BILLINGS, Mont. (AP) — Montana regulators said they expect to have about $400 million in bonds in place by July to pay for future cleanup work at the Colstrip power plant.

But the statement by the Montana Department of Environmental Quality was met with skepticism from state lawmakers who said they received similar assurances in the past that did not come to fruition, the Billings Gazette reported Wednesday.

The state is currently holding $170 million in surety bonds from Colstrip’s owners, said Jenny Chambers, DEQ’s remediation division administrator. The bonds are intended to protect taxpayers from being stuck with a bill for future cleanup costs.

Cleaning up the plant’s ash ponds alone is expected to cost as much as $700 million. Contaminated water leaking from the ponds has polluted underground water supplies.

State officials said more money might be needed as the cleanup begins.

The steep price tag on the cleanup has raised concerns that if DEQ doesn’t get money up front, it will be difficult to collect from the power plant’s owners in the future.

Two of Colstrip’s four electricity generating units were shut down earlier this month. The move came after owners Talen Energy of Pennsylvania and Puget Sound Energy of Washington state said they were no longer economical to operate.

Colstrip’s remaining two units are also slated for eventual closure, but the utilities that own them have given different dates for when that could happen.

Puget Sound Energy and Washington-based Avista Corp. plan to exit the plant by 2025. NorthWestern Energy, Montana’s largest utility, has plans to keep using the two remaining units past 2040.

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