OR/19/032 Hydrogeology

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Monaghan, A A, Starcher, V, Dochartaigh, B Ó, Shorter, K, and Burkin, J. 2019. UK Geoenergy Observatories: Glasgow Geothermal Energy Research Field Site - Science infrastructure Version 2. UKGEOS Programme. British Geological Survey Internal Report, OR/19/032.

Overview

Existing available hydrogeological, hydrogeochemical and groundwater temperature data have been collated for the research area before borehole drilling starts. In Glasgow, neither surface water nor groundwater are used as a drinking water resource.

Hydrogeology of the superficial deposits

Much more is known about the hydrogeology of superficial deposits than about bedrock in Glasgow and the Clyde Gateway area. The Quaternary geological sequence in the central Clyde valley in Glasgow, including the Clyde Gateway area, forms a shallow complex aquifer system with a sequence of hydrogeologically heterogeneous lithostratigraphic units. Three Quaternary lithostratigraphic units — the Bridgeton Sand, Gourock Sand and Paisley Clay members — together form a linear aquifer approximately 2 to 3 km wide and typically between 10 and 30 m thick beneath central Glasgow. This aquifer is highly heterogeneous both naturally, due to varying lithology within aquifer units and to the varying influence of the tidal River Clyde with distance from the river; and due to urban influences, such as altered surface permeability, subsurface flowpaths, and urban recharge (Ó Dochartaigh et al., 2019[1]).

The national map of groundwater vulnerability indicates that groundwater in the uppermost Quaternary aquifer is highly vulnerable across much of the area, with zones of low vulnerability. However, this national-scale map is not likely to provide an accurate assessment of the actual vulnerability of groundwater in the small urban Clyde Gateway area. The widespread presence of anthropogenically altered ground — not accounted for in the national scale map — is likely to have a major impact on local groundwater vulnerability and this has been considered in environmental assessments for the research site (Ramboll, 2018a[2], b[3], c[4], d[5]).

Hydrogeology of the bedrock

Unmined Carboniferous sedimentary rocks in the Central Belt of Scotland typically form multi-layered and vertically segmented aquifers. The typically fine-grained, well-cemented rocks have low intergranular porosity and permeability, and groundwater flow and storage dominantly occur in fractures in the rock. Hydraulic aquifer properties therefore depend largely on the local nature of fracturing in the rock (Ó Dochartaigh et al., 2015[6]). Overall, the unmined rocks tend to form moderately productive aquifers — data on aquifer properties is given in Table 3. Sandstone units within the sedimentary sequence generally have the highest transmissivity and storage capacity, and therefore tend to act as discrete aquifer units, interspersed by lower permeability siltstones, mudstones and (undisturbed) coal seams (Ó Dochartaigh et al., 2015[6]).

Groundwater can be present in the aquifer under unconfined or confined conditions, which can vary between different sandstone and other sedimentary units and at different depths. Groundwater heads therefore vary between different aquifer layers (Ó Dochartaigh et al. 2015[6]).

Groundwater flow paths through the aquifer are thought to be complex, due to their naturally layered nature and the predominance of fracture flow, and potentially to the influence of faults. This may tend to promote preferential sub-horizontal flow, such as within sandstone units, and sub-vertical flow, such as via transmissive fault zones. Flow paths are likely to be relatively deep (100s of metres) and long (1–10 km). Previous assessments suggested that Glasgow acts as the focal point for much of the groundwater discharge from Carboniferous aquifers from the Central Coalfield area, with prevailing groundwater flow paths from the east, north-east and south-east (Hall et al., 1998[7]), but there is little measured hydrogeological data to support this hypothesis.

Table 3    Summary of available data on aquifer properties for Carboniferous sedimentary aquifers of Scotland: (top) not extensively mined for coal; (bottom) extensively mined for coal. From Ó Dochartaigh et al. (2015)[6].
Porosity (%) Matrix hydraulic conductivity (m/d) Transmissivity (m2/d) Specific capacity (m3/d/m) Operational yield (m3/d)
Carboniferous aquifers — not extensively mined for coal 12–17 (34) 0.0003–0.1 (37) 10–1000* (5) 48–132* (46) (minimum 0.43; maximum 1320)* 131–418 (348)
Porosity (%) Matrix hydraulic conductivity (m/d) Transmissivity (m2/d) Specific capacity (m3/d/m) Operational yield (m3/d)
Carboniferous aquifers — not extensively mined for coal 10–1000* (5) 48–132* (46) (minimum 0.43; maximum 1320)* 1987–3279 (171) (minimum 41; maximum 22 248)*

* May refer to both mined and nonmined aquifers
Ranges of values refer to mean and median values except where indicated
Number of values indicated in brackets
Data from the British Geological Survey.

