My research concentrates on the geochemical evolution of low-temperature groundwater systems with a focus on groundwater contamination and remediation. Dissolved inorganic and organic chemicals are commonly affected by a variety of physical and chemical processes, which influence their mobility, but also alter the geochemical composition of the aquifer material. This is particularly true in the vadose zone, where the exchange of gases with the atmosphere can enhance the progress of geochemical reaction processes. Due to the complexity of these systems and the strong non-linear coupling between the processes, existing conceptual models are often incomplete and data interpretation from field and laboratory studies is not always intuitive. The main objectives of my research program are:
- Development of a process-oriented multicomponent reactive transport model, which can be used to investigate these complex systems and which is generally applicable to a large number of reactive transport problems in the fields of environmental sciences and engineering.
- Numerical analysis of groundwater contamination problems and remediation solutions with the goal to quantify, and potentially improve, existing conceptual models.
- Investigation of transport and reaction processes in groundwater systems using dissolved and vapor phase gases as natural tracers (Ar and N2) or indicators for biological processes (CH4, CO2, H2, H2S, O2, N2), .
The model development is based on the reactive transport model MIN3P (Mayer et. al., 2002 - see "Selected Publications"). MIN3P was designed to investigate reactive transport in saturated and unsaturated porous media in partial equilibrium systems. The model is capable of simulating groundwater flow, advective-dispersive transport of dissolved species and advective-diffusive gas transport directly coupled with a variety of bio-geochemical and inorganic reactions. To date, processes considered are aqueous complexation, oxidation-reduction, gas dissolution-exsolution, ion exchange, surface complexation, mineral dissolution-precipitation, and microbially-mediated degradation reactions.
MIN3P has been and is being used to study a number of reactive transport problems including:
- The generation and fate of acid mine drainage in mine tailings and at reclaimed mine sites.
- Treatment of contaminated groundwater by permeable reactive barriers and KMnO4.
- Potential effect of secondary geochemical reactions on the long-term performance of remediation technologies.
- Natural attenuation of organic contaminants in variably-saturated media. Assessment of physical and chemical parameters controlling microbially-mediated degradation reactions.
- Development of an improved conceptual model capable of reproducing observed redox zones in natural and contaminated aquifers.
Field work and lab work revolve around dissolved gas analysis. Microbiological activity in groundwater systems often leads to the generation of dissolved gases. In shallow groundwater systems, gas solubility is limited and if gas production is significant (e.g. due to denitrification or methanogenesis), gas bubbles will form. This will lead to the partitioning of insoluble gases such ad Ar and N2 into the gas bubbles. Due to its non-reactive nature, Ar in particular can be used to quantify this process, and calna then also be used to investigate transport away from a reactive zone. In unsaturated media, zones of Ar depletion or enrichment can be used as an indicator for advective gas transport. Specific research projects currently under way include:
- Investigation of natural attenuation of crude oil in variably saturated sediments using Ar and N2.
- Using dissolved gas analysis to investigate the performance of permeable reactive barriers for the treatment of metals.
STUDENT RESEARCH OPPORTUNITIES:
Student projects on the Master's level primarily focus on the numerical study of groundwater evolution in natural and contaminated aquifers and the assessment of remediation technologies using reactive transport modeling and dissolved gas analysis. These projects may also involve the interpretation of field and laboratory data aided by the modeling approach. Potential applicants should be familiar with geochemical principles and the basic concepts of flow and transport modeling. Research projects at the Ph.D.-level will in addition include model development using state-of-the art modeling approaches. Experience with the development of large complex numerical models would be advantageous. Applicants should also be familiar with Fortran90. To obtain more information about specific research projects, please contact me by e-mail (firstname.lastname@example.org).