The Environmental Protection Agency (EPA) has released for public comment a draft report on its investigation of potential ground water contamination in a part of Wyoming where gas is being produced using hydraulic fracturing (i.e., injection of water, proprietary fluids, and sand under pressure into a geological formation, commonly called fracking) (available at http://www.epa.gov/region8/superfund/wy/pavillion/PavillionAnalyticalResultsReport.pdf) (Draft Report). Comments are due by January 27, 2011 (assuming an extension of time is not requested and granted). These comments will be reviewed by an independent panel of experts that will also peer review the Draft Report. The question of whether fracking causes groundwater contamination is politically fraught, with strong viewpoints on both sides, and much riding on the outcome, so the Draft Report will draw intense interest from many interested parties.
Although many news reports and advocacy groups claim EPA’s Draft Report states that chemicals from fracking “have polluted groundwater in Wyoming,”¹ the Draft Report makes a more modest finding that a “likely impact” can be “explained by hydraulic fracturing”:
Alternative explanations were carefully considered to explain individual sets of data. However, when considered together with other lines of evidence, the data indicates likely impact to ground water that can be explained by hydraulic fracturing. … Further investigation would be needed to determine the extent of gas migration and the fate and transport processes influencing migration to domestic wells.
Various commentators have pointed out that EPA has not explored potential alternative explanations for the contamination of local drinking water wells in equal detail (particularly explanations such as cross-contamination from well construction, the presence of ubiquitous background contaminants, and other site-specific issues), did not perform adequate hydrogeological testing, and apparently failed to include in the report a statistical analysis of the correlation (or lack of statistical correlation) between the contaminated drinking water and fracking. On the other side of the issue are those who view the Draft Report as confirming other reports of allegedly fracking-related groundwater contamination.² Observers hope that these issues will be resolved by the independent review to be done by EPA’s selected expert panel.
Moving beyond these strictly science-based questions, a broader science policy issue surrounds EPA’s use of a “lines of evidence” approach to interpret the data. The “lines of evidence” approach is not defined in the Draft Report nor is a citation provided to a definition. In recent years, this term has been used by some EPA groundwater consultants when application of the principles of causation cannot be met. Generally, this new approach takes a series of individual lines of evidence (e.g., the presence of organic chemicals in a drinking water well or citizen complaints of odor, color, or taste) that in themselves may be weak or inconclusive and argues that combining several inadequate or inconclusive pieces of evidence allows an expert to conclude that the observation is more likely than not caused by a particular source.
In contrast, historically accepted scientific practice generally requires that each piece of evidence be reliable on its own. When a statistical association between a potential cause and effect is found, the researcher evaluates a series of criteria to judge whether causation has been demonstrated, for example, in this context: (a) has a temporal relationship has been established (i.e., the cause must precede the effect); (b) is the association statistically significant; (c) are the effects consistent across different studies; (d) is it plausible that fracking could cause the contamination of the specific drinking water wells (e.g., is there a pathway and are there other explanations); and (e) is a cause-and-effect relationship consistent with what is known about the entire body of knowledge about the subject.³
The author of this post is not aware of any statute, regulation or EPA guidance that has adopted the line of evidence approach. In any case, the more important questions are whether the line of evidence approach, as applied in this Draft Report, can be utilized to prove causation and what role any one incident should play in deciding whether to expand the use of fracking in the U.S. No technology has ever been implemented perfectly in every circumstance and there are clear benefits from the use of fracking. Many in the debate argue that the focus of the public dialogue should be on: (a) developing or updating a generally acceptable environmental engineering practice for safe operation of hydraulic fracturing; and (b) determining whether oil and gas extraction should be regulated primarily at the state level (which has been the historic practice) or at the federal level.
¹CNN, available at http://money.cnn.com/2011/12/09/news/economy/epa_fracking_wyoming/index.htm. BNA Daily Environmental Report, 237 DEN A-15, Drilling: EPA Report Ties Groundwater Contamination In Wyoming Aquifer to Hydraulic Fracturing (December 9, 2011), among many others.
²See articles cited in footnote 2 and “The EPA’s Fracking Scare,” Wall Street Journal Online (December 19, 2011), available at http://online.wsj.com/article/SB10001424052970204026804577098112387490158.html?.
³These principles were first articulated by Sir Arthur Bradford Hill (the founder of modern epidemiology) in 1965 (“The Environment and Diseases: Association and Causation”, 58 Proc. Royal Soc. Med, Sec. Occup. Med. 295-300 (available at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1898525/pdf/procrsmed00196-0010.pdf) and, as noted by EPA, Hill’s principles are “widely used by the scientific community in conducting … evidence-based reviews.” See EPA, Guidelines for Assessment of Carcinogen Risk at 2-11 to 2-12. (2005), available at http://www.epa.gov/raf/publications/pdfs/CANCER_GUIDELINES_FINAL_3-25-05.pdf . These principles apply beyond epidemiology.