Impacts of mining

Mining in Carboniferous sedimentary rocks has significantly changed natural hydrogeological conditions. Groundwater flow paths are likely to be even more complex in mined aquifers than in undisturbed Carboniferous aquifers.

Mine voids (shafts and tunnels) can artificially and greatly increase aquifer transmissivity and can link formerly separate groundwater flow systems both laterally and vertically (Figure 7). Aquifer storage can also be locally increased. Even where mine voids have subsequently collapsed, deformation of the surrounding rock mass is likely to cause further changes in transmissivity and, to a lesser degree, storage (Younger and Robins, 2002[8]).

Figure 7    Mined hydrogeology conceptual model for central Scotland from Ó Dochartaigh et al. (2015)[6].

Quantitative data on aquifer properties from borehole pumping tests are relatively rare for formerly mined aquifer zones in Carboniferous rocks in Scotland. However, records of specific capacity from boreholes drilled in aquifers which have been extensively mined, many of which intercept mine workings, give an indication of the range in aquifer properties and how this varies from the unmined aquifers. There are also many records of yields from mine dewatering boreholes. Table 3 summarises the available data from these sources: in general yield values are higher in aquifers that have experienced extensive coal mining.

Temperature

Though there are no direct borehole temperature measurements within the Clyde Gateway area, there are 13 measurements from within 20 km (Figure 8). This existing dataset indicates that mine water temperature in the planned boreholes is likely to be around 12°C.

Figure 8    Measured temperature and depth within 20 km of the Clyde Gateway area; 10 data points from Burley et al. (1984)[9], Rollin et al. (1987)[10], and DECC Onshore Well archive. The red data point is temperature measured in the Highhouse Colliery. The geothermal gradient is 30.2°C/km with a surface temperature of 7.3°C, reproduced from section 5.2 of Monaghan et al. (2017)[11].

Hydrochemistry

Data on the hydrogeochemistry within superficial and artificial ground is contained within site investigation reports and summarised in reports for the planning application (Ramboll, 2018a[2], b[3], c[4], d[5]). Results are highly variable dependent on location, but some sites close to the planned borehole locations show exceedances of resource protection values in both the shallow (superficial deposits) groundwater and deeper (near top bedrock) groundwater.

There is little recent information on groundwater chemistry in the Carboniferous sedimentary aquifer in Glasgow. Some regional bedrock hydrochemistry information is available from the Baseline Scotland dataset (Ó Dochartaigh et al., 2011[12]). The natural chemistry of groundwater in Carboniferous sedimentary aquifers is often moderately to highly mineralised (values in Ó Dochartaigh et al., 2011[12]).

Groundwater quality can be significantly affected by mining. Groundwater discharges from mine workings are often strongly mineralised, with high specific electrical conductivity (SEC) and particularly high concentrations of HCO3, Ca, SO4, Fe and Mn, and low in dissolved oxygen. pH is generally well buffered and alkalinity is high, indicating significant reaction with carbonate material in the aquifers (Ó Dochartaigh et al., 2011[12]). Acid mine water discharge is not currently a known problem in Glasgow, and past investigations at a number of sites have indicated good quality groundwater in abandoned mine workings (Glasgow City Council, pers. comm.).

Further hydrogeology information is available in: Ó Dochartaigh et al. (2011)[12]; Ó Dochartaigh et al (2015)[6]. Additional hydrogeological modelling information is available in: Bianchi et al. (2015)[13]; Turner et al. (2015)[14].

