Community water supplies from mudstones

Mudstone is not generally considered as an aquifer. However, many people in sub-Saharan Africa have to rely on meagre water resources within mudstones for their only water-supply. This thesis provides the first rigorous study of the factors controlling groundwater resources in mudstone environments and the methods required for finding and developing groundwater. The research was undertaken in the Cretaceous mudstones of southeastern Nigeria. The area was investigated using geophysical techniques, exploratory drilling, mineralogical analysis, test pumping and hydrochemical sampling. The investigations demonstrate that sufficient groundwater for village water supplies can exist within the top 50 m of mudstones. The occurrence of groundwater is controlled by two factors: 1. Low-grade metamorphism. Mudstone that is unaltered (early diagenetic zone) comprises mainly smectite clay and groundwater is rare. Mudstone in the late diagenetic zone comprises mixed illite/smectite clay and groundwater is found in widely spaced fracture zones. Mudstone that has been further altered and approaches the anchizone comprises mainly illite, fractures are widespread and groundwater ubiquitous. 2. The presence of other lithologies. Dolerite intrusions within smectite rich mudstone are fractured and contain groundwater. Thin limestone and sandstone layers can also enhance permeability. The study demonstrates a relation between ground conductivity and the degree of metamorphism of the mudstone, despite the presence of a thick tropical soil. The relation is primarily controlled by the amount of smectite within the clay. In addition, field data and novel computer modelling has demonstrated that fault zones within consolidated mudstones produce characteristic electromagnetic anomalies. A new simple, effective pumping test, the “bailer test”, was developed during the research to give an indication of borehole success. The test can be completed in under an hour and requires little specialised equipment or analysis. In summary, sufficient groundwater for rural water supply can be found in mudstone environments with the careful application of unsophisticated technology.