The ongoing search for east-metro wells contaminated by a former 3M plant has turned up another 200 homes that will get state-funded supplies of bottled water or filtration systems.

The Minnesota Department of Health has found that the homes' drinking water from private wells exceeds an updated federal health standard for a group of industrial chemicals known as PFCs once used by the 3M plant, which have long contaminated nearby groundwater.

Last year the federal government, relying on years of research data, tightened its health guidelines for two PFCs, saying the old ones were no longer valid. It advised states and municipal drinking water systems across the country to reduce the amount of chemicals considered safe for drinking from 300 or 400 parts per trillion down to 70 — a significant difference.

The state has been monitoring groundwater in the east metro since 2002, when it found chemical contamination in public and private wells in Cottage Grove, Lake Elmo and other areas near the Mississippi River. In a settlement with the 3M Co., which used the chemicals at the Chemolite manufacturing plant for decades, local municipal water systems and hundreds of homeowners had their water systems replaced or upgraded to remove the contaminants.

But the EPA's announcement last year prompted state environmental officials to expand their testing programs to find homes with drinking water that exceed the new limit. As of August they had identified 81. Now, after testing 520 private wells, they have found a total of about 200 that are above the new limit, officials said Friday.

The chemicals were used for decades in the manufacture of carpets, clothing, fabrics, furniture, food packaging and other products, such as nonstick cookware and firefighting foam. They have been phased out of industrial use for the most part, but traces can still be found throughout the environment and they are a major contaminant in fish.

PFCs at the concentration found in the east metro do not pose an immediate health threat, but long-term exposure has been linked to certain cancers, liver and thyroid ailments, and developmental problems in infants.

The Health Department has traced contaminated drinking water wells along a new path that follows a storm sewer system running from Lake Elmo to a collection pond near the state rest area on the north side of Interstate 94 near the St. Croix River crossing.

"It has impacted a number of wells in those neighborhoods," said Ginny Yingling, a Health Department scientist. "We are issuing well advisories on the east and west side of Neal Avenue."

She said it's likely that the stormwater system is picking up water from a creek that runs through one of the old dump sites contaminated with the chemicals. It carries the water across that part of the metro area, roughly along a line parallel with I-94 before dumping it into the St. Croix River.

It may be that the sewer pipe is leaking into the ground along the way, or there may be another as-yet unidentified contaminated site, she said, because the concentrations of the PFCs are higher in the collection pond than in the storm sewer water, though those test results must still be confirmed.

"We are seeing higher levels than we expected," Yingling said. "If there is good news, it would be that this problem likely will be limited to a small area near that pathway of stormwater. But it's a long linear path."

The Health Department is expected to sample another 150 private wells this spring.

3M disposed of products containing PFCs, including PFOA and PFOS, in a landfill and three dump sites in Washington County starting in the 1940s until the 1970s. The state and 3M have agreed on a plan to fix drinking water contamination, but a 2010 lawsuit over the costs of environmental cleanup of groundwater and the Mississippi River is ongoing. It is expected to go to trial sometime next year.