Quarry Nov 2020

Page 46

ENVIRONMENT

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.

A

n 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 46

Quarry November 2020

Figure 1. Map of abandoned mines and quarries ranked from low to high level of suitability for flood retention.

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