PORTLAND — After nearly two years of work, Portland’s West Hayden Island advisory committee capped its final meeting Wednesday by voting against a new mitigation proposal released the same day by Mayor Sam Adams.

Adams’ proposal will head to the city’s Planning and Sustainability Commission next week anyway. Adams hopes to advance a proposal — authorizing annexation of 800 acres, development of up to 300 acres for a marine terminal and environmental protection for 500 acres — to the Portland City Council before his term expires Dec. 31.

City officials had difficulty quantifying how Adams’ latest proposal differed from an earlier draft he released Nov. 9. That proposal called for $32.6 million in mitigation.

The version Adams released Wednesday totaled $39.3 million, not including $9.6 million for a road that consistently has been part of the plan but wasn’t included in the recent proposal.

Major changes include reducing off-site Government Island mitigation costs by $4 million and increasing parks expenses by more than $9 million, officials said. But officials stressed that the proposal would still ensure environmental mitigation of more than 700 acres.

Eric Engstrom, Portland’s principal planner, said Adams’ revised proposal increases mitigation expenses for the Port of Portland by about $7 million. The Port also would be responsible for the $9.6 million road if grant funding doesn’t materialize.

With little time to digest Adams’ proposal, the West Hayden Island advisory committee voted against it, with five members opposed, three in favor but with questions and one person fully supportive. The Port’s representative voted against Adams’ proposal.

Bob Sallinger, who quit the committee this summer, calling the process a “sham,” said if Adams was confident with his proposal he would have released it sooner.

“This meeting was absolutely surreal,” Sallinger said. “I think the fact that the committee voted it down says a lot.”