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Response to Comment on “Sustainability of Uranium Mining and Milling: Toward Quantifying Resources and Eco-Efficiency” The comments by Woods et al. (1) on our 2008 paper on uranium mining and sustainability (2) are most welcome and contribute to the debate about the impacts of uranium mining on water resources. Since most uranium companies do not yet report detailed water accounts in sustainability reporting, it was not possible to account for this (as originally noted; page 2629, (2)). Water recycling is clearly important (3), but perhaps the most critical issue, especially in the minds of the public, is the long-term impacts on water resources. A brief discussion of sustainability reporting is presented, the Global Reporting Initiative, followed by a brief review of the critical issues surrounding impacts on groundwater at the Beverley acid leach uranium mine.
Sustainability Reporting, Mining, and Water Over the past decade there has been a need for companies to demonstrate their commitment to sustainable development. By the time of the Johannesburg Earth Summit in 2002, this had evolved into broader sustainability reporting. As discussed in detail by ref 3, mining companies have been at the forefront of this development, with the most popular reporting protocol being the Global Reporting Initiative (4). The principal GRI core environmental indicators of relevance to mining and water are EN8, EN21, and EN22, with voluntary indicators EN9 and EN10. The Beverley uranium mine uses acidic in situ leaching. As noted by Woods et al., it extracts some water from the underlying sandstone of the Great Artesian Basin and extracts and recirculates groundwater from the Namba aquifer where the uranium occurs. All liquid wastes are discharged into the Namba aquifer. The principal aim for in situ leach mining is to always extract slightly more water than injected (difference being ∼1-5%), to ensure a hydraulic gradient toward the mine and minimize potential solution escape. For acid leach mines the degree of water recycling is, without doubt, therefore high. General Atomics (through Heathgate Resources) do not use the GRI, instead using environmental management-style reporting (5) - leaving key gaps. Current reporting includes: solution injection, extraction, and liquid waste disposal for the Namba aquifer (EN8, EN21); and Great Artesian Basin extraction (EN8).
Relevant water data are given in Table 1. If one assumes that GAB is the only water “consumed”, 142 kL/t U3O8 can be derived (years 2004-2007). If one assumes the total water pumped from the Namba aquifer, 8750 kL/t U3O8 can be derived (8207 kL/ t U3O8 originally; (2)). This shows that the unit water production costs continue to rise at Beverley, due to declining production. The explanation by Woods et al. that increasing unit water costs can be allegedly due to improved efficiency of uranium extraction and operating well fields longer is hard to justify. The original premining resource estimate for Beverley was 21,000 t U3O8 and yet according to ref 6 the Beverley project could close in 2009 (pp 2-1), having produced ∼7,500 t U3O8 and leaving the remainder as uneconomic or unextractable (reasons unexplained). For life cycle analysis, it is the convention to use total consumption and account for recycling (e.g., GRI), hence the approach in ref 2 is considered valid. The total water required is clearly ∼8 GL/year, not the ∼0.1 GL/year of GAB water. Another method is to estimate the pore volume under active leaching. Based on wellfield area, ore zone thicknesses, and typical porosities (see 5, 6), a pore volume of 1 GL can be crudely estimated, meaning 8 GL/year represents ∼8 pore volumes and a recycling rate of ∼90%.
Water Resources and Beverley The Beverley mine has approvals which do not require active remediation of groundwater to premining conditions following closure. Some judgements require sound science while others are based on legitimate public expectations for environmental outcomes. In brief, there are three key assumptions for Beverley: the aquifer is hydraulically isolated, water quality is unusable for any purpose (other than mining), and that “natural attenuation” would be sufficient regardless. The Namba aquifer is no longer considered isolated since recent exploration has extended the ore zones, and therefore the aquifer. The principal issue remains the aquifer being mined (risks to the Great Artesian Basin are exceedingly low). Second, Namba salinity ranges from 3 to 16 g/L, one-tenth to onehalf seawater salinity. Acid leach mining leaves Namba groundwater in a significantly worse condition than premining, especially given the greater mobility of metals and radionuclides under acidic, oxidizing conditions. Third, despite repeated claims, no field-based evidence for the success of “natural attenuation” has ever been published for Beverley (see (7)).
