I'm planning to enter concentrations of groundwater contaminants collected from well locations into QGIS and then use interpolation functions to create contours of the groundwater plume. Can QGIS calculate the maximum distance from a known point (e.g. a well) to an interpolated contour line (e.g. a contour line with concentration of 5 ppb)?
It can definitely be done, but I know only one way — through one of the database plugins (and conversion to vector format). Eg. PostGIS' ST_MaxDistance could be used.
Interesting that you need the maximum! I hope you won't have problems with contours that intersect the bounding box, since you have limited data for the edges.