B757-200
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Landed in Emergency Condition; Flight Crew Returned To Departure Airport; General Declared Emergency
Aircraft
Aircraft had a Left Hydraulic System leak about 10 minutes into flight.  All fluid was lost and the left hydraulic system subsequently failed.  Landing required alternate extension of flaps to a non-normal setting of 20 degrees; alternate landing gear extension; and landing without nose wheel steering.  Crew declared an emergency and returned for landing.  The approach and landing were uneventful.  The aircraft was towed to parking. The crew is unaware of the cause of the hydraulic leak.
B757 Captain experiences a failure of the left hydraulic system ten minutes into flight and returns to the departure airport.