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Institut für Wasserbau - IWS

Selected Topics and International Network Lectures

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Donnerstag
10.05.2007
16:00 Uhr
Phillip Binning
Technical University of Denmark

Assessing the risk of contaminated sites: Monitoring mass discharge from contaminant point sources and catchment scale assessment of risk

Ranking of the risks associated with contaminated sites is important when prioritizing remediation effort for a groundwater catchment. Here methods for monitoring contaminant mass discharge from individual sites are tested in a field study at a contaminated site. The results are then put into the context of an assessment of the relative risk of all contaminated sites located within the catchment.

Risk assessments are typically built on measurements of groundwater contaminant concentrations. It can be argued that the mass discharge, which is a measure of the total contaminant load passing an area over time, is a better measure for determining risk. Results from an extensive field campaign aimed at measuring mass discharge of TCE at a contaminated site are reported. It is shown that in the unsaturated zone, vapour phase diffusion can be an appreciable mechanism for spread of contamination. Down stream of the site, various methods for determination of mass discharge including integrated pumping and conventional monitoring are compared.

Results from the field campaign are then included in a catchment scale assessment of risk. Current risk assessment tools are of limited use when determining downstream impacts because they focus on groundwater impacts at, or near, a given contaminant source. Here a new integrated risk assessment tool is developed with the aim of determining impacts on downstream water supply wells and prioritizing the clean up of contaminated sites within a given groundwater catchment. The catchment scale risk assessment tool was used to find the most likely source of the contamination and to rank the risk of known contaminated sites in the catchment. It was shown that a deep free phase plume of TCE is likely to be present at one site. Field work is presented to confirm this hypothesis. The risk assessment has also provided insight into the effectiveness of the pump and treat containment scheme being employed in the