Knud Erik S. Klint

Numerical analysis of water and solute transport in variably-saturated fractured clayey till

This study numerically investigates the influence of initial water content and rain intensities on the preferential migration of two fluorescent tracers, Acid Yellow 7 (AY7) and Sulforhodamine B (SB), through variably-saturated fractured clayey till. The simulations are based on the numerical model HydroGeoSphere, which solves 3D variably-saturated flow and solute transport in discretely-fractured porous media. Using detailed knowledge of the matrix, fracture, and biopore properties, the numerical model is calibrated and validated against experimental high-resolution tracer images/data collected under dry and wet soil conditions and for three different rain events. The model could reproduce reasonably well the observed preferential migration of AY7 and SB through the fractured till, although it did not capture the exact depth of migration and the negligible impact of the dead-end biopores in a near-saturated matrix. A sensitivity analysis suggests fast flow mechanisms and dynamic surface coating in the biopores, and the presence of a plough pan in the till.

Modeling fine-scale geological heterogeneity-examples of sand lenses in tills

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.

Spatial distribution of jet fuel in the vadoze zone of a heterogeneous and fractured soil

The goal of the present work is to screen and evaluate all available data before selecting and testing remediation technologies on heterogeneous soils polluted by jet fuel. The migration pathways of non-aqueous phase liquids (NAPLs) in the subsurface relate closely with soil properties. A case study is performed on the vadoze zone of a military airport of north-west Poland contaminated by jet fuel. Soil samples are collected from various depths of two cells, and on-site and off-site chemical analyses of hydrocarbons are conducted by using Pollut Eval apparatus and GC-MS, respectively. The geological conceptual model of the site along with microscopic and hydraulic properties of the porous matrix and fractures enable us to interpret the non-uniform spatial distribution of jet fuel constituents. The total concentration of the jet fuel and its main hydrocarbon families (n-paraffins, major aromatics) over the two cells is governed by the slow preferential flow of NAPL through the porous matrix, the rapid NAPL convective flow through vertical desiccation and sub-horizontal glaciotectonic fractures, and n-paraffin biodegradation in upper layers where the rates of oxygen transfer is not limited by complexities of the pore structure. The information collected is valuable for the selection, implementation and evaluation of two in situ remediation methods.

Combining steam injection with hydraulic fracturing for the in situ remediation of the unsaturated zone of a fractured soil polluted by jet fuel.

A steam injection pilot-scale experiment was performed on the unsaturated zone of a strongly heterogeneous fractured soil contaminated by jet fuel. Before the treatment, the soil was stimulated by creating sub-horizontal sand-filled hydraulic fractures at three depths. The steam was injected through one hydraulic fracture and gas/water/non-aqueous phase liquid (NAPL) was extracted from the remaining fractures by applying a vacuum to extraction wells. The injection strategy was designed to maximize the heat delivery over the entire cell (10 m × 10 m × 5 m). The soil temperature profile, the recovered NAPL, the extracted water, and the concentrations of volatile organic compounds (VOCs) in the gas phase were monitored during the field test. GC-MS chemical analyses of pre- and post-treatment soil samples allowed for the quantitative assessment of the remediation efficiency. The growth of the heat front followed the configuration of hydraulic fractures. The average concentration of total hydrocarbons (g/kg of soil) was reduced by ∼ 43% in the upper target zone (depth = 1.5-3.9 m) and by ∼ 72% over the entire zone (depth = 1.5-5.5 m). The total NAPL mass removal based on gas and liquid stream measurements and the free-NAPL product were almost 30% and 2%, respectively, of those estimated from chemical analyses of pre- and post-treatment soil samples. The dominant mechanisms of soil remediation was the vaporization of jet fuel compounds at temperatures lower than their normal boiling points (steam distillation) enhanced by the ventilation of porous matrix due to the forced convective flow of air. In addition, the significant reduction of the NAPL mass in the less-heated deeper zone may be attributed to the counter-current imbibition of condensed water from natural fractures into the porous matrix and the gravity drainage associated with seasonal fluctuations of the water table.

