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We present a new method for deriving surface soil gas flux at the field scale, which is less fieldwork intensive than traditional chamber techniques and less expensive than those derived from airborne or space surveys. The “open-field” technique uses aspects of chamber and micrometeorological methods combined with a mobile platform and GPS to rapidly derive soil gas fluxes at the field scale. There are several assumptions in using this method, which will be most accurate under stable atmospheric conditions with little horizontal wind flow. Results show that soil gas fluxes, when averaged across a field site, are highly comparable between the open-field method and traditional chamber acquisition techniques. Atmospheric dilution is found to reduce the range of flux values under the open-field method, when compared to chamber-derived results at the field scale. Under ideal atmospheric conditions it may be possible to use the open-field method to derive soil gas flux at an individual point; however this requires further investigation. The open-field method for deriving soil–atmosphere gas exchange at the field scale could be useful for a number of applications including quantification of leakage from CO2 geological storage sites, diffuse degassing in volcanic and geothermal areas, and greenhouse gas emissions, particularly when combined with traditional techniques.

An assessment of topsoil (5–20cm) metal/metalloid (hereafter referred to as metal) concentrations across Glasgow and the Clyde Basin reveals that copper, molybdenum, nickel, lead, antimony and zinc show the greatest enrichment in urban versus rural topsoil (elevated 1.7–2.1 times; based on median values). This is a typical indicator suite of urban pollution also found in other cities. Similarly, arsenic, cadmium and lead are elevated 3.2–4.3 times the rural background concentrations in topsoil from the former Leadhills mining area. Moorlands show typical organic-soil geochemical signatures, with significantly lower (P

Data conditioning procedures involve the verification, quality control and data levelling processes that are necessary to make data fit for the purpose for which it is to be used. It is something that has to be planned at the outset of any project generating geochemical data. Whether it is in the sampling phase, for example, determining how sites and samples should have a unique identity, or through to the data presentation phase in which disparate data sets may have to be joined to form a seamless map. This account describes the methods currently used by the British Geological Survey's regional geochemical mapping project that has been generating geochemical data for various sample media for nearly 40 years. It is important that users of the data are given information that will help them ascertain whether the provided environmental data is suitable for the purpose of its intended use.

The collection of drainage samples from active stream channels for geochemical mapping is now a well-established procedure that has readily been adapted for environmental studies. This account details the sampling methods used by the British Geological Survey in order to establish a geochemical baseline for the land area of Great Britain. This involves the collection of stream sediments, waters, and panned heavy mineral concentrates for inorganic chemical analysis. The methods have been adapted and used in many different environments around the world. Detailed sampling protocols are given and sampling strategy, equipment and quality control are discussed.

Surface gas and biological monitoring were carried out in 2009 at the In Salah Gas project (Krechba, Algeria), where geological storage of CO 2 has been underway since mid-2004. The CO 2 is removed from produced natural gas and re-injected below the gas-water contact on the flanks of the reservoir. The biological work was the first such study undertaken at the site. Observations were made in: Uplifted areas around the three CO 2 injection wells, around the KB-5 well where breakthrough of CO 2 from the KB-502 injector had occurred, around the KB-4 well and in a background area away from CO 2 injection and gas production. Near ground atmospheric measurements were made with a mobile open path laser system, with soil gas and flux measurements in support of these and of a botanical and microbiological survey. Longer term monitoring was initiated for radon and other gases using buried probes and activated charcoal integrative collectors. Laser measurements appeared to show only natural variations, but interference from the vehicle exhaust, windblown dust and rain was apparent. Modifications are needed to overcome these problems. Natural variation of atmospheric CO 2 needs to be better constrained to identify anomalous values. Soil gas concentrations and fluxes were very low but slightly higher values over the KB-5 well could indicate low-level leakage. This is likely to be a legacy of breakthrough prior to the abandonment of the well. A variety of monocotyledonous and dicotyledenous plants was present, particularly in dry wadis or shallow depressions. The xerophytic flora and the microbial numbers were typical of such desert environments and the data provide baseline values since there were no indications of elevated CO 2 . There were analytical problems with the microbial activity determinations but it can be concluded that activities were low.

