Nearly 200 businesses, cities and school districts got letters from the federal government this week informing them that they “may be liable” to pay for the cleanup of the Freeway Landfill in Burnsville, which has been estimated to cost $64 million.

They were also asked for detailed records of their finances and any materials they put into the landfill.

About 180 entities, many of them construction companies, paid to put garbage in the landfill before it stopped accepting waste in 1990. Now the site, which is full of heavy metals and harmful chemicals, is in danger of polluting groundwater and the Minnesota River, said Kirk Koudelka, assistant commissioner of the Minnesota Pollution Control Agency (MPCA).

Methane gas, a potential explosive emission that has been linked to climate change, was also found in the site, a 150-acre field off Interstate 35W and Black Dog Road in Burnsville, Koudelka said.

For years, officials tried to convince the landfill’s owners to enroll it in the state’s voluntary Closed Landfill Program — an alternative to the federal Superfund program. But those negotiations fell through, Koudelka said.

In the summer, the landfill was turned over to the Environmental Protection Agency (EPA) for cleanup under the Superfund program. That designation requires that anyone responsible for putting garbage in the landfill pays for its cleanup, rather than the state.

“This did not have to happen,” Koudelka said.

The letters ask that businesses and government agencies come together and divvy up mitigation costs and evaluate possible cleanup plans. That list includes cities such as Apple Valley, Bloomington, Roseville and Burnsville, as well as the Edina, St. Louis Park and Burnsville-Eagan-Savage school districts.

Anticipating that the landfill would enter the MPCA’s program, the state agency recommended digging it up and adding a protective liner, Koudelka said. That potential solution’s cost was estimated at $64.4 million.

The city of Burnsville received its letter last week, said Heather Johnston, city manager. She said she’s disappointed the landfill didn’t go through the state’s cleanup process because it is less litigious and expensive, but she’s glad the environmental issues are being remedied.

“The drinking water is safe now, and we want to make sure it stays safe,” Johnston said.

Michael McGowan, whose father owned and operated the landfill, disagrees with the federal government’s assessments.

The landfill “is not a risk for human health and the environment,” McGowan said. “It has been proven empirically that it’s not a danger.”