The baseline concentrations of methane in Great British groundwater : the National Methane Baseline Survey

This report describes the BGS research programme evaluating the baseline concentration of methane in groundwater which ran from November 2011 to completion in March 2016. The aim of the survey has been to improve knowledge of conditions in aquifers overlying potential shale gas source rocks present at depth, thus providing baseline knowledge relevant to the management of future exploration of new hydrocarbon sources. The necessity for doing this has been prompted by evidence from elsewhere (notably the USA) which has revealed very high methane concentrations in groundwater in some areas of shale gas extraction. Although this has often been directly attributed to shale gas operations, there have generally been no pre-development data on methane concentrations available to test this. Before the start of the current survey, BGS held some 170 analyses of methane in groundwaters from aquifers across Great Britain, acquired from the 1980s onwards. These data have been combined with new survey data, to give a total of 439 methane data points. In this combined dataset, 96% of samples show methane concentrations of less than 100µg/l and indicate that methane is rarely present at concentrations high enough to be potentially explosive (there are no health limits for methane in groundwaters). In the minority of samples with elevated concentrations, this was generally considered to be due to the proximity of organic rich coal seams or peats. The highest concentrations were found in the Cretaceous aquifers of the Weald Basin, a known area for occurrences of methane gas in the shallow subsurface. The new survey covers the majority of principal aquifers in Great Britain, including the Chalk, Permo-Triassic Sandstones, Carboniferous Limestone, and the Lower Greensand. Samples from over twenty different aquifers have been collected. In general, methane concentrations in carbonate aquifers (Chalk, limestones, Oolites etc.) are low, similar to those seen in the Permo-Triassic sandstone aquifers, although methane is widely present above detection limit (approximately 1µg/L) in all these aquifers. The Coal Measures of South Wales have the highest median value across Great Britain and this aquifer also shows the greatest temporal variability. Methane concentrations in the Carboniferous sediments of Scotland are also elevated, likely due to the impact of mining and the presence of coal seams. While little temporal variability is generally seen in aquifers used for public water supply or otherwise regularly pumped, further work is required to understand the impact of borehole use, pumping regime and aquifer type on the variability of the methane baseline of Great British aquifers. It should be noted that the Survey is not intended to replace any oil and gas operator’s local monitoring as required by the regulators. This is a national scale survey to enable a broad understanding of the distribution of methane in aquifers across relevant areas of Britain and cannot replace an understanding of groundwater quality at a local scale

Gravitational anomalies in a dispersive approach

The gravitational anomalies in two dimensions, specifically the Einstein anomaly and the Weyl anomaly, are fully determined by means of dispersion relations. In this approach the anomalies originate from the peculiar infrared feature of the imaginary part of the relevant formfactor which approaches a $\delta$-function singularity at zero momentum squared when $m \to 0$.Comment: 10 page

Bell inequality and CP violation in the neutral kaon system

For the entangled neutral kaon system we formulate a Bell inequality sensitive to CP violation in mixing. Via this Bell inequality we obtain a bound on the leptonic CP asymmetry which is violated by experimental data. Furthermore, we connect the Bell inequality with a decoherence approach and find a lower bound on the decoherence parameter which practically corresponds to Furry's hypothesis.Comment: 10 pages, latex, no figure

State permutations from manipulation of near level-crossings

We discuss some systematic methods for implementing state manipulations in systems formally similar to chains of a few spins with nearest-neighbor interactions, arranged such that there are strong and weak scales of coupling links. States are permuted by means of bias potentials applied to a few selected sites. This generic structure is then related to an atoms-in-a-cavity model that has been proposed in the literature as a way of achieving a decoherence free subspace. A new method using adiabatically varying laser detuning to implement a CNOT gate in this model is proposed.Comment: 6 pages, 5 figures. Substantial revision and extension of the introduction and the atoms-in-a-cavity section

Regional freshwater nitrogen budgets for Scotland

Following Carnell et al. (2019) which provided a nitrogen (N) budget for Scotland, this short project aims to provide freshwater N budgets for 10 Scottish hydrometric regions. The regional N budgets quantify key N flows across the hydrosphere and terrestrial systems (agricultural and semi-natural) and include N from human waste and atmospheric deposition. The freshwater model used here ‘LTLS-FM’ provides estimates of total N inputs to freshwater in 2010. The results indicate that total N inputs vary between regions, from 1.7 kT N for Orkney and Shetland, to 33.2 kT N for NE Scotland. However, when N inputs are divided by the area of the region, it becomes apparent that two of the smallest regions, Tweed and Forth, have the highest N inputs/km2. Across Scotland, LTLS-FM estimates of losses of freshwater N to coastal waters (151 kT N) and to the atmosphere (17.3 kT N) in 2010 were substantial, with more than half of the N losses originating from just 3 regions (Tay, Solway and NE Scotland). As much as 68% of Scotland’s N in freshwaters comes from agricultural land management, for which improved nutrient use efficiency could increase environmental as well as economic benefits. These data will contribute to the development of the Scottish Nitrogen Balance Sheet (SNBS), which is mandated under the Scottish Climate Change Act 2019

