Groups Set Mercury Limits for Flyash in Concrete

In 2006, the most recent year for which data is available, the U.S. produced 72 million tons of coal flyash, a waste material left over after coal is burned to generate electricity. While most of that flyash was put in landfills, about 15 million tons went into concrete, often as a substitute for the more carbon-intensive portland cement. Flyash is made largely of silica and lime, but it also contains trace amounts of heavy metals from the coal, including mercury.

The reuse—or “beneficial use,” in industry parlance—of some materials containing toxic substances like mercury, lead, and arsenic is encouraged by industry partnerships and by U.S. Environmental Protection Agency (EPA) policies. Now, two prominent rating systems, the U.S. Green Building Council’s LEED for Healthcare and California’s Collaborative for High-Performance Schools (CHPS), are putting limits on the mercury content for flyash that can be used to earn points in those systems.

CHPS has included flyash requirements in the draft 2009 version of its standards, which is now under review. To qualify for the recycled-content credit under CHPS, California schools must avoid flyash if it contains mercury at a level higher than 11 parts per billion (ppb); projects outside of California must avoid flyash with mercury levels above 5.5 ppb.