I found this in an article that had nothing to do with TWD, but I'm wondering from the description if they might have filmed the reservoir/quarry scenes there:
"Located in the Appalachian foothills, Nelson is a tiny, hilly town with narrow, twisting roads. It used to be a major source of marble, with the local marble quarrying company employing many. But that industry is mostly gone now. Just about everyone leaves town for work, making it a bedroom community for Atlanta."