The debate over unconventional natural gas drilling and high-volume hydraulic fracturing (HVHF), commonly known as “fracking,” has focused on its potential effects on air and water quality and on public health in the surrounding communities that have directly witnessed the rapid growth of this drilling technology. Two recent examples include the ban on fracking in Denton, Texas, in a November 2014 referendum, and the decision by the Governor of New York to ban fracking based on the recommendations of the State Department of Health. The medical and scientific community has warned of the potential environmental risks posed by all stages of unconventional natural gas drilling operations, including site construction and preparation, drilling, fracturing, production, transportation, and waste storage and disposal. This article provides an overview of the potential environmental health effects of this technological advance in the oil and gas industry.
CHEMICAL USAGE Hydraulic fracturing typically occurs over a two-week period in the average 50-year life cycle of an oil or natural gas well. Hydraulic fracturing fluids ar​e complex chemical mixtures designed to enhance gas recovery and protect the well infrastructure. Chemical additives act as biocides, surfactants, friction reducers, viscosity modifiers, buffers, clay stabilizers, scale and corrosion inhibitors, emulsifiers, and proppants. Fracturing fluids may contain amides, amines, petroleum distillates, aromatic hydrocarbons, organic salts, acids, esters, polymers, minerals, metals and other inorganic substances (see Table 1). Chemical additives reportedly constitute less than 2 percent by weight of the total fracturing fluid. However, the nonprofit organization Earthworks estimates that a 4-million gallon HVHF operation would use between 80 and 330 tons of chemicals.
Some chemical ingredients identified in manufacturer safety data sheets are known to be safe while others may be toxic to humans and wildlife, if present in sufficient concentrations. Some chemical constituents remain unknown due to industry proprietary and trade-secret claims. FracFocus is the largely voluntary nationwide system for disclosing chemicals used in HVHF operations performed after Jan. 1, 2011. As of March 2015, more than 94,700 wells were registered on the website. WATER QUALITY CONCERNS A major environmental concern of HVHF is the degradation of drinking water aquifers and surface waters by chemical contamination, natural gas migration, wastewater discharge, accidental spills, and depletion.
Chemical contamination of groundwater is a potential consequence of well drilling, well casing, production, transportation, and waste handling operations. A white paper published in 2011 by the Duke University Center on Global Change estimated that between 15 and 80 percent of injected drilling fluids are returned to the surface during well completion and production. This includes “flowback” water, which is withdrawn from the well after the fracturing process; and “produced” water, which returns to the surface along with the natural gas during production and is recovered throughout the life of the well.
The fate and transport of fracturing fluids not recovered during flowback, and their potential to contaminate drinking water, are largely unknown. Fracturing fluids could migrate along abandoned and improperly plugged oil and gas wells, through an inadequately sealed annulus between the wellbore and casing, or through natural and induced fractures outside the target shale formation.
There is strong disagreement in the scientific community on whether HVHF may impact groundwater aquifers directly through the propagation of cracks in fractured rock, which could serve as a pathway for gas or fracturing fluids to migrate. Many scientists and state regulators consider the thousands of feet of rock layers that overlie the produced portion of a shale formation as a barrier to flow. They also note that the fractures induced in hydraulic fracturing extend several hundred feet from the wellbore and are highly unlikely to reach the potable aquifers.
Methane gas migration into drinking water aquifers has been reported in several states. In one well-known case near Dimock, Pa., methane gas accumulated in a private water well and exploded. This event triggered much debate on whether the methane detected in the wells was caused by drilling or natural processes. The incident was attributed to Marcellus Shale drilling methods and leaky well casings. Many residents claimed that their well water was contaminated with drilling fluid chemicals and sued the oil and gas operator for explosive concentrations of methane gas in their aquifers.
The handling, storage, transportation, and disposal of returned waters also pose a risk of environmental contamination. The flowback and produced waters may contain the chemical additives mixed and injected onsite but also heavy metals such as lead and arsenic, naturally occurring radioactive materials (NORM) such as radium, radon, and uranium, and salts such as bromide and chloride (brine) from the deep geological formations.
