The practice of hydraulic fracturing, commonly known as fracking, generates massive volumes of wastewater that must be managed and disposed of safely. This “used fracking water” is a complex mixture of flowback water and produced water. Flowback is the portion of the injected fracturing fluid—a blend of water, sand, and chemicals—that returns to the surface during the initial days or weeks. Produced water is the naturally occurring brine and formation water trapped in the deep rock that flows to the surface along with the oil and gas over the well’s operational lifespan. The disposal of this high-volume, chemically laden wastewater presents significant environmental and public health challenges.
Induced Seismicity from Subsurface Injection
The most common disposal method for used fracking water is deep underground injection into porous rock formations. This method has been linked to a dramatic increase in seismic activity, or human-caused earthquakes, in areas where it is heavily practiced. These earthquakes are caused by the long-term, high-volume injection of the resulting wastewater, not the hydraulic fracturing process itself.
The mechanism involves the fluid pressure created by pumping millions of gallons of water deep into the earth. This increased fluid pressure, known as pore pressure, can migrate into pre-existing faults. The water lubricates the fault, reducing the friction that holds the rock layers in place, which causes the fault to slip suddenly and release stored energy as an earthquake.
This phenomenon has been observed in regions like Oklahoma, Texas, and Ohio, which historically had low natural seismicity. Oklahoma saw a sharp rise in magnitude 3.0 or greater earthquakes, increasing from less than 25 per year before 2009 to over 300 per year by 2015. Some events have reached magnitudes capable of damaging infrastructure, such as the M 5.8 earthquake near Pawnee, Oklahoma. Factors like the proximity of the injection well to a fault, the rate of injection, and the total volume injected contribute to the likelihood and magnitude of induced seismicity.
Contamination of Water and Soil Resources
The complex chemical composition of used fracking water presents a substantial risk to both soil and water resources. This wastewater contains original fracturing chemicals and elevated concentrations of substances picked up from deep underground. A primary concern is surface contamination resulting from accidental spills and leaks during handling and storage.
Accidents can occur during transportation, transfer at the well pad, or from leaks in temporary storage containers like holding pits or tanks. A rupture in a surface impoundment, which are often unlined or inadequately lined, can release high-salinity brine and toxic chemicals directly into the surrounding soil and local surface water bodies. The high concentration of total dissolved solids (TDS), or salts, can be toxic to aquatic life and contaminate soil, making the area unsuitable for vegetation.
A more insidious pathway involves the deep injection wells, designed to isolate the wastewater permanently. If the integrity of the injection system fails, contaminants can reach shallower freshwater aquifers. Failure points include breaches in the well casing or cement, or the migration of fluids through natural fractures or poorly sealed abandoned wells. The water contains heavy metals like arsenic, lead, and cadmium, along with naturally occurring radioactive materials (NORM) such as radium-226 and radon. If these constituents migrate into drinking water sources, they pose serious long-term health risks.
Air Quality Impacts from Disposal Operations
The disposal phase of used fracking water contributes to localized air quality degradation, distinct from seismic and water contamination concerns. This issue stems from volatile components within the wastewater that escape into the atmosphere during surface storage and treatment processes. When the water is held in open pits or storage tanks, volatile organic compounds (VOCs) and gases can evaporate into the air.
The resulting emissions include potent greenhouse gases like methane, which can leak from storage facilities and contribute to global warming. Local health concerns arise from the release of VOCs such as benzene, toluene, and xylene. These chemicals are known air toxics that can cause respiratory irritation and are associated with an increased risk of cancer.
These airborne pollutants can also react with nitrogen oxides (NOx), often emitted by the diesel engines of heavy equipment used in disposal operations, to form ground-level ozone, or smog. This photochemical reaction generates a regional air quality problem, leading to respiratory issues for nearby populations. Furthermore, intentionally evaporating wastewater to reduce its volume accelerates the transfer of toxic substances from the liquid to the air, increasing the risk of inhalation exposure for workers and residents.