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EPA researchers conducted 17 individual research projects resulting in over 20 peer-reviewed research papers. The draft assessment integrates results from EPA-led research efforts with a broad literature review and input from stakeholders through EPA's technical outreach.
EPA-led research can be categorized under the following research approaches:
This analysis includes a broad literature review, information from spill databases, EPA’s analysis of data from FracFocus 1.0, as well as information provided by nine oil and gas operators in response to EPA's information requests.
Retrospective case studies occur at sites where hydraulic fracturing has already taken place, and where contamination of drinking water resources has been reported. These case studies help the agency assess the potential impacts of hydraulic fracturing on drinking water resources.
The sites identified were selected following extensive input from stakeholders, including the public, local and state officials, industry, and environmental organizations. EPA began field work in some of the selected areas in the summer of 2011:
- Bakken Shale - Killdeer, Dunn County, North Dakota
- Barnett Shale - Wise County, Texas
- Marcellus Shale - Bradford and Susquehanna Counties, Pennsylvania
- Marcellus Shale - Washington County, Pennsylvania
- Raton Basin – Las Animas and Huerfano Counties, Colorado
Criteria for Case Study Location Selection
The sites were identified, prioritized and selected based on a rigorous set of criteria and represent a wide range of conditions and impacts that may result from hydraulic fracturing activities. These criteria included:
- proximity of population and drinking water supplies,
- evidence of impaired water quality (retrospective only),
- health and environmental concerns (retrospective only), and
- knowledge gaps that could be filled by the case study.
Sites were prioritized based on:
- geographic and geologic diversity,
- population at risk,
- site status (planned, active or completed),
- unique geological or hydrological features,
- characteristics of water resources, and
- land use.
Laboratory studies improve existing analytical methods for case study field monitoring activities, and help assess the potential for treated flowback or produced water to cause an impact to drinking water resources if released. Scientists conduct targeted research needed to better understand the ultimate fate and transport of chemical contaminants of concern. The contaminants of concern may be components of hydraulic fracturing fluids or may be naturally occurring substances released from the subsurface during hydraulic fracturing.
Scenario evaluations use computer modeling to allow EPA to explore hypothetical, but realistic scenarios related to hydraulic fracturing activities and to identify scenarios under which hydraulic fracturing activities may adversely impact drinking water resources. Scenario evaluations assess potential long-term quantity impacts resulting from cumulative water withdrawals.
EPA is summarizing existing data regarding toxicity and potential human health effects associated with these possible drinking water contaminants to support future risk assessments.