Mine Rehabilitation and Closure - are you getting the basics right?

Found in: News

In this four part series, Katina De Sousa, Astron’s Rehabilitation Principal Scientist discusses the importance of getting the basics of rehabilitation right. Katina comes from a strong mining background with 10 years’ experience working in the gold mining industry of Western Australia during which she prepared Mine Closure Plans for both large, long mine life (>20 years) operations like Boddington and KCGM; and short mine life operations (

We hope you enjoy Part 1 of the series!

 

Part 1 – Why is that rock turning yellow? The importance of understanding your site.

The Department of Mines and Petroleum have recently released an updated version of the guiding document for closure of mine sites in Western Australia, the Guidelines for Preparing Mine Closure Plans. Given the release of the updated guidance, Katina provides some timely advice to clients on what is required to achieve rehabilitation success.

At all stages of planning for and implementing mine closure it is important to think about whether your team is getting the basics of rehabilitation right, because history has shown that the consequences of getting it wrong can be very costly. Toy and Daniels (1998) break the rehabilitation process into 10 sequential steps:

  1. Site characterisation
  2. Rehabilitation planning 
  3. Material management
  4. Topographic reconstruction
  5. Replacement of topsoil or and soil reconstruction
  6. Surface manipulation
  7. Addition of soil amendments
  8. Revegetation
  9. Irrigation 
  10. Site monitoring and maintenance. 

Each of these steps presents a potential risk to successful rehabilitation and closure of a mine site and needs to be given appropriate consideration based on the specific aspects encountered at the site. Consideration should also be given to the Department of Mines and Petroleum’s principal closure objectives for rehabilitated mines to be “(physically) safe to humans and animals, (geo-technically) stable, (geo-chemically) non-polluting/non-contaminating, and capable for sustaining an agreed post-mining land use” (DMP and EPA 2015).

In this article on the rehabilitation process, the importance of site characterisation is discussed.

The physical and chemical properties of a disturbed area within a particular environmental setting profoundly influence rehabilitation planning, practice and the probability of success (Toy and Daniels 1998). Successful rehabilitation depends on our understanding of critical site-specific conditions and implementation of the best techniques for reconstructing them for a particular land use. Site characterisation usually involves analyses of climate, geology, topography, soils, vegetation and hydrology.

A key area of site characterisation is the physical and geochemical properties of the materials to be mined, particularly the waste materials that will be left behind. Acidic drainage is the largest environmental liability facing the mining industry (MEND 2015). In Australia, generation of acidic runoff due to poor management of acid forming material has resulted in ongoing post-closure treatment costs at numerous mine sites, including Mt Morgan in Queensland and Brukunga in South Australia. At the AMEC Mining and Environment Conference held in Perth in 2015, David Gillinder from the Department of Natural Resources and Mines reported that it is costing the Queensland government $2.6 million per year to run the water treatment plant at Mt Morgan to prevent the open pit, which is filled with water with a pH of 3.2, from overtopping and impacting the Dee River. A number of publications are available documenting acid and/or metalliferous drainage prediction, prevention and remediation, including:

• the industry-funded Global Acid Rock Drainage (GARD) Guide 
• the comprehensive Mine Environment Neutral Drainage (MEND) prediction manual for the drainage chemistry from sulfidic geological materials
Managing Acid and Metalliferous Drainage from the Australian Government Leading Practice Sustainable Development series 

For rehabilitation, another key area of site characterisation is understanding the vegetation that is going to be disturbed by mining and is found in the surrounding area. Monitoring of appropriate analogue sites provides information to guide rehabilitation of the site, such as what species need to be included in seed mixes, what the target ecosystem may be for rehabilitation of different types of disturbance and recalcitrant species that could pose problems for return in rehabilitation.

Stayed tuned for Part 2 – Where has all the topsoil gone? - where the role of rehabilitation planning and material management in the rehabilitation process are discussed.

     

   Formation of AMD at a stockpile                   Formation of AMD at a waste rock dump

 

References

Department of Mines and Petroleum and Environmental Protection Authority 2015, Guidelines for Preparing Mine Closure Plans, DMP & EPA, Perth.

MEND 2015, Mine Environment Neutral Drainage, http://mend-nedem.org/default/

Toy, TJ and Daniels, WL 1998, ‘Reclamation of disturbed lands’, in RA Meyers (ed) Encyclopedia of Environmental Analysis and Remediation, Wiley, New York.

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