Marine and lake disposal of mine tailings and waste rock

International Conference in Egersund, Norway, September 7-10, 2009. Conference summary by Jens Skei, Gert Asmund, Poul Johansen and Jens Søndergaard. 2nd November 2009

Executive summary

This conference addressed disposal of mine tailings and waste rock in lakes and in the sea, which has previously taken place at several mine sites around the world, and still do. Operating-, closed- and planned mines in Norway, Greenland, Indonesia, Canada, and Papua New Guinea were described in three key notes papers and 22 technical papers. Cases with both satisfactory and unsatisfactory environmental impacts were presented. Many papers focused on methods to predict the environmental effects of mine waste disposal in fresh and marine water. Based on the conclusions, it seems that there now exists reliable methods to determine the environmental effect of mine waste disposal in lakes and in the sea, thus making it possible for decision-makers to decide whether a given mine waste disposal project is acceptable. At the end of the conference, the participants listed several important conclusions as well as cases where more research is needed and where better practice should be conducted.

Introduction

The objective of the conference was to gather specialists from the mining sector and the scientific and regulatory communities to present and discuss advantages and disadvantages of placing mine tailings and waste rock in the sea or in lakes. What criteria should be used if we are, for example, to create stable submerged deposits and minimize the risk of extensive smothering of the sea bed, the risk of uncontrolled dispersal of fines and the risk of release of contaminants? What baseline studies are needed?

Many countries are experiencing an increasing interest in exploring for and exploiting minerals. But in mining projects a main challenge is to manage mine tailings and waste rock in a manner that will be environmentally acceptable and work essentially in perpetuity. Often, land-based solutions have been preferred, but these may require maintenance for unpredictable time periods after mine closure, and several instances of dam failure illustrate that land-based disposal can be problematic. Submarine or lacustrine disposal of waste may in some cases offer better opportunities to secure long-term solutions.

The conference was attended by 58 scientists, regulators and people from the industry (see the list of participants in Annex 1). At the conference information related to operating, closed and planned mines in Norway, Greenland, Indonesia, Canada, and Papua New Guinea was described by 3 key notes papers and in 22 technical presentations. Cases included both positive and negative experiences regarding environmental impact. Many papers focused on methods to predict the environmental effects of mine waste disposal in fresh and marine water. It seems that there now exists reliable methods to predict the environmental effect of mine waste disposal in lakes and in the sea, thus making it possible for decision makers to decide whether a given mine waste disposal project is acceptable.

The conference program is given as Annex 2. Here also the list sponsors of the conference is attached.

The speakers kindly offered to have their presentations published with this report. The presentations can be found in Annex 3. Summaries of most of the presentations are also available (see Annex 4).

At the end of the conference, the participants discussed what could be concluded and recommended from the presentations. These conclusions are listed in the following section. It should be noted that the authors of this report take full responsibility for the report including the section about conclusions and recommendations.

Conclusion and recommendations (“Take home messages”)

1. Environmental evaluation of different waste management strategies is important. A thorough site-specific environmental evaluation of all options for disposal of tailings and waste rock is important – not two mine projects, sites, or mine-ores are exactly the same. What is the state of the ecosystem? What can be impacted? The extended Goklany concept (see Derek Ellis’s presentation) may be used as a tool in that process.

2. Good baseline studies prior to disposal of mine waste are essential and should be considered an investment by the mining company when planning the project (included in the project costs). Studies should be able not only to assess the state of the ecosystem but also the seasonal and annual variability of the system (preferable 2-3 years data). When determining the state of a fish population it is important not to rely solely on catch statistics (for several reasons the numbers reported by fishermen are not always correct) but also include on-site counting statistics. Night-time observations are rarely included but are often needed to get an understanding of the system (e.g. some species may only be present at a specific location during night-time). Archiving of samples and data in an accessible way is important and may be valuable for the mining company to assess future impacts.

