City regions geoscience in Wales : scoping study

Several individuals from the public and private sector in Wales contributed to the initial consultation process and their assistance is gratefully acknowledged. We would particularly like to thank Cardiff Council, Newport City Council, City and County of Swansea Council, Neath Port Talbot Council, Rhondda Cynon Taf Council, Torfaen County Borough Council, Caerphilly County Borough Council, Atkins Global, Parsons Brinkerhoff, Welsh Water, Celtic Ltd, Natural Resources Wales, and Welsh Government. This report describes the results of a scoping study to identify key geoscientific knowledge gaps in City Regions in South Wales. The study involved consultation meetings with key stakeholders and reviewed planning policy documents and development plans to establish the demand for subsurface knowledge in City Regions to reduce risk, support urban redevelopment and underpin growth. The first part of the report provides a background to the study placing it in context. The report then goes on to review national and regional policy documents followed by detailed summaries of the Local Development Plans for all councils in South and Mid Wales. A review of these documents has established sustainable development as a priority for the Welsh Government. Councils have been required to produce Local Development Plans which address a number of key issues related to the sustainable development of each area. These include climate change, flooding, sustainable housing, resource efficient construction, employment, brownfield redevelopment, sustainable drainage, waste management, energy and minerals. Several of these key topics require geoscience knowledge and data to underpin planning decisions. The extent to which this is understood by local authorities varies between counties. The second part of this report provides a discussion of information gathered through stakeholder engagement and includes a number of case studies which outline how subsurface data has been shared and reused for the greater benefit to society. Talks with local councils, ground engineering consultancies and water companies have identified the types of data in demand from BGS; these include: existing ground investigation data, information on contaminated land and groundwater, the nature of artificial ground, Infiltration SuDS suitability information and land stability data

Physical properties and micromorphology of till deposits from Talla Earth Observatory, Southern Uplands, Scotland

This factual report describes the 2007 field program at BGS’ Talla Earth Observatory, in the Scottish Southern Uplands, UK. The work involved 12 trial pits with logging of pit walls, soil sampling for particle size analysis and undisturbed sampling for thin sections and micromorphological analysis of a till and a hard pan in moranic deposits. The tills of the Langholm Till Formation (of McMillan & Merritt, 2012) are technically ‘coarse soils’ from a BS5930:1999 ground engineering perspective; typically very dense/hard, very wellgraded silty sandy gravels with a matrix dominated by silt and sand. In thin section the till sandmatrix-supported gravel clasts show a preferred alignment orientated suggesting a micro-fabric indicative of a subglacially deposited till. Clast lithology includes sandstone, siltstone and mudstone, and are consistent with the local bedrock lithology. Cobbles and boulders are often ‘very strong’ from a geotechnical perspective, but may have weaker ‘rotten’ crust in valley floor settings. The work provides new data on the geotechnical properties of Scottish tills and enhances our understanding of the physical and hydrological properties of commonly encountered Quaternary deposits that occur in the Talla Burn and nearby upland catchments

Falling head permeability tests on Till deposits from the Vale of Eden, England - supplementary report including new data

This report describes permeability tests carried out on twenty three samples of glacial till obtained from boreholes drilled in the Vale of Eden area in Cumbria, England. The results of 134 initial tests are also documented in Internal Report IR/13/034 (ibid.). Further samples were obtained in September 2013 and results of an additional 76 tests on seven additional samples are reported here. The report outlines the testing procedure and presents the results of the permeability tests. The laboratory permeability values of till soils from the Moreland and Pow Focus Catchments ranged from 10-5 to 10-10 m/s, suggesting permeability is variable, with Medium Low to Impermeable soils

Falling head permeability tests on Till deposits from the Vale of Eden, England

This report describes permeability tests carried out on sixteen samples of glacial till obtained from boreholes drilled in the Vale of Eden area in Cumbria, England. The report outlines the testing procedure and presents the results of the permeability tests. Measured permeability values were variable and ranged from 10-5 to 10-10 m/s, Medium Low to Impermeable

