On the day Susan Gordon learned Venetucci Farm, in Colorado, was contaminated by toxins, the vegetables looked just as good as ever, the grass as green, and the cattle, hogs, chickens, and goats as healthy. The beauty of the community farm she and her husband managed made the revelation all the more tragic. Chemicals known as per- and polyfluoroalkyl substances, invisible and insidious, had tainted the groundwater beneath her feet.