Modeling subsurface transport in extensive glaciofluvial and littoral sediments to remediate a municipal drinking water aquifer

摘要

Few studies have been carried out that cover the entire transport process ofpesticides, from application at the soil surface, through subsurfacetransport, to contamination of drinking water in esker aquifers. In formerlyglaciated regions, such as Scandinavia, many of the most importantgroundwater resources are situated in glaciofluvial eskers. The purpose ofthe present study was to model and identify significant processes thatgovern subsurface transport of pesticides in extensive glaciofluvial andlittoral sediments. To simulate the transport processes, we coupled a vadosezone model at soil profile scale to a regional groundwater flow model. Themodel was applied to a municipal drinking-water aquifer, contaminated withthe pesticide-metabolite BAM (2,6-dichlorobenzoamide). At regional scale,with the combination of a ten-meter-deep vadose zone and coarse texture, theobserved concentrations could be described by the model without assumingpreferential flow. A sensitivity analysis revealed that hydraulicconductivity in the aquifer and infiltration rate accounted for almost halfof the model uncertainty. The calibrated model was applied to optimize thelocation of extraction wells for remediation, which were used to validatethe predictive modeling. Running a worst-case scenario, the model showedthat the establishment of two remediation wells would clean the aquifer infour years, compared to nine years without them. Further development of themodel would require additional field measurements in order to improve thedescription of macrodispersion in deep, sandy vadose zones. We also suggestthat future research should focus on characterization of the variability ofhydraulic conductivity and its effect on contaminant transport in eskers.