SILVERTON — The Environmental Protection Agency says it will set up a temporary treatment plant for wastewater flowing from the Gold King Mine in southwestern Colorado after 3 million gallons surged out of the mine in August, tainting rivers in three states. The EPA said Wednesday it needs the plant because it will be unsafe to operate the settling ponds now in use when winter temperatures dip below zero. The EPA released documents last week saying it was considering the plant. The $1.8 million plant is expected to start operating by Oct.