9 Evidence for Subglacial Deformation and Deposition during a Complete Advance-Stagnation Cycle of Kötlujökull, Iceland – A Case Study

Abstract A geological section, 70xa0m long and 3–4xa0m high, cut into dead-ice moraine in front of Kotlujokull, has been described. Five-sediment associations were recognized representing (1) proglacial glacio-fluvial sedimentation, (2) deposition and deformation in ice-marginal environment, (3) subglacial deformation and deposition from dynamically active ice, (4) subglacial deposition from stagnant ice and (5) supraglacial re-deposition in dead-ice environment during de-icing. This complete sedimentary sequence represents a single glacier advance-stagnation cycle. The melt-out till displays moderate consolidation, moderate content of fines and angular clasts, and a very strong clast fabric. The lodgement/deformation till displays strong to very strong consolidation, relatively high content of fines, low content of angular clasts, and a weak to strong clast fabric. The occurrence of water-escape structures below the basal till and complete lack of brittle deformations in the lodgement/deformation till suggest water-saturated subglacial conditions during the advance of Kotlujokull.

A poly morphological landform approach for hydrogeological applications in heterogeneous glacial sediments

The ‘poly morphological (PM) concept’ is used to assess geological heterogeneity in glacial sediments and to evaluate groundwater recharge to aquifers, especially those underlying clay till. The novelty of the PM concept is that it enhances the knowledge of, especially, heterogeneity of till units in geological models by using superimposed geomorphological units with typical sediment types related to the individual landforms. The PM concept is demonstrated through the construction of a poly morphological map for Zealand in Denmark and an aggregated map comparing clay-till-thickness distribution within individual PM types. The hydrogeological applicability of the PM concept was tested with a physical-based distributed 3D hydrological model. The aggregated PM map was compared with fracture and redox conditions at 21 field sites to evaluate the PM-type correlation to: (1) till thickness, (2) thickness of the reduced-till zone, and (3) depth to the zone with fracture spacing >1xa0m The results show that the till thickness is a critical parameter for the formation of fracture networks in clay till, and that fracture density decreases in till thicker than 8–10xa0m. However, the amount of data is still inadequate for statistically proving the PM concept.RésuméLe concept (‘poly-morphologique’ ) ‘poly morphologie’ (PM) est utilisé pour estimer l’hétérogénéité de sédiments glaciaires et pour évaluer la recharge des aquifères, en particulier ceux situés sous les tillites argileuses. La nouveauté de ce concept PM est qu’il améliore la connaissance, en particulier, de l’hétérogénéité des unités de tillites dans les modèles géologiques en utilisant des unités géomorphologiques superposées, avec des sédiments types représentatifs de (reliefs) modelés distincts. Le concept de PM est (démontré) exposé (par) avec la construction dune carte poly morphologique (pour) de la Zélande au Danemark, et d’une carte (agrégée) synthétique comparant la distribution de l’épaisseur des tillites argileuses à l’intérieur des types PM individualisés.(L’applicabilité) La transposition du concept PM en hydrogéologie a été testée avec un modèle hydrogéologique déterministe 3D. La carte PM (agrégée) synthétique a été comparée avec (les condition de) la distribution des fractures et (de) du rédox sur 21 sites pour évaluer les corrélations du type PM avec: (1) l’épaisseur des tillites, (2) l’épaisseur d’une zone réduite de tillites et (3) la profondeur jusqu’aux zones (d’écarts) d’espacement entre fractures supérieure à 1m. Les résultats montrent que l’épaisseur des tillites est un paramètre critique pour l’estimation des réseaux de fracture dans les tillites argileuses, et que la densité de fracture décroît dans les tillites d’épaisseurs supérieures à 8–10 m (d’épaisseur). Néanmoins, (les données) le nombre de données est encore insuffisant pour valider statistiquement le concept PM.ResumenEl concepto polimorfológico (PM) se usa para