TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The organic matter is bread or vegetables.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The acidogenic leachate is obtainable by a process of decomposing organic matter in the presence of acid-producing bacteria, such as bacteria producing formic acid, acetic acid, propionic acid and lactic acid, and adding water to the decomposed organic matter to obtain the acidogenic leachate. The process further involves separating the acidogenic leachate from residual solid matter. The step of decomposition of organic matter is performed in the presence of the soil to be washed. The step of exposing of the soil to an acidogenic leachate is perfomed in parallel with the production of the acidogenic leachate by mixing organic material, soil to be washed and water before letting the organic material decompose in acidogenic conditions. The method further involves rinsing the washed soil using a rinsing liquid and/or vacuum filtering to produce clean soil and purifying the contaminated leachate by precipitating contaminants such as metal cations in contaminated leachate, and adding a substance such as a sulfate to the contaminated leachate, and transporting the washing and/or rinsing container to the site, where the contaminated soil is located. The method is performed near the location of the contaminated soil. Preferred Components: The washing container is arranged to hold contaminated soil and organic matter and to let the organic matter decompose under anaerobic conditions, liquid providing unit is arranged to provide water to the mixture of soil and organic matter, thus the acidogenic leachate can be produced by the decomposition of the organic matter. The first and/or second separation units include a tap for releasing the contaminated leachate and/or the contaminated rinsing liquid, and mechanism such as a transport line or a feed screw, for lifting the washed and/or rinsed soil from the washing and/or rinsing container to a next container.