Rivers across Devon and Cornwall are being polluted by abandoned metal mines

The Environment Agency says abandoned mine waste sites are causing serious environmental harm across the region.

Rivers across Devon and Cornwall are being polluted by metals from abandoned mines, monitoring from the Environment Agency shows.

A map from the Environment Agency shows all of the river catchments in both counties that are polluted by at least one metal due to the abandoned metal mines, which have water discharges all over the region.

The metal pollutants affecting about 500km of rivers include cadmium, lead, zinc, copper, nickel, arsenic and iron.

Rivers affected by the metal pollutants are marked in purple.

In this part of the UK, the Water and Abandoned Metal Mines programme manages the Wheal Jane mine water treatment scheme in Cornwall to limit the amount of metals entering watercourses. Wheal Jane is labelled and its approximate location is shown as a green circle, while known mine water discharges are shown as a black cross inside a red circle.

An existing measure to deal with pollution from metal mines is at the former Wheal Jane tin mine.

This was implemented after an uncontrolled release of an estimated 50,000 cubic metres of acidic metal-rich water over a 24-hour period in 1992, which caused significant pollution of the Carnon River and Fal Estuary.

Black triangles show abandoned mine waste sites that are causing serious environmental harm.

In the Fal catchment, a significant source of pollution is the Coombe Adit, an abandoned mine water drainage tunnel that pollutes about 14km of the Coombe Stream, Gwindra Stream and River Fal with zinc, copper and/or cadmium. The Coombe Adit discharges into the Coombe Stream, approximately 800m east of the village of Coombe and 5km to the west of St Austell.

Although the water is discharging from a former tin and copper mine, it also contains high levels of other naturally occurring metals, such as iron and manganese, although these do not cause significant river pollution.

When mine water is released into a river, the iron that is present in the water settles on the bed of the river causing orange staining. Treating the Coombe Adit mine water discharge will significantly improve water quality in 14km of rivers for people and wildlife, and help to achieve the ‘good status’ target in the South West River Basin Management Plan.

The mine water treatment method

An innovative treatment technology which will remove the metals from the Coombe Adit discharge is currently being trialled.

This technology, known as a vertical flow reactor (VFR), was developed by Cardiff University.

The mine water passes down through a bed of gravel that encourages the iron and manganese in the water to precipitate out and coat the gravel with iron hydroxide, also known as ochre. This coating is very effective at capturing the cadmium, copper and zinc in the mine water.

As this is a new technology, a small scheme that will only treat a portion of the full mine water flow is being trialled.

This pilot treatment scheme will provide useful information about the technology, which has a relatively small footprint when compared to alternative methods of treatment, and will allow the Environment Agency to develop a full-scale scheme for the discharge over time.

This is a completely passive treatment technology which means the agency do not have to add any chemicals or use power to operate the scheme.

Planning permission for the pilot mine water treatment scheme was granted by Cornwall County Council in February 2020.

Source:  Cornwall Live 22nd December 2020