Hydraulic fracturing injects water, sand, and chemicals into deep underground rock formations such as shale rock. These fluids open or expand fractures in the rock formations, and the fractures release the oil or natural gas.
Large amounts of water and other chemicals are trucked into the well site. Traffic and diesel fumes from generators and trucks going into and out of the well site contribute to air pollution.
Chemicals associated with fracturing include hazardous air pollutants, carcinogens, and chemicals regulated under the Safe Drinking Water Act. They include di(2-ethylhexyl) phthalate
, diesel, ethylene glycol
, ethylene oxide
, hydrogen fluoride, lead
, naphthalene, sulfuric acid, xylene, and solvents
such as benzene
. Benzene, ethylene oxide, and formaldehyde are listed as human carcinogens in the Fourteenth Report on Carcinogens
published by the National Toxicology Program; di(20ethylhexyl) phthalate, diesel exhaust particulates, and lead are listed as "reasonably anticipated ot be human carcinogens."
Fracturing fluids may leak through fractures into drinking water
aquifers. Fracturing fluids may spill onto the ground and contaminate surface water, groundwater, and drinking water aquifers.
After hydraulic fracturing, the direction of the fluids is reversed to flow out of the well to the surface. This mixture of fluids is called flowback. At least 200 chemicals have been identified in flowback, including heavy metals, carcinogens, and radionuclides, including radon
. Accidental releases of flowback can occur from tank ruptures, overfills, fires, or improper operations. There is a risk that released flowback may flow into groundwater or drinking water aquifers.
Other wastewater from hydraulic fracturing can also contain toxic chemicals, carcinogens, and radioactive materials that occur naturally underground.
Hydraulic fracturing in coalbed methane requires from 50,000 to 350,000 gallons of water per well. Hydraulic fracturing of a shale gas well requires between one and five million gallons of water. This water use may raise concerns in locations where water is scarce and may affect streams, aquifers, and wildlife habitat. Withdrawals of large volumes of groundwater can lower the water levels in aquifers. Lowered water tables may cause growth of bacteria, causing taste and odor problems.
Air quality is another concern associated with hydraulic fracturing. Operations emit volatile organic compounds
, which contribute to ground-level ozone
. The operations emit methane
, a component of natural gas. Methane is a potent greenhouse gas that contributes to global warming and climate change
. Methane may also leak into surrounding water wells, underground mines, and other water sources. Other air pollution concerns include emissions from diesel engines, which are used at hydraulic fracturing sites for various purposes such as running pumps.
Hydraulic fracturing may disturb land, fisheries, and wildlife habitat. It may trigger small earthquakes because the injections lower the confining stress below the surface.
Six states in the Southwest are among the top 11 states for oil and gas production: California, Colorado, New Mexico, Oklahoma, Texas, and Utah. Navajo Nation lands in the Southwest include an estimated 1,572 oil and gas wells.
Between 2005 and 2009, approximately 10.2 million gallons of hydraulic fracturing fluids containing at least one carcinogen were used. Five states in the Southwest were among the top 10 states for these fluids: Colorado, New Mexico, Oklahoma, Texas, and Utah. Hydraulic fracturing has become a concern in other parts of the U.S., including Pennsylvania, New York, West Virginia, Virginia, Ohio, Arkansas, and Wyoming.
This description is based on the information found in the Web links listed with this topic.