Section 304.102  Dilution

a)         Diluting the effluent from a treatment works or any wastewater source is not acceptable as a method of treatment of wastes to meet the standards in this Part.  It is the obligation of any person discharging contaminants of any kind into the waters of the State to provide the best degree of treatment of wastewater consistent with technological feasibility, economic reasonableness, and sound engineering judgment.  In determining what kind of treatment is the "best degree of treatment" within the meaning of this subsection, a person must consider the following:

1)         What degree of waste reduction can be achieved by process change, improved housekeeping, and recovery of individual waste components for reuse; and

2)         Whether individual process wastewater streams should be segregated or combined.

b)         In any case, to determine compliance with the effluent standards, contaminant concentrations must be measured at the point immediately following the final treatment process and before mixture with other waters, unless the Agency designates another point in an individual permit, after considering the elements contained in this Section.  If necessary, the concentrations measured must be recomputed to exclude the effect of any dilution that is improper under this Section.

(Source:  Amended at 47 Ill. Reg. 4601, effective March 23, 2023)