GROUNDWATER VULNERABILITY ASSESSMENT FOR ISLAMABAD CAPITAL TERRITORY; A GIS PERSPECTIVE

Abstract

Groundwater quality is becoming a major concern in Pakistan due to rapid deterioration of aquifers. A preliminary screening analysis to evaluate the vulnerability of groundwater resources of Islamabad has been carried out using a modified DRASTIC model. The model takes into account seven hydrogeological parameters; that include Depth to groundwater, Recharge, Aquifer media, Soil, Topography, Impact of vadose zone and hydraulic Conductivity. The DRASTIC has been modified to include the degree of influence that geological structures have on the groundwater vulnerability. The multi-criteria analysis ability of GIS provided an accurate and time­effective platform for the implementation of the DRASTIC methodology. Overlay analysis was employed on thematic layers of each hydrogeological factor to obtain a spatial distribution of DRASTIC index. The results reveal that highest potential sites for groundwater contamination lie in the urban area of ICT zone 1 and area surrounding Rawal Lake in zone 3. The GIS analysis of groundwater vulnerability indicates that a spatial autocorrelation exists within a distance of 02 Km around each point for which DRASTIC index is calculated. The "Groundwater risk map" has been generated with the help of GIS based map algebra. The study area includes a variety of potential contaminant sources including a landfill site, which have been combined with the susceptibility assessment to generate sector wise groundwater risk maps. The study indicates that sectors F-10, G-10, F-11, G-11 and G-6 and the landfill site are under high risk. The percentage of high risk zone under industrial area in zone 5 is very high (around 45 percent). Further site specific investigations are recommended.