What was found
(CAN) LEFT HYDRAULIC SYS LEAK, EMERGENCY DECLARED, LIVE WITH 5 PASSENGER ON BOARD, AIR RETURN, CREW REPORTED ENROUTE, THE LT HYDRAULIC PRESSURE WENT TO ZERO PSI AND THE LT HYD QTY WAS SHOWING 0 PERCENT AMBER ICAS, SPOILERS FAULT + LT HYD PRESS LOW, POSTED. ACFT DECLARED AN EMERGENCY AND RETURNED TO MAINLAND. ACFT LANDED AND NEEDED TO BE TOWED IN DUE TO NWS WAS FAILED. ON POST-FLIGHT, CREW NOTED LEAKING IN THE AFT EQUIPMENT BAY AREA, BUT COULD NOT ASCERTAIN EXACTLY WHERE THE LEAK WAS EMANATING FROM. PARTS ORDERED: TUBE ASSY PN: 1005354124-005, ELBOW PN: B0302161-0604, UNION PN: B0301010-04.