Method and system for the remediation of contaminated earth from hazardous substances in a batch-wise ex-situ on site manner. At least one mobile earth moving equipment, at least one mobile tumbler reactor and at least one liquid – solid separator are organised at a location in the proximity of the contaminated site. Contaminated earth portions are collected from the contaminated site batch by batch in the mobile earth moving equipment, transported to the location and transferred to the mobile tumbler reactor at the location. The contaminated earth portions in the mobile tumbler reactor are dosed with cleaning agents and water washed in the reactor under agitation or tumbling. The mixture of water washed earth portions and wash water with cleaning agents in the mobile tumbler reactor is transferred into the liquid-solid separator at the location and the wash water with the cleaning agents is separated from the mixture in the separator. The cleaned earth portions in the separator are transferred into the earth moving equipment, transported back to the contaminated site and deposited at the contaminated site until the entire contaminated earth at the contaminated site is remedied. At least one water treatment plant is optionally organized at the location for treating the wash water. The logistics of carrying out the operations are controlled with a controller automatically or are controlled manually or partly manually and partly automatically. The invention achieves efficient and effective remediation of the contaminated site within a short time in a very simple and economical manner. It is particularly advantageous in an emergency or accident like oil spillage.