A software package AHP-DRASTIC has been developed to derive ratings and weights of modified DRASTIC model parameters for use in specific aquifer vulnerability assessment studies. The software is integrated with ArcView Geographical Information System (GIS) software for modelling aquifer vulnerability, to predict areas which are more likely than others to become contaminated as a result of activities at or near the land surface. The ranges of a few of the DRASTIC model parameters have been modified to adapt to local hydrogeologic settings. Analytic Hierarchy Process (AHP) has been used to compute the ratings and weights of the criteria and sub-criteria of all parameters used in the DRASTIC model. The output from AHP generates a MS Access database for these parameters, which is then interfaced with ArcView using Avenue Scripts. AHP-DRASTIC is aimed at providing userfriendly GUI interfaced with GIS for the estimation of weights and ranks of the thematic layers used for aquifer vulnerability assessment. Contingency table analysis indicates that all wells in low and high vulnerability category have concentrations less than 10 ppm and more than 10 ppm, respectively. The model is validated with groundwater quality data and the results have shown strong relationship between DRASTIC Specific Vulnerability Index and nitrate-as-nitrogen concentrations with a correlation coefficient of 0.84 at 0.01 level.