The topsoil of around 10 000 km2 in eastern England has recently been sampled intensely at 4609 sites to characterize its geochemistry. The parent materials, which include both solid geology and Quaternary sediments, range in age from Permian to Holocene. The distributions of the concentrations of major and trace elements have been characterized geostatistically, and the role of parent material on their spatial structure (anisotropy) and their spatial relationships (coregionalization) have been investigated. Analysis of variance with the sites grouped by major parent material type showed that this classification accounted for 14 to 48 per cent of the variance for the various elements. Global variograms of 13 elements (Al, As, Ca, Cr, Cu, Fe, Mg, Mo, Ni, P, Pb, Ti, and U) have been computed and modelled. Eleven of the variograms seem to comprise two structures, both of which we modelled with spherical functions, one of short range, 3·5 to 9 km, and the other with a range of 15 to 23 km. The models included a nugget variance, which varied from 27 per cent (for As, Fe, and Mg) to 63 per cent (for P) of the total. The long-range structures are related to the separations of the major parent materials. The variograms of several elements showed appreciable anisotropy, most notably that of Mg. Anisotropy is evident at short ranges of less than 5 km. This accords with the geological structure of the beds which dip from west to east so that their outcrops are elongated from north to south. A linear model of coregionalization fitted to the data emphasized several important geochemical associations, which we interpret. Elements commonly associated with clay minerals (Mg, Al) and the clay size fraction (Ti) are dominated by the long-range structure of the coregionalization, whilst several trace elements (As, Cr, Ni and U) are spatially correlated with Fe over short distances, through adsorption of the former on the surfaces of Fe oxyhydroxides. The topsoil around large urban areas is enriched in lead, but it is not clear whether anthropogenic sources are responsible for this metal's anomalous spatial relationships with other elements. Crown copyright © 2003. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

Selected European studies have illustrated the impacts of elevated CO2 concentrations in shallow soils on pasture. For the first time, general unified conclusions can be made, providing CO2 thresholds where effects on plants and soil microbiology are observed and making recommendations on how this information can be used when planning projects for CO2 storage. The sites include those where CO2 is being naturally released to the atmosphere from deep geological formations; and a non-adapted site, with no previous history of CO2 seepage, where CO2 has been injected into the unsaturated soil horizon. Whilst soil gas concentrations will be influenced by flux rates and other factors, the results suggest that a concentration of between 10% and 15% CO2 soil gas at 20 cm depth, which is within the root zone, is an important threshold level for observing changes in plant coverage. Site-specific plant ‘indicators’ are also observed for CO2 concentrations at ≥35%. Microbiological changes are seen where CO2 soil gas concentrations are between 15% and 40%. As part of site characterisation, an evaluation of the risks of leakage and their potential environmental impacts should be undertaken.

Data from a regional geochemical survey of topsoils (n=818) in rural and peri-urban areas over a single parent material (Coal Measures) are used to identify two types of trace-metal pollution – severe local contamination at 20 sites and widespread, diffuse pollution in more densely populated areas. Median concentrations of several trace metals in topsoils were significantly higher in areas of high, compared to low, population density (percentage increases in parenthesis): As (31), Cu (39), Fe (7), Mo (26–36), Ni (29), Pb (20), Sn (40), and Zn (11). Four potential pathways of diffuse trace-metal pollution are postulated: coal-ash dispersal, atmospheric aerosols derived from coal combustion, the historical spreading of sewage waste, and those related to road vehicles. The statistical analysis of geochemical data classified by local, human population density can be an effective means of identifying the magnitude and extent of diffuse pollution, and could help to establish natural background levels.

