To facilitate execution of construction work of a permeable reactive barrier (PRB) or replacing work of the same, and to shorten a construction period.

In construction of the PRB 1, H section steels 22 are driven into the ground in a manner enclosing a region where the PRB 1 is constructed, and then the region is excavated. In order to prevent an excavated surface generated by excavation from caving, transparent horizontal planks 23 are fixed to a gap between the H section steels 22. After completion of the excavation, a decontamination material 21 is filled in an excavated hole to back-fill the excavated region, and the H section steels 22 are kept arranged around a decontaminated section 11 formed of the decontamination material 22. The H section steels 22 may be connected together by fixing members 25 in place of arrangement of the horizontal planks 23.

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