Very serious. For one thing, we don't even know all the chemicals being used during the fracking process. But many of the ones we do know about are well-documented (1,2,3) for causing cancer, birth defects, and disorders of the nervous system. The same is true of many naturally occuring but highly toxic substances that are unearthed throughout the process. These materials are disturbed by drilling or fracking, then seep into the water supply.