Sharon Nelson, a state lawmaker who’s been battling Glacier Northwest’s expansion plans on Maury Island for more than a decade, teared up shortly before a news conference Wednesday announcing King County’s anticipated purchase of the 236-acre mine site.

“It’s a new day,” she said, brushing away tears. “It’s a dream come true.”

Indeed, against the backdrop of a slate-blue Puget Sound, King County Executive Dow Constantine stood before a phalanx of television cameras, public officials, environmentalists and others and issued an announcement that only a year ago would have seemed out of the question: The county and Glacier Northwest’s parent company CalPortland have signed an agreement outlining the terms of the property’s sale.

After months of closed-door negotiations, CalPortland has agreed to sell the site on the flanks of Maury Island for $36 million — the bulk of it to come from state and county coffers earmarked for habitat protection or conservation acquisitions.

“This day has been a long time in coming,” Constantine said at the news conference, held at a small overlook in West Seattle perched above the Sound.

Pointing to the bulkhead lining the cobble beach next to the overlook, he noted the impact such beach-hardening has had on fragile nearshore environments. With this purchase, he said, “The longest remaining piece of undeveloped Puget Sound shoreline in King County will be protected.”

“We have reached a historic agreement,” he added.

Under the terms of the deal, the $36 million purchase price would come from three sources: $14.5 million already set aside in the state budget from the Asarco settlement, money Nelson helped to secure during the last legislative session; $19.1 million from the county’s Conservation Futures fund, which can only be used to purchase open space; and $2.4 million from an extension of the county’s existing lease to CalPortland at the company’s small gravel mine next to the Maury Island Regional Park.

Also needed is $2 million in private funds that would be used to restore some of the expenditures from the county’s Conservation Futures fund.

The expansive parcel, once in public hands, would become a King County park. Protected would be about a mile of shoreline and more than 200 acres of madrone forests just south of the 320-acre Maury Island Regional Marine Park.

The two parks combined, Constantine added, “will represent the largest public holding of protected marine shoreline in all of Puget Sound.”

Others at the news conference said the purchase represents the region’s growing commitment to the health and restoration of Puget Sound, an imperiled body of water that many in the conservation world believe is threatened by pollution, invasive species, development, climate change and run-off.

Martha Kongsgaard, a West Seattle resident who chairs the Puget Sound Partnership’s leadership council, praised those “who had the vision and tenacity to stay at the table.”

“The opportunity to protect such a wide swath of intact shoreline is a rarity,” she said, “and it’s a significant opportunity clearly aligned with the science-based priorities for restoring this valuable ecosystem that we as a community have agreed upon.”

Ted Sturdevant, the director of the state Department of Ecology, said Gov. Chris Gregoire fully supports the effort. “We are slowing down on a lot of things,” he said, an apparent reference to the state’s tough fiscal climate, “but she has said that Puget Sound’s recovery is not one of them.”

Ron Summers, a senior vice president for CalPortland, based in California, also stood before the cameras and dignitaries but sounded a slightly different note. “We reached this agreement with somewhat mixed emotions,” he said.

The region, he noted, needs the gravel that the mine site would have provided. “We continue to believe the proposal we made 12 years ago was a reasonable one.”

Even so, he added, the company has always been open to a potential sale, adding that economic issues made it in the company’s interests.

The deal still faces some hurdles before it can come to fruition. The often-divided King County Council has to approve the $19.1 million expenditure from the county’s Conservation Futures fund, the limit to how much the county is able to obligate in the course of a year.

Legislation seeking the request is expected to come before the council on Monday. The council will need to act before the end of December. Bob Ferguson, who chairs the county council, said he believes the council will agree to the request and will do so by mid-December.

“I’m committed to making this happen,” he said.

Wednesday’s announcement reflects a remarkable turn-around in the fate of the Maury mine site. More than a decade ago, Glacier Northwest announced plans to build a 305-foot, state-of-the-art pier — key to the corporation’s plans to dramatically increase its excavation of gravel and ship it off the Island by way of barges that would ply Puget Sound seven days a week.

During the course of the bitter fight that followed, Glacier Northwest won one legal skirmish after another, despite ongoing efforts to block the project by the Vashon-based Preserve Our Islands, a grassroots organization Nelson founded and now led by Islander Amy Carey. By December 2008, Glacier had secured all the permits it needed and quickly began construction, stopping only when a state-mandated fish window for in-water construction closed.

The construction also triggered greater activism on Vashon. Several Islanders took to the water, using kayaks to surround the barge that held the construction crane in an attempt to block the project. Others protested in mass gatherings on the beach, efforts that drew increasing media attention.

Then, last August, a federal judge ruled that the U.S. Army Corps of Engineers erred when it issued one of the final permits to Glacier and ordered the federal agency to require a full Environmental Impact Statement.

After that, according to Nelson, two other significant events transpired: Constantine, a long-time foe of Glacier’s expansion plans, got elected, and she was able to secure an earmark from the Asarco settlement funds.

Peter Goldmark, the state’s Public Lands commissioner, said the governor’s decision to focus on the health and restoration of Puget Sound also marked a turning point. Maury’s fate, he said, was no longer a local issue, of importance only to a sparsely populated island.

“It became a Sound issue,” he said.

Puget Sound, he added, “is a national, global treasure. We need to treat it as such.”