The U.S. Supreme Court on Tuesday declined to review challenges to a 2010 Environmental Protection Agency (EPA) rule setting the acceptable limit for sulfur dioxide (SO2) in the air at 75 parts per billion (ppb) over a 1-hour period. The denial of certiorari leaves intact the EPA’s final revision to the primary National Ambient Air Quality Standard (NAAQS) for SO2 emissions from power plants and other industrial facilities.

The case, Asarco LLC v. U.S. Environmental Protection Agency et al. (U.S. Supreme Court, No. 12-510), stems from a landmark federal court ruling on July 20, 2012, in which the D.C. Circuit Court of Appeals affirmed the agency’s revisions to the SO2 NAAQS rule promulgated in June 2010. The court thwarted claims by several companies and states—including North Dakota, South Dakota, Nevada, Louisiana, and Texas—that the EPA had arbitrarily set the maximum SO2 concentration at a level lower than statutorily authorized and had failed to follow notice-and-comment rulemaking procedures before it finalized the revisions. The EPA “chose a [SO2 NAAQS] level below that which produced adverse effects . . . in order to set a standard that allows an adequate margin of safety," the court ruled.

But several entities appealed the federal court’s decision to the U.S. Supreme Court, including Asarco LLC (which owns one of nation’s three major copper smelters), the Montana Sulphur and Chemical Co., the Utility Air Regulatory Group, and the five states involved in cases with the federal court (North Dakota, South Dakota, Nevada, Texas, and Louisiana). The suits were consolidated into one, Asarco LLC v. U.S. Environmental Protection Agency et al. The EPA was backed by the American Lung Association and Environmental Defense Fund, which intervened as respondents.

In their petition for a writ of certiorari to the Supreme Court, the companies and states asked the high court to examine whether the D.C. Circuit erred when it concluded that the EPA’s authority to include an "adequate margin of safety" allowed the court to avoid determining whether the revised NAAQS was more stringent than needed to protect public health.

On Tuesday, however, the Supreme Court declined—without comment— to review the closely watched case.

The Clean Air Act requires the EPA to promulgate a primary and secondary NAAQS for each pollutant listed in the act and to revise them every five years. After the EPA promulgates a new final standard, the Clean Air Act allows each state to recommend whether areas within their boundaries should be designated as "nonattainment," "attainment," or "unclassifiable," but the EPA makes the final designation. States must then submit state implementation plans (SIPs), which must receive EPA approval, to impose federally enforceable controls on air pollution sources so states can attain the NAAQS.

The EPA reviewed but did not revise its first primary NAAQS for SO2, promulgated in April 1971, until June 22, 2010. In 1988, it had proposed to add a new 1-hour primary standard of 400 ppb to protect against 5- to 10-minute bursts of SO2 concentrations, the pollutant that is released primarily by fossil fuel combustion, and in 1994, it proposed to add a 5-minute standard of 600 ppb. However, in 1996, the agency said it would not revise the NAAQS, saying that adverse effects did "not pose a broad public health problem when viewed from a national perspective." The American Lung Association sued the EPA’s decision not to implement the 5-minute standard, and the D.C. Circuit ruled in 1998 that the agency had not "adequately" explained how it reached its decision.

In response to that court decision, the EPA initiated review of the SO2 NAAQS and proposed a rule in 2006 to revise the primary SO2 standard. That proposal essentially revoked the existing 24-hour and annual standard and established a standard to target short-term bursts of SO2 exposure (a 99th percentile 1-hour daily maximum standard level of between 100 ppb and 50 ppb). The rule also proposed to amend ambient air monitoring, reporting, and network design requirements.

After receiving comments on the rule, the EPA issued the final rule in June 2010, mandating that states meet the new 1-hour SO2 standard using a 99th percentile form set at 75 ppb maximum SO2 concentration. The action, which the EPA said would benefit public health and "provide an adequate margin of safety," prompted legal challenges from industry and several states.

The EPA said in the rule’s 2010-released Regulatory Impact Analysis that the SO2 NAAQS revision to 75 ppb would likely cost electric generating units around the nation $700 million (in 2006 dollars) in 2020.

Sources: POWERnews, EPA

—Sonal Patel, Senior Writer (@POWERmagazine)