Jul. 20--Federal regulators are proposing tougher new air quality standards for Portland cement plants, just as a federal stimulus package creates a greater demand for concrete.

Existing plants, including the Clinchfield Cemex plant in Houston County -- Georgia's only major cement plant -- would face limits on their mercury emissions for the first time.

The changes also would tighten limits on other air pollution for both old and new cement plants.

The outcome of the debate could cause Houston American Cement, which has plans for a plant next to Cemex, to re-evaluate its plans, said project director Ed Buehler.

"At this point in time, I don't think (the proposed limits are) achievable for this plant to reach," he said. "This adds another level of uncertainty to an already major investment."

The Houston American project has already been delayed as the company waits for the economy and cement demand to stabilize.

The Environmental Protection Agency's draft rules would dramatically reduce the amount of mercury, hydrocarbons, hydrochloric acid and particulate matter allowed from kiln smokestacks.

Mercury can damage fetuses and cause developmental problems. The other pollutants can be toxic or cause breathing and heart problems.

Cement plants grind limestone, usually from an adjacent quarry, with other raw materials before heating them in a kiln. The resulting product, called clinker, is ground and mixed with a little gypsum to produce concrete.

Cemex officials said they are still evaluating how the rules could affect that company's plants.

"We don't know the theoretical costs right now because we are first trying to determine what technology exists and if it could even be applied to any of our plants," Jennifer Borgen, Cemex communications director, wrote in an e-mail.

The cement industry contends that the proposal could put more than half of American cement plants out of business just as the demand for cement is likely to skyrocket. Congress's $787 billion economic stimulus package is expected to create a building boom for roads, bridges and schools, all of which rely on concrete.

"Every recovery dollar is going to buy less economic impact in terms of employment if the price of cement goes up," said Scott Segal, a consultant on regulatory and communications matters for the Portland Cement Association. "If you've got to import the cement, you'll be creating infrastructure jobs. ...