Spatial and temporal controls on major ion stream water chemistry are assessed using hydrochemical survey data for Wales and the West Midlands, and time-series data from the intensively studied Plynlimon catchment (mid-Wales). Spatial variations in stream water chemical composition are interpreted in relation to the environmental chemistry of the major ions and controls such as bedrock geology, land-use, anthropogenic activities and atmospheric inputs. Piper diagrams are used to illustrate compositional variation, allowing comparison to be made between samples of widely varying Total Dissolved Solids (TDS). Spatial and temporal data sets are overlaid on Piper plots to determine the relative importance of these two factors in controlling major ion chemistry. Bedrock geology, atmospheric input and land-use can satisfactorily explain compositional variation in the spatial data set. Combined analysis of the spatial and temporal data sets indicated that the variation in cation composition at the Plynlimon site is considerably more constrained than that on the corresponding anion diagram. Time-series data sets for sites of different bedrock geology and at a range of distances from sources of marine derived solute inputs are necessary for further investigation of the relative importance of temporal and spatial controls on major ion stream water chemistry.

The completion of the high-resolution (ca. 1 sample per 1.5 km2) geochemical survey of Wales and part of the West Midlands by the British Geological Survey has created a unique data set containing over 13,500 site-specific hydrochemical and stream-sediment analyses for a typical suite of over 21 major and trace components. The collection of such a wide range of data over an area with contrasting geology, soils, geomorphology and land use has enabled the delineation and study of hydrochemical processes on a regional basis. Methods are presented describing transformations performed from basic concentration-based data (pH, conductivity and 21 major and trace elements) into hydrochemically relevant trilinear and solubility diagrams predicting aqueous speciation and ionic domination. These data are then displayed and interpreted using a series of thematic composites. The utility of coupling speciation diagrams, based upon pure ideal systems, with Geographical Information Systems for describing processes controlling hydrogeochemical evolution at a regional scale is described. The validity of using solubility diagrams to describe large regional hydrochemical data sets is tested using geographically linked representations of aqueous saturation and chemical speciation generated from the individual modelling of each sample using PHREEQC. Comparison of the pure and real (PHREEQC) systems for calcite and gypsum indicated that there was a small over-prediction in the pure system; the greatest differences occurred in samples of the highest ionic strength.

The measurement of gas concentrations and fluxes in the soil and atmosphere is a powerful tool for monitoring geological carbon capture and storage (CCS) sites because the analyses are made directly in the biosphere in which we live. These methods can be used to both find and accurately quantifying leaks, and are visible and tangible data for public and ecosystem safety. To be most reliable and accurate, however, the measurements must be interpreted in the context of natural variations in gas concentration and flux. Such baseline data vary both spatially and temporally due to natural processes, and a clear understanding of their values and distributions is critical for interpreting near-surface gas monitoring techniques. The best example is CO2 itself, as the production of this gas via soil respiration can create a wide range of concentrations and fluxes that must be separated from, and not confused with, CO2 that may leak towards the surface from a storage reservoir. The present article summarizes baseline studies performed by the authors at various sites having different climates and geological settings from both Europe and North America, with focus given to the range of values that can result from near surface processes and how different techniques or data processing approaches can be used to help distinguish a leakage signal from an anomalous, shallow biogenic signal.

