This report describes results from a project investigating possibilities to map or rank clay localities according to their vulnerability to pesticide leaching. The project entailed a combined and multiscale experimental and modelling approach starting from the polymorphological (PM) concept for ranking the heterogeneity of clay-till deposits. The PM concept separate clay-till deposits in landforms differing by their pattern of superimposed geomorphological units. Four large excavations have been established representing different PM landforms.
The lithology and presence of preferential flow paths, including macropores (wormholes, root channels, burrows etc.), tectonic and desiccation fractures, and sand lenses were characterized at each excavation. All sites were geologically highly heterogeneous with different clay units being mixed with sand lenses and sand layers, implying that it may be difficult to attribute defined geological characteristics to PM types.
The geological characterization, though, showed the following general trends: 1) Macropores, including wormholes were present in all upper tills where they proba-bly are the most dominant preferential waterflow routes, 2) fractures changed col-our from grey to red due to iron precipitation at greater depths, and 3) sand deposits were present at all locations in the form of sand layers and sand lenses of different thicknesses.
In order to develop comprehensive vulnerability mapping methods, knowledge about heterogeneities at greater depths below the ‘fracture zone’ investigated in CLAYFRAC is needed as well as a systematic verification with pesticides contamination of groundwater aquifers underlying the clayey till aquitards.