UK Geoenergy Observatories: Glasgow groundwater and surface water chemistry dataset release September 2022 - January 2024

This report describes the hydrochemical monitoring of groundwater and surface water at the UK Geoenergy Observatory in Glasgow (UKGEOS Glasgow) from September 2022 to January 2024. This period coincides with the start of the operational phase for the Observatory, which is designed for research and innovation in mine water geothermal energy and thermal energy storage. Six sampling rounds were completed, with samples collected from 10 boreholes and 6 surface water monitoring points. It is preceded by the previous Glasgow Observatory monitoring report: Glasgow baseline groundwater and surface water chemistry dataset release June 2021- January 2022 report (Bearcock et al. 2023). The groundwater sampling, methods and quality of the water analyses are discussed. The results from the groundwater monitoring include field measurements of redox potential (ORP), pH, dissolved oxygen, electrical conductivity, alkalinity and water temperature, as well as chemical analyses of major, minor, and trace elements, reduced iron, dissolved sulphide, non-purgeable organic carbon (NPOC), polycyclic aromatic hydrocarbons (PAH), total petroleum hydrocarbons (TPH), volatile organic compounds (VOC), oxygen and deuterium isotopes (δ2H and δ18O), carbon isotopes in dissolved inorganic carbon (DIC) (δ13CDIC), ammonium (NH4), dissolved gases radon, methane, ethane and carbon dioxide (Rn, CH4, C2H6, CO2). The results from the surface water monitoring include the same parameters except for NH4, VOC, reduced iron, sulphide and dissolved gases. The new monitoring data indicates that the character of the groundwaters has generally remained unchanged since January 2022, except for the Glasgow Upper mine working borehole GGA01. Following prolonged pumping at the start of the operational phase, the water at GGA01 transitioned from a sulphate (SO₄) type to a bicarbonate (HCO₃) type. This change brought the water chemistry in line with that of other boreholes screened into the Upper Glasgow mine workings. Some variations in the composition of other mine waters were observed, although they were less pronounced than the step change observed in GGA01. Some of these changes can be directly linked to mixing induced by abstraction and injection activities within the mine workings during specific periods of the operational phase. Other changes are observed in the bedrock boreholes, exemplified by peaks in arsenic (As) above the max baseline values measured in GGA03r and GGB05, but with concentrations remaining low (< 5 μg/L). These anomalies will be further examined to determine their causes and assess, through further monitoring, if they are isolated occurrence or indicative of a long-term trend.