Case study:Gategill Beck: Abandoned Metal Mines
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Project overview
| 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 |
Project summary
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 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. • The mine discharges up to 18 tonnes of zinc, and 70 kg of cadmium each year. • At higher river flows, the spoil heaps contribute additional metal pollution. • Up to 16km of the River Glenderamackin, River Derwent and Bassenthwaite Lake fail the EQS for zinc and cadmium, and therefore fail to achieve Good Status.
We are working with the Coal Authority to identify the best way to clean up the pollution. Initial work has gathered information about how to capture the mine water, and during 2015 we will be reviewing suitable treatment technologies. The metal concentrations are so high that finding a passive system with low operating costs is difficult. The Coal Authority will also investigate potential locations for a treatment plant to be built. We will discuss the results of our recommended solution with local stakeholders. The estimated economic benefit of cleaning up the mine water pollution is £5.8m over 25 years.
There is another problem in Gategill Beck - flood risk. The Yellow Dam was created in the 1880’s to provide a water supply and power for mining activities. It consists of a wall and a culvert with mining spoil placed on top to create a dam across the beck. The dam has grown weaker with age and the culvert underneath has become defective. This means water builds up behind the dam after heavy rain, putting pressure on the structure and creating a small risk that it could collapse. If this happened, any water that had built up behind the dam could quickly flow downstream to flood local properties and part of the A66. The private owner of the dam is unable to resolve the issue so the Environment Agency is working with Cumbria County Council, Eden District Council, the Lake District National Park Authority and the Highways Agency to identify a solution. Work started in October 2014 to make the dam safe.
Mine water discharge summary • Length of watercourse affected: 16km • Average metal concentration: Zinc = ~37,500μg/l (up to 18tonnes/yr), Cadmium = 78μg/l (up to 69kg/yr), Lead = 470μg/l, Nickel = 270μg/l • Water body ecological status/potential: Moderate (River Glenderamackin, River Derwent)
Flow = 6 l/s
Magnitude of impact: • Zinc: up to 1,900 times EQS • Cadmium: up to 375 times EQS
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 16km of river (Glenderamackin, Derwent) • Local properties and infrastructure could be protected from a flooding and pollution event
Monitoring surveys and results
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