Case study:Gategill Beck: Abandoned Metal Mines

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Location: 54° 37' 15.38" N, 3° 2' 44.44" W

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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

The Wood End low level adit

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.

Since 2010, we have been investigating the impacts from the mine with funding from Defra in partnership with the Coal Authority. Our monitoring confirms that the Woodend Low Level is one of the most polluting mine waters in the UK. Key findings from our monitoring are: • Immediately downstream of the mine, metal concentrations in Gategill Beck are up to 1,770 times the zinc environmental quality standard (EQS) and 525 times the cadmium EQS. Two km downstream, after dilution in the River Glenderamackin, zinc and cadmium are still up to 30 and 10 times the EQS respectively. • The mine discharges up to 29 tonnes of zinc, and 91 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, so fail to achieve Good Status.

We're working with the Coal Authority to identify the best way to clean up the pollution with funding from Defra. Initial work has gathered information about how to capture the mine water, and during 2016 we have been reviewing suitable treatment technologies. The minewaters at Gategill are challenging due to their low pH and high metal concentrations which are different from water treated by other full, pilot and laboratory based passive systems in the UK. Passive treatment is still the preferred option but pilot testing may be required and operating costs may be higher than for other passive schemes. The Coal Authority will also investigate potential locations for a treatment system to be built. We will discuss the results of our recommended solution with local stakeholders. Cleaning up the mine water pollution is estimated to deliver environmental and economic benefits of up to £4m over 25 years.

Until recently there was another problem in Gategill Beck. 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 grew weaker with age and the culvert underneath was corroded by the acidic mine water. This meant water built 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 was unable to resolve the issue so the Environment Agency worked with Cumbria County Council, Eden District Council, the Lake District National Park Authority and the Highways Agency to identify a solution and funding. During 2014 and 2015, the dam was made safe by lowering the crest height, sealing the culvert and installing a new overflow channel. The Coal Authority paid for the EA contractors to install a pipe through the dam to transfer mine water to a future treatment scheme.

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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Lessons learnt

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Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district North West River basin Derwent (NW) Subcatchment River name Glenderamackin (Greta) Area category 10 - 100 km² Area (km2) Maximum altitude category 500 - 1000 m Maximum altitude (m) 863863 m <br />0.863 km <br />86,300 cm <br /> Dominant geology Siliceous Ecoregion Great Britain Dominant land cover Acid Grassland Waterbody ID GB112075070460 Site Edit site Name WFD water body codes GB112075070460 WFD (national) typology WFD water body name Glenderamackin (Greta) Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body No National/international site designation Local/regional site designations Protected species present No Invasive species present No Species of interest Dominant hydrology Dominant substrate River corridor land use Average bankfull channel width category Average bankfull channel width (m) Average bankfull channel depth category Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 16km16,000 m <br />1,600,000 cm <br /> Project started 2010 Works started Works completed Project completed Total cost category Total cost (k€) Benefit to cost ratio Funding sources Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Stakeholder engagement and communication Works and works supervision Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Pollution incident, Mine drainage metal concentrations Hydromorphology Biology Physico-chemical Nutrient concentrations Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Deculverting, Sealing the culvert Floodplain / River corridor Dam lowering Planform / Channel pattern Lowering of impoundment, Pipe through dam for mine water to travel to future treatment scheme Other Non-structural measures Management interventions Clean up pollution with Defra funding, research on how to capture mine water, reviewed treatment technologies, Passive treatment, potential locations for a treatment system to be constructed Social measures (incl. engagement) Other Improving water quality Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit Physico-chemical quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Any other monitoring, e.g. social, economic Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information