Groundwater residence time in basement aquifers of the Ochi-Narkwa Basin in the Central Region of Ghana. (October 2017)

• Record Type: Journal Article
• Authors: Ganyaglo, Samuel Y.; Osae, Shiloh; Akiti, Tetteh; Armah, Thomas; Gourcy, Laurence; Vitvar, Tomas; Ito, Mari; Otoo, Isaac
• Is Part Of: Journal of African earth sciences. Volume 134(2017)
• Page Start: 590
• Page End: 599
• Publication Date: 2017-10
• Subjects: Groundwater age -- Recharge mechanism -- Basement aquifers; Earth sciences -- Africa -- Periodicals; Earth sciences -- Middle East -- Periodicals; Geology -- Africa -- Periodicals; Geology -- Middle East -- Periodicals; Sciences de la terre -- Afrique -- Périodiques; Sciences de la terre -- Moyen-Orient -- Périodiques; Géologie -- Afrique -- Périodiques; Géologie -- Moyen-Orient -- Périodiques; Earth sciences; Geology; Africa; Middle East; Periodicals; Electronic journals; 556.05
• DOI: 10.1016/j.jafrearsci.2017.07.028
• Languages: English
• ISSNs: 1464-343X

Abstract

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 (δ 18 O, δ 2 H and δ 13 C) and radioisotopes ( 3 H and 14 C) 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 δ 18 O = −3.8‰ V-SMOW and δ 2 H = −18‰ 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 14 C 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 3 H and 14 C data distinguished three groups of water namely (1) waters characterised by high 3 H and high 14 C depicting modern recharge, (2) waters showing a mixture of young and old water due to fractures and (3) waters showing low 3 H and low 14 C 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 BP based 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. Highlights: The mechanism of recharge to the groundwaters is by direct infiltration of past local rainfall. Three groups of water have been distinguished based on 3 H and 14 C data. Older groundwater has age 19, 459 years BP. The months contributing to recharge were February, March, April, May, June, August, September and October.