At present, hydraulically fracturing a well requires 3-5 million gallons of water, mixed with sand
grains of different sizes and a number of chemicals, to be pushed into the rock at very high pressures. The
chemicals perform various functions in the fracturing process, like killing bacteria and reducing the viscosity of
the hydraulic fracturing fluid. While some of the chemicals are considered benign, others can be considered
toxic: even when diluted with the large quantities of water used in the process. The fluid is injected into the
well, and when the pressure of the fracturing fluid exceeds the pressure of the rock at depth, the rock breaks
at weak points, usually along planes of weakness. The direction of these planes of weakness can be predicted
to some extent based on the physical characteristics of the rock and the orientation of stresses the rock is
under. During a hydraulic fracture, the rock breaks, creating fractures, or joints, which would, without
something to prop them open, naturally close when the water pressure is subsequently lowered. The sand
or sand-like grains in the fracturing fluid act as propping agents (proppants) remaining in the joints after
the water is removed and the pressure is lowered to keep the joint networks open for natural gas extraction.