(CN) - Data collection may continue before regulators propose new rules to reduce acid rain, the D.C. Circuit ruled, shooting down the environmentalists calling for quicker resolution.
In 2012, the Environmental Protection Agency decided that it needed to conduct further studies before it could set a new air quality standard for nitrogen and sulphur oxides, compounds that combine with water in the air to form acid rain.
The existing standards, established in 1971, were designed to protect against the direct effect of acid rain on plants, but did not account for the acidification of rivers and lakes, which may kill animal life in certain ecosystems.
But the climate, geology, surrounding land use and myriad other factors make it difficult to determine how detrimentally acid rain will impact a given body of water.
In the rulemaking process, the EPA developed an Aquatic Acidification Index to quantify the connection between nitrogen and sulphur oxides in the air and the expected harm from acid rain in a particular region.
"But, like any model, the index may be scientifically sound in theory, or general concept yet, without the appropriate inputs, too uncertain to apply in practice," the EPA said in defense of its decision to postpone new rulemaking.
Instead, the agency announced a new pilot program to gather additional data, and to solidify the accuracy of its acidification index.
The Center for Biological Diversity and other environmental groups challenged the decision, but the D.C. Circuit sided with the EPA on Tuesday.
"Even if we had no obligation to defer to EPA's interpretation of the Clean Air Act - but of course we do - EPA has by far the better of the argument," Judge Arthur Randolph wrote for the three-judge panel. "If, as EPA found, the available information was insufficient to permit a reasoned judgment about whether any proposed standard would be 'requisite to protect the public welfare,' promulgating that standard would have been arbitrary and capricious."
Petitioners claim that the EPA had sufficient scientific information to make a new rule, but the court's task is to decide only whether the agency's judgment was rational, not to weigh conflicting scientific evidence.
Given the huge variation in acid-neutralizing capacities across water bodies among the nation's 84 ecoregions, the EPA found that its small sample sizes were insufficient to accurately extrapolate to an ecoregion scale.
"EPA concluded that 'given the current high degree of uncertainties and the large complexities inherent in quantifying the elements of' the Aquatic Acidification Index, it had 'no reasoned way to choose' a nationwide Acid Neutralizing Capacity or to apply the Index to each of the ecoregions throughout the country," Randolph wrote. "In light of the deference due EPA's scientific judgment, it is clear that its judgment must be sustained here."