Groundwater Vulnerability Assessment using Drastic Index and GIS in Kumasi Metropolitan Assembly, Ghana.

The assessment of groundwater vulnerability to contamination has become an important element for landuse planning and groundwater resource management. This study aims at estimating groundwater vulnerability using an integration of Geographic Information System (GIS) and DRASTIC method in the Kumasi Metropolitan Assembly (KMA). The groundwater vulnerability map was prepared using index and overlay analysis with the aid of Arc GIS 10. The DRASTIC Index (DI) computed ranged between 70 and 164 as the lowest and highest contamination potential respectively. The eastern and western flanks and north-west tip of KMA are underlain by the granites which bear water due to the combined effect of weathering and fracturing and are dominated by "Very High", "High" and "Moderate" vulnerability based on the vulnerability index computed. The "Low" and "Very Low" vulnerability are located at the northern, central and southern parts of KMA which are underlain by phyllites. These suggest that boreholes located in the Birimian metasedimentary units which comprise mainly phyllites would be less likely to be vulnerable to contamination than those located in the intrusive rocks dominated by the granites. Keywords : Groundwater Vulnerability, Soil Media, Hydraulic Conductivity, Overlay Analysis