© 2010 19 th World Congress of Soil Science, Soil Solutions for a Changing World 106 1 – 6 August 2010, Brisbane, Australia. Published on DVD. Mine landform cover design and environmental evaluation Ian Hollingsworth A , Inakwu Odeh B , Elisabeth Bui C and John Ludwig D A HORIZON Environmental, Soil Survey & Evaluation, 38 Witherden Street, Nakara, NT, Australia, Email iholling@bigpond.net.au B Faculty Agriculture and Natural Resources University of Sydney, Sydney, NSW, Australia C CSIRO Land & Water, GPO Box 1666, Canberra ACT 2601, Australia. D CSIRO Sustainable Ecosystems, PO Box 780, Atherton, Qld 4883 Australia Abstract Water balance processes critical to environmental restoration were measured for a reconstructed soil on a waste rock landform. This cover trial, involving four years of monitoring, identified temporal changes in water balance in the near surface and found that tree roots interacted with a drainage-limiting layer at one metre below the land surface in just over two years leading to altered hydraulic properties of the layer. Water balance simulations found that increasing the depth to, and thickness of, the drainage-limiting layer would reduce drainage flux and limit tree root penetration. A mine landform cover design based on soil profile properties and catchment hydrology of a natural analogue area is recommended to reconstruct the endemic natural ecosystems and restore environmental processes. Key Words Mine rehabilitation, cover design, ecosystem reconstruction, water balance. Introduction The objectives for designing landform cover systems can include control of dust and water erosion, chemical stabilisation of acid-forming mine drainage (through control of oxygen ingress), contaminant release control (through control of infiltration) and providing a growth medium for vegetation establishment (O’Kane and Wels 2003). The last objective is perhaps the most important one for addressing off-site impacts on water quality and catchment hydrology at closure (Croton and Reed 2007) although it is often overlooked. Restoring the capacity of the soil zone to support natural ecosystems is an important aspect of ecosystem reconstruction. Consequently, this paper investigates aspects of landform cover design that are relevant to ecosystem reconstruction. A case study is made of a constructed cover at Ranger uranium mine and potential environmental performance issues at this site. Enhancing cover design by referring to soil profile and landform properties of natural analogue areas are suggested. Objectives Our objective was to assess the water balance of a waste rock cover that was constructed from barren mine waste at the Ranger uranium mine. The cover was intended to: (i) limit erosion and thereby contain mineralised waste rock; (ii) limit deep drainage through mineralised material; (iii) reduce water quality impact in the receiving environment; and (iv) support native woodland revegetation. Methods Climate and profile monitoring A continuous logging system was installed to monitor the water balance (2001-2004) in a cover over mineralised waste rock constructed with a subsoil drainage limiting layer and a surface erosion resistant – ecosystem support layer. Two soil profiles were instrumented to measure soil water content (θ v ) and soil water potential (Ψ). One profile was in a bare area and the other in a revegetated area ten metres distant. The revegetated area had been ripped to 0.3 metres and planted in December 2000 with nursery grown plants. Drainage flux estimate Long-term drainage flux was predicted using a profile water balance model, SWIMV2.1 (Verburg et al. 1996) and the sensitivity of this parameter to variations in properties of the cover was assessed. Results Monitored rainfall and drainage in bare and vegetated plots are depicted in Figure 1. In the vegetated plot, enhanced infiltration through the land surface in the 2001 wet season and retention of moisture above the