But it turns out that this idyllic garden of corporate harmony sits on land that since 1989 has been a Superfund site, a designation the EPA gives some of the most contaminated or polluted land in the country. And while thousands of tons of contaminants have since been removed, it is still being cleaned up. For a few weeks at the end of 2012 and into 2013, toxic vapors got into two campus buildings, possibly exposing the office workers there to levels of chemicals above the legal limit set by the EPA. A spokesman for Google said that while the pollution levels required remedial action, they did not necessarily put employees in danger. He added that the issue was resolved in less than four weeks.

Santa Clara County has 23 active Superfund sites, more than any other county in the United States. All of them were designated as such in the mid to late 1980s, and most were contaminated by toxic chemicals involved in making computer parts. Completely cleaning up these chemicals may be impossible.

Read: Not even Silicon Valley escapes history

The sites came to the attention of the EPA after groundwater testing in the area revealed that toxic chemicals—notably, a solvent called trichloroethylene—were present, possibly from leaking pipes or underground storage tanks. Trichloroethylene, which was used to clean semiconductors (a component of computer chips) during the production process, is associated with increased risk of certain cancers, developmental disabilities among children exposed in utero, increased rates of miscarriage, and endocrine disruption.

Back in the ’80s, IBM, Fairchild, and other companies accused of polluting the groundwater denied that the chemicals posed any sort of threat to human health. In 1985, a California Department of Health Services study reported a significantly higher than expected rate of miscarriage and birth defects near the leaking tanks, though the department did not have conclusive evidence to tie the health problems to the leaks. (Neither IBM nor Schlumberger Technology Corporation, the company responsible for cleanup at the former Fairchild site, responded to requests for comment.)

Over the past three decades, the EPA and the companies involved in polluting Silicon Valley’s groundwater have filtered and cleaned some of it, but the agency’s website acknowledges that the cleanup will continue for many decades. That’s in part because the toxic molecules have spread throughout the area—NBC Bay Area reported in 2014 that, according to government officials, there are 518 toxic plumes of groundwater in Santa Clara County, a number that advocates say is an underestimate.

Read: The looming Superfund nightmare

The EPA maintains that there are no direct-exposure pathways to the contaminated groundwater anymore, but the problem now is that the toxins can get from the groundwater into the air in buildings via a process called vapor intrusion, which is what happened at Google. And while it’s not entirely clear yet what the consequences of lifetime environmental exposure are, research from South Korea suggests they may be serious. According to one study, Bloomberg Businessweek reported in 2017, miscarriage rates among women who worked at several South Korean microchip factories were nearly three times those of the general population. At one Samsung factory, two young women who worked next to each other were diagnosed with the same form of aggressive leukemia, a cancer that affects three out of every 100,000 South Koreans every year. The women died within months of each other.