Application of physical clogging models to Managed Aquifer Recharge: a review of modelling approaches from engineering fields

Managed Aquifer Recharge (MAR) sites suffer from the long-lasting problem of clogging. The causes of clogging are physical, biological, chemical and mechanical processes and their complex interaction, with physical clogging being recognised as the predominant process. The intrusion and deposition of particles during water recharge affect the hydraulic properties of the infiltration surface, resulting in a decline in the infiltration capacity of the site over the operating years. Cleaning operations are necessary to restore the original infiltration rates. For this purpose, assessing the risk of clogging can determine the site’s vulnerability and improve the scheme’s design. Numerical models are essential to replicate physical clogging processes and predict the decline in infiltration rates. So far, predictive tools for physical clogging assessment have been missing in MAR literature. Hence, the purpose of this study is to analyse and reorganise physical clogging models from applied engineering fields dealing with water infiltration in natural heterogeneous systems. The modelling approaches are illustrated, starting from the main assumptions and conceptualisation of the soil volume and intruding particles. The individual processes are untangled from the multiple studies and reorganised in a systematic comparison of mathematical equations relevant to MAR applications. The numerical models’ predictive power is evaluated for transferability, following limitations and recommendations for a process-based model applicable to surface spreading schemes. Finally, perspectives are given for clogging risk assessment at MAR sites from modelling and site characterisation. The predictive tool could assist decision-makers in planning the MAR site by implementing cost-effective strategies to lower the risk of physical clogging

Grundwasser - Altlasten - Boden aktuell

Neun Fachbeiträge dokumentieren die Ergebnisse der aktuellen Projekt- und Forschungsarbeit des Landesamtes in den Themenbereichen Grundwasser, Altlasten und Boden

Kritische Evaluierung vertikal hochauflösender Methoden für die kf-Wert-Ermittlung

Environmental site investigations aim at delineating surface near (hydro-) stratigraphic units and their characterization. Knowledge about the spatial distribution of hydraulic conductivity (K) is the prerequisite for understand flow and fluid transport processes. Soil sampling and laboratory analysis of soil samples as well as the use of Direct Push (DP) technology are commonly applied methods for high resolution vertical characterization of sedimentary deposits. The objective of this thesis is to provide a critical evaluation of these methods regarding their ability to reflect the structure of a complex sedimentary aquifer and their ability to predict K. Extensive field testing was conducted at different test site with focus of the field work at highly heterogeneous aquifer at the Bitterfeld test site. Evaluation of methods to determine K from grain size analyses are based on the analyses of soil samples and multi level slug tests. Differences on calculated K between the different commonly applied formulas to calculate K were observed. Nevertheless, a high correlation was found between calculated and in situ measured K for most of the applied formulas. However, uncertainties that are associated with the (semi-) empirical nature of this method, heterogeneity of samples, and insufficient porosity estimates were identified to reduce the reliability of calculated K. DP tools and sensor probes proved to be a reliable and efficient alternative for characterizing complex sedimentary systems in this thesis. Despite resolution differences, all of the applied methods captured the main aquifer structure. Results show that it is possible to describe the aquifer hydraulic structure on less than a meter scale by combining DP slug test data and continuous DP profiling data. However, the appropriate tool has to be chosen and parameter relations are site specific. Correlation between of high resolution DP profiling and grain size data on a centimeter scale was not possible due the small scale soil variability at the Bitterfeld test site.Die Erfassung und Charakterisierung oberflächennaher (hydro-)stratigraphischer Einheiten ist die Grundlage jeder umweltgeologischen Untergrunderkundung. Die Erfassung der räumlichen Verteilung der hydraulischen Leitfähigkeit (K) ist die Voraussetzung für Strömungs- und Transportmodellierungen. Bodenprobenahme und Laboruntersuchung sowie der Einsatz von Direct Push (DP) Verfahren sind häufig angewandte Methoden zur vertikal hochauflösenden Untergrunderkundung. Das Ziel dieser Arbeit besteht in der kritischen Evaluierung dieser Methoden hinsichtlich ihrer Eignung zur Erfassung komplexer sedimentärer Ablagerungen und der Ermittlung von K. Der Hauptteil der Geländearbeiten konzentrierte sich auf die stark heterogenen Ablagerungen am Standort Bitterfeld. Die Auswertung von Bodenproben und Multilevel Slug Tests bildet die Grundlage für die Evaluierung von Methoden zur Berechnung von K aus Siebanalysen. Unterschiede zwischen den errechneten K-Werten ergaben sich dabei in Abhängigkeit der benutzten Verfahren. Nichtsdestotrotz konnte eine gute Korrelation zwischen gemessen und errechneten K-Werten für den Großteil der getesteten Verfahren nachgewiesen werden. Der (semi-) empirische Charakter, Heterogenität der Proben, Messungenauigkeit und ungeeignete Porositätsschätzungen verringern jedoch die Aussagekraft dieser Methoden. Die Ergebnisse dieser Arbeit zeigen, dass DP Anwendungen und Sensorsonden eine zuverlässige und effiziente Alternative zur Untergrunderkundung komplexer sedimentärer Systeme darstellen. Trotz unterschiedlicher räumlicher Auflösungsvermögen konnten alle getesteten Methoden die sedimentäre Schichtenfolge in Bitterfeld erfassen. Diese Arbeit zeigt, dass die Kombination von DP Slug Test Daten und hochauflösenden DP Profilen eine hydraulische Charakterisierung von Grundwasserleitern mit einer Auflösung von unter einem Meter ermöglicht. Allerdings müssen die geeigneten DP Methoden gewählt werden und die ermittelten Parameter-Beziehungen sind nur lokal gültig. Aufgrund der starken Heterogenität der Ablagerungen in Bitterfeld ist eine Korrelation zwischen Siebdaten und hochauflösenden DP Daten im Zentimeterbereich nicht möglich

