40 CFR §463.21

1. (a)The “average process water usage flow rate” of a cleaning water process in liters per day is equal to the volume of process water (liters) used per year by a process divided by the number of days per year the process operates. The “average process water usage flow rate” for a plant with more than one plastics molding and forming process that uses cleaning water is the sum of the “average process water usage flow rates” for the cleaning processes.
2. (b)The “volume of process water used per year” is the volume of process water that flows through a cleaning process and comes in contact with the plastic product over a period of one year.