UK Geoenergy Observatories : Glasgow baseline groundwater and surface water chemistry dataset release June 2021 - January 2022

Bearcock, J.M.; Palumbo-Roe, B.; Mulcahy, A.; Walker-Verkuil, K.; MacAllister, D.J. ORCID: https://orcid.org/0000-0001-8893-9634; Darling, W.G.; Gooddy, D.C.. 2023 UK Geoenergy Observatories : Glasgow baseline groundwater and surface water chemistry dataset release June 2021 - January 2022. Edinburgh, UK, British Geological Survey, 144pp. (OR/23/029) (Unpublished)

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Abstract/Summary

This report follows the Glasgow baseline groundwater and surface-water chemistry dataset release report September 2020 – May 2021 (data release/ monitoring period 1) (Bearcock et al., 2022), and describes baseline water chemistry sampling and analysis results for groundwater and surface water at the United Kingdom Geoenergy Observatory (UKGEOS) in Glasgow between June 2021 and January 2022. The report accompanies the Glasgow Observatory groundwater chemistry data release and the Glasgow Observatory surface water chemistry data release for the same periods (data release/ monitoring period 2). The monitoring period is eight months long, with six rounds of surface water and groundwater sampling during this time. Sampling during non-consecutive months was a result of COVID-19 restrictions and construction activities at site. The Glasgow Observatory comprises twelve boreholes drilled into the main hydrogeological units, known as target horizons. These are the superficial deposits, bedrock, Glasgow Upper mine workings and Glasgow Main mine workings. The ten boreholes used for groundwater sampling are located at the Cuningar Loop in South Lanarkshire. There are two additional boreholes in the Observatory, one seismic monitoring borehole in Dalmarnock in the east end of Glasgow, and one borehole used for sensor testing. Three boreholes are drilled into the superficial deposits, two into the unmined bedrock, three into the Glasgow Upper mine workings and two into the Glasgow Main mine workings. The boreholes are designed to assist geological and hydrogeological characterisation, including baseline water chemistry monitoring, and to act as mine water abstraction and reinjection wells. The aims of the Observatory are to: 1) provide baseline environmental characterisation, 2) assess changes in ambient conditions induced by mine water abstraction/re-injection cycles and, 3) provide data and evidence to de-risk low-temperature shallow mine water heat energy and heat storage in former coal mine workings. Groundwater sampling was conducted using either a submersible or bladder pump. Field parameters (pH, specific electrical conductance (SEC), redox potential (Eh) and dissolved oxygen (DO)) were measured in a flow-through cell. The flow-through cell was discharged to a plastic beaker containing a thermometer probe. Field parameters were measured for a period of 20 minutes and at least three readings were taken five minutes apart. After field parameters were taken, the flow cell was disconnected, and samples were taken directly from the pump discharge tube. Field alkalinity was measured by titration against H2SO4. Groundwater samples were analysed for: major, minor, and trace elements, reduced iron (Fe), non-purgeable organic carbon (NPOC) and total inorganic carbon (TIC), polycyclic aromatic hydrocarbons (PAH), total petroleum hydrocarbons (TPH), volatile organic compounds (VOC), 2H and 18O abundance in water (δ2H and δ18O), 13C abundance in dissolved inorganic carbon (DIC) (δ13CDIC), ammonium (NH4), dissolved gases (methane, ethane and carbon dioxide (CH4, C2H6, CO2)), noble gases (helium, neon, argon, krypton, and xenon (He, Ne, Ar, Kr and Xe)), chlorofluorocarbons (CFC-12 and CFC-11), sulphur hexafluoride (SF6), and sulphide (S2-). The pH of groundwater samples (range 6.6 – 7.4) is circum-neutral, with a similar range across all target horizons. Groundwater from all four horizons is highly mineralised with median SEC values 1440 μS/cm - 1670 μS/cm. GGA01, installed in the Glasgow Upper mine working, had the most highly mineralised groundwater with a range of 2930 μS/cm – 3140 μS/cm. The range of recorded groundwater temperatures is largest in the superficial deposits (11.0°C – 16.6°C). The bedrock and mine workings groundwaters all have similar temperatures, and a narrower range of 10.1°C – 13.4 °C. In all target horizons the dissolved oxygen concentration is very low, all DO values are ≤0.81 mg/L. In general major elements and physico-chemical parameters measured in the groundwater