Monitoring the impact of intensive shallow geothermal energy use on groundwater temperatures in a residential neighborhood

Abstract The use of shallow geothermal energy increasingly receives attention as a suitable alternative to fossil fuel-based space heating and cooling, warm water provision, as well as for seasonal heat storage throughout Europe. With the advent of shallow geothermal energy use on large scales, a vivid discussion of potential ecological and economic impacts has arisen but actual field data are scarce. An intensive groundwater temperature-monitoring program over a period of 3 years with consecutive measurements was, therefore, initiated at a residential neighborhood in the city of Cologne, Germany, under intense shallow geothermal use. The aim of the monitoring program was to overcome the existing data scarcity by pinpointing the effects of the intensive thermal use of the subsurface on groundwater temperatures and to foster understanding of urban groundwater temperature evolution. Results show that even though energy demands of the individual houses and energy extraction rates of the shallow geothermal systems were comparably small in this case, the accumulation of shallow geothermal users had a measurable impact on overall groundwater temperatures

Application of multi-scale variography for inferring the spatial variability of the hydraulic conductivity of a sandy aquifer

In the framework of the disposal of short-lived low- and intermediate-level radioactive waste in a near-surface disposal facility in Dessel (Belgium), extensive characterization of the hydraulic conductivity (K) in the shallow Neogene aquifer has been performed at a regional scale. In the last few years the small-scale heterogeneity has been additionally characterized by outcrop analogue, hydraulic direct push, and borehole core air permeameter studies. The gathered data now include a) more than 350 hydraulic conductivity measurements on samples from 8 cored boreholes, mostly reaching depths of 50 m and data at 2 m intervals, b) more than 5000 air permeability measurements on the same borehole cores, c) more than 250 cone penetration tests (CPTs) with depths down to 40 m and data at 2 cm intervals, d) over 100 dissipation tests performed during the CPT campaigns, e) 17 direct push injections loggings, 6 hydraulic profiling tool logs, and 6 direct push slug tests, f) several hundreds of air permeability measurements on outcrop analogues of the aquifer sediments, and g) numerous grain size analyses. The current study aims to quantify the heterogeneity of K from the centimetre- to the kilometre-scale and to check the compatibility of the spatial variability revealed by the different datasets. This is achieved through gathering all K values (either direct measurements, calibrated relative K values, or K estimates from secondary data), and the use of variography to quantify spatial variability in terms of two-points geostatistics. The results are discussed, and the main differences between the different data sources are explained. In a final step, different multi-scale variogram models are proposed for capturing the main characteristics of multi-scale variability within the shallow Neogene aquifer in Belgium

How to chase a tracer – combining conventional salt tracer testing and direct push electrical conductivity profiling for enhanced aquifer characterization

Tracer testing is a well-established technique in hydrogeological site characterization. However, certain a priori knowledge of the hydraulic regime is required beforehand to avoid test failure, e.g. miss of tracer. In this study, we propose a novel tracer test concept for the hydraulic characterization of shallow unconsolidated sedimentary deposits when only scarce a priori information on the hydraulic regime is available. Therefore, we combine conventional salt tracer testing with direct push vertical high resolution electrical conductivity logging. The proposed tracer test concept was successfully tested on coarse, braided river deposits of the Tagliamento River, Italy. With limited a priori information available two tracer tests were performed in three days to reliably determine ground water flow direction and velocity allowing on-site decision-making to adaptively install observation wells for reliable breakthrough curve measurements. Furthermore, direct push vertical electrical profiling provided essential information about the plume characteristics with outstanding measurement resolution and efficiency

Innovative strategies for high resolution site characterization: application to a flood plain

Solving complex hydrogeological problems often requires a thorough understanding of (hydro-) geological subsurface conditions. This is especially true for sedimentary deposits with complex architecture, where lithology and/or hydraulic properties can significantly vary over short horizontal and vertical distances. At these sites, a traditional, solely sample-based investigation approach is often not applicable due to limited data accuracy, resolution, and efficiency. Instead, an adapted investigation approach is required that combines exploration technologies of different resolution and investigation scales. This paper aims to demonstrate the feasibility of such a multi-scale approach for the characterization of a test site near the city of Löbnitz, Germany, that is comprised of heterogeneous alluvial deposits. Our focus is on site characterization in terms of lithology and hydraulic properties, as well as on the delineation and characterization of an aggradated oxbow as a typical example of a small scale geological structure