Drastic model application to groundwater vulnerability elucidation for decision making: the case of south western coastal basin, Ghana

The health of the population is intertwined with the availability and supply of potable water. With many people around the world resorting to groundwater resources as a source potable water supply, it becomes imperative that the state of groundwater susceptibility to contamination is known. The DRASTIC model has been applied to determine the state of aquifer vulnerability to contaminants. The seven hydrogeological parameters were considered in the standard model and the resulting vulnerability, DI were classified into three vulnerability zones; low, moderate and high. The model was then modified to include land use/land cover (LU) and lineament density (LIN) parameters and net recharge (rm). The modified vulnerability indices were designated as DI-LU, DI-LIN, DIrm and MDI (combined modification). The results revealed the land area under high vulnerability under DI, DI-LU, DI-LIN, DIrm and MDI were 32.2, 26.2, 33.7, 26.2 and 40.4% respectively. There were no significant difference between the standard moderate vulnerability class and the modified derivatives (DI + LU, DI + Lin). The combined modification (MDI) however led to 17% decrease in this class of vulnerability. The model was validated using a nitrate concentration of 36 samples collected for the purpose. The validation assessment revealed that the performance of the model was improved with modification.