The Evolution of Evapotranspiration Cover Systems at Barrick Goldstrike Mines

Abstract

Barrick Goldstrike Mines Inc. (BGMI) has developed a comprehensive closure planning, materials characterization and in-situ monitoring program for the closure of its mine waste facilities. Facility closure techniques use topsoil and in-pit material to construct evapotranspiration (ET) cover systems to reduce or eliminate infiltration of meteoric water. One major facility at BGMI, the AA Leach Pad (AA Pad) has been closed. The Bazza Waste Rock Facility (WRF), which will hold about 1.75 billion metric tonnes (mt) of waste rock within an area of 950 hectares (ha), is undergoing concurrent closure over the next 10 years. Hydrologic performance of the AA Pad cover and the inventory, suitability and timing of in-pit materials dictated the ET cover design approach for the Bazza WRF.The AA Pad ET cover system was constructed in 2000 using two comparative cover systems; 1.2 m of fine-grained Tertiary-aged valley fill deposits of the Carlin formation, and 1.5 m of salvaged topsoil materials. The flux of meteoric water through the AA Pad cover was measured using in-situ vadose zone monitoring. Both covers had very low deep percolation rates, especially after vegetation matured. The AA Pad monitoring results were used to optimize the Bazza cover. First, an unsaturated flow model was calibrated to the in-situ monitoring data from the AA Pad. Next, the hydraulic properties of cover materials to be used for the Bazza cover were determined in large-diameter cores to minimize scale effects. Large scale in-situ hydraulic testing was also conducted to assess material variability. Finally, in-situ monitoring systems were installed in concurrent reclamation areas at the Bazza WRF.

Design of Inclined Covers with Capillary Barrier Effect by S.-E. Parent and A. Cabral

“…These calculations have been complemented by laboratory experiments (Bussière et al 1998) and validated using monitoring data obtained from in situ cover systems (e.g. Bussière 1999; Bussière et al 2003a;Zhan et al 2001aZhan et al , 2006. The results obtained through these studies have shown that the behavior of inclined CCBEs is intrinsically dynamic.…”

“…Stormont 1996;Bussière et al 1998;Morris and Stormont 1998;Kämpf et al 2003;Tami et al 2004) and more representative simulations that better reflect the actual field behavior of covers (e.g. Zhan et al 2001aZhan et al , 2006Bussière et al 2003a). …”

“…The results obtained through these studies have shown that the behavior of inclined CCBEs is intrinsically dynamic. In fact, the diversion length is not a constant but varies in time depending on the local climatic conditions (affected by slope and Table 2 Main hydraulic properties of the simulated inclined CCBE and calculated effective length of the capillary barrier (L) for the three analytical solutions of Table 1 Brooks and Corey (1964) Gardner (1958) aspect), cover geometry and configuration, and material properties (see Bussière et al 2003b;Cifuentes et al 2006;Zhan et al 2006). This general behavior, observed in the lab, in the field, and through numerical modeling, strongly suggests that the analysis and design of inclined CCBEs should not be based on (pseudo) steady-state conditions, which in practice do not exist.…”

Assessment of the Design of an Experimental Cover with Capillary Barrier Effect Using 4 Years of Field Data

“…The effectiveness of CCBEs has been assessed in the laboratory (Bussière et al , 1998Kämpf and Montenegro 1997;Stormont and Anderson 1999;Kämpf et al 2003;Tidwell et al 2003;Yang et al 2004), in the field (Stormont 1995a;Stormont et al 1996;Aubertin et al 1997;Barth and Wohnlich 1999;von Der Hude et al 1999;Cabral et al 2007), as well as by numerical simulations (Akindunni et al 1991;Oldenburg and Pruess 1993;Bussière et al 1995Bussière et al , 2003Kämpf and Montenegro 1997;Webb 1997;Morris and Stormont 1999;Khire et al 2000;Zhan et al 2001Zhan et al , 2006Aubertin et al 2006Aubertin et al , 2009Cifuentes et al 2006).…”

Conceptual Model for Hydrology-Based Geomorphic Evapotranspiration Covers for Reclamation of Mine Land

“…An ET cover is a selfrenewing biological system and is expected to last much longer than the conventional compacted clay barrier. ET covers have been used above landfills (e.g., Albright et al, 2004;Apiwantragoon et al, 2015;Barnswell and Dwyer, 2011;Benson et al, 2001;Benson et al, 2007;Santini and Fey, 2014;Scanlon et al, 2005), waste sites (e.g., Bowerman and Redente, 1998;Gee et al, 1997;Link et al, 1995;Pettit et al, 1994;Rutqvist et al, 2011;Scanlon et al, 1997;Waugh et al, 2010;Waugh et al, 2007;Wing and Gee, 1994;Zhang, 2015), and mine lands (e.g., Barber et al, 2015;Meiers et al, 2015;O'Kane and Wels, 2003;Zhan et al, 2006). The function of an ET cover is to protect the underlying materials, provide a medium for vegetation growth, store precipitation within the cover, and release the stored precipitation later into the atmosphere so that the infiltration of precipitation waste zone is minimized.…”