See Also : Case Against ISL and Overview of ISL and ISL Ref's and ISL's Jivin' Jargon!
Despite numerous industry assurances that ISL is now "a controllable, safe, environmentally benign method of mining which can produce uranium with low capital and operating costs and can operate under strict environmental controls" (1), the track record of significant and often intractable problems with ISL mines across the world speaks for itself. While freely admitting problems of the early field trials and operating mines, the industry assures us that the same mistakes are no longer made today. Somehow, they still haven't learnt and many sites across the world remain contaminated, often seriously threatening public water supplies.Most operating uranium mines in the USA use ISL techniques, with the leaching agents used being primarily bicarbonate and hydrogen peroxide (alkaline chemistry). In Europe, many ISL mines operate with some being converted from underground mines to ISL. The main leaching agent used is sulphuric acid and oxygen (acidic chemistry). Rehabilitation of groundwater many old sites across the USA and Europe has been quite problematic - with quality targets often being relaxed in order to argue the site has been "restored".
There are numerous ways in ISL can lead to significant contamination of surrounding groundwater systems or the wider environment : Potential Problems with ISL
Escape of leaching solutions - water moves from high pressure to low pressure, and thus any hole or opening away from the ore zone could act as a flow path for solutions. These may include features such leaking boreholes, fault planes running across the aquifer system, old underground workings, or any other similar opportunity for water to flow freely.Difficulties in geochemistry - when the solutions are injected into an orebody aquifer to mobilise uranium, many other minerals are dissolved into solution and many other radionuclides and heavy metals are mobilised also. These can include radium, arsenic, vanadium, molybdenum, cadmium, nickel, lead and others. The subsequent increase in concentrations can be up to a thousand times higher or more.
Precipitation of solids - due to the nature of the groundwater and orebody chemistry, it is possible to form solid minerals that precipitate from solution and thereby act to reduce or at worst block the flow of solutions through the intended areas. These can include the formation of calcite (calcium cabornate - CaCO3), gypsum (2) (calcium sulphate - CaSO4.2H2O), jarosite (2) (potassium iron sulphate - KFe3(SO4)3.9H2O) and other minerals.
Waste water disposal - the inherent nature of ISL is that it produces extremely large quantities of waste water and solutions which need to be disposed of in an environmentally responsible manner. These are from the bleed water (excess pumping water) and waste solutions from the uranium extraction plant. Typically these solutions are mixed and re-injected into the same groundwater as that being mined, or injection into a deep aquifer remote from other groundwater users of the area or potential environmentally sensitive areas. Extremely high concentrations of radionuclides and heavy metals can be found in these waste waters, and the disposal area chosen also undergoes rehabilitation after the cessation of ISL mining.
High radon exposures - due to the mobilisation of uranium in the groundwater and circulating solutions, high concentrations of radium and radon are often found, leading to possibly high radiation exposures.
The majority of ISL mines across the world have led to either direct contamination of surrounding groundwater systems, some of which are used for town water supply, or attempts to rehabilitate the groundwater after the completion of ISL were unsuccessful. Some famous cases : ISL's Questionable Track Record
Königstein, Germany - initially an undergound uranium mine, it was converted to an ISL mine in 19??, and finally ceased uranium production in 1990. A total of 100,000 tonnes of sulphuric acid was injected into the aquifer. There is still 1,900 Ml (3) (1.9 million m3) of contaminated water remaining within the mining zone and a further 850 Ml recirculating through the recovery plant. The mining area is within an aquifer that the nearby town of Dresden uses for it's water supply. The concentrations of contaminants still remaining above background are : cadmium 400x, arsenic 280x, nickel 130x, uranium 83x, etc.The Nuclear Regulatory Commission of the USA (US-NRC) is still reporting ISL mine sites in the mid-1990's where there has been escape of leaching solutions due to leaking boreholes (8).Stráz pod Ralskem, Czech Republic - a total of 28,700 Ml of contaminated water is still contained in the leaching zone, covering an area of 5.74 km2. This zone contains 1.5 million tonnes of sulphate (SO4), nearly half that injected, and 37,500 tonnes of ammonium (NH4), over a third of that injected, and others. The contaminated groundwater has escaped outside the mining zone both horizontally and vertically, extending over a further area of 28 km2 and a 235,000 Ml of groundwater. To the southwest, the groundwater contamination has already reached the second zone of groundwater protection of the potable water supply of the town of Mimon. In southeastern direction, the contaminated groundwater is still at a distance of 1.2 - 1.5 km from the second zone of groundwater protection of the Dolánky potable water wells, which supply 200 l/s for the city of Liberec (4). The migration of the contaminated liquids in an easterly direction towards the Hamr I underground mine is at present intercepted by a hydraulic barrier: decontaminated water is injected into a chain of wells to prevent further migration of the contaminated groundwater.
