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Groundwater residence time in basement aquifers of the Ochi-Narkwa Basin in the Central Region of Ghana

Abstract : Groundwaters from basement aquifers in the Ochi-Narkwa basin of the Central Region together with rain and surface waters have been analysed for stable isotopes (delta O-18, delta H-2 and delta C-13) and radioisotopes (H-3 and C-14) to determine sources of recharge, groundwater residence time and flow path. The mechanism of recharge to the groundwaters is by direct infiltration of past local rainfall of mean isotopic composition delta O-18 = -3.8 parts per thousand V-SMOW and delta H-2 = -18 parts per thousand V-SMOW. Tritium in the groundwaters ranged from 0.05 +/- 0.07 to 4.75 +/- 0.16 TU. Tritium data revealed that 85% of the groundwater samples were of modern recharge or young waters. The C-14 content of the groundwaters ranged between 9.50 pMC in borehole CR2-50 at Ekumfi Asokwa to 113.56 pMC in borehole CR3-26 at Onyaadze. Evaluation of H-3 and C-14 data distinguished three groups of water namely (1) waters characterised by high H-3 and high C-14 depicting modern recharge, (2) waters showing a mixture of young and old water due to fractures and (3) waters showing low H-3 and low C-14 contents referred to as very old waters and include borehole CR2-50 at Ekumfi Asokwa. The estimated age or residence time of this older water is 19,459 years BRbased on uncorrected age. The major flow direction is northwest-southeast. The dominant months contributing to recharge in the study area were February, March, April, May, June, August, September and October. Groundwater residence times in the basement aquifers of the Ochi-Narkwa basin showed that groundwater abstraction is sustainable and requires that the recharge areas are protected from contamination.
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https://hal-brgm.archives-ouvertes.fr/hal-01849374
Contributeur : Myriam Chergui <>
Soumis le : jeudi 26 juillet 2018 - 10:14:01
Dernière modification le : mardi 31 mars 2020 - 16:06:21

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Samuel Ganyaglo, Shiloh Osae, Tetteh Akiti, Thomas Armah, Laurence Gourcy, et al.. Groundwater residence time in basement aquifers of the Ochi-Narkwa Basin in the Central Region of Ghana. Journal of African Earth Sciences, Elsevier, 2017, 134, pp.590 - 599. ⟨10.1016/j.jafrearsci.2017.07.028⟩. ⟨hal-01849374⟩

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