Surface water management and encapsulation of mine waste to reduce water pollution from Frongoch Mine, Mid Wales

Abandoned metal mines are the principal cause of failure to achieve Water Framework Directive (WFD) standards in Wales, with 1,300 mines impacting over 100km of rivers. Frongoch was one of Wales' most productive lead mines during the 18th and 19th centuries, consequently becoming one of our most polluting abandoned mines. NRW received financial support from the European Regional Development Fund (ERDF) via the Welsh Government (WG) to implement a remediation scheme and reduce impacts. A stream was diverted in 2011 to prevent it flowing into mine workings that discharge via Frongoch Adit, reducing its metal load. A perimeter channel was created in 2013 to direct surface water away from spoil towards a new flood attenuation pond. Three hectares of mine waste were re-profiled and capped in 2015 to minimise water ingress and to convey clean runoff via drainage channels into a series of ponds, creating a new wetland habitat. Wide consultation at design stages ensured the remediation didn't adversely affect the mine's unique features or statutory designations. NRW engaged ecologists to enhance biodiversity and archaeologists to supervise construction. Although further monitoring is required, this project demonstrates how water quality improvements can be achieved with low ongoing maintenance, whilst providing local biodiversity and landscape benefits. The scheme will not achieve compliance with WFD in all recipient watercourses, but virtually all water from the mine is now controlled via one surface water and two groundwater discharges, one of which has reduced in volume by 80%. These discharges have flow gauging weirs, providing opportunity for ongoing research and development for institutions, innovators and regulators. This paper discusses the scheme, its achievements and opportunities going forward.