This paper is the result of environmental geological survey engineering.
[Objective] Organic pollutants, such as chlorinated hydrocarbons and BTEX, have an important threat to groundwater environment in China. Natural attenuation monitoring plays an important role in contaminated sites remediation. Researches on natural attenuation monitoring will be conductive to promoting the development of groundwater organic pollution control and environmental remediation technologies. [Methods] In order to study the natural attenuation of 1,2,3-trichloropropane (TCP) and benzene in different aquifers groundwater, the 3-year monitoring data of TCP, benzene, oxidation reduction potential (ORP), nitrate (NO₃^-) and biodiversity in an organic contaminated site has been collected and analyzed. Natural attenuation capacity of the pollution source area of the site was calculated using first order attenuation kinetic equation. [Results] The results show that the natural attenuation of TCP and benzene occurred in the aquifer for different degrees, and ORP values of the groundwater in phreatic and confined aquifer were -225~-57 mV and -182~-3 mV, respectively, which were medium-high reducing environment with basic environmental conditions for anaerobic biodegradation of organic pollutants. Moreover, the effect of microbial degradation was stronger in the pollution source area and phreatic aquifer than that in non-pollution source area and confined aquifer, and the degradation rates of TCP and benzene in the phreatic aquifer of MMW02 monitoring well were 80.00% and 77.88%, respectively. The attenuation rate of TCP and benzene were 0.0018 d^-1 and 0.0016 d^-1 in phreatic aquifer, and 0.001 d^-1and 0.0015 d^-1 in confined aquifer. [Conclusions] According to the different degree of groundwater pollution, the natural attenuation monitoring technology can be used alone or combined with other remediation methods and technologies, which is a low cost and high efficiency method to reduce groundwater organic pollution for this kind of industrial contaminated sites.