Mit Hilfe von phosphathaltigen Inhibitoren ist es möglich, hoch übersättigte Gipslösungen über einen vorgegebenen Zeitraum zu stabilisieren, und anschließend, zu einer definierten Zeit, Gips auszufällen. Damit können derartige Lösungen zur Permeabilitätsreduzierung von Grundwasserleitern eingesetzt werden. Untersuchungen zum Verlauf der Kristallisation zeigten die Abhängigkeit der Induktionszeit der Gipsbildung von pH-Wert, Temperatur, anwesenden Feststoffen und von der Übersättigung der Lösung. Die Wechselwirkungen zwischen Inhibitor und übersättigter Lösung, Gipskristallen und Sand werden sowohl durch Polyphosphathydrolyse als auch durch Adsorption des Inhibitors und Absorption im entstehenden Kristallisat bestimmt. In Säulenversuchen gelang es, in weiten Bereichen Gips abzuscheiden und die Porösität zu reduzieren. Ausgehend von den Untersuchungen zur Injektionsmethodik in den Säulenversuchen konnten im Feldtest technologische und geotechnische Parameter praxisnah getestet werden. Die Permeabilität des Grundwasserleiters wurde erfolgreich reduziert. Damit wurde ein weiteres niedrig viskoses Injektionsmittel zur Permeabilitätsreduzierung in Sedimenten mit niedrigen kf-Werten gefunden.

The aim of this thesis was to investigate the impact of a direct oxygen injection as a potential remediation strategy for contaminated aquifers on a bench scale. The mass transfer between a multi-component trapped gas phase and a mobile water phase was studied. Column experiments with dynamically compressed sediments and a direct gas injection of pure oxygen gas were performed. In addition, a new developed kinetic multi-component model was used to describe the experiments. The amount of gas that could be captured in the pore space during direct oxygen injection and the time needed for a complete dissolution of the trapped gas phase were determined. Varying influences of different gases already dissolved in the mobile water phase on the dissolution process of a trapped oxygen gas phase were described for different flow regimes and confirmed by the model results. Finally, on the basis of the experimental and model results obtained in this thesis, predictions for an application of a direct oxygen injection in the field were discussed.

Zugl.: Stuttgart, Univ., Diss., 2004

University, Diss., 2002--Tübingen.

Universiẗat, Diss., 1998--Heidelberg.

Universiẗat, Diss., 2004--Kiel.

University, Diss., 2004--Tübingen.

Universiẗat, Diss., 2005--Kiel.

