Abstract: Monitoring of groundwater contamination needs to consider the hydrogeological conditions, groundwater flow and characteristics of contaminates in the study site. Using spatial distributions of hydrochemical tracers to identify groundwater flow and solute transportation has advantages in easy operation and cost saving. In this study, a petrochemical contamination site was used as an example. By mapping contours of the measured ion concentrations and comparing among them, the source area and plume of the contaminations were identified. In order to make contours for the measured properties, we use four statistic values: P95, P75, P50 and P25 to classify the concentration levels of the measured properties based on their percentage rank. For example, P50 represents the medium number which is 50% of the total concentrations for a certain ion. In so doing, the ten measured ions can compare their relative concentrations with the contours. The area enclosed by contour of P95 is considered as the contamination hotspots. The other contour maps show the probable contamination plume and immigration direction. The results show that the hotpots (P95 contour) of all measured properties are located in a narrow band, and the contours of P75 are similar, indicating close relationship of those solutes. The contour mapping indicates that the contamination source is located in the southwest of the manufactory or the contamination site and move toward southwest with the groundwater flow. This method enhances the reliability of contamination hotspots detection, and can be good reference for contamination monitoring.