samples have concentration ranges similar to those found in bedrock and mine workings across the Carboniferous sedimentary aquifers of the Midland Valley (Ó Dochartaigh et al., 2011). The chemistry of most groundwater samples is unchanged from pumping tests conducted in early 2020 (Palumbo-Roe et al., 2021), and the previous period of baseline monitoring that spanned the period from September 2020 to May 2021 (Bearcock et al., 2022). Groundwaters are generally HCO3 type, with no dominant cation. The exception is GGA01, where groundwaters changed from HCO3 type during the pumping test to Ca-SO4 type at the start of the previous round of monitoringThe Glasgow Observatory comprises twelve boreholes drilled into the main hydrogeological units, known as target horizons. These are the superficial deposits, bedrock, Glasgow Upper mine workings and Glasgow Main mine workings. The ten boreholes used for groundwater sampling are located at the Cuningar Loop in South Lanarkshire. There are two additional boreholes in the Observatory, one seismic monitoring borehole in Dalmarnock in the east end of Glasgow, and one borehole used for sensor testing. Three boreholes are drilled into the superficial deposits, two into the unmined bedrock, three into the Glasgow Upper mine workings and two into the Glasgow Main mine workings. The boreholes are designed to assist geological and hydrogeological characterisation, including baseline water chemistry monitoring, and to act as mine water abstraction and reinjection wells. The aims of the Observatory are to: 1) provide baseline environmental characterisation, 2) assess changes in ambient conditions induced by mine water abstraction/re-injection cycles and, 3) provide data and evidence to de-risk low-temperature shallow mine water heat energy and heat storage in former coal mine workings. Groundwater sampling was conducted using either a submersible or bladder pump. Field parameters (pH, specific electrical conductance (SEC), redox potential (Eh) and dissolved oxygen (DO)) were measured in a flow-through cell. The flow-through cell was discharged to a plastic beaker containing a thermometer probe. Field parameters were measured for a period of 20 minutes and at least three readings were taken five minutes apart. After field parameters were taken, the flow cell was disconnected, and samples were taken directly from the pump discharge tube. Field alkalinity was measured by titration against H2SO4. Groundwater samples were analysed for: major, minor, and trace elements, reduced iron (Fe), non-purgeable organic carbon (NPOC) and total inorganic carbon (TIC), polycyclic aromatic hydrocarbons (PAH), total petroleum hydrocarbons (TPH), volatile organic compounds (VOC), 2H and 18O abundance in water (δ2H and δ18O), 13C abundance in dissolved inorganic carbon (DIC) (δ13CDIC), ammonium (NH4), dissolved gases (methane, ethane and carbon dioxide (CH4, C2H6, CO2)), noble gases (helium, neon, argon, krypton, and xenon (He, Ne, Ar, Kr and Xe)), chlorofluorocarbons (CFC-12 and CFC-11), sulphur hexafluoride (SF6), and sulphide (S2-). The pH of groundwater samples (range 6.6 – 7.4) is circum-neutral, with a similar range across all target horizons. Groundwater from all four horizons is highly mineralised with median SEC values 1440 μS/cm - 1670 μS/cm. GGA01, installed in the Glasgow Upper mine working, had the most highly mineralised groundwater with a range of 2930 μS/cm – 3140 μS/cm. The range of recorded groundwater temperatures is largest in the superficial deposits (11.0°C – 16.6°C). The bedrock and mine workings groundwaters all have similar temperatures, and a narrower range of 10.1°C – 13.4 °C. In all target horizons the dissolved oxygen concentration is very low, all DO values are ≤0.81 mg/L. In general major elements and physico-chemical parameters measured in the groundwater samples have concentration ranges similar to those found in bedrock and mine workings across the Carboniferous sedimentary aquifers of the Midland Valley (Ó Dochartaigh et al., 2011). The chemistry of most groundwater samples is unchanged from pumping tests conducted in early 2020 (Palumbo-Roe et al., 2021), and the previous period of baseline monitoring that spanned the period from September 2020 to May 2021 (Bearcock et al., 2022). Groundwaters are generally HCO3 type, with no dominant cation. The exception is GGA01, where groundwaters changed from HCO3 type during the pumping test to Ca-SO4 type at the start of the previous round of monitoring (September 2020). During this monitoring period the concentrations of Ca and SO4 in