MEMPHIS — The Tennessee Valley Authority began seeking public comments Wednesday on a proposal to retire the coal-fired Allen Fossil Plant in Memphis and replace it with a natural gas facility.

The TVA said it has completed a draft environmental assessment looking at replacing the Allen plant. TVA spokesman Chris Stanley said the proposal is a step in the process of replacing the coal plant with a natural gas plant.

"It's the best way we can provide reliable, low-cost power in a diversified portfolio," Stanley said.

In May, TVA president and CEO Bill Johnson said the utility would make a decision on the future of the Allen plant sometime this year. The final decision rests with the TVA's board, which could vote on the proposal at an Aug. 21 meeting, Stanley said.

TVA committed to install emission controls or retire Allen's coal units by December 2018 under a 2011 agreement with the Environmental Protection Agency to reduce emissions across its coal-fired generating fleet.

The Allen plant generates about 4.8 billion kilowatt-hours of electricity a year, enough for 340,000 homes. The TVA says the plant consumes about 7,200 tons of coal daily.

Environmental groups say the Allen plant causes an air pollution hazard and it should be shut down and replaced with a facility that generates cleaner energy.

One of those groups, the Sierra Club, said it supports the TVA's proposal to retire the coal facility, while encouraging the utility to replace it with wind or solar power rather than natural gas.

"Investments in clean energy will protect the health of our families, lower energy bills, and create high paying jobs in Memphis," said Scott Banbury, conservation program coordinator with the Tennessee chapter of the Sierra Club. "TVA doesn't have to trade coal for natural gas, another expensive fossil fuel which pollutes our air."

The public comment period runs through Aug. 5. An open house will be held next Tuesday in Memphis.

TVA is the nation's largest public utility, supplying power to about 9 million people in Tennessee, Alabama, Mississippi, Kentucky, Georgia, North Carolina and Virginia.