"Half a Ton"
!!!!!!! blimey Thats loads ? well 625 ltrs.. if that much "leaked" I would be more than concerned.
That much fuel on the apron would amount to a small lake. It would be more like an a/c tech problem, than over fuelling unless crew are asking to fill the wings (752's) with 13.2T. thus pushing the limits and filling the vent boxes, and so fuel does have a tendency to leak, or in 737's over riding closed valves( topping off the tanks) will do the same.