1 Department of Earth Sciences, Faculty of Science, Aarhus University, Aarhus University2 unknown3 Department of Geoscience - Geology, C.F. Møllers Allé, Department of Geoscience, Science and Technology, Aarhus University4 Department of Geoscience - Geology, C.F. Møllers Allé, Department of Geoscience, Science and Technology, Aarhus University
We describe a procedure for rapid characterization ofshallow-water, contaminated wetlands. Terrain-conductivityTC, vertical-magnetic-gradiometry, and surface-waterchemistrydata were obtained from a shallow-draft paddleboatoperable in as little as 0.3 m of water. Measurementswere taken every 2 s, with data-acquisition rates exceeding10 km of line 12 000 data points per 8-hr field day.We applied this procedure to an urban wetland that is affectedby point and nonpoint sources of pollution.We used aone-dimensional, laterally constrained inversion algorithmto invert the apparent-conductivity data set obtained from theTC survey and to create a pseudo-2D image of sediment conductivity.The continuously recorded surface-water depthand conductivity values were input as a priori information inthe inversion.We used soil chemistry determined for 28 sedimentsamples collected from the site, as well as lithologiclogs from across the wetland, to constrain interpretation ofthe geophysical data. The inverted sediment conductivity describesa pattern of contamination probably attributable toleachates from adjacent landfills and/or to saltwater ingressfrom a partial tidal connection that is not obvious in the surface-water data. Magnetic-gradiometry values and the inphasecomponent of an EM31 response both reflect primarilythe distribution of junk metal associated with a legacy of illegaldumping. Historic aerial photographs suggest that thisdistribution reflects land-use history and defines the maximumprevious extent of an adjacent landfill and a pattern ofdumping correlated with historic roadways.