Environmental concerns over fracking have heightened as the practice has grown to address the nation’s demand for fossil fuel.

Fracking involves injecting water mixed with sand and chemicals into shale formations at high pressures to extract fuel.

The recent spread of fracking has raised concerns among environmentalists, public health advocates and some neighbors of shale wells who worry about issues such as water contamination and increased truck traffic. Some have also linked earthquakes to disposal of waste water from shale wells.