Applied Geochemistry (v.27, #10)

IAGC Awards for 2010 (1865-1870).

The geochemist, Vladimir Ivanovich Vernadsky has only recently become recognised internationally, despite being regarded as one of the greatest names in science of the 20th century in his homeland Russia. There are several reasons for his lack of renown in the west, but mainly because his most important work “The Biosphere” was only fully translated into English in 1997. This book and the ideas it contains are now becoming regarded as one of the pioneering works of the last century. It defines the biosphere as a unifying, holistic concept for the earth system at a time when reductionism was the driving motivation in scientific research. Above all, for earth scientists, Vernadsky regarded life as the driving geological force. However another, as yet unpublished work (in three volumes) entitled “The History of Natural Waters” also deserves similar attention. This book explores many concepts in hydrogeology, geochemistry, geofluid circulation and especially biology in which water is described as an integral part of the biosphere.Vernadsky’s teachers, including Mendeleev, Butlerov and Dokuchaev had a special influence on his early career path. He published prolifically in the 1920s and 1930s as well as founding several key institutions in Russia and Eastern Europe. The influence of the Russian school of landscape geochemistry, led by Dokuchaev also had a great influence on Vernadsky’s scientific work and productivity, as was a period of study in France in the 1920s. The History of Natural Waters covers the spectrum of hydrogeochemical phenomena, in rather a descriptive way, yet its influence as the foundation of later ideas on hydrochemical processes and water–rock interaction, as well as hydrogeology, can easily be recognised. As well as including the role of biology in hydrogeochemistry, this work clearly emphasises the role of mans’ influence on changing the chemistry of natural waters. Vernadsky adopted the concept of the ‘Noosphere’ (the evolution of human thought) to emphasis man’s role as a geological agent. His publications foreshadow Gaia theory some half a century later.Vernadsky’s works thus made a huge contribution to the development of many science areas and have changed the scientific world view; moreover they have defined the position of mankind in the evolution of the Earth and the biosphere and also put urgent questions for future generations with significance at the present time. His ideas have not always been understood and even more so recognised. He always remembered the words of Alexander von Humboldt: “A hundred years are necessary to reach the truth and another hundred in order to start following it”.

As an important part of the Mediterranean-Himalayas geothermal belt, southern Tibet and western Yunnan are the regions of China where high-temperature hydrothermal systems are intensively distributed, of which Rehai, Yangbajing and Yangyi have been investigated systematically during the past several decades. Although much work has been undertaken at Rehai, Yangbajing and Yangyi to study the regional geology, hydrogeology, geothermal geology and geophysics, the emphasis of this review is on hydrogeochemical studies carried out in these geothermal fields. Understanding the geochemistry of geothermal fluids and their environmental impact is critical for sustainable exploitation of high-temperature hydrothermal resources in China. For comparison, the hydrogeochemistry of several similar high-temperature hydrothermal systems in other parts of the world are also included in this review.It has been confirmed by studies on Cl and stable isotope geochemistry that magma degassing makes an important contribution to the geothermal fluids from Rehai, Yangbajing and Yangyi, though meteoric water is still the major source of recharge for these hydrothermal systems. However, the mechanisms of magma heat sources appear to be quite different in the three systems, as recorded by the 3He/4He ratios of escaping geothermal gases. A mantle-derived magma intrusion to shallow crust is present below Rehai, although the intruding magma has been heavily hybridized by crustal material. By contrast, the heat sources below Yangbajing and Yangyi are inferred to be remelted continental crust. Besides original sources, the geochemistry of characteristic constituents in the geothermal fluids have also been affected by temperature-dependent fluid–rock interactions, boiling and redox condition changes occurring in the upper part of hydrothermal systems, and mixing with cold near-surface waters. The geothermal fluids from Rehai, Yangbajing and Yangyi contain very high concentrations of some toxic elements. Since local drinking water sources may be mixed with geothermal water, and irrigation with water containing geothermally-derived harmful elements, possibly leading to accumulation in crops consumed by human beings, the natural geothermal spring discharge or anthropogenic geothermal wastewater drainage of these fields poses a threat to the environment and human health.Future research work should focus on estimation of stable O and H isotope compositions of magmatic water related to high-temperature hydrothermal systems in China, which is of significance for the quantitative source study of geothermal fluid recharged by degassed magmatic waters. Attention should also be paid to some constituent species in geothermal fluid of strong environmental significance, such as thioarsenate that is crucial for the fate of As discharged from geothermal springs, especially sulfidic hot springs.

Models have become so fashionable that many scientists and engineers cannot imagine working without them. The predominant use of computer codes to execute model calculations has blurred the distinction between code and model. The recent controversy regarding model validation has brought into question what we mean by a ‘model’ and by ‘validation.’ It has become apparent that the usual meaning of validation may be common in engineering practice and seems useful in legal practice but it is contrary to scientific practice and brings into question our understanding of science and how it can best be applied to such problems as hazardous waste characterization, remediation, and aqueous geochemistry in general. This review summarizes arguments against using the phrase model validation and examines efforts to validate models for high-level radioactive waste management and for permitting and monitoring open-pit mines. Part of the controversy comes from a misunderstanding of ‘prediction’ and the need to distinguish logical from temporal prediction. Another problem stems from the difference in the engineering approach contrasted with the scientific approach. The reductionist influence on the way we approach environmental investigations also limits our ability to model the interconnected nature of reality. Guidelines are proposed to improve our perceptions and proper utilization of models. Use of the word ‘validation’ is strongly discouraged when discussing model reliability.

