The Environmental Protection Agency is requiring the Navajo Generating Station to reduce emissions at the plant to improve visibility at nearby national parks including the Grand Canyon.

The EPA released a proposal earlier this year to reduce emissions at the coal-fired power plant in northern Arizona. The plant’s operators said the agency’s proposed upgrades would cost them more than $1 billion.

David Modeer, general manager at Central Arizona Project, which relies on the power plant to pump Colorado River Water to Southern Arizona, said plant owners have submitted their own alternate plans to the EPA.

“The first which is highly likely to be the one that would be utilized (is) the closure of one of three units at the Navajo Generating Station, which would allow substantially lower emissions from the plant,” Modeer said.

The other options include simply reducing the plant’s output or establishing a new emissions cap for the coal-fired plant without specifying how that would be accomplished.

The public has until Jan. 6, 2014 to comment on either proposal.

Read the federal register notice here.