How Dangerous is coal fly ash?

Coal fly ash contains many toxic, carcinogenic and poisonous substances that are particularly dangerous in aquatic ecosystems.
Most fly ash and coal combustion residue (CCR) is sent to landfills or abandoned mines. In some cases, such as the TVA Kingston plant, it is kept on site.
( Althought there are “green” or “beneficial” uses for coal fly ash, these involve mixing it with cement, stabilizing it and keeping it away from groundwater. Only about 43 percent of coal fly ash nationwide is stabilized in this way. )
Scientists have long known that big trouble can result when coal fly ash comes in contact with aquatic ecosystems or ground water tables.
“The presence of high contaminant levels in many coal combustion residue leachates may create human health and ecological concerns,” the National Academy of Sciences National Research Council said in a 2006 report. Coal combustion residues are about sixty percent fine aluminum silicate glass compounds and most of the rest are quartz, lime, magnesium, iron and other compounds, according to the NAS study. Other constituents of CCR can be very dangerous. Fly ash contains many Class 1 (proven) carcinogens. For example, fly ash contains 43 parts per million of arsenic, a known carcinogen.
Arsenic, thallium, antimony, molybenum, lead and cadmium — in that order — pose the largest cancer risks, EPA said in a 2007 risk assessment report.