Field-scale evaluation of collection methods for dissolved methane samples in groundwaters

This report presents the findings of a jointly funded project by the British Geological Survey (BGS) and Environment Agency (EA project SC210014) that addresses some of the research needs identified in the EA project SC190007 “Methods for sampling and analysing methane in groundwater: a review of current research and best practice”. Primary field sampling allowed comparison of sample collection techniques for dissolved methane in groundwaters, to provide a field evidence base to help establish good practice guidelines (or protocols). This included evaluation of purging protocols, groundwater sampling devices, surface collection protocols, and the influence of methane concentration. The field study used two boreholes previously shown to have groundwater of contrasting low methane concentration (~1mg/l) ‘Site A’, and high methane concentration (~25 mg/l) ‘Site B’ in close proximity in the Vale of Pickering. The boreholes were previously used for hydrochemical baseline monitoring and were similar in construction and hydrogeological setting, each having shallow (~ 1 m depth) water table and a conventional 3-m long well screen sampling a fractured Kimmeridge Clay unit with methane naturally present from elevated organic matter contents. A stage 1 zero-purge passive sampling device was used to obtain initial samples, followed by a low-flow methodology with parallel use of submersible, bladder and peristaltic pumped samples, with stage 2 sampled after purging a single screen volume, and stage 3 sampled after purging to hydrochemical parameter stabilisation over 5.7 – 7.5 pumped screen volumes. Finally, a post-purge stage 4 sample was obtained with the same passive sampling device. Sample collection protocols tested were open (direct fill vial), semi-closed inverted (submerged-inverted vial), semi-closed upright (submerged-upright vial) and closed (double valve cylinder closed to atmosphere). All samples were obtained in triplicate from each pump during stages 2 and 3, but in stages 1 and 4 only open samples were possible from the passive sampling device. Data interpretation was supported by logged hydrochemical borehole groundwater depth profiles before and after the sampling programme, and by the historical methane baseline record. Methane concentrations measured at Site A are challenging to interpret: they are highly sensitive to purging volume, with a decrease in mean concentration of 72% over the purging stages. This, and the time required to obtain multiple samples, obscured specific sensitivity of methane concentration to pump and sample collection protocol variables at Site A. Although the differences in concentrations seen between pumps and between collection protocol are not statistically significant, the high variability in Site A data overall, 52-117% relative standard deviation (RSD), mean these data are generally not useful for developing good practice proposals. Site B, with high methane concentration, provided more consistent data that allowed meaningful comparisons of methane sensitivity between purging volume, pump type and collection methods with findings that are generally consistent with existing literature. Methane concentrations had a lower sensitivity to purging than at Site A (21% mean concentration declines with ~30 % RSD). Most of the conclusions made from Site B data can reasonably be expected to also apply to sites with lower concentrations. In isolation, pump selection - bladder, submersible or peristaltic pump - makes little difference to sampled methane concentrations. The HydasleeveTM passive sampler consistently produced the lowest concentrations, but is very likely to have sampled different water in the borehole to that sampled mid-screen by the active pumps. However, bladder and peristaltic pump closed samples yield higher concentrations, which is attributed to their capacity to provide increased pressure at low flow, thereby reducing degassing potential. The bladder pump is preferred for this use, due to its lower closed sample concentration variability, which is attributed to the controllability of the bladder pump pressure. The peristaltic pump was tested under favourable shallow water table conditions, and a negative concentration bias that is generally expected from suction pressure was not evident, but this is acknowledged as a concern, especially for deeper water tables, where its use may need more caution. Closed sampling at Site B consistently yielded the highest methane concentrations across all pumps with lowest variability, and is the recommended sample collection protocol. Commercial availability of closed sample analysis is, however, limited. The semi-closed (inverted and upright) methods yielded intermediate concentrations between closed and passive samples, with inverted methods generally giving higher concentrations than semi-closed. When using the inverted protocol, exsolving gas headspace accumulation leads to uncertainties in concentration measurements, meaning that the semi-closed upright protocol is often preferred, especially where degassing is evident or expected although results in this study do not directly support this. Open samples consistently produced the lowest concentrations and should only be used where other protocols are impractical, e.g. sampling from a non-pumped collection device. Switching protocols from open sampling to upright sampling requires minimal investment, and is likely to produce more robust concentration data and/or reduced variability, although results from this study do not provide undisputable evidence of this. The observed sensitivities of measured methane concentrations to different parts of the sampling methodology underline the central importance of using an identical protocol with specific pumps, similar deployments, identical purging volumes or stabilisation criteria, and specific sample collection protocol, in order to generate robust temporal records. Reliable cross comparison of data produced by different organisations requires sampling protocols to be as identical as possible. Any protocol change should be done using an overlap period in which both old and new protocols are used simultaneously, to prevent a sampling-related step change in data. This study also indicates that extended purging of any borehole leads to lower concentration samples over time, which critically has the potential to underestimate methane risk. Combining the findings of this study and wider literature reviewed under EA project SC190007, a concise ‘lookup’ sheet is presented as a non-prescriptive aid to assist practitioners in ‘Groundwater methane sampling protocol development’. It covers: site selection, pump/sampler selection/deployment, supporting reconnaissance measurements, sample collection and protocol, data management and wider use. Finally, outstanding field research needs are indicated. The foremost of these is comparative field testing of down-hole devices for obtaining closed system samples at in-situ groundwater pressure

