Issues arising from Acid Mine Drainage (AMD) can be complex. URS provides comprehensive AMD and mine water quality management services for all stages of mining operations to ensure compliance with environmental conditions during operations, and to minimise risks of AMD discharge following mine closure and rehabilitation.

AMD is internationally recognised as a major mining environmental hazard, as it can severely impact aquatic environments and water resources. It is a natural process which occurs when sulphuric acid is produced as a result of sulphides (pyrite) in rocks being exposed to air and water, and is primarily a function of the geology, hydrology and mining technology employed for the mine site.

The process is magnified when large quantities of rocks are disturbed from a naturally occurring state, or excavated in the course of mining. The iron-oxidising activity of naturally occurring bacteria, Thiobacillus ferroxidans, has the potential to accelerate the oxidation and acidification processes. Leaching - the removal of chemical constituents from rocks and soil by water - is accelerated under low pH conditions. The acidic condition generated by mining activity will continue to leach metals, including heavy metals, as long as the source rock is exposed to air and water until such time the reactive sulphides are exhausted – a process that can last for hundreds of years.

Determining the rate of recovery of this process requires specific hydrological, hydrogeological, geochemical studies and predictive modelling in some cases.

URS offers the following AMD services for each phase of the mine life:

• Evaluation of drill core logging techniques to ensure geological information relevant to AMD management is recorded
• Performing base line geochemical test programs including preliminary acid base accounting
• Sampling of drill core for AMD testing
• Analysing waste rock types for acid and non-acid forming categories
• Optimising sampling and testing programmes to efficiently meet regulatory and preliminary mine planning requirements

• Developing conceptual waste mining schedules for the mine life
• Developing conceptual waste dump designs, tailings storage facilities and mine water management plans
• Investigating and designing in-mine waste disposal and co-disposal
• Performing kinetic tests on waste rock and tailings materials to assess their long term geochemical behaviour
• Modelling the rate of recovery of the pit-lake levels and status at its final stage
• Modelling geochemical reactions and potential water quality impacts which may arise from mine wastes and mine openings
• Development of conceptual rehabilitation designs to minimise any adverse long term water quality impacts
• Preparing and managing documentation for regulatory approval

• Designing and supervising waste rock dump and tailings storage facility construction to minimise AMD
• Developing and monitoring waste blending schedules
• Designing and constructing AMD controls
• Designing and implementing surface and groundwater quality monitoring programmes and reporting/response protocols
• Refining and implementing rehabilitation programmes

• Developing mine closure and rehabilitation plans to minimise any long term adverse water quality impacts
• Supervision of final rehabilitation construction
• Finalising and implementing water management and monitoring plans
• Performing and reporting long term water quality monitoring programs
• Investigating any adverse water quality impacts and designing