Tracing leachates at waste sites using geophysical and geochemical modelling

Tracing leachates at landfills is usually carried out using either geophysical methods or chemical analyses of groundwater. There are often problems with fingerprinting pollution sources or clarifying the spreading pattern due to a wide variety of possibilities giving similar anomalies. The aims of the project were to evaluate the advantages of combining results from multigeophysical modelling and statistical/chemical modelling in order to identify pollution sources and the spreading pattern and to test a new technique for chemical fingerprinting. The project was carried out at a landfill in central Sweden using geophysical measurements and modelling of CVES, GPR and VLF as well as chemical modelling using M3 (multivariate mixing and mass balance calculations). The results indicate that by combining geophysical modelling and chemical calculations, the possibilities of fingerprinting the origin of pollution as well as delineating the spreading pattern are significantly increased.     

The provenance of northern Kalahari Basin sediments and growth history of the southern Congo Craton reconstructed by U–Pb ages of zircons from recent river sands

The southern Congo Craton is widely overlain by Meso- to Cenozoic sediments of the northern Kalahari Basin, which hamper any correlation of basement units. The latter are represented by the Archaean Angola and Kasai Blocks, while the southern cratonic margin is framed by several Meso- to Neoproterozoic orogenic belts. For provenance analysis of the sedimentary cover and reconstruction of the main zircon-forming events, we studied zircons from recent sediments of the largest rivers at the southern margin of the Congo Craton. U–Pb zircon ages suggest a major amount of the sediments to originate from E Lufilian and Kibaran Belts, while input from the S Damara Belt seems to increase to the W. Ages related to the Angola Block were only noticed in the westernmost parts of the working area, which is not in accordance with the SE-trending drainage pattern, proposed to have been onset during the Cretaceous. Thus, it is assumed that the Meso- to Cenozoic sedimentary cover extended further west than today prior to the Mesozoic to Neogene uplift of the Angola Block and that subsequent erosion exhumed the basement stepwise from west to east. A recurrent destabilisation of the southern margin of the Congo Craton at ~2.7, 1.9, 1.0 and 0.6 Ga is supposed to be represented by major peaks in the age distribution pattern of the total amount of concordant zircons. This is in accordance with similar studies in adjacent areas. Additionally, the obtained data fit well to several hypothesised major events during the supercontinent cycle.     

Mass fluxes of xenobiotics below cities: challenges in urban hydrogeology

Urban areas are the focus of major ecological, social and economical activity. They are thus also prime locations of increasing conflict with regard to water use and water protection. As a direct and/or indirect consequence of urban land use and human activity, urban water systems are frequently polluted with organic contaminants including waste water-born xenobiotics such as pharmaceuticals, personal care products (collectively known as PPCPs) and endocrine-active substances. This study reviews new integrated methodologies including flux calculations as well as chemical investigations for determining the impact of human activities on urban water systems and on processes within the urban watershed. The use of indicator substances, representing different contaminant sources and pathways, integral pumping tests and mass balance approaches are suitable alternatives within these environments. The issues are explored using contaminant mass balance examples from Halle/Saale and Leipzig, Germany.     

Feasibility of pre-earthquake strengthening of buildings based on cost-benefit and life-cycle cost analysis, with the aid of fragility curves

There are two fundamental questions this article aims to deal with. First, whether a pre-earthquake strengthening of a large and heterogeneous building stock (the emphasis here is on building types common in S. Europe), is economically feasible or not, and second what is the optimal retrofit level for mitigating the seismic risk. To this purpose contemporary decision making tools, namely cost-benefit and life-cycle cost analyses, are tailored to the needs of the present study, and implemented with the aid of an ad-hoc developed new software application (COBE06). A method for estimating the reduction in structural vulnerability due to retrofit is proposed, as well as a methodology to determine the optimum retrofit level using the fragility curve approach. Finally, the proposed methodology is used in a pilot application that concerns the city of Thessaloniki, and results are drawn for the feasibility of strengthening the reinforced concrete building stock in this city.     

