AREVA NC (AREVA) retained SRK Consulting between 2005 and 2007 to undertake the feasibility and detail design of a dedicated heap leach pad and associated ponds for lower-grade uranium ore at their SOMAIR operation in Niger. The heap leach design work undertaken by SRK included determining the pad capacity and footprint area, designing the environmental containment and lining system, stability analyses, surface hydrology and pad water balance, pond sizing and the leach pad drainage system.
AREVA and its subsidiary, SOMAIR, have a long history of leach pad operation; the current leach pad is constructed over preexisting leach pads from the late 1970s and early 1980s. SRK optimized the design to limit the cut-and-fill earthworks, while still providing pad-drainage slopes for gravity drainage through a solution channel to the ponds.
As designed, the leach pad has a capacity of 17 million tonnes of uranium ore, based on an annual production of 1.4 million tonnes. The final pad was designed with a height of 30m, comprising five-6m lifts. The leach pad and pond has a composite lining system consisting of a 300mm-thick, low-permeability clay layer overlain by a 2mm-high density polyethylene (HDPE) liner.
The drainage system is made up of perforated pipes placed in a herring bone pattern within individual cells, and connected to collection pipes that drain to the process ponds. This piping was then covered with overliner material, consisting of selected and screened ore material.
In 2008, SRK assisted AREVA with quality assurance and quality control (QA/QC) for the project by providing an engineer. The SRK engineer oversaw and coordinated the construction QA/QC on site during critical earthwork stages of pad and process pond construction. SRK also provided engineering and design support to the project during construction.
At the completion of the earthworks construction phase, SRK produced an as-built report and drawings, detailing the construction process and any changes to the design that occurred during the earthworks construction phase.
