EPA draft assessment finds no widespread, systemic impacts to drinking water resources from fracking
The US Environmental Protection Agency (EPA) released a draft assessment on the potential impacts of hydraulic fracturing activities on drinking water resources in the United States. The assessment, done at the request of Congress, found that hydraulic fracturing activities in the US are carried out in a way that have not led to widespread, systemic impacts on drinking water resources.
The assessment followed the water used for hydraulic fracturing from water acquisition; chemical mixing at the well pad site; well injection of fracking fluids; the collection of hydraulic fracturing wastewater (including flowback and produced water); and wastewater treatment and disposal. The assessment also identified potential vulnerabilities in the water lifecycle—some of which are not unique to hydraulic fracturing—that could impact drinking water.
|The stages of the hydraulic fracturing water cycle. Source: EPA. Click to enlarge.|
Although EPA’s review of data sources available to the agency found specific instances where well integrity and waste water management related to hydraulic fracturing activities did impact drinking water resources, these were small compared to the large number of hydraulically fractured wells across the country.
The report did not address other concerns raised about hydraulic fracturing specifically or about oil and gas exploration and production activities more generally, including acquisition and transport of constituents of hydraulic fracturing fluids besides water (e.g., sand mining and chemical production) outside of the stated water cycle; site selection and well pad development; other infrastructure development (e.g., roads, pipelines, compressor stations); site reclamation; and well closure.
Nor was the report a human health risk assessment. It did not identify populations exposed to chemicals; estimate the extent of exposure; or estimate the incidence of human health impacts.
The assessment reviewed relevant scientific literature and data; no new field work was performed. Literature evaluated included articles published in science and engineering journals; federal and state government reports; non-governmental organization (NGO) reports; and industry publications. Data sources examined included federal- and state-collected data sets; databases maintained by federal and state government agencies; other publicly-available data and information, and data, including confidential and non-confidential business information, submitted by industry to the EPA.
Major findings. There are above- and below-ground mechanisms by which hydraulic fracturing activities might impact drinking water resources, including water withdrawals in times of, or in areas with, low water availability; spills of hydraulic fracturing fluids and produced water; fracturing directly into underground drinking water resources; below ground migration of liquids and gases; and inadequate treatment and discharge of wastewater.
EPA reviewers found no evidence that these mechanisms have led to widespread, systemic impacts on drinking water resources in the United States. Although the reviewers did find specific instances in which one or more mechanisms led to impacts on drinking water resources, including contamination of drinking water wells, the number of identified cases was small compared to the number of hydraulically fractured wells.
This finding could reflect a rarity of effects on drinking water resources, but may also be due to other limiting factors. These factors include: insufficient pre- and post-fracturing data on the quality of drinking water resources; the paucity of long-term systematic studies; the presence of other sources of contamination precluding a definitive link between hydraulic fracturing activities and an impact; and the inaccessibility of some information on hydraulic fracturing activities and potential impacts.—EPA draft assessment
The report identified potential vulnerabilities to drinking water resources, but was not designed to be a list of documented impacts. These vulnerabilities to drinking water resources include:
water withdrawals in areas with low water availability;
hydraulic fracturing conducted directly into formations containing drinking water resources;
inadequately cased or cemented wells resulting in below ground migration of gases and liquids;
inadequately treated wastewater discharged into drinking water resources; and
spills of hydraulic fluids and hydraulic fracturing wastewater, including flowback and produced water.
Water acquisition. Water is a major component of nearly all hydraulic fracturing operations. It typically makes up almost 90% or more of the fluid volume injected into a well; each frac’d well requires thousands to millions of gallons of water.
High fracturing water use or consumption alone does not necessarily result in impacts to drinking water resources, the reviewers found. Rather, impacts result from the combination of water use or consumption and water availability at local scales. The potential for impacts to drinking water resources from hydraulic fracturing water withdrawals is highest in areas with relatively high fracturing water use and low water availability.
Chemical mixing. Hydraulic fracturing fluids are developed to perform specific functions, including: create and extend fractures; transport proppant; and place proppant in the fractures. The fluid generally consists of three parts: (1) the base fluid, which is the largest constituent by volume and is typically water; (2) the additives; and (3) the proppant.
On-site storage, mixing, and pumping of chemicals and hydraulic fracturing fluids have the potential to result in accidental releases, such as spills or leaks. Potential impacts to drinking water resources from spills of hydraulic fracturing fluids and chemicals depend on the characteristics of the spills; and the fate, transport and toxicity of the chemicals.
EPA identified a list of 1,076 chemicals used in hydraulic fracturing fluids. These chemicals include acids, alcohols, aromatic hydrocarbons, bases, hydrocarbon mixtures, polysaccharides, and surfactants.The analysis indicated that chemical use varies and that no single chemical is used at all well sites across the country, although several chemicals are widely used.
Well injection. Hydraulic fracturing fluids are injected into oil or gas wells under high pressures. The fluids flow through the well (commonly thousands of feet below the surface) into the production zone (i.e., the geologic formation being fractured) where the fluid injection pressures are sufficient to create fractures in the rock.
There are two major subsurface mechanisms by which the injection of fluid and the creation and propagation of fractures can lead to contamination of drinking water resources: (1) the unintended movement of liquids or gases out of the production well or along the outside of the production well into a drinking water resource via deficiencies in the well’s casing or cement; and (2) the unintended movement of liquids or gases from the production zone through subsurface geologic formations into a drinking water resource. A combination of the two is also possible.
Flowback and produced water. Water, of variable quality, is a byproduct of oil and gas production. After hydraulic fracturing, the injection pressure is released and water flows back from the well. Initially this water is similar to the hydraulic fracturing fluid, but as time goes on the composition is affected by the characteristics of the formation and possible reactions between the formation and the fracturing fluid.
Water initially produced from the well after hydraulic fracturing is sometimes called flowback. Hydraulic fracturing fluids and any formation water returning to the surface are often referred to as produced water.
The amount of produced water varies, but typically averages 10% to 25% of injected volumes, depending upon the amount of time since fracturing and the particular well.
US EPA. Assessment of the Potential Impacts of Hydraulic Fracturing for Oil and Gas on Drinking Water Resources (External Review Draft). US Environmental Protection Agency, Washington, DC, EPA/600/R-15/047, 2015.