Scrub mussels under cold running water. Remove beards. In an 8-quart Dutch oven combine 4 quarts cold water and 1/3 cup salt; add mussels. Soak for 15 minutes; drain and rinse. Discard water. Repeat soaking, draining, and rinsing twice.
In a Dutch oven cook pancetta over medium heat until crisp. Using a slotted spoon, remove pancetta from Dutch oven; drain on paper towels. Drain fat from the Dutch oven, reserving 1 tablespoon in Dutch oven. Add leeks; cook and stir about 3 minutes or until tender.
Add orange peel, orange juice, and wine to Dutch oven. Bring to boiling. Add mussels to Dutch oven; reduce heat. Simmer, covered, for 5 to 7 minutes or until mussels open. Discard any mussels that do not open. Sprinkle with pancetta and chives. If desired, serve with crusty country bread.