Groundwater recharge potential and vulnerability to contamination in the Sunyani West Municipality, Ghana

Abstract

Abstract Groundwater resources in crystalline basement settings are increasingly exposed to abstraction and contamination pressures, posing challenges for sustainable groundwater management in data-scarce regions. Despite their importance, integrated assessments of groundwater recharge potential and intrinsic aquifer vulnerability remain limited. This study assessed groundwater recharge potential and intrinsic aquifer vulnerability to contamination in the Sunyani West Municipality, Ghana. Groundwater recharge potential was mapped using a GIS-based Analytical Hierarchy Process (AHP) integrating seven hydrogeologically relevant factors (geology, geomorphology, slope, soil type, land use/land cover, drainage density and lineament density), while intrinsic aquifer vulnerability was evaluated using the F-HYDRA model based on flow accumulation, hydraulic conductivity and land use/land cover. All datasets were standardised to a spatial resolution of 30 m. The selected criteria represent key controls on infiltration, structural permeability and surface–subsurface connectivity within the Birimian crystalline basement terrain. The resulting recharge map delineated five recharge potential classes, with high and highest recharge zones occurring as discontinuous patches across the Municipality rather than being confined to a single area. A spatial consistency assessment using borehole yield data from 102 boreholes showed a positive association between recharge index and borehole yield (R² = 0.7863), although borehole yield also reflects aquifer transmissivity, weathering, fracture connectivity and well characteristics. The vulnerability assessment identified moderate vulnerability as the dominant class, while high to very high vulnerability occurred mainly in the northern-central and eastern parts of the Municipality. Nitrate concentrations measured from 20 boreholes exhibited a positive spatial association with the intrinsic vulnerability index (R² = 0.7435), although the relationship also reflects contaminant loading and local hydrogeological conditions. The integrated assessment identified areas where relatively high recharge potential coincides with elevated intrinsic vulnerability, highlighting priority zones for groundwater protection and land-use planning. The integrated AHP–F-HYDRA approach supports groundwater management in data-scarce crystalline basement environments, while recognising that recharge potential and intrinsic vulnerability represent relative spatial indices.