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Foam agents used for a method of rheological foam shield-tunneling are mainly comprised of anionic surfactants which are toxic to fish. According to the previous studies, the foaming agent in soil mixed with the foam can be evaluated that environmental impact of toxicity is small because that is inhibited elution from soil mixed with foam and is reduced by biodegradation after elution. In this paper, we analyzed assuming disposal site at sea based on parameter obtained by the previous test results and studied the environmental impact of the foam agent. As a result, elution of foaming agent out of the disposal site and elution concentration of foaming agent in the disposal site were sufficiently small, and concentration of the foaming agent degreased at time. As an environmental impact assessment, the amount of maximum elution was estimated to be sufficiently small, 1/100 or less, compared to the predicted no-effect concentration calculated from acute toxicity. It is possible that we evaluate the environmental impact of soil mixed with the foam by analysis based on test results.

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