Determination of aquifer vulnerability using DRASTIC model and a single parameter sensitivity analysis and acts and omissions (Case Study: Salafchegan-Neyzar Plain)

Nowadays one of the solutions to protect aquifers in developed countries is to prevent contamination of aquifers. In this study Salafchegan-Neyzar Aquifer vulnerability against agricultural pollution was evaluated, by Drastic and GIS models. In this method, seven hydrogeological factors that were effective in groundwater pollution were combined. The seven factors are: watertable depth, the net recharge aquifer, aquifer media, soil media, topography and the unsaturated hydraulic conductivity. Vulnerability zoning maps were drawn from the results obtained. Zones vulnerable to nitrate pollution were determined. Using GIS techniques and by single-parameter sensitivity analysis, the influence of parameters used were investigated. Results showed that depth to water table aquifer of Salafchegan was the most important factor influencing vulnerability in Salafchegan-Neyzar aquifer. The results of different qualitative zones was shown in four categories of very low, low, medium, high which were 550, 853, 150 and 498 square kilometers before the correction of model were converted to 351, 486, 401 and 425 after the model correction. In general, sensitivity analysis showed that effective and theoretical weight of using parameters, aren’t fully coincide and in some cases have considerable differences.