EPA researchers conducted 17 individual research projects resulting in over 25 peer-reviewed research papers.The final assessment integrates results from EPA-led research efforts with approximately 1,200 cited sources of data and literature, and input from stakeholders through EPA's technical outreach. 

 EPA-led research can be categorized under the following research approaches:

• Analysis of Existing Data
• Case Studies
• Laboratory Studies
• Scenario Evaluations
• Toxicity Studies

Analysis of Existing Data

This analysis includes 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.

Case Studies

Retrospective case studies were completed at sites where hydraulic fracturing had already taken place, and where contamination of drinking water resources was reported. These case studies helped 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,
• health and environmental concerns, 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

Laboratory studies improved existing analytical methods for case study field monitoring activities, and helped assess the potential for treated flowback or produced water to cause an impact to drinking water resources if released. EPA conducted targeted research needed to better understand the ultimate fate and transport of chemical contaminants of concern. The contaminants of concern included components of hydraulic fracturing fluids or naturally occurring substances released from the subsurface during hydraulic fracturing.

Scenario Evaluations

Scenario evaluations used computer modeling to allow EPA to explore realistic scenarios related to hydraulic fracturing activities and to identify scenarios under which hydraulic fracturing activities may adversely impact drinking water resources. 

Toxicological Studies

EPA summarized existing data regarding toxicity and potential human health effects associated with these possible drinking water contaminants to support future risk assessments.