To economically create a water permeable bed having reliability.

In the bottom part water barrier structure provided to the bottom part of the ground so as to cover the ground containing a polluted region from below, a plurality of injection pipes traversing the area under the ground and curved in a protruding state so that the central parts thereof are positioned at the lowermost end to be extended and arranged in parallel and the water barrier beds formed between the adjacent injection pipes by injecting a solidifying material in the circumfernetial ground by the injection pipes are provided. This bottom part water barrier structure is formed by parallelly extending and arranging a plurality of the curved injection pipes so that the intermediate parts thereof are positioned at the lowermost end between a start base A and an arrival base B and injecting a solidifying material into the circumferential ground from the injection pipe to form the water barrier beds and integrating the injection pipes and the water barrier beds to cover the ground of a ground predetermined region containing a polluted region 11 from below.