Others maintain the supposed monster is a just a myth, and is in reality a benign cement plant located on Stevens Canyon Road.

The issue surfaced last month following the release of a study of highly toxic fish found in area reservoirs. The San Francisco Bay Water Quality Control Board study of 10 reservoirs showed Cupertino's Stevens Creek Reservoir had the highest levels of mercury in its fish, particularly large-mouth bass.

For some residents, the finger of blame for the mercury points directly to the cement plant, Hanson Permanente. In June 2004, a different report listed the cement plant as one of the leading sources of air pollution in Santa Clara County. The study by the Bay Area Air Quality Management District examined stationary sources of pollution (excluding moving sources such as automobiles).

Whether Hanson Permanente, is indeed responsible for the high mercury levels or is not responsible is an open question.

"It is a monster in the room, and not talked about," said Cupertino resident John Mracek. "We end up with an incredible amount of pollutants, most people don't realize there is an incredible coal burning operation in our backyard."

However, John Giovanola, a community affairs officer for Hanson Permanente, said regulatory measures help mitigate the environmental affects. "We are monitored by the Bay Area Air Quality Management District and they assess our health risks," he said. "They set certain specifications for us to follow and a number of studies show we are not directly involved."

The plant produces pollutants through burning coal used to heat its kiln, and through chemical changes in the limestone used to manufacture cement. As a result, the emissions are considered toxic and hazardous to human health according to Environmental Protection Agency regulations. One such toxin emitted by coal, benzene, for example, is a known carcinogenic. The EPA Web site also said mercury in air pollution is largely harmless to humans, but becomes more dangerous in water bodies. There, the mercury becomes highly toxic due to biological processes In this highly toxic form, the mercury is then absorbed by fish and enters the food chain.

Scientists say Hanson Permanente does contribute to the highly toxic mercury levels in the reservoir, but by how much is uncertain.

Mark Jacobson, a Stanford University professor specializing in atmospheric pollution, said Hanson Permanente's proximity to the reservoir plays a role. "It is probably a good bet some of [the mercury] settles to the bottom [of the reservoir]," he said, where it is then absorbed into the food chain. Whether it is main the cause of mercury depends on the concentration, he said.

Barbara Turpin, an environmental scientist at Rutgers University-Cook College in New Jersey said emissions are more likely to be highly toxic closer to the source. "[Emissions] drop off with time," she said. "The farther you go, the lower the concentration since the dispersal process dilutes it."

However, Will Bruhns, a spokesman for the Water Quality Control Board, said a more likely source of the mercury in Stevens Creek is the local geology. "The suspicion is most of the mercury from the reservoir comes from the geological landscape," he said. "I'm not aware of any studies that correlate emissions to a particular water body."

The geology surrounding the Stevens Creek Reservoir is indeed well known for mercury. A century ago, the prevalence of mercury led to a number of small mercury mines in the area. Bruhns also said mercury in the reservoir had come from distant power plants and from outdated farming and industrial practices.

Even so, this is not reassuring for some nearby residents. Paul Roberts, a former Cupertino planning commissioner, said of Hanson's emissions, "there is a lot of fallout less than a mile away, it really caught my notice."

Roberts also pointed out Hanson Permanente is home to a stone quarry in operation since 1939. The quarry has created a gradually expanding scar in the earth that reportedly can be seen across the bay in Milpitas. "I'm concerned because they are expanding their operations."

Roberts, a retired professor of environmental engineering, also said noises of hot gasses escaping from Hanson Permanente often occur at night. "There is a roar, a big cloud, and later cars are covered by dust."

According to Stanford's Jacobson, such dust also layers vegetation and can be corrosive overtime. According to the EPA, long-term exposure to toxic contaminants similar to those emitted by Hanson Permanente can also lead to health hazards, such as eye irritation and respiratory problems.

For now, residents—particularly young children and expectant mothers—are advised to not eat fish from Stevens Creek.

But the broader environmental hazards remain a concern to Mracek. "We have to look at the big picture," he said. "We have to keep an eye on [Hanson Permanente] to protect the community's health."

As for the second leading source of stationary air pollutants in Cupertino according to the June 2004 study: it's dry cleaners.

For more information on the mercury in fish report, please visit: http://www.oehha.ca.gov/fish/so_cal/bayareares.html

For more information on the air pollutants report, please visit: http://www.baaqmd.gov.