Monitoring by the Environment Agency over many years shows that the mine water flowing out of the Sharnberry mine adit (the drainage tunnel built by the miners) is the most significant source of zinc and cadmium, releasing around 900kg of these harmful metals each year, and polluting 15km of the Euden Beck and Bedburn Beck (see Wear management catchment: baseline length of rivers and estuaries polluted by abandoned metal mines – GOV.UK).
The Sharnberry mine adit mine water contains very high levels of dissolved metals:
- Zinc: up to 2,800 μg/l (micrograms per litre or parts per billion)
- Lead: up to 400 µg/l
- Cadmium: up to 4.7 μg/l
The average flow from Sharnberry mine adit is 14 litres per second and ranges from 8 litres per second to more than 100 litres per second throughout the year.
The safe levels of metals for river wildlife are set by Government using “Environmental Quality Standards” which are based on extensive ecotoxicological testing. The Environment Agency compares the results of water quality sampling with the Environmental Quality Standards. If the measured concentration is higher than the Environmental Quality Standards, then river wildlife is expected to be harmed, and the river is legally considered to be polluted.
Just downstream of the Sharnberry mine adit, the metal concentrations are so high that they cause severe harm to river wildlife like river insects and fish. The highest metal concentrations are found at lower river flows when there is less dilution by clean rainfall.
The map below shows the rivers polluted by the Sharnberry mine.
