A catchment scale model for assessing the risk associated with pointsource contaminated sites
25.11.05, 11:00 – 12:30 Uhr
Philip Binning, Associate Professor in Subsurface Hydrology and Numerical Modelling, Institute of Environment & Resources, Technical University of Denmark
Point sources are one of the main threats to groundwater quality. It isessential that remediation efforts are prioritised to ensure that thepoint sources which constitute the largest groundwater risk areremediated first. Currently, no systematic procedure is available forevaluating and comparing the contamination risk associated with variouspoint sources within a catchment area. Here a simple method is presentedthat provides the basis for a ranking of point sources according totheir impact on groundwater quality. The method is designed for realcatchments where data availability is a major limitation on riskassessment. The model consists of two components: a source model and alarge scale transport model. The source model describes the discharge ofcontaminant from a polluted site where the source of contaminant islocated both in the unsaturated zone and in a secondary aquifer. Itincludes separate phase organics and degradation processes. Thetransport model applies particle tracking for simulating groundwaterflow and residence time in the aquifer. The solute transport descriptionincludes sorption effects as well as transformation processes.Degradation is spatially variable and depends on the redox conditions inthe aquifer.The risk assessment concept was tested at a contaminated site,Østerparken 5-7, located in Tåstrup, Denmark. The site is heavilycontaminated with TCE, where residual phase in a hot spot in theunsaturated zone and the secondary aquifer is present. The simulationsperformed with the developed models show that the contamination atØsterparken 5-7 poses a large risk for the groundwater resource bothlocally and at the catchment scale. This risk will be present for anextended period of time. Sensitivity- and scenario analyses wereperformed to identify the most critical parameters for the riskassessment of Østerparken. Comparisons with existing risk assessmenttools were also made.