When permits for the discharge of chemicals into a waterway are issued, they are issued in terms of the number of pounds of each chemical that can be discharged into the waterway per day  These figures, calculated separately for each chemical for which a permit is issued, are based on an estimate of the effect of the dilution of the chemical by the amount of water flowing through the waterway
The waterway is ttherefore protected against being adversely affected by chemicals discharged under the permits
there are no chemicals for which discharge into waterways is entirely prohibited