One hundred and nineteen samples were collected and measured to study the pollution degree and distribution characteristics of total petroleum hydrocarbon (TPH) in vadose zone and water-bearing medium in a petroleum contaminated site. The method of cumulative frequency was used to identify the background threshold by solving the intersection point of the linear regression lines. This method has solved the inaccurate problem in identifying the background threshold caused by difference in drawing of the cumulative frequency curve. The contamination status was analyzed and evaluated by method of single factor index. The results show that the site background threshold of TPH was 36.7 mg·kg^-1. In the south of the contaminated site (pollution source), the TPH pollution level of medium in vadose zone gradually decreased with the increase of depth. That of water-bearing medium increased first, decreased after stability, and finally stabilized at the secondary pollution level. As for the central area of the site, the contaminated characteristics in vadose zone were similar to that in the southern area. The water-bearing medium was polluted by petroleum hydrocarbons only in the shallow part. In the north of the site, there was no or low TPH contamination. The pollution degree of medium in vadose zone was higher than that of water-bearing medium.

vadose zone  /  water-bearing medium  /  petroleum hydrocarbon  /  background threshold concentration  /  pollution characteristics