That is an excellent question. The Wyoming Department of Environmental Quality, Water Quality Division, thinks that it is, with the caveat that it is done correctly.
From their website: “If done correctly and in accordance with the requirements of the Wyoming Oil and Gas Commission (WOGCC), oil and gas drilling and fracking should not cause contamination of your well. While no one can guarantee that an accident or equipment failure will not occur, the Niobrara Shale play is an extremely high profile development and both the industry and regulatory agencies are watching the development carefully to insure environmental protection requirements are being met. It should be noted that fracking has been a common practice in the oil & gas industry for many decades. It is fracking of shale formations which is a relatively new development.”