Hydrochemical characterisation of the Sherwood Sandstone Group in the vicinity of Thoresby Colliery, Nottinghamshire

This report describes the detailed ground investigations that were carried out in the vicinity of Thoresby Colliery as part of the BGS HiRES research programme and their results. The introduction to the report briefly describes the background airborne geophysics acquired as part of the joint Geological Survey of Finland (GTK) - British Geological Survey (BGS) trial airborne environmental and geological surveys flown in June 1999. The main objective of these surveys was to test the efficiency of the GTK airborne electromagnetic (AEM) system in the mapping of potential pollution problems in the UK environment. The survey in the vicinity of Thoresby Colliery identified a conductivity anomaly that was attributed to migration of colliery spoil leachate as a groundwater plume to the east of the site. Three boreholes were drilled into the geophysical anomaly. Section 2 of the report discusses the results of groundwater monitoring and pore water extraction from the drill core. The groundwater flow direction has been determined to be to the east of the colliery. Down hole geophysical logging is reported and it is demonstrated that there is a very strong correlation between the borehole induction logs, total dissolved solids and chloride in the pore waters. A comparison of background groundwater quality and pore water chemistry with published colliery spoil leachate data indicates that it is possible to explain the core, pore water chemistry as a result of mixing of groundwater with a colliery spoil leachate source term. The close similarity of the Cl/Br ratio of pore waters in the groundwater plume with Thoresby Colliery process waters provides supporting evidence for this model to explain the origin of the plume and hence of the AEM anomaly.