Also, be sure your salt doesn't have any additives. Some "table" salts have anti-clumping ingredients added. These will prevent the ferment. I ferment a lot and use sea salt (Meeressalz) without any troubles. Good luck!
OTOH thinking about the large trucks, tractors, and other machinery operating down there, there is probably contamination too, just by abrasion from the rubber tires, or beltways.
Pick your poison :)