A drilling rig tipped over at a construction site in Peterborough on Thursday morning and fell into the Contoocook River.The massive rig was stuck on its side as it slid down the river embankment. It was being used in construction work on the Route 202 bridge.”This machine was working to set piles in the bank that will be used to create that retaining wall,” said Peterborough fire Chief Ed Walker.The machine operator was not hurt, and once he was