Our studio guest is Prof. Holger Weiß, of the Helmholtz Center for Environmental ResearchAnd here to tell us more about the different methods currently being used for groundwater remediation is an expert from Germany’s Helmholtz Center for Environmental Research, Holger Weiss. You are working on the project of purification of contaminated water. What's the actual state of art there? Holger Weiss: Well, we just finished our first project phase of three years and one of the models that we have developed, the technological model we are right now upgrading to real, let me say industrial size, to be used in the future for groundwater remediation at that proper site.   ..which is in Leuna in east Germany. ..which is in Leuna, a former refinery site and chemical production site. And what kind of problem is there with the groundwater? Well, we have petroleum, hydrocarbons, diesel, all kinds of stuff that has been produced there since back there in the 1920s. How much petroleum is that actually on the groundwater? Well, that's hundreds of thousands of liters, it's floating, like all of these old refinery sites; they are floating on their own products. And you are able to get rid of all this oil and petroleum products with plants? Well, of course the pure oil phase is being recovered, the first step of the site remediation. But some of the petroleum hydrocarbons are diluted in the groundwater and that's the problem because these groundwater forms contaminant plumes that will reach some day a river or a waterworks and that's going to be managed. But I suppose there is a catch. It probably takes forever till the water is clean again. Well, we are taking about remediation timescales about decades, maybe hundreds of years and because of this long time span the operational costs are the critical factor and as long as we can use those quite cheap natural remediation approaches we can save a lot of taxpayers' money. And probably from an ...