Reducing water pollution from historic metal mines across Wales

Groundwater and river pollution originating from abandoned metal mines is a global problem but remediating historical mine sites is typically complex and expensive, especially in ecologically sensitive areas. We have worked to overcome these challenges using a science-based, innovation-focussed approach to treating mine water.

Our work is part of the Welsh Metal (Non-Coal) Mine Programme, implemented by Natural Resources Wales (NRW) and the Coal Authority, and funded by Welsh Government. This aims to minimise the impact of 129 historical metal mine priority sites in Wales – a major step in tackling approximately 1,300 known sites which currently cause around 700 km of Welsh rivers to fail to achieve ‘Good’ Water Framework Directive (WFD) status.

Zinc pollution at Abbey Consols

The River Teifi in Ceredigion, mid Wales, is one such river. It suffers zinc pollution from the former Abbey Consols lead and zinc mine on the edge of the Cambrian Mountains. With a history stretching back to at least the 12th century, the mine was closely linked to the nearby Strata Florida Abbey, one of Wales’ most important historical locations. 

Active mining at Abbey Consols ceased around 100 years ago and since then water polluted with heavy metals has discharged from the partially flooded workings. Assessments showed that on average approximately 1,200 kg per year of dissolved zinc is released from the site into the River Teifi, resulting in WFD failure for at least 11 km. 

Natural Resources Wales chose Abbey Consols as a priority site – the first in its programme to be fully remediated, including a mine water treatment solution. The project also has to be delivered in line with the Well-being of Future Generation (Wales) Act (2015), which requires generation of additional benefits to the local communities and Welsh society. 

How could we come up with a solution that would not only remove the pollution, cost-effectively, but also be sustainable and which could transform the site into a valuable asset for the Welsh community? Challenges on this scale require collaboration between the academic sector and industry.

Close collaboration and fast-track research

We worked closely with Cardiff University – with whom we’ve collaborated for two decades on solutions to polluted mine waters. The process began with an innovation workshop, hosted by WSP, in which the team brainstormed potential solutions. We then moved rapidly through proof-of-concept in the laboratory and on to field-scale trials with support from specialist contractor Geochemic.

Following the laboratory and field trials, we were able – despite the challenges of working collaboratively during the Covid-19 pandemic – to identify an effective and efficient approach. This involves using an impermeable membrane to prevent further rainwater infiltration through mine waste and treating the discharging mine water using a combination of active dosing with sodium carbonate and passive settlement/filtration. In trials, this approach removed over 95% of dissolved zinc from the water.

The precipitate contains predominantly zinc carbonate, which is used in a range of industries and could ultimately be sold rather than disposed of – making this a potential zero-waste process. With the treatment lagoons and sand filters fed with mine water by gravity, the only power required is for dosing pumps and the sensors that control dosing. This low-level power demand will be met with solar PV, keeping the process carbon neutral. If waste CO2 can be used to manufacture the sodium carbonate for dosing, the water treatment could even become carbon negative. Our remediation design also creates habitats for rare lichens and bryophytes, creating a test site that is valuable for further academic research and is accessible from the Strata Florida visitor centre.

With construction underway at Abbey Consols, researchers from Cardiff University are continuing to examine how to optimise the process and whether the water chemistry at other sites around Wales will enable it to be used there too. NRW and Cardiff University presented the treatment approach at the 2021 International Mine Water Association conference and are firmly establishing Wales as an internationally leading centre of expertise for resolving environmental issues related to historical mining.