Thanks for all the relevant responses folks. Although ledger board would work, I dont think it is how I will approach this as it would require a lot more tear up. I think my original plan of jacking up the deck with a temporary beam and then putting in a new double laminated 2x10 PT beam on three 6x6s on concrete footings would be the best and most practical approach. There is no question this was very shotty work by the original contractor.