Flowback and produced water is typically impounded in surface evaporation ponds or pits for subsequent disposal, treatment, or re-use. Wastewater impoundments have been known to leak and contaminate surface water, soil, and groundwater.
The majority of wastewater from oil and gas production in the U.S. is disposed of by deep well injection. In some states, the wastewater is injected into old abandoned conventional gas wells or other underground storage disposal facilities. There is concern that excessive pressure from injection wells may cause the underground rock layers to crack, which could enhance the migration of wastewater into drinking water aquifers.
In the Marcellus Shale region, most wastes have been brought to municipal wastewater and sewage treatment plants or publicly owned treatment works, which are not designed or equipped to handle the chemical and radiological contamination. Radioactive radium that is commonly present in wastewaters will likely be deposited in the solids that form in the wastewater treatment process, thus generating a low-level radioactive waste that must be handled appropriately and has potential onsite and community human health implications.
Similarly, surface and subsurface soils may be adversely affected from spills and leaks of drilling muds, chemical additives, flowback water, and production brine as well as stormwater run-off.
The amount of water required by HVHF ranges from hundreds of thousands to millions of gallons per well, depending on the shale formation and the depth and length of the horizontal portion of the well. Water is derived largely from surface waters with the remainder provided by public water utilities (with a groundwater source). Water is generally supplied by tank trucks with a 5,000-gallon capacity, requiring up to 100 truck trips per well. This huge water consumption has significant impact in areas affected by drought, such as west Texas.​
Governmental research includes an ongoing EPA study on the hydraulic fracturing water cycle and a national produced waters geochemical database developed by the U.S. Geological Survey.
American Petroleum Institute: Hydraulic Fracturing, Unlocking America’s Natural Gas Resources (February 2015).
Environment Texas Research and Policy Center: “Fracking by the Numbers” (October 2013).
New Solutions: “Impacts of Gas Drilling on Human and Animal Health” (May 2012).
New York State Department of ​Health: A Public Health Review of High Volume Hydraulic Fracturing for Shale Gas Development (December 2014).
Science: “Impact of Shale Gas Development on Regional Water Quality” (May 2013).

Debate Continues Over ​Environmental Health Effects

Focus on Fracking
Several public health and medical associations have urged a precautionary approach to natural gas extraction and hydraulic fracturing processes, with particular emphasis on protecting infants and children.
AIR QUALITY CONCERNS Natural gas drilling and hydraulic fracturing can significantly affect local and regional air quality during site preparation, drilling, production, transportation, and waste management operations. Activities such as venting methane gas, using diesel-powered equipment, and handling proppant can release hazardous gaseous and particulate constituents into the ambient air. Potential air contaminants include methane, carbon dioxide, ozone, nitrogen oxides, hydrogen sulfide, volatile organic compounds (VOCs) including benzene, and fine particulate matter (PM10 and PM2.5) including crysta​lline silica. The large number of diesel-powered trucks used for transport of equipment and supplies to the w​ell pads is a significant source of air pollution.
Industrial hygienists can apply their ambient air monitoring experience on construction sites and environmental remediation projects to assess air quality effects from HVHF drilling operations for downwind receptors. This may include screening with real-time direct-reading instruments such as photoionization detectors for total VOCs and particulate aerosol monitors in addition to sampling and using analytical methods for respirable crystalline silica and petroleum hydrocarbons. Pertinent information such as equipment operations, prevailing wind direction and velocity, observations of dust clouds and dispersion patterns, and odor detections for VOCs and gases should be documented.