Effects of human activities on karst groundwater geochemistry in a rural area in the Balkans by David T. Long; Thomas C. Voice; Nedialka D. Niagolova; Shawn P. McElmurry (1920-1931).
The geochemistry of three drinking water sources (wells, springs, and tap) in the Vratza region of northern Bulgaria was investigated to gain an understanding of how human activities influence natural geochemical processes in a carbonate aquifer system. Numerous villages have been identified within this highly agricultural area as endemic for the environmental disease Balkan endemic nephropathy, with some suggesting a link to the geochemistry of the region. We observe that water quality varies significantly as a function of source. Hydrochemical facies analysis reveals trends not typical for limestone systems, with cation trajectories falling along the Ca2+–Mg2+ axis and the anion trajectories lying along the HCO 3 - – SO 4 2 - axis. R-mode factor analysis reveals: (i) an increasing dominance of a Cl–Na+– SO 4 2 - – NO 3 - association from tap to spring to well waters, (ii) a strong association between Mg2+ and U, and (iii) a lack of associations between Ca2+ and Mg2+ and between Ca2+ and HCO 3 - that is atypical for limestone systems. These observations are interpreted to indicate that human activities have influenced all sources across the Vratza region and that Mg and U concentrations result from the dissolution of limestone, which is enhanced due to the input of anthropogenic chemicals. Geochemical modeling indicates that Ca2+ concentrations are in equilibrium with calcite, but that Mg2+ concentrations remain conservative, resulting in the decoupling of a Ca2+ and Mg2+, association. Uranium concentrations also appear to be conservative, aided by a poised redox state due to high concentrations of NO 3 - and the formation of CO 3 2 - and PO 4 3 - ion pairs. The similar source and conservative nature of both Mg2+ and U can account for their association. Finally, cluster analysis indicates that the pattern of water geochemistry in the endemic area differs from the surrounding non-endemic area, may be explained by differences in the underlying geology. This study has shown that the general water quality in this rural area, whether in endemic or non-endemic villages, is poor and that agricultural activities have not only added chemicals to the groundwater system, but that these chemicals have likely disrupted geochemical processes. More work is required to understand the specific details of anthropogenic influences on geochemical processes on water quality in karstic terrains.

Refining the estimation of metal loads dissolved in acid mine drainage by continuous monitoring of specific conductivity and water level by Laura Galván; Manuel Olías; Carlos Ruiz Cánovas; Ester Torres; Carlos Ayora; José Miguel Nieto; Aguasanta Miguel Sarmiento (1932-1943).
► A methodology to calculate reliably metal loads in AMD affected rivers is presented. ► Relationships between element concentration and specific conductivity are investigated. ► Mixing calculations allow to distinguish changes in hydrochemical conditions. ► River Meca transports in a year 1950 tonnes of iron, 1000 of Al and 380 of Zn.The accurate estimation of metal loads transported by streams is necessary to calculate reliable mass transfers of metals between compartments, both at local and global scales. This estimation is particularly relevant in the case of the Tinto and Odiel Rivers (SW Spain) due to their significant contribution to the total metal transfer from continents to the ocean. At a local scale, the metal load transported by streams plays a key role in predicting the biogeochemical evolution of water reservoirs affected by Acid Mine Drainage (AMD). This work uses the relationships between specific conductivity (SC) and dissolved elements to calculate the metal load of the River Meca, a tributary of the Odiel. The SC and the water level were continuously monitored from April 2009 to June 2010. Water samples were also collected and measurements of the discharge were carried out manually once a month. The relationships between the SC and the concentration of dissolved elements are, in general, very good (R 2  > 0.90). However, some key elements such as Fe show a very poor correlation. A simple methodology based on the MIX code (a maximum likelihood method to estimate mixing ratios) was used to elucidate their different behaviours. During the dry period (April–December, 2009) the Fe concentration was lower than that deduced from the SC recorded value due to the precipitation of Fe-oxihydroxides, which also reduced the concentrations of As, Cr, Pb and, to a lesser extent, Cu. At the same time Na, Sr, Ca and Li were enriched because of the higher interaction with the riverbed materials. Correlations between the SC and the metal concentration improved significantly when each period was considered separately. A second dry period (April–June 2010) shows high SC values, although no dissolution/precipitation of solid phases is evidenced. This indicates that SC alone is not enough to predict the dissolved metal loads in Mediterranean AMD streams. The metal load transported by the River Meca was determined for the hydrological year 2009/10 as 1933 ± 129 tonnes of Fe, 990 ± 155 of Al and 378 ± 41 of Zn.

Dissolved and particulate metals and arsenic species mobility along a stream affected by Acid Mine Drainage in the Iberian Pyrite Belt (SW Spain) by Aguasanta M. Sarmiento; Manuel A. Caraballo; Daniel Sanchez-Rodas; José Miguel Nieto; Annika Parviainen (1944-1952).
► The Fe2+/Fe3+ and As3+/As5+ ratios show a decrease along the watercourses. ► These ratios increase with pH except for the samples coming from gold cyanidation wastes. ► Concentrations of dissolved and total phases do not show differences except for Fe, As and Pb. ► In the particulate phase, As is associated with the Fe minerals while Pb is with the clay colloids.Intensive mining has taken place in the Iberian Pyrite Belt since 3000 B.C. generating Acid Mine Drainage (AMD) and releasing high amounts of SO4, acidity, metals and metalloids into surface water. Concentrations of elements in AMD-impacted waters are regulated by the precipitation of Fe-rich materials and particulate matter can influence the mobility and the bioavailability of metals. In this paper a study on the dissolved As species concentration along a polluted stream has been performed. Two sampling campaigns were conducted during the dry and the rainy seasons. Concentrations of dissolved elements are higher during the dry season and increase progressively along the water course in both seasons. Concentrations up to 80 μg L−1 of As3+ and 5 mg L−1 of As5+ were determined. The concentration of As species increases and the As3+/As5+ ratio decreases downstream. The Fe2+/Fe3+ and As3+/As5+ ratios show the same pattern with respect to pH for all the examined samples, except those taken from Au cyanidation wastes. The particulate phase is mainly composed of Fe, As and Pb, with As being associated with the Fe minerals while Pb seems to be associated with the clay colloids.

