The Louvicourt project was multifaceted with contributions from industry, university, consulting and government organizations. These groups completed a broad range of studies and investigations. This provided the rare opportunity to assess and compare the effectiveness of different test procedures, equipment and predictive techniques.

Previous investigations funded through the MEND (Mine Environment Neutral Drainage) Program had determined that subaqueous disposal of acid generating tailings in natural lakes was an effective mitigation strategy for the prevention of acid generation. Similar benefits were also attributed to constructed tailings basins but little scientific demonstration of this technology was presented in the literature. The primary objectives of the Louvicourt project were to assess and
demonstrate the effectiveness of shallow water covers in a man-made basin and determine the benefits of the placement of organic or inorganic barriers at the tailings/water cover interface. This demonstration would enhance the current state of knowledge with both site-specific design information for the closure of the full scale Louvicourt basin as well as generic design and predictive modelling information for application to other reactive tailings sites.

This report has been prepared to provide a summary of the key findings from these studies as well as to provide a synthesis of what this body of work has contributed to the understanding of water covers in man-made tailings basins.

The key findings from this work are:

· Shallow water covers in man-made basins are an effective means of controlling sulphide oxidation. Oxidation rates are reduced by at least 3 orders of magnitude as compared with unsaturated surface tailings deposits.

· The low rates of oxidation observed in the column and field cell studies result in metals release (notably Cd and Zn) to the overlying water cover. Measured metal fluxes would not likely result in metals levels in the effluent exceeding discharge standards.

· The measured depth of oxygen penetration into the tailings is typically less than 1 cm. Sampling and measurement of porewaters within such a very small zone is difficult and complicates the interpretation of the geochemistry within this layer.

· It is apparent that periphyton growth affects oxidation and the transport of oxygen into the tailings. Although the exact role and impact of vegetation is uncertain, other studies to date have shown no significant degradation of water cover quality as a result of plant growth.

· Barriers between the tailings and the water cover generally serve to limit the access of oxygen to the submerged tailings and act to reduce the diffusive flux of contaminants from the tailings porewater. From this study it is clear that barrier materials may be a significant source of dissolved contaminants and full characterization of these barrier materials must be included in the cover design process. Careful consideration must begiven to the short-term impacts that these materials may have on water quality, and whether these impacts outweigh the longer-term benefits. From the Louvicourt column studies, there was no short-term benefit to barriers at the tailings/water interface. Given the similar performance of the water cover option without barriers, there would be no basis at this time to suggest additional barriers would be warranted for the Louvicourt site.