Photo courtesy of Michelle Le/Mountain View Voice. Reprinted with permission. This post by Lynne Peeples was originally published on Ensia.com, a magazine that highlights international environmental solutions in action, and is republished here as part of a content-sharing agreement When Jane Horton bought her dream 800-square-foot farmhouse in 1975, she thought little of the semiconductor manufacturing plant across the street. Even after the company’s buildings were demolished and a chain-link fence went up around the campus, she still had no knowledge of the toxic dangers lurking beneath her feet — let alone of the fact that they were invading her home. It wasn’t until the early 2000s that Horton and other residents of Mountain View, California, heard about the underground plume of trichloroethylene, or TCE — a cancer-causing liquid used at the facility to clean silicon chips. Horton learned that vapors from the TCE were seeping up from the groundwater and soil into local buildings. When investigators tested the air inside her family’s house in 2004, they found concentrations of TCE exceeded a site-specific threshold set by the U.S. Environmental Protection Agency (EPA). And that was after approximately 75 percent of the contamination had already been cleaned up. “Are my kids going to die?” Jane Horton wondered after officials discovered TCE vapors invading her home. Photo courtesy of Michelle Le/Mountain View Voice. “We’d been over the plume the whole time,” says Horton, whose youngest son was still in elementary school when the vapors were discovered. “I can remember being so outraged that everything took so long. I’m wondering: Are my kids going to get cancer? Are my kids going to die? How am I going to be?” A venting system the EPA installed in her cellar now sucks toxic gases up from the soil, sending them through pipes and out a rooftop stack into the air, where they would be quickly diluted to acceptable levels. Periodic monitoring by the agency has since shown that the TCE levels at the house are safe. “It took them about a year to get the system working right,” Horton says. “It will be in the house until the house is no longer there.” Meanwhile, similar stories of toxic vapors intruding into buildings continue to surface around the country — from a mobile home park near San Diego, California, to sites throughout Minnesota, about 2,000 miles (3,200 kilometers) away. The implicated contaminants — most notoriously chlorinated solvents, such as TCE and tetrachloroethylene (known as perc), as well as benzene — can migrate through soil and groundwater from where they have seeped into the earth from a leak or a spill. Common sources include dry cleaners, gas stations, auto repair shops, military bases and industrial sites, even those whose doors closed decades ago. While exposure to high levels of these vapors can cause immediate effects, such as irritation and fatigue, breathing small amounts over a period of time is more concerning, according to Phil Landrigan, a pediatrician and epidemiologist at the Mount Sinai School of Medicine in New York. “Babies and small children can especially be damaged by very low concentrations of some of these materials,” he says. Long-term exposure to TCE, perc or benzene is known or suspected to raise the risk of certain cancers and other health effects, although it still remains unclear if intruding vapors reach high enough concentrations to pose a significant threat to human health. Research also hints at a link between a woman’s exposure to TCE during the first trimester of pregnancy and fetal heart malformations — a finding that has added considerable controversy and complication in addressing vapor intrusion. Soil bacteria readily biodegrade benzene and other hydrocarbons into relatively benign products such as water and carbon dioxide, making these contaminants a lesser concern. The breakdown of chlorinated solvents, on the other hand, can be slow and generate even more toxic by-products. Perc, for example, breaks down into TCE, which in turn creates dichloroethene and vinyl chloride, a potent carcinogen that is particularly persistent and mobile in the environment. Drawn by air movement above ground, toxic fumes can move from contaminated soils and water into homes and other buildings. Illustration by Sean Quinn/Ensia. Experts, including EPA officials, are not able to estimate the full scale of vapor intrusion. But it is likely extensive. Amy Graham, an EPA spokesperson, noted 91 existing sites that are part of the EPA's Superfund Redevelopment Initiative — dedicated to cleaning up contaminated land — where unacceptable human health risks associated with vapor intrusion triggered mitigation.