The U.S. Environmental Protection Agency has released a draft of its hotly anticipated hydraulic fracturing study, finding that the controversial practice has not led to widespread, systemic impacts on drinking water, as some environmentalists had feared.

Dubbed “Assessment of the Potential Impacts of Hydraulic Fracturing for Oil and Gas on Drinking Water Resources” and undertaken at Congress’s urging, the study was over five years in the making, during which time approximately 25,000 to 30,000 wells were drilled and hydraulically fractured annually. While EPA found multiple mechanisms that might lead to adverse impacts on drinking water, “[t]he number of identified cases [with drinking water impacts], however, was small compared to the number of hydraulically fractured wells.”

In carrying out the study, EPA conducted a sweeping literature review, developed new analytical methods and models, obtained data from well operators and fracturing service companies and scoured data from FracFocus, a hydraulic fracturing chemical registry maintained by the Interstate Oil and Gas Compact Commission. The final draft assessment, however, contains no reference to the prospective case studies the agency intended to include at the outset of the effort. No reason was cited for the omission.

The agency looked at five stages in the hydraulic fracturing water life cycle in assessing the potential for adverse impacts, including water acquisition, chemical mixing, well injection, flowback and produced water, and wastewater management and waste disposal. Some potential impacts seem obvious. For example, EPA notes that hydraulic fracturing water usage (totaling 44 billion gallons of water annually or enough to fill almost 67,000 Olympic swimming pools) may have an adverse impact on drinking water supplies, especially in arid areas of the country. Other impacts, like spills associated with chemical mixing, appear to occur with a known frequency: from about 1 spill for every 100 wells fractured in Colorado, to 0.4 to 12.2 spills for every 100 wells fractured in Pennsylvania.

EPA concedes that the study has serious limitations and that the relative paucity of known adverse impacts may reflect data gaps, rather than reality. Likewise, the EPA study did not assess the disposal of billions of gallons of hydraulic fracturing wastewater in underground disposal wells, a practice that has been correlated with earthquakes. The U.S. Geological Survey, the Department of Energy and other agencies continue to analyze that problem, while states have implemented stricter siting and management rules for underground wells that accept hydraulic fracturing wastewater.

These limitations are sure to figure largely in the public comments the agency is seeking on the draft assessment. Comments are due by August 28, 2015. Pundits on both sides of the issue have already been squaring off in the blogosphere, and it is unclear how much the comments will affect the final assessment.

What is clear is that the agency appears not to have found a wake of horrors in hydraulic fracturing’s path. That may reduce, for now, the repeated calls for more vigorous regulation of hydraulic fracturing, but is unlikely quell the protests of environmentalists who claim that this industrial process, which is responsible for an overall reduction in the nation’s greenhouse gas emissions, requires stricter oversight.

EPA’s Science Advisory Board is planning to hold a public meeting and three public teleconferences this September and October to receive additional input on the draft assessment. Interested parties may learn how to participate by reviewing the Federal Register notice announcing the meetings and teleconferences.