The invention relates to a method to repair a leak in a geological structure or a construction comprising a geological material, comprising administering a liquid nutrient composition, comprising an energy source for anaerobic bacteria and a multivalent metal ion upstream of the leak allowing micro-organisms present in the structure or construction to ferment the energy source and to grow, thereby increasing biomass in and/or around the leak releasing mineral particles upstream of the leak allowing the mineral particles to migrate to the leak; and allowing the mineral particles to settle in the biomass.