Hydraulic fracturing, the natural gas extraction method known popularly as fracking, has been controversial in large part to the concern about groundwater contamination by the fluids used in the process, especially the so-called flowback fluids that re-emerge at the surface from fracking wells and are usually disposed of by waste water fluid injection into other formations. Now, researchers have developed a geochemical method of identifying fracking fluids in the environment. The tool could be used to identify hazardous spills in the future and may even lead to better use and disposal of fracking wastewater.