What was found
AFTER PARKING AT THE GATE A FUEL SMELL CAME THROUGH CABIN. MOMENTS LATER IN MID-SECTION OF THE CABIN FOG APPEARED. INSPECTED APU AREA & VERIFIED FUEL LEAK COMING FROM APU FUEL FILTER LINE AREA. DEFERRED APU IAW MEL 49-01 SIT 1 & PLACARDS INSTALLED. ALL M ACTIONS COMPLIED WITH. MEL CONTROL NUMBER 14686 CAT C ITEM DUE 03/16/215. PERFORMED ACFT WATER SEPARATOR & PACK BURNOUT PROCEDURES, NO FURTHER SMELL. OPERATIONS CHECKED GOOD IAW WC 21-059-008.