Skip to main content
Article thumbnail
Location of Repository

BGS Consultancy : UNICEF IWASH Project, Northern Region, Ghana. Final report

By B.E. O Dochartaigh, J. Davies, D. Beamish and A.M. MacDonald

Abstract

Introduction\ud The British Geological Survey (BGS) were commissioned to investigate the low drilling success\ud rates encountered by the UNICEF IWASH (Water, Sanitation and Hygiene) programme in the\ud Northern Region of Ghana. BGS’s activities have focussed on gathering existing\ud hydrogeological data generated by the IWASH programme; reviewing the groundwater\ud development practices used by IWASH consultants; building the capacity of key implementing\ud IWASH partners and other groundwater development agencies through a two week workshop\ud and training course held in the Northern Region; and producing a preliminary groundwater\ud development potential map for the Northern Region.\ud Overview of the hydrogeology of the Northern Region\ud The rocks beneath most of the Northern Region form low or very low productivity aquifers with\ud limited groundwater potential. Borehole success rates (boreholes capable of supplying a hand\ud pump) are typically between 40 and 60%, but range from 20% in the lowest productivity aquifer\ud to around 70% in the highest. Fractures in sandstones are the most important groundwater target.\ud Only small amounts of groundwater are found in fractures in siltstones. Groundwater is rarely\ud found in mudstones. The most important zone of groundwater flows is thought to be between\ud approximately 30 and 70m depth. There is little groundwater inflow below 70m, particularly in\ud mudstones and siltstones, but sandstones do sometimes show significant inflows up to 100m and\ud occasional smaller inflows below 100m. However, there is no evidence in the available data of\ud significant groundwater flows at depths of over 100m.\ud Overview of good groundwater development practice\ud Good practice in developing groundwater resources should start with a detailed reconnaissance\ud survey involving both a desk study of available information – such as geological,\ud hydrogeological and lineation maps and results of previous siting and drilling in the same area –\ud and field observations of existing water sources and any surface indicators of groundwater. The\ud knowledge gained by interpreting this information is used to choose appropriate geophysical\ud techniques and locate lines for geophysical surveys. Ideally, geophysical surveys should first\ud involve profiling (using EM34 and/or 2D resistivity equipment) over long lines that are designed\ud to cross potential linear water bearing features. Deeper penetrating VES resistivity surveys could\ud then also be carried out over promising features to provide more detailed lithological\ud information, such as the likely presence of sandstone which is more likely to contain water\ud bearing fractures. Ideally, more than one geophysical technique should be used and the results\ud compared to look for features present in all sets of results. All geophysical surveying should be\ud undertaken with good field procedure; deep penetration (i.e. using as wide an equipment spacing\ud as possible); rigorous analysis using the correct geophysical models; and interpreted with respect\ud to the known geology and hydrogeology of the area. Borehole drilling should be treated as an\ud opportunity to gain valuable geological and hydrogeological information, as well as to develop a\ud water source, with rigorous collection and recording of data throughout the drilling process.\ud Borehole construction should be designed to maximise potential groundwater inflows, which\ud may mean screening boreholes throughout most of their length. Borehole development should be\ud done thoroughly until the hole is fully clear, and in mechanised boreholes the pump should be\ud used to further develop the borehole before test pumping

Publisher: British Geological Survey
Year: 2011
OAI identifier: oai:nora.nerc.ac.uk:14724

Suggested articles


To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.