You can't see it. You can't smell it.

But toxic vapor rising from soils contaminated decades ago by industrial solvents is creating new and expensive headaches for property owners across Minnesota.

Pollution officials have identified hundreds of sites across the state that are contaminated by "vapor intrusion," and this month they began rolling out a new set of rules requiring property owners to test for vapors and address them before transferring property.

Even as state officials scramble to understand the scope of the problem, business owners are facing millions of dollars in new costs to make their buildings — and their neighbors' buildings — safe from the carcinogenic fumes that collect inside from widely used solvents long since discarded.

Danger from below: Vapor intrusion risk sites in Minnesota

"It's like working on an engine while the car is driving down the road," said Hans Neve, who runs the vapor intrusion program for the Minnesota Pollution Control Agency. "And it hasn't peaked yet."

The chemicals are in a class called volatile organic compounds and are still used by industry. In Minnesota, the main sources of contamination are dry-cleaning fluids and metal degreasers discarded or spilled by large and small businesses across the state, health officials say. The chemicals can continue to generate fumes long after the businesses closed.

Since 2000, research has shown that exposure to the fumes carries far greater health risks than had been known previously. That, in turn, is driving down the safe exposure limits set by state and national regulators.

For instance, in Minnesota, the new long-term health limit for fumes from dry-cleaning solvents has dropped 10-fold, from 20 parts per billion to an infinitesimal 2 parts per billion, said Jim Kelly, environmental health manager at the Minnesota Department of Health. That's because long-term exposure to even very low concentrations can result in cancer, as well as fetal development problems for pregnant women.

"People have a lower tolerance to being exposed to something in the air they can't feel or smell," Kelly said.

To date, Minnesota pollution officials have investigated and fixed 298 contaminated sites that the state manages, with 152 more underway and another 181 on a backlog list. But that doesn't include another 1,400 known sites that are yet to be investigated — manufacturers, dry cleaners, auto repair shops and gas stations.

Some of big sites are well known, like the polluted groundwater plume from an old General Mills research facility in the Como neighborhood of Minneapolis, where 1,000 gallons of toxic chemicals, such as trichloroethylene, or TCE, were dumped yearly from 1949 to 1962. Vapors from the spreading plume have contaminated hundreds of homes and businesses.

But the more the state looks, the more it finds. Last year, toxic vapors caused the state to place 10 more of the biggest problem sites onto Minnesota's Superfund list — contaminated properties that need expensive cleanups — bringing the total to 92. But the state doesn't have enough money to keep up.

Neve said this year the state's Superfund program is spending $6.7 million overall for testing and clean up on 53 projects. About a third of that is dedicated to vapor testing and mitigation.

"We are in triage," he said.

Now, the MPCA is holding meetings with businesses and environmental consultants to explain new guidelines on how building owners will be expected to handle the vapor problems they encounter.

Starting this year, the state is asking owners to add soil vapor testing to the environmental review that is often standard in the transfer of property. If a building is suspected of having contaminated soil below or around it, sellers must test for vapors, report high results to the MPCA, and fix it before the property can be sold to a new owner.

"And it's freaking out the real estate industry," said Jeff Broberg, a Rochester environmental consultant.

In part, that's because the vapors are more complicated than run-of-the-mill soil and groundwater contamination, say environmental consultants. Groundwater doesn't ordinarily need to be cleaned up unless it's a source for drinking water. Contaminated soil can stay put if it's below a concrete slab. But vapor moves. It can penetrate a building's foundation slab, and then concentrate inside a basement or building — and other homes and buildings nearby — multiplying the problem and raising tangled questions about liability and who should pay for the fix.

"You have obligations to investigate and remediate everyplace where it goes," said Ken Haberman, a consultant with Landmark Environmental in Bloomington.

That's true even if the property's owner didn't cause the problem in the first place.

A few months ago, real estate broker Nick Pompeian helped his father buy the land and building for the John Hardy's BBQ restaurant he runs in an industrial area of Rochester. Testing showed that it had a vapor problem, but didn't specify the source.

Fixing it cost $50,000, and, fortunately, the seller was willing to foot the bill, said Pompeian. But that won't always be the case.

"That's the big question — who's going to pay for it?" he said. "That's the thing that can derail a deal."

Other real estate brokers say they are starting to see cases where a vapor problem scares off prospective buyers and lenders, or delay transactions by months.

"Time kills deals," said Mark Robinson, a Wayzata shopping center broker who recently had a couple of sales fall apart over vapor intrusion issues. "That's the nature of our business."

Sometimes the costs are low. But not for larger buildings. The city of Rochester, for one, had to spend $450,000 on vapor barriers and a removal system for a new biosciences building erected on an old dry-cleaning site. And now it's spending $10,000 a year on regular testing and monitoring, said city officials.

"It didn't help the [city] budget," Assistant City Administrator Terry Spaeth said. "But we made it work."

Still, many say that business owners and the real estate industry will in time figure out how to resolve the problems, just as they did with radon and other types of contamination.

"We'll get there," Pompeian said. "We're all working on it together."

Josephine Marcotty • 612-673-7394