A trace amount of vapors from the dry cleaning chemical tetrachloroethylene, also known as perc, has been detected at the Mildred Avenue Middle School in Mattapan. The school was completed in 2003 on a handful of formerly industrial sites that were cleaned up and patched together by the city.
Boston Public Schools and the Department of Environmental Protection both agree that the amount detected in air quality tests is not enough to be threat to students, but plans are being made to address the problem before it gets any worse.
The amount detected was between .3 to 13 micrograms per cubic meter, or .04 to 1.9 parts per billion.
â€œThatâ€™s not an imminent threat,â€ said DEP spokesman Joe Ferson. â€œItâ€™d have to be four times that. But it still should be reduced.â€
Over the next two weeks, the city and the DEP will be searching the building to discover the source of the vapors and working to eliminate it. One question will be whether or not they will need to replace or alter the vapor barrier under the building. Another will be whether the carbon filtration system needs to be improved.
According to a letter sent to parents from principal Kris Taylor, the DEP will return within a couple of weeks to retest the school.
DEP inspectors first detected the perc at the Mildred in a review of over 600 sites that were â€œclosed outâ€ (DEP-talk for cleaned up) prior to April 2006. At that time, DEP adopted new standards for site clean-ups for vapor-intruding chemicals due to new scientific knowledge about how those compounds rise through the subsurface from the groundwater and seep into nearby buildings.
â€œNow that we have a stricter standard than we did back then, weâ€™re going back and checking those old sites,â€ said Ferson.
The Mildred, having been cleaned up prior to 2003, was part of this multi-site review, and perc was detected seeping into the school.
In very high concentrations, such as those that might be found at a hypothetical dry cleaner in total violation of current laws about the chemical, perc can cause dizziness, headaches and even unconsciousness and death.
Before the Resource Conservation and Recovery Act of 1983 that regulates its use, perc was not considered a hazardous chemical, legally. Dry cleaning machines often leaked the chemical, and many shop owners disposed of it simply by tossing it in their dumpster. Because of this history, many contaminated areas have been found throughout the city, some much worse than the Mildred site. Officials suspect many more are still undiscovered.
Perc use is on the decline in the state, however. In 1997, when DEP began taking surveys, dry cleaners statewide reported using 111,836 gallons. In 2005, they used only 50,720.
The cityâ€™s Bostonâ€™s Environmental Hazards Program and the DEP are both considering a hunt for yet undiscovered contaminated sites. The only way they are currently found is during routine soil tests required for large construction projects.
Perc was also found at the new Mattapan branch of the Boston Public Library on Blue Hill Avenue before its construction, but Ferson said that site is not comparable to the Mildredâ€™s.
â€œThey are very complicated sites and I donâ€™t think you can make that kind of conclusion,â€ he said. When asked if the chemical release at the library site was worse in any way than the one at the Mildred, he said, simply, â€œno.â€