Phase relations of phlogopite with magnesite from 4 to 8 GPa

To evaluate the stability of phlogopite in the presence of carbonate in the Earth’s mantle, we conducted a series of experiments in the KMAS–H₂O–CO₂ system. A mixture consisting of synthetic phlogopite (phl) and natural magnesite (mag) was prepared (phl₉₀-mag₁₀; wt%) and run at pressures from 4 to 8 GPa at temperatures ranging from 1,150 to 1,550°C. We bracketed the solidus between 1,200 and 1,250°C at pressures of 4, 5 and 6 GPa and between 1,150 and 1,200°C at a pressure of 7 GPa. Below the solidus, phlogopite coexists with magnesite, pyrope and a fluid. At the solidus, magnesite is the first phase to react out, and enstatite and olivine appear. Phlogopite melts over a temperature range of ~150°C. The amount of garnet increases above solidus from ~10 to ~30 modal% to higher pressures and temperatures. A dramatic change in the composition of quench phlogopite is observed with increasing pressure from similar to primary phlogopite at 4 GPa to hypersilicic at pressures ≥5 GPa. Relative to CO₂-free systems, the solidus is lowered such, that, if carbonation reactions and phlogopite metasomatism take place above a subducting slab in a very hot (Cascadia-type) subduction environment, phlogopite will melt at a pressure of ~7.5 GPa. In a cold (40 mWm⁻²) subcontinental lithospheric mantle, phlogopite is stable to a depth of 200 km in the presence of carbonate and can coexist with a fluid that becomes Si-rich with increasing pressure. Ascending kimberlitic melts that are produced at greater depths could react with peridotite at the base of the subcontinental lithospheric mantle, crystallizing phlogopite and carbonate at a depth of 180–200 km.     

Simulation of DNAPL infiltration and spreading behaviour in the saturated zone at varying flow velocities and alternating subsurface geometries

The influence of varying groundwater flow velocities on DNAPL infiltration and spreading behaviour was investigated by multiphase modelling using TMVOC and PetraSim. The multiphase models were calibrated by results of previously conducted laboratory experiments for the complete spatio-temporal range of the experiments. The small scale 2D scenario modelling was applied to qualify and quantify changes in position, architecture, geometry and dissolution of a TCE body in a fully saturated homogeneous sandy medium. The applied flow velocities ranging from 0.05 up to 40.00 m/day exhibited that the DNAPL TCE is affected even at the lowest flow velocity in its position, its size and its architecture. Additionally, several impermeable lenses with simple geometry were assumed in the model, to investigate the influence of stratified subsoil. In the experimental set-ups, the DNAPL body reacts more sensitive to the applied groundwater flow velocities than to the geometrical set-up of the scenarios. A possible consequence can be the transportation and displacement of a DNAPL pool due to natural or anthropogenic induced high groundwater flow velocities, as by Pump and Treat facilities, complicating site investigation process and planning of remediation activities.     

Calcite Dissolution Kinetics

We compare the canonical treatment of calcite’s dissolution rate from the literature in a closed system, particle batch reactor, with the alternative approach suggested by Truesdale (Aquat Geochem, 2015). We show that the decay of rate over time can be understood in terms of the evolution and distribution of reactive sites on the surface of these particles. We also emphasize that interpretation of observed rates must not exclude the fundamental role of crystal defects, whose importance is already implicitly reflected in the common form of rate laws in geochemistry. The empirical behavior of overall rate in closed systems, such as those described by Truesdale, may thus reflect relationships between defect centers and the generation of steps over the calcite surface (previously documented for silicates), such that below a critical free energy limit, there is insufficient driving force to open hollow cores and thus a loss of reaction mechanism. Dissolution in this very-near-equilibrium regime will be dependent on the distribution of extant steps and the energetics of new kink site nucleation. However, these sensitivities are complicated in the case of particle systems by grain boundaries, edges, corners, and other terminations. Such discontinuities constitute a defect class whose overall kinetic importance will be strongly tied to particle diameter and which can act independently of the internal strain field imposed by screw and edge dislocations.     

The Nordic geological surveys： Geology for society in practice

Since the mid-nineteenth century., when the first of the Nordic Geological Surveys were established, they have generated a substantial amount of information on the Earth＇s crust, its natural resources, its processes, and on the geological history of Nordic areas. The collective mission of the geological surveys is to carry out ＂Geology for Society＂, by doing research and providing services, and by making geological information and data easily accessible to all the varied end users in industry, government agencies, government institutes, public administrations, technical offices, academia and research institutes, as well as for private individuals. The present paper gives a brief overview of a few, selected, research areas and projects currently undertaken by the Nordic geological surveys. These serve as practical examples of how the Nordic geological surveys address important societal problems and challenges that require geological input for their solution.