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Management of Risks to Groundwater from Past Coal Mining

Keith Parker

Head of Estates and Environment

The Coal Authority

Issues facing the Coal AuthorityIssues facing the Coal Authority

CA is responsible for liabilities of Coal Mining CA is responsible for liabilities of Coal Mining pre 1994 privatisationpre 1994 privatisation

Typically collieries closed 1980-1990sTypically collieries closed 1980-1990s Modern deep collieriesModern deep collieries

Often final closures in the coalfieldOften final closures in the coalfield Often under Permo-Triassic coverOften under Permo-Triassic cover

Mine Water levels still risingMine Water levels still rising Decades needed for full recoveryDecades needed for full recovery

Potential for aquifer contaminationPotential for aquifer contamination Via shafts, direct connections, faults, etc Via shafts, direct connections, faults, etc

Minewater will contaminate aquifers withMinewater will contaminate aquifers with Salinity, Sulphates, Chlorides, Iron, Manganese, etcSalinity, Sulphates, Chlorides, Iron, Manganese, etc

Risk arises through-Risk arises through- development of Driving Head from surface inflows development of Driving Head from surface inflows

through worked coal measures results in migration through worked coal measures results in migration into overlying aquifer strata via man made into overlying aquifer strata via man made connections or mining induced fracturesconnections or mining induced fractures

Major Aquifers at riskMajor Aquifers at risk

Key risk areasKey risk areas

Aquifers at riskAquifers at risk Triassic Sandstone Aquifers in Triassic Sandstone Aquifers in

Yorkshire, Nottinghamshire, Derbyshire, Lancashire, Yorkshire, Nottinghamshire, Derbyshire, Lancashire, StaffordshireStaffordshire

Magnesian Limestone Aquifer inMagnesian Limestone Aquifer in County Durham (East of River Wear)County Durham (East of River Wear)

Aquifers historically impactedAquifers historically impacted Magnesian Limestone Aquifer inMagnesian Limestone Aquifer in

South Durham – HartlepoolSouth Durham – Hartlepool

A new threat to Groundwater ResourceA new threat to Groundwater Resource Requires strategy covering decadesRequires strategy covering decades

East of Wear Case StudyEast of Wear Case Study

Dawdon

Horden

Area of East of Wear mining block

Source Protection Zones in Magnesian Limestone aquifer, courtesy of Environment Agency

Groundwater RiskGroundwater Risk

SourceSource Initially hypersaline water – up to 40,000 mg/l chlorides!Initially hypersaline water – up to 40,000 mg/l chlorides!

offshore Permian evaporitesoffshore Permian evaporites Driving head developing from inland collieriesDriving head developing from inland collieries

PathwayPathway Direct links (adits) from coastal shafts into LimestoneDirect links (adits) from coastal shafts into Limestone Potential links through mining induced fractures over workingsPotential links through mining induced fractures over workings

ReceptorReceptor Magnesian Limestone Aquifer Magnesian Limestone Aquifer Public supply wells (c 35 million litres/day)Public supply wells (c 35 million litres/day) Some very close to mine aditsSome very close to mine adits Cones of depression induce minewater pollutionCones of depression induce minewater pollution

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Time-scales dictated by rising minewater

The pollution threat in E DurhamThe pollution threat in E Durham

Water well Old colliery

“water drift”

Old colliery sea drift

Capped colliery shaft

Further inland along the River Wear uncontrolled discharges will also occur.

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East of Wear SummaryEast of Wear Summary

Horden offers only temporary protectionHorden offers only temporary protection Insufficient capacity to control whole areaInsufficient capacity to control whole area Risk due to limited connections to other workingsRisk due to limited connections to other workings

A second plant at Dawdon is required imminentlyA second plant at Dawdon is required imminently Two pump stations will achieve long term controlTwo pump stations will achieve long term control

It will take several years of balancing water levels and It will take several years of balancing water levels and abstraction ratesabstraction rates

East of Wear aquifer on the path to full protectionEast of Wear aquifer on the path to full protection Many other areas where aquifers will need protection Many other areas where aquifers will need protection

from rising minewaterfrom rising minewater

Groundwater Policy - Approach?Groundwater Policy - Approach?

Working togetherWorking together CA/EA Memorandum of UnderstandingCA/EA Memorandum of Understanding Common goalsCommon goals Different skills and dutiesDifferent skills and duties

View the big pictureView the big picture Groundwater is part of the environmental mixGroundwater is part of the environmental mix Solutions inevitably have other impacts (waste, global warming Solutions inevitably have other impacts (waste, global warming

etc)etc) Consider the environmental ‘balance sheet’ when assessing Consider the environmental ‘balance sheet’ when assessing

problems and identifying solutionsproblems and identifying solutions Don’t compartmentalise the issueDon’t compartmentalise the issue Prioritisation is keyPrioritisation is key

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Thank YouThank You

www.coal.gov.ukwww.coal.gov.uk