Coal combustion produces three kinds of solid waste: fly ash, that which goes up the chimney, bottom ash found in the furnace, and scrubber sludge. Fly ash, one of the main causes of smog, is collected as it leaves the smokestack, bottom ash, heavy and rock like, is collected from the combustion chamber, and the scrubber sludge is liquified gypsum used to capture effluents from exhaust gases. A typical power plant produces 125,000 tons of ash and 193,000 tons of slurry, all unregulated by the EPA, and is generally stored in unlined fields (top middle of image), in spite of the arsenic, selenium, cadmium, lead, and mercury it contains.