Fracking

Just attended a summer geographic seminar on oil, water, and people in ND.  I learned a lot about fracking.  The 2 days we spent on oil and fracking made me not totally sure whether it is good or not.  Of course, going into it, I thought I knew that fracking caused fire water, sink holes, and earthquakes.  Now I am not sure as wells for water are 1800 feet above the fracking and wells have naturally occurring methane, earthquakes happen 498 miles below fracking, and the shale is left in place, so... sink holes???  It will make for an interesting discussion with my students.  Any thoughts?