A planned US$400m cement plant is worrying environmentalists and some residents in the eclectic Arizona town of Seligman.

Cemex, a global conglomerate and a building materials titan, wants the plant to be finished by 2012. It will be located about 15 miles northwest of the town limits and less than 50 miles south of the Grand Canyon.

While some see the facility as an economic boon that would bring badly needed jobs, a steady supply of building material and a burgeoning tax base to a sleepy part of the state, environmental groups and nearby landowners fear the company will be a major polluter, dirtying the air over Grand Canyon National Park and in nearby communities.

"The primary issue is air quality," said Stacey Hamburg, conservation program coordinator for the Sierra Club in Arizona. "There is just no reason to locate this type of highly polluting industry so close to the Grand Canyon. We will fight it as much as possible."

The Arizona Department of Environmental Quality has yet to issue an air permit for the plant and will conduct an environmental assessment before doing so.

Cemex spokesman Jennifer Borgen said the plant will use a variety of state-of-the-art materials, including high-tech fabric filters and storage systems to capture dust and new kilns that cut down on nitrogen oxide emissions.

The company also says it will employ a host of water conservation practices at the site and that it has had discussions with the Arizona Game & Fish Department regarding possible conservation projects in the area.

"We want to make sure we are a good neighbor," Borgen said.

Cemex, whose corporate headquarters are in Monterrey, Mexico, has already purchased a 7,400-acre site for the plant, which could operate for the next half-century.

It chose Seligman because of its rich limestone deposits, low population density and close railroad access.