Section 406.101  Averaging

a)         Compliance with the numerical standards of this Part must be determined based on 24-hour composite samples averaged over any calendar month. A single 24-hour composite sample must not exceed two times the numerical standards in this Part, and any grab sample taken individually or as an aliquot of any composite sample must not exceed five times the numerical standards in this Part.

b)         Despite subsection (a), if a permittee elects monitoring and reporting by grab samples under Section 406.102(f), then compliance with the numerical standards must be determined based on three or more grab samples averaged over a calendar month. A single grab sample must not exceed two times the numerical standards in this Part.

c)         The numerical standards for settleable solids are maximum values not to be exceeded at any time and are not subject to averaging.

d)         The numerical standards for pH must be within the specified range at all times and are not subject to averaging.

(Source:  Amended at 43 Ill. Reg. 11620, effective September 25, 2019)