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Sand lenses at various spatial scales are recognized to add heterogeneity to glacial sediments. They have high hydraulic conductivities relative to the surrounding till matrix and may affect the advective transport of water and contaminants in clayey till settings. Sand lenses were investigated on till outcrops producing binary images of geological cross-sections capturing the size, shape and distribution of individual features. Sand lenses occur as elongated, anisotropic geobodies that vary in size and extent. Besides, sand lenses show strong non-stationary patterns on section images that hamper subsequent simulation. Transition probability (TP) and multiple-point statistics (MPS) were employed to simulate sand lens heterogeneity. We used one cross-section to parameterize the spatial correlation and a second, parallel section as a reference: it allowed testing the quality of the simulations as a function of the amount of conditioning data under realistic conditions. The performance of the simulations was evaluated on the faithful reproduction of the specific geological structure caused by sand lenses. Multiple-point statistics offer a better reproduction of sand lens geometry. However, two-dimensional training images acquired by outcrop mapping are of limited use to generate three-dimensional realizations with MPS. One can use a technique that consists in splitting the 3D domain into a set of slices in various directions that are sequentially simulated and reassembled into a 3D block. The identification of flow paths through a network of elongated sand lenses and the impact on the equivalent permeability in tills are essential to perform solute transport modeling in the low-permeability sediments.

The topic of this PhD thesis is an integrated investigation of sand lenses in glacial diamictons. Sand lenses indicate various deposition regimes and glaciotectonic deformation styles and are as such important features in studies of glacial sediments.In a hydrogeological framework, sand lenses further constitute conductivefacies within low-permeability tills and are suspected to affect hydraulic conductivity fields and subsurface transport behaviour. The purpose of the study is to characterize sand lenses in terms of occurrence, geometry and connectivity and to assess their importance for contaminant transport in clayey tills.Sand lenses are considered enigmatic geological features resulting from complex interplay of glacial deposition and deformation. The subglacial hydraulic conditions and the predominant deforming forces are determining the appearance of sand lenses. Despite the abundance and the variability of occurrence, there is only sparse systematic information reported in the literature. As an example there is no consistent nomenclature for the different types of sand and gravel deposits in tills.In this study, the specific geometry of sand lenses was characterized by means of a field observation study and a literature survey. A number of geometric parameters (length, thickness, anisotropy, orientation, etc.) were selected to describe the size and shape of sand lenses. The resulting characteristic measures were used to define a classification scheme and to categorize five types of sand lenses. These are: sand layers, sand sheets, sand bodies, sand pockets and sand stringers. The scheme is a useful tool to include sand lenses in future till investigations and it supports rapid identification of till types.The spatial distribution of sand lenses is variable because of generally complex architectures of till successions. On the other hand, it is a relevant parameter to describe because mean lengths and spacing determine the connectivity between lenses. Pixel-based mapping of geological cross-sections was performed to facilitate geostatistical analyses of spatial variability. Variogram models yield nonstationary patterns including trending in vertical direction, variable size of lenses and strong geometric anisotropy. Non-stationarity complicates the identification of correlation functions and hampers the simulation of facies distribution. Transition probability-based geostatistics applied abundantly in modeling complex facies architecture were used in this study to simulate the variability of sand lenses in tills. Multiple-point statistics, however, showed enhanced capabilities to reproduce characteristic geological structures. Especially strong anisotropy and variablesize of sand lenses were best represented in multiple-point realizations. Stochastic models enable the identification of connectivity functions and can be used to simulate heterogeneity at poorly or unsampled locations.Once the specific structures of sand lenses are reproduced to satisfaction, hydraulic parameters can be assigned to the different geological facies. The average hydraulic conductivity between the sand lenses and the clayey matrix differ by three to four orders of magnitude. The influence of sand lenses on the transport regime thus depends primarily on the connectivity between lenses. Three-dimensional realizations indicate clear channel networks, whereas only limited connectivity was found for the two-dimensional case. This is an important aspect because it emphasizes the need to collect data and to represent this type of heterogeneity in 3D.The physical response of sand lens heterogeneity was evaluated performing solute transport modeling mimicking leaching from a contaminated site in clayey till. It emphasized the need to include geological heterogeneity even if occurring at the finest scale. Compared to average or random conductivity fields, simulated sand lenses with specific hydraulic properties enhance the horizontal spreading of contaminants without a significant increase of the equivalent permeability in the till.Overall, sand lenses occur in all types of glacial sediments and with a broad range of shapes and hydraulic properties. Geometric characterization enabled classification of the most common types. Geostatistical analyses suggested that sand lenses in tills create connected channel networks in 3D. Consequently, sand lens heterogeneity is an important aspect when modeling transport processes of contaminants or performing risk assessment in clayey till settings. In either case it is recommended to consider and to include detailed representations of heterogeneity and sand lenses.

