Groundwater Risk Assessment of Shallow Aquifers within the Atankwidi Basin of Northeastern Ghana

Abstract

The potential leaching of harmful chemicals (heavy metals) due to application of large quantities of agro-chemicals in an impending up-scaling of dry-season irrigational farming into shallow groundwater aquifers has necessitated the study to assess the potential risk to contamination of the shallow (weathered) aquifers within the Atankwidi basin of Ghana using the combination of DRASTIC and Arc GIS. The DRASTIC indices ranged from 41 to 117 representing the lowest to highest vulnerable (risk) areas. 34.4 km2, 93.3 km2 and 63.9 km2 representing 20, 48.8 and 33.2% of the area had low, moderate and high risk with indices ranging between 41–71, 71–88 and 88–117, respectively. Moderate and high risk areas which constituted approximately 80% of the area are underlain with clay-loam and sandy-loam soils, where major farming takes place. High risk areas are located in elevated areas (recharge), having the shallowest depth-to-water table and highest conductivity values. Sensitivity analysis revealed influential parameters in order of Hydraulic conductivity (C) > Soil media (S) > Depth to water table (D) > Net recharge (R) > Impact of vadose zone (I) > Topography (T) > Aquifer media (A). Validation of the DRASTIC model using heavy metals revealed that elevated concentrations were found within the high risk and vice versa. It is recommended that pollution-prevention measures would be taken account during the planning and implementation of the up-scaling program.