Commonwealth of Australia 2010
Practical measures to protect wildlife at gold mines
Download 2.29 Mb.
|
- Navigate this page:
- 89.Species differences in bird behaviour
- 89.1.1Reducing the attractiveness of facilities to wildlife
- 89.1.2Using a combined approach of controlling CN concentrations and minimising exposure
88.3Practical measures to protect wildlife at gold mines88.3.1Limiting access and the use of hazing techniquesVarious strategies can be used to minimise exposure of wildlife to tailings and other process and waste solutions in TSFs and associated infrastructure as a means of reducing risks to wildlife health from cyanide in those solutions. However, there are various considerations in determining appropriate measures at a particular site, and there are difficulties with some approaches which may limit their usefulness or practicability, as discussed below. Most TSFs in Australia are not fenced or netted off to exclude wildlife. Netting an entire TSF would generally be impracticable because of their large size (Section 5.2.2), but netting of decant ponds is done in some cases (e.g. where WAD CN levels are known to be high), and netting of other limited areas may be practicable (e.g. a netting structure is used to protect the supernatant area on the TSF at Gidji Roaster in WA: Environment Australia, 1998; KCGM, 2005). Similarly, the strategies of covering ponds or floating a dense bed of plastic, hollow balls on the surface to reduce access by birds may not be feasible for large areas, or where high evaporation rates are desirable (Read, 1999). Read (1999) also observed that because many long-distance waterfowl movements occurred at night, any non-illuminated structures, such as cables or netting, are unlikely to be efficient deterrents and may in fact themselves cause injuries. Hence these additional measures may also be needed (e.g. additional flagging tape and a strobe light have been installed to deter birds from landing on the bird netting at night at Gidji Roaster: KCGM, 2005). Most wildlife hazing techniques practiced at mine sites (e.g. loud noises from propane gas guns, shotguns, bird whalers, and music, movement from coloured streamers, flags, flying kites, flagging tape, fishing line) are ineffective at deterring wildlife in the long term or are impractical, and are also ineffective once wildlife are exposed to the toxic solutions (Donato, 2002; USFWS, 2000; Eisler et al., 1999; Ramirez, 1999; Read, 1999; Donato, 1999; Donato et al., 2007). A major difficulty is the sheer size of the area that needs to be protected. While these techniques may have some value for small areas such as a decant dam, their impact is much too localised for them to work on a TSF that may be equivalent to several football fields or more in size (Donato, pers. comm., 2006). Donato (pers. comm., 2006) explains that many of the hazing techniques described, although intended as preventative measures, have traditionally been implemented as contingencies in much of the industry. Thus, an increase in hazing effort is usually triggered by incidences. Subsequent studies suggest that some hazing techniques may have increased effectiveness as a proactive measure when combined with a reduction in suitable habitat area, thereby reducing the spatial scale over which hazing needs to be effective.
Ducks, coots and grebes habitually retreat to water when threatened by predators (e.g. wedge-tailed and little eagles and peregrine falcon, which had been observed taking waterfowl disturbed from the Olympic Dam ponds during the day), hence even if the waterfowl were coerced to leave a toxic waterbody during the day, they would often retreat to the safety of the water after a short flight. Read (1999) therefore proposed that a deterrent to waterfowl should operate at night. Tests with various sound and light deterrents at night indicated that a bright, focused searchlight beam held close to the water was most effective at scaring the majority of waterbirds from the ponds. It was considered that this light should be intermittent, as continuous light may attract birds, or insects which may themselves attract birds, and to avoid habituation. A floating, solar-powered, rotating beacon was found to reduce total waterfowl abundance by more than 90% during trials, but with some interspecific differences, such as grebes, which dived under the water when the searchlight was activated, or masked lapwings, black-fronted dotterels and red-necked avocets, which were neither attracted nor deterred. These differences illustrate the need for multiple measures to deter all species. For example, Read (1999) suggested that an underwater sonic alarm could be added to deter grebes. 89.1.1Reducing the attractiveness of facilities to wildlifeThe above and various other measures are described in publications or papers such as Adams et al.. (2008b), Donato (1999, 2002, 2005), Donato et al. (2004, 2007), Donato and Smith (2007), Smith and Donato (2007); NTDME (1998), and Read (1999). They need to be considered on a site specific basis and for some measures, with a knowledge of the species present. Read (1999) indicated the need for a multifaceted site-specific management approach to deter or prevent birds from accessing areas containing cyanide residues and listed the following additional measures which can be considered together with those discussed above:
