In August, the US Environmental Protection Agency’s (EPA) four-year effort to summarize the environmental risks of fracking for oil and natural gas got its evaluations from a panel of outside experts. The highlight was a determination that the report’s summary painted slightly too rosy a picture of the practice.

The original draft led by saying, “We did not find evidence that these mechanisms have led to widespread, systemic impacts on drinking water resources in the United States.” While it noted that there had been instances of contamination (mostly from spills at the surface), the number “was small compared to the number of hydraulically fractured wells.”

The outside reviewers said that was not clear enough and not sufficiently supported by the evidence in the rest of the report. They also wanted to see more explicit descriptions of the gaps in our knowledge that led to uncertainty in certain conclusions.