Horizontal hydrofracking is a means of tapping shale deposits containing natural gas that were previously inaccessible by conventional drilling. Vertical hydrofracking is used to extend the life of an existing well once its productivity starts to run out, sort of a last resort. Horizontal fracking differs in that it uses a mixture of 596 chemicals, many of them proprietary, and millions of gallons of water per frack. This water then becomes contaminated and must be cleaned and disposed of.