To provide a method enabling to perform a detoxicating treatment for soil contaminated with an organic chlorine compound whose object is the soil in a saturation band lower than a water level of the underground water but also the soil in an unsaturated band higher than a water level of the underground water or dug and cut soil, relatively inexpensively with an addition of a small quantity of single iron material compared to a conventional method, in a short time and at the normal temperature.

This process consists of an addition and mixing method by means of spraying iron powder as a reducing agent into the soil in the earth together with a high pressure medium, or mechanically mixing by utilizing an construction machinery, etc. Preferably, the iron powder contains 0.1 wt% or more carbon, and has particle sizes whose 50 wt% or more the carbon passes through a sieve of 150μm mesh, has a specific surface area of 500cm2/g or more, and is added to the soil in the range of 0.1-10%. Sponge-like iron powder is used as the iron powder to efficiently attain the object.

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