Groundwater recharge and dating in crystalline basement aquifers of Vea catchment: An integrated environmental tracers’ approach

Abstract

The crystalline basement aquifers host significant groundwater resources for the communities in Vea catchment for public and irrigational water supply. As part of measures to understand the hydrogeological processes of the area, multi-tracers (SF6, CFC-12, CFC-11, 3H, δ18O and δ2H) were employed to elucidate the groundwater residence time, recharge mechanism and mixing process of the shallow groundwater. Ambient concentrations of these tracers were taken from 10 sampling locations in the Vea catchment of Upper East Region of Ghana. A purge and trap method was used to take the samples and electron capture detector gas chromatography (GC-ECD) was used to analytically measure the SF6 and CFCs gases in the groundwater. The SF6, CFC-11 and CFC-12 dating complimented with 3H revealed that the groundwater age in the catchment was relatively young ranging from 5 to 42 years with a mean age of 23 years. This corroborates well with the stable isotopes data , which showed that the catchment receives modern recharge from meteoric origin. The results also indicated that the estimated SF6 ages were younger compared to the CFCs ages, suggesting additional inputs of SF6 from terrigenous sources. Similarly, a comparison of 3H and CFCs showed little variations in ages in some wells, a possible indication of CFCs degradation. The conceptual groundwater flow model developed showed three groundwater flow regimes along the topographical line. Despite some uncertainties in age interpretations, the multi-environmental tracers have been successfully used to date shallow groundwater in the Vea catchment. To reduce the uncertainties in the age determination, the use multi tracer approach is highly recommended.

Keywords

• Groundwater age
• Crystalline basement aquifers
• SF6
• CFCs dating
• Vea catchment