Geological and hydrogeological investigations in the Colchester Northern Gateway boreholes : February 2020 survey

This research report describes borehole geophysical and passive seismic surveys done at the Colchester Northern Gateway (CNG) geothermal district heat network and housing development in Essex, UK, between 10-13 February 2020. The first part of the report introduces the project context, the second part describes survey methods, and the third presents the ‘baseline survey’ results and stratigraphic interpretation. The final section summarises the key learnings, relevance of the findings to future geothermal district heating schemes in the Chalk and London Basin, and makes some recommendations for follow-up monitoring research. Five recently drilled production/injection boreholes at CNG were logged with Calliper, Temperature and Conductivity, Natural Gamma, Optical Televiewer (OPTV) tools. Some of the holes also had Resistivity and Impeller flow tools run but results were inconclusive. A site-wide Tromino H/V passive seismic survey was acquired to characterise the resonant frequency of the subsoils between the boreholes, to aid stratigraphic correlation, profile the concealed chalk ‘rockhead’ surface (i.e. depth of bedrock aquifer), and look for any evidence of the presence of faults/fracture zone, and characterise the thickness of karst and weathering profiles. The main geological formation boundaries were identified based on a combination of interpretation of Natural Gamma logs and correlation of sedimentary features observed in the OPTV images. The eroded top of the Newhaven Chalk is around 72 m below ground level (-24 m OD) in all five boreholes (BH1-5). The high-resolution OPTV images provide rich visual information on the fracture state of the upper ‘productive’ part of the chalk aquifer. A notable feature in BH4 is an 18 m long NW-SE orientated open vertical fracture that persists through the Newhaven Chalk but terminates at the top of the Seaford Chalk. The OPTV data also aids identification of key litho-stratigraphic marker horizons, such as tabular flint bands, hard grounds and marls seams. The Natural Gamma aids identification of key marls, such as the Buckle Marl and Shoreham Marls and the top and base of the London Clay and top of Chalk. Marls and flint bands are useful litho-stratigraphic markers for site- to regional-scale correlation and structural analysis, and for developing hydrogeological and thermo-geological conceptual and observational geo-models to inform the set-up of numerical flow models (e.g. FeFLOW models). The interpretation of the new survey data concluded that the near-surface geology at CNG comprises c.72 m of thin Superficial deposits and Palaeogene sediments resting on Cretaceous Chalk bedrock (White Chalk Sub-group). The two deepest (200 m) boreholes (BH2 and BH4) penetrate 4-5 m of superficial deposits (cover sand and gravels) resting on c.36 m of London Clay, c.8.5 m of Harwich Formation, c.10 m of Lambeth Group, c.12 m of Thanet Formation, c.23 m of slightly karstified and fractured basal Newhaven Chalk, c.59.4 m of Seaford Chalk and terminate within c.31 m of upper Lewis Nodular Chalk Formation. Groundwater temperature profiling in February 2020 suggests a shallow geothermal gradient of around 2.4°C per 100 m in the top 200 m of the Chalk aquifer in the Colchester area. Under natural conditions (i.e. no influence from other subsurface users), groundwater source heat pump schemes can therefore expect seasonally stable ambient source temperatures of around 11.7°C and 14.3°C at 100 m and 200 m depths, respectively, with 130m open loop schemes predicted to yield borehole inflow temperatures of around 12.5°C all year round (assuming no thermal interactions/breakthrough), making open loop ground source heat pump schemes a viable option for low carbon/no carbon heating systems. Pumping tests in the CNG wells (undertaken by the developer Amphora Energy Ltd in c.2019) yielded 2 to 10 l/s. The highest yields were from BH4 & 5 located on the far western side of the CNG development site and were attributed to the switch to a reverse-circulation drilling technique, however the presence of karstified open fractures (BH4) may also be a contributing factor. Open loop GSHP heating capacities of between 60 and 300 kW thermal per 130m well-doublets (depending on local aquifer properties) are therefore probably feasible for similar schemes in the region, assuming a sustainable thermal productivity (ΔTgw) of 7°C (i.e. abstraction at 12.5°C and injection at 5.5°C). Larger yields may be possible using larger diameter boreholes and in more fractured, weathered or karstified parts of the aquifer (i.e. fracture systems associated with the major NW-SE bedrock lineaments described by Woods and Chacksfield (2012)). The passive seismic H/V data collected across the CNG site in 2020, prior to the new house construction, suggests chalk aquifer and seismic rockhead surface in-between the boreholes (BH1-5) is relatively level and planar at an elevation of around -24 m OD, although some karstification may have occurred in the upper 10-20m of the aquifer. This top chalk elevation is consistent with the old borehole records from the nearby Severalls Hospital. From interpretation of the closely-spaced H/V survey results there is no suggestion of a major fault/fracture system within the chalk at the CNG site, although there could be undetected fault systems at other locations in the region and potentially at depth in the area