International audience; Soil gas and CO2 flux measurements were conducted above and in the vicinity of the Weyburn oil field during the period 2001-2005 and in 2011 to determine baseline values and distributions, and to monitor for surface leaks, above this well-established and intensely studied CO2-Enhanced Oil Recovery (CO2-EOR) project in southern Saskatchewan, Canada. Multiple sites were studied which had sample spacing that ranged from 25 to 200 m, including a 360 point regional grid above the CO2 injection field, a background site off the oil field, and a new site where a landowner claimed CO2 leakage on his property from the storage reservoir. Typically 400-500 points were sampled during each of the seven field campaigns and analysed for a wide range of components, thus yielding a large and varied database collected during different seasons and years. Results show no sign of leakage of the injected CO2. Spatial and seasonal trends and measured values from discrete sampling of soil gas CO2, O2 + Ar, N2, δ13C-CO2, He, Rn, and CH4, from continuous monitoring of soil gas CO2 and Rn, and from discrete sampling of CO2 flux can all be explained by the interplay between near-surface biochemical processes, seasonal environmental conditions, and soil properties. Other light hydrocarbon gases, like C2H4 and C2H6, were generally near or below the instrument detection limit. Lessons learned during the research are described to help improve future near-surface gas geochemistry surveys for site assessment, baseline definition, and leakage monitoring at active CCS sites.

The stream water hydrogeochemical database, prepared by the British Geological Survey's Geochemical Survey Programme, in conjunction with databases for stream sediments, soil samples and mineral concentrates, has recently been enhanced for a range of economic and environmental objectives. The density of systematic stream water sampling and analysis has been increased to one sample per km 2 and a broader spectrum of determinands introduced. An orientation suite of hydrogeochemical maps has been produced from water samples collected at 1279 sample sites in North Wales to test the methodology. Preliminary results indicate that bedrock geology and mineralisation are the most important variables which influence the surface water chemistry. The primary control by geological parameters is variously modified by secondary influences which include geomorphological factors (especially altitude) atmospheric (climatic and coastal effects), and anthropogenic (agriculture, urban and industrial developments). Regional hydrogeochemical stream water maps have a wide range of economic and environmental applications, especially when interpreted in conjunction with geological data. Results obtained so far indicate that interpretation is likely to be further enhanced in the future by intercomparison with regional stream sediment, hydrogeological, geomorphological, pedological, agricultural, landuse, climatic and remotely sensed datasets in a GIS environment. Hydrogeochemical sampling and analysis represents a cost-effective addition to the Regional Geochemical Survey of the UK.

New methods for the monitoring of CO2 near the ground surface at geological CO2 storage sites have been tested over areas of natural CO2 emission. Mobile open path laser measurements and ground-surface portable infrared measurements show great promise for rapid assessment of large areas. Such techniques would help to focus more detailed investigations needed to verify the extent and source of the gas being emitted. It is envisaged that they would be used in conjunction with established field and laboratory techniques and continuous monitoring methods as part of an overall monitoring strategy for a CO2 storage site.

When comparing soil baseline measurements with resampled values there are four main sources of error. %RML3 some changes follow These are location (errors in relocating the sample site), sampling errors (representing the site with a sample of material) subsampling error (selecting material for analysis) and analytical error (error in laboratory measurements). In general we cannot separate the subsampling and analytical sources of error (since we always analyse a different subsample of a specimen), so in this paper we combine these two sources into subsampling plus analytical error. More information is required on the relative magnitudes of location and sampling errors for the design of effective resampling strategies to monitor changes in soil indicators. Recently completed soil surveys of the UK with widely differing soils included a duplicate site and subsampling protocol to quantify ii) and iii) above. Sampling variances are estimated from measurements on duplicate samples --- two samples collected on a support of side length 20~m separated by a short distance (21~m). Analytical and subsampling variances are estimated from analyses of two subsamples from each duplicate site. After accounting for variation caused by region, parent material class and land use, we undertook a nested analysis of data from 196 duplicate sites across three regions to estimate the relative magnitude of medium-scale (between site), sampling and subsampling plus analytical variance components for five topsoil indicators: total metal concentrations of copper (Cu), nickel (Ni) and zinc (Zn), soil pH and soil organic carbon (SOC) content. The variance components for each indicator diminish by about an order of magnitude from medium-scale, to sampling, to analytical plus subsampling. Each of the three fixed effects (parent material, land use and region) were statistically significant for each of the five indicators. The most effective way to minimise the overall uncertainty of our observations at sample sites is to reduce the sampling variance.

