After visiting heritage sites in Wales, in a series of three articles Katina De Sousa (Astron’s Rehabilitation Principal Scientist) discusses whether we have anything to learn from historic mines. This second article focuses on the Dolaucothi gold mine located in central Wales.
Mining is known to have been occurring in Wales since the Bronze Age. At Dolaucothi the Romans began the first extensive mining between 70AD and 80AD. This included a large open pit mine and several adits (tunnels) to exploit the gold rich quartz veins. At this site, the Romans utilised technological advances and the resources they had at hand to mine the quartz veins. They constructed a network of aqueducts (leats) up to 11 kilometres long and large clay lined ponds (the size of an Olympic swimming pool) to bring water to the site for the purposes of:
- scouring away the vegetation and topsoil to reveal the quartz veins, and
- washing the crushed ore.
Once you know what you are looking at you can see evidence of the historic Roman mining everywhere – a large open pit, small pits, trenches and spoil tips. However, you have to get your eye in because at first glance there is nothing more to see than a hillside, undulating woodland and small hills. Even after the devastation that would have been caused by the Romans stripping the area of all vegetation and topsoil and the lack of active rehabilitation, over the years the site has naturally rehabilitated itself to woodland.
So what can we learn from the Romans…
Observing the natural regeneration at Dolaucothi and the way the Romans harnessed the environment made me think about how important it is that we consider the particular climatic and physical factors of a mine site when planning for rehabilitation and closure. The natural regeneration observed at Dolaucothi would have been significantly aided by the reliable, year round low intensity rainfall that is generally received in Wales. Unfortunately Western Australia (and particularly the Pilbara and Goldfields) experiences periodic, unreliable high intensity rainfall. This high intensity rainfall in combination with vegetation that is slow to establish often results in landforms that are unstable and ecosystems that are not sustainable.
In the Guidelines for Preparing Mine Closure Plans the objectives of the Department of Mines and Petroleum (DMP) and Environmental Protection Authority (EPA) for rehabilitated mines are specified. For the DMP the principal objectives are “for rehabilitated mines to be (physically) safe to humans and animals, (geo-technically) stable, (geo-chemically) non-polluting/non-contaminating, and capable of sustaining an agreed post-mining land use” (DMP and EPA 2015). The EPA’s objective is to “ensure that premises are decommissioned and rehabilitated in an ecologically sustainable manner”. To meet the closure objectives of the EPA and DMP we need to ensure that we consider the environment that we are working in. This can be done in several ways, including:
- Ensuring studies are conducted in the planning stage to ensure a good understanding of the environment.
- Using the information gained via studies to guide initial planning for rehabilitation and closure.
- Learning from the successes and failures of other sites with similar environmental conditions.
- Undertaking trials to try to identify alternative approaches which may achieve better outcomes.
- Incorporating findings from ongoing studies, trials and monitoring into refining rehabilitation and closure strategies.
- Utilising the available resources (such as topsoil and vegetation mulch) optimally. For example, a study by Alcoa (Koch et al 1996) found that for stockpiled topsoil, only 5% of the original seed was within 5 centimetres of the soil surface after rehabilitation compared to 14.7% for topsoil that was direct returned. To further maximise the benefit of the soil seedbank, Alcoa have also incorporated sieving of the topsoil to concentrate the seed which is then applied in a very thin layer to rehabilitation areas.
For those involved in the planning for rehabilitation and closure of mine sites, we need to think like the Romans and work out how to get the local environment to work for us.
The final article of this series will look at whether we have anything to learn from a World Heritage Site and the world’s fastest zip line.
Small open pit at Dolaucothi gold mine
Roman adit at Dolaucothi gold mine
Entrance to Roman adit at Dolaucothi gold mine
Koch, JM, Ward, SC, Grant, CD and Ainsworth, GL 1996, ‘Effects of Bauxite Mine Operations on Topsoil Seed Reserves in the Jarrah Forest of Western Australia’, Restoration Ecology, vol. 4, pp. 368-376.