Baseline studies into the groundwater resources in the Bosomtwi-Atwima-Kwanwoma District of Ashanti Region, Ghana

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The Bosomtwi-Atwima-Kwanwoma district has about 86% of its population living in the rural communities. Groundwater has always been the main source of water supply to the people in the district. A lot of work has been done in this district in terms of groundwater development by different organizations, institutions and agencies. Potable water is however still inadequate in the district. The boreholes and hand-dug wells are not adequate as regards the number in a particular community when viewed against the population threshold of 300 persons per water point. There is therefore the need for further groundwater exploitation in the study area in a bid to meet the potable water demand in the district. The objectives of this research are therefore to take inventory of groundwater point systems in the study area, viz, to determine the distribution, occurrence and potential of groundwater in the district and also to produce a groundwater database for the district. To achieve these objectives, information was obtained through literature review, consultation with stakeholders, and administration of questionnaires, interviews, field observations and laboratory analysis. In all, 170 boreholes, 60 hand-dug wells, 41 test- holes and 2 springs were tracked for evaluation. The BAK district is located in the Pra basin and it is underlain by three main geologic formations namely, Lower Birimian, Upper Birimian and the associated granitoids. The Lower Birimian occupies about 75% of the district and it exhibits the richest groundwater potential in the district with about 80% success rate of drilling. The Upper Birimian records about 64% success rate and the granites about 53%. The overall percentage of drilling successful wells in the district is estimated as 70%. Average yield of boreholes range from 6 1/min to 200 1/min, 13 1/min to 150 1/min and 17 l/min to 60 1/min in the granites, Lower Birimian and the Upper Birimian respectively. The specific capacities of the wells in the granites are in the range of 0.4 to 70 1/min/m whilst in the Lower and the Upper Birimian, specific capacities are in the range of 0.6 to 105 1/min/m and 0.4 to 50 1/min/m respectively. Transmissivity values also vary from about 0.7 to 23 m2/day in the granites and from about 0.7 to 54.7 m2/day in the Lower Birimian. Average annual precipitation is high (about 1500mm) and the groundwater recharge of Ashanti region was estimated to be 28 — 35% of the total rainfall. Thick weathering profiles are found in most areas in the study area. Average thickness is about 40m and 35m for the Birimian formations and the granites respectively. Aquifers occur in the permeable horizons in the weathered zone and fractures. Higher yields are anticipated in the fracture zones. Shallow groundwater is tapped through hand-dug wells under perched or water table conditions. Hand-dug wells are successful in the granites and the Lower Birimian but not in the Upper Birimian. The groundwater quality of the district is generally good except that pH levels are lower than the acceptable WHO standards in all the formations and manganese concentrations are higher than the acceptable WHO standard in all the geologic formations. Iron concentrations in a few wells in the granites and the Lower Birimian are also higher than the acceptable WHO standards. With the high groundwater potential of the study area, and the good groundwater quality, groundwater could be recommended as a dependable source of potable water for the over 150,000 inhabitants of the Bosomtwi-AtwimaKwanwoma District.
A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology in partial fulfilment of the requirements for the award of Master of Science, 2002