The Bay Area Air Quality Management District voted unanimously on Wednesday to tighten regulations on the Lehigh Permanente cement plant in Cupertino.

Cement plant — Lehigh Permanente has historically provided around 50% of San Francisco Bay Area cement. (KQED Quest)

The new rules, will cut the plant's mercury emissions by 90% by 2013, according to BAAQMD engineers. Currently the plant emits more mercury into the Bay Area air than any other facility.

BAAQMD engineers say the rules will also limit other pollutants from the plant, which include, dust, benzene, ammonia, hydrocarbons, dioxins and nitrogen oxides.

Neighbors, including city council members, asked the district to immediately draw up even tighter regulations.

"Right now this is the only plant in the country that is located in a metropolitan area and its exhaust plums are literally raining down on our citizens of the entire South Bay," said Los Altos Hills Vice Mayor Gary Waldeck.

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But the board instead voted to put the current proposal into place while researching what else could be done. "I think this is the best we can get right now," said Director Liz Kniss.

A public relations consultant for Lehigh said no one there would comment.

The U.S. Environmental Protection Agency tentatively passed tough new regulations on cement plants nationwide, but the industry is working through Congress to delay or scrap them.

For some background on Lehigh and cement plant pollution, listen to this report for which KQED reporter Amy Standen visited the plant, then known as Hanson Permanente, in 2010.

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Rules Tightened on Cupertino Cement Plant, a Big Source of Bay Area Mercury Pollution