JACKSON (AP) — Mississippi Power Co. said Monday that it needs one more month and another $99 million to finish its $7.2 billion Kemper County power plant.

The subsidiary of Atlanta-based Southern Co. said in a stock filing that it has finished repairs from a March tubing leak. The company aims to have the plant fully running by April 30, completing work more than three years behind schedule.

Mississippi Power said it will absorb $70.2 million in additional costs announced Monday. The company’s 186,000 customers could be asked to pay $28.6 million in additional costs, mostly interest.

Kemper’s two gasifiers convert soft lignite coal mined at the site into a synthetic gas using high pressure and heat. The tubes broke March 9 in a cooling unit that reduces the heat of the gas that comes out of one gasifier before piping it into a chemical plant that removes carbon dioxide and other chemicals. The gas is then burned in turbines to generate electricity.

Spokesman Jeff Shepard said the company is working on restarting the second gasifier. The first one continues to run.

Kemper is designed to capture 65 percent of the carbon dioxide from the burning coal, releasing only as much of the climate-warming gas as a typical natural gas plant does.

Overall, customers could be asked to pay $4.3 billion for Kemper. Southern shareholders have taken $2.8 billion in losses.

Mississippi Power must submit a rate plan to the state Public Service Commission by June 3, outlining how Kemper will be paid for. That elected three-member regulatory body will ultimately decide how much customers pay. The commission granted Mississippi Power a rate increase in 2015 covering $840 million worth of assets that began generating electricity burning conventional natural gas.