Downstream changes in antimony and arsenic speciation in sediments at a mesothermal gold deposit in British Columbia, Canada by Suzanne Beauchemin; Y.T. John Kwong; Alexandre J. Desbarats; Ted MacKinnon; Jeanne B. Percival; Michael B. Parsons; Kumi Pandya (1953-1965).
► We study the mobility of antimony in the vicinity of a mesothermal gold deposit. ► Stibnite oxidizes faster than arsenopyrite. ► Secondary antimony species are dominantly associated with Fe-oxyhydroxides. ► Sb shows distinct oxidation reactions as compared to As under similar redox conditions.This study investigates Sb speciation in sediments along the drainage of the Upper Peter adit at the Bralorne Au mine in southern British Columbia, Canada, and compares the behavior of Sb with that of As. The Upper Peter mineralization consists of native Au in quartz-carbonate veins with 1 wt.% sulfides dominated by pyrite and arsenopyrite although stibnite, the primary Sb-bearing sulfide mineral, can be locally significant. Dissolved Sb concentrations can reach up to 349 μg L−1 in the mine pool. Sediments were collected for detailed geochemical and mineralogical characterization at locations along the 350-m flow path, which includes a 100-m shallow channel within the adit, a sediment settling pond about 45 m beyond the adit portal and an open wetland another 120 m farther downstream. From the mine pool to the wetland outlet, dissolved Sb in the drainage drops from 199 μg L−1 to below the detection limit due to the combined effect of dilution and removal from solution. Speciation analyses using X-ray absorption near-edge structure (XANES) spectroscopy indicate that Sb(III)–S accounts for around 70% of total Sb in the sediments in the main pool at the far end of the adit. At a short distance (24 m) downstream of the main adit pool, however, Sb(III)–O and Sb(V)–O species represent ⩾50% of total Sb in the bulk sediments, indicating significant oxidation of the primary sulfides inside the adit. Although Sb appears largely oxidized in the bulk samples collected near the portal, Sb(III)–S species are nevertheless present in the <53-μm fraction, suggesting a higher oxidation rate for stibnite in the coarser grains, possibly due to galvanic interaction with pyrite. Secondary Sb species released from the sulfide oxidation are most likely sorbed/co-precipitated with Fe-, Mn-, and Al-oxyhydroxides along the flow channel in the adit and in the sediment settling pond, with the Fe phase being the dominant sink for Sb.

► Waterfalls can cause notably high Fe oxidation and deposit rates in mine drainage. ► Rapid schwertmannite precipitation yields swift sorption and low partitioning of As. ► Rate uplift by elevated seasonal temperature can be shadowed by waterfall effects. ► Large dissolved contaminant loads exist despite of evident natural attenuation.Dramatic seasonal changes in water chemistry and precipitate mineralogy associated with acid-mine drainage (AMD) in the waterfall and creek sections of the Chinkuashih area, northern Taiwan were investigated. Special attention has been paid to the kinetic effects of seasonal temperature variation and waterfall aeration. Precipitation of schwertmannite associated with removal of metals and As are indicated by delicate growth microstructures on precipitate surfaces, X-ray diffraction data, and downstream reductions of metal and As concentrations. Geochemical modeling suggested a downstream increase of the degree of saturation/supersaturation with respect to schwertmannite in the waterfall section, which can be attributed to high Fe2+ oxidation rates. The waterfall section was characterized by high rates and model rate constants of Fe2+ oxidation (6.1–6.7 × 10−6  mol L−1  s−1 and 2.7–2.9 × 10−2  s−1) and Fe (schwertmannite) precipitation (1.7–2.1 × 10−6  mol L−1  s−1 and 3.5–4.1 × 10−7  mol L−1  s−1). A high As sorption rate (4.7–6.3 × 10−9  mol L−1  s−1) and low As distribution coefficient (7.9–11.8 × 10−9  mol−1  L) were observed. The creek section showed up to 1–2 orders of magnitude slower rates and lower rate constants than the waterfall section and had seasonal variations comparable to those in areas polluted by AMD elsewhere. The summer rates were 4–5 times higher than the winter rates in the creek section, and are largely attributed to a temperature effect. In contrast, the seasonal differences in rate and rate constant were small in the waterfall section. Several factors associated with the waterfall aeration in addition to elevated temperature and As concentration enhanced Fe and As attenuation in the waterfall section. The waterfall effects on Fe precipitation rate were enhanced when the flow rate was large in the winter. Despite the remarkable removal of metals and As by the rapid precipitation of As-bearing schwertmannite, large effluent loads of potentially hazardous contaminants including As, Cu and Zn discharged to the sea in the Chinkuashih area.

