1930s: Crown corporation Eldorado Nuclear Ltd. begins refining radium, used for treating cancer, and uranium that helps the Manhattan Project develop the first atomic bombs.

1940s-1960s: Low-level radioactive byproducts and other toxins from the plant enter the environment through use of contaminated fill, and to some extent through sloppy transport, and water and wind erosion in storage areas. At the time, it is not considered a health hazard. Contaminated fill ends up in parks, industrial properties, ravines and fields, and in the yards of many of Port Hope’s 16,000 residents.

1970s: Newfound concerns prompt Atomic Energy Control Board to scour the town in search of hot spots. Cleanups are undertaken in 22 residential buildings, 122 yards, 46 businesses and public properties, and nine roads and ravines. Minor work is needed in 135 more locations.

1988: Eldorado is sold to the private sector and becomes Cameco.

• 1990s: Worried about health effects, local citizens began taking an active part in the nuclear licence reviews of Cameco and ask the federal government to study the effects of radioactive waste in the town.

2001: Ottawa pledges $260 million for cleanup. An estimated 1.2 million cubic metres of soil contaminated with low-level radioactive waste and industrial toxins will be dug up and trucked to a new storage facility north of town.

2002: A federal study finds that death rates, including cancer deaths, are no higher in Port Hope than elsewhere in Ontario.

2004: Families Against Radioactive Exposure (FARE) is formed to counter Cameco’s plan to produce a more potent fuel known as enriched uranium. It demands an environmental assessment of the proposal by a review panel, but the Canadian Nuclear Safety Commission says a screening is sufficient.

2005: Dr. Asaf Durakovic, research director of the Uranium Medical Research Center in Washington, D.C., agrees to carry out a study of Port Hope residents for evidence of illness resulting from exposure to radioactive materials.

2007: The study finds small levels of radioactive elements in the urine of four of the nine people tested, including a child younger than 14. More calls follow to put the town under a health microscope.

2009: In spring, the nuclear safety commission reiterates that no adverse health effects have occurred in Port Hope, and that its cancer rates are comparable to other Ontario towns.

2010: In fall, the cleanup begins with a trial dig in a backyard.

November 2010: Acclaimed anti-nuclear activist Helen Caldicott calls the presence of contamination in Port Hope “a disaster” and says the only solution is to relocate the 16,000 residents.

2011: A full-scale cleanup will begin later this year, lasting a decade and costing at least $260 million. The final scope and price tag are unknown.