Grid-based simulation of soil moisture in the UK: future changes in extremes and wetting and drying dates

Soil moisture, typically defined as the amount of water in the unsaturated soil layer, is a central component of the hydrological cycle. The potential impacts of climate change on soil moisture have been less specifically studied than those on river flows, despite soil moisture deficits/excesses being a factor in a range of natural hazards, as well as having obvious importance for agriculture. Here, 1 km grids of monthly mean soil moisture content are simulated using a national-scale grid-based hydrological model, more typically applied to look at changes in river flows across Britain. A comparison of the soil moisture estimates from an observation-based simulation, with soil moisture deficit data from an operational system developed by the UK Met Office (Meteorological Office Rainfall and Evaporation Calculation System; MORECS), shows relatively good correspondence in soil drying and wetting dates, and in the month when soils are driest. The UK Climate Projections 2018 Regional projections are then used to drive the hydrological model, to investigate changes in occurrence of indicative soil moisture extremes and changes in typical wetting and drying dates of soils across the country. Analyses comparing baseline (December 1981–November 2011) and future (December 2050–November 2080) time-slices suggest large increases in the spatial occurrence of low soil moisture levels, along with later soil wetting dates, although changes to soil drying dates are less clear. Such information on potential future changes in soil moisture is important to enable the development of appropriate adaptation strategies for a range of sectors vulnerable to soil moisture levels

Entanglement, Bell Inequalities and Decoherence in Particle Physics

We demonstrate the relevance of entanglement, Bell inequalities and decoherence in particle physics. In particular, we study in detail the features of the ``strange'' $K^0 \bar K^0$ system as an example of entangled meson--antimeson systems. The analogies and differences to entangled spin--1/2 or photon systems are worked, the effects of a unitary time evolution of the meson system is demonstrated explicitly. After an introduction we present several types of Bell inequalities and show a remarkable connection to CP violation. We investigate the stability of entangled quantum systems pursuing the question how possible decoherence might arise due to the interaction of the system with its ``environment''. The decoherence is strikingly connected to the entanglement loss of common entanglement measures. Finally, some outlook of the field is presented.Comment: Lectures given at Quantum Coherence in Matter: from Quarks to Solids, 42. Internationale Universit\"atswochen f\"ur Theoretische Physik, Schladming, Austria, Feb. 28 -- March 6, 2004, submitted to Lecture Notes in Physics, Springer Verlag, 45 page

Generation of entangled states and error protection from adiabatic avoided level crossings

We consider the environment-affected dynamics of $N$ self-interacting particles living in one-dimensional double wells. Two topics are dealt with. First, we consider the production of entangled states of two-level systems. We show that by adiabatically varying the well biases we may dynamically generate maximally entangled states, starting from initially unentangled product states. Entanglement degradation due to a common type of environmental influence is then computed by solving a master equation. However, we also demonstrate that entanglement production is unaffected if the system-environment coupling is of the type that induces ``motional narrowing''. As our second but related topic, we construct a different master equation that seamlessly merges error protection/detection dynamics for quantum information with the environmental couplings responsible for producing the errors in the first place. Adiabatic avoided crossing schemes are used in both topics.Comment: 14 pages, 6 figures. Minor changes. To appear in Phys. Rev.

A baseline survey of dissolved methane in aquifers in Great Britain

Interest in dissolved methane (CH4) concentrations in aquifers in England, Scotland and Wales (‘Great Britain’ or GB) has grown concurrently with interest in the exploitation of unconventional gas sources (UGS). Experience, mainly from North America, has shown the importance of a pre-production baseline against which changes possibly due to UGS extraction can be compared. The British Geological Survey, aided by water utilities, private users and regulators, has compiled a unique dataset for CH4 in groundwaters of GB. This focuses principally on areas where UGS exploration is considered more likely, as indicated by the underlying geology. All the main water supply aquifers (Principal aquifers) were targeted, plus Secondary aquifers where locally important. The average dissolved CH4 concentration across GB in the aquifers sampled was 45 μg/l. Out of a total of 343 sites, 96% showed dissolved CH4 concentrations b100 μg/l, 80% b10 μg/l, and 43% b 1 μg/l. No site had a CH4 concentration above the US Department of the Interior suggested risk action level of 10,000 μg/l. While most sites were sampled only once, a sub set was monitored quarterly to determine the magnitude of seasonal or other variations. Generally these variations were minor, with 84% of sites showing variations within the range 0.5–37 μg/l, but some aquifers where the porosity was primarily fracture-related showed larger changes (0.5–264 μg/l). This may have been due to the nature of sampling at these sites which, unlike the others, did not have installed pumps. Since the regulatory compliance monitoring attending UGS operations will include the measurement of parameters such as dissolved CH4, it is essential that sampling methods are tested to ensure that reliable and comparable datasets can be obtained