► We conducted a field experiment to examine trace element release from poultry litter. ► Trace element concentrations increased in soil water after application. ► Arsenic is leached at the fastest rate from litter, followed by Cu and Zn. ► Vadose sediment was the main sink for trace elements released from litter.A poultry litter application was conducted to examine field scale release and transport of trace elements from poultry litter into the subsurface. Field monitoring before and after litter application demonstrated increases in major ion, nutrient, and trace element concentrations in soil water after application, but concentrations of trace elements were all below regulatory standards. Using laboratory stepwise extractions of litter, calculated leaching rates of trace elements are fastest for As, followed by Cu and Zn. Comparison of the projected (from laboratory extractions) to actual (measured in the field) trace element concentrations in litter show that laboratory-derived rates generally over-predict leaching, but the long-term projections of Cu and Zn concentrations remaining in litter are within 20% of the field measurement. Arsenic leaching from litter was under-predicted by the laboratory leaching model by over 100%, suggesting that other processes (perhaps biological) occurring in the field allowed for additional As to be leached/removed. Mass balance coupled with conservative tracer calculations reveal that the vadose sediment was the main sink for the trace elements, with lesser uptake of Cu and Zn (not As) by orchard grass. Overall, results of this study showed that the fate and transport of trace elements from poultry litter are controlled by their leaching rate from litter, adsorption, uptake in vegetation and dilution. An additional process affecting As is biotransformation.

Weathering processes in waste materials from a mining area in a semiarid zone by Cortes Navarro-Hervás; Carmen Pérez-Sirvent; María José Martínez-Sánchez; Mari Luz García-Lorenzo; José Molina (1991-2000).
► An abandoned Pb–Zn and Ag mining site in Spain has been studied. ► Chemical and mineralogical characterization of waste materials was carried out. ► Surficial materials in the study area have experienced a weathering process. ► Supergene assemblages were formed.Chemical and mineralogical characterization of waste materials present in an abandoned Pb, Zn–Ag mining site (SE, Spain) was carried out. In unaltered rocks, the mineralogy is characterized by plagioclase, pyroxene, magnetite, ilmenite, amphibole, biotite and quartz. Trace-element contents of these samples represent unaltered values. In mine-waste materials, pH ranged from acidic to slightly acidic and trace-element content was generally high, especially for Pb and Zn, although there were also substantial As concentrations. X-ray diffraction results suggested that these samples have a complex mineralogy, including alteration products. Surficial materials in the study area were affected by weathering processes, generating supergene assemblages, including Fe and Mn oxides and hydroxides, carbonates, hydrated sulfates and jarosite. Knowledge of the geochemical processes that took place in the past and which are still taking place provide an important tool for assessing associated environmental problems in this area.

► Acid sulphate soil materials are identified in a wetland during drought conditions. ► Metals leached from upper soil profile by movement of acidic water. ► Pyrite redox chemistry traced by combined sulphur isotope/Cl:SO4 analysis. ► Fe salt dissolution is complicated by changing pH/redox chemistry during flooding.The hydrogeochemical processes associated with the precipitation and oxidation of pyrite during the development of acid sulphate soils was investigated in the coastal floodplain environment of the Heart Morass, Victoria, Australia. During drought conditions in 2009, low-lying areas of the floodplain (0–2 m elevation) were the most affected by acid sulphate soils, with a median soil pH (pHF) of 3.56 to approximately 50 cm depth. Soils below ∼100 cm depth in these areas contain pyrite and have reduced inorganic S concentrations of up to 0.85 wt%. Higher areas of the floodplain (2–6 m) do not contain acid sulphate soils, with a median pH of 4.74 to approximately 50 cm depth, an average neutralising capacity of 3.87 kg H2SO4/t, and no appreciable unoxidised pyrite. In low-lying areas concentrations of Co, Ni, Zn, Mn and Fe in soil increased from <2.0, 4.0, 10, 20 and 2000 mg/kg, respectively, at 56 cm depth to 10, 20, 45, 152 and 15,000 mg/kg at 221 cm depth. In areas of higher elevation, concentrations of Co, Ni, Zn and Fe increased from 6, 11, 21 and 12,500 mg/kg at 44 cm depth to 10, 19, 47 and 19,400 mg/kg at 239 cm depth. These data indicate acidic leaching of metals from the upper soil profile in both low-lying and more elevated areas. The lowest concentrations of Al, Co, Fe, Mn and Ni in surface water or pit water from low-lying areas were 2.43, 0.06, 2.90, 2.89 and 0.09 mg/L, respectively. These concentrations are 1–2 orders of magnitude higher than in any potential water sources around the morass and are higher than can be accounted for by evapotranspiration, indicating the leaching of metals into surface water and groundwater. Excess SO 4 2 - from pyrite oxidation in the central low-lying area of the morass was characterised by molar Cl:SO4 ratios <5 and δ34S values <10‰. The Cl:SO4 ratios combined with δ34S values define zones of SO 4 2 - depletion during reduction (Cl:SO4  ∼ 24, δ34S = 22.7‰) and contemporary SO4 reduction of water enriched with oxidised pyritic SO 4 2 - (Cl:SO4  = 9.9, δ34S = 26.2‰). Average concentrations of Fe in the upper soil profile decreased from 129 g/kg during drought conditions to 15.2 g/kg after flooding in 2011, suggesting the dissolution of Fe mineral salts accumulated in the upper soil profile. Average concentrations of Al, Ni, Cr and Cu increased in the upper soil profile from 9,522, 18.4, 17.0 and 14.4 mg/kg during drought to 12,800, 22.4, 22.6 and 22.4 mg/kg after flooding, suggesting that metal precipitation and dissolution is the result of changing pH and redox chemistry during flooding. This highlights the need for continuous measurement and sampling during flood events in order to better constrain these processes.