The British Geological Survey is responsible for the national strategic geochemical survey of Great Britain. As part of this programme, the Geochemical Surveys of Urban Environments (GSUE) project was initiated in 1992 and to date, 21 cities have been mapped. Urban sampling is based upon the collection of top (0.05 to 0.20 m) and deeper (0.35 to 0.50 m) soil samples on a 500 m grid across the built environment (1 sample per 0.25 km2). Samples are analysed for c. 46 total element concentrations by X-ray Fluorescence Spectrometry (XRFS), pH and loss on ignition (LOI) as an indicator of organic matter content. The data provide an overview of the urban geochemical signature and because they are collected as part of a national baseline programme, can be readily compared with soils in the rural hinterland to assess the extent of urban contamination. The data are of direct relevance to current UK land use planning, urban regeneration and contaminated land legislative regimes. An overview of the project and applications of the data to human health risk assessment, water quality protection and contaminant source identification are presented.

A model of soil variability as a continuous background process with superimposed point contamination was applied to 569 measurements of metal concentrations (Cr, Ni and Pb) in the topsoils of Sheffield, England. Robust estimators of the variogram were shown to be required to describe spatial variation of the metal concentrations at most sampled locations. This is diagnostic of the presence of a contaminant process. Values of the standardized kriging error from the cross-validation of each datum were used to identify spatial outliers for each metal. The ordinary kriged estimates of Cr, Ni and Pb were mapped after removing the outliers to estimate the background variation. Each of the 35 spatial outliers that occured in gardens have concentrations exceeding their Soil Guideline Value for residential land use with plant uptake, highlighting a potentially significant exposure pathway. The frequent observation of coal and furnace waste at these sites suggests that their dispersal, following domestic use and industrial processes, respectively, represents a significant point contaminant process. There was no evidence for spatial clustering of the point process. However, the spatial outliers of Cr and Ni showed a significant association with disturbed sites identified from historical land use maps, in part due to their prevalence in areas of historical steel manufacture. The magnitude of diffuse pollution for each metal in the urban soil was estimated by removing the spatial outliers and comparing robust measures of location with those from a survey of soils developed over the same parent materials in adjacent rural and peri-urban environments. The Winsorized mean Pb concentrations in urban topsoil (203 mg kg(-1)) were twice the value in the rural environment (101 mg kg(-1)), highlighting a very substantial diffuse Pb load to urban soils. The equivalent estimated diffuse components in urban soils for Cr and Ni were, respectively, 25% and 14% higher than the rural soils.

The spatial distribution of stream water composition, as determined by the Geochemical Baseline Survey of the Environment (G-BASE) conducted by the British Geological Survey (BGS) can be successfully related under baseflow conditions to bedrock geochemistry. Further consideration of results in conjunction with site-specific monitoring data enables factors controlling both spatial and temporal variability in major element composition to be highlighted and allows the value of the survey to be enhanced. Hence, chemical data (i) from streams located on Lower Silurian (Llandovery) bedrock at 1 km2 resolution collected as part of the G-BASE survey of Wales and the West Midlands and (ii) from catchment monitoring studies located in upland mid-Wales (conducted by Institute of Terrestrial Ecology), have been considered together as an example. Classification of the spatial survey data set in terms of potentially controlling factors was carried out so as to illustrate the level of explanation they could give in terms of observed spatial chemical variability. It was therefore hypothesised that on a geological lithostratigraphic series of limited geochemical contrast, altitude and land-use factors provide better explanation of this variability than others such as lithology at sampling site and stream order. At an individual site, temporal variability was also found to be of considerable significance and, at a monthly time-step, is explicable in terms of factors such as antecedent conditions and seasonality. Data suggest that the degree of this variability may show some relationship with stream order and land-use. Monitoring data from the region also reveal that relationships between stream chemistry and land-use may prove to be strong not only at base flow but also in storm flow conditions. In a wider context, predictions of the sensitivity of stream water to acidification based on classifications of soil and geology are successful on a regional scale. However, the study undertaken here has shown that use of such classification schemes on a catchment scale results in considerable uncertainty associated with prediction. Uncertainties are due to the large degree of variability in stream chemistry encountered both spatially within geological units and temporally at individual sampling sites.

