A modelling study of the South Bay mine site.

Abstract

The former gold mine at South Bay, Ontario adjacent to Confederation Lake north of Ear Falls, Ontario has been shut down for over 10 years. Presently the mine site is undergoing closeout using ecological engineering and bioremediation technology. An extensive monitoring program has been in effect at the South Bay mine site for the past several years. The results of this monitoring program have been used to provide direction for several remedial actions on the site. In addition, it has been used to monitor the effectiveness of these actions and focus future remedial work. As part of the investigations on the site, predictive modelling was used in 1988 to attempt to predict the movement of contaminants in the groundwater, using the hydrogeological model developed for the site at that time and the CHINTEX model. During the ensuing years, it was discovered that the main seepage pathway from the tailings was not into Confederation Lake but rather into Mud Lake through a large deposit of gravel which was named the “Kalin canyon”. In light of the increased data base collected during the past ten years and the reinterpretation of the site hydrogeology, it was decided appropriate at this time to construct a numerical model that can be used to simulate the existing groundwater flow patterns and be used to predict contaminant movement. The model, once calibrated can be used to assess the effectiveness of the various remedial alternatives and to assess the impact of changing properties such as porosity and hydraulic conductivity as a result of some of the biological processes used in the remediation. The three basic objectives of the Phase one modelling described in this report were the following: Develop a global site-wide model encompassing all of the significant water sheds in the vicinity of the site in order to determine the effective dilution via groundwater of contaminated water with water from uncontaminated areas. This can then be used together with measured surface water flows to determine expected contaminant concentrations in various water bodies. Use the results of the global site-wide model to construct a more detailed tailings area model and calibrate this model to simulate the measured existing flow patterns. Use the detailed tailings area model to simulate the release and transport of contaminants from the tailings area into the various receiving water bodies As stated above, two models were developed for this study, a global site-wide model and a more detailed tailings area model. The major input parameters required by both of the models are summarized in Chapter 2 and the development and results of the global site-wide model are described in Chapter 3. The development and results of the failings area model are given in Chapter 4. Conclusions and recommendations for further work are given in Chapter 5.