Effect of contaminant concentration on in situ bacterial sulfate reduction and methanogenesis in phenol-contaminated groundwater by Kieran M. Baker; Simon H. Bottrell; Steven F. Thornton; Kate E. Peel; Michael J. Spence (2010-2018).
► Study investigated the inhibiting effect of phenols on biogeochemical processes. ► Bacterial sulfate reduction is inhibited when phenols concentration is >2 g L−1. ► Methanogenesis occurs at much higher phenols concentration in comparison to BSR. ► Toxic inhibition may be a significant limitation on in situ bioremediation.The availability of dissolved O2 can limit biodegradation of organic compounds in aquifers. Where O2 is depleted, biodegradation proceeds via anaerobic processes, including NO3-, Mn(IV)-, Fe(III)- and SO4-reduction and fermentation/methanogenesis. The environmental controls on these anaerobic processes must be understood to support implementation of management strategies such as monitored natural attenuation (MNA). In this study stable isotope analysis is used to show that the relative significance of two key anaerobic biodegradation processes (bacterial SO4 reduction (BSR) and methanogenesis) in a phenol-contaminated sandstone aquifer is sensitive to spatial and temporal changes in total dissolved phenols concentration (TPC) (= phenol + cresols + dimethylphenols) over a 5-a period. In general, 34SO4-enrichment (characteristic of bacterial SO4 reduction) is restricted spatially to locations where TPC < 2000 mg L−1. In contrast, 13C-depleted CH4 and 13C-enriched CO2 isotope compositions (characteristic of methanogenesis) were measured at TPC up to 8000 mg L−1. This is consistent with previous studies that demonstrate suppression of BSR at TPC of >500 mg L−1, and suggests that methanogenic microorganisms may have a higher tolerance for TPC in this contaminant plume. It is concluded that isotopic enrichment trends can be used to identify conditions under which in situ biodegradation may be limited by the properties of the biodegradation substrate (in this case TPC). Such data may be used to deduce the performance of MNA for contaminated groundwater in similar settings.

Isotopic evidence of lead sources in Loire River sediment by Philippe Négrel; Emmanuelle Petelet-Giraud (2019-2030).
► Sediments along the Loire River (France) were investigated by means of lead isotopes. ► Crustal weathering is the main natural source of lead in the Loire River. ► Anthropogenic sources are from agricultural inputs and from gasoline.Sediments along the Loire River (central France) were investigated by means of Pb isotopes determined on the labile sediment fraction, or acid-extractable matter (AEM). The combination of trace elements and Pb isotopes allows deciphering the origin of the elements (i.e. natural or anthropogenic) and their history, in the sediment from two small watersheds (one draining basalt, the other one granite–gneiss), both in present-day suspended matter in Loire River water, and in sediment from the Loire estuary. Crustal weathering, as confirmed by the Pb-isotope ratios for most sample points, is the main source of Pb in the upstream part of the Loire River, as well as that transported in the middle part of the basin and in the estuary. Among anthropogenic sources, the use of Pb-isotopic compositions shows an influence of agriculturally-derived Pb inputs and a major input of Pb derived from gasoline, particularly in the estuary due to harbor activities.

► Decrease in δ37Cl with increase in Cl was observed along groundwater flow direction. ► Released pore water from compacted clay by over-exploitation accounted for increasing Cl. ► Upward flux of Cl from the Tertiary aquifer could occur at the fault areas. ► Cl isotope fractionation mechanisms indicated solutes migration and hydraulic connection between aquifers.Deep Quaternary groundwater is the main source for industrial, domestic, and agricultural water supply in the North China Plain (NCP). There is currently a regional decline of groundwater levels, deterioration of water quality and environmental geological problems induced by increasing exploitation of the NCP Quaternary aquifer system. To trace sources and transport processes of dissolved Cl in a regional aquifer system and to reveal hydrogeological characteristics of Quaternary complexes, δ37Cl, δ18O and δD, and chemical compositions (including F, Cl, Br) of the deep groundwater sampled from the northern flow system of the NCP were measured along the west–east groundwater flow paths. The measured δ37Cl values decreased from 0.39‰ to −2.22‰ (SMOC) along the groundwater flow direction, with increasing Cl concentrations. Marine aerosol input via rainfall is the main source of Cl in the deep groundwater near the recharge areas, and subsequent evaporation/evapotranspiration appears to be responsible for Cl accumulation. Mixing of recharge water with water of high-Cl and low-δ37Cl accounts for the pattern of δ37Cl and Cl concentration observed in Aquifer-3 along the west–east transect. The water with high-Cl and low-δ37Cl is likely from pore water released from compacted clays induced by over-exploitation of deep groundwater, suggesting that clay is a dominant subsurface source of Cl for groundwater where a regional depression cone is present in the Quaternary aquifers. The groundwater of Aquifer-4 in the Huang-Hua depression is potentially mixed with an upward flux of Cl from the Neogene aquifer through subvertical faults. Diffusion and ion filtration are two mechanisms invoked to explain the highly negative δ37Cl data for groundwater of Aquifer-4 in the Yanshan–Haixing areas, which provides new insight into solute migration and the hydraulic relationship in the strongly exploited groundwater system. This study using the conservative solute Cl provides additional important information for further investigations of the geochemistry of a wide range of reactive solutes in the Quaternary aquifer system, so guiding water resource management.

