In recent years, elevated nitrate content of groundwater has become a growing concern in the SandA +/- klA +/- basin. Groundwater is the major source for using as irrigation and drinking water in the basin. The average nitrate concentration of groundwater is 23.64 mg/l, and 37 % of these water samples exceeded the maximum acceptable level (50 mg/l NO3) according to WHO regulations. Agricultural practices involving inorganic fertilizer and animal manure applications are the main sources of nitrate contamination in groundwater in the study area. The most important aim of the study is to analyze the temporal and spatial variability of nitrate concentrations in groundwater and to determine the impact of key parameters such as groundwater depth and flow direction, hydraulic conductivity, land use, soil type, vadose zone, topography, and net recharge. R-mode factor analysis was used to identify parameters that are more effective for increase of nitrate contents in groundwater. According to factor analysis results, land use and vadose zone are the most effective parameters for increase of nitrate concentrations in dry and wet seasons.