1950: Dunkirk units 1 and 2, each 75-MW simple-steam coal plants, go into operation on Lake Erie, 55 miles southwest of Buffalo, N.Y.

1959-1960: Dunkirk adds units 3 and 4, 185 MW coal-fired, simple-steam units.

1999: NRG Energy acquires Dunkirk from Niagara Mohawk Power. NRG later converts the plant to use low-sulfur Powder River Basin coal and installs controls on mercury and nitrogen oxide emissions.

March 2012: NRG says it will mothball Dunkirk effective Sept. 10, 2012.

August 2012: The New York Public Service Commission approves a reliability support services agreement between NRG and Niagara Mohawk parent National Grid to keep Dunkirk operating to maintain system reliability. National Grid agrees to pay NRG $2.9 million per month for the nine-month period of Sept. 1, 2012, through May 31, 2013, with additional cost adjustments for taxes and coal costs, and credits for capacity market revenues earned by Dunkirk.

May 2013: The PSC approves a new RSSA between NRG and National Grid through May 31, 2015, at a cost of $2.1 million per month, with the same cost adjustments as the original RSSA.

February 2014: The Federal Energy Regulatory Commission accepts and suspends National Grid’s proposed rates to cover the cost of the RSSA. FERC accepts the changes subject to refund and further order, saying it was not convinced the changes were just and reasonable.

June 2014: The PSC approves a $140 million plan to upgrade three Dunkirk units from coal to natural gas, with a capacity of 435 MW. The PSC selected the repowering over a plan to invest up to $76 million in transmission upgrades, which would have addressed reliability concerns and allowed the plant to close. Closing the plant, Chautauqua County’s largest taxpayer, would have reduced the city’s property tax revenues by more than 40%. The repowered plant is expected to pay about $8 million in property taxes annually.

October 2014: The Sierra Club files suit against the PSC over the repowering plan.

January 2015: National Fuel Gas and NRG announce a settlement allowing National Fuel to build a 9.3-mile pipeline to supply Dunkirk. National Fuel and Dunkirk Gas, an NRG affiliate, had originally offered competing pipeline proposals to the PSC.

February 2015: Entergy sues the PSC, alleging it infringed on FERC authority by approving the repowering plan.

March 2015: Niagara Mohawk informs PSC it will exercise its option to extend the RSSA for seven months through Dec. 31, 2015.

September 2015: Projected completion date of Dunkirk repowering.