Groundwater vulnerability and pollution risk assessment of porous aquifers to nitrate: Modifying the DRASTIC method using quantitative parameters

In the present study the DRASTIC method was modified to estimate vulnerability and pollution risk of porous aquifers to nitrate. The qualitative parameters of aquifer type, soil and impact of the vadose zone were replaced with the quantitative parameters of aquifer thickness, nitrogen losses from soil and hydraulic resistance. Nitrogen losses from soil were estimated based on climatic, soil and topographic data using indices produced by the GLEAMS model. Additionally, the class range of each parameter and the final index were modified using nitrate concentration correlation with four grading methods (natural breaks, equal interval, quantile and geometrical intervals). For this reason, seventy-seven (77) groundwater samples were collected and analyzed for nitrate. Land uses Were added to estimate the pollution risk to nitrates. The two new methods, DRASTIC-PA and DRASTIC-PAN, were then applied in the porous aquifer of Anthemountas basin together with the initial versions of DRASTIC and the LOSN-PN index. The two modified methods displayed the highest correlations with nitrate concentrations. The two new methods provided higher discretisation of the vulnerability and pollution risk, whereas the high variance of the (ANOVA) F statistic confirmed the increase of the average concentrations of NOT, increasing from low to high between the vulnerability and pollution risk classes. The importance of the parameters of hydraulic resistance of the vadose zone, aquifer thickness and land use was confirmed by single-parameter sensitivity analysis. (C) 2015 Elsevier B.V. All rights reserved.