.

Recent developments of techniques for extracting and analysing porewaters from carefully preserved drill cores are summarised in this paper. It identifies practical challenges and suggests best practice strategies based on experience gained by various national research and repository programs in crystalline and sedimentary rocks.