Much like the shape-shifting substance it regulates, the mercurial enforcement rule that governs mercury emissions from coal-fired power plants has changed unpredictably several times in recent years. During the past decade, the rule has undergone a number of major revisions driven by political pressures from environmentalists, public health entities, electric utility advocacy groups, and other interested stakeholders.

Mercury’s Impact on Human Health

The U.S. Environmental Protection Agency (EPA) is mandated to regulate mercury emissions based on concerns about the contaminant’s effect on human health. Exposure to mercury can occur from breathing contaminated air and ingesting contaminated water and food. Mercury exposure at high levels may damage the brain, kidneys, and developing fetuses, according to the U.S. Agency for Toxic Substances and Disease Registry.

The most common mercury exposure route for the majority of people is not through inhalation of air-borne fumes but, rather, through the consumption of fish and shellfish that contain large quantities of mercury. After mercury is released into the environment as part of the emissions from coal-fired power plants, it enters the air and then rains down into streams and other water bodies, where it can be ingested by microscopic organisms that convert it into methylmercury. This form of mercury can accumulate in the tissue of fish and other organisms. Currently, the U.S. Food and Drug Administration has set the maximum permissible level of methylmercury in seafood at 1 part per million.

The Mercury Rule’s Recent Roller Coaster History

In February 2008, the U.S. Court of Appeals for the District of Columbia Circuit threw out the EPA’s Clean Air Mercury Rule (CAMR). The 2005 CAMR required coal- and oil-fired power plants to cut their mercury emissions by 70% by 2018 and created a national emissions trading program to cut industry compliance costs.

A companion rule issued at the same time as CAMR reversed the 2000 Clinton-era determination that utility emissions of mercury and other hazardous air pollutants (HAPs) must be regulated under the maximum achievable control technology (MACT) standard, which is a much stricter requirement than the 70% reduction required under CAMR.

Once the appeals court’s order went into effect in 2008, the Clinton EPA’s finding was reinstated as the law governing mercury emissions, pending the EPA developing a new MACT standard. In February 2009, the Obama administration’s EPA asked the U.S. Supreme Court to dismiss a petition brought by the Bush EPA in 2008 asking the high court to review and overturn the U.S. Court of Appeals’ 2008 ruling that struck down CAMR.

EPA’s Current Efforts to Develop a New Rule

Now the EPA is working on a new air toxics emissions standard for power plants under the Clean Air Act (Section 112), consistent with the D.C. Circuit’s opinion regarding CAMR. The EPA intends to propose air toxics standards for coal- and oil-fired electric generating units by March 10, 2011, and finalize a rule by November 16, 2011, as ordered under the court’s consent decree.

On December 24, 2009, the EPA approved an Information Collection Request requiring all U.S. power plants with coal- or oil-fired electric generating units to submit emissions information for use in developing the agency’s proposed air toxics emissions standards.

Based on mercury controls in place or proposed for power plants, the new federal standard is likely to be in the range of 85% to 90% mercury removal, according to many industry analysts. If the EPA moves to adopt the MACT standard for utility HAPs, including mercury, that will probably mean that all U.S. coal-fired plants will either have to install scrubbers and particulate controls by 2015, dramatically cut their hours of operation, or shut down.

Seeking Certainty in Mercury Regulation

As quirky as quicksilver, the mercury rule has moved all over the regulatory landscape in recent years and left electric utilities guessing what steps they might need to take in order to comply. Now electric utilities once again are waiting to see what the latest version of the rule will be. In particular, power companies seeking to build new coal-fired units have to deal with the hurdle of changing laws driven by the political agendas of diverse groups. Many projects are on hold until utility management has some certainty about what their facilities’ compliance obligations will be under the new rule that is scheduled to go into effect in late 2011.

Fortunately, some utilities, such as Southern Co., are finding that one possible cost-effective approach to complying with the upcoming revised mercury rule may be to use “co-benefits” from air quality control systems already in service that are designed to remove other pollutants (see “Determining AQCS Mercury Removal Co-Benefits” in our July 2010 issue).

The U.S. electric power industry needs regulatory predictability in order to operate efficiently. Hopefully, once the EPA takes action next year, its new mercury rule will allow utilities to act with certainty as far as implementing effective mercury control measures to protect human health and the environment.

Angela Neville, JD, is POWER’s senior editor.