Alternative Design and Instrumentation of Covers Over Potentially Acid Forming Mine Wastes

The design of earthen covers for potentially acid forming mine wastes is site specific, largely dictated by climatic conditions, the materials available for cover construction, and the expectations of stakeholders. The “store/release” cover system is the preferred approach in semi-arid conditions, such as those that exist over much of Australia. It typically comprises a compacted clayey sealing layer overlain by a vegetated, loose “rocky soil mulch”. As an alternative, a thick mono-layer of overburden may be used. The performance of such a cover system in a coastal, sub-tropical, seasonal climate is being monitored using time domain reflectrometry to measure volumetric water content, thermocouple sensors to measure soil suction, and lysimeters to measure percolation rates at the cover/waste interface and the waste/foundation interface. The paper describes the site setting, laboratory and field testing of cover and waste materials, the instrumentation of the cover system, and preliminary monitoring data illustrating the successful performance of the trial cover to date.