Abstract: A process for the treatment of soil in situ involving examination and cleaning of contaminated soil. Treating medium and/or any other material for treating the contamination is introduced into the soil intended to be treated. The process involves the use of oblique angled connecting pipes which are connected to a perforated pipe-system fitting to the dominant position of the contaminated layer or the layer intended to be treated. One branch of the pipe system collects the contaminated liquid and/or contaminated soil water and brings it to the earth's surface. The other branch of the system delivers treating medium to the contaminated soil. Optionally, the contaminated liquid or contaminated soil-water can be cleaned and reintroduced into the same branch of the pipe system into which the treating medium is introduced.