The Heath Steele Mine site is located approximately 50 km northwest of the City of Miramichi, along Highway 430 in north central New Brunswick.
The tailings basin covers an area of about 215 hectares and is divided into three cells (the North, Upper and Lower Cells), all of which are hydraulically linked. The North Cell discharges through the North dam spillway into the Upper Cell, then to the Lower Cell through the internal dam spillway and finally to the environment via the main dam spillway. The Old Tailings Area is located in the northeast corner of the tailings basin. It contains oxidized tailings from the early operation of the mine (1957). This area is hydraulically connected with the Upper Cell. The old tailings deposit has been partly covered with high density sludge produced by the water treatment plant and partly by soil.
The mine and milling operations ended in 1999. During operations, tailings in the North Cell were deposited underwater, while in the Upper Cell, the deposition of tailings was sub-aerial. Providing a water cover, to form an oxygen barrier designed to prevent/reduce acid generation and metal leaching, was considered to be the preferable option for the tailings basin (Lower, Upper and North Cells). In order to meet one of the cover design criteria that calls for a water cover of no less than one meter over the tailings under normal operating conditions, tailings in the Upper and North Cell were dredged to lower elevations in 2000 and 2001. A large volume of potentially oxidized tailings of the Upper Cell was moved to the North Cell.
The water level in the Old Tailings Area was allowed to equilibrate with the water level in the Upper Cell by hydraulic connection created through a permeable sludge pond dam built on top of old tailings dam in 2001. The Closure Plan had anticipated that some AMD generation in the old tailings deposit was expected to occur in the long term and that the flushing of contaminant may affect the water cover quality of the North and/or Upper Cells.
Heath Steele Mine monitors the performance of the water cover in terms of surface water quality. It has observed a pH variation between the North and Upper Cells. The addition of lime at the internal dam is necessary to raise the pH in order to meet the final effluent requirement. Based on the water quality improvement observed downstream, the water cover had a positive impact on the environment. Only 2 years after the completion of the water cover, a reduction of the metal loadings to the environment was observed. In accordance with the Closure Plan, the tailings water cover is in the midst of a transition period in terms of water quality.
