Austin Caperton's vision for bringing land-based salmon farming to a part of the US that previously relied on coal as its primary source of employment involves turning the area's formerly big industry's biggest pest into one of his company's most vital resources.   Appalachian Salmon (AS), in Raleigh County, West Virginia, plans on using millions of gallons of water that have flooded an abandoned coal mine to help it grow up to 5,000 metric tons of fish per year.   Caperton, a former long-time coal-mining executive, knows one of the first reactions to expect when he tells people about his plan is concern about the quality of the water. All coal contains some level of sulfur. The coal found in the mines of the southern part of West Virginia where AS is looking to build has very low sulfur levels, less than 1% [...]