A turbine airfoil for a rotating blade or stationary nozzle vane includes an airfoil body including a leading edge and a trailing edge. A coolant supply passage extends within the airfoil body, and a coolant return passage extends within the airfoil body. A first trench is in an external surface of the airfoil body, the first trench extending to the trailing edge and being in fluid communication with the coolant supply passage. A second trench is in the external surface of the airfoil body, the second trench extending to the trailing edge and being in fluid communication with the coolant return passage and the first trench. A cover seats in the airfoil body and encloses the trenches to form coolant passages with the airfoil body. In embodiments, two coolant passages to and back from the trailing edge may be used to allow for a recycling flow.