Groundwater abstracted from aquifers in the Vale of Pickering, North Yorkshire, UK and monitored over the period 2015-2022, shows evidence of variable but commonly high concentrations of dissolved CH4. Sampled groundwater from the Jurassic organic-rich Kimmeridge Clay Formation (boreholes up to 180 m depth) has concentrations up to 57 mg/L, and concentrations up to 59 mg/L are found in groundwater from underlying confined Corallian Group limestone (borehole depths 50-227 m). The high concentrations are mainly from boreholes in the central parts of the vale. Small concentrations of ethane (C2H6, up to 800 & mu;g/L) have been found in the Kimmeridge Clay and confined Corallian groundwaters, and of propane (C3H8, up to 160 & mu;g/L) in deeper boreholes (110-180 m) from these formations. The concentrations are typically higher in groundwater from the deeper boreholes and vary with hydrostatic pressure, reflecting the pressure control on CH4 solubility. The occurrences contrast with groundwater from shallow Quaternary superficial deposits which have low CH4 concentrations (up to 0.39 mg/L), and with the unconfined and semi-confined sections of the Corallian aquifer (up to 0.7 mg/L) around the margins of the vale. Groundwater from the Quaternary, Kimmeridge Clay formations and to a small extent the confined Corallian aquifer, supports local private-water supplies, that from the peripheral unconfined sections of Corallian also supports public supply for towns and villages across the region. Dissolved methane/ethane (C1/C2) ratios and stable-isotopic compositions (& delta;13C-CH4, & delta;2H-CH4 and & delta;13C-CO2) suggest that the high-CH4 groundwater from both the Kimmeridge Clay and confined Corallian formations derives overwhelmingly from biogenic reactions, the methanogenesis pathway by CO2 reduction. A small minority of groundwater samples shows a more enriched & delta;13C-CH4 composition (-50 to -44 & PTSTHOUSND;) which has been interpreted as due to anaerobic or aerobic methylotrophic oxidation in situ or post-sampling oxidation, rather than derivation by a thermogenic route. Few of the existing groundwater sites are proximal to abandoned or disused conventional hydrocarbon wells that exist in the region, and little evidence has been found for an influence on groundwater dissolved gases from these sites. The Vale of Pickering has also been under recent consideration for development of an unconventional hydrocarbon (shale-gas) resource. In this context, the monitoring of dissolved gases has been an important step in establishing the high-CH4 baseline of groundwaters from Jurassic deposits in the region and in apportioning their sources and mechanisms of genesis.

ABSTRACTSurface sediments from a 160-km stretch of the River Clyde, Scotland, were analysed for persistent organic pollutants to investigate distribution, source and environmental effect. Glasgow's urban tributaries polyaromatic hydrocarbons (PAH) ranged from 2.3 to 4226mgkg–1, total petroleum hydrocarbons (TPH) 72 to 37879mgkg–1 and polychlorinated biphenyls (PCB) 3 to 809μgkg–1, which were more polluted than the upper River Clyde PAH that ranged from 0.1 to 42mgkg–1, TPH 3 to 260mgkg–1 and PCB 2 to 147μgkg–1. Intermediate values of the inner Clyde estuary PAH ranging from 0.6 to 30mgkg–1, and PCB ranging from 5 to 130μgkg–1, were attributed to point sources and sediment transfer from the urban tributaries. Comparison with sediment quality criteria suggested possible adverse effects on aquatic biota. PAH isomeric ratios confirmed a pyrolytic source throughout the Clyde and benzo[a]pyrene/benzo[g,h,i]perylene ratios >0.6 confirmed that upper, urban and estuarine domains all to a lesser or greater extent accumulated PAH from traffic emissions. The degree of chlorination determined from PCB homologues differed in each of the three domains, suggesting variable source or that the process aerobic/anaerobic degradation varied in each of the three domains. The anthropogenic impact of the city of Glasgow can be quantified in that the urban tributary sediment mean values were 60 (PAH), 33 (TPH) and 11 (PCB) times higher than the rural upper Clyde counterpart.

ABSTRACTThree collated geochemical surveys of surface water in the Clyde catchment have established the spatial variability in water composition, primarily under baseflow conditions. The waters are broadly pH-neutral to alkaline (maximum pH 8.7) in the lowlands, but mildly acidic in uplands on the catchment periphery. Electrical conductance is relatively high in lowland streams (maximum 8320μgL–1), with lower values in the uplands. Dissolved chromium (Cr; <0.05–971μgL–1) and lead (Pb; <0.05–19.4μgL–1) are of importance due to recognised pollution sources within the catchment. High aqueous Cr concentrations (>5μgL–1) are recorded in urban areas associated with the disposal of alkaline industrial chromite ore processing residue. Under such conditions, Cr probably occurs as Cr(VI). Numerous relatively high Pb values occur in the upland and urban areas. These are likely to be associated with a combination of soil reactions, diffuse pollution and contamination from Pb mineralisation/mining. Pb has a stronger correlation with water pH than with stream sediment Pb content, suggesting that pH has a greater control on Pb mobility than host-rock Pb. Exceedances of water-quality standards are <1% for both Cr and Pb across the catchment. Absolute exceedances are more extreme for Cr than for Pb, highlighting the scale of the Cr pollution problem for urban surface water within the catchment.

