Geochemical and isotopic characterisation of groundwater from the Magnesian Limestone aquifer, South of the Butterknowle Fault

This report details the results of a geochemical and isotope study of selected EA monitoring boreholes and public water abstraction boreholes from the Magnesian Limestone aquifer and underlying Coal Measures, focussing on the area around Bishop Middleham and Sedgefield, south of the Butterknowle Fault, Co Durham. The groundwater sampling was carried out during January and February 2024 from 39 sites by Environment Agency staff. The dataset expands a previous isotope study with sampling undertaken in July 2018, to improve the understanding of the source of elevated dissolved sulphate in the Magnesian Limestone aquifer in the study area. The application of stable isotopes (δ34SSO4, δ18OSO4, δ18OH2O, and δ2HH2O) integrated with hydrochemical data has supported aspects of the current conceptual hydrogeological model, but limitations in some of the data interpretation persist due to uncertainties regarding the representativeness of certain samples in reflecting aquifer conditions and water chemistry.