Clay, conductivity, and rural water supplies. A hydrogeological investigation

In regions where the underlying geology is comprised of few aquifers other sources of groundwater must be tapped into. Mudstones and clay-bearing rocks are traditionally thought of as being aquicludes. Mudstones and clay-bearing rocks, however, can contain groundwater in robust fracture networks. The main control as to whether or not these fractures will develop is the clay type. Smectite clay is poor at developing robust fracture networks, whereas illite clays can support them. EM34 surveying is a tool used by geophysicists which determines the conductivity of the subsurface. Borehole, EM34, and clay analysis data, taken by the British Geological Survey in a region of Nigeria, has been used to identify a relationship between clay type and measured conductivity. A strong, linear, positive correlation has been found between measured conductivity and smectite content in the rock. From this, rural groundwater potential has been inferred by counter-intuitively coming to the conclusion that areas of low conductivity are likely to hold groundwater in clay-bearing formations. The findings of the experimental data have been tested against theoretical models- the Bussian and Revil and Glover equations. The implications of this research within the WATSAN sector have been explored. Furthermore, information has been presented on the usefulness of this research in other sectors such as the nuclear industry, engineering applications, geohazards and remote sensing.