Sewage-tainted runoff behind the Olema House hotel and Due West restaurant prompted a precautionary shutdown of oyster farming in Tomales Bay for five days last week, but operations returned to normal on Sunday after shellfish testing showed no public health threat. Rangers from the National Park Service discovered the contamination during routine testing of Olema Creek, a winter spawning stream that runs behind the hotel before merging with Lagunitas Creek and then the bay. The…