3. Environmental impact assessments (EIA’s) should be of highest quality, especially if sensitive areas are considered (e.g. high-biodiversity areas, spawning areas, threatened species, and species of great importance). The sensitive areas have to be defined. What are the gains vs. costs? Socio-economical studies should also be considered in the EIA. Documentation as well as good stakeholder dialog and transparency are important for both the mining company and the public in the EIA process. High quality EIA’s are important: 1) as a background for advisers (competent hearing institutions); 2) as background for the managers – decision makers; 3) to help politicians make the decisions they really want; and 4) to obtain legitimacy in the population and among other stakeholders.

4. Detailed scientific investigations including chemical characterization of tailings and waste rock as well as studies of reactions within a tailings/water interface, simulating site-specific conditions as well as possible, are needed prior to deciding upon submarine tailings or lake disposal. Site-specific studies of any process (chemical/physical/biological), which may have an impact on the mobilization, transport, and accumulation of contaminants related to the tailings/waste rock in the recipient ecosystem, is important. This includes an understanding of the natural processes in the recipient. Near shore disposal of waste rock should be managed properly. Presented cases of previous dumping of mine waste in tidal zones or in shallow water near high-energy beaches clearly illustrate that this should be avoided, particularly if sulfidic waste rocks or tailings are being dumped.

5. Seabeds affected by tailings disposal often ’recover’ within 1-10 years after closure (Maarmorilik, Greenland > 15 years) depending on tailings composition, deposition rate and toxicity potential. However, the definition of ‘recovery’ is also not clear and can be debated (benthos reappears, but species and biodiversity are often changed). A ‘sustainable ecological succession’ was mentioned in the discussions as a possible definition. It also has to be noted that not all ecological changes may be negative and some may even have a positive effect on the ecosystem. However, quantifications of ecological effects are difficult and both local and regional ecosystem effects should be considered. More studies of the recovery dynamics including more detailed investigations of the benthos in these ‘recovered’ states (e.g. the concentration of contaminants in tissues of benthos and the composition of species) are required. It has to be noted that even in deep sea areas, it is possible to obtain good quality monitoring data e.g. using remote vehicles for underwater camera-transects. In addition to recovery dynamics there is a need for more studies of the linkage between ecosystem effects – How does a local ecosystem impact affect the regional ecosystem? Last, it was commented that the impact of the seabed should be considered relative to the impact of the land in the mining areas, where large forest areas are typically cut to allow building of roads, building etc.

6. There is no consensus on the water quality standards to be used as criteria for waste disposal and local water quality standards tend to vary a lot (within approximately a factor of 10). As a proxy for the environmental impact of metals, it is better to use the ‘dissolved’ fraction (filtered water samples) rather than the total fraction (unfiltered samples). As an improvement to that, it would be preferable if an indirect measure of the bioavailable fraction of metals was measured (e.g. using diffusive gels). In practice, this is difficult and time-consuming, but has to be considered in order to get a more thorough understanding of the potential biological impact (the possible demand for the bioavailable fraction measurements has to be driven by the science community).

7. Disposal of all chemicals (flotation agents etc.) should be considered carefully and should be subject to toxicity tests before submarine disposal. The Oslo-Paris (OSPAR) convention must be considered. Waste minimization and alternative useful application of waste products should be in focus and environmental evaluation of different waste management strategies should be investigated.

8. Waste minimization should be in focus. More research should be directed towards reuse of mine waste instead of disposal. (i.e. capping material for contaminated sediments.)

The conclusions and recommendations are based on discussion after the individual presentations, on reviews made by small groups of each presentation, and on a discussion session at the end of the conference.

 

Annex 1
List of participants
 

 

 
Annex 2
Programme
 

 

 
Annex 3
The PowerPoint
presentations as pdf files
   
 
 

 

Annex 4
Abstracts
 

 

 
Annex 5
2nd announcement of conference
 

 

 


 

Sist oppdatert 27.02.2015