The Lehigh Cement Plant in the hills near Cupertino has a long history; for decades it was known as the Hanson Permanente Plant. Mining at the limestone quarry has been going on since 1939. Lehigh supplies the Bay Area with more than half of the cement it uses in constructing everything from bridges to buildings.
But as homes near the plant increased, so too has the chorus of complaints.
"What we do know is that there is a huge amount of dangerous and toxic emissions coming out of the plant," said Joyce Eden who represents a group called West Valley Citizen Air Watch.
Lehigh and the Bay Area Air Quality Management District say the plant has consistently operated by the rules and poses no significant health risks. It is required to follow limits and standards for 1,500 air pollutants.
"We're very heavily regulated," said Tim Matz with Lehigh environmental affairs. "We're very proud of our compliance and our compliance history in air regulation."
But one toxic emission that has never been regulated is mercury, which naturally exists in the limestone. When it is burned in the plant's kilns, the mercury vaporizes and is released into the air. The EPA expects to issue historic new guidelines in June.
"Nationwide we expect an 80 percent reduction in mercury emissions from cement plants," said Gerardo Rios with the EPA regional air division.
In 2007, Lehigh released 710 pounds of mercury. In 2008, production levels dropped and the release was 582 pounds. Under the proposed EPA guidelines, the maximum amount of mercury Lehigh would be allowed to release is a dramatically reduced 69 pounds.
The EPA's new rules are coming at a time when the plant's five-year permit renewal process was well underway.
The Bay Area Air Quality Management District decided to combine efforts.
"We're in a situation now where we could go ahead and finalize the permit without these rules being in effect, but then we'd just have to reopen them and revise them anyway," said Brian Bateman with the air district.
It is not just mercury from Lehigh that concerns a lot of residents. There is a wide range of contaminants that require scrutiny -- everything from arsenic to hydrogen chloride.
Bill Almon is the founder of a group called QuarryNo with some 400 members. They oppose Lehigh's permit renewal with complaints that range from continuous truck traffic, to dust that seems to settle on everything. They say their biggest concerns though are about people's health issues, ranging from asthma to cancer.
"You can show the location of the quarry and you'll see unusual health issues, you know just draw a circle," said Almon.
To address some of those concerns, the air district has set up monitoring equipment at two sites, including an elementary school about two miles from the plant. A more complete community testing facility will be established later this year.
Not everyone living near Lehigh thinks the precautions are necessary. Barbara Jones says she represents a silent majority.
"Much of the town is not not even affected by the trucks, which I believe is the biggest problem. The actual pollutant, that's just a red herring," she said.
Some of those pollutants, and most notably mercury, will be restricted like never before. It could cost Lehigh $40 million for new equipment to comply with the EPA's current proposal. The plant manager says it will do whatever is necessary.
"We have been working diligently with the community," said plant manager Henrik Wesseling. "We have done a lot of things, way above and beyond what we are required to and we will continue doing that."
The plant's critics vow to press forward, but say they do view restrictions on mercury output as a victory.
"This would be a giant, huge, completely different step in the right direction," said Eden.
Once the new EPA standards are finalized, Lehigh and more than 150 cement plants across the country will have until 2013 to comply.