Tectonic and climatic considerations for deep geological disposal of radioactive waste: a UK perspective

Identifying and evaluating the factors that might impact on the long-term integrity of a deep Geological Disposal Facility (GDF) and its surrounding geological and surface environment is central to developing a safety case for underground disposal of radioactive waste. The geological environment should be relatively stable and its behaviour adequately predictable so that scientifically sound evaluations of the long-term radiological safety of a GDF can be made. In considering this, it is necessary to take into account natural processes that could affect a GDF or modify its geological environment up to 1 million years into the future. Key processes considered in this paper include those which result from plate tectonics, such as seismicity and volcanism, as well as climate-related processes, such as erosion, uplift and the effects of glaciation. Understanding the inherent variability of process rates, critical thresholds and likely potential influence of unpredictable perturbations represent significant challenges to predicting the natural environment. From a plate-tectonic perspective, a one million year time frame represents a very short segment of geological time and is largely below the current resolution of observation of past processes. Similarly, predicting climate system evolution on such time-scales, particularly beyond 200 ka AP is highly uncertain, relying on estimating the extremes within which climate and related processes may vary with reasonable confidence. The paper highlights some of the challenges facing a deep geological disposal program in the UK to review understanding of the natural changes that may affect siting and design of a GDF

A geological fence diagram for England and Wales

This report contains a brief description of the data and methodology used to compile the National Geological Fence Diagram (NGFD). The NGFD comprises a network of intersecting geological cross-sections covering England and Wales, to a minimum depth of 1 km and a total section length of approximately 5,500 km. It was compiled by the British Geological Survey (BGS) on behalf of the Environment Agency (EA) and is based upon lines of section agreed between both parties at the inception of the project. The model includes generalised bedrock strata based principally on the BGS 1:625 000 scale digital geological data and superficial deposits greater than 10m in thickness. Additional sources of model data were also considered, largely taken from published BGS data holdings. In total 41 cross-sections were constructed and geologically correlated within the GSI3D software

A crustal magnetic model of Britain obtained by 3D inversion

The national baseline aeromagnetic survey of Britain allows a uniform assessment of the shallow and deep magnetic properties of the British tectonic terranes. The most significant is that associated with destruction of early Palaeozoic oceanic lithosphere across the Iapetus Suture separating Baltica and Avalonia from the Laurentian terranes. Here a formal 3D inversion of a continuous swathe of the data is considered. The study provides a uniform volumetric whole crust assessment extending for over 1000 km. Normally a 3D inversion of magnetic data is controlled using a variety of constraints however this is not appropriate at the crustal scale due to our increasingly imprecise knowledge of lithology at increasingly greater depths. The main crustal interface encountered occurs at the Curie isotherm depth. We demonstrate the behaviour of introducing different magnetic crustal depths and suggest the crustal ‘magnetic depth’ of our models can be independently constrained using global or regional studies of the deep geotherm. Static magnetic data have no inherent depth resolution. Here an empirical ‘1D depth’ weighting and a more formal ‘3D distance’ weighting are assessed. The inversion procedure is regularised to provide stable models appropriate to the data and their errors. To gain confidence when using such a ‘geologically-unconstrained’ inversion, we compare our 3D inversion results with an existing geologically-constrained 2.5D profile inversion across northern Britain. A surprising agreement in the 3D susceptibility magnitudes is observed. The chosen study area traverses 10 British terranes and images their tectonic fabric by way of non-magnetic zones (i.e. susceptibilities <0.0001 to 0.001 SI) and magnetic zones displaying geological relevance and tectonic significance at deeper crustal levels. Here we discuss the more significant 3D model features which, by virtue of a continuous crustal-scale assessment and fitting the data with a high degree of fidelity, provide additional structural insights

