In April 2011 TVA reached an agreement with the Environmental Protection Agency (EPA), four state governments, and three environmental groups to drastically reduce pollution and carbon emissions. Under the terms of the agreement, TVA was required to retire at least 18 of its 59 coal-fired units by the end of 2018, and install scrubbers in several others or convert them to make them cleaner, at a cost of $25 billion, by 2021. As a result, TVA closed several of its coal-fired power plants in the 2010s, converting some to natural gas. These include John Sevier in 2012, Shawnee Unit 10 in 2014, Widows Creek in 2015, Colbert in 2016, Johnsonville and Paradise Units 1 and 2 in 2017, and Allen in 2018.