When Megan Diediker was first diagnosed with breast cancer at age 34, the high school geometry teacher wondered whether something in the environment could have played a role.

But she eventually let the questions go, she said, to focus on getting better.

Then a colleague fell ill last year with an aggressive brain cancer. It was the seventh cancer diagnosis among staff at Park High School in Cottage Grove in six years, Diediker said — nearly all in people under age 50. Before long, she and some colleagues had drawn up a list of nearly 30 current and former Park High staff who contracted various cancers since 1990, some of them twice. Two — one of whom since died from the cancer — shared the same classroom.

"I revisited everything and thought 'What is going on here?' " Diediker said.

The Minnesota Department of Health reviewed the matter and concluded it is not a cancer cluster. Proven cancer clusters are rare.

Even so, Diediker sees red flags. She and another teacher have retained a lawyer and plan to submit individual workers' compensation claims to the South Washington County School District, along with three other current and former employees.

Diediker says they don't know whether something in the school played a role in their cancers, but they hope that the process of vetting the workers' comp claims will shed light on the situation. Diediker, who coaches girls basketball and lives in Mahtomedi, said she loves working at Park High and just wants to know that the people who work there are safe.

As it happens, Cottage Grove is ground zero in Minnesota for water contamination from a set of compounds known PFAS (per- and polyfluoroalkyl substances), the cancer-linked "forever chemicals" that are the subject of a 20-year remediation project. 3M Co. manufactured the original chemicals for decades at its Chemolite Plant there and dumped contaminated waste in four nearby landfills. Washington County is the focus of an $850 million court settlement the state reached with 3M in 2018 for damage to drinking water and the environment.

Lawsuit a possibility

If the workers' comp investigation establishes a link between the diseases and some third factor, the teachers may consider a lawsuit, said Dean Salita, the personal injury lawyer they retained. Salita said the worker's comp claims should be filed within two months.

The cancers just seem too coincidental, Salita said. "Mother Nature is not that unkind to that many people in one school."

Keith Jacobus, superintendent of South Washington County Schools, said he's taking the matter seriously. He discussed it with the district's facilities staff last fall and directed them to contact the state Department of Health, where officials said they didn't think there was a health risk at the school.

"We have to follow the expertise of people who know this, versus making judgment calls of our own," Jacobus said.

'Our water is clean and safe'

Salita and the teachers say they can't point to a culprit in the cancers. Diediker mentioned PFAS. One idea they've floated is asbestos.

The school's asbestos abatement was carried out by a state-approved contractor in 2008-2010 while school was in session and involved the installation of a new ventilation system. But asbestos is primarily associated with lung cancer, and only one employee on the Park High list was stricken with that form.

Several of the city wells that serve the school, wells No. 3-9, have tested above the current Minnesota health limits for different PFAS compounds over the last decade, according to a Star Tribune review of state Department of Health well testing data. In some of those tests, concentrations were more than twice the state's safety limit.

But city officials say they're confident the school's water is not an issue; the wells that supply Park High are regularly tested for PFAS, and the city has dealt with the wells that have tested above the state's health-based values for various PFAS compounds.

Well No. 3, for example, was outfitted with a carbon filter system. Wells No. 4 and 6 were shut down in 2017 when the state tightened safety benchmarks for certain PFAS. Concentrations of certain PFAS in three other wells have spiked a few times in recent years, but that water is blended with the water from a safe well and is within all thresholds, according to City Engineer Ryan Burfeind.

"Our water is clean and safe to drink," Burfeind said.

It might not have been in years past, however.

Margee Brown, a research scientist at the state Health Department, said she doubts the Park High case meets the American Cancer Society definition of a cancer cluster: "a greater-than-expected number of cancer cases that occurs within a group of people in a defined geographic area over a specific period of time."

Brown said the Park High list includes people with several different types of cancer over nearly 30 years, which suggests no single environmental cause. "It does not appear that unusual, based on what we know about cancer and how common it is," she said.

"Roughly four out of 10 of us will be diagnosed with cancer at some point in our lives,'' Brown added. "I think a lot of people are not aware of that."

Dozens of inquiries

The Health Department fields dozens of inquiries about perceived community cancer clusters each year but has confirmed only two in the past 40 years that were linked to environmental or occupational exposures: mesothelioma related to asbestos exposure on the Iron Range, and lung cancers and mesothelioma in northeast Minneapolis related to asbestos from a W.R. Grace & Co. vermiculite processing plant.

Brown said she empathizes with the fear and anxiety that cancer provokes. "People make these associations, naturally," she said.

Brown's findings echo the department's larger investigation of health outcomes in areas of Washington County contaminated with PFAS. It found no clusters of cancer, premature births or low-birth-weight babies.

But an expert witness hired by then-state Attorney General Lori Swanson when she sued 3M came to different conclusions. David Sunding, a natural resources economist at the University of California, Berkeley, concluded that Washington County residents have elevated rates of cancer, infertility and low-birth-weight babies.

Not all the Park High cancer survivors see a connection between their illnesses.

Retired teacher Christine Norton, who was diagnosed with breast cancer in 1990 and co-founded the Minnesota Breast Cancer Coalition, said that 28 cases "just does not seem like a high number" for a school of that size. "People want an explanation," Norton added.

Diediker is not persuaded. She strongly disagrees with the state's finding.

"I think it's totally [wrong], and the lawyers agree," she said. "There's something in the building."

Staff writer MaryJo Webster contributed to this report.