The NS 6702 waits in the East Yard for the recently delivered load of limestone to be unloaded. This is used in the plant WFGD or "scrubber" system and is injected into the flue gas to help reduce Sulfur Dioxide, the key ingredient in Acid Rain. The byproduct from this process is synthetic Gypsum, which is sold to produce wallboard or Sheetrock as is is better known.