► Groundwater 14C ages suggests subglacial infiltration at about 14,000–27,000 BP. ► Properties of groundwater show varying hydrodynamical conditions during infiltration. ► δ13C composition of Cambrian–Vendian groundwater is influenced by bacterial activity.Groundwater in the Cambrian–Vendian aquifer system has a strongly depleted stable isotope composition (δ18O values of about −22‰) and a low radiocarbon concentration, which suggests that the water is of glacial origin from the last Ice Age. The aim of this paper was to elucidate the timing of infiltration of glacial waters and to understand the geochemical evolution of this groundwater. The composition of the dissolved inorganic C (DIC) in Cambrian–Vendian groundwater is influenced by complex reactions and isotope exchange processes between water, organic materials and rock matrix. The δ13C composition of dissolved inorganic C in Cambrian–Vendian water also indicates a bacterial modification of the isotope system. The corrected radiocarbon ages of groundwater are between 14,000 and 27,000 radiocarbon years, which is coeval with the advance of the Weichselian Glacier in the area.

Hydrochemical data and groundwater dating to infer differential flowpaths through weathered profiles of a fractured aquifer by J. Jaunat; F. Huneau; A. Dupuy; H. Celle-Jeanton; V. Vergnaud-Ayraud; L. Aquilina; T. Labasque; P. Le Coustumer (2053-2067).
► The development of a weathered layer conditioned the groundwater flows settings. ► The water geochemistry is also conditioned by the development of a weathered layer. ► In case of high weathering, apparent age of groundwater is between 10 and 42 a. ► In case of low weathering, a mixing between recent and oldest water is observed. ► In the underlying fissured layer, apparent ages are between 25 to more than 50 a.The Northern Basque Country (Southwestern France) is subject to a constant need of increasing water due to a rising population. The fissured aquifer of the Ursuya Mount is one of the main water supplies able to meet these needs. Unfortunately, there is a lack of knowledge on the residence time of groundwater and flow pattern in this strategic resource. Geochemical monitoring of groundwater was carried out from 2009 to 2011 in conjunction with CFC–SF6 measurement and with a detailed geological field characterization. It appears that groundwater flows and water geochemistry are conditioned by the development of a weathered layer overlying the fissured aquifer. When the weathered layer is absent, groundwater flows take place in unconfined conditions along fractures and fissures. The rapid circulation (mean residence time between 11 and 15 a) and the low solubility of the matrix generates low mineralization (mean about 61 μS cm−1). When a weathered layer is present, the flow depends on the degree of weathering, with groundwater circulating in the deep fissured zone in the case of a high degree of weathering. The apparent age is then between 10 and 42 a and the mineralization tends to increase concomitantly with the residence time, and particularly terrigenic element concentrations. In the case of a lesser degree of weathering, mixing between recent water from the shallow weathered layer and the oldest water (25 to >50 a) from the underlying fissured aquifer is observed. These results allow the definition of a conceptual model of flow characteristics in the study area which is also applicable to other weathered–fractured systems worldwide.

Quantifying saline groundwater seepage to surface waters in the Athabasca oil sands region by Scott Jasechko; John J. Gibson; S. Jean Birks; Yi Yi (2068-2076).
► Target formations for bitumen extraction may actively discharge fluids to the surface. ► Natural saline groundwater discharges influence the Athabasca River’s chemistry. ► Natural saline groundwater discharges in the AOSR are constant for 1987–2010. ► AOSR groundwaters are glaciogenic with solutes derived from evaporite dissolution.Western Canadian oil sands contain over 170 billion barrels of proven unconventional petroleum reserves currently extracted at 1.8 million barrels per day by either surface mining, or by in situ techniques that require subsurface injection of steam and hydrocarbon solvents. Natural high-salinity springs are known to add water and entrained inorganic and organic constituents to the Athabasca River and its tributaries in the region of ongoing bitumen production. However, the magnitude and synoptic distribution of these saline inputs has remained unquantified. Here, a chloride mass balance is used to estimate saline groundwater discharge to the Athabasca River from 1987 to 2010. Results show that the highest saline water discharge rate to the Athabasca River occurs between Ft. McMurray and the Peace-Athabasca Delta, supported by subcrop exposure of lower Cretaceous- and Devonian-aged formations bearing saline waters. Further, the input of saline groundwater is found to be an important control on the chemistry of the lower Athabasca River, despite comprising 10−1 to 3% of the Athabasca River’s discharge. The flux of natural saline groundwater entering the Athabasca does not appear to have increased or decreased from 1987 to 2010. The origin of seep salinity is interpreted as relict subglacial meltwater that has dissolved Devonian-aged evaporites, supported by saline Na-Cl type waters with low 18O/16O and 2H/1H ratios relative to modern precipitation. The magnitude of groundwater discharge and its impact on the Athabasca River’s chemistry in the area of ongoing bitumen development warrants the incorporation of natural groundwater seepages into surface water quality monitoring networks.

Distribution of trace elements in waters and sediments of the Seversky Donets transboundary watershed (Kharkiv region, Eastern Ukraine) by Y. Vystavna; F. Huneau; J. Schäfer; M. Motelica-Heino; G. Blanc; A. Larrose; Y. Vergeles; D. Diadin; P. Le Coustumer (2077-2087).
► The observed spatial variations are mainly due to grain size variations. ► The regional background for trace elements in river sediments is defined. ► Water and sediments are contaminated by Ag, Pb, Cd, Cu, Cr and Zn. ► Concentrations in the sediments are potentially toxic for the aquatic organisms.This paper reports on the aquatic chemistry of trace elements in terms of spatial and temporal distribution, but also pollution sources in the transboundary watershed of the Seversky Donets River (Ukraine/Russia). Bed sediments and filtered water were collected from the Udy and Lopan Rivers at sites from the river source in the Belgorod region (Russia) to rural and urban areas in the Kharkiv region (Ukraine) in May and August 2009. Priority trace elements (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn), an urban tracer (Ag) and additional metals (Co, Mo, V) and Th were measured in stream water and sediments. The low levels and variability of Th-normalized concentrations indicated the absence of geochemical anomalies in the upstream part of the rivers and suggested that these data represent a regional baseline for trace elements in bed sediments. In contrast, water and sediments within the city of Kharkiv were contaminated by Ag, Pb, Cd, Cu, Cr and Zn, which are mainly attributed to municipal wastewater inputs and urban run-off. Results of the environmental quality assessment showed that element concentrations in the sediments can be considered as potentially toxic to aquatic organisms in sites downstream of the wastewater discharges.

