The Reminder is making its archives back to 2003 available on our website. Please note that, due to technical limitations, archive articles are presented without the usual formatting.
During Winnipeg's November 2008 Manitoba Mining and Minerals Convention, Andrea Hachkowski, an engineer with AECOM Environment, presented a progress report on Snow Lake closure activities as they relate to the large arsenopyrite residue stockpile that sits on the New Britannia Mine property. Although I was unable to attend that particular presentation, Ms. Hachkowski was gracious enough to provide me with its content material. The primary concern brought forward by this report is no different than those that have been expressed since the pile first began to take shape back in the late 1940s. That is unease over the fact that Snow Lake, the community's water supply, is just four kilometers from the tailings area. The tailings stockpile resulted from the progression of the original Nor-Acme Mine, which operated from 1949 and 1958. The technology of the day allowed them to recover only 83 per cent of the available gold from the ore they milled. As a result, arsenic laden tailings were stockpiled in an open containment area constructed from waste rock placed directly on clay. This stockpile remained uncovered for 50 years, eventually becoming an orphaned site under the responsibility of the Government of Manitoba. In 1999, TVX Gold, operator of a reincarnation of the Nor-Acme, the New Britannia Mine, capped the pile to reduce oxidation of the tailings and further contamination via surface runoff. "It has caused elevated levels of arsenic to leach into the surrounding soil," said Gary Halverson, then-general manager of New Brit, in a 1999 interview. "It wasn't really our responsibility, but we undertook this project thinking that it was good for our employees, good for the Town of Snow Lake, and good for the long-term restoration abatement of the mine." Even though it was capped, Hachkowski reports that during recent sampling, arsenic concentrations in the stockpile's pore water increase with depth and are highest just below the water table. The highest concentration of solid phase arsenic 120,000 ppm (parts per million) was observed in October 2008. "Clay beneath (the) stockpile may have settled under its weight, allowing for arsenic to pass more rapidly into the underlying sandy till," Hachkowski noted. "Hydraulic gradient and local topography indicate a flow path from the stockpile to the low-lying wetlands that feed Snow Lake." The pathway mentioned is 300 metres long and 20-40 metres wide, and concentrations of up to 39,000 ppm have been detected in the top half-metre of soil beneath it. Apparently, the 50 years that the pile was left uncovered resulted in the elevated arsenic concentrations. Prior to any further remedial action, it appears that there are a number of questions that need answering. Included among these is the potential impact on the wetlands in the Snow Lake area, as well as the amount of contaminants currently in the area and their distribution. Additionally, there are questions about the ability of mosses and other vegetation to ease the effects of leachate from the stockpile. Once further investigation and a complete site categorization has been done, Hachkowski states the information derived from it will have to be analyzed and evaluated for trends in area covered and movement of leachate, as well as any secondary sources of arsenic at the site. From there, options and objectives for source containment can be considered, such as capping the site and/or putting in cut-off walls, source removal, and re-vegetation. As a matter of note, it appears that area swamps continue to do their job, as annual reports on the community's drinking water over the past number of years have returned showing arsenic levels in Snow Lake are well below the maximum acceptable levels. In relation to last week's column, I would like to acknowledge that the members of Thompson's USW Local 6166 donated $300 to the Rice/Woosey project. Wow! My Take on Snow Lake runs Fridays.