GGA01 have continued to increase, albeit at a slowing rate, while HCO3 concentrations, which had initially fallen, are slowly increasing. Oxidation of sulphide minerals (e.g. pyrite) could have caused the dominance of the SO4 anion in GGA01 groundwaters. Dissolved organic carbon (as NPOC) is present in the range 1.05 mg/L to 5.46 mg/L, except for one outlier of 23.5 mg/L at GGA01. NPOC concentrations in the superficial deposits, with a median 4.39 mg/L, are at the upper end of this range, while all other target horizons have similar, lower, median values (medians from 2.32 mg/L to 2.54 mg/L). Groundwater samples from two boreholes have low ammonium (NH4) concentrations throughout the monitoring period (GGB04 in the superficial deposits and bedrock borehole GGA03r have a combined median of 3.15 mg/L). The remaining groundwaters in the Glasgow Observatory have high NH4 concentrations (combined median 23.2 mg/L). There was a large concentration range of trace elements in the Glasgow Observatory groundwaters. In general, the lowest concentrations were found in groundwaters from the Glasgow Main mine workings. In contrast the highest trace element concentrations were found in the groundwaters from the Glasgow Upper mine workings and the superficial deposits. TPH was detected in low concentrations in all units at some point during the sampling period. VOCs were not detected in any groundwater sample. Water stable isotopes (δ2H and δ18O), inorganic carbon δ13C and groundwater residence time data were consistent with findings from the pumping test results and previous monitoring period (Bearcock et al., 2022; Palumbo-Roe et al., 2021). Groundwaters are recharged by modern recharge from local rainfall. Median concentrations of dissolved methane (CH4) in the groundwaters range from 16.6 μg/L in the superficial deposits to 224 μg/L in the Glasgow Upper mine workings. These values lie within the upper range of groundwaters reported in other studies from Carboniferous sedimentary rocks in the Midland Valley of Scotland (Ó Dochartaigh et al., 2011). Dissolved ethane (C2H6) was below detection limits in all but one sample (5.2 μg/L at GGA01). Dissolved CO2 has a median value of 141 mg/L with little variation between units. Water chemistry cluster analysis shows that the superficial deposits, bedrock, mine working, and surface water samples cluster into statistically distinct groups. Notable exceptions are groundwaters from GGA01 which form their own separate group, and GGB05 groundwaters from the bedrock horizon which group with the mine workings. Surface water samples were taken using an angular beaker and telescopic rod. Samples were taken from the River Clyde and the Tollcross Burn. Surface water samples were analysed for: major, minor, and trace elements, non-purgeable organic carbon (NPOC) and total inorganic carbon (TIC), polycyclic aromatic hydrocarbons (PAH), total petroleum hydrocarbons (TPH), 2H and 18O abundance in water (δ2H and δ18O) and carbon 13 abundance in dissolved inorganic carbon (DIC) (δ13CDIC), . While both the Clyde and Tollcross Burn have a near-neutral to alkaline pH (7.3 – 8.7), the pH values measured at the Tollcross Burn tend to be higher (median 8.3 from the Tollcross Burn and 7.7 from the Clyde). The waters all follow a similar temporal trend, with the highest value each month measured at the Tollcross Burn. The SEC measurements are higher in the Tollcross Burn samples (median 872 μs/cm) than those measured in the River Clyde samples (median 372 μs/cm). Surface water samples are all generally Ca-HCO3 type. The samples taken from the Tollcross Burn tend to have a greater HCO3 proportion than the river Clyde samples. Most detected trace elements are present in higher concentrations in the River Clyde than in the Tollcross Burn. With the exception of Cr, the trace element concentrations are similar between all sites on the River Clyde, which would be expected given these sites are all on a relatively short stretch of the same river. The Cr concentrations are much higher at the sampling site closest to a former chemical works (median 4.18 μg/L) than elsewhere within the Glasgow Observatory (median 0.4 μg/L). In general, the surface water results are consistent with findings from previous work (Bearcock et al., 2022; Fordyce et al., 2021). (September 2020). During this monitoring period the concentrations of Ca and SO4 in GGA01 have continued to increase, albeit at a slowing rate, while HCO3 concentrations, which had initially fallen, are slowly increasing. Oxidation of sulphide minerals (e.g. pyrite) could have