The Environmental Protection Agency ordered Sunnyside Gold Corp. to begin a costly investigation of complicated underground water flows as part of the federal government’s Superfund cleanup of toxic mining sites above Silverton. Figuring out where contaminated water flows through a maze of mining tunnels and natural cracks has emerged as a primary challenge for moving forward in one of the most ambitious toxic mining clean ups attempted in the West. Sunnyside’s properties are included in the 48-site Bonita Peak Mining District cleanup launched in 2016 after the Gold King Mine spill that was accidentally triggered on Aug.