Friday 18th October 2019
Hydrogeological Consultancy
Groundwater Protection & Leachate Management

Opencast Coal Backfill Risk Assessments

See links to Nick’s experience of water quality issues associated with deep mines and with mine spoil heap leaching.

The Mining Waste Directive (2006/21/EC) makes operators responsible for taking appropriate measures to prevent the pollution of soil, surface water and groundwater when backfilling mine voids with extracted waste rock.The Directive is transposed into law through the Environmental Permitting (England and Wales) Regulations 2010 (SI 2010 No 675) and Management of Extractive Waste (Scotland) Regulations 2010.   In Scotland, where opencast coal mining was until recent years very much ongoing, SEPA has published a Code of Practice (See Reference #19 on Downloads page) and Section 3.4.6 of that Code outlines what is required in terms of assessing the polluting potential of the backfilled waste rock on groundwater quality.  The Code points to more detailed guidance prepared by Younger and Sapsford (See Reference #20 on Downloads page) on evaluating the potential impact of opencast coal mining on water quality.

Prior to the SEPA guidance being published, Nick undertook two backfill risk assessments, including one for a complex opencast coal site.  It was complex due to there already being spoil heaps from two deep coal mines, each having worked a number of seams with different sulphide contents.  The opencast mining proposals were also to work a number of coal seams with different leaching potentials and buffering potentials in the waste rock.  Nick designed a strata testing strategy and reviewed whole rock, leaching test and existing water quality data.  After a review of North American literature and use of some first principles, Nick then evaluated the potential risks to groundwater and subsequently developed a backfill strategy that would help minimise the possibility of groundwater (and surface waters) being contaminated by the operation.

Following publication of the SEPA Guidance, against which Nick’s pre-guidance approach was compatible with the more challenging requirements of that guidance, Nick guided and reviewed backfill risk assessments on three further opencast coal site developments.