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From pit to pit lakes: could abandoned sites be reborn?

 

It is believed that up to 90,000 extractive sites are located across Australia today. Academics from the Universities of Monash and Melbourne explain the potential for reviving these sites as vital assets for flood events, water retention and waste management.

An estimated total of 70,000 abandoned mine sites5 exist across Australia, lying among communities and giving rise to a myriad of social, health and environmental concerns.2 Most of these mines exist from Australia’s prosperous gold mining era, yet the impacts from these mines are still felt by communities today and are well-documented. Dust pollution and contamination of natural waterways are a few of the serious issues that surrounding communities face. However, options exist where areas can be revitalised while bringing value back to the mine.3 

Recent legislation around Australia has focused on the issue of progressive rehabilitation during an existing mine’s life cycle. However, it remains unclear what purpose these mines should serve at the end of their life. More specifically, what can we do with the thousands of abandoned mines and quarries littered across the country? 

POST-CLOSURE VALUE OPPORTUNITIES

The abandoned mines do not have to be a liability, instead they can become an asset if properly managed. Australia’s national policy for old mines recommends “valuing abandoned mines”. There are several options available for utilising old mines, eg: further mineral extraction via secondary mining such as reprocessing tailings; industrial archaeological heritage conservation and tourism; unique habitats for biodiversity enhancement; collaborative research into innovative solutions to contamination problems which could guide the broader industry; and indigenous and other employment and training opportunities for regional Australia.

The mine data used in this analysis was derived from various states’ databases. However, for the purpose of this piece, we focused on mine sites located within Victoria. This research contributes to the ongoing research project at the Department of Civil Engineering, Monash University that aims to create a national database for neglected mining occurrences.

Victoria’s rising population6 has led to urban fringe expansion and promotion of growth across regional cities and towns.7 This presents opportunities to repurpose abandoned mines and quarries located within these areas, giving them a second life. Around the world, abandoned mines have been rehabilitated and repurposed to support the local community. Case studies worldwide1 and in Victoria4 have demonstrated it to be entirely possible to repurpose mine sites to bring additional value at their end of operation. 

Our research analyses the multi-functional potential of rehabilitating mines and employs a multi-criteria decision analysis to determine feasible locations for alternative end uses, including storage for water supply, flood retention and municipal waste containment. This method of analysis enabled the ranking of sites based on the distinct weighting of conflicting criteria, highlighting the most to least feasible locations for rehabilitation for each respective end use. This research solely focused on mines and quarries that are abandoned but we recognise the opportunity to replicate the process across a wider selection of mines to assist the industry in identifying the most appropriate site-specific end uses. 

FLOOD RETENTION 

As populations continue to rise, increasing urbanisation alters the natural hydrologic cycle and we face more incidence of extreme and heavy rainfall events. Many communities in rural areas and along the urban fringes will face increasing flood risk. If an abandoned mine is located nearby, water can potentially be redirected to it, thereby providing storage and attenuation of flood waters, thus reducing the vulnerability of the catchment and affected regions downstream. Retention basins like these also provide additional benefits, such as increasing biodiversity conservation through the restoration and provision of natural areas.8

Past research on mapping flood vulnerability13 and guidelines for stormwater management14 were used to establish a criterion for the analysis. The criteria included population growth, flood accumulation, soil suitability, biodiversity levels, proximity to wetlands, and areas subject to inundation.

Through spatial analysis, which included hydrologic analysis, a score was calculated for each location and abandoned mine within Victoria, as shown in Figure 1. The score indicates the feasibility of rehabilitating a particular site into a flood retention basin, higher scores indicate a higher level of suitability and vice versa. 

The analysis highlights two clusters of abandoned mines most suitable for rehabilitation. One is north of Melbourne’s urban fringe, in Kilmore, and another is in northwestern Victoria. This is largely due to higher levels of population growth expected in Kilmore, and greater soil suitability in northwestern Victoria. Our analysis defines greater soil suitability as areas with sandy soils due its ability to infiltrate water faster. 

WATER SUPPLY STORAGE

Another use for abandoned mines is water supply storage. This will improve water security to the local community and provide a form of rehabilitation. Such an effort is currently underway in Atlanta, Georgia, USA where an abandoned granite quarry is currently being rehabilitated for water supply storage. The quarry receives water from a nearby water treatment plant roughly eight kilometres away and will extend Atlanta’s water supply from five days to 30 days. Additionally, the project also creates significant recreational space for the surrounding area, with the quarry being the centrepiece.10 

As with the mapping for flood retention, the same methodology was applied on the database of abandoned mines across Victoria. The criteria considered are the expected population growth, biodiversity levels, the sites’ proximity to historic groundwater pollution, future urban developments and existing water network infrastructure. 

Significant weight was applied to restoring damaged ecosystems and to expected population growth. Abandoned mines with higher scores are more desirable for this form of rehabilitation (Figure 2).

Even though the most desirable mine for water supply storage is located southwest of Kilmore, further investigation showed that it was too small to make any significant impact on the water supply, highlighting the importance of also considering site characteristics. The second most desirable mine exists southeast of Mount Eliza. It is located in the Moorooduc nature conservation reserve and has a potential maximum capacity of 665 megalitres (ML). Furthermore, the quarry is also situated 9.7km away from the Mount Martha Water Recycling Plant. This plant produces Class A recycled water and could potentially provide a stable supply of water to the proposed water supply storage. The rehabilitation of this quarry would also improve the damaged landform as well as add an aesthetic feature to the nature reserve.