Groundwater is a very important resource since water volumes stored underground are much larger compared with those located at the surface, such as rivers and lakes. Aquifers supply a high percentage of freshwater for human consumption as well as supplying economic activities like industry, agriculture, and livestock production. Among them, karst aquifers stand out due to their special hydrologic characteristics and behaviour. In karst aquifers, infiltration occurs faster in comparison with unconsolidated aquifers, due to high permeability features at the surface like dolines, karren, epikarst, and swallow holes that allow precipitating water to recharge the aquifer at higher rates. Nevertheless, these characteristics also increase the aquifer’s susceptibility to being affected by pollution generated by anthropogenic practices. With a low natural pollutant degradation capacity, karst systems mostly experience problems related with water quality rather than water quantity. At present, this represents a significant challenge because a high percentage of the world population is settled on karst areas and is solely dependent upon karst aquifers to fulfil their necessary water supply. A good example to represent this case is the Yucatan Peninsula. The Peninsula is a transboundary limestone platform, covering parts of Mexico, Belize, and Guatemala, whose characteristics do not allow surface streams to generate. Therefore, the karstic aquifer provides water for nearly 4.5 million inhabitants within Mexican territory; this estimation excludes water volumes used for economic activities. The anthropogenic impacts over this karst aquifer have generated problems for water intended for human consumption, furthered by weak environmental regulations that allow the disposal of wastewater without adequate treatment. In the Mexican state of Yucatan, roughly 10% of the population has access to public sewer services where wastewater is treated. Additionally, the use of fertilizers and pesticides is not regulated in agricultural areas, while pig farming is an increasing activity, which fails to keep the necessary standards for the proper disposal of pig slurry. Similar situations can be found around the world, thus the development of plans and strategies to preserve karst groundwater quality that aim to find a balance between resource protection and regional development is increasingly necessary. One important tool emerged to support decisions regarding groundwater protection: the groundwater vulnerability concept. However, due to the hydrologic differences among detritus and karst aquifers, the vulnerability concept, which was first promoted for the former aquifer type, necessitated the development of a specialized vulnerability method to consider the natural characteristics of karst landscapes. Nevertheless, due to the high heterogeneity and anisotropy present in karst systems several methodologies to estimate karst groundwater vulnerability have arisen. Current methodologies are theoretical approximations to differentiate areas where an assumed pollutant particle, released at the surface, is more likely to reach the aquifer due to the natural characteristics of the area. These methods have shown themselves to be useful in defining protection areas and in highlighting regions in which further studies can be performed. However, the high subjectivity and exclusion of anthropogenic influences as part of the analysis is a drawback for these methods. In order to estimate karst groundwater vulnerability for current and future scenarios, an integrated approach is highly necessary. Since most of the methods focus solely on the travel time of a theoretical pollutant from the surface towards groundwater or to a spring, inclusion of pollutants residence time and concentration as parameters to estimate vulnerability is of the uttermost importance. To reach this goal, it is necessary to investigate current intrinsic-based methods in terms of their applicability and regional congruence in order to highlight advantages and probable misclassifications among them and to propose improvements. Pollutant residence time and concentration can be estimated from modelling, which can highlight areas where pollution can represent a problem due to anthropogenic practices, such as wastewater disposal and water extraction fields influencing groundwater flow. Other problems to be contemplated are the data availability and the variable processes by which areas are classified as vulnerable or not. Evaluation of multiple criteria to define degrees of vulnerability is complicated, since several factors, such as subjectivity, data quality, scale, and regional conditions, will always be present. This work presents the results from the application of eight karst groundwater vulnerability methods to the Yucatan karst and outcomes from solute transport. Important considerations are explained in order to improve the workflow for intrinsic groundwater vulnerability assessment. Possible parameters, to be included as part of vulnerability analysis, are evaluated by modelling, demonstrating the importance of anthropogenic impacts for current vulnerability scenarios. Results obtained in this research are displayed as the basis for an Integrated Karst Aquifer Vulnerability (IKAV) method proposed as an alternative for vulnerability studies.

Zur in situ Messung von Richtung und Geschwindigkeit des Grundwasserstromes in nur einer Bohrung wurde ein Mikroflowmeter auf der Basis der kontinuierlich thermischen Anregung entwickelt. Das Messprinzip beruht auf der Deformation des Temperaturfeldes, das sich in Abhängigkeit vom antreibenden Gradienten des Grundwasserstromes mehr oder weniger stark unsymmetrisch als Wärmefahne im Messbereich der Sonde abbildet. Von Interesse sind dabei horizontale Fluidbewegungen mit sehr geringen Fließgeschwindigkeiten. Zur Realisierung der Aufgabenstellung werden sowohl eine Modellierung des Wärmetransports als auch Versuche zur Simulation von Strömungsvorgängen und Testmessungen im Gelände durchgeführt. Als Ergebnis der Abhandlung verschiedener numerischer Randwertprobleme erweist sich die Temperaturabhängigkeit der Fluiddichte als eine nicht zu vernachlässigende Einflussgröße, die in Form einer nach oben gerichteten Auftriebsströmung den Wärmetransport maßgebend bestimmt. Infolge der Überlagerung von freier und erzwungener Konvektion wird eine Mitführung von Wärme mit der Grundwasserbewegung gehemmt und die Ausbildung einer in Strömungsrichtung weisenden Wärmefahne drastisch eingeschränkt. Laborversuche bestätigen die am numerischen Modell gewonnenen Ergebnisse.