Frozen cover actions limiting AMD from mine waste deposited on land in Arctic Canada

Mining in permafrost-affected areas presents unique characteristics and pos sibilities that need to be considered in order to investigate alternative a ctions to minimize, the environmental impact of mining. Encapsulating mine waste within the permafrost zone by covering is considered one of the most promising actions to limit acid mine drainage and has been investigated nea r Nanisivik Mine in northern Canada. Quadrant test pads consisting of appro ximately 2 in of inactive (non-sulfidic) material have been constructed on top of oxidizing sulfidic mine tailings. A one-dimensional physically based soil water and heat model (WinSoil) has been calibrated and used to simula te observed subsurface temperatures within and below covers. Model input pa rameters include meteorological data such as air temperatures as well as th ermal conductivity of cover material. The model was calibrated against grou nd temperatures measured in 1998 and validated against ground temperatures measured since 1995. WinSoil simulations were found to match observed groun d temperatures reasonably well without calibration and almost perfect match es were obtained by varying the thickness of snow cover by a few centimetre s. Observations and simulations reveal that temperatures within mine tailin gs have been below 0 degreesC since covering 6 years ago. In addition to si mulating observed ground temperatures, WinSoil was used to predict ground t emperatures in relation to cover thickness and snow cover. The simulations question whether a 2-m cover will hinder sulfide oxidation processes within covered tailings if winter snow increases significantly due to either larg e-scale application of covers or global climate changes. (C) 2001 Elsevier Science B.V. All rights reserved.