Hydraulic placement of a dry cover system - Design and performance monitoring of the Kennecott Ridgeway Mine tailings dam cover system

Abstract

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.