“Narrative standard” specific enough

The Illinois State Pollution Control Board adopted specific numeric standards or concentration limits allowable in a discharger's waste for toxins such as arsenic and cyanide. For all others, a “narrative standard” provided that state water “…shall be free from any substances or combinations of substances in concentrations toxic or harmful to human health, or to animal, plant or aquatic life.” Violations of the narrative standard were noted if concentrations exceeded any of five “criteria” that had no fixed values but were derived case by case. Several steel companies asserted the regulations were so vague and uncertain that they did not provide fair warning of prohibited conditions. Trial and appellate courts upheld the regulations, and the supreme court agreed.