Sen. Brownie Carson, D-Harpswell, talks to other members of the Senate about the budget at the Maine State House in Augusta in 2017. Credit: Ashley L. Conti

A bill that could delay state permitting of the controversial $1 billion Central Maine Power corridor through western Maine won approval from a legislative committee on Wednesday.

Now to be vetted by the full Legislature, the proposal from Sen. Brownie Carson, D-Harpswell, would mandate a carbon-emissions impact study of the proposed 145-mile transmission line through Maine to send Hydro-Quebec power from Canada to Massachusetts.

Endorsed by all of the committee’s Democrats and Rep. Thomas Skolfield, R-Weld, Carson’s bill poses an immediate legislative threat to the regional project, which Democratic Gov. Janet Mills threw her support behind after CMP offered a 40-year, $250 million benefits package. Regulators voted unanimously last week to grant a key permit for the corridor, agreeing that the environmental benefits outweigh the cost.

The bill, backed by project opponents, derives from their skepticism that the transmission line would reduce global carbon emissions. A 2018 report found the corridor would reduce greenhouse emissions at the same rate as removing 767,000 cars from roads in New England, but a study for opponents said the contract doesn’t guarantee that hydropower could be replaced with electricity from more emission-heavy sources.

“Are the climate benefits real, or are they not?” Carson said during the Environment and Natural Resources Committee hearing on Wednesday. “That’s the question that I’m hoping and believe this study would address.”

But even if Carson’s bill secures two-thirds majorities in both chambers to take effect immediately, completion of the study is firmly affixed to an Aug, 15 deadline, which even Carson admitted was tight. Skolfield, the only Republican on the committee to vote for the bill, said he was doing so “in good faith,” knowing that even a failure to complete the study would “not hold the project up.”

The bill initially called for the DEP to study the project, but the department has said it does not have the funds or time to do so. Carson amended the bill to allow the department to commission a study from a non-government agency, but the bill provides no funding for it.

It’s not known whether the study’s findings would completely neuter the project, but it could delay the state’s final approval, which isn’t expected to happen until late October at the earliest.

Though the department could accept public funds for the study if offered, Carson insisted he did not want to attach a fiscal note to the bill, which could drag out questions about funding and further delay the study’s start. Instead, he’s hoping for other contributions.

On Wednesday, he mentioned a recent conversation about his bill with Mills, who “seemed, at the time, open to the study,” and said she “might be able to help find some money to get an analysis done,” Carson said.

Mills did not confirm by the end of Wednesday whether that was still true. However, she said last Friday in an interview, “I’m not sure what he wants to study,” but that she would work with Carson and others to identify information on the project already in the public record.

BDN writer Michael Shepherd contributed to this report.