Groundwater Vulnerability Assessment of the Kingston Hydrological Basin in Jamaica Using the GIS ‐Based DRASTIC Model

The Kingston Hydrological Basin (KHB) in Jamaica faces serious challenges in water security due to increased urbanisation, limited water resources and inadequate sewage treatment facilities. Nitrate contamination of the alluvial aquifer, coupled with a decrease in rainfall patterns, has resulted in the closure of many groundwater wells and a heavy reliance on surface water systems. This has created an increase in demand for potable water from inadequate surface water resources and water shortages during periods of drought within the KHB and adjoining basins. In this study, the Intrinsic DRASTIC Vulnerability Model, an overlay index method, was used to evaluate the aquifers' intrinsic and specific vulnerability to nitrate contamination. This model determines the vulnerability of aquifers based on seven hydrogeologic factors, including depth to the water table (D), aquifer recharge (R), aquifer media (A), soil media (S), topography (T), the impact of vadose zone (I) and hydraulic conductivity (C). To match the local hydrogeological context and incorporate the influence of human activities on the vulnerability, the model was modified to include ‘land cover’. To further improve the predictivity of the DRASTIC Model, logistic regression (LR) was applied to statistically identify the factors that influence the aquifer's vulnerability to nitrate contamination (concentration > 7.5 mg/L permissible limit accrued to local standard). The results showed that, based on the intrinsic parameters within the basin, areas with shallow water tables and very permeable and porous geology are classified as very high vulnerability. When the land cover is incorporated, the vulnerability is enhanced with the introduction of the source of contaminants. Most of the KHB is highly vulnerable to nitrate contamination, resulting in a higher chance of contaminants entering the system quickly, especially beneath urban areas.