Members of the public in England were invited in 2010 to take part in a national metals survey, by collecting samples of littoral sediment from a standing water body for geochemical analysis. To our knowledge, this is the first national sediment metals survey using public participation and reveals a snapshot of the extent of metals contamination in ponds and lakes across England. Hg, Ni, Cu, Zn and Pb concentrations exceeding sediment quality guidelines for the health of aquatic biota are ubiquitous in ponds and lakes, not just in areas with a legacy of industrial activity. To validate the public sampling approach, a calibration exercise was conducted at ten water bodies selected to represent a range of lakes found across England. Sediment concentrations of Hg, Ni, Cu, Zn and Pb were measured in samples of soil, stream and littoral and deep water sediment to assess inputs. Significant differences between littoral sediment metal concentrations occur due to local variability, but also organic content, especially in upland, peat soil catchments. Variability of metal concentrations between littoral samples is shown to be low in small (<20 ha) lowland lakes. Larger and upland lakes with more complex inputs and variation in organic content of littoral samples have a greater variability. Collection of littoral sediments in small lakes and ponds, with or without voluntary participation, can provide a reliable sampling technique for the preliminary assessment of metal contamination in standing waters. However, the heterogeneity of geology, soils and history/extent of metal contamination in the English landscape, combined with the random nature of sample collection, shows that systematic sampling for evaluating the full extent of metal contamination in lakes is still required.

ABSTRACTSurface sediments (n=85) from a 160-km river-estuarine transect of the Clyde, UK, were analysed for total mercury (Hg), saturated hydrocarbons and unresolved complex mixtures (UCMs) of hydrocarbons. Results show that sediment-Hg concentration ranges from 0.01 to 1.38mgkg–1 (mean 0.20mgkg–1) and a spatial trend in Hg-content low–high–low–high, from freshwater source, to Glasgow, to estuary, is evident. In summary, sediment-Hg content is low in the upper Clyde (mean of 0.05Hg mgkg–1), whereas sediments from the Clyde in urbanised Glasgow have higher Hg concentrations (0.04 to 1.26mgkg–1; mean 0.45mgkg–1), and the inner estuary sediments contain less Hg (mean 0.06mgkg–1). The highest mean sediment Hg (0.65mgkg–1) found in the outer estuary is attributed to historical anthropogenic activities. A significant positive Spearman correlation between Hg and total organic carbon is observed throughout the river estuary (0.86; P<0.001). Comparison with Marine Scotland guidelines suggests that no sites exceed the 1.5mgkg–1 criterion (Action Level 2); 22 fall between 0.25 and 1.5mgkg–1 dry wt. (Action Level 1) and 63 are of no immediate concern (<0.25mgkg–1 dry wt.). Saturated (n-alkane) hydrocarbons in the upper Clyde are of natural terrestrial origin. By contrast, the urbanised Glasgow reaches and outer estuary are characterised by pronounced and potentially toxic UCM concentrations in sediments (380–914mg/kg and 103–247mgkg–1, respectively), suggesting anthropogenic inputs such as biodegraded crude oil, sewage discharge and/or urban run-off.

ABSTRACTAn 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<0.05) concentrations of geogenic elements such as chromium, copper, nickel, molybdenum and zinc, but higher levels of cadmium, lead and selenium than most other land uses due to atmospheric deposition/trapping of these substances in peat. In farmland, 14% of nickel and 7% of zinc in topsoil samples exceed agricultural maximum admissible concentrations, and may be sensitive to sewage-sludge application. Conversely, 5% of copper, 17% of selenium and 96% of pH in farmland topsoil samples are below recommended agricultural production thresholds. Significant proportions of topsoil samples exceed the most precautionary (residential/allotment) human-exposure soil guidelines for chromium (18% urban; 10% rural), lead (76% urban; 45% rural) and vanadium (87% urban; 56% rural). For chromium, this reflects volcanic bedrock and the history of chromite ore processing in the region. However, very few soil types are likely to exceed new chromiumVI-based guidelines. The number of topsoil samples exceeding the guidelines for lead and vanadium highlight the need for further investigations and evidence to improve human soil-exposure risk assessments to better inform land contamination policy and regeneration.

