Completion of the North End Box Cut waste landform rehabilitation: implementation challenges and learnings

Abstract

The North End Box Cut (NEBC) waste dump at Rio Tinto's Tom Price iron ore operation is a historic waste dump containing an estimated 2.6 Mt of potentially acid forming (PAF) shale material. The waste dump is positioned on the edge of the site's current operational footprint. Construction of the NEBC waste dump began in the 1990s, prior to the current standards for PAF material management and landform design. An overview of the planning and design work to apply best practice standards to this legacy waste dump was presented at the Mine Closure 2019 conference. Following 25 months of project implementation, the rehabilitation earthworks for this landform were completed in February 2022. The project required material movement of 3 million cubic metres, enough to fill the Melbourne Cricket Ground (MCG) twice. It spanned an area of 72 hectares (~36 MCG fields) and utilised 550 kg of seed. The NEBC waste dump is regarded as one of the most technically challenging rehabilitation projects ever undertaken within the Rio Tinto Iron Ore product group. The project navigated the COVID-19 pandemic, along with contractual changes and challenges that provide key learnings on rehabilitation planning and the onboarding of rehabilitation teams and contractors. The learnings from the NEBC rehabilitation project have subsequently been incorporated into an optimised 'tip-to-close' design at a second PAF waste dump at Tom Price, Marra Mamba South (MMS), aimed to significantly reduce closure liability and enable progressive rehabilitation. Earthworks at MMS are currently in progress and due for completion in 2022. This paper reviews the implementation challenges that have arisen throughout both projects and highlights the closure liability reduction opportunities that can present when rehabilitation activities are integrated into the mine plan. © 2022 Australian Centre for Geomechanics, Perth.