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Crude Oil Contaminated Soil (COCS) is considered as hazardous waste due to presence of petroleum hydrocarbon (PH) above requirement level indicated in applicable environmental law and may result in environmental concerns to ecosystem. Conventionally, ex-situ remediation was chosen by transporting COCS to processing facilities, and further processed through bioremediation at designated facilities or other hazardous waste treatment facilities. A new approach of “hybrid on-site bioremediation” has been implemented to remediate the COCS at Rokan field. The method uses microorganisms to breakdown contaminants of petroleum hydrocarbons on-site that significantly reduced about 70% the needs of transporting the COCS to different processing facilities hence reducing support infrastructure required to conduct remediation. The on-site bioremediation method involves mixed process of biostimulation and bioaugmentation to improve effectiveness of the process while still keeping critical parameters such as humidity and temperature, as well as microorganisms levels within control to maintain their contaminant degradation performance.

As a result, through careful implementation, original level of petroleum hydrocarbon in the range of 10.000 – 50.000 mg/kg could be reduced rapidly to <1.000 mg/kg within 4-month. This process potentially results in significant cost reduction about 30% of project cost compared to conventional fully ex-situ process while still meeting success criteria standards set by the government. Hybrid on-site remediation method also reduces risks for transportation accidents due to lower traffic required.