Land use and wildlife
The construction and land disturbance required for oil and gas drilling can alter land use and harm local ecosystems by causing erosion and fragmenting wildlife habitats and migration patterns. When oil and gas operators clear a site to build a well pad, pipelines, and access roads, the construction process can cause erosion of dirt, minerals, and other harmful pollutants into nearby streams.
A study of hydraulic fracturing impacts in Michigan found potential environmental impacts to be “significant” and include increased erosion and sedimentation, increased risk of aquatic contamination from chemical spills or equipment runoff, habitat fragmentation, and reduction of surface waters as a result of the lowering of groundwater levels .
Water use and pollution
Unconventional oil and gas development may pose health risks to nearby communities through contamination of drinking water sources with hazardous chemicals used in drilling the wellbore, hydraulically fracturing the well, processing and refining the oil or gas, or disposing of wastewater . Naturally occurring radioactive materials, methane, and other underground gases have sometimes leaked into drinking water supplies from improperly cased wells; methane is not associated with acute health effects but in sufficient volumes may pose flammability concerns . The large volumes of water used in unconventional oil and gas development also raise water-availability concerns in some communities.
Groundwater
There have been documented cases of groundwater near oil and gas wells being contaminated with fracking fluids as well as with gases, including methane and volatile organic compounds. One major cause of gas contamination is improperly constructed or failing wells that allow gas to leak from the well into groundwater. Cases of contamination have been documented in Ohio and Pennsylvania .
Another potential avenue for groundwater contamination is natural or man-made fractures in the subsurface, which could allow stray gas to move directly between an oil and gas formation and groundwater supplies.
In addition to gases, groundwater can become contaminated with hydraulic fracturing fluid . In several cases, groundwater was contaminated from surface leaks and spills of fracturing fluid. Fracturing fluid also may migrate along abandoned wells, around improperly sealed and constructed wells, through induced fractures, or through failed wastewater pit liners .
Surface Water
Unconventional oil and gas development also poses contamination risks to surface waters through spills and leaks of chemical additives, spills and leaks of diesel or other fluids from equipment on-site, and leaks of wastewater from facilities for storage, treatment, and disposal. Unlike groundwater contamination risks, surface water contamination risks are mostly related to land management and to on- and off-site chemical and wastewater management.
The EPA has identified more than 1,000 chemical additives that are used for hydraulic fracturing, including acids (notably hydrochloric acid), bactericides, scale removers, and friction-reducing agents. Only maybe a dozen chemicals are used for any given well, but the choice of which chemicals is well-specific, depending on the geochemistry and needs of that well [20]. Large quantities — tens of thousands of gallons for each well — of the chemical additives are trucked to and stored on a well pad. If not managed properly, the chemicals could leak or spill out of faulty storage containers or during transport.
Drilling muds, diesel, and other fluids can also spill at the surface . Improper management of flowback or produced wastewater can cause leaks and spills. There is also risk to surface water from deliberate improper disposal of wastewater by bad actors.
Water Use
The growth of hydraulic fracturing and its use of huge volumes of water per well may strain local ground and surface water supplies, particularly in water-scarce areas. The amount of water used for hydraulically fracturing a well can vary because of differences in formation geology, well construction, and the type of hydraulic fracturing process used . The EPA estimates that 70 billion to 140 billion gallons of water were used nationwide in 2011 for fracturing an estimated 35,000 wells . Unlike other energy-related water withdrawals, which are commonly returned to rivers and lakes, most of the water used for unconventional oil and gas development is not recoverable. Depending on the type of well along with its depth and location, a single well with horizontal drilling can require 3 million to 12 million gallons of water when it is first fractured — dozens of times more than what is used in conventional vertical wells . Similar vast volumes of water are needed each time a well undergoes a “work over,” or additional fracturing later in its life to maintain well pressure and gas production. A typical shale gas well will have about two work overs during its productive life span .
Earthquakes
Hydraulic fracturing itself has been linked to low-magnitude seismic activity—less than 2 moment magnitude (M) [the moment magnitude scale now replaces the Richter scale]— but such mild events are usually undetectable at the surface . The disposal of fracking wastewater by injecting it at high pressure into deep Class II injection wells, however, has been linked to larger earthquakes in the United States . At least half of the 4.5 M or larger earthquakes to strike the interior of the United States in the past decade have occurred in regions of potential injection-induced seismicity . Although it can be challenging to attribute individual earthquakes to injection, in many cases the association is supported by timing and location of the events .