It was a sunny, crisp October morning. The rainy grey mist from the week before had cleared to reveal a stunning panorama of mountains, lake, and sand. On a beach just north of Burlington a group of volunteers, bundled in warm layers against the morning chill, were ranged in a staggered line. Those with muck boots waded through the shallow water, while the others walked along the shoreline. Every few paces each stopped to kneel and scoop up sand in a small steel sieve. They then shook away the sand, as if panning for gold, examined the contents briefly – and discarded them.