caused the dominance of the SO4 anion in GGA01 groundwaters. Dissolved organic carbon (as NPOC) is present in the range 1.05 mg/L to 5.46 mg/L, except for one outlier of 23.5 mg/L at GGA01. NPOC concentrations in the superficial deposits, with a median 4.39 mg/L, are at the upper end of this range, while all other target horizons have similar, lower, median values (medians from 2.32 mg/L to 2.54 mg/L). Groundwater samples from two boreholes have low ammonium (NH4) concentrations throughout the monitoring period (GGB04 in the superficial deposits and bedrock borehole GGA03r have a combined median of 3.15 mg/L). The remaining groundwaters in the Glasgow Observatory have high NH4 concentrations (combined median 23.2 mg/L). There was a large concentration range of trace elements in the Glasgow Observatory groundwaters. In general, the lowest concentrations were found in groundwaters from the Glasgow Main mine workings. In contrast the highest trace element concentrations were found in the groundwaters from the Glasgow Upper mine workings and the superficial deposits. TPH was detected in low concentrations in all units at some point during the sampling period. VOCs were not detected in any groundwater sample. Water stable isotopes (δ2H and δ18O), inorganic carbon δ13C and groundwater residence time data were consistent with findings from the pumping test results and previous monitoring period (Bearcock et al., 2022; Palumbo-Roe et al., 2021). Groundwaters are recharged by modern recharge from local rainfall. Median concentrations of dissolved methane (CH4) in the groundwaters range from 16.6 μg/L in the superficial deposits to 224 μg/L in the Glasgow Upper mine workings. These values lie within the upper range of groundwaters reported in other studies from Carboniferous sedimentary rocks in the Midland Valley of Scotland (Ó Dochartaigh et al., 2011). Dissolved ethane (C2H6) was below detection limits in all but one sample (5.2 μg/L at GGA01). Dissolved CO2 has a median value of 141 mg/L with little variation between units. Water chemistry cluster analysis shows that the superficial deposits, bedrock, mine working, and surface water samples cluster into statistically distinct groups. Notable exceptions are groundwaters from GGA01 which form their own separate group, and GGB05 groundwaters from the bedrock horizon which group with the mine workings. Surface water samples were taken using an angular beaker and telescopic rod. Samples were taken from the River Clyde and the Tollcross Burn. Surface water samples were analysed for: major, minor, and trace elements, non-purgeable organic carbon (NPOC) and total inorganic carbon (TIC), polycyclic aromatic hydrocarbons (PAH), total petroleum hydrocarbons (TPH), 2H and 18O abundance in water (δ2H and δ18O) and carbon 13 abundance in dissolved inorganic carbon (DIC) (δ13CDIC), . While both the Clyde and Tollcross Burn have a near-neutral to alkaline pH (7.3 – 8.7), the pH values measured at the Tollcross Burn tend to be higher (median 8.3 from the Tollcross Burn and 7.7 from the Clyde). The waters all follow a similar temporal trend, with the highest value each month measured at the Tollcross Burn. The SEC measurements are higher in the Tollcross Burn samples (median 872 μs/cm) than those measured in the River Clyde samples (median 372 μs/cm). Surface water samples are all generally Ca-HCO3 type. The samples taken from the Tollcross Burn tend to have a greater HCO3 proportion than the river Clyde samples. Most detected trace elements are present in higher concentrations in the River Clyde than in the Tollcross Burn. With the exception of Cr, the trace element concentrations are similar between all sites on the River Clyde, which would be expected given these sites are all on a relatively short stretch of the same river. The Cr concentrations are much higher at the sampling site closest to a former chemical works (median 4.18 μg/L) than elsewhere within the Glasgow Observatory (median 0.4 μg/L). In general, the surface water results are consistent with findings from previous work (Bearcock et al., 2022; Fordyce et al., 2021).

Item Type:	Publication - Report
Digital Object Identifier (DOI):	https://doi.org/10.5285/9da2a537-b8f5-4520-bed8-5c629dce0bd9
Funders/Sponsors:	British Geological Survey
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed, but not externally peer-reviewed.
Additional Keywords:	UKGEOS_GLASGOW
Related URLs:	Dataset
Date made live:	15 Sep 2023 12:35 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/535831

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