Hydraulic fracturing, often shortened to “fracking,” is a technique used to stimulate the production of oil and natural gas from deep underground rock formations. This process involves injecting a high-pressure mixture of water, sand, and chemicals into a wellbore to create small fissures, allowing hydrocarbons to flow more freely. While this extraction method has brought previously inaccessible energy reserves to the market, it has also raised concerns regarding its environmental consequences. This review examines the impacts of hydraulic fracturing on water resources, air quality, surface ecosystems, and geological stability.
Water Resource Stress and Contamination
Hydraulic fracturing operations require immense volumes of water, placing stress on local supplies, especially in water-scarce regions. A single fracturing event can require between 1.5 million and 9.7 million gallons of water, with some wells needing up to 10 million gallons. This high-volume withdrawal intensifies competition for water among energy operations, agriculture, and residential use, particularly during drought conditions. The depletion of local surface water bodies and groundwater aquifers impacts surrounding communities and ecosystems.
Contamination is a risk from the fluids used and produced during extraction. The injected fluid, containing chemical additives, returns to the surface as “flowback” and “produced water.” This wastewater is toxic, containing the original chemicals, high concentrations of salts (brine), heavy metals, and naturally occurring radioactive materials (NORM), such as radium, mobilized from deep rock formations.
Contaminants can enter shallow groundwater aquifers through several pathways, including surface spills of wastewater or integrity failures in the well infrastructure. Over time, the cement and steel casings that isolate the wellbore from freshwater zones can degrade, creating routes for the migration of fluids and gases. Faulty well construction has been linked to the migration of methane, the primary component of natural gas, into drinking water supplies near drilling sites.
Atmospheric Emissions and Air Quality
Hydraulic fracturing and associated infrastructure contribute to atmospheric pollution through the release of potent greenhouse gases and conventional air pollutants. The most significant climate concern is methane, the main constituent of natural gas, which can leak into the atmosphere at various points in the production system. Methane is a powerful greenhouse gas with a warming potential substantially greater than carbon dioxide. Leakage, or fugitive emissions, occurs from the wellhead, compressors, pipelines, and during the flowback phase after fracturing.
Estimates suggest that the total methane leakage from shale gas development is substantial. When these methane emissions are fully accounted for, the total greenhouse gas footprint of shale gas extraction can be greater than that of other fossil fuels, including coal and oil. This leakage means a portion of the product is vented or escapes into the atmosphere, contributing to climate impact.
Operations also release conventional air pollutants, including Volatile Organic Compounds (VOCs) and nitrogen oxides (NOx). These pollutants are generated primarily by the combustion of diesel fuel in the heavy machinery and vehicles used for drilling, fluid transport, and site operations. Both VOCs and NOx are precursors to the formation of ground-level ozone, or smog, which is a respiratory irritant and an air quality concern. VOCs can also include toxic air pollutants such as benzene, toluene, ethylbenzene, and xylene (BTEX), which pose risks to human and environmental health.
Land Use and Ecosystem Disruption
The physical footprint of hydraulic fracturing operations results in significant land use change and disruption to local ecosystems. Developing an unconventional well requires clearing land for the construction of the well pad, access roads, pipelines, and processing facilities. This infrastructure leads directly to the loss of natural habitat, including forests and wetlands.
Land clearing results in habitat fragmentation, breaking up continuous habitats into smaller, isolated patches. This fragmentation reduces biodiversity by isolating wildlife populations and disrupting migration and breeding patterns. The new infrastructure can also alter the landscape, increasing the vulnerability of some ground-nesting birds to predators.
Surface disturbances lead to issues related to soil integrity and erosion. Construction of well pads and roads involves removing topsoil, which causes soil compaction and increases the risk of erosion by wind and water. This degradation depletes the land’s natural productivity and affects local flora. Continuous activity also generates noise and light pollution, disturbing wildlife behavior and the ecological balance near the well sites.
Induced Seismicity from Wastewater Disposal
A distinct environmental concern is induced seismicity, the potential for oil and gas operations to induce earthquakes. The actual hydraulic fracturing process itself is rarely the cause of earthquakes large enough to be felt at the surface. Instead, the vast majority of significant induced seismic events are linked to the deep underground injection of wastewater produced by the extraction process.
After oil and gas extraction, the flowback and produced water must be managed. This wastewater is commonly disposed of by injecting massive volumes of fluid into deep Class II disposal wells over long periods. The injection increases the fluid pressure within the deep rock formations, a parameter known as pore pressure.
If this highly pressurized fluid migrates into a pre-existing geological fault, the increased pore pressure reduces the effective stress holding the fault together. This lubrication allows the fault to slip and release built-up tectonic stress, which is felt as an earthquake. The rise in seismic activity in regions like Oklahoma and Texas has been directly correlated with the high volumes of wastewater injected into these deep disposal wells.