Marina Pantazidou

EMPLACEMENT OF NONAQUEOUS LIQUIDS IN THE VADOSE ZONE

The results of experimental and analytical investigations of the movement of lighter than water organic liquids in the vadose zone are presented. The experiments consisted of physical model tests simulating nonaqueous phase liquid (NAPL) spills in unsaturated, two-dimensional domain above the water table. The evolution of the plume was observed through the transparent side of a tank containing sand, and the contaminant front was traced at appropriate intervals. Visual observations were supplemented with pressure and saturation measurements suitable for quantitative analysis of the process. The experiments show that during infiltration the front advances at constant speed (area/time). After spreading comes to a halt, the bulk of the contaminant is contained within a pancake-shaped lens situated on top of the capillary fringe. Fluctuations of the phreatic surface result in trapping the NAPL below the water table and in spreading the contaminant over a larger area. In layered samples, the behavior is largely geometry dependent, although heterogeneities invariably result in extensive horizontal spreading. Simplified analytical relationships were developed to estimate the spreading rate of the contaminant during infiltration and the thickness of the final immobilized oil lens observed during the experiments. These relationships are based on capillary pressure considerations, which have to be included in order to model the immobilization of the plume at saturations higher than the residual values, which typically occur in vadose zone, when the NAPL encounters the capillary fringe in its downward migration.

DNAPL distribution in the source zone: effect of soil structure and uncertainty reduction with increased sampling density.

This paper focuses on parameters describing the distribution of dense nonaqueous phase liquid (DNAPL) contaminants and investigates the variability of these parameters that results from soil heterogeneity. In addition, it quantifies the uncertainty reduction that can be achieved with increased density of soil sampling. Numerical simulations of DNAPL releases were performed using stochastic realizations of hydraulic conductivity fields generated with the same geostatistical parameters and conditioning data at two sampling densities, thus generating two simulation ensembles of low and high density (three-fold increase) of soil sampling. The results showed that DNAPL plumes in aquifers identical in a statistical sense exhibit qualitatively different patterns, ranging from compact to finger-like. The corresponding quantitative differences were expressed by defining several alternative measures that describe the DNAPL plume and computing these measures for each simulation of the two ensembles. The uncertainty in the plume features under study was affected to different degrees by the variability of the soil, with coefficients of variation ranging from about 20% to 90%, for the low-density sampling. Meanwhile, the increased soil sampling frequency resulted in reductions of uncertainty varying from 7% to 69%, for low- and high-uncertainty variables, respectively. In view of the varying uncertainty in the characteristics of a DNAPL plume, remedial designs that require estimates of the less uncertain features of the plume may be preferred over others that need a more detailed characterization of the source zone architecture.

Landfill Base Liners: Assessment of Material Equivalency and Impact to Groundwater

This paper gathered available flow and transport solutions and used them for two composite liners, consisting of geomembrane (GM) overlying either a compacted clay liner (CCL) or a geosynthetic clay liner (GCL). Its aim is to provide a guiding framework for the possible choices of (a) approaches to bottom liner design, (b) respective analytical solutions to flow and transport equations, as well as (c) parameters required for each type of solution. On the basis of the obtained results, the following recommendations are made. When the goal of analysis is to determine material equivalency, leachate flow rate is an adequate key parameter for GM-CCL composite liners. For GM-GCL composite liners, it is necessary to compute contaminant concentration or mass flux, considering (a) transport through defects for inorganic contaminants and (b) diffusion and the contribution of any available attenuation layer for organic contaminants. When the goal of analysis is to assess impact to groundwater, it is advised to calculate both discharge rate and contaminant mass flux regardless of liner type. The critical parameter for the transport calculations is the retardation factor of the contaminant, for the case of CCLs, while the results for GCLs are much less sensitive to this parameter.

Evaluating Management Options for the Disposal of Dredged Sediments

This paper presents a screening framework that evaluates management options for the dis- posal of dredged sediments on the basis of chemical and toxicological characterization tests. The paper provides a combined brief overview of disposal options for dredged sediments and relevant testing, to- gether with simplified decision rules for the feasibility of each option. The framework provides for two stages of assessment. In Stage I, disposal in open waters is evaluated based on the combination of results from chemical and toxicological analyses, supplemented by physical characteristics of sediments. For sediments that do not meet requirements for open-water disposal, Stage II evaluates the suitability of disposal in landfills or in confined facilities, upland and underwater. Decisions in Stage II are facilitated by well- established effluent criteria applied to ambient water and wastes admitted to landfills, as well as by calcu- lations estimating the impact of sediment contaminants to the vicinity of the subaqueous confining struc- tures. The application of the decision-making methodology is demonstrated using test results from sediment samples from Piraeus Harbor, Greece, and Indiana Harbor, IL, USA. Results showed that the framework is able to discriminate well among sediments from different subareas to be dredged. Disposal to open water is not feasible for most contaminated sediments from areas with increased shipping activities. Disposal in confined facilities subaqueous or upland proved to be a viable option for most of the sedi- ments, whereas all sediments were characterized as nonhazardous and can therefore be accepted in an ordinary landfill.

Modeling Instruction in an Environmental Geotechnics Course

Although modeling of physical systems is a key engineering task, the educational literature provides little guidance on how to systematically include modeling exercises in instruction. To this end, this paper presents work-in-progress involving the introduction of a framework of modeling in an environmental geotechnics course. The framework unpacks the components of the modeling process, placing particular emphasis on the simplifications made when considering relevant phenomena, determining parameters and variables, specifying geometry and boundary conditions, selecting and solving governing equations. Explicit modeling instruction required modification of learning outcomes and corresponding revisions of instructional material, example problems and exam questions. The development of a larger-scale term project is underway, designed so that students gain confidence when selecting different levels of approximations, through comparisons of numerical solutions at different degrees of idealization with simplified analytical solutions.

