Development and testing of three hybrid methods for the assessment of aquifer vulnerability to nitrates, based on the drastic model, an example from NE Korinthia, Greece

The assessment of groundwater vulnerability to pollution has proved to be an effective tool for the delineation of protection zones in areas affected by groundwater contamination due to the intensive fertilizer applications. The main objective of this study has been to develop and check the results of three hybrid methods for specific aquifer vulnerability assessment based upon the parameters, classification and rating principles of the well known DRASTIC model. The first method, proposed by [Panagopoulos, G., Antonakos, A., Lambrakis, N., 2006. Optimization of DRASTIC model for groundwater vulnerability assessment, by the use of simple statistical methods and GIS. Hydrogeology Journal (published online).], has proved to be an effective way to modify the DRASTIC model in order to achieve better correlation with actual nitrates occurrence. Descriptive statistics and simple statistical tests on a hydrochemical dataset are used by the method in order to change the initial factor ratings and factor weights participating in the vulnerability assessment equation. The other two methods were developed by the use of logistic regression and weights of evidence statistical procedures and the use of the same hydrochemical dataset, and attain relatively high correlation factors when referring to sample points while correlation was significantly lower for the entire distributions of vulnerability estimation and actual nitrates occurrence.