. >> sabina valdez is the president of the association of miners at the river manuani. skyrocketing gold prices have pitted small artisanal miners like the manuanis against larger illegal operations run by outsiders. but these miners have a stake in the land. >> in 2013 they began working with francisco roman and a group of government and research facilities. the goal - to find out how to grow new life in the soil mining leaves behind. >> what do miners do to the earth when they do mining? >> the process turns the soil into 95% sand almost deviod of all organic matter. this may be the biggest challenge scientist face. >> another problem is miners often contaminate the soil with mercury. they use it to bind those tiny flecks of gold into a clump. tropical ecologist luis fernandez is the director the carnegie amazon mercury ecosystem project. >> the gold here is not very concentrated. it's only about 2 grams per ton of rock. instead of manually concentrating that tiny amount of gold in a awful lot of rock, you take some of the sediment, some water, and a little bit of mer