ST. PAUL — It can take years of work and millions of dollars for contaminated land and water sources in Minnesota to be declared safe.

There are more than 90 entries on the state priority list of hazardous waste sites, according to state Pollution Control Agency data. Of those, approximately 29 have been listed for longer than 30 years.

In 2017, the agency reported that it cost approximately $7.75 million to treat and maintain them all. In 2018, that figure rose to nearly $11 million.

Oftentimes, the owners of former wood treatment facilities and pesticide manufacturers that make up the list help to share cleanup costs. But in industrial hubs like the Twin Cities metro area, where the bulk of the sites are located, the widespread use of hazardous chemicals can make it difficult to pinpoint a polluter.

"Tracing the source of polluted sites to one specific company is sometimes really hard," said agency spokesman Walker Smith.

Created by the state Legislature in 1983, the priority list contains those sites that are a part of the Minnesota Superfund program. In addition to several other state cleanup initiatives, the program exists alongside the U.S. Environmental Protection Agency's federal Superfund.

There are another 138 sites not listed on the state priority list, that according to one PCA report are "are being addressed by responsible cooperative parties." A further 1,005 hazardous waste projects are being addressed jointly by the PCA and the Department of Agriculture through a voluntary cleanup program.

At the same time, Minnesota is home to 25 federal Superfund sites, the list of which overlaps somewhat with its state counterpart.

Making the list

In some cases, Smith said that sites on the state priority list were contaminated because their owners or operators used them to dispose of hazardous material in ways that regulators later deemed to be unsafe. For that same reason, he said that many businesses are reluctant to share cleanup costs for actions that, at the time, didn't break the rules.

Once brought into the program, sites become eligible to receive funds for investigation and cleanup efforts that the PCA collects partly through the use of regulatory fees. If an investigation yields a "responsible party" that refuse to chip in, Smith said that the agency will pay upfront to clean a site — which can involve the removal of contaminated soil or treatment of contaminated water out — and then sue to recoup costs.

Finding the party responsible for the pollution of a site, he said, is not always easily done. After 15 years of investigations, for example, state regulators have yet to identify an entity or company responsible for the contamination of an aquifer beneath St. Louis Park and Edina. According to the PCA, the water it stored was found to contain industrial solvents including trichloroethylene and tetrachloroethylene, both of which been linked to cancer.

"Despite all the time and money we spent investigating it, we cannot find a responsible party," Smith said.

Contamination of the aquifer has affected several drinking water wells in the area, although Smith said that treatment has rendered them safe for consumption. The PCA in August filed to add the site to the federal Superfund program. The EPA began to review the request in late October.

Being added to the national program would make the site eligible for additional funds. It would also give Minnesota greater legal backing, Smith said, should the fight to hold a polluter responsible head to court.

Even after a site is investigated and cleaned up, however, parts or the whole of a site can remain on the list for years of testing and monitoring. Sites are only removed and able to be redeveloped after they are deemed to no longer pose health risks.

Approximately 250 sites have been listed on the state Superfund program since it was created. More than 170 have been removed, the most recent of which came off in 2014.

Top priorities

Neither the U.S. nor Minnesota ranks the sites on either of their lists, making it to difficult to name the most pressing case of contamination.

In Minnesota, however, sites in a different program are ranked by severity. Created in 1994, the state's Closed Landfill Program targets inoperative garbage dumps that leak gas or contaminate groundwater. It is funded by a mix of state taxes on solid waste management as well as general obligation bonds and landfill insurance among other instruments.

By 2015, one report show that the program's expenditures had already amounted to approximately $435 million. Officials estimate expenses over the next five years will total more than $300 million.

Hans Neve, one of the program's managers, likens the program to an orphanage where "most of the kids never leave."

"We'll be taking care of them forever," he said.

There are 112 shuttered landfills in the program, many of which Neve said were in use before stronger waste management standards were implemented. He said they lack liners that are now commonplace and help to delay the contamination of groundwater and soil that can arise from trash decomposition. They also lack the means to vent out potentially explosive gasses such as methane that can result from decay.

At the top of the list is the 150-acre Freeway Landfill in Burnsville, which was also entered into the federal Superfund program in 1986. In addition to generating methane and leaching into groundwater, the site neighbors a quarry that is in the process of dewatering.

Smith said that has had the effect of lowering groundwater levels. When that process completes and they begin to rise again, he said, the concern is that they will be contaminated by landfill byproducts.

Regulators have debated several different ways to get the landfill in order, ranging from hauling its contents elsewhere to fitting it with a liner. Because the site is a part of two separate programs, Neve said the final plan for it will be up to the legislature to approve.

Public meetings on the proposals are being planned.