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2007 Ground Water Summit |
Wednesday, May 2, 2007 : 8:40 a.m.
Quantification of Contaminant Mass Flow Rates in Ground Water at Field Scale: Comparison of Two Approaches
The quantification is performed using an integral investigation approach at multiple control planes (integral pumping tests, based on a numerical inversion of contaminant concentration time series measured during pumping), which are positioned at three different distances downgradient of the source zone, with a spacing of about 150 m. Natural attenuation processes result in a reduction of the total contaminant mass flow with increasing transport distance. Degradation rates can be obtained from multi-process-based reactive transport modeling which considers all processes (sorption, volatilization etc.) contributing to mass flow reduction.
The results from the integral investigation approach were compared to contaminant mass flow rate estimates obtained from point scale concentration measurements within a closely spaced direct-push monitoring well fence. The usually employed point scale approach is subject to a certain degree of uncertainty due to the required interpolation of point scale concentration values. In comparison, as a consequence of its integrating nature, the pumping test based investigation approach provides site assessment at a high level of certainty, especially at large polluted sites with a complex contamination pattern within the aquifer. However, more effort due to pumping is required, compared to the point scale measurements.
The comparison results suggest that unless a dense monitoring well network is available, only the integral investigation method presented can yield adequate results for the quantification of contaminant mass flow rates, especially at sites with heterogeneous aquifer conditions.
Thomas Ptak, University of Goettingen Prof. Dr.-Ing. Thomas Ptak is the leader of a groundwater research group at the University of Goettingen in Germany. He received his Dipl.-Ing. degree in civil engineering from the University of Karlsruhe and the Ph.D. degree from the University of Stuttgart. His work is mainly focused on development of subsurface investigation methods and instrumentation, on quantification of natural attenuation, and on numerical stochastic transport modelling techniques, which are based on geostatistical approaches. He has been responsible for numerous field scale research projects dealing with groundwater hydraulics, tracer hydrology, contaminant transport, investigation of contaminated sites and stochastic modelling of non-reactive and reactive transport processes in groundwater. His group is also operating several groundwater research sites, where new subsurface investigation methods and groundwater transport modelling techniques can be tested and improved.