Figure 2. Map of abandoned mines and quarries ranked from low to high level of suitability for water supply storage.

WASTE MANAGEMENT

Victoria’s growing population also causes greater demand for waste management facilities. Increasing urban sprawl creates challenging restrictions for the placement of municipal landfill facilities. Particular abandoned quarries and mines could present viable opportunities for additional waste disposal sites. The Victorian Environment Protection Authority’s publication for the “Siting, design, operation and rehabilitation of landfills”9 sets out a best practice for the entire landfill lifecycle. We examined Victoria’s abandoned mines and quarries using this framework to find suitable sites that meet the guidelines’ minimum safety requirements. Some of these included a minimum of 100 metres from all surface water, 500 metres from any building or structure and two metres separation from the groundwater table.

After establishing the suitable sites, each site was ranked based on forecasted population growth of the local municipality, existing site capacity and location-based strategic biodiversity (see Figure 3).

This analysis showed a particularly high ranking set of sites in the Kilmore region. These could be strong candidates for future landfill sites to service Greater Melbourne. As demonstrated in the water supply storage case, additional site-specific analyses would be required to ensure the long-term suitability and safety for landfill facilities, finer-scale data for which would need to be gathered. 

Figure 3. Map of abandoned mines and quarries ranked from low to high level of suitability for municipal waste management.

MOVING FORWARD

These three alternatives provide viable competing uses for abandoned quarries and mines. Not only do they transform debilitated and damaged land, they provide substantial future benefits to local communities. Notwithstanding, these are just a few of a myriad of potential end uses. Other options for rehabilitation have been undertaken including a research lab to find dark matter11 or luxury hotels12 among the variety of uses.15 

Mine site rehabilitation is a growing challenge that all states and territories will need to face in the foreseeable future. The right solution depends not only on the mine itself but also the community and opportunities around it. Our work has demonstrated a quantitative approach for how these opportunities can be ranked and compared in order for stakeholders to make better decisions about the rehabilitation of these sites. However, more research is needed to better understand how the potential end uses for these sites can be evaluated and if we can transform these sites into multi-functional spaces that can deliver a greater suite of ecosystem services for the benefit of local communities and the natural environment. Such suitable approaches would also lead to improvements in the current rehabilitation regulatory framework, would greatly reduce the impacts of mining operations and provide further clarity for future rehabilitation requirements and end use planning.

Innovative ideas and partnerships (government-industry-academia) and timely investment can give us the opportunity to create a positive legacy from which the extractive industry, community and government will all benefit. •

Melissa Truong, Han Chung Chia, Tom Richards, David Whittle, Mohan Yellishetty and Stuart Walsh are based at Resources Engineering, Monash University, Clayton, Victoria. Peter Bach is based at the School of Geography, University of Melbourne, Carlton, Victoria.

REFERENCES & FURTHER READING

1. Drake J. From mine to wine: Creative uses for holes in the ground. The Conversation, 16 September, 2011.

2. Bennett K. Abandoned mines – Environmental, social and economic challenges. In: Fourie AB, Tibbett M (eds). Proceedings of the 11th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth; pp. 241-252.

3. Senate Standing Committees on Environment and Communications, Parliament of Australia. 20 March, 2019. Rehabilitation of mining and resources projects as it relates to Commonwealth responsibilities. 

4. Harper L, Bennett A, Brewin R. After life of the mine: Lessons in how towns remake challenging sites. The Conversation, 17 December, 2018.

5. Werner TT, Bach PM, Yellishetty M, Amirpoorsaeed F, Walsh S, Miller A, et al. A geospatial database for effective mine rehabilitation in Australia. Minerals 2020;10, 745.

6. Department of Environment, Land, Water and Planning (Victoria). Victoria in future (Victoria’s future population projections).  

7. Department of Environment, Land, Water and Planning (Victoria). Melbourne 2030 – Planning for sustainable growth. 

8. Fehér J, Gáspár J, Tamás J, Mosný V, Muller R, Istenič D, Potokar A, Kardel I, Mioduszewski W (ed), Okruszko T (ed). Guidelines: Natural small water retention measures: Combining drought mitigation, flood protection, and biodiversity conservation. Global Water Partnership Central and Eastern Europe/World Meteorological Organization, 2015.

9. Environment Protection Authority Victoria. 788.3: Siting, design, operation and rehabilitation of landfills. 12 August, 2015.  

10. City of Atlanta Department of Watershed Management. https://h2o4atl.com/

11. Clausen L. Digging for dark matter. SBS Science.

12. The Tianma Pit Hotel, The Shimao Quarry Hotel, is incredible. China Underground, 11 November, 2017.

13. Feloni E, Mousadis I, Baltos E. Flood vulnerability assessment using a GIS‐based multi‐criteria approach — The case of Attica region. In: Journal of Flood Risk Management, Wiley Online Library, 23 August, 2019.

14. CSIRO Engineering. WSUD Engineering Procedures: Stormwater (e-book). June, 2015.

15. Pearman G. 101 Things to Do with a Hole in the Ground. Eden Project, 2009, Cornwall, UK.