The impact of aluminium sacrificial anodes on the marine environment: A case study by C. Gabelle; F. Baraud; L. Biree; S. Gouali; H. Hamdoun; C. Rousseau; E. van Veen; L. Leleyter (2088-2095).
► Aluminium sacrificial anodes do not increase the concentration of Al in the waters. ► Al enrichments are evident in sediments near sacrificial anodes. ► Al mobility is enhanced in sediments near sacrificial anodes.Cathodic protection using Al sacrificial anodes is a method of corrosion control that is often applied to submerged metallic structures. This technique leads to the progressive dissolution of the sacrificial anode and the metal(s) constituting the anode are inevitably released into the surrounding aquatic environment with potentially detrimental effects. The chemistry of sediments and waters from a French harbour where Al sacrificial anodes are deployed is examined in this study. In order to assess the potential influence of Al dissolution from the anode on the aquatic environment, total Al concentrations in water and sediment were determined and corresponding Al enrichment factors were calculated. Single and sequential extractions were also undertaken in order to evaluate the mobility of Al in the sediments. Results showed that whilst anodic dissolution does not significantly increase the concentration of Al in the water, both enrichment and an increase in the mobility of Al were evident in sediments sampled from the vicinity of the sacrificial anodes.

► Fracture grouting with a low-pH-cement grout could trigger a high-pH plume. ► The simultaneous hydration and leaching of the grout has been modeled. ► Model results show a very limited formation of a high-pH plume. ► Results are in qualitative agreement with observations (grouting test). ► Assumption of long-lived high-pH plumes moving by advection may be unrealistic.Grouting of water-conducting fractures with low-alkali cement is foreseen for the potential future repository for spent nuclear fuel in Finland (ONKALO site). A possible consequence is the formation of high-pH solutions which will be able to react with the host rock. Calculations have been performed including the hydration and simultaneous leaching of the grout. The effect of different possible groundwater compositions has been studied. The results show that after grouting, the duration of the initial high-pH peak is short (<0.5 a), which compares well with observations at a test borehole. Magnesium in the groundwater induces the precipitation of brucite at the grout–fracture interface, which consumes OH. In the longer term, the results show a gradually decaying pH tail (pH < 9) controlled by the precipitation of calcite at the grout–fracture interface. The duration of this tail correlates inversely with the carbonate content of the inflowing groundwater.A major finding of this study is that mineral precipitation controls the formation of a potential high-pH plume by consuming alkalinity and limiting diffusive solute exchange between the grout and the circulating groundwater. As a consequence, assumption of long-term interaction between rocks or engineering-barrier materials with flowing high-pH (>12) solutions may not be very realistic.

Thermoddem: A geochemical database focused on low temperature water/rock interactions and waste materials by Ph. Blanc; A. Lassin; P. Piantone; M. Azaroual; N. Jacquemet; A. Fabbri; E.C. Gaucher (2107-2116).
► Thermodynamic database for geochemical calculations. ► Mineralogical information as a help for modellers. ► Guide lines for thermodynamic data selection. ► FeII–H2O and FeIII–H2O chemical system refinement.

Thermodynamics of AFm-(I2, SO4) solid solution and of its end-members in aqueous media by Laure Aimoz; Dmitrii A. Kulik; Erich Wieland; Enzo Curti; Barbara Lothenbach; Urs Mäder (2117-2129).
Display Omitted► Solid solution formation between AFm-SO4 and AFm-I2. ► AFm-SO4 as a good candidate for retarding 129I. ► Gibbs energy of AFm-(I2, SO4) solid solution obtained from solubility experiments. ► Sub-regular solid solution model with end-members defined using Vanselow convention.Cementitious materials are foreseen as being used for the immobilization of radionuclides in deep-storage facilities for nuclear waste. The 129I contained in the waste is of major concern due to its long half-life and its anionic speciation in groundwater (I), which hinders the retention by most minerals due to their negatively charged structural surfaces at near-neutral pH. AFm-SO4 is one of the phases present in cementitious materials. Experimental data suggest that the formation of solid solution between AFm-SO4 and AFm-I2 has the potential to retard 129I mobility. In order to improve the present geochemical models, thermodynamic properties of AFm-I2 and of its solid solution with AFm-SO4 were evaluated based on precipitation and dissolution experiments in aqueous solutions between 4 °C and 60 °C. The solubility product of AFm-I2 was determined at 23 °C ± 2 °C to be log K s 0 = - 13.57 ± 0.28 (2σ) for the dissolution reaction Ca 2 Al ( OH ) 6 I · 2 H 2 O ↔ 2 Ca 2 + + Al ( OH ) 4 - + 2 OH - + I - + 2 H 2 O . The Gibbs energy of formation of AFm-I2 at standard state (1 bar, 25 °C) was assessed to be −3325.0 ± 2.4 (2σ) kJ mol−1. The experimental data for AFm-(I2, SO4) phases were consistent with the formation of a continuous solid solution without miscibility gaps. A good fit to these data was obtained using a sub-regular solid solution model with negative Margules interaction parameters W SO4  = −1.0 kJ mol−1 and W I  = −8.0 kJ mol−1, and end-members (Ca2Al(OH)6I and Ca4Al2(OH)12SO4) defined according to the Vanselow convention for ion exchange. The results show the potential of AFm-SO4 to act as a sink for 129I, notably in carbonate-free systems. Small amounts of calcite can hamper the formation of AFm-(I2, SO4) solid solution. The study provides relevant thermodynamic data for geochemical modeling of 129I in the cementitious near-field of a nuclear waste repository.

