Keywords: 
• in-situ bioaugmentation /
• physicochemical properties /
• biochemical properties /
• vertical distribution /
• anaerobic remediation

Abstract: The in-situ bioaugmentation strategy was used for bioremediation a oil contaminated soil for 16 months, the vertical distribution of the physicochemical, biochemical properties and hydrocarbon composition were studied. The test results showed that the order of oil removal rate was surface soil(IN-3)(50.42%)> middle soil(IN-2)(23.54%)>subsurface soil(IN-1)(10.51%). As sulfate reduction and nitrate reduction took place in subsurface soil, the pH reduced from 7.86±0.03 to 7.27±0.03, and the TN reduced from 2.53±0.13 g/kg to 0.77±0.04 g/kg. The order of anaerobic bacterial count was IN-1(10.43±0.71×104 CFU/g)>IN-3(6.74±0.39×104 CFU/g)>IN-2(5.15±0.42×104 CFU/g),and there had a negative and significant impact on the level of trust(r=-0.989, p=0.011<0.05) between actinomycetes count and TPH. The saturate and aromatic removal rates of surface soil were highest compare to the IN-2 and IN-1 soil, reached 70.27% and 54.52%, respectively. The GC results showed that the n-alkanes of the surface soil was degraded extremely, and the nalkanes of the subsurface soil was degraded very small. The removal rate of resin and asphaltene was related to the anaerobic bacterial count. The anaerobic bioremediation strategy should be considered when the in-situ remediation was applied in the oil contaminated area which polluted dispersively.