Reasons for sediment (7)
I believe the answer is:
grounds
I believe this clue is a double definition.
'reasons' is the first definition.
(grounds or reasons for an action)
'for sediment' is the second definition.
(as in coffee grounds)
(Other definitions for grounds that I've seen before include "Dregs" , "justification" , "Coffee sediment" , "they make coffee" , "enclosure around house" .)