Characterisation of seasonal temperature variation in a shallow, urban aquifer: implications for the sustainable development of ground source heating systems

Groundwater thermally enhanced by the Urban Heat Island effect can be utilised by ground source heating systems (GSHSs). However, the near subsurface is subject to seasonal temperature variation reflected in shallow groundwater that can differ by several degrees throughout the year. To sustainably manage the near surface thermal resource an understanding of factors which control variation in groundwater temperature and how these are transmitted through the aquifer is needed. We show that even in relatively small urban areas (Cardiff, U.K., situated on a shallow gravel aquifer) the Zone of Seasonal Fluctuation (ZSF) can vary in depth by 8m. GSHSs are more efficient if they are sited below the ZSF, where temperatures are more stable. In Spring 2014, 48 groundwater monitoring boreholes were profiled at a 1m resolution to measure groundwater temperature across Cardiff. These were reprofiled that Autumn and compared to the Spring temperatures, defining the ZSF. The average depth to the base of the ZSF was 9.5mbgl but ranged from 7.1-15.5mbgl. The amplitude of the differences between Spring and Autumn temperatures also varied. To better understand the high spatial variability 60 boreholes were instrumented with in situ temperature loggers, recording at half-hourly intervals. The first year’s data revealed the amplitudes of temperature variation within boreholes with loggers at similar depths were not always consistent. It was also noted that lag times between air temperature and groundwater temperature were not uniform across the sites. The data also showed that where gravels occurred at shallower depths the ZSF tended to be shallower and lag times shorter. The wide spatial variability of the ZSF may be partially explained by differing landuse. Those boreholes in open, grassed areas showed a deeper ZSF than those in built-up areas but built-up areas generally showed the greatest variation between Spring and Autumn temperature profiles, suggesting heat loss from buildings and underground infrastructure plays a part. Natural and anthropogenic factors affecting spatial and temporal groundwater temperatures, either separately or in combination, that have been considered in this study include landuse, depth, lithology/lithostratigraphy, material properties, hydrogeological setting, thermal conductivity, buried infrastructure, land surface temperature, weather effects and solar radiation. This study shows that urban groundwater temperatures can vary greatly across a small area, which has implications for the successful development, and long-term performance of open- and closed-loop GSHSs, and the environmental regulation of these systems. Key to the effective wide-scale use of GSHSs is an understanding of the hydrogeological setting, chiefly how heat is transferred across the aquifer. This study attempts to provide insight into an array of factors which determine heat transfer in the ZSF

