Cominco advances tailings plan despite delays at lead

Uncertainty surrounding the startup date of a new lead smelter at Trail, B.C., has prompted Cominco (TSE) to advance by 18 months its planned move to a land-based system for treated tail slag from the long-standing practice of discharging it to the Columbia River.

The company said the decision was also motivated by uncertainty about the implications of new information arising from bioassay tests conducted on the tail slag by the Department of Fisheries and Oceans, and Environment. “Uncertainty leads to anxiety, and Cominco is very sensitive to the concerns of people living downriver from Trail,” said Graham Kenyon, Cominco’s manager of environment and health at Trail. “That is why we are taking these measures.”

Tail slag is specially treated by an intense fuming process to reduce and limit residual metals before being discharged to the river at a rate of 360 tonnes per day.

Early this year, Cominco announced it was committed to diverting this slag to a land storage site in conjunction with the completion of the final phase of smelter modernization. The switch was scheduled to have been completed by the end of 1996 at the latest, depending on the smelter technology chosen. Cominco’s new QSL lead smelter has been shut down since March, 1990, due to process and mechanical problems that surfaced at the initial startup. A decision on whether to proceed with QSL modifications or switch to the Kivcet process was to have been made in June, but necessary plant-scale tests delayed that decision until year-end or early 1993.

Cominco expects that construction of the new system will begin in mid-1993, and that it will be in operation by mid-1995. This advances the switch to a land-based system by 18 months.

The recent bioassay tests, while not intended to simulate conditions actually occurring in the river environment, showed the slag material to be detrimental to five species of aquatic organisms under laboratory conditions. Levels of copper and zinc exceeding the tolerance limit of these organizations is believed responsible, together with physical abrasion from the sharp slag particles.