Complex sentence: Contaminated water surfacing below waste rock and ore stockpiles is collected and treated on-site at a water treatment plant, then discharged into Blue Creek, which enters the Spokane Arm of Franklin D. Roosevelt Lake.
Split into simpler sentences: Contaminated water surfacing below waste rock and ore stockpiles is collected for treatment on-site. Surface water from the minesite flows to Blue Creek, which enters the Spokane Arm of Franklin D. Roosevelt Lake.