MONONA, Wis. -

Soil contamination next to Monona Grove High School is causing vapors to seep inside the building, but state Department of Natural Resources officials said that the vapors pose no hazard to students or staff.

Monona Grove Superintendent Craig Gerlach informed parents about the contamination in a letter written on Sunday. The vapors of tetrachloroethylene, also known as PCE, originated at Klinke Cleaners next to the school.

"Absolutely it's a concern of everyone, especially those who have children," Gerlach said. "The building's safe. If the building was not safe, we would not send children and staff into that building."

After meeting with the school, DNR officials tested the air inside the building. Investigators told Gerlach on Saturday that the results showed that vapors beneath the school have seeped inside the building, but the levels measured don't pose a threat to humans.

However, the PCE level was above the DNR action level for a residential site, so the school district has increased air circulation inside the school, caulked foundation cracks and capped a drain tile vent.

Klinke Cleaners, which used the PCE chemical until 2005, will pay for additional tests and the eventual cleanup, director Steve Klinke said.

"This situation for us is critically important," he said. "We are moving as fast as we can to get as much done as we can, because this is our community and we're proud to call it home."

Experts will be on site starting on Tuesday to develop a long-term plan, Klinke said.

How long the problem persisted before it was discovered remains a mystery. The state does not require testing for PCE, which about 70 percent of dry cleaning businesses still use to clean clothing, Klinke said.

The state is supervising the cleanup of about 230 sites, but the real problem is much bigger, said James Walden, a hydrogeologist with the state Department of Natural Resources.

"There are large numbers of properties that have been used, particularly for dry cleaning, and which ones of these are contaminated is really uncertain," Walden said. "The numbers are probably in the thousands (statewide)."