evaluar la heterogeneidad geológica en sedimentos glaciales y la recarga de agua subterránea a los acuíferos, especialmente aquellos que subyacen a un till de arcilla. La novedad del concepto PM es que enriquece el conocimiento de, especialmente, la heterogeneidad de unidades de till en modelos geológicos usando unidades geomorfológicas superimpuestas con tipos de sedimentos típicos relacionados con los paisajes individuales. El concepto PM está demostrado a través de la construcción de un mapa polimorfológico de Zealand en Dinamarca y un mapa agregado comparando la distribución del espesor del till de arcilla con tipos individuales de PM. La aplicabilidad hidrogeológica del concepto PM fue testeada con un modelo hidrológico tridimensional distribuido de base física. El mapa PM agregado fue comparado con las condiciones redox y de fractura en 21 sitios de campo para evaluar la correlación con el tipo PM con: (1) espesor del till, (2) espesor de la zona de till reducida, y (3) profundidad a la zona con espaciamiento de la fractura > 1m Los resultados muestran que el espesor de till es un parámetro crítico para la formación de redes de fractura en el till de arcilla, y que la densidad de fractura decrece en aquellos till de mayor espesor que 8–10 m. Sin embargo, la cantidad de datos es aún inadecuada para demostrar estadísticamente el concepto de PM.摘要采用了“多边形态(PM)概念”来评价冰川沉积物的地质多相性,并评估了地下水对含水层的补给,尤其是粘性冰碛下的含水层。PM的新奇在于增强了认识,尤其是对地质模型中多相冰碛单元的认识,这些地质模型叠加了带有与单独地形有关的典型沉积物类型的地貌单元。通过一个丹麦西兰岛多边地形图和一个内部带有单独PM类型比较粘性冰碛厚度分布的聚合地图的组建来演示了PM概念。PM概念的水文地质应用利用以物理基础分布的三维水文模型进行了检测。聚合的PM地图与21个野外现场的裂隙和氧化还原条件进行了比较,来证明PM型与以下因素的相关性:(1)冰碛厚度,(2)冰碛减退区厚度,和(3)到裂隙间距>1m地区的深度。结果显示:冰碛厚度是粘性冰碛区裂隙网络形成的关键参数,且在冰碛厚度超过8-10m处裂隙密度减少。无论如何,对于证明PM概念统计数据量仍然是不够充分的。ResumoO ‘conceito polimorfológico (PM)’ é utilizado para avaliar a heterogeneidade geológica em sedimentos glaciais e para calcular a recarga dos aquíferos, em particular os aquíferos subjacentes a till argiloso. A novidade do conceito PM é que aumenta o conhecimento sobre, em particular, a heterogeneidade das unidades de till em modelos geológicos, utilizando unidades geomorfológicas sobrepostas com tipos de sedimentos representativos relacionados com os acidentes geográficos individuais. O conceito de PM é demonstrado através da construção de um mapa polimorfológico para Zelândia, na Dinamarca, e de um mapa agregado que compara a distribuição da espessura do till argiloso dentro de tipos PM individuais. A aplicabilidade hidrogeológica do conceito PM foi testada com um modelo hidrológico distribuído determinístico 3D. O mapa PM agregado foi comparado com condições de fratura e redox em 21 locais de campo para avaliar a correlação do tipo PM com: (1) a espessura do till, (2) a espessura da zona de till reduzida, e (3) a profundidade até à zona com espaçamento de fraturas > 1m. Os resultados mostram que a espessura do till é um parâmetro crítico para a formação de redes de fraturas em till argiloso e que a densidade das fraturas diminui em till com espessura superior a 8–10 m. No entanto, a quantidade de dados ainda é insuficiente para provar o conceito PM em termos estatísticos.

Factors affecting the hydraulic performance of infiltration based SUDS in clay

The influence of small scale soil heterogeneity on the hydraulic performance of infiltration based sustainable urban drainage systems (SUDS) was studied using field data from a clayey glacial till and groundwater simulations with the integrated surface water and groundwater model HydroGeoSphere. Simulations of homogeneous soil blocks with hydraulic properties ranging from sand to clay showed that infiltration capacities vary greatly for the different soil types observed in glacial till. The inclusion of heterogeneities dramatically increased infiltration volume by a factor of 22 for a soil with structural changes above and below the CaCO3 boundary. Infiltration increased further by 8% if tectonic fractures were included and by another 61% if earthworm burrows were added. Comparison of HydroGeoSphere infiltration hydrographs with a simple soakaway model (Roldin et al., 2012) showed similar results for homogeneous soils but indicated that exclusion of small scale soil physical features may greatly underestimate hydraulic performance of infiltration based SUDS.