Additional characterisation and monitoring data sources

Summaries of surface water, soil chemistry, baseline seismicity and engineering geology datasets are given in Monaghan et al. (2017)[11] with other summaries of baseline datasets:

  • Surface water: Fordyce et al, (2004)[15], Smedley et al. (2017)[16]
  • Soil chemistry: Fordyce et al. (2012)[17], Kim et al. (2019)[18]
  • Ground motion: Bateson et al. (2018)[19]
  • Stress and seismicity of central Scotland: Baptie et al. (2016)[20]* Geological models: Kearsey et al. (2019)[21], Williams et al. (2019)[22]
  • Mine geothermal in Glasgow: Banks et al. (2009)[23]

References

  1. Ó DOCHARTAIGH, B, BONSOR, H, BRICKER, S. 2019. Improving understanding of shallow urban groundwater: the Quaternary groundwater system in Glasgow, UK. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 108 (2–3). 155–172. https://doi.org/10.1017/S1755691018000385
  2. 2.0 2.1 RAMBOLL for GGERFS planning application for South Lanarkshire Council. 2018a. GLASGOW GEOTHERMAL ENERGY RESEARCH FIELD SITE: CUNINGAR LOOP, GGERFS01-05 PHASE I ENVIRONMENTAL REVIEW. Available online at https://publicaccess.southlanarkshire.gov.uk/online- applications/caseDetails.do?caseType=Application&keyVal=P7OTP9OPHQJ00
  3. 3.0 3.1 RAMBOLL for GGERFS planning application for South Lanarkshire Council. 2018b. UK GEOENERGY OBSERVATORIES: GLASGOW GEOTHERMAL ENERGY RESEARCH FIELD SITE ENVIRONMENTAL REPORT. Available online at https://publicaccess.southlanarkshire.gov.uk/online- applications/caseDetails.do?caseType=Application&keyVal=P7OTP9OPHQJ00
  4. 4.0 4.1 RAMBOLL for GGERFS planning application for Glasgow City Counci. 2018c. GLASGOW GEOTHERMAL ENERGY RESEARCH FIELD SITE: DALMARNOCK, GGERFS10 PHASE I ENVIRONMENTAL REVIEW. Available online at https://publicaccess.glasgow.gov.uk/online-applications/applicationDetails.do?keyVal=P70V2DEXFH600&activeTab=summary
  5. 5.0 5.1 RAMBOLL for GGERFS planning application for Glasgow City Council. 2018d. UK GEOENERGY OBSERVATORIES: GLASGOW GEOTHERMAL ENERGY RESEARCH FIELD SITE ENVIRONMENTAL REPORT. Available online at https://publicaccess.glasgow.gov.uk/online-applications/applicationDetails.do?keyVal=P70V2DEXFH600&activeTab=summary
  6. 6.0 6.1 6.2 6.3 6.4 6.5 Ó DOCHARTAIGH, B E, MACDONALD, A M, FITZSIMONS, V, and WARD, R. 2015. Scotland's aquifers and groundwater bodies. Nottingham, UK, British Geological Survey OR/15/028, 63pp. http://nora.nerc.ac.uk/id/eprint/511413/
  7. HALL, I H S, BROWNE, M A E, and FORSYTH, I H. 1998. Geology of the Glasgow district. Memoir of the British Geological Survey, Sheet 30E (Scotland). ISBN 0-11-884534-9.
  8. YOUNGER, P L, and ROBINS, N S. 2002. Challenges in the characterisation and prediction of the hydrogeology and geochemistry of mined ground. In Mine Water Hydrogeology and Geochemistry. Younger PL and Robins NS (editors). Geological Society of London Special Publication, No. 198, 1–16.
  9. BURLEY, A J, EDMUNDS, W M, and GALE, I N. 1984. Investigation of the geothermal potential of the UK: catalogue of geothermal data for the land area of the United Kingdom. British Geological Survey, 161pp. (WJ/GE/84/020) (Unpublished).
  10. ROLLIN, K E. 1987. Catalogue of geothermal data for the land area of the United Kingdom. Third revision: April 1987. Investigation of the geothermal potential of the UK, British Geological Survey, Keyworth.
  11. 11.0 11.1 MONAGHAN, A A, Ó DOCHARTAIGH, B, FORDYCE, F, LOVELESS, S, ENTWISLE, D, QUINN, M, SMITH, K, ELLEN, R, ARKLEY, S, KEARSEY, T, CAMPBELL, SDG, FELLGETT, M, and MOSCA, I. 2017. UKGEOS — Glasgow Geothermal Energy Research Field Site (GGERFS): Initial summary of the geological platform. British Geological Survey Open Report, OR/17/006. 205pp. http://nora.nerc.ac.uk/id/eprint/518636/
