Last year, the US Environmental Protection Agency (EPA) released the draft of a major report on the practice of hydraulic fracking—a technique to harvest oil and natural gas trapped within shale rocks. Although the report is only a draft, it was four years in the making and represents one of the first formal evaluations of fracking in the US as a whole.

In general, the EPA report is positive. While various problems with fracking are brought up, the report seems to suggest that the technique has no systemic issues. With proper caution, the evaluation says, it should be possible to frack while keeping water sources safe.

Or, to use the EPA's own words:

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[...] 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.

The release of the draft report was followed by EPA’s review process, which includes an assessment by a thirty-member Science Advisory Board composed of academic and industry experts. The board’s assessment was released Thursday.

As might be expected, the review highlights a laundry list of information the panel would like to see added or clarified. That includes a more detailed description of the potential impacts of various risks in the process, along with associated probabilities. The reviewers would also like to see the EPA draw from a wide pool of information on the potential toxicity of the chemicals that are added to the water used to fracture the shale rock. The review also calls for greater acknowledgement of localized impacts that have occurred in some instances, even if they aren’t representative of intrinsic risks elsewhere around the country.

And as usual, the Science Advisory Board’s review asks for the readability of the EPA report’s summary section to be improved so that the general public might actually be able to understand it.

But the board’s review also criticizes the widely-reported summary statement mentioned above. It states, “The [Science Advisory Board] finds that the EPA did not support quantitatively its conclusions about lack of evidence for widespread, systemic impacts of hydraulic fracturing on drinking water resources, and [it] did not clearly describe the system(s) of interest (e.g., groundwater, surface water), the scale of impacts (i.e., local or regional), nor the definitions of ‘systemic’ and ‘widespread.’”

Basically, the expert panel believes that the EPA’s statement needs to be clarified, backed up more explicitly, and accompanied by better caveats about “data limitations and uncertainties.” In particular, the board takes issue with the conclusion that surface spills of fluids being handled on the well pad don’t pose a substantial risk to drinking water supplies, which the panel says is poorly supported.

The panel had thirty members, and four of them produced a dissenting opinion that appears as an appendix to the review. They write that the summary statement is “clear, unambiguous, concise, and does not need to be changed or modified.” It’s notable, however, that three of the four dissenters work in the oil industry.

The EPA will now have to consider and incorporate the recommendations in the Science Advisory Board’s 160 page review before publishing its final report.