 Herders worry that Oyu Tolgoi is draining the region's water supply, since it uses more than a billion gallons of water a month.In addition, there is a substantial risk of acid rock drainage from the mine, from tailings storage facilities and from any overburden or waste rock stored on the surface and not deposited back into the mine.South Gobi is also a critical habitat for at least six endangered and threatened species found nowhere else in the world.