The Geochemical Survey programme (GSP) of the BGS is currently undertaking the systematic multi-element regional geochemical mapping of the UK landmass.

s 91 Orientation studies of stream water hydrogeochemistry for environmental and economic applications in North Wales P.R. Simpson 1, W.M. Edmunds 2, N. Breward 1, J.M.Cook 3, D. Flight 1 G.E.M. Hall4and T.R. Lister 1 1Geochemistry Group, British Geological Survey Nottingham NG12 5GG. UK 2Hydrogeology Group, British Geological Survey, Wallingford, OXlO 8BB, UK 3Analytical Geochemistry Group, British Geological Survey, Nottingham, NG 12 5GG, UK 4Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, KIA OE8, Canada The stream water hydrogeochemical database, prepared by the BGS's Geochemical Survey Programme in conjunction with databases for stream sediments , soil samples and mineral concentrates, has recently 'been enhanced for a range of economic and environmental objectives. The density of systematic stream water sampling and analysis has been increased to one sample per km 2 and a much broader spectrum of additional determinands introduced. An orientation suite of coregistered hydrogeochemical maps has been produced from water samples collected at 1,279 sample sites in North Wales. The preliminary results obtained indicate that bedrock geology and mineralisation are the most important variables which influence the surface water chemistry. These primary geological parameters are variously modified by secondary influences which include a tmospher ic (c l imat ic and coastal effects) , a n t h r o p o g e n i c ( ag r i cu l tu re and urban developments) and geomorphological factors. Such regional hydrogeochemical stream water maps have a wide range of economic and environmental appl icat ions, especial ly when interpreted in conjunction with geological data. Results obtained so far indicate that interpretation is likely to be further enhanced in the future by comparison with regional stream sediment , hydrogeolog ica l , geomorphologica l , pedological , agricultural, landuse, climatic and remotely sensed datasets in a GIS environment. Hydrogeochemical sampling and analysis therefore represents a costeffective addition to the Regional Geochemical Survey of the UK. The identification of mining related contamination in the UK using high resolution geochemical mapping: examples from Northeast England and North Wales D.M.A. Flight, T.R. Lister and F.M. Fordyce Geochemistry Group, British Geological Survey, Nottingham NG 12 5GG, UK The Geochemical Survey programme (GSP) of the BGS is currently undertaking the systematic multi-element regional geochemical mapping of the UK landmass° The GSP database presently holds information on the concentration of up to 35 elements determined in stream sediment, stream water, heavy mineral concentrate and soil samples collected at an average aensity of one sample per 1.25 km 2 in an area of northern Britain extending f rom S h e t l a n d to Nor th Wales. R e g i o n a l geochemical maps based on analysis of high density stream sediment samples from Northeast England and North Wales, both of which contain historically important mining fields are considered here. The Northern Pennine Orefield has been worked from Roman times until the early parts of this century primarily for galena but also for associated Zn, Ba and Cu bearing ores. The many historical mining centres of North Wales include Halkyn-Minera (Pb-Zn), Llanlwst (Pb-Zn), Llansannan (Cu-Pb-Zn), Beddgeler t (Cu-Pb-Zn) and Parys Mountain, Anglesey (Cu).

Range charts for the acritarchs of the Ludlow succession are presented. They show the ranges of 84 species present. A conspicious change takes place in the Lower Eltonian where Estiastra and Pulvinosphaeridium die out. Progressive changes take place throughout and there is a dramatic reduction in the variety of the assemblages as the Late Silurian regression develops.