Assessment of Soil Cover System Performance at the Antamina Mine, Peru

• Author / Creator

  Perez-Licera, Juan

• A study was implemented to evaluate different alternatives of soil cover systems for the closure of approximately 1539 Mt of waste rock at the Antamina Mine (Peru). The soil covers were designed to limit water percolation to the underlying waste rock, by combining a store/release and low permeability barrier layers. A total of four cover systems were built and installed on lysimeters where net percolation and runoff were measured continuously. Initial results showed net percolations of up to 63% of the total precipitation received by the covered lysimeters. No runoff was observed. The same net percolation and runoff trends were maintained during the four years that the experiment has been monitored. This thesis presents the different activities developed to monitor and assess the covers’ performance. A field investigation program was conducted to measure the hydraulic, geotechnical, and unsaturated properties of the installed cover materials. The program included density and in-situ permeability tests, soil matric suction and moisture content measurements, the recording of oxygen levels in the underlying waste rock, and the installation of complementary instrumentation. The in-situ material properties were used to create and update a series of numerical models in SoilCover, with the objective of evaluating alternatives to improve the observed performance. The field tests showed the material characteristics and the construction process affected the hydraulic properties of the barrier layers. The in-situ saturated hydraulic conductivity values were one to four orders of magnitude greater than those measured in the laboratory. Field-testing and records from the recently installed instrumentation showed that the soil water characteristic curves of the materials also differed from the values measured in the laboratory. Oxygen levels measured in the waste rock revealed that one cover (topsoil and compacted clayey gravel till) has the potential to hinder oxygen diffusion from the atmosphere. The results of the SoilCover models proved to be effective, with predicted net percolation and runoff values matching those measured in the field-scale experiment. The sensitivity analyses based on these models indicated that the saturated hydraulic conductivity is the primary soil property that limits percolation. The simulations showed that decreasing the saturated hydraulic conductivity by one order of magnitude would reduce the net percolation up to 40%. The simulations also confirmed the potential for one of the cover profiles to provide a barrier to oxygen diffusion.

• Subjects / Keywords

  • Lysimeter
  • Soil covers
  • Unsaturated soils
  • Infiltration
  • Evaporation
  • Modelling

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3K931J8T

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.