I forskningsprojektet REMTEC testes effekten af tre stimuleringsmetoder i forbindelse med in situ oprensning af chlorerede opløsningsmidler i moræneler/1/. Sideløbende med stimulering og oprensningsforsøg er der udviklet nye metoder til karakterisering af moræneler, herunder implementering af GIS-værktøjer for at kunne vurdere geologisk og hydraulisk heterogenitet i områder dækket af moræneler. Resultatet af disse aktiviteter bliver nu publiceret, dels som et koncept, der på regional/mark skala opdeler større områder dækket af moræneler i mindre områder med potentielt ensartet geologisk heterogenitet /1/ og dels på siteskala, som et web-baseret simpelt multiple choice værktøj: ”SiteEval”, der kan bruges til at lave en mere detaljeret geologisk karakterisering af punktkildeforureninger i morænelersområder.

Accurate measurements of the 8B neutrino spectrum are important for the interpretation of solar neutrino data. Experimentally, the 8B neutrino spectrum can be obtained from the measurement of the β-delayed α spectrum. We report on an α-α coincidence measurement performed at the IGISOL facility in Jyväskylä, Finland. Our measurement allows extensive cross-checks to be performed and gives a more intense neutrino spectrum at high energies compared to the present standard. The deviation reaches 4% at the end point of the spectrum. Below 11 MeV, the deviation is less than 1%.

The construction of detailed geological models for heterogeneous settings such as clay till is important to describe transport processes, particularly with regard to potential contamination pathways. In low-permeability clay matrices transport is controlled by diffusion, but fractures and sand-lenses facilitate local advective flow. In glacial settings these geological features occur at diverse extent, geometry, degree of deformation, and spatial distribution. The high level of heterogeneity requires extensive data collection, respectively detailed geological mapping. However, when characterising the geology of e.g. a contaminated site, it is not always possible to gather enough information to build a representative geological model. Mapping in analogue geological settings and applying geostatistical tools to simulate spatial variability of heterogeneities can improve ordinary geological models that are predicated only on vertical borehole information. This study documents methods to map geological heterogeneity in clay till and ways to calibrate geostatistical models with field observations. A well-exposed cross-section in an excavation pit was used to measure and illustrate the occurrence and distribution of sand-lenses in clay till. Sand-lenses mainly account for horizontal transport and are prioritised in this study. Based on field observations, the distribution has been modeled using two different geostatistical approaches. One method uses a Markov chain model calculating the transition probabilities (TPROGS) of alternating geological facies. The second method, multiple-point statistics, uses training images to estimate the conditional probability of sand-lenses at a certain location. Both methods respect field observations such as local stratigraphy, however, only the multiple-point statistics can truly represent every measured point in the model. Thus, it allows more realistic models of the heterogeneity, but is constricted when only vertical borehole data is available. Overall, the integration of stochastic models of sand-lenses distribution was found very useful to enhance the accuracy of ordinary geological models of heterogeneous clay till.