Characterization of contaminant fate and transport processes in sediments and aquifers through high-resolution passive sampling

There is a legacy of contaminated sites worldwide because of the historic release of chemicals into the environment. Sediments of bodies of water are among the most affected areas since their affinity to organic compounds and heavy metals makes them an excellent sink of contaminants. However, when the levels of pollutants in surface water drop due to efforts to remove the original sources, the affected sediments have the potential to become a new source of contamination. Therefore, assessing contaminated sites is essential to understand the risks and remediate them properly and efficiently. In a stable sediment environment, the movement and availability of chemicals in pore water define exposure and risk to living organisms. Several processes such as advection, diffusion, bioturbation, and biogeochemical transformations affect this availability. Thus, the best evaluation of pore water is in-situ to capture the actual conditions of the sediment environment. In this regard, passive sampling stands out as a technique to assess pore water with minimal disturbances to the local conditions. This dissertation presents a high-resolution passive sampler that collects information on contaminants, biogeochemical indicators, microbial populations, and pore water velocity. By measuring these parameters, we do not only seek to evaluate levels of pollutants in pore water but also to understand the sediment processes affecting the long-term mobility and availability of the chemicals of concern. This work presents the efforts at three contaminated sites to demonstrate the applicability of the high-resolution device and the sampling approach. First, the high-resolution sampling was used to evaluate a biowall to treat a plume of chlorinated solvents in a shallow aquifer. Compared to traditional monitoring wells, the results highlighted the advantage of passive sampling of pore water to understand transport and degradation processes. Second, the approach was used to sample sediments of a tidally affected creek. Observations provided evidence to understand and quantify sediment processes such as evapotranspiration and inundation/drainage. The implications included cyclic changes in redox conditions affecting the sequestration and release of metals. Effects were validated and quantified through measurements of Zn. Third, the sampling approach was combined with historical measurements of polycyclic aromatic hydrocarbons in capped sediments of a river. The results helped constrain transport and quantify attenuation processes to assess the remediation cap and predict its long-term effect on the mobility and availability of contaminants. In summary, the content of this dissertation shows the advantage of collocated parameters obtained via passive sampling to assess contaminants and sediment processes in-situ. The presented results also highlight this approach's importance in developing conceptual models that can be translated to mathematical forms to predict the fate and transport of contaminants in the environment.

Embargo status: Restricted until 09/2023. To request the author grant access, click on the PDF link to the left.