Viscous hydroplaning can
occur at much lower speeds than dynamic....most likely on a smooth dirty
surface.
The touch down areas of the runways will have a fair
amount of rubber deposit left as aircraft land...modern airfields have a fairly
rigorous runway cleaning program to remove it, but some airfields don't. Here,
the first section of the runway could just be 'black rubber deposit'. This will
show up very clearly on a concrete runway. Hence the question...viscous
hydroplaning...smooth dirty surface...touch down
areas of the runway.