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

Time:	May 10, 2007, 4:00 p.m. – 5:30 p.m.
Lecturer:	Phillip Binning Technical University of Denmark
Venue:	Pfaffenwaldring 61, Raum U1.003 (MML), Universität Stuttgart
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Ranking of the risks associated with contaminated sites is important when prioritizingremediation effort for a groundwater catchment. Here methods for monitoringcontaminant mass discharge from individual sites are tested in a field study at acontaminated site. The results are then put into the context of an assessment of therelative risk of all contaminated sites located within the catchment.

Risk assessments are typically built on measurements of groundwater contaminantconcentrations. It can be argued that the mass discharge, which is a measure of thetotal contaminant load passing an area over time, is a better measure for determiningrisk. Results from an extensive field campaign aimed at measuring mass discharge ofTCE 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 dischargeincluding integrated pumping and conventional monitoring are compared.

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