Ground is stained, so decontaminated (9)
I believe the answer is:
sanitised
'decontaminated' is the definition.
(I've seen this before)
'ground is stained' is the wordplay.
'ground' indicates anagramming the letters ('grind' the letters into a new form).
'is'+'stained'='isstained'
'isstained' with letters rearranged gives 'SANITISED'.
'so' is the link.
(Other definitions for sanitised that I've seen before include "decontaminated" , "purified" , "Make less offensive by removing objectionable features" , "cleansed" , "cleaned up" .)