Fracking and Well Stimulation

Hydraulic fracturing or fracking is among the extreme techniques the oil and gas industry uses to extract oil and gas from hard-to-reach places. It involves injecting high volumes of water, toxic chemicals,  sand and other materials deep into the ground to break up soil and rock. Increasingly, the industry also uses a form of well stimulation, often called acid stimulation, which involves injecting high concentrations of exremely powerful acids deep into the ground to dissolve rock.
For a good overview of fracking and acid stimulation in California, see Robert Collier's series of articles published on the website of the Next Generation.
Sierra Club California has developed fact sheets that provide brief overviews of various fracking issues. Here's the list of those fact sheets that can be downloaded:
Frack Facts List--A list of interesting facts and figures about fracking.
Basic Fact Sheet--A basic fact sheet about fracking and well stimulation, developed by a coalition of environmental groups.
Fracking and Human Health Fact Sheet--A fact sheet about human health impacts from fracking and acidization.