This permeable reactive barrier (spherical panorama) needs to clean a strongly contaminated water, percolating from a dump containing the solid residues of the abandoned arsenic mine of Baccu Locci near the town of Villaputzu in the south-east of Sardinia. Every day the filter can receive between 500 liters and 10 cubic meters of waste water, depending on the season and the amount of rain fall. The acid water contains almost 1 gram of dissolved toxic heavy metals per liter, such as aluminium, cadmium, copper, nickel, lead and zinc. Before it can leave the filter and be discharged into a nearby stream bed, the concentration of heavy metals must be lowered almost 1000 times, to less than 1 milligram per liter, so 99.9% has to be removed. The filter contains granules of porous rock that we have specially prepared for this job. They give off a harmless metal in exchange for the toxic ones that take its place and become immobile solids. In the winter, when it rains a lot, the water can only remain half a day in contact with the granules, moving through the 5 cubic meters of pore space in the filter. In the summer, when it is mostly sunny and dry, the water can remain up to 10 days to react, because of the much lower volumetric flow rate. From the entrance to the exit, the water becomes progressively cleaner as it passes through sectors in the filter. From the exit to the entrance, the granules become progressively dirtier as the toxic metals precipitate. In the end, after a couple of months, the granules lose their capacity, become exhausted, must be discharged in a normal waste dump and have to be replaced with fresh ones. Of course, it is always exciting to wait for the results of the measurement of the samples of water and granules returning from the laboratory; and a great relief if what you have concocted works as well as promised. But most rewarding is when you see that wild live appreciates what you have done. You open the filter and in the last sectors with cleaned water are specimen of the toad Discoglosso sardo. They look a bit annoyed that you dared to enter their new home. Fortunately you can leave and close the door behind after half an hour of sampling work, letting them undisturbed for 2 weeks before the next sampling day arrives. I guess we should start thinking for a solution when we need to exchange the granules. A day and night in a hotel, kind of bowl of water below a rock, might this suit the protected species?