Bulgaria - a total of 2.5 million tonnes of sulphuric acid was injected into the ore deposits exploited by in-situ leaching. It is estimated that about 10% of the surface area used for ISL could be contaminated from solution spills. This is of concern, since the area is to be returned to its previous owners for agricultural use. After termination of ISL operations, the contaminated groundwater spreads offsite. Some in-situ leaching facilities (for example Bolyarovo, Tenevo/Okop) are located close to drinking water wells (5).
The impacts of ISL on surface and groundwater are catastrophic (6) :
"Very high concentrations of sulfate ions are measured in surface water and even in wells of private owners as a result of accidental spilling of solutions in sites of in-situ leaching. At the site "Cheshmata" (Haskovo), in the valley downstream from the sorption station, the measured content of sulfates is 1,400 mg/l, free H2SO4 is 392 mg/l and pH is 2.2 (5.5 - 8.5 for 3-rd category water). A similar case has been recorded in Navusen where in a valley the sulfate concentration is 13,362 mg/l and almost 5 g/l H2SO4, which means that actually the water is leaching solution.Devladovo, Ukraine - was leached with sulphuric and nitric acid. The surface of the site was heavily contaminated from spills of leaching solutions. Groundwater contamination is spreading downstream from the site at a speed of 53 m/year. It has traveled a distance of 1.7 km already and will reach the village of Devladovo after 24.5 years (7).In the underground water of such sites the salt content is >20 g/l, from which the sulfates are 12-15 g/l."
Wyoming, USA -
Texas, USA -
Nebraska, USA -
Thus it is quite easy to see that ISL is not the "controllable, safe, environmentally benign method of mining" (1) it is claimed to be - many of the early problems of ISL mines yet to be satisfactorily overcome.
Another important point to note is that sulphuric acid leaching chemistry has never been used at a commercial scale ISL mine in the western world as yet. There have been many cases of such ISL mines in Eastern Europe, but a quick review of the above list demonstrates the intractable problems found from ISL operations there. The only site where ISL has been trialled at a small field scale is at Casper in Wyoming, America. A detailed review by the Wyoming and federal environmental regulators of the trial proved to be a damning indictment of the ISL technique, as the groundwater of the site was not rehabilitated to pre-trial quality and standards had to relaxed in order to consider the area "restored" (9). At the Irigary ISL mine also in Wyoming, there were repeated problems of solutions escaping, site accidents and shut downs. The mine was abandoned in 1981 by the Wyoming Mineral Corporation (subsidiary of Westinghouse).
1 - In Situ Leaching Method of Extracting Uranium, Appendix 1.1, The Report of the Senate Select Committee on Uranium Mining and Milling Uranium Mining and Milling in Australia (SSCUMM), tabled May 15, 1997.
Page developed by Gavin Mudd for SEA-US Inc.
Many thanks to the ISL page by Peter Diehl, WISE Uranium Project.
References :
2 - Appelo & Postma (1993), "Geochemistry, Groundwater & Pollution", A. A. Balkema, Netherlands, pages 263-264.
3 - Ml - megalitre, one million litres (106 l).
4 - Andel,P & Pribán,V; 1996, "Environmental restoration of uranium mines and mills in the Czech Republic". In: Planning for environmental restoration of radioactively contaminated sites in central and eastern Europe, Vol. 1: Identification and characterization of contaminated sites, IAEA-TECDOC-865, Vienna 1996, pages 113-135.
5 - Vapirev, E I, Dimitrov, M, Minev, L, Boshkova, T, Pressyanov, D S & Guelev, M G; 1996, "Radioactively contaminated sites in Bulgaria". In: Planning for environmental restoration of radioactively contaminated sites in central and eastern Europe, Vol. 1: Identification and characterization of contaminated sites, IAEA-TECDOC-865, Vienna 1996, pages 43-63.
6 - Dimitrov, M & Vapirev, E I; 1996, "Uranium Industry in Bulgaria and Environment: Problems and Specific Features of the Period of the Technical Close-Out and Remediation of the Negative Consequences". In: Planning for environmental restoration of radioactively contaminated sites in central and eastern Europe, Vol. 2: Planning for environmental restoration of contaminated sites, IAEA-TECDOC-865, Vienna 1996, pages 43-52.
7 - Molchanov, A, Soroka, Y, Isayeva, N & Mordberg, E; 1995, "The State of Environment on Former Site of In-Situ Leaching of Uranium". In: Slate, S, Baker, R & Benda, G (Eds.), Proceedings of the Fifth International Conference on Radioactive Waste Management and Environmenttal Remediation, ICEM'95, Vol. 2 - Management of Low-Level Waste and Remediation of Contaminated Sites and Facilities, ASME, New York, 1995, pages 1507-1510.
8 - NRC Information Notice 97-58 : Mechanical Integrity of In-Situ Leach Injection Wells and Piping, July 31, 1997.
9 - Engelmann, W H, Phillips, P E, Tweeton, D R, Loest, K W & Nigbor, M T; 1982; "Restoration of Groundwater Quality Following Pilot-Scale Acidic In-Situ Uranium Leaching at Nine-Mile Lake Site Near Casper, Wyoming". In: Society of Petroleum Engineers Journal, June 1982, pages 382-398.
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