The temperature of Britain's coalfields

Low temperature heat recovery, cooling and storage schemes, using abandoned flooded mine workings are a viable option for low carbon heating solutions within many abandoned British coalfields. The temperature of mine water is a useful parameter, coupled with depth to water, sustainable yield and recharge potential, to identify suitable locations and calculate the likely performance of heat recovery schemes. This paper aims to provide the first mapping and synthesis of the temperature of Britain's coalfields to support this emerging technology. Using the best available evidence, a median geothermal gradient of 24.1 °C/km was calculated for the British coalfields. However, geothermal gradients between separate coalfields can vary from 17.3 to 34.3 °C/km. The North East, Cumbria and Yorkshire coalfields all have mean geothermal gradients generally >30 °C/km, whilst geothermal gradients of generally <23 °C/km are measured in the Warwickshire, South Wales, Staffordshire, Douglas and Fife coalfields. Active dewatering schemes are shown to locally increase the apparent measured geothermal gradient by ingress and mixing of deeper water into the pumping shafts. This baseline spatial mapping and synthesis of coalfield temperatures offers significant benefit to those planning, designing and regulating heat recovery and storage in Britain's abandoned coalfields

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

Urban geology of Swansea: Neath : Port Talbot

The conurbation of Swansea–Neath–Port Talbot is one of the main centres of industrial development in South Wales. A long history of mineral extraction and processing, which stoked the initial growth of the towns, declined during the 20th Century. Many of these former industries have left a legacy of groundwater, watercourse and land contamination. A project funded by the Environment & Hazards Directorate (British Geological Survey) between 2000-2005 used available geological data to determine potential areas of contaminated land and understand the influence of the geology to pollutant pathways (Waters et al., In press a). The study covered 100 km2 of the Swansea- Neath-Port Talbot area (Fig. 2.1) and was aimed at providing data relevant to contaminated land issues, to augment the study by Arup (1997) on earth science information relevant to planning and development for the Swansea-Llanelli district, and look at new methodologies of presenting the data

Establishing an urban geo-observatory to support sustainable development of shallow subsurface heat recovery and storage

Low-enthalpy ground source heating and cooling is recognised as one strategy that can contribute towards reducing reliance on traditional, increasingly insecure, CO2-intense thermal power generation, as well as helping to address fuel poverty. Development of this technology is applicable in urban areas where high housing density often coincides with the presence of shallow aquifers. In urban areas groundwater temperatures can be elevated due to the subsurface Urban Heat Island effect. Uptake and development of this technology is often limited by initial investment costs, however, baseline temperature monitoring and characterisation of urban aquifers, conducted in partnership with local authorities, can provide a greater degree of certainty around resource and sustainability that can facilitate better planning, regulation and management of subsurface heat. We present a novel high-density, city-scale groundwater temperature observatory and introduce a 3D geological model aimed at addressing the needs of developers, planners, regulators and policy makers. The Cardiff Geo-Observatory measures temperature in a Quaternary aged sand and gravel aquifer in 61 boreholes and at a pilot shallow open-loop ground source heating system. We show that repurposing existing infrastructure can provide a cost effective method of developing monitoring networks, and make recommendations on establishing similar geo-observatories

Detector Description and Performance for the First Coincidence Observations between LIGO and GEO

For 17 days in August and September 2002, the LIGO and GEO interferometer gravitational wave detectors were operated in coincidence to produce their first data for scientific analysis. Although the detectors were still far from their design sensitivity levels, the data can be used to place better upper limits on the flux of gravitational waves incident on the earth than previous direct measurements. This paper describes the instruments and the data in some detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial change

Search for Gravitational Waves from Primordial Black Hole Binary Coalescences in the Galactic Halo

We use data from the second science run of the LIGO gravitational-wave detectors to search for the gravitational waves from primordial black hole (PBH) binary coalescence with component masses in the range 0.2--$1.0 M_\odot$. The analysis requires a signal to be found in the data from both LIGO observatories, according to a set of coincidence criteria. No inspiral signals were found. Assuming a spherical halo with core radius 5 kpc extending to 50 kpc containing non-spinning black holes with masses in the range 0.2--$1.0 M_\odot$, we place an observational upper limit on the rate of PBH coalescence of 63 per year per Milky Way halo (MWH) with 90% confidence.Comment: 7 pages, 4 figures, to be submitted to Phys. Rev.