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The Kennecott Ridgeway Mining Company (KRMC) tailings facility was built using run of mine waste and downstream embankment construction techniques. Approximately 60% of the 60 million tons of processed tailings have a negative net neutralization potential. KRMC conducted a cost-benefit analysis supported by a detailed cover system design and determined that a hydraulically placed cover system was the preferred closure option for the tailings facility. The tailings mass (124 ha, or 307 acres) was covered with 2.7 million tons of clay material (saprolite) using hydraulic placement from both centre-point and ring discharge points following cessation of operations in November 1999. Approximately 90% of the tailings surface area is now covered with greater than 90 cm (36 inches) of cover material.Monitoring was initiated in September 2001 to evaluate the field performance of the tailings dam cover system. Three primary tailings monitoring sites were established to provide continuous measurements of in situ suction, moisture content, and temperature conditions. Sixteen secondary tailings monitoring sites were also installed. The secondary monitoring sites provide spatial coverage to evaluate cover system performance. Surface runoff across the cover surface during precipitation events is also monitored. This paper summarizes the design and implementation of the hydraulically placed KRMC tailings dam cover system. The cost benefit of implementing this novel cover placement technique is discussed. The field performance monitoring system is described and field data is discussed and summarized in light of the cover system design objectives for minimizing oxygen ingress.

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Little is known regarding the influence of termites on the performance of mine waste cover systems. This paper attempts to qualify the potential effects by reviewing existing termite research and relating it to cover system design and performance. It has been well documented that termites alter soil physically, chemically and hydrologically; however, the results tend to be highly variable. Four key properties relating to long-term cover performance were used to evaluate the effects of termites, namely, soil water characteristics, soil integrity, saturated hydraulic conductivity, and soil chemical characteristics/vegetation. Subterranean foraging holes and galleries created by a wide range of termite species tend to increase the rate of infiltration by a factor of one to three depending on termite activity, soil type, and rainfall intensity. However, the effect of termites on infiltration is typically only significant on soils with low hydraulic conductivity. Termites preferentially select finer textured material for their constructions and in extreme cases have been known to burrow up to 55 m in search of moist soils. Preferential selection and movement to the surface of finer textured materials could have an effect on soil water characteristics, and physical integrity. In addition, termites could potentially improve conditions for the development of sustainable vegetation by improving nutrient cycling, aeration, and soil moisture. Cover systems with shallow barrier layers are likely the most susceptible to damage by termites. The hydraulic conductivity of barrier layers could be increased; however, the effect has been found to be overshadowed by the presence of extensive vegetation. The potential usage of barrier layer material for termite constructions would be damaging to long-term performance and emphasises the need for an appropriately designed growth medium for protection. Cover systems that utilise the moisture store-and-release concept may very well benefit from termite activity. By improving conditions for the development of a sustainable vegetative system, termites could potentially improve moisture cycling and physical stability. Similar to cover systems with barrier layers, the preferential usage of finer textured material has the potential to reduce homogeneity and create unplanned pathways for water. Understanding the effects of termites on cover performance and subsequently incorporating them into the design process should increase the over performance of soil covers over the long term. Preliminary termite nest density counts on cover systems may improve modelling efforts if incorporated into the performance modelling process. Current research which examines the chemical, physical, and hydrological effects of termites on soil can be quite variable. Variability makes it difficult to quantify the significance of termite activity on mine waste cover systems. Future research should focus on quantifying termite abundance over the successional life of cover systems for each termite feeding and nesting be...

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