Zarin Abad plain is located in Zanjan province in the western part of Iran. In this study, spatial analysis was used to interpret some of the chemical parameters of groundwater samples collected from the unconfined aquifer. For this reason, groundwater samples (61) were collected from groundwater monitoring wells to investigate the characteristics of groundwater quality. Maps showing the geographical distribution of hydrochemical parameters were prepared and the impact of various geological formations on the groundwater quality in the region is considered. High values of EC value in the western parts of the plain could be associated with the lithological formations composed of marls and evaporates. Based on SAR values, it is concluded that the majority of groundwater samples is relatively suitable for irrigation use. Analysis of the spatial coherence of the variables from each other was performed using selected models and the Kriging, Co-Kriging and Inverse Weighted Distance (IWD) methods were ultimately used to decipher the spatial variation of the parameters. The results obtained through these methods were compared by root-mean-square error (RMSE) and mean absolute error (MAE). It was found that the Co-Kriging model is the most optimal technique, for studying the spatial distribution in groundwater quality parameters.
