DESIGN OF FIELD TEST PLOTS FOR A SLOPED WASTE ROCK SURFACE

摘要

Westmin Resources Limited is a Western Canadian mining company with producing interests in base and precious metals and coals. Westmin's Myra Falls Operations produce copper, zinc, and gold concentrates. The Myra Falls Operations are located in the central interior of Vancouver Island in a hanging glacial valley. Mean annual precipitation is approximately 3,000mm with more than 75% occurring during the months of October to April. Historic surface deposition of waste rock has resulted in acid rock drainage (ARD). An applied research program was initiated to develop a cover system for the waste rock material at the Myra Falls site. The objective is to develop a cover system which controls the ingress of oxygen and infiltration of water, while providing a medium for sustainable vegetation that is consistent with the end land use of the area. Progress to date suggests that modified local till materials (amended with either fly ash or bentonite) can be used in soil cover construction. Four test plots were designed using two-dimensional saturated-unsaturated modelling tools to ensure that the performance of each test plot was representative of a full scale ARD cover system. This paper summarizes the design philosophy and principles of the cover system as well as the methodology for the two-dimensional numerical modelling program. Conclusions and results from the numerical modelling program are presented with a focus on implications for construction of the field test plots and installation of the performance monitoring instruments. The numerical modelling demonstrated that the hydraulic performance of a soil cover system placed on a sloped waste rock surface will be much different than that predicted by idealized one-dimensional numerical models, and in general current design methodologies. The modelling clearly demonstrated that the design of small scale field test plots was not a simple task. The physical dimensions of the field test plots had a significant impact on the ideal location for monitoring instruments and incorrect placement of instruments would lead to an erroneous measure of test plot performance.