In addition, industrial hygienists can support oil and gas operators with methane gas screening surveys of buildings, structures, water wells, and potential migration pathways to evaluate risks to public health and property. COMMUNITY HEALTH The peer-reviewed medical and scientific literature has little information about the public health aspects of fracking, due to the fact that hydraulic fracturing has been in use for a relatively short time in mostly rural areas with low population densities. Additional barriers to sound scientific investigations include limited baseline environmental and human health data, latency of chronic health effects including cancer, geographical and historical variations in hydraulic fracturing operations, and lack of access to complete information on chemical composition from the manufacturers of drilling fluids, fracturing fluids, and additives due to proprietary claims, non-disclosure agreements in place with claimants, and confidentiality agreements with treating physicians. Further, for many of the listed chemicals in fracturing fluids, there is little information pertaining to chronic low-level exposures and associated health effects in humans, which would be the likely result of groundwater contamination from an accidental spill or release that went undetected or was not remediated.
Information regarding adverse health effects in communities near drilling sites is largely anecdotal. The most commonly reported human health problems are burning of the eyes, nose and throat, nosebleeds, rashes, vomiting, and diarrhea. A rural health clinic in the Marcellus Shale region of southwest Pennsylvania reported that the most common health complaints experienced by residents are skin rashes and irritation, nausea and vomiting, breathing difficulties, coughing, abdominal pain, and nosebleeds. Other complaints have included anxiety, stress, headaches, dizziness, eye and throat irritation, and sleeping problems. The clinicians linked the neurological, respiratory, and eye symptoms to airborne exposures; dermal effects were associated with contact with a water source. Some health scientists note that these early clinical findings after six years of drilling in the region point to environmental contamination and that chronic illnesses linked to the air and water pollutants will take years to manifest. They further note that as well casings fail with age, there may be further contamination and delayed health responses.
The first legal judgment against a well operator, drilling contractor, or service company for contamination of groundwater caused by hydraulic fracturing was rendered in June 2014. A Texas jury awarded $2.9 million to a north Texas family who claimed that 24 gas extraction wells had caused pollution since 2008, resulting in health effects such as asthma, nausea, nose bleeds, tinnitus, and depression, all of which were related to hydrocarbon exposures. Medical tests revealed their blood contained benzene, toluene, ethyl benzene, and xylenes.
Several public health and medical associations have urged a precautionary approach to natural gas extraction and hydraulic fracturing processes, with particular emphasis on protecting infants and children due to their heightened sensitivity to environmental toxins.
Large-scale academic studies of community health complaints and environmental contamination associated with natural gas extraction are underway or planned in Pennsylvania, North Carolina, and Texas. One comprehensive epidemiological study undertaken by Geisinger Health System is analyzing more than 2.6 million electronic health records of patients in 31 Pennsylvania counties for respiratory, cardiovascular, and cerebro-vascular system effects and pregnancy outcomes.
Reported adverse health effects in domestic animal, livestock, and wildlife ranging from dermal, gastrointestinal, neurological, musculoskeletal, and reproductive effects (major effect) to sudden death may have resulted from exposure to contaminated well or spring water from leaks and spills of wastewater, drilling fluids, and fracturing fluids from natural gas drilling sites in several states. A 2012 investigation published in the journal New Solutions entailed in-depth interviews with animal owners and their veterinarians and a review of medical records and environmental sampling data to ascertain both human and animal health effects five years prior to the onset of the local drilling operations. The investigators noted that animals may serve as “sentinels of human health” for hydraulic fracturing due to their more frequent exposure to ambient air, soil, and groundwater, and shorter reproductive cycles.
The subject of HVHF is a moving target with national, state and local governments addressing environmental and public health and safety, and the oil and gas industry promoting its technological improvements and best practices for well integrity and environmental protection. It is likely that the legal system will continue to address the association between air and water contamination and public health effects before ongoing environmental health studies are completed. MICHELLE F. GILLIE, CIH, CPEA, FAIHA, is a member of the AIHA Environmental Issues Committee, which is working jointly with the AIHA Oil and Gas Working Group and Risk Assessment Committee on a white paper on the occupational and environmental health impacts from hydraulic fracturing. She can be reached at (832) 251-5189 or
Editor’s note: This article is adapted from a forthcoming AIHA white paper on the occupational and environmental health effects of fracking.