Modelling the risk of chloridnated hydrocarbons in urban groundwater

The main target of this work is the development of a risk assessment approach of groundwater
contaminations in an urban area. A multidisciplinary approach was performed to assess
degradation potential of contaminant species in soil and the inherent risk posed by anthropogenic
substances. Experimental and theoretical methods range from chemical and biochemical to geoengineering
applications. This especially concerns molecular biological, wet-chemistry techniques
and Finite Element groundwater transport and reaction modelling. The spatial dimensions
considered in the studies range from small laboratory to field scales. With regard to these applied
methods the overall goal was a holistic risk approach to intertwine both, reactive transport of
contaminants in groundwater and human health risks.
An experimental area polluted with chlorinated ethenes and located in Braunschweig was chosen
to validate the model. Based on repeated measurement campaigns pollutant concentrations as
well as other environmental parameters and chemical data were determined and their quality was
valued at assessed literature data. With the obtained experimental data a groundwater reactive
transport model was established and validated. Further, to test the influence of the flow, transport
and reaction model parameters a sensitivity analysis was performed. Based on this analysis,
contaminant specific probabilities of occurrence were calculated with a Monte-Carlo simulation
approach. Additionally, model optimisation techniques were applied to improve conformity of
simulated and experimental data.
It could be shown, that a simplified first-order reaction kinetic is only partially capable of rendering
the measured field data. Hence, it was necessary to extend and improve the underlying
degradation kinetics by means of modified Monod-equations. Here, the extension mainly
comprises the introduction of inorganic electron acceptors as well as inhibiting reactions to refine
the reductive dechlorination process of the chlorinated hydrocarbons. The next important step
concerns the derivation of a health risk approach from the aforementioned concentration
probabilities of occurrence. The combined model approach finally enables to calculate spatial and
temporal health risk occurrence.