The baseline chemistry of groundwater from two aquifers in the Vale of Pickering, North Yorkshire, has been investigated ahead of a proposal to explore for shale gas, planning permission for which has recently been granted. Groundwater in a shallow aquifer including Quaternary and/or Jurassic Kimmeridge Clay deposits shows compositions distinct from a Corallian (Jurassic) Limestone aquifer, reflecting different lithologies and hydrogeological conditions. Corallian groundwaters along the margins of the vale are controlled by reaction with carbonate, with redox conditions varying according to degree of aquifer confinement. Superficial aquifer groundwaters are confined and strongly reducing, with some observed high concentrations of dissolved CH4 (up to 37 mg/L; Feb 2016 data). This appears to be of mixed biogenic-thermogenic origin but further work is needed to determine whether the source includes a deeper hydrocarbon reservoir contributing via fractures, or a shallower source in the Quaternary or Kimmeridge sediments. The data show a shallow aquifer with a high-CH4 baseline which pre-dates any shale-gas activity. (C) 2017 Published by Elsevier B.V.

Stream water is a key medium for regional geochemical survey for mineral exploration and environmental protection. However, stream waters are transient, and measurements are susceptible to various sources of temporal variation. In a regional geochemical survey stream water data comprise 'snapshots' of the state of the medium at a sample time. For this reason the British Geological Survey (BGS) has included monitoring streams in its regional geochemical baseline surveys (G-BASE) at which daily stream water samples are collected, over variable time intervals, to supplement the spatial data collected in once-off sampling events.In this study we present results from spatio-temporal analysis of spatial stream water surveys and the associated monitoring stream data. We show that the variability of monitoring stream data from the G-BASE surveys has a temporally correlated component which can be treated as independent between streams, and therefore as a component of the nugget (spatially uncorrelated variance) of the spatial variograms of stream water survey data. For the variables examined this component was small relative to the spatial variability, which indicates that the value of stream water data to provide spatial geochemical information is not compromised by temporal variability. However, these conclusions are conditioned on the particular data set which was collected only in the summer months, specifically to limit temporal variability. Temporal variation in stream water analyses may be less tractable in wetter conditions. We show how the spatial data from stream water surveys can be mapped by ordinary kriging, with the predictions interpreted as an estimate of the temporal (summer months) mean, and the kriging variance reflecting the partition of the nugget variance of the spatial variogram between spatial and temporal components. (C) 2016 The Authors. Published by Elsevier B.V. All rights reserved.

Green rust, an Fe (II) and (III) oxyhydroxy salt, can alter the aqueous oxidation state, mobility and toxicity, of inorganic contaminants and thus could have applications in water treatment. This paper discusses a series of stirred, open batch experiments designed to evaluate green rust, and its oxidised equivalent in this context comparing it to a ferrihydrite/goethite 'ochre'. Natural green rust was added to different mine waters as either a wet, reduced material or a dry, partially oxidised material. Experiments showed that the addition of either form accelerated the removal of potentially harmful elements from solution. Within one hour Fe, Al and Cu were completely removed from mine waters with initial concentrations of 80, 70 and 8.5mg/L, respectively, and Zn was reduced from 60 to <5mg/L. These experiments show the potential of green rust in mine water treatment, especially as it is able to remove problematic elements such as Al and Zn. The material is effective even after being dried and mostly oxidised. Changes to the pH and ORP of the mine waters and surface catalysis are the suggested mechanisms of accelerated removal of contaminants.

Metal-rich mine drainage is a worldwide environmental problem, its treatment can be passive or active. This paper presents examples from a series of laboratory scale experiments which investigated the accelerated precipitation of ochre for the treatment of metal-rich mine waters. This paper discusses the effects that the addition of the FeII,III hydroxy salt green rust (GR), found in an unusual deposit in the South Wales Coalfield, has on 2 polluted discharges. The Parys Mountain discharge contains 79 and 8 mg L-1 Fe and Cu respectively. The addition of GR was able to acclerate precipitation of ochre and reduce the concentration to ~10 and 0 mg L -1 for Fe and Cu respectively. The Bwlch effluent releases high levels of Zn (~20 mg L-1), the addition of GR aided its complete removal within 5 minutes. This effect is attributed to a combination of the neutralisation effect of the GR, the additional sites available for sorption and the potential for the GR to aid surface catalysed oxidation of ferrous iron. The accelerated precipitation of Fe has the potential to enhance passive and/ or active treatment of mine waters. The ochre produced can be recycled back into the system to encourage precipitation of Fe oxy-hydroxides from these toxic mine waters. The rapid nature of the precipitation causes co-precipitated elements to be adsorbed, which generates a more stable solid waste

'Green rusts' are a group of reduced Fe hydroxides with a pyroaurite-like structure. In a new occurrence, green rust is present as a 45-60 mm thick band which lies just below the surface (similar to 4 mm) of an ochreous deposit at an abandoned coal mine site. The sample is characterized by the presence of pm-sized hexagonal crystals which have been identified from SEM imaging. Chemical analyses reveal an Fe(II):Fe(III) ratio which is close to the characteristic 2:1 ratio, and XRD analysis identifies the material by characteristic lattice spacings. The green rust layer also contains aragonite which is not present in the surrounding ochre. Green rusts are important as they have the potential to be used in water treatment.