Identification and Development of Different Plumes of Chlorinated Hydrocarbons in Groundwater by Numerical Modeling Based on Carbon Isotope Dynamics

At Hamburg-Neuland groundwater monitoring revealed an area wide groundwater contamination by CHCs. The marshland is characterized by complex groundwater hydraulics. In order to understand plume development, a numeric groundwater flow and solute transport model has been set up. Unknown boundary conditions with respect to emission rate at the location of origin lead to the development of an innovative approach. The analysis of compound specific carbon isotope ratios revealed the complete transformation of PCE and TCE to ET and further on to CO2. The isotope enrichment factor could be derived directly from the field data. The introduced sum parameter ‘potential of source’ was extrapolated from the sum of measured concentrations of PCE-VC (μmol/l) and the calculated amount of degradation. The emission rate over time at location of source was calculated based on the ‘potential of source’ determined for the monitoring wells. To achieve a decisive reduction of uncertainties, solute transport was calculated for the sum parameter ‘potential of source’ instead of considering PCE/TCE and their degradation compounds. Three distinct plumes were delineated and an area of unknown hydraulic characteristics identified.