Rehabilitation

COSMOLSESC is specialized in acid metalliferous drainage treatment and soil amelioration. A civil package will be developed to ensure acid waste rocks and unmineralized rocks are appropriated managed. A site-based construction plan will be established to verify that soil and stormwater management are considered as part of the project and that it is possible to effectively control stormwater runoff to achieve the required active and passive discharge limits.

Best practice principles for waste rock dump management include the following:

Implement an ongoing geochemical characterization and investigation program;
Segregation and selective backfill placement of ARD rock types to minimize the exposure of PAF and high Arsenic NAF to atmospheric oxygen and leaching;
Place oxidized NAF within the unsaturated zone under the final top surfaces of the pit. Exclude PAF and High Arsenic NAF from the top of the pit under final outer cover;
Bottom up construction in appropriate lift heights to minimize the development of convective/advective gas movement within the backfill, to minimize the exposure time of reactive PAF rock and facilitate selective placement of ARD rock types;
Compaction of the surface of each lift to reduce permeability and control diffusive transfer of oxygen and water into backfill;
Crushed agriculture limestone is recommended for PAF rock hot spots. If the pH is less than 5.5, broadcast crushed limestone at 20-40 tonnes per hectare;
Diversion of clean upstream catchments or installation of drainage system to convey surface runoff to minimize the top cover seepage;
Selective placement of NAF rock on final top surfaces and slopes to ensure good quality runoff, control erosion and promote vegetation.