(CBSNews) EDMONTON, Alberta -- A phased return of more than 80,000 residents of the fire-damaged oil sands city Fort McMurray will begin Wednesday as planned, Alberta's premier announced Tuesday.

Rachel Notley said that the wildfire is no longer an imminent threat to the city and critical infrastructure has been repaired. The massive wildfire destroyed about 2,400 structures almost a month ago in Fort McMurray but 90 percent of the city remains intact. Residents of three neighborhoods won't be able to return because of environmental concerns.

A boil water advisory remains in effect and many businesses will not be open. Notley urged residents to bring food, water and any other supplies needed for the next two weeks.

Scott Long, executive director of the Alberta emergency management agency, pleaded for patience and asked residents to respect their zone date for an orderly return. He estimated that 40 to 50 percent of residents will return this week and warned of travel delays.

The fire and mass evacuation forced a quarter or more of Canada's oil output offline. Canada's central bank said last week the Canadian economy will shrink in the second quarter because of the wildfire.

The Alberta oil sands have the third-largest reserves of oil in the world behind Saudi Arabia and Venezuela. Its workers largely live in Fort McMurray, a former frontier outpost-turned-city whose residents come from all over Canada.

Kevin Lewis is anxious to get back into his apartment in Thickwood, a relatively undamaged neighborhood that's slated to reopen on Friday.

Lewis has been unable to run his transportation brokerage business since the evacuation and he figures he's lost some $40,000 over the last month.

"I definitely need to get to work," Lewis said from Lac La Biche, Alberta, a small town about 2 1/2 hours southeast of Fort McMurray that's taken in thousands of evacuees.

Lewis knows it's a possibility that smoke damage may have rendered his place uninhabitable.

"If it's not really livable there yet, I could at least be able to grab my computers and I'll be able to work," he said.

Jim Mandeville, senior project manager with FirstOnSite Restoration, has been in Fort McMurray since May 8 to help critical businesses such as banks, grocery stores and pharmacies get running again.

Dozens of FirstOnSite workers have been working long days disposing of spoiled food, cleaning ventilation systems and removing smoky odors from upholstery and carpets. Mandeville said provincial and municipal officials aren't underplaying how challenging it will be for residents to return.

"When they say to bring 14 days worth of food and water, they mean it. And when they say people with respiratory conditions shouldn't come up here, they mean it -- and they have a really good reason why," he said. "It is not a clean, safe, normal environment that you're walking into."