The company has been burning coal for more than 120 years, but once that final coal is consumed in March, the plant will burn only natural gas.
Citizens Energy Group, which operates the plant, began to switch the plant to natural gas in 1998.
The amount of coal it burned each year reduced from 1 million short tons to 150,000t.
Transferring to natural gas was deemed the most cost-effect way of meeting strict emission standards.
Upgrading the old coal burners would have cost CEG more than $USS24 million, while the switch to gas cost just $US9million.
