ORIGINAL PAPER Modelling nonpoint source pollution by nitrate of soil in the Mateur plain, northeast of Tunisia Nesrine Nasri & Mohamed Chebil & Lamia Guellouz & Rachida Bouhlila & Abdellatif Maslouhi & Mohamed Ibnoussina Received: 5 July 2012 /Accepted: 26 November 2013 # Saudi Society for Geosciences 2014 Abstract In order to quantify groundwater contamination by nitrate diffuse pollution in Mateur plain (northeast of Tunisia), it is necessary to evaluate the amount of pollutants, rejected at soil surface as fertilizer or as farm discharge, that passed through the unsaturated zone. For this purpose, we used two methods: the first one is to determine a vulnerability map of Mateur aquifer through the empirical DRASTIC method. The second method consists of determining the average water flows of percolation to the aquifer and the amount of nitrate lixiviation by using Leaching Estimation Chemistry Mode (LEACHM): a one-dimensional difference element model. In order to obtain annual average values, we have been simulating many profiles with the same average daily data to obtain a constant annual recharge and nitrate mass reaching the aquifer. Integrating these results on the whole plain allowed us to produce maps of the groundwater recharge and their nitrate concentrations. The results of nonpoint agricultural pollution modelling are compared to those of index method DRASTIC. We noticed a good correlation between LEACHM simulation and DRASTIC index results. Water table depths, surface soil permeability, and soil texture are the most important factors governing nitrate leaching to groundwater. Keywords Diffuse pollution . Modeling . LEACHM . Soil . Percolation . Vulnerability . Nitrate Introduction The preservation of groundwater quality constitutes a major preoccupation to avoid health problems caused by polluted water resources. Aquifer ’ s pollution by ni- trogen resulting from fertilization, effluents of farm, and wastewater leakage constitutes an environmental problem for areas of intense agricultural practices (Brindha and Elango 2013; Dar et al. 2013). The deterioration of water quality generates significant health and environmental problems. Prediction of contamination risks requires the comprehension of the whole processes involved in the circulation and transformation of pollutants in the unsatu- rated zone which constitutes an interface of water ex- change, pollutants, and microorganisms between the aquifer and the biosphere. Several approaches have been proposed to evaluate groundwater contamination such as using GIS and groundwater modelling (Baalousha 2011) to elaborate the risk map which helps the government to set the strategy of groundwater use. Boughriba et al. (2010) have established groundwater vulnerability and risky zones maps using DRASTIC model. In this work, we have first carried out a vulnerability study of the Mateur plain (Chebil 2009) based on DRASTIC method (Berdai et al. 2004; Wen et al. 2008; Awawdeh and Jaradat 2010; Srinivasamoorthy et al. 2011) which constitutes an index method (Haag and Kaupenjohann 2001; Koo and O’Connell 2006; Al Hallaq and Elaish 2012). This method was developed N. Nasri (*) : M. Chebil : L. Guellouz : R. Bouhlila Ecole Nationale d’Ingénieurs de Tunis, Laboratoire de Modélisation en Hydraulique et Environnement, Université de Tunis El Manar, BP 37, Le Belvedere, 1002 Tunis, Tunisia e-mail: nasri.hydro@gmail.com A. Maslouhi : M. Ibnoussina Laboratoire Interdisciplinaire en Ressources Naturelles et en Environnement, University Ibn Tofail, Kenitra, Morocco Arab J Geosci DOI 10.1007/s12517-013-1215-8