Matrix Porewater In Crystalline Rocks: Extraction and Analysis

• Main Authors: Eichinger, Florian, Waber, H. Niklaus
• Format: Report
• Language: English
• Published: Nuclear Waste Management Organisation 2013
• Subjects: 550 Earth sciences & geology; Greenland; Kangerlussuaq
• Online Access: https://boris.unibe.ch/67613/1/Waber.pdf; https://boris.unibe.ch/67613/; http://www.nwmo.ca/uploads_managed/MediaFiles/2404_nwmo_tr-2013-23_matrix_porewater_crystalline_rock_.pdf

The chemical and isotopic characterization of porewater residing in the inter- and intragranular pore space of the low-permeability rock matrix is an important component with respect to the site characterization and safety assessment of potential host rocks for a radioactive waste disposal. The chemical and isotopic composition of porewater in such low permeability rocks has to be derived by indirect extraction techniques applied to naturally saturated rock material. In most of such indirect extraction techniques – especially in case of rocks of a porosity below about 2 vol.% – the original porewater concentrations are diluted and need to be back-calculated to in-situ concentrations. This requires a well-defined value for the connected porosity – accessible to different solutes under in-situ conditions. The derivation of such porosity values, as well as solute concentrations, is subject to various perturbations during drilling, core sampling, storage and experiments in the laboratory. The present study aims to demonstrate the feasibility of a variety of these techniques to charac-terize porewater and solute transport in crystalline rocks. The methods, which have been de-veloped during multiple porewater studies in crystalline environments, were applied on four core samples from the deep borehole DH-GAP04, drilled in the Kangerlussuaq area, Southwest Greenland, as part of the joint NWMO–Posiva–SKB Greenland Analogue Project (GAP). Potential artefacts that can influence the estimation of in situ porewater chemistry and isotopes, as well as their controls, are described in detail in this report, using specific examples from borehole DH-GAP04