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States are finding dangerous concentrations of a degreasing chemical in indoor air in reviews of thousands of contaminated sites.
In some states, many properties—often dry cleaners and gas stations as well as residential and industrial sites—have previously been assessed for trichloroethylene, or TCE. The chemical solvent can migrate from contaminated groundwater up into soil and indoor air through a process called vapor intrusion, or sub-surface intrusion.
In Massachusetts, about one in four of the sites state officials are assessing for TCE need “further work,” though that may not indicate unsafe levels, said Paul Locke, assistant commissioner for the state’s Bureau of Waste Site Cleanup.
“The problem is not as bad as we had feared, perhaps, but we are finding that there are older sites that still have elevated levels and impacts of concern,” he said.
In Michigan, officials estimate more than 3,000 properties will need to be tested for unsafe levels of TCE.
The chemical’s levels of concern, which the Environmental Protection Agency revised in 2011, led states to take a second look at some sites and ask whether people should be evacuated from buildings where high concentrations of the chemical are found.
“We’ve been doing vapor intrusion work for many, many years,” said Susan Leeming, a division director under Michigan’s Department of Environmental Quality. “The difference now is that we have better technologies where we can detect lower levels of these compounds.”
According to the National Institute of Environmental Health Sciences, companies are developing improved sensors that will be able to detect TCE at concentrations of 20 parts per trillion by volume.
Decades ago, the main concern was developing cancer from long-term exposure to the chemical. Short-term exposure to TCE can also cause liver and kidney damage and affect the nervous system, according to the Agency for Toxic Substances and Disease Registry.
But states’ environmental and health officials are now concerned about trichloroethylene’s short-term effects on pregnant women and the development of their babies.
“I don’t know of any other contaminant that has the dramatic change in toxicity that TCE has,” said David Gillay, partner at Barnes and Thornburg LLP in Indianapolis.
Though the risk of getting cancer from TCE initially drove remedial action, non-cancer effects now drive that risk, he said.
States vary widely in their approach to potentially unsafe sites. Michigan is mainly selecting potential sites by their current use.
“We know we’ve got a couple thousand dry cleaners, a thousand gas stations,” Leeming said.
The state has evacuated some sites after finding dangerous levels of TCE and other volatile organic compounds such as vinyl chloride, Leeming said.
Massachusetts is selecting sites from a database of locations that had contaminated groundwater. When dangerous levels of TCE are found, Locke said the state will move in special air purifiers within 24 to 48 hours instead of opting for evacuation and eventual cleanup.
The EPA has not dictated whether sites with unsafe levels of TCE should be evacuated. The agency’s silence has fostered inconsistency among states, Gillay said.
Minnesota is using screening values developed by the EPA to look at TCE contamination by vapor intrusion at residential sites. A lifetime exposure at or below 2 micrograms per cubic meter is considered safe.
In Minnesota, if TCE is found below the sub-slab of a residence at concentrations above 20 micrograms per cubic meter, state officials recommend mitigation.
Massachusetts considers concentrations above 6 micrograms of TCE per cubic meter in indoor residential air to be an acute health concern.
Oregon’s new pilot program to review its site-monitoring process includes an assessment of potential vapor intrusion. The program will also look at cost-recovery policies and lasts for the remainder of the year.
The pilot program covers only 30 sites. State officials there don’t anticipate “re-opening” waste sites administratively to look for vapor intrusion.
“We’ve had vapor intrusion protocols in place for close to 10 years,” said Bruce Gilles, a program manager on the Oregon Department of Environmental Quality’s vapor intrusion guidance team. “We’re comfortable with where we’re at with the vapor pathway.”
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