UK Geoenergy Observatories Glasgow : groundwater chemistry data collected during the borehole construction phase

Shorter, K.M.; Palumbo-Roe, B.; Fordyce, F.M.; O Dochartaigh, B.E.; Walker-Verkuil, K.. 2021 UK Geoenergy Observatories Glasgow : groundwater chemistry data collected during the borehole construction phase. Edinburgh, UK, British Geological Survey, 45pp. (OR/21/015) (Unpublished)

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Abstract/Summary

The United Kingdom Geoenergy Observatory (UKGEOS) in Glasgow comprises 11 boreholes at the Cuningar Loop, South Lanarkshire and one seismic observation borehole in Dalmarnock in east Glasgow. Boreholes are drilled into superficial deposits, unmined bedrock and mined bedrock to characterise the geological and hydrogeological setting, and to provide access for baseline monitoring and mine water abstraction/ reinjection. The aims of the Observatory include de-risking key technical barriers to low-temperature shallow mine water heat energy and heat storage from groundwater in former coal mine workings; and providing environmental characterisation and monitoring to assess any change in ambient conditions. This report details baseline groundwater monitoring carried out during the construction phase of the Glasgow Observatory. It includes a description of the sampling methods and hydrochemical data for groundwater samples collected between December 2018 and December 2019. Eight groundwater samples and two mains water samples were analysed to determine the concentrations of selected chemical parameters at the British Geological Survey (BGS) and associated laboratories. The samples were collected to provide an initial indication of groundwater chemistry, primarily for water discharge purposes. The report accompanies the release of the construction phase groundwater hydrochemistry dataset. Sampling locations and methodology Groundwater samples were collected from the main Observatory borehole cluster at the Cuningar Loop, Rutherglen, South Lanarkshire from boreholes GGA02 at Site 1, GGA05 at Site 2, GGB04, GGB05 at Site 5, as well as from the seismic monitoring borehole GGC01 at Site 10 in Dalmarnock, Glasgow City. In the case of boreholes GGA02 and GGC01, they are the only groundwater chemistry samples that will be collected from these boreholes. Water was obtained from the Glasgow Upper mine working in GGA02 and Glasgow Main mine working in GGA05 by stopping the drilling at the mine working and retrieving a sample during and after purging. Groundwater from the bedrock and the superficial deposits was drawn from borehole GGB04 and borehole GGB05, respectively. Scope of analysis Groundwater samples were collected for analysis of major, minor and trace elements, Cr(VI), NPOC and stable isotopes (δ2H, δ18O, δ13C). In addition, field measurements of water temperature, pH, specific electrical conductance (SEC), redox potential (Eh) and dissolved oxygen (DO) were made. Total petroleum hydrocarbons (TPH) and polycyclic aromatic hydrocarbons (PAH) were analysed in samples from GGA02 and GGA05 only. Key Findings Both mine waters are net–alkaline with a near–neutral pH (Glasgow Upper pH 6.92 and Glasgow Main pH 7.12); they have a high alkalinity (as field-HCO3) (Glasgow Upper field-HCO3 609 mg/L and Glasgow Main field-HCO3 792 mg/L) and a high SEC of 1637 to 1723 µS/cm. Similarly, the bedrock and the superficial deposits waters have pH values of ~7.5 and alkalinity as field-HCO3 between 415 mg/L and 462 mg/L. The SEC is also high 1078–1183 µS/cm. All the waters belong to the bicarbonate (HCO3) type, with sodium (Na) as the dominant cation in the superficial deposits and bedrock groundwaters (Na–HCO3 waters), and Na, calcium (Ca) and, to a lesser extent, magnesium (Mg) in the two mine waters (Na–Ca–(Mg)–HCO3 water type). Water from all four lithologies ranges in sulphate (SO4) concentration between 165 and 302 mg/L. The chloride (Cl) range is 51–82 mg/L, with the highest value in the Glasgow Main mine working groundwater. Iron (Fe) concentrations range between 1.8 to 2.6 mg/L in the mine water and bedrock; a much lower concentration of 0.007 mg/L is measured in the superficial deposits groundwater. Chromium(VI), a known industrial contaminant in the area, was not detected above the lower limit of detection (LLD) in any samples. The stable isotope δ2H, δ18O values plot broadly on the global meteoric water line with no evidence of evaporation prior to recharge. The O-isotope values (δ18O -7.4 ‰ and -7.1 ‰) are all within the range of groundwater samples reported previously from Carboniferous sedimentary aquifers across the Midland Valley of Scotland. The mine waters have heavier δ13C (-9.9 and -10.8 ‰) than the bedrock and superficial deposits (-15.6 and -12.1 ‰). All lithologies’ groundwaters fall on the middle to upper range of the δ13C values from -22 ‰ to -10 ‰ of groundwater samples from other studies of the Coal Measures Group across the Midland Valley of Scotland. All samples are saturated with respect to calcite, dolomite, siderite, rhodochrosite, amorphous ferric hydroxide, gibbsite, and barite, and remain undersaturated with respect to gypsum, halite and jarosite. Water was also obtained during the installation of the GGC01 seismic monitoring borehole. However, given the sampling method (a bailer lowered to only a few meters from the top of the borehole) and evidence of dilution during flushing and residual contamination from the tracer/additive and drilling fluid, the chemical analyses of the groundwater samples from this borehole are not to be considered representative of the unmined Coal Measures aquifer(s) intercepting the borehole. Very high concentrations of boron (B) and dissolved organic carbon (NPOC) were found, which decreased between the two sampling dates, showing an increase in groundwater flowing into the borehole after drilling and flushing. The water was alkaline, and with a SEC of 310–650 µS/cm. Sodium was the most enriched cation, with HCO3 and Cl the most enriched anions. Chromium(VI) was not detected above the LLD in either sample. The δ2H, δ18O signature of the groundwater was similar to the samples taken in the four Cuningar Loop boreholes while the δ13C isotope signature was lighter.

Item Type:	Publication - Report (Technical Report)
Digital Object Identifier (DOI):	10.5285/295984e5-5f2a-43aa-aa3d-6995a80ac8ed
Funders/Sponsors:	Natural Environment Research Council, 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, GroundwaterBGS, Groundwater
NORA Subject Terms:	Earth Sciences
Date made live:	03 Jun 2021 09:55 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/530443

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