Adams et al.. (2008b), Donato (1999, 2002, 2005), Donato et al. (2004, 2007), Donato and Smith (2007), Smith and Donato (2007); and NTDME (1998) elaborate on such strategies and make various other suggestions on managing and designing TSFs so they are not attractive as refuges or for nesting or settling to feed or drink. These include avoiding the formation of islands (favoured roosting sites) and pools against the walls (habitat for waders and drinking access for granivorous birds), placing decant ponds near mining infrastructure, lining dam or pond walls with black plastic, using steep sides (so birds feel unsafe because their sightlines are impaired), removing vegetation so that no nearby roosting trees are available, and removing dead animals promptly so they do not attract predators. The area and duration of ponding of water to which birds might be attracted and/or exposed can be minimised by strategies such as the use of thickened slurry or paste discharge to minimise the volume of water discharged with tailings, actively decanting supernatant water to netted or screened ponds, use of a Central Tailings Discharge design, using multiple cells and limiting cell size in paddock facilities, and managing discharge from multiple spigots (see Section 5.2.2). It is clear that measures which may be practicable and effective at one site may not be at another, and measures need to be compatible with modern large scale operations. There are aspects peculiar to certain situations that may also be relevant, e.g. it has been thoroughly demonstrated that a higher concentration of WAD CN in hypersaline tailings water can be tolerated because birds do not drink it, together with other aspects of hypersaline sites that minimise food availability and make the habitat unattractive (Section 59.1.2). Salinity may provide partial protection, but cannot be considered reliable. Clearly, if hypersalinity/salinity is relied upon as a means of minimising exposure, it is important to monitor waters for salinity levels to ensure they remain hypersaline. Tailings pH and Cu levels affect the rate of volatilisation of HCN (Section 23.6.4). Adams et al.. (2008b) made specific recommendations (below) for monitoring and managing the sites examined in their study which would need to be adapted as necessary to suit other sites:
Eisler et al. (1999) indicated that some chemical repellents when added to dump leachate pond water showed promise at reducing consumption of leachate water when tested on European starlings (citing *Clark and Shah 1993). However, this approach appears not to have been taken up, possibly because it is not successful with other species and/or because of the costs of maintaining an adequate concentration of the repellent. 89.1.2Using a combined approach of controlling CN concentrations and minimising exposureAs discussed above as well as Sections 27.3.1 and 10.2.2, control of the concentration of WAD CN present in tailings waters is not the only means available for mitigating the risk presented by TSFs and associated facilities. Other measures which could be taken include hazing techniques to actively deter wildlife, reducing or preventing access by birds and mammals to the contaminated water, and designing and operating facilities in such a way that they do not attract wildlife. The latter is particularly relevant to flying species (birds and bats), though some of the measures listed below would also reduce attractiveness to terrestrial animals. For terrestrial animals, fencing to prevent access is likely to be a practicable and effective option that also reduces the risk of animals being harmed by becoming bogged. Wildlife deterrent or hazing techniques such as loud noises from scare guns, lights and flagging are ineffective and/or impractical at deterring wildlife in the long term because of habituation, species differences in response, the sheer size of the areas that may need protection, as well as difficulties gaining access close to critical areas in a large TSF. However, hazing techniques may have increased effectiveness as a proactive measure when combined with other measures, such as a reduction in suitable habitat area. Hazing techniques may also be of value as short term reactive techniques in response to monitoring. The use of chemical repellents has been considered, but has evidently been found insufficiently effective and/or impracticable. Measures to inhibit or prevent access include fencing to keep out emus, livestock and marsupials, netting ponded areas or covering them with floating balls or other means to reduce access or exclude birds and bats, and minimising or avoiding pond formation in the first place. Practical considerations and the scale of the area needing protection determine what may be effective and affordable, e.g. netting of decant ponds may be practicable, whereas netting of an entire 50 ha or larger TSF would not, and reduced evaporation may be a problem if ponds are covered or enclosed. Strategies in managing and designing TSFs so they are not attractive to wildlife (specifically birds) as refuges, for nesting or for settling to feed or drink include:
