Sequenced biobarriers use successive treatment zones containing different reactive materials or reactants which modify the system biogeochemical conditions to remediate a wide range of complex waste streams (e.g. mixed metal-organic wastes and mixed solvent plumes) in situ. Lab studies will deduce processes, biogeochemical limitations and design parameters (e.g. residence time, reaction kinetics, biofilm stability and barrier composition) for treatability, in model barriers using organic-metal contaminant mixtures. Related field studies at sites with existing reactive barriers and diffuse pollution will examine up-scaling of design parameters from lab to field applications, effect of heterogeneity in system properties (e.g. hydrogeology, contaminant flux) and treatment optimisation. Geochemical, molecular microbiological and stable isotope analysis will be used to study biogeochemical processes at the lab and field-scale. The effect of non-target species on treatment of target compounds and the link between hydrodynamic flux, microbiological activity and biofilm growth in the lab and field-scale biobarriers will be examined. At field-scale, changes in treatment capacity from variations in hydrogeological, geochemical and microbiological parameters controlling attenuation will be quantified using similar approaches. The results will be interpreted with multi-scale modelling tools and statistical methods to develop performance-based criteria for the design, monitoring and assessment of sequenced reactive barriers.