Arizona environmental advocates are calling for stricter air quality standards at the Navajo Generating Station, one of the largest coal-powered plants on the West Coast.

For most of last year, the Environmental Protection Agency pushed owners of coal-fired power plants to meet increasing air quality standards under the Clean Air Act.

The standards would require retrofitting the plants’ smoke stacks to reduce pollution, a move plant operators say is expensive. Instead, some utility companies have chosen to partially shut down operations to reduce emission, oftentimes increasing energy costs for consumers.

Such was the case last week at the Four Corners Power Plant in New Mexico. Arizona Public Service, the plant’s owner, shut down three power units instead of making upgrades to the entire facility.

Now environmental groups are calling on the EPA to not back down from enforcing higher air quality standards at the Navajo Generating Station in Northern Arizona.

The plant serves a large portion of the Southwest, including Tucson, Las Vegas and Los Angeles. It also provides power for the Central Arizona Project, the state’s biggest water system.

Kevin Dahl, a spokesman for the National Parks Conservation Association, said the cost to retrofit the plant is not unreasonable.

“Controls that are being proposed are economical and if part of the alternative is to shut down the plant maybe it’s time for us to transition to the cleaner energy alternatives of solar and wind," he said.

Dahl said the EPA has proposed three deadlines for reducing emissions at the Navajo Generating Station. One would require plant operators to take action within five years. The other plans would push the deadline to 2030 or possibly far beyond that.

Public comment on the proposals ended Monday.