► Alkanes in soil gas are result of microseepage from subsurface accumulations. ► Surface gas anomalies confirmed the presence of deep hydrocarbon accumulations. ► Main Dolomite can modify the gas flux ascending from the deeper gas fields. ► Geochemical signature from deeper dry gas fields can be obscured by Main Dolomite.A surface geochemical survey was carried on in an area with a cluster of petroleum deposits in western Poland. The largest of these accumulations is the Paproć-Cicha Góra dry gas deposit reservoired in the Rotliegend sediments. Other, similar gas deposits are: the Paproć gas field discovered in the top part of the Carboniferous formation and the Paproć W, Paproć N, and Nowy Tomyśl gas fields localized in the Zechstein Limestone reef structures. Moreover, the Paproć gas-condensate and the Jastrzębsko oil deposits were found at shallower depths, in the Main Dolomite formation. This paper aims to analyze the variability of composition and distribution of near-surface gaseous hydrocarbons in relation to hydrocarbon accumulations reservoired in various stratigraphic units at depths.The occurrence of CH4, its heavier homologues and unsaturated hydrocarbons was measured in 267 soil gas samples. The sampling sites were located along six survey lines (A–A, B–B, C–C, D–D, E–E and F–F) at a 200 m spacing. Concentrations of CH4, total alkanes (C2–C4) and total alkenes (C2–C3) reached maxima of 0.26 vol.%, 5.32 ppm and 5.88 ppm, respectively. Soil–gas alkanes heavier than CH4 were interpreted as being derived from subsurface hydrocarbon accumulations. These compounds penetrated to the near-surface zone by means of active and passive microseepage. Source strength of alkanes microseepage from subsurface accumulations to the land surface (determined by the C2H6/C2H4 ratio) is not a factor that substantially changes the patterns of surface anomalies. Analysis of the values of CH4/C2H6 and C2H6/C3H8 coefficients confirmed the presence of compositionally diversified, deep hydrocarbon accumulations. The study revealed that even small accumulations of gas condensate produce very strong surface geochemical signatures, contrasting with dry gas deposits. The reason may be a specific effect of hydrocarbon migration within the existing petroleum system. The Main Dolomite, which is both the source and the reservoir rock in the Fore-sudetic monocline, plays the role of a “filter”, which modifies the flux of gases ascending from deep-seated reservoirs. As a result of such “filtering”, the geochemical signature of hydrocarbons recorded at the surface indicates the dominance of gas condensate and oil–gas accumulations at depths, giving rise to obviously incorrect interpretations. These interpretations were evidenced by compositional analysis of soil gases, which did not explicitly confirm the existence of a dry gas deposit in the Rotliegend reservoir (Paproć-Cicha Góra gas field). On the other hand, the identified anomalies generally reflect the outline of this accumulation. It supports the applicability of surface geochemical surveys to hydrocarbon exploration in the Fore-sudetic Monocline. The presence of the Main Dolomite at shallower depth must be taken into account in the interpretation of data used for positioning of seismically identified Rotliegend structures. The results of this project indicate that the Main Dolomite may obscure the geochemical signature of near-surface gases derived from dry gas accumulations in both the deeper Rotliegend and Carboniferous reservoirs.

Method for the determination of residual carbon dioxide saturation using reactive ester tracers by Matthew Myers; Linda Stalker; Andrew Ross; Christopher Dyt; Koon-Bay Ho (2148-2156).
► Environmentally safe and cheap “food-grade” esters have been identified as potential tracers. ► These hydrolyse in the subsurface to form daughter compounds with different characteristics. ► In a single-well “push–pull” test, these can be used to estimate CO2 residual saturation. ► Modelling shows that these give more accurate predictions compared to inert gas tracers.The mechanisms for storage of CO2 in rock formations include structural/stratigraphic, mineral, solubility and residual trapping. Residual trapping is very important in terms of both containment security and storage capacity. However, to date, the contribution from residual trapping (i.e. immobilisation of supercritical fluid via capillarity in pore spaces) is still relatively difficult to quantify accurately. Using a laboratory-based testing program, this study demonstrates the feasibility of using reactive ester tracers (i.e. triacetin, propylene glycol diacetate and tripropionin), which partition between a mobile water phase and a stationary supercritical CO2 phase, to quantify the residual CO2 saturation, Sgr , of a rock formation. The proposed single-well test involves injecting these tracers into the subsurface, followed by CO2 saturated water, where the ester tracers slowly hydrolyse to form products with differing partition coefficients. After a suitable period of time, allowing for partial hydrolysis, water containing the tracer mixture is produced from the subsurface and analysed using gas chromatography mass spectrometry (GCMS). A numerical simulator of the tracer behaviour in a reservoir is used to explain the differential breakthrough of these tracer compounds during water production to estimate Sgr . Computer modelling suggests that the use of esters tracers to determine CO2 residual saturation is a potentially robust method. The supercritical CO2/water partition coefficients directly dictate the amount of time that each tracer spends in the CO2 and water phases. As such for modelling of tracer behaviour and estimating Sgr , knowing the tracer partition coefficient is essential; in this paper, the first laboratory study to determine the partition coefficients of these reactive ester tracers is described.