The implementation of the IPPC directive mandates that industries use techniques which have the same effectiveness as Best Available Techniques (BAT). BAT represents the combination of technical processes and management practices with overall positive environmental and cost benefits. Article 13 of the IPPC directive is about the revision for initial permit conditions. To comply, industries should adopt a rigorous approach to justify to the authorities that all of their existing techniques are equivalent to BAT environmental performances. This analysis must be done technique by technique. For this, technical guides have been established at the European level: the BREF. Unfortunately, these documents are not easy to use nor particularly clear. Therefore, the aim of this research project is to develop an environmental performance process assessment methodology in order to compare and then validate in house processes as BAT. Our methodology will be tested on wastewater treatment processes for metal finishing sectors. This decision making tool emphasizes the cross media effects and thus corresponds to an integrated approach for the IPPC directive.