TABLE 1. Water Reporting for the Beverley Acid Leach Uranium Mine (5)
year 2000 2001 2002 2003 2004 2005 2006 2007 averageb
unit water unit water injected Namba extracted Namba bleed Great Artesian production liquid waste costs - GAB costs - Namba a c Water (ML) Water (ML) difference (ML) Basin (ML) (t U3O8) disposal (ML) basis (kL/t U3O8) basis (kL/t U3O8) 0 no data 5,735.6 5,894.1 7,940.1 8,552.6 8,726.9 7,767.0 7,436
0 3,661 5,726 5,878.1 7,903.9 8,580.8 8,732.5 7,776.0 7,433
0 9.60.17% 16.00.27% 36.20.46% -28.2-0.33% -5.6-0.06% -9.0-0.12% 3.20.04%
3.92 63.74 47.5 51.29 123.09 136 126 136 103
0 546 746 717 1,084 977 824.6 748 849
0 49.09 76.8 156.67 187.0 131 102 104 126
0 116.7 63.7 71.5 113.6 139.2 152.8 181.8 122
a Positive represents net injection, negative represents net extraction (percentage relative to injection). 2000-2001 to ensure equivalent averages. c Liquid waste included in the injected water budget.
10.1021/es900742b CCC: $40.75
Published on Web 04/16/2009
2009 American Chemical Society
0 6,705.1 7,675.6 8,198.2 7,291.4 8,782.8 10,590.0 10,395.7 8,750 b
Excluding
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In the authors’ long experience in the environmental area, the public always have significant concerns about any project that clearly leaves the environment in a worse condition than premining, commonly viewed as unsustainable and inappropriate in the modern era of environmental standards. The Woods et al. commentary is most welcome, but it is critical to recognize that there is more required in understanding the life cycle water costs of mining any element than simple water extraction from one aquifer alone. Sustainability requires a complete understanding of all complex relationships between water and mining, an understanding still clearly incomplete for Beverley.
Literature Cited (1) Woods, P. H.; Carter, S. D.; Wedd, M. J.; Jeuken, B. M. Comment on “Sustainability of Uranium Mining and Milling: Toward Quantifying Resources and Eco-Efficiency”. Environ. Sci. Technol. 2009, DOI: 10.1021/es9002197. (2) Mudd, G. M.; Diesendorf, M. Sustainability of Uranium Mining and Milling: Toward Quantifying Resources and Eco-Efficiency. Environ. Sci. Technol. 2008, 42 (7), 2624–2630. (3) Mudd, G. M. Sustainability Reporting and Water Resources: a Preliminary Assessment of Embodied Water and Sustainable Mining. Mine Water Environ. 2008, 27 (3), 136–144.
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(4) GRI. Sustainability Reporting Guidelines, 3rd ed.; Global Reporting Initiative: Amsterdam, 2006; 44 pp. (5) HR. Annual Environment Report; Heathgate Resources Pty Ltd/ General Atomics Corporation, var., years 2001-2007. (6) HR. Mining Proposal for Proposed Extension of Beverley Mine - Public Environment Report; Heathgate Resources Pty Ltd/General Atomics Corporation, December 2006. (7) Mudd, G. M. Critical Review of Acidic In-Situ Leach Uranium Mining: 1 USA and Australia. Environ. Geol. 2001, 41 (3-4), 390–403.
Gavin M. Mudd Institute for Sustainable Water Resources, Department of Civil Engineering, Monash University, Clayton, VIC, Australia 3800
Mark Diesendorf Institute of Environmental Studies, University of New South Wales, Sydney, NSW, Australia 2052 ES900742B
