Hydraulic fracturing is the use of sand, water, and chemicals injected at high pressures to blast open shale rock and release the trapped gas inside. Horizontal drilling (also called "directional drilling") is just like it sounds: after the well drill reaches a certain vertical depth in the ground, the well is then drilled horizontally.
Unfortunately, this process can go wrong, and if the oil or gas wells are not built sturdily enough, they can leak and contaminate groundwater. “Flowback” water can contaminate streams and water supplies. The rush into fracking has not kept pace with important environmental safeguards. For example, toxic fracking fluids, including known cancer-causing chemicals like benzene and toluene, are exempt from federal regulation under the Safe Drinking Water Act.