Donnie Burke remembers walking into the office of his new job more than four years ago and staring down at the large pools of black muck that had become one of the country's most notorious industrial blights.

It was an intimidating site for Burke, who was charged with cleaning up the toxic mess left behind after almost a century of steelmaking at the Sydney Steel plant in Cape Breton.

His job was to transform ponds containing one million tonnes of raw sewage, heavy metals, dioxins, PCBs and other toxins into a green space for hundreds of residents in the working-class neighbourhood.

"I remember the black, miry water, shopping carts that got washed down, logs and large pieces scattered throughout -- it was very dark and quite intimidating, especially for someone who had to clean it up," Burke, project director for the Sydney Tar Ponds Agency, said with a laugh from his office in Sydney.

"And to look out that window now are beautiful trees, green grass and public art and sports fields, it's quite a dramatic transformation."

The remediated site of the plant's tar ponds and coke ovens is being unveiled Friday as Open Hearth Park, a 39-hectare green area that features several sports fields, walking trails, art installations, a playground and panels chronicling the plant's troubled history.

The park, named for the mill's old open furnaces, sits atop a solidified mixture of cement and the toxic brew from the former steel plant that went into operation in the early 1900s and employed generations of Cape Bretoners.

The sediment is buried about two metres below and topped with various layers, covering up the residual slag that residents said sickened them, led to high rates of cancer, fouled the air and poisoned their homes and yards.

Jean Crawley grew up in the neighbouring Whitney Pier and remembers the stench from the ponds and the clouds of red ore that wafted above her home.

"Years ago, I could never, ever imagine it looking like it does now," the 84-year-old said from her home. "It's really, really beautiful."

Crawley, who raised her three sons there and whose father worked at the plant, said the restoration of the green space should ease the anger that has festered among residents over 20 years of false starts and broken promises to clean up the mess.

Since 1986, other multimillion-dollar cleanup plans had been proposed but led nowhere. Then in 2007, the federal and provincial governments announced a $400-million plan to solidify and stabilize the sludge and then bury it. The plan includes setting aside $15 million for long-term monitoring and maintenance.

The decision to bury the waste came after an independent panel issued 55 recommendations on how to handle it. The panel cautioned against the stabilization and solidification process, saying it might not be the most appropriate technology.

Green party Leader Elizabeth May agreed with the plan's opponents, saying the technology is untested and won't likely contain the contaminants.

May, who staged a 17-day hunger strike in Ottawa in 2001 to press for the relocation of families living near the tar ponds, still maintains that testing done before the panel made its recommendations determined that concrete and the sludge that fouled the ponds won't solidify properly.

"They've done a cosmetic cleanup for purposes of making it look like it's all gone away," May said in an interview Thursday from Sidney, B.C.

"But it's a giant toxic sarcophagus and the chances that it's actually going to keep the toxic materials of the Sydney tar ponds out of the environment forever are slim to none."

Resident Joe Petitpas has similar reservations about the method, which was selected after a widespread public outcry led to the rejection of earlier proposals to incinerate or encapsulate the material.

"All we can do is wait and see what happens in the future," said Petitpas, who grew up in Whitney Pier.

"The fact that it is usable space now is wonderful ... but that method is not a proven method. Only time will tell."