A pioneering pilot scale scheme to tackle mine water pollution at Cwm Rheidol mine is delivering excellent results, with metal removal rates as high as 99%, a year on from the project launch.

Work to improve water quality in the area began in September 2010 as part of a unique pilot scheme by Environment Agency Wales.

Cwm Rheidol mine, near Aberysywyth, Ceredigion has been abandoned for nearly a century, and is connected to several other mines, all of which drain into the Rheidol river. Historically this has led to large amounts of zinc and other metals entering the river, which is failing to meet the ‘good’ water quality standards required by the European Union’s Water Framework Directive.

Toxic metals stripped from water

As part of the process, toxic metals are stripped out of the mine water before it enters the River Rheidol, using an environmentally friendly method that requires no energy source apart from gravity. Results taken over the last year show removal rates of up to 99% for zinc, lead and cadmium.

The treatment system uses a mixture of waste products, including cockle shells and compost, to encourage natural biological and chemical processes that clean the mine water. Similar methods have been successfully used to remove iron from coal mine waters, but this is the first time the method has been used to remove zinc and other metals from abandoned metal mines, which are numerous in West Wales.

Paul Edwards, Environment Agency Wales said:

“Results from this innovative pilot scale scheme at Cwm Rheidol show that this is a viable process for treating mine water pollution that could prove beneficial to sites elsewhere in Wales in the future.

“If the scheme at Cwm Rheidol was implemented at full scale, it is estimated that up to 98 tonnes of harmful metals could be prevented from entering the River Rheidol each year. This could be instrumental in helping us achieve some of the challenging targets set by the Water Framework Directive in parts of Wales.”

The project is the result of a partnership with the Welsh Government, The Coal Authority and Newcastle University, with co-operation from Statkraft Ltd. It has also received financial support from the European Union under the Objective 1.

Further monitoring will allow better estimates of how much metal will be removed through the year, how the system can be managed to optimise long term performance, and how big a full-scale system will need to be.

The Water Framework Directive sets new and more challenging standards for Wales’ rivers and other water bodies to benefit people and wildlife, placing greater emphasis on the ecological status of the water environment.