Allotment site behind health centre (10)
I believe the answer is:
allocation
'allotment' is the definition.
('allocation' can be a synonym of 'allotment')
'site behind health centre' is the wordplay.
'site' becomes 'location' (I've seen this before).
'behind' means one lot of letters go next to another.
'centre' indicates the central letters.
The central letters of 'health' are 'al'.
'location' after 'al' is 'ALLOCATION'.
(Other definitions for allocation that I've seen before include "Distribution, assignment" , "Apportionment" , "Share" , "budget" , "Allotment" .)