  12. 12.0 12.1 12.2 12.3 Ó DOCHARTAIGH, B É, SMEDLEY, P L, MACDONALD, A M, DARLING, W G, and HOMONCIK, S. 2011. Baseline Scotland: groundwater chemistry of the Carboniferous sedimentary aquifers of the Midland Valley. British Geological Survey Open Report OR/11/021. http://nora.nerc.ac.uk/id/eprint/14314/
  13. BIANCHI, M, KEARSEY, T, and KINGDON, A. 2015. Integrating deterministic lithostratigraphic models in stochastic realizations of subsurface heterogeneity. Impact on predictions of lithology, hydraulic heads and groundwater fluxes. Journal of Hydrology, 531 (3). 557–573. 10.1016/j.jhydrol.2015.10.072
  14. TURNER, R J, MANSOUR, M M, DEARDEN, R, O DOCHARTAIGH, B E, and HUGHES, A G. 2015. Improved understanding of groundwater flow in complex superficial deposits using three-dimensional geological-framework and groundwater models: an example from Glasgow, Scotland (UK). Hydrogeology Journal Vol 23 (3), 493–506.
  15. FORDYCE, F M, Ó DOCHARTAIGH, B É, LISTER, T R, COOPER, R, KIM, A, HARRISON, I, VANE, C, and BROWN, S E. 2004. Clyde Tributaries: Report of Urban Stream Sediment and Surface Water Geochemistry for Glasgow. British Geological Survey Commissioned Report CR/04/037. http://nora.nerc.ac.uk/18996/
  16. SMEDLEY, P L, BEARCOCK, J M, FORDYCE, F M, EVERETT, P A, CHENERY, S, and ELLEN, R. 2017. Stream-water geochemical atlas of the Clyde Basin. Nottingham, UK, British Geological Survey, 168pp. (OR/16/015) http://nora.nerc.ac.uk/id/eprint/519332/
  17. FORDYCE, F M, NICE, S E, LISTER, T R, Ó DOCHARTAIGH, B É, COOPER, R, ALLEN, M, INGHAM, M, GOWING, C, VICKERS, B P, and SCHEIB, A. 2012. Urban Soil Geochemistry of Glasgow. British Geological Survey Open Report OR/08/002. http://nora.nerc.ac.uk/18009/
  18. KIM, A W, VANE, C H, MOSS-HAYES, V L, BERIRO, D J, NATHANAIL, C P, FORDYCE, F M, and EVERETT, P A. 2019. Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in urban soils of Glasgow, UK. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 108 (2–3). 231–247. https://doi.org/10.1017/S1755691018000324
  19. BATESON, L, NOVELLINO, A, and JORDAN, C. 2018. Glasgow Geoenergy Research Field Site-Ground motion survey report. British Geological Survey Open Report OR/18/054.
  20. BAPTIE, B, SEGOU, M, ELLEN, R, and MONAGHAN, A A. 2016. Unconventional Oil and Gas Development: Understanding and Monitoring Induced Seismic Activity. British Geological Survey Open Report, OR/16/042. 92pp. Available from https://beta.gov.scot/publications/unconventional-oil-gas-understanding-monitoring-induced-seismic-activity/
  21. KEARSEY, T I, WHITBREAD, K, ARKLEY, S L B, FINLAYSON, A, MONAGHAN, A A, MCLEAN, W S, TERRINGTON, R L, CALLAGHAN, E A, MILLWARD, D, and CAMPBELL, S D G. 2019 Creation and delivery of a complex 3D geological survey for the Glasgow area and its application to urban geology. Earth and Environmental Science Transactions of The Royal Society of Edinburgh, 108 (2–3). 123–140. https://doi.org/10.1017/S1755691018000270
  22. WILLIAMS, J D O, DOBBS, M R, KINGDON, A, LARK, R M, WILLIAMSON, J P, MACDONALD, A M, O DOCHARTAIGH, B E. 2019. Stochastic modelling of hydraulic conductivity derived from geotechnical data: an example applied to central Glasgow. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 108 (2–3). 141–154. https://doi.org/10.1017/S1755691018000312.
  23. BANKS, D, FRAGA PUMAR, A, and WATSON, I. 2009. The operational performance of Scottish minewater-based ground source heat pump systems. Quarterly Journal of Engineering Geology and Hydrogeology, 42, 347–357. doi:10.1144/1470-9236/08-081.