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Threlkeld Mines
Rivers Polluted by the Threlkeld Lead Mines
Environmental monitoring by the Environment Agency since 2010 shows that the mine water flowing out of the Woodend Low Level contains some of the highest metal concentrations in England. This mine water pollutes up to 25 km of rivers – in Gategill Beck, the rivers Glenderamackin, Greta and Derwent, all the way into Bassenthwaite Lake. Lower concentrations of metals are also washed out of the mine wastes found along the steep banks of Gategill Beck.
In Gategill Beck, the metal concentrations are so high that they cause severe harm to river wildlife like river insects and fish. At lower river flows, the zinc concentration measured in the beck below the Yellow Dam can be more than 2,500 times the safe level for river wildlife whilst cadmium can be more than 800 times the safe level.
The safe level for river wildlife is set by Government using “Environmental Quality Standards” (EQS) based on extensive ecotoxicological testing. The Environment Agency compares the results of water quality sampling with the EQS. If the measured concentration is higher than the EQS, then experts expect there to be harm to river wildlife and the river is legally considered to be polluted.
The Environment Agency’s monitoring over several years shows that removing metals from the mine water flowing out of the Threlkeld Lead Mines would significantly improve up to 25 km of river length. These water quality improvements would be seen within a few months of a treatment scheme starting to operate.
Unless action is taken, the pollution will continue for hundreds more years and so the WAMM Programme wants to build a mine water treatment scheme. Once built, the scheme would need to be operated indefinitely.
The Woodend Low Level (2010 to 2024) mine water typically contains (dissolved metals):
- Zinc = 37,000 μg/l
- Cadmium = 78 μg/l
- Nickel = 265 μg/l
- Lead =430 μg/l
- Iron = 3,800 μg/l
- pH = 3.6
- Flow = 6 litres per second
Although these are average values, the metal concentrations and flows do not vary very much with rainfall.