Case study:Gategill Beck: Abandoned Metal Mines

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Project overview

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Status	In progress
Project web site
Themes	Environmental flows and water resources, Habitat and biodiversity, Monitoring, Water quality
Country	England
Main contact forename	Hugh
Main contact surname	Potter
Main contact user ID
Contact organisation	Environment Agency
Contact organisation web site
Partner organisations	The Coal Authority (UK)
Parent multi-site project
This is a parent project encompassing the following projects	No

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Project summary

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The Threlkeld mine was worked for lead and zinc between 1661 and 1928. The mine has a long history of causing pollution and fish kills, and the owners were first prosecuted in 1890. The mine is a significant source of heavy metal pollution, particularly cadmium and zinc, in Gategill Beck and the River Glenderamackin, which fails to achieve 'Good' status for the Water Framework Directive. The metal pollution also affects the River Derwent and Bassenthwaite Lake Special Area of Conservation (SAC) and Site of Special Scientific Interest (SSSI). The main source of metals is the Woodend Low Level but there is also diffuse pollution from waste spoil heaps. Until March 2011, the Woodend Low Level drainage tunnel was partially blocked and mine water had built-up behind the entrance. We have now cleared this blockage to prevent an uncontrolled breakout that might have caused a significant pollution incident.

In 2010, we investigated the impacts from the mine with funding from Defra. Our monitoring confirmed that the Woodend Low Level is one of the most polluting mine waters in the UK. In April 2012 we started more detailed monitoring of pollution from the mine using new funding from Defra. To help us, the Coal Authority installed a weir at the Woodend Low Level so we can measure the flow more accurately. We have also built three temporary weirs in Gategill Beck to work out how much pollution comes from the spoil heaps. We are collecting samples monthly for a year to confirm the pollution caused by the mine. We will then work with the Coal Authority to identify what can be done to clean up the pollution.

Key findings from the 2010 monitoring and the initial 2012 data are: • Immediately downstream of the mine, metal concentrations in Gategill Beck are up to 1900 times the zinc environmental quality standard (EQS: 8 μg/l) and 375 times the cadmium EQS (0.08 μg/l). Even after dilution in the River Glenderamackin, two kilometres downstream, the zinc and cadmium concentrations are still up to 40 and 8 times the EQS respectively. • Zinc and cadmium concentrations in the River Glenderamackin upstream of the confluence with Gategill Beck are almost always below the EQS. Copper is slightly above the EQS. • At the Threlkeld flow gauging station on the River Glenderamackin, the average zinc loading from Gategill Beck is 8 tonnes per year, plus 24 kg/yr cadmium. At higher flows, this increases to 18 t/yr zinc and 69 kg/yr cadmium. • Metal concentrations and flow from the Woodend Low Level do not significantly change, so the increased metal loading measured in the river at high flow is probably due to diffuse inputs from spoil heaps and re-suspension of contaminated sediments.

There is another problem in Gategill Beck. Two dams that were built in the stream to provide water for the mine are thought to be unstable. There is a high risk that culverts beneath them could collapse or be blocked up by trees or other debris during high flows. This could lead to the dams collapsing or flooding, which may affect properties and the A66 trunk road. In June 2012 a storm event caused a land slip at the top of Yellow Dam, and destabilised banks of the watercourse immediately downstream.

Impact of the mine • Length of watercourse affected: 16 km • Average metal concentration: Zinc = 39,820 μg/l, Cadmium = 79 μg/l, Lead = 441 μg/l, Nickel = 283 μg/l • Load of zinc discharged per annum: up to 18 tonnes • Load of cadmium discharged per annum: up to 69 kg • Water body ecological status/potential: Moderate (River Glenderamackin, River Derwent)

Benefits of remediation • Bassenthwaite Lake SSSI would be protected from a major pollution source • The river corridor in a Special Area of Conservation would be improved • Ecological improvements would be made to up to 16 km of river (Glenderamackin, Derwent) • 18 tonnes of zinc and 69 kg of cadmium would be prevented from entering the river • The estimated economic benefit of achieving Good Ecological Potential in the River Glenderamackin downstream of the mine is approximately £1.9 million over 25 years, with a further £1.6 million benefit from improving the River Derwent (upstream of Bassenthwaite Lake) • Local properties and infrastructure could be protected from a significant flooding and pollution event • Partnerships with the local community, Eden District Council, Natural England and the National Park could be developed. The Environment Agency is working with the Coal Authority to clean up pollution from abandoned metal mines to deliver a cleaner water environment with funding from Defra.

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