Site-specific protocols for evaluating environmental compatibility of spoil materials produced by EPB-TBMs

The EPB-TBM performance relies on the selection of the appropriate conditioning additives. The anionic surfactant sodium lauryl ether sulphate (SLES) is the main component of several foaming agents. Consequently, tunneling spoil material can contain SLES residual concentrations. Owing to the lack of SLES threshold limits in soil in both European and Italian legislation, it is necessary to apply an ecological approach to produce a site-specific Protocol to be used during the excavation phase for classifying spoil material as a by-product. The approach includes: preliminary environmental risk assessment based on the ecotoxicity of each compound inside the conditioning additives; microcosm/mesocosms studies for evaluating the SLES biodegradability in the spoil materials during their temporary deposit and, finally, the evaluation of the potential ecotoxicity on test organisms selected on the basis of the possible scenarios of soil and water exposure to SLES residual concentrations in the final destination site.