A byproduct from the process of burning finely ground coal in an electric power generating plant. Fly ash composition is mainly spherical glassy silica particles released after the combustion cycle through exhaust gases. It's composed of additional elements that form mostly oxidized compounds that condense when they cool down from the combustion process. In December 2008, 2. 6 million cubic yards of fly ash sludge stored in a large retaining pond at a coal-fired power plant near Kingston, TN was released when a retaining dike failed. The sludge was found to contain arsenic, mercury, cadmium, chromium, thallium, and lead, and these toxic metals were found in the river(s) water in which the sludge spilled. ~New York Times Dec 26, 2008`