Geoelectrical mapping for improved performance of SUDS in clay tills

Many cities of the Northern Hemisphere are covered by low permeable clay tills, posing a challenge for stormwater infiltration practices. However, clay tills range amongst the most heterogeneous types of sediments and infiltration rates can vary by several orders of magnitude. This study evaluates if a 2D geoelectrical system can reveal such heterogeneity at field scale and thus be used to optimize the hydraulic performance of stormwater runoff infiltration systems. The assessment is based on a field study where data from non-invasive geoelectrical data are compared with data from invasive geological methods, including borehole soil sample descriptions, one excavation description and a near-surface spear auger-mapping project. The experiments returned a significant correlation of geoelectrical and spear auger-mapped surface sediments. Furthermore, a highly permeable oxidized fracture zone in greater depths could be revealed on the 2D geoelectrical profiles. The successful determination of highly permeable zones harbors potential for improved hydraulic performance of infiltration SUDS (sustainable urban drainage systems).

Geophysics‐Based Contaminant Mass Discharge Quantification Downgradient of a Landfill and a Former Pharmaceutical Factory

Contaminant mass discharge is a commonly applied tool to evaluate the environmental impact of contaminated sites on water resources. At large contaminated sites with heterogeneous sources, such as landfills, the number of wells available is often not sufficient, leading to a high uncertainty of mass discharge estimates. In this study, we tackle the uncertainty of the contaminant mass discharge due to low sampling densities by interpolating limited water-sample data with the support of surface direct current resistivity and induced polarization geophysical data. The method relies on finding a conceptual link between the bulk conductivity imaged from geophysics and the contaminant concentrations. We investigate the link between (1) imaged bulk and electrical water conductivity, (2) water conductivity and conservative ionic species, (3) water conductivity and redox-sensitive species, (4) water conductivity and semipersistent organic species, and (5) water conductivity and biodegradable organic compounds. The method successfully identify similarities between the distribution of the bulk conductivity and chloride and pharmaceutical compounds in a landfill leachate plume and between the bulk conductivity data and benzene and chlorinated ethenes for a contaminant plume from a former pharmaceutical factory. Contaminant concentrations were interpolated through regression kriging, using geophysical data as the dependent variable. The distribution of concentration determined with the novel method showed a lower mean relative estimation error than the traditional method of kriging only contaminant concentration data. At large sites, the method can improve contaminant mass discharge estimates, especially if surface geophysical measurements are integrated in the site investigation at an early stage.

Use of geological mapping tools to improve the hydraulic performance of SuDS

Most cities in Denmark are situated on low permeable clay rich deposits. These sediments are of glacial origin and range among the most heterogeneous, with hydraulic conductivities spanning several orders of magnitude. This heterogeneity has obvious consequences for the sizing of sustainable urban drainage systems (SuDS). We have tested methods to reveal geological heterogeneity at field scale to identify the most suitable sites for the placement of infiltration elements and to minimize their required size. We assessed the geological heterogeneity of a clay till plain in Eastern Jutland, Denmark measuring the shallow subsurface resistivity with a geoelectrical multi-electrode system. To confirm the resistivity data we conducted a spear auger mapping. The exposed sediments ranged from clay tills over sandy clay tills to sandy tills and correspond well to the geoelectrical data. To verify the value of geological information for placement of infiltration elements we carried out a number of infiltration tests on geologically different areas across the field, and we observed infiltration rates two times higher in the sandy till area than in the clay till area, thus demonstrating that the hydraulic performance of SuDS can be increased considerably and oversizing avoided if field geological heterogeneity is revealed before placing SuDS.