Sometime this summer, when the water levels in the South McQuesten River are low, Environment Canada technicians will set out in a canoe and take samples of sediment from the bottom of the river. The samples will be analyzed to track pollution emitted into the river by the United Keno Hill Mine. This mine, discovered in 1906, serves as a good example of the detective work involved in monitoring older mines in the territory.

Old mines present a particular challenge for people responsible for protecting the Yukon's environment. It is difficult to determine how the environment has changed when you do not know what was there in the first place. And when the concern is about pollution in moving water, the task becomes even more challenging.

New mines are much easier to monitor because government and company officials can begin testing before development takes place. Once they have this baseline data, they can track any changes that occur in the environment. But many of the Yukon's old mines were established before there was much concern about potential impacts on the environment.

"It is very important to have good baseline data because a definition of impact is only as good as your ability to prove it," says Benoit Godin, head of Environmental Contaminants with Environment Canada in the Yukon. Godin says that with an older mine like United Keno Hill, you have to infer what has happened in the past.

Environment Canada has been trying to figure out the industrial impacts at this mine for more than a quarter of a century, and the department keeps coming up with new tools for the job. In 1978, the dam below the tailings pond failed and 200 million litres of effluent and tailings were washed down Flat Creek, which empties into the South McQuesten.

A 1985 study showed that there were significantly higher levels of heavy metals in the creek sediments than on other parts of the property. There were also fewer types of benthic invertebrates in the creek. These bottom-dwelling organisms are important indicators of water quality.

When the department conducted fieldwork on the South McQuesten in 1990, it did not find any significant impacts on the river, but Godin says that could just be because of the approach that they were taking.

"We think there is not much impact left, but maybe that is because our tools were too rough. If we have more precise tools and more refined methodologies, then we can go back and we might find that there have been impacts we just could not measure before."

The sediment samples taken from the South McQuesten River will be part of this new approach. Effluent and sediments from mine tailings precipitate out in the gravel beds of streams and are carried downstream.

The departmental technicians use a GPS system to establish exactly where in the river the samples are collected. A sieve is used to separate out silts and clays from the larger pieces of gravel. These fine sediments absorb the metal ions more effectively because they have more surface area for their size than larger particles.

Then these sediments are analyzed back in a lab. "We're looking for peaks in the river sediment profile" explains Godin. "A peak is an area where there is a high concentration of heavy metals in the sediment."

Environment Canada is trying to map where the contaminated sediments in the bottom of the river are concentrated. "We know that there have been failings in the tailings system in the past and contaminated sediments were released. We have already found some peaks in the creek system, and we will try to relate those back to past events," says Godin.

If the department can establish that certain peaks in contaminated sediments are related to specific releases of pollutants from the mine, then they can better judge the impacts of the mine and how contaminants move in the system. They can also evaluate how the environment recovers from these stresses. The next step in finding this correlation is radio-dating the contaminated sediments.

This process has its own set of problems because one expects to find minerals in the environment around a mine. The trick is establishing whether the minerals are naturally occurring, or whether they are the result of mining contamination.

Lead 210 is used for radio dating because it has a relatively short half-life of 22 years and it is part of the orebody in the area. Lead released into the environment as a result of mining will start to degrade once it attaches to sediments in the water. This lead will have a different radio date than lead in the surrounding bedrock that has never been disturbed.

In addition to tracking this underwater contamination, the department is also trying to figure out what benthic invertebrate populations would have lived in waters around the mine before it was developed. In summer, crews head out to creeks near the mine that have not been polluted and collect information on characteristics such as stream flows, substrates, vegetation and invertebrates. This data will be used to try and reconstruct what the polluted creeks would have been like before development.

The United Keno Hill Mine closed down in 1989, but there has been interest in reopening it. If the mine does reopen, this environmental detective work will help the department set appropriate standards for protecting the environment. If the mine does not reopen, the information can be used to set standards for abandoning the site.

"Abandoned mines will continue to haunt us in the Yukon," says Godin. "At mines like United Keno we are left with some problems, but we keep refining our tools."

For more information on environmental contaminants in the Yukon, contact Environment Canada at 667-3400.