Academe vs Babel

The future of the university is most frequently discussed in terms either of its market and economic viability, or of the changes brought about by technological advances that facilitate information transfer. We choose to discuss the university as the birthplace of a new body of knowledge. We argue for the need of this new body of knowledge—of a metadisciplinary (or transdisciplinary) scholarship that will allow disciplines to converse with each other and with the world. Here we begin to describe this new kind of knowledge, establish its usefulness and propose ways it can be produced.

CREATING AN ONLINE VERSION OF AN ENVIRONMENTAL GEOTECHNICS COURSE: PEDAGOGICAL OPPORTUNITIES

This paper describes the changes prompted by transforming a lecture-based course to an online version, as well as the intended and some unintended outcomes resulting from these changes. Changes implemented are discussed in two separate categories: (1) logistical changes, i.e. modifications imposed by the constraints of studying online educational materials and (2) pedagogical changes, i.e. changes stemming from research-based learning principles, which, for presentation convenience are further subdivided in (2a) methodology-driven changes and (2b) content-related changes. The overarching aim of the implemented changes was to make transparent the major decisions involved in course design. The immediate goal of the paper is to make explicit the relationship between good instructional practices and the research evidence that supports them. The ultimate goal of the paper is two-fold: to enable sharing of educational material in the belief that material developed to address stated instructional needs can be useful to other instructors and to encourage engineering instructors to contribute their work to the communal instructional resources.

Modelling Microbial Dechlorination of Trichloroethene: Investigating the Trade-off Between Quality of Fit and Parameter Reliability

This work puts forth a heuristic approach for investigating compromises between quality of fit and parameter reliability for the Monod-type kinetics employed to model microbial reductive dechlorination of trichloroethene. The methodology is demonstrated with three models of increasing fidelity and complexity. Model parameters were estimated with a stochastic global optimization algorithm, using scarce and inherently noisy experimental data from a mixed anaerobic microbial culture, which dechlorinated trichloroethene to ethene completely. Parameter reliability of each model was assessed using a Monte Carlo technique. Finally, an alternate quantity of applied interest was evaluated in order to assist with model discrimination. Results from the application of our approach suggest that the modeler should examine the implementation of conceptually simple models, even if they are a crude abstraction of reality, as they can be computationally less demanding and adequately accurate when model performance is assessed with criteria of applied interest, such as chloroethene elimination time.

Effects of different electron donor feeding patterns on TCE reductive dechlorination performance.

Abstract This study investigates how the feeding pattern of e− donors might affect the efficiency of enhanced in situ bioremediation in TCE-contaminated aquifers. A series of lab-scale batch experiments were conducted using butyrate or hydrogen gas (H2) as e− donor and a TCE-dechlorinating microbial consortium dominated by Dehalococcoides spp. The results of these experiments demonstrate that butyrate is similarly efficient for TCE dechlorination whether it is injected once or in doses. Moreover, the present work indicates that the addition of butyrate in great excess cannot be avoided, since it most likely provide, even indirectly, significant part of the H2 required. Furthermore, methanogenesis appears to be the major ultimate e− accepting process in all experiments, regardless the e− donor used and the feeding pattern. Finally, the timing of injection of H2 seems to significantly affect dechlorination performance, since the injection during the early stages improves VC-to-ETH dechlorination and reduce methanogenic activity.

Geotechnical engineering education: promote links with research on engineering education

Within almost 25 years from the landmark lecture and paper ‘The Teaching of Soil Mechanics’ (Burland 1989), the community of geotechnical engineering has produced a good size literature on geotechnical engineering education. This literature is disseminated in the proceedings of conferences on geotechnical engineering and geotechnical engineering education, as well as in the proceedings of conferences and journals in the field of engineering education. Early papers focused almost exclusively on content-related issues: several discussed physical and numerical simulations that complemented lectures, aiming to facilitate understanding of key concepts. During the same time period, funding policies supported initiatives for improving engineering education, thus contributing to the emergence of a research community expending dedicated efforts on advancing engineering education. The major change that resulted from this new body of literature is a shift of emphasis from teaching (what the teacher does) to learning (what the learner does), e.g. de Graaff and Kolmos (2007). This shift brought the learner to the centre stage and supported initiatives meant to engage students actively in the learning process. To this end, a sizeable proportion of the literature on engineering education focuses on learner-centred teaching methods that recognise students’ higher responsibility for their learning. Accordingly, papers appeared in the literature of geotechnical engineering education also focusing on methodrelated issues, such as the introduction of elements of problem-based learning in geotechnical engineering courses. More recently, the increasing appreciation of engineering education needs that are domain-specific brought about an interest in discipline-based research in education (NRC 2012). This interest holds the promise to restore the balance between method and content in educational innovations within the disciplines. This special issue brings together papers providing examples of good practices in geotechnical engineering education with the goal of answering the question ‘How can innovations in geotechnical engineering education forge connections with engineering education research?’ (For the purposes of this discussion, adopting a good pedagogical practice not widely used is also considered to be an innovation.) These connections, which are natural meeting points of geotechnical engineering instruction and engineering education research, are of two kinds. The first kind of connection includes the instances where geotechnical engineering education adopts research-based instructional methods, i.e. methods the effectiveness of which is supported by research findings. All papers in this special issue provide examples in this category. Fiegel (this issue) restructured an introductory geotechnical engineering course with the aid of detailed learning outcomes, which in turn guided the development of targeted questions and problems aiming to assess achievement of these specific outcomes: research indeed shows that offering students opportunities to study towards clearly stated goals enhances learning (Ambrose et al. 2010). Kunberger (this issue) transformed a lecture-based course to a project-based one, a change that