A study was undertaken to determine seasonal variations in nitrate concentrations in a transnational groundwater resource beneath the Ceylanpinar Plain near the border between Turkey and Syria. Spatial distribution maps of nitrate pollution for groundwater in the study area were created using a geographical information system (GIS), and the potential for contamination in the entire plain was determined. Seasonal variations of nitrate concentrations in groundwater were assessed by sampling during spring, summer, autumn, and winter in the period April 2012 to January 2013. The groundwater samples were analyzed for nitrate (NO3). The results obtained were evaluated using a number of national and international standards and classifications. Seasonal average concentration distribution maps were established for nitrate to determine the extent and severity of contamination by this parameter in groundwater in the region. The monitoring indicated that nitrate concentrations in only two wells exceeded the recommended drinking water limit and that groundwater beneath the basin is currently suitable for irrigation.