Mapping shallow urban groundwater temperatures, a case study from Cardiff, UK

Low-enthalpy ground source heating systems can help to reduce our dependence on fossil fuels, in turn reducing greenhouse gas emissions and increasing energy security. To de-risk and support the sustainable development, regulation and management of ground source heating systems in urban areas, detailed baseline mapping of groundwater temperatures is required. Groundwater temperatures were measured in 168 monitoring boreholes primarily within a Quaternary sand and gravel aquifer in the city of Cardiff, UK. The data have been used to create the first city-wide map of shallow groundwater temperatures in the UK. This map can be used both to support development of ground source heating and to act as a detailed baseline from which to measure change. Shallow groundwater temperatures under the city were found to be 2°C warmer than the UK average groundwater temperature and this additional heat is attributed to the urban heat island. The zone of seasonal fluctuation varies from 7.1 and 15.5 m below ground level (mbgl) within the shallow Quaternary aquifer, averaging 9.5 mbgl. Deeper groundwater temperature profiles incorporating both the Quaternary and bedrock aquifers suggest that a ‘zone of anthropogenic influence’ exists down to about 70 mbgl. Around a third of the UK's greenhouse gas emissions are produced by space heating, and the UK Government recognizes the need to change the way heat is produced and consumed so as to reduce the impacts of climate change and improve energy security (DECC 2013). In response to this driver the UK Government has established targets in the legally binding Climate Change Act 2008 to reduce greenhouse gas emissions by 80% from the 1990 baseline by 2050. In Wales the Well-being of Future Generations (Wales) Act 2015 requires public bodies to take action to undertake sustainable development to drive social, economic and environmental benefits, both now and into the future. Low-enthalpy ground source heating systems, when deployed in a sustainable manner, can provide a low-cost, low-carbon and secure form of heating (e.g. Allen et al. 2003). Ground source heat pumps can broadly be classified as either ‘open-loop’ or ‘closed-loop’ systems. Open-loop systems require the abstraction of groundwater, which is passed through a heat exchanger before being returned to the aquifer. Open-loop systems can have a higher coefficient of performance (COP) and require fewer boreholes where shallow groundwater is available. Open-loop systems may not be suitable if water cannot be successfully recharged to the same aquifer and there are also requirements for abstraction licences and discharge permits or exemptions. The closed-loop system uses a sealed pipe that can be either laid flat or installed vertically into a borehole. These systems often require a greater number of boreholes, increasing cost; however, in the UK they do not require licensing and this can reduce costs. Sustainable development of ground source heat pump (GSHP) systems for both heating and cooling requires characterization of baseline groundwater temperatures. Knowledge of baseline conditions is important to support the design and regulation of GSHP. Baseline temperature data are required to assess the potential impacts of multiple ground source heating and cooling systems so as to avoid interactions between neighbouring systems (Fry 2009; Headon et al. 2009). It is anticipated that if negative interactions between ground source heating and cooling systems continue, some aquifers, mainly in densely populated cities, will need to be managed in terms of heat as well as groundwater resources (Banks et al. 2009). Regulators need legal, policy and scientific tools to support risk-based management of the subsurface, and one such tool is baseline temperature data and mapping of groundwater heat resources. The shallow gravel aquifer in Cardiff is a favourable geological setting in which to develop open-loop ground source heating systems. To support the sustainable development of this technology we have produced the first city-wide baseline map of groundwater temperatures and better defined the depth of the zone of seasonal fluctuation. The data and supporting map outputs will provide an independent source of information for system designers and installers, housing developers, space planners and regulators that is intended to help inform planning decisions and optimize design of GSHP schemes. Additionally, we describe observed seasonal groundwater temperature variation and define the base of the ‘zone of seasonal fluctuation’, which will allow developers to locate abstraction boreholes at depths unaffected by seasonal temperature changes. An initial estimate of available thermal energy that could be transferred from existing dewatering abstractions is made as an illustration of the city-wide potential

Shallow groundwater temperatures and the urban heat island effect: the first U.K. city-wide geothermal map to support development of ground source heating systems strategy

U.K. Government aims to reduce greenhouse gas emissions by 80% by 2050 (Climate Change Act, 2008). Ground source heating systems could contribute to the U.K.’s energy future but uptake has been slow due to a lack of case studies. The aim of this work was to produce the 1st U.K. city-wide heat map to support the development of ground source heating. We also sought to describe groundwater temperature variation with lithology & estimate the available thermal energy beneath the city