Canada's Environmental commissioner's 2012 report identifies four sites as having the highest reported financial liabilities - although the report does not disclose the financial details, which are "protected information."

1. Port Hope Area Contaminated Sites, Ont.

Natural Resources Canada responsible for remediation of about 1,380,000 cubic metres of low-level radioactive waste, including radium 226, uranium and arsenic. The project is funded through the Port Hope Area Initiative.

2. Welcome Waste Management Facility, Port Hope, Ont.

Natural Resources also responsible for an estimated 620,000 cubic metres of low-level radioactive waste at this above-ground facility and operation of treatment ponds and effluent discharge. Funded through the Port Hope Area Initiative.

3. Faro Mine, Yukon

Aboriginal Affairs and Northern Development Canada is responsible for this former mine, whose owner went bankrupt. Estimated 64,000 hectares of contaminated soil and groundwater, leaching of acids and metals into groundwater and surface water. Requires at least 100 years of treatment of contaminated water and potential physical instability of tailings dams and waste rock dumps. Contaminents include petroleum hydrocarbons, metal, metalloid and organometallics.

The federal government is trying to figure out how to keep thousands of tonnes of arsenic trioxide frozen forever underground at the Giant Mine site in Yellowknife, N.W.T.

4. Giant Mine, Yellowknife, NWT

Another bankrupt mine site managed by AANDC, with 237,000 tonnes of arsenic trioxide dust stored in 15 underground chambers; 16,000,000 tonnes of tailings, which is also arsenic rich; three large tailings ponds that require water treatment and discharge; and eight open pits, with 35 mine openings. Requires more than 100 years freezing of arsenic trioxide and contaminated soil to prevent release; treating and discharging water from tailings ponds; and covering tailings and open pits.

Other high-priority contaminated sites:

The Commissioner's report offers two examples of sites categorized as Class 1 (high priority for action). Both have completed step 7 (remediation strategy) of a 10-step process.

Attawapiskat Soil Remediation Project, Ont. (Aboriginal Affairs and Northern Development Canada)

Includes the J.R. Nakogee Elementary School, a former water treatment plant and underground fuel supply lines. Site was contaminated in 1979 when 24,450 litres of diesel fuel seeped into the soil and groundwater. In 2000, the school was closed due to health concerns. Students were relocated to portables. The school was demolished in 2009.

Contaminants: Diesel fuel contains toxins such as benzene, toluene, xylene and other chemicals. Health and safety concerns are immediate and long term, including headaches, nausea and possibly cancer.

Closure objectives: Since 1997, $3.6 million has been spent on the school site. $10.1 million more has been approved under AANDC’s Federal Contaminated Sites Action Plan budget by 2014–15. In 2011, AANDC announced a new school was to be built on a new site by 2014.

Victoria Coast Guard Base, Victoria, B.C. (Fisheries and Oceans Canada)

Base covers a 7.26-hectares on Shoal Point in Victoria, B.C. There are nine buildings, some dating to the 1970s. Site assessments identified contamination of about 91,000 cubic metres in soil, sediment, groundwater and surface water in four areas. The contamination is being addressed by a combination of remediation and risk management measures.

Contaminants: Petroleum hydrocarbons, polycyclic aromatic hydrocarbons and metals.

Closure objectives: About $360,000 has been spent since 2005–06. There will be ongoing risk management, assuming no change in operations.

Source: 2012 Spring Report of the Commissioner of the Environment and Sustainable Development