I am trying to estimate flow paths between contaminant sources and the catchment offtake (exposure point) at the catchment.
Can anybody give me some help in how to proceed?
You can use the following model/workflow to get started:
This very basic model yields drainage basins and streams/ephemeral streams from a digital elevation model (DEM). You can expand on this to include watersheds and expanded flow analysis if you care to. From here you should start to see which areas are likely to be affected by point source pollution.