When coal is burned in the boilers, two types of ash are produced.
The heavier ash, which collects in the bottom of the boiler, is called "bottom ash". This ash is collected and trucked back to the mine site, where it is buried before the land is reclaimed.
The remaining, lighter ash, which is carried through the boiler with the exhaust gas, is known as "flyash". The flyash is removed from the furnace exhaust by electrostatic precipitators. With the flyash removed, the remaining flue gases are discharged up the stack.
Much of the collected flyash is sold to be used in the manufacture of concrete. The remaining flyash is returned to the mine for burial.