Comparative study for assessment of groundwater vulnerability to pollution using DRASTIC methods applied to central Nile Delta, Egypt

Groundwater (GW) is a significant source of freshwater supply because of the increasing the demand of for water for agriculture, industrial, rapid population growth and domestic consumption. In this paper, DRASTIC vulnerability model was implemented to assess vulnerability zones in the middle Delta, Gharbia Governorate (Egypt). DRASTIC maps are developed for modified pesticide DRASTIC, modified DRASTIC and pesticide DRASTIC. Analytical hierarchy process (AHP) was applied to optimize the ratings and the weights of vulnerability DRASTIC model input parameters. Quantile classification approach was applied to classify the areas as follow: very high, high, moderate, low and very low vulnerable to groundwater contamination in all DRASTIC models. Based on all DRASTIC models, obtained results demonstrate that South of Zefta is classified as a very high vulnerable zone. Most of Qutur region is classified as moderate vulnerable zone based on all DRASTIC models, except AHP-pesticide DRASTIC and AHP-modified pesticide DRASTIC are classified as highly vulnerable zone. The majority of Samanod region as well as north of Al-Mahalla Al-Kubra region are categorized as a very low vulnerable zone. Single-parameter sensitivity analyses demonstrated that groundwater depth characteristic possesses the maximum influence on vulnerability assessment. The models are validated with measured nitrate concentration for water samples collected from 75 wells. Obtained results show accepted correlation between nitrate concentration and AHP pesticide modified DRASTIC.