ST. PAUL (AP) — Levels of a chemical once used by 3M Co. to make Scotchgard continue to decline in the blood of longtime residents of the eastern Twin Cities a decade after a drinking water-filtering project was started, the Minnesota Department of Health said.

According to department findings released Tuesday, levels of perfluorochemicals, or PFCs, in the blood of those residents have dropped by 35 percent to 60 percent since 2008. The project’s lead investigator, Jessica Nelson, said that those levels are still above the U.S. average but are “getting closer.”

“It confirms that all those efforts made to reduce the PFCs in drinking water are working,” Nelson said.

Water sources were found to have “potentially unsafe” levels of the chemicals in 2004, due to leaching from old dumps in the area. 3M manufactured PFCs for several decades starting in the 1940s. The Maplewood-based company has since paid part of the cost to clean and filter groundwater in the east metro.

In 2006, filtration systems were installed in both municipal and private wells, and some private well owners were connected to city water to reduce residents’ exposure to PFCs. The state Health Department then began studying the chemicals in residents’ blood to see if the filters were having an effect.

“We’re very happy that the results continue to go down,” Oakdale city administrator Bart Fischer said. “The filtering and the other things that are being done are working.”

Nelson said scientists are still studying whether PFCs cause health problems. In a statement, 3M’s vice president and corporate medical director Carol Ley said the company’s own studies showed “no adverse health effects” in workers who handled PFCs.