A St. Paul elementary school has delayed the first day of school over concern that toxic vapors under its foundation could have sneaked into the building and contaminated the air.

But the Minnesota Pollution Control Agency (MPCA) said the results of its indoor air quality tests showed “negligible results” for any toxic vapors inside Crossroads Elementary Science and Montessori School. In other words, none of the toxic vapors under the school’s foundation are seeping into the school and the air is not contaminated, said Walker Smith, an MPCA spokesman.

Even though its air got the green light, the school will still delay the start date for grades 1-5, which will now begin on Thursday, instead of Tuesday. Prekindergarten and kindergarten will begin on Thursday, as scheduled.

“We are pleased that the results came back and showed that Pollution Control wasn’t able to detect a presence of any chemicals of concern. That’s reassuring to us, and I’m sure it will be reassuring to the staff and families,” said St. Paul Public School interim communications director Toya Stewart Downey.

The school has already begun installing a vapor mitigation system to prevent future problems, said Smith of the MPCA.

Smith described the fix as similar to the one homeowners with radon problems might use, involving a combination of fans and pipes to vent out toxic vapors under the foundation of the building.

The school delay is just the latest sign of the vapor intrusion problem the MPCA has been tackling around the state, as toxic vapors rise from soil and groundwater that were contaminated by industrial chemicals years ago.

“It’s part of the legacy of our industrial history,” said David Jones, supervisor of the site assessment and consultation unit at the Minnesota Department of Health.

Jones said he was extremely pleased to learn about Friday’s test results. He said the Health Department didn’t order school officials to delay the first day at Crossroads, but that school officials themselves made the call out of an abundance of caution.

The chemicals in question are trichloroethylene, a common industrial degreaser, and perchloroethylene, a common chemical used in dry cleaning. Both are colorless nonflammable liquids that quickly evaporate in the air, and are carcinogens if exposure is high enough or long enough.

The year-round school, located at 543 Front Av. in St. Paul’s North End neighborhood, sits on a site that was once home to a carpet manufacturing operation, said Smith. Machine shops and an ammunition maker were also on the site at one point, too.

This site was redeveloped to be a school in the late 1990s, and contaminated soil was removed, Smith said.

But it wasn’t known then that chemical vapors could rise back up through soil and leak into buildings through cracks in the foundation, and the potential health risks are still being studied.

The MPCA first began testing for vapor intrusion five years ago with new technology and equipment that can measure vapor at relatively low levels.

“There are hundreds of sites in Minnesota that might have this problem, and we are making it a priority to look into sites near schools and day cares,” Smith said. “It’s turning out to be a problem that’s taking a lot of resources.”

More than 600 sites could have a vapor intrusion problem, with about 150 sites near schools and day cares. Smith said this was the first time a school closed due to concerns.

A contractor hired by the MPCA tested the soil beneath Crossroads around Aug. 14, drilling more than 30 holes through the school’s foundation to test for vapor intrusion, Smith said. They quickly began testing the air inside the school.

Jones, at the Health Department, said small children are not necessarily more susceptible to vapor risks but that they do breathe more closely to the ground where toxic vapors could concentrate. It’s just not acceptable to expose small children to it, he said.

The school district said in its news release announcing the delay Friday that “chemical vapor in the soil is generally safe and does not affect the playground or school grounds.”

“The concern of having the vapors under the building is that it could get into the building,” the district said in the e-mail.

Parents who don’t have child care for the days in question can call the district’s Discovery Club at 651-231-7315 for help.