UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Since the early 2000s, oil and natural gas production in the United States has been transformed
through technological innovation. Hydraulic fracturing, combined with advanced directional drilling techniques, made it possible to economically extract oil and gas resources previously inaccessible. The resulting surge in production increased domestic energy supplies and brought economic benefits to many areas of the United States.
The growth in domestic oil and gas production also raised concerns about potential impacts to human health and the environment, including potential effects on the quality and quantity of drinking water resources. Some residents living close to oil and gas production wells have reported changes in the quality of drinking water and assert that hydraulic fracturing is responsible for these changes. Other concerns include competition for water between hydraulic fracturing activities and other water users, especially in areas of the country experiencing drought, and the disposal of wastewater generated from hydraulic fracturing.
The U.S. Congress urged the U.S. Environmental Protection Agency (EPA) to study the relationship between hydraulic fracturing and drinking water. This report synthesizes available scientific literature and data to assess the potential for hydraulic fracturing for oil and gas to change the quality or quantity of drinking water resources, and identifies factors affecting the frequency or severity of any potential changes. This report can be used by federal, tribal, state, and local officials; industry; and the public to better understand and address any vulnerabilities of drinking water resources to hydraulic fracturing activities.
What is Hydraulic Fracturing?
Hydraulic fracturing is a stimulation technique used to increase oil and gas production from underground rock formations. Hydraulic fracturing involves the injection of fluids under pressures great enough to fracture the oil- and gas-producing formations. The fluid generally consists of water, chemicals, and proppant (commonly sand). The proppant holds open the newly created fractures after the injection pressure is released. Oil and gas flow through the fractures and up the production well to the surface.
Hydraulic fracturing has been used since the late 1940s and, for the first 50 years, was mostly used in vertical wells in conventional formations.Figure ES-1). These formations include: 1 Hydraulic fracturing is still used in these settings, but the process has evolved; technological developments (including horizontal and directional drilling) have led to the use of hydraulic fracturing in unconventional hydrocarbon formations that could not otherwise be profitably produced (see Figure ES-1). These formations include:
- Shales. Organic-rich, black shales are the source rocks in which oil and gas form on geological timescales. Oil and gas are contained in the pore space of the shale. Some shales contain predominantly gas or oil; many shale formations contain both.
- Tight formations. “Tight” formations are relatively low permeability, non-shale, sedimentary formations that can contain oil and gas. Like in shales, oil and gas are contained in the pore space of the formation. Tight formations can include sandstones, siltstone, and carbonates, among others.
- Coalbeds. In coalbeds, methane (the primary component of natural gas) is generally adsorbed to the coal rather than contained in the pore space or structurally trapped in the formation. Pumping the injected and native water out of the coalbeds after fracturing serves to depressurize the coal, thereby allowing the methane to desorb and flow into the well and to the surface.
The combined use of hydraulic fracturing with horizontal (or more generically, directional) drilling
has led to an increase in oil and gas activities in areas of the country with historical oil and gas production, and an expansion of oil and gas activities to new regions of the country.
Scope of the Assessment
We defined the scope of this assessment by the following activities involving water that support hydraulic fracturing (i.e., the hydraulic fracturing water cycle; see Figure ES-2):
- Water acquisition: the withdrawal of ground or surface water needed for hydraulic fracturing fluids;
- Chemical mixing: the mixing of water, chemicals, and proppant on the well pad to create the hydraulic fracturing fluid;
- Well injection: the injection of hydraulic fracturing fluids into the well to fracture the geologic formation;
- Flowback and produced water: the return of injected fluid and water produced from the formation (collectively referred to as produced water in this report) to the surface, and subsequent transport for reuse, treatment, or disposal; and
- Wastewater treatment and waste disposal: the reuse, treatment and release, or disposal of wastewater generated at the well pad, including produced water.
From our assessment, we conclude there are above and below ground mechanisms by which hydraulic fracturing activities have the potential to impact drinking water resources. These mechanisms include 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.
We did not find evidence that these mechanisms have led to widespread, systemic impacts on drinking water resources in the United States. Of the potential mechanisms identified in this report, we found specific instances where one or more mechanisms led to impacts on drinking water resources, including contamination of drinking water wells. The number of identified cases, however, 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.
Below, we provide a synopsis of the assessment’s key findings, organized by each stage of the hydraulic fracturing water cycle. We provide answers to the research questions presented in the Study Plan and Chapter 1. While come citations are provided here, individual chapters should be consulted for additional detail and citations.
About the United States Environmental Protection Agency
Born in the wake of elevated concern about environmental pollution, EPA was established on December 2, 1970 to consolidate in one agency a variety of federal research, monitoring, standard-setting and enforcement activities to ensure environmental protection. Since its inception, EPA has been working for a cleaner, healthier environment for the American people.