35 Ill. Adm. Code 304.102
Dilution
Section 304
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.