A Blue Hill Avenue dry cleaner may be held responsible for the release of a toxic chemical called perchloroethylene into the groundwater underneath the construction site of the new Mattapan Library. The chemical is a suspected carcinogen and worse in large quantities, but city officials said the site poses no imminent health hazard to residents and will not delay the library's construction.

It might, however, have to be cleaned up.

Boulevard Cleaners, uphill from the library at 1328 Blue Hill, has been given a 'notice of responsibility' for the contamination, and was ordered to hire a professional to determine if the chemical originated from the shop. Donald Maggioli, a licensed site professional (LSP) hired by the city, said he ran into Boulevard's LSP, who told him that he had not found any evidence of a current leak on the premises.

"From what I see, this is from years before," said Boulevard owner Peter Papadogiannis. "They used different machines before, they had just replaced them when I bought the place five years ago. If somebody else spilled it before, why should I responsible?"

But according to the Department of Environmental Protection, which would enforce any decision against Papadogiannnis, the liability for clean-up costs can be the current or the former owner's. Who will pay is determined by the DEP, case-by-case. "If you are putting cash down to buy property or a business, you should also be doing due diligence to check out the property," said DEP spokesperson Joe Ferson.

In the amounts it has been found in, the perc, as it is called for short, is not harmful to humans. If it reached air, it could be inhaled, but the release is deep underground and the library's foundation will be a slab type, difficult to penetrate.

Cleaning up the spill will not be as simple as trucking a few loads of dirt away. Unlike hydrocarbons and other chemicals, perc is heavier than water. When it percolates down into the groundwater, it tends to keep sinking until it reaches bedrock.

"To clean up the perc is extremely difficult, because it's going down deep," Maggioli told a meeting of abutters at the Mildred Avenue Community Center last Thursday. But if the site is tested again and falls within minimum guidelines for groundwater, he said, it may not have to be cleaned up. "It's not a significant release. The highest number we've found is 900 parts per billion." The legal limit, he said, is 50 parts per billion. Maggioli also found byproducts of perc that had been chemically broken down by the soil.

"If that library had not come up, nobody would have known what was happening around here," said Bishop Hezron Farrell of the Glad Tidings Pentecostal Assembly, a nearby church. "We wanted that lot, but the city took it over. It was God where we're concerned, because we would not be able to produce that kind of money."

Before the Resource Conservation and Recovery Act of 1983, 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 Mattapan site. Officials suspect many more are still undiscovered.

"We're considering looking at dry cleaning throughout the whole city and the DEP is looking at them in the whole state," said John Shea, director of Boston's Environmental Hazards Program.

Currently, discoveries of perc are only discovered through large new construction projects - such as the Mattapan Library - which require soil and groundwater inspections or when someone takes out a bank loan to buy a business. The banks often require site inspection to insure against potential liabilities such as the one faced by Boulevard Cleaners.

In addition to the groundwater threat, perc can be a workplace hazard that causes dizziness, headaches and even unconsciousness and death in high concentrations. Some anti-perc activists say consumers could also be risking cancer, just by inhaling fumes off their recently dry-cleaned suits and evening gowns.

A federal law is phasing out the use of perc at dry cleaners in apartment buildings by 2020, and California is phasing out its use completely by 2023. In Massachusetts the laws are still lax by comparison. The DEP requires dry-cleaners to self-report using detailed surveys, and then audits or randomly checks up on them. New machines using perc require seals and systems to dispose of the used chemical, and as a result perc use has dropped. In 1997, when DEP began taking surveys, dry cleaners statewide reported using 111,836 gallons. In 2005, they used only 50,720.