OAKDALE, Minn. — The Minnesota Pollution Control Agency has discovered that potentially harmful chemicals are still leaching into surface water from a former 3M waste disposal site in Oakdale, despite the company’s efforts to contain them, regulators told 3M in a letter last week.

The MPCA has given the Maplewood-based manufacturer 45 days to come up with a new plan to keep perfluoroalkyl substances — better known as PFAS — from contaminating nearby water sources, the letter said.

“This is a continuing evolution of what needs to be done at this site to address the contamination,” MPCA Assistant Commissioner Kirk Koudelka said. “The system there to capture and keep any contamination on site is not entirely working.”

The MPCA recently found PFAS-containing foam along Raleigh Creek in Washington County, which the agency said originated at the 3M site.

PFAS-containing foam was also discovered along Battle Creek in Ramsey County, but Koudelka said an investigation into the source of that contamination won’t be complete until February.

“They’re two different sites and we’re treating them as such,” Koudelka said.

PFAS, which 3M developed decades ago for use in products like non-stick pans, are especially troublesome chemicals for three reasons, Koudelka said.

They don’t break down naturally in the environment, they spread farther and faster through ground and surface water than other pollutants, and they accumulate in human bodies.

High levels of PFAS in a person’s body have been linked to higher cholesterol, changes to liver function, reduced immune response, thyroid disease, and increased kidney and testicular cancer, according to the Minnesota Department of Health.

3M has been working with the MPCA to contain PFAS contamination from the Oakdale site for nearly two decades, but Koudelka said their understanding of how the area’s ground water interacts with its surface water has improved in that time.

“I think we have a better understanding of that now, and that’s why we’re going to ask them to do additional work,” Koudelka said.

3M said in an emailed statement that it “is committed to continuing our working relationship with the Minnesota Pollution Control Agency to monitor former disposal sites.”

“We will review the MPCA’s full report and take appropriate steps consistent with our regulatory obligations and our commitment to environmental stewardship,” the company said.