A method of prying oil from rock layers is fueling controversy in Kansas, with opponents saying it could threaten the water quality of the Ogallala Aquifer.

The method, called hydraulic fracturing — or fracking — involves drilling deeply into the rock and then injecting water filled with chemicals to open seams in the rock.

Critics say the process involves unhealthy chemicals and heavy consumption of water, and could contaminate water resources.

Energy producers defend the method, which has been used for 60 years. They say there is no documented case of fracking causing water contamination.

The Kansas Independent Oil and Gas Association is scheduled to testify on fracking before a Statehouse committee on Friday.