ABSTRACT: Since most of models for estimation of groundwater contamination are developed for agricultural applications and they are often sophisticated, in this paper a combined approach based on analytical methods that need limited input data has been developed. To estimate nitrate contamination of unsaturated zone in large areas, a Lumped Parameter Model (LPM) and the mass balance approach have been used together. In the case study, model results show an acceptable correlation with field measurements. In addition, the fate of nitrogen in the unsaturated zone is simply defined.