Abstract

Geological disposal of radioactive wastes poses a number of technical challenges that must be met to ensure the long-term isolation of radionuclides from the environment. The characterisation of faults, especially their influence on patterns of groundwater flow, is an important aspect of characterising a site for geological disposal.  One important challenge is to develop an understanding of the potential for vertical migration of radionuclides along faults, and to incorporate this understanding into the design of a successful geological disposal facility. Over-simplistic conceptualisations of faults, in which they are represented as uniform features with a permeability that is either higher or lower than the surrounding bedrock, generate models that indicate short travel times for groundwater to reach the surface.  The accuracy of such models is open to doubt, hence, the development of skills related to characterisation of the hydrogeological characteristics of faults is important to future site characterisation work. Faults are highly heterogeneous, both in time and space. Limited research exists on quantifying spatial permeability variation within individual fault zones but this has largely been focussed on predicting across-fault flow in sedimentary sequences of interest to the hydrocarbon industry. No research has been published to-date that enables prediction of temporal variations in along-fault flow. Yet long time-scale temporal (episodic) variations in along-fault flow are known to occur, and can be caused by: build up of tectonic stress; activity on neighbouring faults or large regional faults; changes in surface/groundwater pressure (e.g. due to changing climate or reservoir construction); mining; oil and gas production and exploration; and other underground excavations. I will present research from a number of projects, based on multi-disciplinary data sources, that collectively aims to characterise fault flow over both space and time. This research investigates behaviour of a range of analogue systems by combining numerical modelling and statistical analysis with data from seismic events, hydrothermal flows and structural fault architecture.