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Diffuse Metals

Abandoned metal mines cause significant pollution in England and harm fish and river insects. They contribute up to half of all the metals, like cadmium, lead, zinc and copper, found in our rivers, streams and lakes. Most mines closed more than 100 years ago but continue to pollute about 1,500km of rivers. These metals are one of the most widespread causes of chemical pollution in rivers.


The metals enter rivers from two main sources: 


“Point”: mine water draining from the abandoned mines; 

“Diffuse”: metals washed out of mine waste heaps (“spoil”) by rainfall, resuspension of contaminated sediments and erosion of river bank soils and direct inputs to groundwater.


In Weardale the impact of historic metal mining is still with us today. The North Pennine orefield was once a huge producer of lead and zinc ore. Mining, processing and smelting was carried out for over 200 years - mainly for lead, zinc and fluorspar along with small deposits of copper and iron. This has left a legacy of mine water drainage adits and spoil heaps throughout the area. On the Rookhope Burn the last working fluorspar mine in the north of England, at Grove Rake, closed in 1999. We are currently working to deliver diffuse metal controls in Middlehope and Killhope Burns. We must work in conjunction with Historic England as many of these areas are historically important. 


We also work with Natural England to protect nationally important ‘Calaminarian Grasslands’ which are a unique flora that has evolved to tolerate metal rich mine soils and floodplain deposits.


The most severe river pollution takes place under lower river flows when there is less dilution of point sources of mine water. However, most metals are transported down the river system at higher river flows and after heavy rainfall since more of the diffuse landscape sources are ‘activated’. Since climate change is causing intensive rainfall events to be more frequent, these diffuse sources of metals will become an increasingly important source of metals in rivers. The Water and Abandoned Metal Mines (WAMM) Programme was set up in 2011 by Defra, the Environment Agency and the Coal Authority to begin to clean up river pollution by abandoned metal mines. It has primarily focussed on mine water discharges since these require significant capital investment. Some diffuse pollution control measures have been implemented with Wear Rivers Trust. The trust maps, monitors, surveys and designs remediation schemes to reduce the input of metal contamination from historic mine sources in partnership with the EA and Coal Authority. The trusts approach is one of stakeholder and community engagement to prioritise and develop site specific approaches. We utilise a range of techniques to prevent mine spoil ingress to watercourses such as bank and spoil heap revetments using stone or large woody debris, leaky dams, installing silt traps and managing surface water drainage.

 

Actions to deal with this legacy of historic pollution will deliver the following benefits: 


Cleaner rivers for current and future generations, more wildlife for people to enjoy, more tourism and opportunities for industries which rely on clean water, writing the next chapter in the mining story.