Contaminant migration from disposal of acid tar wastes in fractured Coal Measures strata, southern Derbyshire

In excess of 60 000 m³ of acidic tar wastes from a lubricating oil factory have been disposed in old clay pits at a site on Coal Measures strata near Belper, southern Derbyshire, UK. A site investigation was carried out to assess the nature and volume of the waste, the extent of contaminant migration and possible remediation options. The wastes have migrated as free phase, gravity-driven flows of semi-fluid tar. These tar flows have led to contamination of on-site ponds by hydrocarbon emulsions and dissolved phase contaminants. Limited groundwater contamination by dissolved phase contaminants has also occurred. At present, no impact on off-site surface water receptors has been detected and no risk to any water abstraction has been identified. The site investigation has confirmed the exceedingly complex nature of the Coal Measures sequence. The Coal Measures exhibit some aspects of a multilayer aquifer system, dominant fracture flow mechanisms, strong anisotropy governed by fracture orientation and a heterogeneous and discontinuous distribution of groundwater heads. Indications of strong vertical head gradients, possibly related to under-drainage by mine workings, were detected.