At an absolute push, it *can* be safely
tipped down the nearest rainwater road drain.
A neighbour of mine recently disposed of
about six large sacks of the stuff, plus a sack
of gravel that was surplus to his needs.
Obviously not the preferred method but I'm
'led' to believe that most local authorities don't
actually mind this type of activity providing
it is approached with copious amount of
common sense and restrain!

Grossly iresponsible advice and illegal with a heavy fine if you are caught.
Most amenity refuse sites will take small amounts but it is worth phoning
and asking what their policy is.