Enhanced volatilization and redistribution of volatile organic compounds (VOCs) in contaminated aquifers subject to borehole thermal energy storage: Model development and applications

<p>In urban areas where the shallow subsurface is used for thermal energy storage (TES), interactions between the introduced heat and groundwater pollution caused by toxic organic contaminants can be expected. Temperature elevations may affect the transfer of these volatile organic compounds (VOCs) from the groundwater to the unsaturated zone, creating a redistribution or release of the contaminants in/from the subsurface environment. Such effects are particularly important considering the intersection of the unsaturated zone with the land surface and the remediation capacity of polluted aquifers. In this work, a non-isothermal multi-component two-phase flow model was developed to investigate the thermally induced volatilization and migration of the VOCs in contaminated aquifers. The numerical model, which is implemented in the open source framework <em>OpenGeoSys</em>-6, is able to simulate temperature-dependent mass and heat transfer processes in partially-saturated soils while allowing for phase change. Verification of the model against various benchmark problems and experimental data showed good accuracy. Simulation results revealed that a temperature-driven migration of dissolved trichloroethylene (TCE) from the groundwater to the drier regions of the unsaturated zone can be observed in general. A temperature increase of 20 K around the borehole led to a maximum decline of the total TCE concentration by 63% assuming zero TCE concentration at the soil surface. In addition, the TCE concentration distribution varied considerably with the depth-dependent water saturation. Further investigations were carried out to study the effects of different parameters, e.g. groundwater velocity, contaminant type and boundary conditions. Based on our analysis, the planning of subsurface TES systems can be optimized to account for the possible interactions with pre-existing groundwater contamination.</p><p><strong>References:</strong></p><p>Kolditz, O., Bauer, S., Bilke, L., Böttcher, N., Delfs, J. O., Fischer, T., ... & Zehner, B. (2012). OpenGeoSys: an open-source initiative for numerical simulation of thermo-hydro-mechanical/chemical (THM/C) processes in porous media. <em>Environmental Earth Sciences</em>, <em>67</em>(2), 589-599.</p>

Biological effects of tourmaline treatment on Dehalococcoides spp. during the reductive dechlorination of trichloroethylene

To explore the application of mineral in bioremediation of contaminated aquifers, this study investigated tourmaline-induced changes in TCE degradation, community structure, cell proliferation and gene expression of dechlorinating bacteria.

Unraveling biogeochemical complexity through better integration of experiments and modeling

The evolution of groundwater quality in natural and contaminated aquifers is affected by complex interactions between physical transport and biogeochemical reactions. Identifying and quantifying the processes that control the overall...

Vadose Zone Monitoring as a Key to Groundwater Protection

Currently, monitoring programs designed for groundwater protection are mainly based on information from observation wells. This, however, creates a paradox, since identification of pollution in well water is clear evidence that the groundwater is already polluted. The poor state of contaminated aquifers all over the world, and the inability, in practice, to fully remediate contaminated aquifers suggest that groundwater monitoring alone has failed to provide the vital information required to prevent groundwater pollution. That said, groundwater pollution initiates on the land surface, and the contaminants have to traverse the unsaturated zone, long before reaching the water table. Therefore, monitoring programs that can provide real-time information on the hydraulic and chemical state of the unsaturated zone are essential for achieving early warnings of pollution potential and providing imperative protection from pollution hazards. Currently, most of the commercially available monitoring technologies are rather limited in their capability to provide early alerts of pollution processes taking place deep in the unsaturated zone, above the water table. Accordingly, monitoring technologies for the unsaturated zone have to be engineered as “off-the-shelf” commercial products, made available for application by practitioners in all fields of hydrology. From scientific and technological points of view, such ambitions are not out of reach. Yet they require an urgent call for a revolutionary shift in monitoring focus, from the groundwater itself to the unsaturated zone above it.