Federal monitors are taking a closer look at an abandoned Northwest Territories uranium mine that was supposed to be cleaned up 13 years ago, but still has some debris and radioactive waste on site.

The defunct Rayrock mine site, located 74 kilometres northwest of Behchoko, N.W.T., in the Tlicho region, operated for only two years until 1959. It was cleaned up in 1996-97.

"Our monitoring has recently — in the last two to three years — indicated that some debris had been left on site," Ron Breadmore, an environmental scientist with the federal Indian and Northern Affairs Department, told CBC News.

Breadmore said monitors found "some non-hazardous steel and building foundations, a small volume of asbestos, as well as a small volume of tailings."

Under its licence with the Canadian Nuclear Safety Commission, the Rayrock site has been inspected once a year for the last 10 years.

The mine site has remained a source of concern for the Tlicho people, especially those living in Behchoko, since the mine was upstream from its drinking water supply.

Clay caps deteriorating

During the original cleanup, buildings were torn down, machinery were removed, and two basins containing 71,000 tonnes of radioactive waste tailings were capped with one-metre thick caps of silt and clay.

But Breadmore said the monitoring has revealed that parts of the clay caps have been deteriorating.

"While it's performing quite well, over the years there has been some expected deterioration around the perimeter of the cap, indicating that we may have to go back in and look at some maintenance in those areas," he said.

Mining industry watchdog MiningWatch Canada has called for a moratorium on developing new uranium mines, saying there is no good way to deal with the radioactive tailings.

"We don't really have a great permanent solution for these wastes," MiningWatch spokesman Ramsey Hart said.

"In the case of the clay caps, they may age and dry, and changing climates and permafrost may affect the integrity of the clay cap," he added.

Federal monitors have also noticed elevated levels of uranium and other metals in some surface water at the Rayrock site, but Breadmore stressed that water testing has shown the mine has no effect on Behchoko's drinking water.

As well, about 1,000 square metres of tailings were missed during the initial cleanup and remain exposed on the surface of the mine site.

The federal department would not release its monitoring reports on the Rayrock site, as they want to show those reports to Tlicho aboriginal leaders first.

Breadmore said the department plans to conduct a detailed health risk assessment at Rayrock this summer, in part by collecting and analyzing samples of fish, small animals, vegetation and sediment from the site.