The use of thickened slurry or paste discharge minimises the volume of water discharged with tailings so that less ponding or flowing water occurs on the TSF. Appropriate design and operation (e.g. a Central Tailings Discharge, or multiple cells and controlled discharge from multiple spigots in paddock facilities) can enable the area of surface water forming to be restricted and controlled, and/or water to be directed to smaller, deeper ponds where it can be netted or screened. A complementary measure to reducing the attractiveness of areas where cyanide presents a risk to wildlife is to provide alternative safe areas to attract birds away from toxic ponds, but care may be needed so numbers attracted to the overall area are not exacerbated. Concentration control is not a feasible option for heap leach facilities, as the solutions applied must contain effective levels to recover the gold. For tank leach facilities (the predominant situation in Australia), various processes to detoxify or recover cyanide in tailings streams are available (Section Error: Reference source not found). These enable mines to reduce WAD CN concentrations to levels comparable to those specified by the ICMC (50 mg WAD CN/L) or lower levels currently specified at some sites (e.g. 20-30 mg WAD CN/L at Lake Cowal in NSW). Some of these techniques also enable concentrations to be reduced to very low levels to protect downstream aquatic environments, e.g. ~1 mg WAD CN/L in Tasmania. However, a requirement to achieve this level of CN destruction in tailings discharge to protect birds and mammals appears unlikely to be generally practicable at present. Field observations indicate that few mortalities are likely to occur provided the WAD CN concentration remains satisfactorily below 50 mg/L, but some lethal and sublethal impacts may still be expected based on studies conducted with birds exposed to water containing cyanide in a fashion reasonably representative of field exposure (Section 66.1.2). The environmental implications presented by the volumes of various reagents that would be required to drive WAD CN concentrations to low levels and the relatively high concentrations of cyanide degradation products (e.g. thiocyanate) and reagent products that could be produced may also need to be considered if such extensive treatment were required. Depending on the ore characteristics and method used, destroying remaining WAD CN may also become more difficult with decreasing concentration (Schulz, pers. comm. 2006). For these reasons, concentration control is not likely to be a practicable mitigation measure at the concentrations that would be needed to assure safety to wildlife if it were the only measure used. This has been recognised by the industry in development of the ICMC, and suitable guidance information has been prepared, as discussed in Section 27.3.1 and above. From evaluation of the available information, it is concluded that a combination of site specific exposure limitation measures, including access limitation, habitat modification and the use of deterrents should be applied, together with a practicable concentration-based approach to help minimise the risk to wildlife where exposure does occur. As part of such an approach, suitable monitoring and response programs are essential, including monitoring of cyanide concentrations in water accessible to wildlife, monitoring to ensure netting or other exclusion methods remain sound, monitoring for the presence of wildlife and impacts on wildlife, and monitoring to look for the development of habitat attractive to wildlife (the emphasis being on habitats attractive to birds) on or near TSFs. Active measures could then be applied, including hazing to deter birds while a hazard is present, and correction of conditions creating higher concentrations of cyanide. This risk control framework and supporting information is discussed in much greater depth in the recommendations from this assessment.
Directory: data -> assets -> word doc -> 0017 0017 -> National Industrial Chemicals Notification and Assessment Scheme word doc -> Priority Existing Chemical word doc -> Rail safety news issue 6 – October 2011 word doc -> Review of Multiple Chemical Sensitivity: Identifying 0017 -> Rail Safety News Edition 8, December 2012 0017 -> Real-Time License Plate Localisation on fpga 0017 -> Careers network bulletin issue 6 July 16 2012 0017 -> Wiser science: Finding References inspec for Physics and Engineering 0017 -> Part A: Depth Study: The globalising world Popular culture and public policy Download 2.29 Mb. Share with your friends:
|