The Dalles Lock and Dam navigation lock will return to service Wednesday morning at 6:30 a.m.  The U.S. Army Corps of Engineers says technicians are finalizing repairs on cracking engineers found in the downstream miter gate during annual inspections.  The return to service is 36 hours earlier than officials initially predicted.  The Dalles navigation lock, completed in 1957, is 650 feet long and is 86 feet wide.  On an average day, around six commercial vessels pass through the lock.  Portland District locks on the Columbia River pass 10 million of the 50.5 million tons of commerce shipped annually in the nation.  The Columbia River is the number one U.S. export gateway for wheat and barley, the number two U.S. export gateway for corn and soy, and the number one U.S. export gateway for West Coast mineral bulk.  The Columbia River system is also a national leader for wood exports and auto imports and exports.